Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Study of lead isotopes from mineral deposits in southeastern British Columbia and from the Anvil range,… LeCouteur, Peter Clifford 1973

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1973_A1 L42.pdf [ 12.42MB ]
Metadata
JSON: 831-1.0302659.json
JSON-LD: 831-1.0302659-ld.json
RDF/XML (Pretty): 831-1.0302659-rdf.xml
RDF/JSON: 831-1.0302659-rdf.json
Turtle: 831-1.0302659-turtle.txt
N-Triples: 831-1.0302659-rdf-ntriples.txt
Original Record: 831-1.0302659-source.json
Full Text
831-1.0302659-fulltext.txt
Citation
831-1.0302659.ris

Full Text

A STUDY OF LEAD ISOTOPES FROM MINERAL DEPOSITS I N SOUTHEASTERN BRITISH COLUMBIA AND FROM THE ANVIL RANGE, YUKON TERRITORY by PETER CLIFFORD LeCOUTEUR B.Sc,  U n i v e r s i t y of Auckland, 1964  M.Sc.(Hons), U n i v e r s i t y of Auckland, 1967  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  i n the Department of  G e o l o g i c a l Sciences  We accept t h i s t h e s i s as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA January, 1973  In presenting  this thesis i n p a r t i a l fulfilment of the requirements for  an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t freely available for reference  and study.  I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may by his representatives.  be granted by the Head of my Department or  It i s understood that copying or publication  of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission.  Department of  C^p^o^e_cJL  The University of B r i t i s h Columbia Vancouver 8, Canada  Date  <23^A Kc^rJL  lIlX  i  ABSTRACT  The objective of the research was to determine the source and age of emplacement of lead i n mineral deposits i n three regions of the Western C o r d i l l e r a — Arc,  the East Kootenay d i s t r i c t , the adjoining Kootenay  and the A n v i l Range.  Measurements were made of the i s o t o p i c composi-  t i o n of lead i n 132 samples by gas source techniques and a p r e c i s i o n higher than ± 0.16% (2a) was obtained f o r a l l isotope r a t i o s r e l a t i v e to Pb **. 20  In the i n t e r p r e t a t i o n of these analyses, the reasonable, but  unproved, view that "primary" lead i s well-mixed lead from upper c r u s t a l rocks was accepted as a working hypothesis.  Consequently,  correlations  of i s o t o p i c data with geological occurrence, p a r t i c u l a r l y with stratigraphy, were sought. Galena deposits i n the East Kootenay d i s t r i c t f a l l i n t o two d i s t i n c t i s o t o p i c groups; a uniform group and a v a r i a b l e , more radiogenic a  group.  Deposits of the uniform group, including many of the large deposits  and a l l those of s t r a t i f o r m type, are r e s t r i c t e d to lower P u r c e l l (Aldridge Formation) rocks and seem to represent a widespread episode of lead-zinc mineralisation 1.2 to 1.4 BY ago.  A possible source of t h i s lead i s the  Aldridge Formation i t s e l f , and a possible agent of extraction i s connate brine.  On the assumption  that Aldridge sediments were the source, c a l c u l a -  tions indicate an age of about 2.6 BY for the provenance of these sediments. In contrast to the uniform leads, the v a r i a b l e leads are found i n small veins throughout the P u r c e l l sequence, and probably were emplaced i n Mesozoic or Cenozoic times. represent lead scavenged  The i s o t o p i c data suggest that these deposits  from P u r c e l l rocks, perhaps by f l u i d r e s t r i c t e d  ii  mostly to fracture systems.  Lead isotope analyses reported for other  parts of the B e l t - P u r c e l l basin are s i m i l a r to those presented  here,  permitting speculations on the evolution of lead isotopes over a very large region. For Kootenay Arc deposits, a close correspondence can be demonstrated, between lead isotope compositions and geological characteristics.  S t r u c t u r a l l y concordant deposits, mostly i n Cambrian carbonate  rocks, d i f f e r i n lead isotope composition  from transgressive deposits.  Other workers have suggested on geological grounds that the concordant deposits are s i g n i f i c a n t l y older (100 to 500 MY older) than those of transgressive type, and the i s o t o p i c data are consistent with suggestion.  Pb  206  /Pb  201  this  * r a t i o s of samples from Slocan City and Sandon  camps f i t a simple concentric zonal pattern, perhaps r e l a t e d to leaching of  lead from country rocks by r i s i n g o r e - f l u i d . Lead isotope compositions of four s i m i l a r s t r a t i f o r m deposits  i n the A n v i l Range area are nearly i d e n t i c a l and approximate "primary" leads.  The lead may have been derived from the l a t e Proterozoic or  Cambrian host rocks at the onset of Cambrian-Ordovician? metamorphism. In conclusion, the w r i t e r has demonstrated some close c o r r e l a tions between lead isotope data and observable geological features.  ( i . e . shallow, crustal)  These c o r r e l a t i o n s are regarded as supporting,  but  not demanding, the conclusion that i n a l l three areas studied the lead (including "primary" leads) i s of shallow c r u s t a l o r i g i n .  iii  TABLE OF CONTENTS ABSTRACT  i  TABLE OF CONTENTS  iii  LIST OF TABLES  vi  LIST OF FIGURES  vii  ACKNOWLEDGMENTS  xii  CHAPTER 1. INTRODUCTION 1.1 OBJECTIVES OF THIS STUDY  1  1.2 LEAD ISOTOPE AND GEOLOGICAL MODELS FOR THE GENESIS OF LEAD-ZINC ORES  3  CHAPTER 2.  LEAD ISOTOPES FROM THE EAST KOOTENAY DISTRICT, BRITISH  cowmiA 2.1 INTRODUCTION  10  2.2 AN OUTLINE OF THE GEOLOGY OF THE EAST KOOTENAY DISTRICT AND ADJOINING PARTS OF IDAHO AND MONTANA  10  Stratigraphy  10  Igneous Activity  15  Regional Metamorphism, Folding  and Faulting  16  Geochronology  19  Lead-Zinc  21  Mineralisation  2.3 PREVIOUS LEAD ISOTOPE WORK  23  2.4 DISCUSSION OF NEW LEAD ISOTOPE DATA  24  Late Precambrian  27  Leads  The mantle as a source The crust as a source The age of the source Mesozoic-Cenozoic  Leads  27 32 41 50  iv  2.5  COMPARISON WITH GALENA LEADS FROM BELT SUPERGROUP ROCKS IN NORTHWESTERN U.S.A. Late Precambrian  Leads  Pre-Ravalli leads Ravalli and Piegan Mesozoia-Cenozoia 2.6  53 56 62  leads  Leads  64  SUMMARY  CHAPTER 3.  52  67  LEAD ISOTOPES FROM THE KOOTENAY ARC, BRITISH COLUMBIA  3.1 PREAMBLE  71 71  3.2 OUTLINE OF THE GEOLOGY AND LEAD-ZINC MINERALISATION OF THE KOOTENAY ARC Geology Lead-Zinc  71 71  Mineralisation  74  Concordant deposits Transgressive deposits  75 75  3. 3  PREVIOUS LEAD ISOTOPE STUDIES  76  3. 4  DISCUSSION OF NEW LEAD ISOTOPE DATA  81  Concordant  Group  Transgressive Evolution  81  Group  of Lead Isotopes  88 in the Kootenay Arc  3.5 LEAD ISOTOPE ZONING IN SANDON, SLOCAN CITY, AND AINSWORTH CAMPS Slocan City and Sandon Camps Ainsworth  Camp  3.6 POSSIBLE RELATIONSHIPS BETWEEN KOOTENAY ARC LEADS AND LEAD IN PURCELL ROCKS 3.7 SUMMARY •  CHAPTER 4. 4.1  90 95 98 102 102 106  LEAD ISOTOPES FROM THE ANVIL RANGE, YUKON TERRITORY  INTRODUCTION  108 108  V  4.2 OUTLINE OF TEE GEOLOGY AND LEAD-ZINC MINERALISATION OF TEE ANVIL RANGE  108  Geology  108  Lead-Zinc Mineralisation  111  4.3 DISCUSSION OF LEAD ISOTOPE DATA  113  4.4 SUMMARY  123  CHAPTER 5.  124  SUMMARY  5.1 PURCELL LEADS 5.2 KOOTENAY ARC LEADS 5.3 ANVIL RANGE LEADS  1 2 4  1 2 5  1 2 6  REFERENCES  APPENDIX NOTES ON SAMPLES, ANALYTICAL METHODS, CALCULATIONS, PRECISION AND CONTAMINATION A.1 SAMPLES  A-l  A.2 ANALYTICAL METHODS  A-2  A.3 CALCULATIONS  A-6  A.4 PRECISION  A-10  A.5 CONTAMINATION  A-10  vi  LIST OF TABLES  Table 2.1  Isotopic composition of lead in galena from lead-zinc deposits in Purcell rocks, British Columbia  25  Table 2.II  Pb /Pb ratios and total lead contents of a l l minerals of a Precambrian ('vl.l BY) granite studied by Tilton and others (1955) . (The precision of these measurements i s low by present-day standards.)  35  Table 2 . I l l  Recorded production of some metals from a l l significant deposits i n Purcell rocks to 1970 (inclusive)  40  Table 2.IV  Two-stage model ages for Mesozoic-Cenozoic leads from Purcell Supergroup rocks.  52  Table 2.V  Isochron slopes and two-stage ages for Pre-Ravalli leads  60  Table 3.1  Some important lead-zinc deposits of the Kootenay Arc. Taken from Fyles (1967; p. 66, 67).  77  Table 3.II  Isotope compositions of lead in galena from concordant deposits, Kootenay Arc  82  Table 3.Ill  Isotope compositions of lead in galena from transgressive deposits, Kootenay Arc  83  Table 3.IV  Two-stage model ages for concordant deposits, upper anomalous line on f i g . 3.4. (Slope 0.119 ± 0.004)  88  Table 3.V  Slopes of least-squares lines through transgressive group leads (the lower anomalous lead line on f i g . 3.4)  89  Table 4.1  Lead isotope analyses, Anvil Range galenas  114  Table 4.II  Age of source rocks of sedimentary host of Anvil Range stratiform deposits (assuming a two-stage model)  121  Table A.I  Replicate analyses  A-7  Table A.II  Measurements of Broken H i l l Standard, Set A  A-8  206  20lt  vii  LIST OF FIGURES  F i g . 1.1  Location the East B i s the geologic  of the two regions studied. Region A i s Kootenay d i s t r i c t and Kootenay Arc. Region A n v i l Range, Yukon T e r r i t o r y . Major subdivisions are a f t e r Douglas (1970).  F i g . 1.2  Lead-zinc deposits of B r i t i s h Columbia and neighbouring parts of the United States.  F i g . 2.1  Approximate outcrop l i m i t of rocks deposited i n the B e l t - P u r c e l l basin (heavy l i n e ) . Map i s a f t e r Harrison (1972, p. 1218). Section AB i s taken d i r e c t l y from Gabrielse (1972, p. 526) and shows various formations of the P u r c e l l Supergroup (see f i g . 2.2) overlying Hudsonian? basement.  12  F i g . 2.2  Regional c o r r e l a t i o n scheme f o r B e l t - P u r c e l l s t r a t a proposed by Smith and Barnes (1966, p. 1409).  13  F i g . 2.3  Isopach map (not p a l i n s p a s t i c ) f o r the middle B e l t P u r c e l l carbonate u n i t . Taken from Harrison (1972, p. 1230). Contour i n t e r v a l i s 1000' .  15  F i g . 2.4  Scheme proposed by Harrison f o r the chronology of some events which have affected B e l t - P u r c e l l rocks. Taken d i r e c t l y from Harrison (1972, p. 1236).  21  F i g . 2.5  Generalised geological map, East Kootenay and Kootenay Arc regions.  26  F i g . 2.6  Plot of P b / P b v. P b / P b f o r a l l the analysed galena leads i n P u r c e l l rocks (table 2.1). The key i d e n t i f i e s the host rock . The growth curve is for (U /Pb ) = 9.09. present P l o t of P b / P b v. P b / P b f o r P u r c e l l galenas l i s t e d i n table 2.1. Growth curve i s f o r (Th /Pb ) „ = 39.60. present 2 0 7  2 3 8  2 0 1 t  1  2  2 0 6  2 0 l t  28  2 0 6  2 0 l t  29  2 0 l t  fc  F i g . 2.7  2 0 8  2 3 2  2 0 l +  2 0 l t  F i g . 2.8  P l o t of P b / P b v. P b / P b f o r the " l a t e Precambrian group" of galena leads l i s t e d i n table 2.1. The key i d e n t i f i e s the host rock of the galena mineralisation.  30  F i g . 2.9  Analyses of the l a t e Precambrian leads (table 2.1) are a r b i t r a r i l y divided above into two sets of d i f f e r e n t i s o t o p i c composition. These samples are plotted on the accompanying map and a c o r r e l a t i o n of composition with geographic l o c a t i o n i s suggested.  37  2 0 7  2 0 1 t  2 0 6  2 0 t t  vlii  Fig. 2.10  Correlation between size of producing mines in 206 Purcell rocks and their lead isotope ratio P b / P b 2 0 V Data from table 2.1 and 2.III. Note log scale for tonnages.  38  Fig. 2.11  The results of "frequent mixing" of leads for threeand eleven-stage models. Taken from Kanasewich (1968; p. 169 and 170).  43  Fig. 2.12a Calculated compositions for 50 hypothetical leads at various times in a five-stage history. Small dots, circles and large dots show compositions after 2.7, 1.8, and 1.3 BY (end). Primary growth curve i s for (U /Pb ) = 9.09, and numbers indicate b i l l i o n now ' years.  48  Fig. 2.12b Large circles represent the compositions of 50 hypothetical leads after five stages of evolution in various randomly chosen U/Pb environments since 3.0 BY, with f a i r l y thorough mixing at 1.3 BY (see text for details). Solid dots represent measured ratios of Purcell leads of the late Precambrian group. The growth curve shown i s the primary growth curve (U /Pb *=9.09) . If more complete mixing is assumed in the calculations, the scatter of the calculated values would more closely resemble the observed scatter.  49  Fig. 2.13  In Model A, the underlying basement i s supposed to be a source of radiogenic lead; i n Model B, distant basement supplies this component v i a the sediments.  50  Fig. 2.14  Region studied by Zartman and Stacey (1971). from p. 858 and 859 of their paper.  54  Fig. 2.15  Lead isotope results of Zartman and Stacey (1971). Taken from p. 851 of their paper.  55  Fig. 2.16  Plot of P b / P b v. P b / P b for analyses of Purcell galena leads (table 2.1) and Belt galena leads (Zartman and Stacey, 1971; their tables 1 and 2). The key identifies the host rock. The growth curve i s drawn for ( U / P b ) ^ = 9.09. present Plot of P b / P b v. P b / P b for the "late Precambrian group" of galena leads in Purcell rocks (table 2.1) and i n Belt rocks (Zartman and Stacey, 1971; p. 852 and p. 854). The symbols identify the host rock of the galena deposit. 20lt  57  20£t  58  Belt-Purcell leads of the late Precambrian group plotted above are split arbitrarily into three sets and these are plotted on the accompanying map using the same symbols. A correlation between isotopic composition and geographic location is suggested. Data from Zartman and Stacey (1971, p. 852, 854) and table 2.1 (this thesis).  59  238  238  20tt  20l  207  20lt  206  238  Fig. 2.17  Fig. 2.18  2 0 7  2 0 4  Taken  204  206  ix  F i g . 2.19  Large c i r c l e s represent the compositions of 50 hypot h e t i c a l leads a f t e r f i v e stages of evolution i n various U/Pb environments since 3.0 BY, with mixing at 1.3 BY. For the large open c i r c l e s , 5% of 2.7 BY lead has been added; for the large s t r i p e d c i r c l e s , 10% of 2.7 BY lead has been added. The s o l i d dots are measured P u r c e l l leads (table 2.1), the small c i r c l e s are Belt leads (Zartman and Stacey, 1971). Growth curve i s the primary growth curve of Stacey and others (1969), for ( U / P b ) = 9.09. now Diagram showing three possible interpretations of the slope for o l d Ravalli-Piegan leads.  61  F i g . 2.21  Comparison of Rb/Sr dating of B e l t i a n sediments by Obradovich and Peterman (1968) with the lead isotope i n t e r p r e t a t i o n of the " o l d " B e l t - P u r c e l l galenas given i n t h i s t h e s i s .  64  F i g . 2.22  The pattern of compositions which r e s u l t s from evolut i o n (growth, mixing) from two arrays i s shown i n the upper sketch. In the lower diagram, actual compositions from B e l t - P u r c e l l rocks are shown. I t i s suggested that the Mesozoic-Cenozoic leads could be controlled by the compositional pattern of the Precambrian leads.  66  F i g . 3.1  The Kootenay Arc  72  F i g . 3.2  Relationships of formations i n the southern part of the Kootenay Arc. Taken from Monger and Preto (1972, p. 32).  74  F i g . 3.3  P l o t of ore and rock leads from the Kootenay Arc, reported by Reynolds and S i n c l a i r (1971, p. 261).  80  F i g . 3.4  P l o t of P b / P b v. P b / P b for a l l the Kootenay Arc data l i s t e d i n tables 3.II and 3.III. Growth curve i s f o r ( U / P b ) , = 9.09. present P l o t of P b / P b v. P b / P b for a l l the Kootenay Arc data l i s t e d i n tables 3.II and 3.III. Growth curve i s for ( T h / P b ) „ = 39.60. present Sketches of three models which show d i f f e r e n t "non anomalous" components (A,B,C) for Kootenay Arc leads. S o l i d t r i a n g l e s represent "concordant" leads, open t r i a n g l e s represent "transgressive" leads. 2 0 l +  84  2 0 l t  85  2 3 8  F i g . 2.20  2 0 7  2 0 t t  2 0 6  2 3 8  F i g . 3.5  2 0 8  2 0 t t  Fig.  3.7  62  2 0 1 t  2 0 6  2 3 2  F i g . 3.6  2 0 1 +  2 0 l f  Two examples of zonal patterns. S i n c l a i r (1971).  Taken from Orr and  91  96  F i g . 3.8  Sectional sketch showing a simple model to explain lead isotope zonation i n mineral deposits by addition of lead from country rocks to lead i n a c i r c u l a t i n g fluid.  97  F i g . 3.9  Contoured P b / P b r a t i o s f o r Slocan City and Sandon data (table 3.III). Geology a f t e r Cairnes (1934) and L i t t l e (1960). Two samples (901 and 887) do not f i t the contours.  99  F i g . 3.10  Contoured P b / P b r a t i o s f o r analyses of samples from Ainsworth camp (table 3.III). Geology a f t e r Fyles (1967).  101  F i g . 3.11  Diagrammatic i l l u s t r a t i o n of two extreme p o s s i b i l i t i e s f o r r e l a t i o n s h i p s between the three main families of leads (A,B,C).  103  F i g . 3.12  A comparison of isotope r a t i o s of samples from A n v i l Range (table 4.1), Pine Point (Cumming and Robertson, 1969, p. 731), and Shuswap deposits (table 3.II).  105  F i g . 4.1  Geological map of A n v i l Range. K l u i t (1968, pp. 46-47).  109  F i g . 4.2  Outlines of the three main A n v i l Range lead-zinc deposits drawn to a common scale and o r i e n t a t i o n . S i t e s of the analysed samples l i s t e d i n table 4.1 are indicated by the numbered dots.  110  F i g . 4.3  V e r t i c a l cross sections of Faro deposit. Taken from Tempelman-Kluit (1968, p. 50). Sections of Swim and Vangorda deposits are somewhat s i m i l a r but lack the greenstones and the quartz d i o r i t e (Tempelman-Kluit, 1968, p. 51).  112  F i g . 4.4  P l o t of P b / P b v. P b / P b for a l l Anvil Range leads l i s t e d i n table 4.1. Growth curve i s for ( T h / P b ) = 39.60. present Plot of P b / P b v. P b / P b for a l l Anvil Range leads l i s t e d i n table 4.1. Growth curve i s for ( U / P b ) = 9.09 ± 0.06. present  2 0 6  2 0 6  2 0 8  2 3 2  F i g . 4.5  2 0 l t  2 0 4  After Tempelman-  2 0 t t  2 0 6  2 0 1 +  116  2 0 l +  2 0 6  2 0 1 t  . 116  2 0 £ t  2 0 7  2 3 8  2 0 l +  fc  F i g . 4.6a  Plot of P b / P b v. P b / P b f o r some early analyses (on an older mass spectrometer) of leads from Swim, Vangorda and Faro deposits. These analyses, which are not normalised to the Broken H i l l Standard, were discarded.  118  F i g . 4.6b  Plot of P b / P b v. P b / P b f o r the analyses of Swim, Vangorda and Faro samples l i s t e d i n table 4.1.  118  2 0 7  2 0 7  2 0 l t  2 0 1 t  2 0 6  2 0 6  2 0 l f  2 0 t t  xi  F i g . 4.7  Some features of A n v i l Range deposits which show increases with increasing metamorphic grade (Swim to Faro). Grain s i z e data from Tempelman-Kluit (1970). Isotope data from table 4.1. Tonnage of lead and z i n c : Faro, Findlay (1969); Vangorda, Chisholm (1957); Swim, Northern Miner (March 9, 1967, p. 5).  119  F i g . 4.8  Relation of occurrence of base-metal deposits of northern B.C. and southeastern Yukon to facies of Lower Cambrian and Eocambrian s t r a t a . Taken from Gabrielse (1969, p. 28). Faro, Vangorda, Swim shown as s t a r s , other deposits as dots.  122  F i g . A. 1  Chart record of spectrum produced by e l e c t r o n bombardment (about 120 ev) of tetramethyl lead vapour. P r i n c i p a l ions responsible for each set of peaks are i d e n t i f i e d . Note mass scale below spectrum and the attenuation factors ( i n brackets).  A-3  F i g . A.2  Chart record showing d e t a i l of peaks at masses 251 (mainly P b ( C H ) + ) and 252 (mainly P b ( C H ) ) . Resolution of the mass spectrometer i s about 460, peak shape i s about 0.67 (10% value). The distance (dispersion) between the centres of the two ion beams which these peaks represent i s about 0.05 inches.  A-3  T y p i c a l chart record of trimethyl lead spectrum. Attenuation f a c t o r s , atomic mass numbers, time s c a l e , and p r i n c i p a l peak r e l a t e d to each of the four isotopes of lead are shown. The height of the l a r g e s t peak (253 a.m.u.) corresponds to an ion current of about 5*10 amp. As w e l l as being output i n chart form, the spectrum i s d i g i t i s e d (5 readings/sec) and f i l t e r e d to remove frequencies above about 0.6 hz. Four or f i v e f i l t e r e d readings are obtained on each peak top.  A-4  Plot of mean values obtained by other workers f o r the Broken H i l l Standard, and the r e s u l t s of table A.II. The expected (fractionated) r a t i o s were calculated from the two absolute values reported by Stacey and others (1969) and Cooper and others (1969) , and i t was assumed that gas flow into the source was viscous and flow out was molecular (Halsted and Nier, 1950; Whittles, 1964).  A-9  206  2 0 7  3  F i g . A. 3  3  +  3  3  -11  F i g . A.4  xii  ACKNOWLEDGMENTS  The work of my supervisor, Dr. A.J. Sinclair, f i r s t interested me i n the use of lead isotopes i n the study of ore deposits.  Dr. Sinclair  suggested the present project and his ready assistance during i t s progress i s sincerely appreciated. Analytical work was carried out i n laboratories of the Department of Geophysics and Astronomy, and I am indebted to many members of this department for support and guidance.  Dr. R.D. Russell and Dr. W.F.  Slawson helped i n various ways, and the generous fashion in which they made f a c i l i t i e s available i s much appreciated.  It i s a special pleasure  to thank Dr. J . Blenkinsop for his help, advice, and encouragement. Capable technical assistance was provided by E.J. B e l l i s , R.D. Meldrum, S.N. Newman, K.D. Schreiber and H. Verwoerd ( a l l of the Department of Geophysics and Astronomy), by E.G. Montgomery (Geological Sciences Centre) and E. Williams (Physics Department). The help and guidance of two geologists, Dr. D.J. TempelmanKluit and R.G. Gifford, has been of great value to me and i s gratefully acknowledged.  Others kindly provided me with samples, including Dr. A.E.  Aho, R.G. Chaplin, Dr. J.T. Fyles, G. Jilson, Dr. G.B. Leech, A.S. Macdonald, Dr. H.C. Morris, J.F.W. Orr, B. Price, J.B.P. Sawyer, and W.M. Sirola. Members of the committee, and Dr. R.D. Russell, are thanked for reading and commenting on drafts of this thesis.  The time spent by  Dr. K.C. McTaggart in editing is particularly appreciated.  The thesis  was typed by R. Rumley. Financial aid provided by a Killam Predoctoral Scholarship is gratefully acknowledged.  1  CHAPTER 1.  1.1  INTRODUCTION  OBJECTIVES OF THIS STUDY  The writer has determined the isotopic composition of lead i n 132 galena samples taken from two regions i n the Canadian part of the Western Cordillera ( f i g . 1.1). In this thesis an attempt i s made to relate this isotope data to the regional geology.  Fig. 1.1  Location of the two regions studied. Region A i s the East Kootenay district and Kootenay Arc. Region B i s the Anvil Range, Yukon Territory. Major geologic subdivisions are after Douglas (1970). The belt containing the Coeur d'Alene district of Idaho and the  mining camps of the East Kootenay district and Kootenay Arc i n British Columbia i s one of the most productive lead—zinc—silver metallogenic  W \  FIG. 7-2 Lead-zinc deposits of > British Columbia and \ ^neighbouring parts of the United States  BRITISH  Ruddock Creek  COLUMBIA  ancouver  WASHINGTON  V  ( o f f e r Fyles and others, , m o p 14-1 C.I.M. Special \f\Volume No. 8 , 1966)  3  provinces ( f i g . 1.2) in the world.  By studying lead isotopes from galena  deposits in the Canadian part of this belt i t was hoped to identify the source of the lead and to account for the persistence of lead-zinc mineralisation from Precambrian to Tertiary times. Three large "stratiform" lead-zinc deposits were recently discovered i n the Anvil Range, Yukon Territory (fig. 1.1).  It was  thought that study of the lead isotope composition of these deposits might reveal the origin and history of the lead.  The origin of " s t r a t i -  form" lead-zinc deposits has been a subject of debate since Stanton and Russell (1959) f i r s t suggested that the lead in many deposits  of this  type came from a uniform U-Th-Pb system, possibly the mantle.  1.2  LEAD ISOTOPE AND GEOLOGICAL MODELS FOE THE GENESIS OF LEAD-ZINC ORES  It i s widely accepted that "anomalous"* ore-leads are derived from upper crustal rocks.  In contrast there has been long-standing  dis-  agreement as to whether the crust or mantle is the source of the "primary"* leads of many large stratiform lead-zinc deposits, such as Mt. Isa and Broken H i l l in Australia, and Sullivan i n Canada. However, in recent years, evidence from lead isotope and other studies has tended to converge in support of a crustal origin for both primary and anomalous lead.  Only  an outline of this evidence i s given here for there are many recently  •anomalous" lead; •"primary" lead;  lead that has developed in more than one U-Th-Pb system (= multistage lead) lead that appears to have developed in a unique U-Th-Pb system which i s world-wide. Primary leads f i t "primary" growth curves on graphs of P b / P b v. P b / P b and P b / P b v. P b / P b \ (See Stacey and others, 1969; Cooper and others, 1969 0 207  206  204  208  20l+  2 0 6  2 0  201+  4  published discussions dealing with the origins of lead in ore deposits (e.g.  Krauskopf, 1967; 1971; White, 1968; Doe, 1970; Richards, 1971;  and Russell, 1972).  Richards (1971) has given a more complete account  of many of the arguments mentioned here. Those who suggested the mantle as a possible source of primary lead ores (e.g. Russell, 1956; Stanton and Russell, 1959; Ostic and others, 1967; Kanasewich, 1968) emphasized the apparent uniformity of the U/Pb and Th/U ratios calculated for the source of many stratiform deposits.  In contrast they pointed out that these ratios are highly  variable i n the crust.  Others (e.g. Shaw, 1957; Chow and Patterson,  1962; Brown, 1965; Armstrong, 1968) suggested that i f lead was concentrated from a large volume of crustal rock, sediment for example, and thoroughly mixed, the result could be lead with an apparently uniform U/Pb and Th/U source, like that calculated for primary leads.  A conse-  quence of this suggestion i s that the primary growth curve represents the evolution throughout time of average lead in the upper crust, rather than the mantle.  To test this hypothesis, Kanasewich (1962) and  Russell and others (1966) investigated by computer-simulation what the effect of mixing heterogeneous crustal leads would be, and they concluded that although such mixing might give rise to an apparent primary lead, i t would have to be thorough to escape detection. There i s some evidence, however, that isotopes can be thoroughly mixed in crustal environments by natural processes. For example, there is a remarkable homogenisation of sulphur isotopes during migration of oils (Monster, 1972), and sulphur from a single o i l f i e l d can be extremely uniform over a wide area (Thode and others, 1958).  Thus, i t i s conceiv-  5  able that thorough homogenisation of crustal leads could give rise to the narrow range of Th/U values calculated from primary leads, the feature that Kanasewich (1968) considered to be the most convincing evidence for a uniform mantle source.  It might be significant that the actual value  of the Th/U ratio calculated for the source region of primary leads is about 4 (Stacey and others, 1969; Cooper and others, 1969), similar to the average of measured Th/U values from shales (Rogers and Adams, 1969). Numerous authors have suggested thick shale sequences as possible sources of the lead and zinc in mineral deposits. One measure of the early success of the hypothesis of mantle origin was that single-stage ages calculated from primary leads were reasonably close to independent estimates of ages of mineralisation, generally within 150 MY according to Kanasewich (1968).  With a better  knowledge of ages of individual ore bodies, however, discrepancies have become more obvious (see Richards, 1971).  Although these differences  in age can be accounted for to some extent by making the mantle-origin hypothesis more complicated, i t would be more convincing i f these discrepancies did not exist. Stanton and Russell (1959) were careful to state that i t was the "stratiform pyritic" type of lead-zinc deposit that they considered might contain lead derived from the mantle.  These deposits commonly  occur in fine-grained carbonaceous sediments and they are associated consistently with fragmental volcanic rocks.  Stanton (1960) concluded  that these deposits resulted from the biologic concentration of basemetal and sulphur emitted during volcanic activity, and that they were lenses of sulphide-rich sediment (see also Stanton, 1966).  Although i t  i s true that leads from many deposits of the stratiform type are primary,  6  some leads from other types of deposits where links with volcanism are not obvious also seem to be primary, for example, Pine Point (Cumming and Robertson, 1969) and the Kupferschiefer (see Doe, 1970, p. 47; Wedepohl, 1971).  Therefore, i t i s suggested that volcanic activity,  with the implication of access to the mantle, i s not necessary  for the  formation of a primary lead. There have been many studies of the isotopic composition of trace amounts of lead i n rocks (see Doe, 1970) that have some bearing on the sources of lead i n mineral deposits. For example, basalts are among the rocks most likely to contain samples of mantle lead and a comparison of basalt leads and primary leads i s therefore of interest.  If  primary ore leads came from the mantle, i t would be reasonable to expect leads of Cenozoic basalt to have uniform isotopic ratios with values similar to those of a Cenozoic primary ore lead.  As analyses of basalt  (mostly oceanic) leads have become more numerous and more reliable, i t has been found that they are not in the least l i k e primary ore leads, and they are not uniform (Houtermans and others, 1964; Tatsumoto, 1966; Russell, 1972).  This latter fact implies that the mantle has non-uniform  U/Pb and Th/Pb ratios, whereas these ratios were thought to be constant for the source of primary leads.  Furthermore, values for the present  day ratio U /Pb * (y) for the source region of basalt leads are sig238  201  nificantly lower than that for stratiform leads (Gast, 1967).  With  present analytical accuracy i t has become clear that the primary leads of stratiform ores and basalt leads are products of two different and long-distinct geochemical systems, and that the lead of one of these systems can not be easily derived from the other (Russell, 1972).  As  7  Richards (1971) has argued i n some detail, the case for a more-or-less direct mantle source for the primary leads found in many large lead-zinc deposits i s now weak, i f not untenable. In recent years there has been a shift i n geochemical and geological opinion towards a crustal and non-igneous source for the lead of most lead ore deposits.  This view, an old one (e.g. see Posepny,  1902) , has been strengthened by several developments.  One is the dis-  covery of some modern lead-bearing brines, for example i n the Red Sea (Degens and Ross, 1969; Ross, 1972), near the Salton Sea in California (White, 1968), and on the Cheleken Peninsula, U.S.S.R. (looms, 1970). Another development includes laboratory studies of brine-filled inclusions from ore deposits (e.g. Roedder, 1967), of hydrogen and oxygen isotopes of brines and of some fluid inclusions (e.g. White, 1968; Ohmoto and Rye, 1970), and of sulphur isotopes of sulphides (e.g. Sangster, 1971).  A third development includes theoretical studies (e.g. Helgeson,  1967, 1968), and a fourth includes f i e l d studies of some ore-deposits such as Pine Point (Jackson and Beales, 1967; Billings and others, 1969)-. As a result of such investigations there i s support for the idea that connate* Na-Ca-Cl brines can leach lead and zinc from clays, organic matter, feldspars and other minerals of common fine-grained sediments, and can selectively precipitate these metals, perhaps where the migrating brine encounters H S-bearing gas, or reacts with wall 2  rocks, or mixes with other waters.  Analogies have been made between the  generation, migration and accumulation of o i l and of lead and zinc (e.g. •connate brine:  this term has many meanings, and i t i s used here in a loose sense to refer to i n t e r s t i t i a l waters of sediments and volcanic rocks (see White, 1968; p. 302).  8  I l l l n g , 1968; Dozy, 1970), and Jackson and Beales (1967) have argued that the accumulation of many lead-zinc deposits can be viewed as a part of the normal evolution of a sedimentary basin.  The many variations  on this hypothesis have been discussed by Knight, 1957; Noble, 1963; Davidson, 1967; White, 1968; Beales and Jackson, 1968; Krauskopf, 1971; Dunham, 1970; Tooms, 1970; and E l l i s , 1971, among others. In contrast, accumulating information has given l i t t l e support to theories that the mantle, cooling igneous rocks, or sea-water are significant direct sources for large lead-zinc deposits i n sedimentary rocks. The writer, i n view of the discussion above, accepts as a working hypothesis  that "primary" leads can originate from crustal rocks,  in particular from sequences of fine-grained sediments.  Interpretation  of lead isotope data presented i n this thesis was guided by this conclusion, which was found to be useful in that i t offers a simple explanation for a number of relationships between isotopic data and geology, stratigraphy in particular.  *  *  *  Recent discussions on the mathematical models used i n interpretation of lead isotope data w i l l be found i n Hamilton, 1965; Slawson and Russell, 1967; Kanasewich, 1968; Stacey and others, 1968; Doe, 1970; and Russell, 1972. Analyses reported i n this thesis were made on a gas-source mass spectrometer i n the Department of Geophysics and Astronomy of the University of British Columbia.  Isotope ratios are presented as absolute  9  ratios, having been normalised to the absolute ratios of the Broken H i l l Standard as reported by Stacey and others (1969).  The precision of the  analyses presented i s better than ±0.16% (2a sample) for a l l the isotope ratios relative to P b  204  .  Some details of analytical work, including  the calculation of precision, are given in the appendix.  10 CHAPTER 2.  LEAD ISOTOPES FROM THE EAST KOOTENAY DISTRICT, BRITISH COLUMBIA  2.1 INTRODUCTION The lead Isotope compositions of 47 samples from galena deposits in Precambrian rocks of the East Kootenay district were determined.  In  this chapter these results are interpreted i n relation to regional geology, and are compared with published lead isotope data from galena deposits of northwestern U.S.A. Although this thesis i s mainly concerned with Purcell rocks of southeastern British Columbia, i t deals i n a general way with the BeltPurcell rocks exposed on both sides of the Canada-U.S.A. border (fig. 2.1). Harrison (1972) referred to this region as the "Belt Basin", a convenient term for what he suggests was an epicratonic re-entrant of a Precambrian sea that extended along the western edge of North America.  2.2 AN OUTLINE OF THE GEOLOGY OF THE EAST KOOTENAY DISTRICT AND ADJOINING PARTS OF IDAHO AND MONTANA Stratigraphy Sedimentary rocks of the late Precambrian Belt-Purcell succession and their correlatives extend in a discontinuous strip from northern Alaska into California.  The fine-grained clastic and carbonate rocks of the Belt-  Purcell Supergroup are weakly metamorphosed, are commonly from 15,000' to 35,000' thick, and generally show l i t t l e variation over large areas (Gabrielse, 1972; Smith and Barnes, 1966; Ross, 1970; Harrison, 1972). The base of the Belt-Purcell sequence i s rarely exposed, but in southwestern Montana Belt sediments rest unconformably on crystalline rocks in  11  several places (e.g. McMannls, 1963; G i l e t t i , 1968).  Belt-Purcell and  correlative rocks are unconformably overlain by approximately  coextensive  Precambrian (Windermere and equivalents) to Lower Palaeozoic sedimentary rocks.  The basal Windermere rocks are diamictites in many places  (Aalto, 1971; Stewart, 1972; Gabrielse, 1972). Belt-Purcell sediments were deposited in an extensive, longlived, stable marine basin.  Modern analogues that have been suggested  are the Gulf Coast Geosyncline (Reesor, 1957; Price, 1964) and the continental shelf off eastern North America (Gabrielse, 1972). Attempts have been made to correlate Belt-Purcell rocks throughout the basin, and the scheme of Smith and Barnes (1966) i s followed in this thesis.  These authors recognised two major cycles in the Belt-  Purcell succession, each cycle consisting of a lower carbonaceous and/or carbonate-bearing sequence and an upper reddish or greenish carbonate-poor sequence.  They proposed a four-fold division (fig. 2.2), Pre-Ravalli and  Ravalli sediments forming the older cycle and Piegan and Missoula Groups the younger cycle.  Smith and Barnes (ibid.) suggested that the cycles  were related to slow fluctuations in water depth on a large scale. The carbonaceous, "varved", pyritic (pyrrhotitic in Purcell) siltstone deposited near the axis of the basin was considered to imply stable, deep-water reducing conditions, whereas the mud-cracked, reddish (hematitic) and greenish siltstone of the upper half of the cycle suggested a shallowwater, oxidising environment.  Pre-Ravalli rocks (Prichard and Aldridge  formations) were probably deposited in deeper water than were succeeding strata (Price, 1964). Results of an extensive mineralogic and geochemical study by  12  0  KIlOMITiaS —  |0 MIIIS  Restored section showing postulated configuration of miogeocline during early Purcell time. Data mainly from Price, 1964.  Fig. 2.1 Approximate outcrop limit of rocks deposited i n the Belt-Purcell basin (heavy line). Map is after Harrison (1972, p. 1218). Section AB is taken directly from Gabrielse (1972, p. 526) and shows various formations of the Purcell Supergroup (see f i g . 2.2) overlying Hudsonian? basement.  13 H7°W  50 N  CAN. U.S."  i  *-» 3  111°  MARYSVILLE & DUCK CRK.  PASS  Greenhorn Mt  40-"  LEGEND  Salt—cast-bearing Carbonate —bearing,  strata carbonaceous  formations Carbonaceous  formations  Fig. 2.2 Regional correlation scheme for Belt-Purcell strata proposed by Smith and Barnes (1966, p. 1409).  14  Harrison and Grimes (1970) of some Belt rocks from Idaho and Montana probably can be applied to the bulk of Belt-Purcell sediments.  Harrison  and Grimes concluded that the overall chemical composition, excellent grain-size sorting and the uniformity of mineralogy were the result of very effective homogenisation of clastic components from a granitic source.  Evidence that the craton to the east was the important source  of Purcell sediment is provided by facies changes and eastward thinning of strata (Reesor, 1957; Price, 1964).  There i s no evidence in Prichard  and Aldridge strata of a basin margin or a sediment source to the west, although there i s evidence for sediment transport from a southerly direction, perhaps along the axis of the basin (McMannis, 1963; Bishop and others, 1970; Huebschman, 1972).  Facies changes in Ravalli and younger  rocks show, however, that these sediments were deposited i n a  N.W.  trending trough (Smith and Barnes, 1966). The carbonate-bearing middle part of the Belt-Purcell Supergroup is apparently the principal correlation marker in the sequence (Smith and Barnes, 1966), and the nature of the basin at this time is suggested by the isopach map (fig. 2.3) of Harrison (1972). Great thickness of strata, uniformity of sediment supplied to the basin, stability of depositional environment, the slow change in facies controlled by water depth, and the long duration of deposition (presumably intermittent) are important features of Belt-Purcell sedimentation.  15  Fig. 2.3  Isopach map (not palinspastic) for the middle Belt-Purcell carbonate unit. Taken from Harrison (1972, p. 1230). Contour interval i s 1000' .  Igneous Activity  .  Igneous activity of Precambrian age includes the extrusion of Purcell lava, and the intrusion of the granitic Hell-Roaring Creek Stock, of lamprophyre dikes, and of widespread s i l l s and dikes of diabase.  The  16  age of the Purcell lava relative to the sedimentary record (fig. 2.2) i s well known, and the Hell-Roaring Creek Stock (1260 MY*) seems reliably dated, but the lamprophyres and diabase s i l l s are not well dated.  For  example, there seem to be both Precambrian and Tertiary lamprophyre dikes (Hobbs and Fryklund, 1968; Leech and Wanless, 1962), and the extensive t h o l e i i t i c diabase s i l l s (Purcell intrusives or Moyie intrusives) are probably of more than one age.  In Purcell rocks, these diabase s i l l s  are concentrated at several stratigraphic levels, particularly in Aldridge and Kitchener strata (Leech and Wanless, 1962), but they occur in decreasing volume as high as the Mt. Nelson Formation (Rice, 1941). Granodiorite to quartz monzonite batholiths and stocks of Jurassic to Tertiary age intrude and metamorphose Belt-Purcell rocks. The largest of these are the Idaho Batholith, Boulder Batholith, Kaniksu Batholith and White Creek Batholith, a l l of which seem to be Cretaceous in age (McDowell and Kulp, 1969; Yates and Engels, 1968; Wanless and others, 1968). Regional Metamorphism, Folding  and  Faulting  Except near major intrusions, Belt-Purcell sediments are weakly metamorphosed, rarely beyond greenschist facies (Leech and Wanless, 1962; Harrison, 1972).  The age of this regional metamorphism of Belt-Purcell  sediments i s not well known. The principal metamorphism probably i s Precambrian i n age, although later metamorphism might also be involved. Leech (1962, 1963) was one of the f i r s t to recognise the importance of  *A summary of geochronology, with references, is given on p. 19 . Units used for ages are MY = million years (10 years) and BY = b i l l i o n years (10 years). 6  9  17  Precambrian (probably Pre-Windermere) metamorphism, a conclusion he reached from K/Ar dating of metamorphic micas in Aldridge rocks, and from the discovery (Leech, 1962) that the Hell-Roaring Creek Stock was Precambrian. Many dates from micas in Aldridge rocks are probably meaningless hybrid ages, but one date of 710 MY might be reliable according to Leech (Wanless and others, 1967).  In Idaho, two areas of high grade metamorphic  rocks have been dated at about 1500 MY (Reid and others, 1970; Clark, 1971) and these are the earliest ages of metamorphism yet obtained in Belt-Purcell rocks. With the exception of tight E-W folds near Coeur d'Alene, most folds in Belt-Purcell rocks are open and trend NW to NE.  The Purcell  Geanticline (fig. 2.1) i s the major regional structure, a north-trending, north-plunging broad anticlinorium that Leech and Wanless (1962) argued was principally a Mesozoic structure, but which Harrison (1972) suggests could be Precambrian.  In Coeur d'Alene region, the major folding i s  regarded by Hobbs and Fryklund (1968) as being older than a 1250 MY old uraninite vein, and near Kimberley, B.C., the Hell-Roaring Creek Stock (1260 MY) intrudes Aldridge rocks that might have been deformed previously (Leech and Wanless, 1962; Ryan and Blenkinsop, 1971).  Leech and Wanless  (1962) showed that some folds near Kimberley were cut by lamprophyres with a minimum age of 765 MY.  Belt-Purcell sedimentation was terminated  by an episode of mild metamorphism and folding that resulted i n a slight angular discordance between Belt-Purcell and overlying Windermere rocks (Reesor, 1957).  A few apparently reliable ages of between 700-800 MY  have been determined from metamorphic minerals in Belt and Purcell rocks (Goldich and others, 1959; Wanless and others, 1967), and these dates could represent the age of this pre-Windermere metamorphism.  In any case,  18  this metamorphism and deformation must be younger than about 930 MY, the age obtained by Obradovich and Peterman (1968) for some uppermost Beltian strata. In summary, although the evidence i s incomplete and partly unconvincing, i t seems there was metamorphism and folding before 1200 MY (approximately) that affected at least small areas of lower Belt-Purcell rocks, and a later deformation (700-800 MY?) reflected i n the slight angular discordance between Windermere and Belt-Purcell sequences.  Simi-  lar conclusions have been reached by Reid and Greenwood (1968) and by Harrison (1972).  High grade regional metamorphism and intense deformation  has affected Windermere to Mesozoic rocks west of the Purcell Geanticline and there may have been some mild deformation and metamorphism of BeltPurcell rocks at the same time(s) (Leech and Wanless, 1962). Although i t i s d i f f i c u l t to assess the relative Intensities of the various episodes of Precambrian and Phanerozoic metamorphism and folding, their cumulative effect has not been great. For example, in most exposures, Belt-Purcell sediments s t i l l contain clearly recognisable primary sedimentary structures, such as mud cracks, ripple marks, salt crystal casts.  As Gabrielse (1972) observes, the thick Belt-Purcell  sedimentary wedge seems to have served as "pseudo-basement" from Windermere times on, although i t was affected by thrust faulting and probably became separated from the craton during Rocky Mountain deformation in late Mesozoic - early Tertiary time (Bally and others, 1966). There is evidence for Precambrian motion on some major faults, including Osburn Fault (Hobbs and others, 1965) and Hope Fault (Harrison and others, 1972) in Idaho, and some small faults near Kimberley (Leech  19  and Wanless, 1962; Freeze, 1966).  Repeated movement and complex histories,  including later folding, have been suggested for some faults (Hobbs and Fryklund, 1968; Leech and Wanless, 1962; Dahlstrom, 1970). Geoohronology Geochronology of basement rocks, Belt-Purcell sediments, intrusives, and ages of deformation and of mineralisation have been summarised by numerous writers, including Obradovich and Peterman, 1968; G i l e t t i , 1968; Hobbs and Fryklund, 1968; Gabrielse, 1972; and Harrison, 1972.  Harrison (1972) made an attempt to unify the available information  and reconcile the conflicts (fig. 2.4).  Some of these conflicts l i e i n  the fact that metamorphic and intrusive events that affected lower BeltPurcell rocks seem to have occurred while sedimentation was s t i l l in progress in the upper part of the sequence, but they are not reflected obviously in the sedimentary record. Especially confusing i n this regard are the 1260 MY old stock and ?coeval sillimanite-grade metamorphism near Kimberley (Ryan and Blenkinsop, 1971), and the 1500 MY ages determined on zircons of gneisses in Idaho that are thought to be metamorphosed lower Beltian sediments (Reid and others, 1970; Clark, 1971).  As another  example, Obradovich and Peterman (1968) concluded from a Rb/Sr study of Belt sediments that there were three distinct periods of sedimentation (>1300, 1100, <s900 MY) separated by breaks of about 200 MY — breaks not yet  identified in the f i e l d .  Other conflicts are probably due to the  variety of techniques and materials used —  U/Pb on zircon, Rb/Sr on  sediments, K/Ar on altered s i l l s , and to interpretations of spurious data. As Harrison (1972) remarks, there are a number of alternative interpretations of present data, none of them completely satisfactory.  In the  20  writer's opinion, only a rough sense of the order and probable ages of events can be surmised at present, despite the fairly extensive geochronologic work. Geochronological work to date in that segment of the BeltPurcell basin exposed in British Columbia is summarised below. Reynolds and Sinclair (1971) calculated a single-stage lead age of 1.2 BY for galena from Sullivan Mine.  The Hell-Roaring Creek Stock was dated at  1260 ± 50 MY by whole rock Rb/Sr methods (Ryan and Blenkinsop, 1971), after preliminary K/Ar dates of 705 MY and 769 MY were obtained by Leech and Wanless (1962), and by Hunt (1962), respectively. This stock i n trudes Aldridge strata (previously deformed?) and a Moyie s i l l .  Nearby  regionally-metamorphosed Aldridge rocks have given K/Ar ages of 745 and 790 MY (Leech and Wanless , 1962), and a Rb/Sr age of about 1000  MY  (Ryan and Blenkinsop, 1971) and this metamorphism could be the same age as the stock.  Moyie intrusions contain amphibole dated by K/Ar methods  (6 analyses) at 883 - 1580 MY (Hunt, 1962).  Hunt (1962) also dated  hornfels of the Purcell lava at 1075 MY by whole-rock K/Ar methods. Leech and Wanless (1962) obtained a K/Ar age of 765 MY (and of 580  MY)  on biotite from a lamprophyre dike that cuts Sullivan ore, and they interpreted this as a minimum age for both dike and ore.  Leech (e.g.  i n Wanless and others, 1965; Wanless and others, 1967, 1968) attempted to date mica from Aldridge rocks, but he considered most of the ages (209 to 1310 MY) were meaningless hybrid ages.  In his opinion, the  age of only one sample (in Wanless and others, 1967) seemed likely to be a true metamorphic age (710 MY), and Leech commented that this age was d i f f i c u l t to reconcile with the prevailing view that the age of Important metamorphism was Mesozoic.  21  GEOLOGIC AGE (nvy.)  SEDIMENTARY OEPOSITS AND THICKNESS  UNCONFORMITIES  700  MAGMATIC E V E N T S  Volcanics Gabbroic sills  Windermere System of Conoda (22,000+ ft)  TECTONIC EVENTS  METAMORPHIC EVENTS  East Kootenay eventEast Kootenay orogeny biotire-grade regional Purcell anticlinorium metamorphism at depth  800  Upper part o f Missoulo Group (13,200-+ ft)  900  1000  McNomoro Bonner  1100  Shepord Purcell Lovo  Upper port of the lower port cf Missoula Group (11,000 ft)  Minor folding and tilting along eastern edge  Lower part of the lower part of Missoula Group 16,300 ft)  Purcell Lava; gabbroic sille  Snowiiip Middle Belt carbonate unit (14,500 ft)  1200  Major change in bosin Coeur d'Alene event(7)Coeur d'Alene lead and shape. Questionable high grade to south, biouranium veins (calculated faulting and folding in tite grade in basin ages may be too old) Coeur d'Alene area  H«2jnp-Wolloct_ 1300  St. Regis-Spokone  I4O0  Rovollf Group (18, SOO ft)  Granodiorite at Hellroaring Creek  Lower Belt (22,000+ ft)  Gabbroic sills  Granitic intrusions, now augen gneisses, in Elk City and Priest River areas, laaho(pre-Balt?)  1300  Warping to form upper Ravalli basin  Elk City event(7) (pre-Belt?)  Regional metamorphism affecting Prichard near Alberfon, Montana  Elk City event!?) (pre-Belt?)  1600  1700  Pre-Belt magmafic and metamorphic events  Estimated times of some Belt events. Extent o f unconformities: basin wide, indicated by  F i g . 2.4  Lead-Zinc  solid line; local, long dashed l i n e ; inferred, short dashed line.  Scheme proposed by Harrison for the chronology of some events which have affected Belt-Purcell rocks. Taken directly from Harrison (1972, p. 1236).  Mineralisation Lead, zinc, and silver are the economically important metals of  mineral deposits in Belt-Purcell rocks, although there are widespread occurrences of low-grade strata-bound copper mineralisation (Clark, 1971;  22  Harrison, 1972).  The largest Pb-Zn-Ag production has come from the  Sullivan Mine (B.C.), and from the mines of the Coeur d'Alene district (Idaho).  Ore deposits of the Coeur d'Alene are mainly replacement veins  along steeply-dipping fracture systems in Prichard, Burke, Revett, St. Regis 1968).  and,to a lesser extent, Wallace formations (Hobbs and Fryklund, The Sullivan Mine is an unusually large, gently-dipping s t r a t i -  form deposit at the boundary of the lower and middle divisions of the Aldridge Formation (Swanson and Gunning, 1945; Leech and Wanless, 1962; Freeze, 1966). A convenient non-genetic classification of lead-zinc* deposits of the East Kootenay district is that of Leech and Wanless (1962), summarised below. (1)  Conformable to sedimentary to host-rocks.  This group includes  Sullivan and some other important mines in Aldridge strata. (2)  Small fissure veins within Moyie s i l l s that intrude Aldridge strata.  (3)  Veins and replacements localised by fractures i n Purcell sedimentary rocks.  Most veins belong to this class. Deposits  in Coeur d'Alene district are of this type (in Belt rocks). Some deposits are known to be Precambrian and others are Tertiary but the ages of most are unknown. Although Hobbs and Fryklund (1968) argue that at Coeur d'Alene the principal mineralisation was Late Cretaceous, lead isotope and other evidence suggest that the principal mineralisation (Pb-Zn-Ag and Cu) throughout the Belt-Purcell basin i s *No distinction is made in this thesis between deposits that contain more zinc than lead (zinc-lead deposits) and those containing less zinc than lead (lead-zinc deposits).  23  Precambrian (Leech and Wanless, 1962; Zartman and Stacey, 1971; Clark, 1971; Harrison, 1972).  However, a convincing reconciliation of a l l the  isotopic and geologic evidence has not yet been made (see Hobbs and Fryklund, 1968; Zartman and Stacey, 1971; Sorenson, 1972).  2.3  PREVIOUS LEAD ISOTOPE WORK Studies of lead isotopes in Belt-Purcell galena deposits by  Long and others, 1960; Cannon and others, 1962; Leech and Wanless, 1962; and Sinclair, 1966; have resulted in two main conclusions. (1)  Most of the principal galena deposits are isotopically similar, and contain lead with single-stage ages in the range 1.2 - 1.4 BY.  Leech and Wanless (1962) confirmed a Precambrian age of  emplacement for Sullivan ore by dating a post-ore lamprophyre dike but there has been argument over the age of the main mineralisation at Coeur d'Alene, where both Precambrian and Late Cretaceous emplacement ages have been suggested. (2)  Small deposits generally contain lead of variable, relatively radiogenic composition, except for vein deposits within Moyie intrusions (group 2) which generally contain unradiogenic Precambrian lead (Leech and Wanless, 1962). Many more precise analyses have not changed these conclusions  significantly.  However, the low precision of most earlier analyses  imposes a severe limit to more detailed interpretation.  The improved  precision of the analyses recently reported by Zartman and Stacey (1971) and of the present study has permitted an evaluation of the earlier conclusions and the interpretation of small differences in isotopic  compositions.  24  Zartman and Stacey (1971) reported a large number of analyses of galena leads from Belt-Purcell rocks i n northwestern Montana and northern Idaho, including the Coeur d'Alene d i s t r i c t . the existence over this whole region of a Precambrian  They confirmed (1.5 - 1.2  BY)  group of leads and a variable group of Mesozoic — Cenozoic leads. Assuming a two-stage model for the evolution of the Mesozoic — Cenozoic leads and mineralisation at 100 MY, they calculated beginning ages for the second stages of 2.7 and 2.8 BY for Montana leads and 1.6 and 1.4 BY for Idaho leads. Two principal linear belts of Precambrian mineralisation were identified, one associated with the Osburn Fault system, the other extending northward from Coeur d'Alene to British Columbia.  They con-  sidered that the Precambrian Coeur d'Alene leads were introduced into Belt rocks during or soon after sedimentation, but they could not completely dismiss the possibility of concentration of disseminated lead into vein deposits at a later time.  Precambrian  The work of Zartman and Stacey  i s later considered in more detail (section 2.5) because combining their analyses with those of the present writer permits discussion of the history of leads from almost the entire Belt-Purcell basin.  2.4  DISCUSSION  OF NEW LEAD ISOTOPE  DATA  A l l analyses obtained i n this study of galena leads from Purcell rocks are listed i n table 2.1. f i g . 2.5.  Sample locations are shown on  The writer's results (table 2.1) are shown in figs. 2.6 and  2.7, and two distinct isotopic groups are apparent.  These groups were  also noted by earlier workers (Leech and Wanless, 1962). To simplify comparison with the work of Zartman and Stacey (1971), their terminology  TABLE 2.1  ISOTOPIC COMPOSITION OF LEAD IN GALENA FROM LEAD-ZINC DEPOSITS IN PURCELL ROCKS, BRITISH COLUMBIA  Pb20B PbZOI  Pb2 0 7 Pb20M  Pb20 8 Pb204  82F/NF7206  16.524  15.478  36.191  II  16.531  15.486  36.197  16.449  15.460  36.103  847  It  16.518  15.469  36.162  848  It  16.519  15.477  36.187  849  It  16.529  15.481  36.169  850  It  16.616  15.464  36.192  It  16.521  15.484  36.190  UBC NO.  NAME OF MINE OR PROSPECT  NTS / UTM SHEET/GRID REF.  GEOLOGICAL  RELATIONSHIPS  LATE PRECAMBRIAN LEAD IN ALDRIDGE SEDIMENTS 844  SULLIVAN  845 846  323  "  Huge (roughly 1 mile 1 mile * 300'), inverted-saucer shaped s t r a t i f o r m body near lower/middle Aldridge boundary. Gently dipping. Superimposed on weak metamorphism of host a r g i l l i t e - q u a r t z i t e are t o u r m a l i n i s a t i o n , c h l o r i t i s a t i o n , a l b i t i s a t i o n . Mud-flake b r e c c i a below. Moyie i n t r u s i o n below i s pre-ore, lamprophyres are post-ore. The samples analysed are spread over the s e c t i o n o f the ore body i l l u s t r a t e d on p. 281 of Freeze (1966). x  Tin-zone  f r a c t u r e , cuts main deposit.  778  KOOTENAY KING  82G/PF0209  16.405  15.451  36.151  Replacement of dolomitic a r g i l l i t e and s i l t i t e of mid A l d r i d g e . Mostly conformable.  779  ESTELLA  82G/PF0014  16.393  15.442  36.156  Replacement and f i s s u r e veins i n sheared a r g i l l i t e and s i l t i t e of mid Aldridge, and i n Moyie i n t r u s i o n . Monzonite nearby.  780  NORTH STAR  82F/NF7103  16.434  15.449  36.052  Oxidised, e r o s i o n a l remnants of conformable body near boundary of lower and middle d i v i s i o n s of A l d r i d g e . Preserved i n two shallow s y n c l l n e s .  781  STEMWINDER  82F/NF7105  16.444  15.450  36.087  Tabular lens of galena-sphalerite ore i n hanging w a l l of steep, t a b u l a r , thick (over 100') p y r r h o t i t e body c u t t i n g lower/mid Aldridge i n s y n c l i n e .  761  VULCAN  82F/NF4817  16.339  15.404  35.962  Extensive but weak disseminated g a l e n a - s p h a l e r i t e , mostly along bedding at lower/mid Aldridge boundary. Above mud-flake b r e c c i a .  773  FORS  82G/NE8168  16.388  15.421  36.071  Disseminated s p h a l e r i t e , galena i n bleached mid Aldridge s t r a t a near (above) No. 808.  808  FORS  82G/NE8168  16.341  15.404  35.981  Lens of disseminated of mid Aldridge.  853  FORS  82G/NE8167  16.324  15.401  35.957  Disseminated s p h a l e r i t e , galena, boulangerite i n s i l i c i f i e d e r r a t i c near (below) No. 808.  762  KID CREEK  82F/NE5550  16.332  15.406  35.985  Weak, disseminated galena mostly along bedding. at s e v e r a l horizons i n mid Aldridge q u a r t z i t e s .  832  ST. EUGENE  82G/NE8659  16.340  15.415  36.015  Replacement and f i s s u r e veins i n a steep f r a c t u r e system. shoots important. In mid and.upper A l d r i d g e .  833  AURORA  82G/NE8460  16.337  15.409  36.024  Veins (to 6') i n steep f r a c t u r e system i n mid and upper A l d r i d g e . Extension o f St. Eugene?  835  SOCIETY GIRL  -82G/NE8759  16.314  15.410  35.996  Veins i n zone of shearing and f r a c t u r i n g i n uppermost A l d r i d g e . Subp a r a l l e l to nearby S t . Eugene break. Oxidised upper part.  836  DOMINION  82F/NE5397  16.393  15.429  36.058  Quartz veins (to 1') i n f a u l t zone i n middle Aldridge q u a r t z i t e above Moyie I n t r u s i o n .  760  RIMROCK (B+V)  82G/NE7981  16.426  15.430  36.106  Numerous t h i n (to 1') quartz veins i n mid Aldridge q u a r t z i t e above mudf l a k e b r e c c i a . Near Cretaceous-Tertiary syenite stock.  837  ALICE  82F/NE3542  16.374  15.417  36.073  Veins and lenses of galena-bearing quartz veins i n mid Aldridge a r g i l l i t e and q u a r t z i t e i n major f a u l t zone.  888  MARYSVILLE D.D.H.*  82G/NE7297  16.603  15.467  36.392  Disseminated s p h a l e r i t e - g a l e n a - p y r r h o t i t e i n laminated q u a r t z i t e near boundary of lower and mid Aldridge ( d r i l l - h o l e sample).  889  MARYSVILLE D.D.H.*  82G/NE7297  16.558  15.467  36.329  (as above).  galena, s p h a l e r i t e i n q u a r t z i t e and a r g i l l i t e ?Aldridge  Laterally persistent Oblique  sheared  LATE PRECAMBRIAN. LEAD IN MOYIE INTRUSIONS 774  MOYIE TUNGSTEN  82F/NE6869  16.383  15.423  36.066  Coarse grained q u a r t z - c a l c i t e - e p i d o t e - g a r n e t vein (to 1') with small galena lenses i n Moyie i n t r u s i o n i n t o mid A l d r i d g e .  765  HOPE  82C/NE8272  16.319  15.406  35.996  Quartz c a l c i t e vein (to 1') i n Moyie i n t r u s i o n into mid Aldridge.  775  PARK  82G/NE7899  16.406  15.436  36.079  Thin q u a r t z - c a l c i t e v e i n i n top of Moyie i n t r u s i o n i n t o mid A l d r i d g e .  769  LONE PINE HILL*  82G/NE7998  16.431  15.433  36.104  Sparsely mineralised q u a r t z - c a l c i t e v e i n (to 3') i n top of sheared Moyie i n t r u s i o n into mid A l d r i d g e .  776  LEADVILLE  82F/NE4852  16.333  15.411  35.997  Q u a r t z - c a l c i t e v e i n (to 18") i n t h i n Moyie i n t r u s i o n i n mid Aldridge quartzite.  777  VULCAN SILL*  82F/NF4818  16.421  15.413  36.072  Lenses of quartz (to 50' long) i n Moyie i n t r u s i o n i n t o lower middle A l d r i d g e . White Creek B a t h o l i t h nearby.  851  PEDRO  82G/NE7500.  J.6..438  15.433.  3o..082._. • Quartz-calcite, .vein (1.'.-?'). In top. of Moyie i n t r u s i o n i n mid Aldridge.  852  POLLEN BASIN  82F/NE5090  16.542  15.444  36.306  Q u a r t z - c a l c i t e veins (to 6') i n top of Moyie i n t r u s i o n i n mid A l d r i d g e .  MESOZOIC-CENOZOIC LEADS IN VARIOUS PURCELL ROCKS 759  DAN HOWE  82F/NE5694  17.269  15.532  37.096  Thin quartz veins (to 2') i n shear zone i n lower A l d r i d g e . (20') Moyie s i l l .  736  LEADER (WELLINGTON)  82F/NE6388  18.532  15.612  39.009  Narrow (to 2') banded quartz veins p e r s i s t over 1000' l n intense shear zone of f a u l t separating Creston and Kitchener f f . G r a n i t i c stock nearby.  764  WARHORSE (BOY SCOUT)  82F/NE5991  18.929  15.702  38.805  Very p e r s i s t e n t steep mineralised (to 12') shear zone i n lower A l d r i d g e . Precambrian stock and pegmatite dikes adjacent.  768  ANDERSON  82F/NE7089  18.792  15.638  38.778  Quartz veins (to 9') i n sheared, a l t e r e d , a r g i l l a c e o u s Creston sediments. In s p l i n t e r of Perry Creek F a u l t .  838  MIDWAY  82G/NE8153  17.940  15.564  38.593  B r e c c i a t e d , recemented quartz v e i n i n shear zone contains sulphides along hanging w a l l . Cuts middle A l d r i d g e .  839  BIRDIEL  82F/NE7187  18.596  15.624  38.779  Steep quartz veins i n shear zone of Perry Creek Fault cut Creston p h y l l i t i c a r g i l l i t e and q u a r t z i t e .  840  MINERAL KING  82K8W/NF408763  18.503  15.640  38.466  Complexly shaped ore-bodies occur as replacement of f r a c t u r e d Mt. Nelson dolomite i n a t i g h t l y - f o l d e d , fault-bounded s y n c l i n e .  841  PARADISE  82K8W/NF498911  19.287  15.708  39.892  P a r t i a l l y o x i d i s e d replacement and f i s s u r e f i l l i n g deposits i n shattered s i l i c e o u s , magnesian limestone of Mt. Nelson formation i n small a n t i c l i n e .  842  LOCKHART CREEK*  82F/NE2384  18.847  15.680  39.231  Thin (about 6") vein of coarse galena i n lower Horsethief Creek  766  PAL MAY RA  82G/PF0408  19.082  15.674  39.319  Galena i n quartz vein (over 10') c u t t i n g f r a c t u r e d l u s t r o u s paper a r g i l l i t e of Aldridge and shattered s y e n i t e dike. In core o f major a n t i c l i n e .  767  LILY MAY EXTENSION  82G/PF0406  18.908  15.650  39 . 054  Quartz v e i n i n shattered syenite dike (to 7') and contorted a r g i l l i t e s of A l d r i d g e . In core of major a n t i c l i n e .  891  PITT CREEK*  82F/NE7396  18.613  15.618  38.600  Thin quartz veins i n mid Aldridge near S t . Mary F a u l t .  892  POLARIS  82F/NE7298  18.520  15.655  38.657  A 6" quartz v e i n i n lower Aldridge between two Moyie s i l l s .  893  ROSE PASS  82F/NF2712  18.952  15.708  38.870  One o r more quartz veins (about 1') i n c l o s e l y - f o l d e d black s l a t e of Mt. Nelson formation. Small g r a n i t i c stock nearby.  •Names are those used i n the l i t e r a t u r e except where marked by *. Sources: Rice, 1941; Leech and Wanless, 1962; S c h o f i e l d , 1915; Freeze, 1966; B.C. Dept. Mines Ann. Repta. (consult indexes G i f f o r d (pers. comm.).  Beneath  Formation.  fissile  3 and 4 ) ; R.G.  26  27  is used here, thus the closely clustered group of leads is referred to as "late Precambrian leads", the more radiogenic and variable group as "Mesozoic-Cenozoic leads".  These two groups of lead seem to represent  two periods of galena mineralisation of very different ages and are therefore treated separately in the following discussion. Late Precambrian  Leads  Deposits which are known to contain lead of the late Precambrian group are restricted to the Aldridge Formation, or to diabase s i l l s that intrude the Aldridge Formation (table 2.1).  On f i g . 2.6, 2.7 and  2.8  the compositions of the late Precambrian leads show a small scatter that is not due to experimental  error, but to real differences. Because this  scatter i s in the form of a linear array (;in isochron?), and because of the restricted stratigraphic occurrence of these leads the late Precambrian leads are considered to be genetically related to each other. The source and the age of these leads are discussed below. The mantle as a source Single-stage ages calculated for the late Precambrian leads f a l l within the range 1.2 - 1.4 BY.  These single-stage ages appear to  be reasonable estimates of the time of mineralisation, but the assumption that any of the leads are in fact products of a single-stage (presumably mantle) development i s unreasonable, for the following arguments. Of the whole group, lead of Sullivan composition most closely satisfies the criteria for a primary (= ?mantle) lead (Kanasewich, 1968; Stacey and others, 1969; Cooper and others, 1969).  To obtain the other  leads substantial contamination of Sullivan-like primary lead with older  Late Precambrian group •  164  Fig. 2.6  •  •  170  180  Plot of P b / P b v. P b / P b The key identifies the host rock. 207  20l+  206  20l+  •  19-0  for a l l the analysed galena leads i n Purcell rocks (table 2.1). The growth curve i s for (U /Pb ) - 9.09. present 238  201+  15-5  0  7< • O  g KEY in Aldridge Formation  15-4  Moyie  O  Sullivan  16-3  16-4  intrusive Mine  16-6  16-5  1 Fig. 2.8  Plot of P b / P b v. P b / P b for the "late Precambrian group" of galena leads listed in table 2.1. The key identifies the host rock of the galena mineralisation. 207  2014  206  204  31  crustal leads would be necessary.  According to this argument, the sheer  quantity of mantle lead in the Sullivan deposit might have swamped any contaminating crustal lead, but this would not account for the fact that other large lead deposits (notably in Coeur d'Alene district) do not contain lead of Sullivan composition.  The converse argument, that small  deposits should show least similarity to Sullivan lead, i s also untenable. The amount of crustal "contaminant" required for some of the larger ore bodies could easily be a larger fraction of the total lead in the deposit than the original mantle-lead component.  Faced with the necessity of a  crustal source for at least some of the lead, i t is reasonable to speculate that the crust could be the source of a l l the lead. The second argument against a mantle origin of any of the Precambrian leads is that, as discussed in section 1.2, lead i n modern basalts seems to be too variable and too deficient in P b  2 0 7  for the  mantle to be the source of primary leads (Richards, 1971; Russell, 1972). For this general reason, a mantle origin of Sullivan or the other Late Precambrian leads seems unlikely. Suggestions that Sullivan lead was introduced from the mantle into the crust at the same time as the Moyie intrusions (e.g. Swanson and Gunning, 1945)  or Purcell lava, or migrated from the mantle up deep  faults (e.g. Kanasewich, 1968a) are therefore not supported by the evidence of lead isotopes.  Precambrian granitic rocks could possibly  supply lead of the required composition but they are too rare for this idea to be considered seriously.  Furthermore, evidence that granitic  rocks are the source of metals in lead-zinc deposits in sediments i s generally weak or absent both i n this area and elsewhere.  32  The crust as a source To the writer, the most plausible explanation for the Late Precambrian leads is that they were leached from lower Purcell sediments (probably Aldridge Formation) by circulating connate brines.  Some com-  ments on this general hypothesis were made in chapter 1. The connate brine hypothesis accounts for, in a simple way, the uniformity old  Purcell leads, their slight variation,  perhaps also for the large size  of the  their wide distribution,  and  of some deposits which contain old lead.  The writer must say, however, that there is very l i t t l e independent evidence which might serve to test this hypothesis.  At least until studies  of geochemistry, fluid inclusions, stable isotopes, etc. are available, the connate brine theory seems acceptable as the most straight-forward explanation for the origin of the "old" Purcell leads.  Some details of  this explanation follow. If a circulating connate brine did exist in Aldridge strata, presumably i t began i t s chemical evolution (White, 1965) soon after sedimentation, and may have continued until folding and faulting disrupted the circulation system, and compaction and metamorphism prevented circulation by reducing permeability.  The widespread occurrence of Late Pre-  cambrian galena i n fractures in Moyie s i l l s , and sulphides replacing a Moyie intrusion at Sullivan (Freeze, 1966)  could mean that the brine was  s t i l l actively circulating after this widespread intrusive episode.  In  fact, the Moyie s i l l s might have played two important roles in mineralisation.  They could have supplied thermal energy to drive the circulation  system and they could have channeled and restricted brine flow.  Control  of the path of brine flow is necessary i f large volumes of dilute metalbearing brine are to result in a large deposit.  33  Isotopic compositions of the late Precambrian group of Purcell galenas are consistent with the model sketched above. compositional  F i r s t l y , the  similarity of these leads over a vast area could be due  partly to the observed mineralogic homogeneity of lower Purcell rocks, and partly to the homogenising effects of a far-ranging brine.  Secondly,  the small scatter in isotopic compositions could be the result of slight i n i t i a l differences in source lead laterally or vertically in the sedimentary column.  It is also possible that leads of different composition  could be extracted from the same rocks depending on the extraction efficiency of the brine.  This suggestion is based on the  observation  that lead in sediments and other rocks occurs in various physical sites, and the availability and composition of lead in each site can be very different.  The principal sites of lead in a fine-grained sediment, such  as Aldridge rocks, can be identified as follows. (a) or as  Lead loosely held by clays, organic matter, Fe and Mn hydroxides, PbS. According to Wedepohl (1956), the bulk of lead in sediments i s  contained in the clay mineral fraction. However, a detailed study by Vine and Tourtelot (1969) of black shales showed that, in these sediments at least, lead has various associations with organic material, detrital minerals, carbonates, sulphides, etc.  The sorption of lead by clays,  organic matter and Fe and Mn hydroxides has been demonstrated to be very effective by laboratory experiments (e.g. Krauskopf, 1956; Weiss and Amstutz, 1966), but just when this sorption occurs in sediments is d i f f i cult to say.  Vine and Tourtelot (1970) suggest that sorption of metals  in black shales is an accumulative process.  For example, they suggest  34  that metal enrichment i n the organic matter component of shales begins during the l i f e of the organism, proceeds during drift to the burial site and can continue until f i n a l expulsion of i n t e r s t i t i a l waters. The isotopic composition of lead in the clay/organic fraction i s apparently variable, being chiefly dependent on the mean age of the source rocks (Doe, 1970).  A study by Chow and Patterson (1962) of  easily-leachable leads from Pacific and Atlantic Ocean sediments indicates that where sediments represent well-mixed samples of average crustal rocks, lead i n the clay fraction at the time of sedimentation w i l l l i e close to the primary growth curve or i t s extension. However, in restricted basins draining Precambrian terrains, such as Hudson's Bay (Chowand Johnstone, 1963), leads are likely to be variable and radiogenic. (b)  Radiogenic lead in U- and Th-bearing minerals (e.g. zircon,  sphene, monazite). Although they contain only a small percentage of the total lead i n most rocks, minerals containing uranium and thorium generally have very high lead isotope ratios (relative to Pb **). 20  zircon commonly has P b  206  /Pb  20lt  For example,  ratios i n the range 200 to 1,000  (see  Doe, 1970), which i s extremely radiogenic i n comparison with lead compositions in the clay fraction or in feldspars. (c)  Lead i n silicate lattice sites, mainly in substitution for K  +  (e.g. i n feldspars). The bulk of lead i n crystalline rock is in the feldspars. Extensive studies of lead isotopes i n feldspars from granitic rocks (e.g. Zartman and Wasserburg, 1969; Doe, 1970) show that these leads do not depart markedly from the primary growth curve, partly because feldspars  35  contain very l i t t l e U and Th. Table 2.II shows some results from a unique study of lead i n different mineral phases of a Precambrian granite, and the isotope ratios quoted give a good indication of the sort of isotopic variation that can be expected to exist in the minerals of sediments derived from Precambrian shield areas.  Table 2.II  Pb /Pb ratios and total lead contents of a l l minerals of a Precambrian (^1.1 BY) granite studied by Tilton and others (1955). (The precision of these measurements i s low by present-day standards.)  Mineral (acid washed)  206  20tt  Pb  Mineral wt. %  perthite quartz plagioclase  52 24 20  sphene magnetite zircon apatite pyrite  0.4 0.4 0.04 0.02 0.02 Total 97%  206  /Pb  201+  Approximate % of total lead in each mineral  18.6 18.6? 18.2  57.9 15.5 8.9  39.1 36.7 »1,000 ? 31.9 20.3  11.3 0.1 2.2 0.3 0.9  acid washed composite  ^ 2  (total about 6 ppm)  From the above discussion, i t i s concluded that the lead released to an i n t e r s t i t i a l brine depends on the amount, availability and composition of lead in each site.  Variations of these quantities,  coupled with variations in the extracting efficiency of the brine, say with time, temperature or salinity, could easily be the cause of the variations i n composition shown by the late Precambrian group of Purcell leads (figs. 2.6,2.7,2.8).  36  If leaching occurs on a large scale, the amounts of lead normally found in fine-grained sediments (20-25 ppm.; enough to form large deposits, i f concentrated.  Wedepohl, 1971a) are Because the brine must  therefore leach lead from a f a i r l y large (but not unreasonably large) volume of sediment, the brine must have a f a i r l y large circulation system. It i s suggested, therefore, that different deposits in the same general area should have similar isotope compositions because of hcmogenisation in the brine.  Figure 2.9 illustrates changes in lead isotope compositions  which could be due to regional changes in the composition of lead in connate brine. There is a correlation between lead isotope composition and the size of lead-zinc ore deposits i n Purcell rocks.  Leech and Wanless (1962)  showed that large deposits (and small veins in Moyie intrusives) have similar compositions. Precambrian leads".  They belong to the group referred to here as "late Small deposits are more radiogenic, are isotopically  variable, and belong to the "Mesozoic-Cenozoic" group.  The same generali-  sation i s apparently true for deposits in Belt rocks (Cannon and others, 1962).  The correlation between size and isotopic composition for Purcell  galenas is shown in f i g . 2.10.  A l l the productive mines (table 2.Ill)  are in lower Purcell host rocks with the exception of two large mines (Mineral King and Paradise) that are in upper Purcell rocks.  These two  deposits are also an exception to the generalisation that large deposits contain "late Precambrian lead". A possible explanation for the similarity of lead isotopes in producing mines in Purcell strata i s as follows.  If the lead deposits  were precipitated from f a i r l y dilute metal-bearing brines, large volumes  37  Oo D  • Creston  Fig. 2.9  Q  \2  Analyses of the late Precambrian leads (table 2.1) are arbitrarily divided above into two sets of different isotopic composition. These samples are plotted on the accompanying map and a correlation of composition with geographic location i s suggested.  38  10000  LEAD  +  ZINC 10* lb. 1000  100  10  1 r-  0-1  DISTRIBUTION Of ANALYSES  I 164)  17-0  1  I III I 19-0  18-0  206 /  F i g . 2.10  Correlation between size of producing mines in Purcell rocks and their lead isotope ratio Pb /Pb . Data from table 2.1 and 2.III. Note log scale for tonnages. 206  20l+  I  39  of f l u i d are required.  Such large volumes would be able to circulate  only before induration and metamorphism reduced permeability and caused most of the water to escape from the sedimentary p i l e .  Thus, the brine  can only have been effective early in the history of the sediment, so that large scale circulation was possible only in lower Purcell time, before about 1.2 BY.  This large-scale circulation could account for the  large size of some deposits that contain late Precambrian leads.  The  later economically unimportant Mesozoic-Cenozoic mineralisation may  repre-  sent lead scavenged by small volumes of f l u i d that were mostly confined to fault systems.  The writer's work supports the suggestion of Leech  and Wanless (1962) that the relationship between size and lead isotope composition may turn out to be useful for prospecting (also see Cannon and others, 1962; Cannon and others, 1971; Zartman and Stacey, 1971). The position of Sullivan leads at the upper end of the short array in f i g . 2.8 i s curious and i t is tempting to suggest a link between the unusual size and special isotopic composition of this ore body. livan lead is enriched in P b  2 0 6  and P b  2 0 7  Sul-  relative to the other "old"  leads and i f Sullivan lead evolved from any of these other leads, say from a composition like the nearby North Star (or Sullivan 846) , admixture of large amounts of slightly more radiogenic lead, or small amounts of much more radiogenic lead are required.  If Sullivan ore was emplaced at about  the same time as the local high-grade metamorphism (^1.3  BY?; see section  2.2) in the St. Mary River area, the lead released from silicates and from accessory minerals rich in radiogenic lead during recrystallisation of Aldridge rocks could conceivably account for both the large size and slightly more radiogenic composition of the Sullivan.  E l l i s (1970) has  discussed leaching experiments in the laboratory and analyses of natural  40 brines which show that both salinity and temperature can increase considerably the amount of extractable lead and other metals i n rocks (also see looms, 1970).  It i s interesting to note that Harrison and Grimes  (1970) report a loss of boron with increasing grade of metamorphism of some Belt sediments in Montana and Idaho, this being the only obvious trend they observed in minor or trace element contents. Possibly the widespread tourmalinisation at the Sullivan represents boron removed from high-grade metamorphic rocks, just as the galena may represent trace leads from the same source.  Table 2 . I l l  Recorded production of some metals from a l l significant deposits in Purcell rocks to 1970 (inclusive) Pb Zn Cd Cu Au Ag million lb million lb million lb million lb million oz thous.oz  Mine Sullivan  13,768  11,902  1.6  1.9  Estella  11.4  North Star  48  21.7 1  Kootenay King  Stemwinder St. Eugene  2.1  7.9  229.5  4.6  0.028 0.17  0.03  1.3  8.8  0.063  32  249  5.9  3  1  Aurora Society Girl  (0.32)  Alice  (0.047)  Park  0.024  (0.05)  (0.004) (0.0008)  Midway  (0.002)  Mineral King  81  200  Paradise  16  8  Sources;  3.24  (0.001)  (0.0008) 0.69 (0.01)  1.1  1.8 0.7  Min. Mines, B.C., Ann. Repts.; L i t t l e (1970); Leech and Wanless (1962). Figures in brackets are minima, rest unrecorded. ? = unknown, but significant.  (0.39)  41  The model proposed above is that a l l the late Precambrian leads were leached from the enclosing Aldridge sediments and were precipitated from connate brine.  Although this model accounts, in a simple way, for  a number of isotopic and geologic features of Purcell leads, i t is d i f f i cult to test with independent evidence from Purcell rocks.  However,  isotopic and other evidence do provide support for a similar origin for the modern lead-bearing brines of the Salton Sea (Doe and others, 1966; White, 1968) and for some lead-zinc deposits such as Pine Point (Beales and Jackson, 1968; Billings and others, 1969), and perhaps the ore deposits of the Pennines, England (Mitchell and Krouse, 1971). The age of the source The late Precambrian type of lead has been interpreted above as being derived from Purcell sediments, but the galena leads could also contain evidence of the age of the source of the sediments themselves. The array of late Precambrian lead compositions resembles a very short anomalous lead line (fig. 2.6) and  the slope of a least-squares line  through a l l of these points i s 0.244 ± 0.009 (la). If, for simplicity, a two-stage model is assumed with termination (by mineralisation) of the second stage at 1.3 BY (=t ) , then t 2  x  = 2.62 ± 0.08 BY.  This age  (2.6 BY) is interpreted to be the minimum age of source rocks of the lower Purcell sediments, which were in turn the source of the lead in the galena deposits.  However, because the two-stage model assumed is a  gross simplication of the history of the lead in these sediments, a more complicated, multistage history must therefore be considered. The distribution of isotope ratios shown on f i g . 2.6 and  2.8  resembles the patterns for theoretical multi-stage leads calculated from  42  the "frequent mixing model" (fig. 2.11) by Kanasewich, 1962, Russell, 1963; and Russell and others, 1966.  1968;  The "frequent mixing model"  i s a multistage model that assumes there i s variation in the U/Pb  ratio  from place to place and that lead is transferred from one U/Pb environment to another at various times, such as during an orogeny. (see Kanasewich, 1968) that the isotopic ratios P b  206  It can be shown  /Pb  and p b  20lt  207  /Pb  20lt  of a multistage lead after n stages are: ( 206/ 204) now Pb  Pb  =  (pb  206/p 20i ) b  2(Tj238/p 20^ b  now  +  (  X t e  primeval  + 1 2 38/p 204) (U  b  l _ e 2 ) + ....+ X t  n  ( now  X t e  (112 3 8 ^ 2 0 4 )  0_  ( now  X t e  l) +  X t n _ 1 e  -  X t n e  )  (1) (^207/^204) = (p 207/ 204) + 1 2 38/ 'now . primeval b  v  2  Pb  (U /137.8 Pb204) now  (U  238  v  (e  where:  -e  x / t ( e  l_  x / t e  t  t t ,..,t l t  2  +  '  8P b  204)  23  2  1  now  (2)  2 3 8  , U  2 3 5  respectively  = ages of mixing of leads into new U/Pb systems  n  ) values vary from place to place. now values are extrapolated to the present day. n  1  = 4.55 BY (age of the earth)  0  and *» '** * (u 2  (e^O-e** ) + 'now  .... + (U 8/i37.8 Pb " *) n  )  .  )  \ )( = decay constants of U t  2  1 3 7  238  /Pb  20lt  Note these  By assuming a range of values for the ratio (U/Pb) for 60 hypothetical leads and up to 11 stages of development, Kansewich (1962) and Russell (1963) showed that after each stage the lead compositions scattered about a straight line.  The slope of this line depends only on  the time of commencement of the f i r s t stage and the time at the end of  43  204  p b  16.2  6.2 Single - stoge growth curve  15.8 Anomalous lead line between O and 3 0 0 0 m.y.  15.4  18.4  18.8  19.2  2 0 6 Pb 2 0 4 Pb  Graph of lead isotope ratios for a theoretical threestage model. Diastrophism lias caused a random mixing of uranium and lead at 3000 and 1500 m.y. ago. Mineralization occurs at 0 m.y.  Fig. 2.11  Anomalous lead line Between O and 3 0 0 0 m. y.  15.4  16.4  18.8  19.2  206  p t )  2 0 4 Pb  Graph of lead isotope ratios for a theoretical elevenstage model. Diastrophism is postulated to occur every 300 m.y. between 3000 m.y. ago and the present time when mineralization takes place.  The results of "frequent mixing" of leads for three- and eleven-stage models. Taken from Kanasewich (1968; p. 169 and 170).  the last stage, even though evolution i n many stages of different U/Pb ratio may have occurred between these two times.  For this reason, a two-  stage model can be a satisfactory mathematical simplification of the history of multistage leads even though i t i s untrue geologically.  Another  feature of the "frequent mixing model" i s that as the number of stages increases, the distribution of points along the line decreases considerably, and the lateral scatter increases slightly (see f i g . 2.11). The mixing process simulated by Kanasewich (1962) and by Russell and others (1966) was, however, restricted to incomplete mixing of lead i n one stage with that of successive  stages, and the possibility of mixing leads of  the same stage was not considered.  If partial or complete mixing of  leads of the same stage i s considered, there w i l l be further reduction i n the length of the anomalous lead line and i n the lateral scatter.  Richards  (1971) has suggested that frequent mixing of crustal leads with more or less complete homogenisation between stages could account for the primary  44  lead ores.  The addition of this second mixing process could help remove  the objection raised by Kanasewich (1962) and by Russell (1963) that,if primary leads were due to frequent mixing of crustal leads, then evidence of this should be observed.  It i s suggested here that the Purcell leads  could be the result of mixing of crustal leads with partial homogenisation at the end of some stages.  The slight scatter of points i s taken as  evidence that mixing has been incomplete, as Kanasewich (1962, 1968) and Russell and others (1966) expected of crustal materials, whereas the association with a primary lead (Sullivan) appears to support the view of Richards (1971). The source of the leads i s considered to be the Belt-Purcell sediments, as discussed previously.  These sediments were derived largely  from the craton to the east and i t i s mixing of lead during the history of these source rocks, including orogenic activity, erosion, sedimentation and brine migration that i s considered responsible for the present composition of old Purcell leads.  The most important homogenisations are con-  sidered to be those effected during Purcell sedimentation and during brine movement.  If a reasonable history can be inferred for the lead i n  Purcell sediments, then the approximate composition of the lead can be calculated from equations 1 and 2. Although some Purcell sediment was transported from the south or southwest, the major source of sediment was the shield to the east (section 2.2).  Pre-Purcell K/Ar ages obtained  from the North American shield show concentrations at 1.7 BY (Hudsonian Orogeny) and at 2.5 BY (Kenoran Orogeny) according to Stockwell (1970) and King (1969).  There i s also some evidence that a considerable part of  the shield i s as old as 3.0 - 3.5 BY, younger ages being the result of  45  successive tectonic overprinting (Slawson and others, 1963; Kanasewich, 1968; Catanzaro, 1968; G i l e t t i , 1968; Goldich and others, 1970).  Accord-  ing to Price (1964, p. 422) "The large volume of fine terrigenous sediment that constitutes the bulk of the Purcell succession was derived from the older Precambrian rocks that occur i n the interior of the continent, far from the site of deposition.  It can be compared with the large volume  of fine sediment that has been transported to the margin of the continent and discharged into the Gulf of Mexico by the Mississippi River."  Thus,  Belt-Purcell sediments were probably eroded from as far east as the region where Hudson Bay and the Great Lakes are today and, i f so, the detritus supplied to the basin was therefore from rocks which range in age from about 3.5 BY to 1.7 BY old. For  the purposes of calculation, the history of the lead in  Purcell sediments i s inferred from the above to be as follows. t = 4.55 BY  Lead homogenous throughout the Earth.  t = 3.0 BY  Substantial s i a l i c crust formed, now part of North American Shield.  Considerable variation in U/Pb from  place to place from 3.0 BY on (previously uniform, (U /Pb *) =9.09). now Kenoran Orogeny begins. Leads developed in one U/Pb 238  t = 2.7 BY  201  environment since 3.0 BY mixed into other U/Pb environments. t = 1.8 BY  Hudsonian Orogeny begins. Leads developed in one U/Pb environment since 2.7 BY are mixed into other U/Pb environments .  t - 1.5 BY  Sediment eroded from rocks of Kenoran and Hudsonian age begins to be deposited into the Belt-Purcell basin and forms the Pre-Ravalli strata.  Lead i s partly homogenised  during erosion and sedimentation but different U/Pb environments s t i l l exist in the sediments.  46  t = 1.3 BY  Lead leached from Purcell sediments by connate brine i s nearly homogenised and i s deposited as galena ("late Precambrian group") at about 1.3 BY.  No further change  occurs in the isotopic composition of this lead. To simulate the above history, the compositions of 50 hypotheti c a l leads were calculated from equations 3 and 4 below, which are based on the general equations given previously (1 and 2).  (p 206 204) b  /pb  now  (p 206 20t)  =  b  /pb  +  primeval  l(238/20»») U  pb  + «J /Pb '*)  (e - -e - ) + (U now  238  + *(U /Pb  ( l - - e - ) + (U now  238  2  238  1  20  238  20l+  )  X 3  X  0  X 2  8  7  X l  3  5  5  e  /Pb  /Pb  ( * • 55_*3.0) Xj  e  e  now  20u  )  (e* • - e now  201+  )  (e - -e - ) now  2  7  X l  X l  5  •) 8  X l  3  (3) (Pb  207  /Pb  201+  )  now  = (Pb  207  /Pb  + (U /137.8Pb 2  238  201+  v  20l+  )  X/  238  e  + (U /137.8Pb 5  238  20l+  )  Fifty values of (U J  1  238  4  (e 2.7„ l.8) + Vu X  ) . + (U /137.8Pb primeval  238  20lt  )  ( e ^ - S S - e ^ .  now  (e^-O-e^ - ) + (U /137.8 P b now 2  /137.8 Pb  201t  7  /Pb  20l+  )  now  238  ) (e* • ^ now  ( e ^ - S - e * '  now  3  1  1  '  3  )  204  )  now  •) 5  (4)  were taken from random number  tables and were drawn from a normal distribution with a mean value of 9.09 and a standard deviation of ± 2.0.  This mean value was selected to equal  that calculated for primary lead ores, and the assumption here i s that the primary lead growth curve represents the evolution of average crustal leads (see chapter 1).  Selection of a different standard deviation or  a distribution other than a normal one would not significantly affect the results of the calculations.  The calculated distribution of isotope  47  compositions at several times i s shown i n f i g . 2.12a.  In f i g . 2.12b,  the leads of the l a s t stage have been averaged i n groups of f i v e to simulate p a r t i a l mixing during erosion, sedimentation and brine movement i n the l a s t stage of development.  The model shown as equations 3 and 4  assumes that leads of previous stages no longer exist and cannot be added to P u r c e l l sediment at 1.5 BY.  Rocks of Kenoran age and possibly  older ages do s t i l l e x i s t , however, and the isotope r a t i o s of lead i n feldspar, quartz and other minerals lacking U and Th may be unchanged since these times.  As w e l l , analyses of rocks from the  Precambrian  (2600-1600 MY) Lewisian basement complex of Scotland (Moorbath and others, 1969)  suggest that such ancient basement complexes might be depleted i n  uranium and therefore preserve p r i m i t i v e isotope r a t i o s .  To simulate  the e f f e c t of addition of d e t r i t a l minerals from rocks of Kenoran age to P u r c e l l sediments 5% of average  (U  2 3 8  /Pb  2 0 1 +  = 9.09)  2.7 BY old lead was  included i n the c a l c u l a t i o n of composition of each of the well-mixed leads i n f i g . 2.12b.  For comparison with the calculated values, the  observed compositions of o l d P u r c e l l leads are also shown on f i g . 2.12b. No claim i s made that there i s an exact correspondence between the true h i s t o r y of lead i n P u r c e l l sediments and the simple model discussed.  The  discussion does show, however, that the isotope r a t i o s obtained from c a l c u l a t i o n s based on a f a i r l y simple modified "frequent mixing model" do approximate  the observed r a t i o s .  In many published interpretations (e.g. Zartman and Stacey,  1971)  the calculated age of source rocks i s equated with the age of the basement underlying  the mineralised region and i t i s important to note that  i n the above i n t e r p r e t a t i o n the basement source i s "imported" as a sediment  F i g . 2.12a  Calculated compositions f o r 50 hypothetical leads at various times i n a five-stage h i s t o r y . Small dots, c i r c l e s and large dots show compositions a f t e r 2.7, 1.8, and 1.3 BY (end). Primary growth curve i s f o r ( U / P b * ) - 9.09, and numbers indicate b i l l i o n years. 238  Zo<  49  16-0  F i g . 2.12b  16-5  17-0  Large circles represent the compositions of 50 hypothetical leads after five stages of evolution i n various randomly chosen U/Pb environments since 3.0 BY, with f a i r l y thorough mixing at 1.3 BY (see text for details). Solid dots represent measured ratios of Purcell leads of the late Precambrian group. The growth curve shown i s the primary growth curve (U /Pb =9.09) . If more complete mixing i s assumed i n the calculations, the scatter of the calculated values would more closely resemble the observed scatter. 238  20It  and no estimate of age of the underlying rocks i s made (see f i g . 2.13). In effect, the Belt-Purcell sediments are regarded as a large sample of the shield to the east, a sample that s t i l l contains faint lead isotope evidence of i t s original age. There are several studies of lead isotopes i n sediments i n which reasonable estimates have been obtained for the age of source rocks. For example, Muffler and Doe (1968) calculated (from lead isotopes) a mean age of 1.7 BY for Cenozoic detritus i n the Salton Trough, California.  They  50  interpreted this as the age of basement to the east, the ultimate source of the sediments.  Hart and Tilton (1966) obtained an age of 2.75 BY from  lead i n a sample of present-day Lake Superior sediment and they noted that this age corresponded with ages obtained from the Superior Province, the source of the lake sediments.  In both these studies anomalous lines  that formed the basis of age calculations were obtained by leaching sediments with acid or water and analysing the leaches and residues. The galena analyses that have been interpreted in this thesis could also represent lead leached from sediments, but in this case by natural  pro-  cesses.  Model A  Fig. 2.13  Model B  In Model A, the underlying basement i s supposed to be a source radiogenic lead; i n Model B, distant basement supplies this component via the sediments.  Mesozoic-Cenozoic  Leads  Leads of the Mesozoic-Cenozoic group are shown on f i g . 2.6 and 2.7 along with the late Precambrian group.  Evidence of an exotic  source for the Mesozoic-Cenozoic lead i s lacking and the simplest explanation i s that they evolved i n the surrounding Purcell sediments.  If so,  their composition w i l l be the result of addition of radiogenic lead to pre-existing lead, like the widespread Late Precambrian group.  The age(s)  51  of emplacement of the variable radiogenic leads i s uncertain. Scattered, inconclusive evidence suggests a Mesozoic-Cenozoic age for some mineralisation.  For example, Leech and Wanless (1962) inferred a Mesozoic age  for leads i n faults with important Mesozoic movement (e.g. Leader, Pitt Creek).  As another example, two minor deposits (Palmyra, L i l y May  Extension) i n the Rocky Mountains occur i n quartz veins cutting syenite dikes (Rice, 1937), and these intrusives are probably of the same age as Cretaceous or ?Tertiary intrusives elsewhere in the southern Rocky Mountains (Leech, 1958; Price, 1962).  It i s not possible to say from  lead isotope data whether or not a l l the radiogenic leads are of Mesozoic-Cenozoic  age.  The data on f i g . 2.6 appear related to two near-parallel anomalous lines, both of which intersect the array of Late Precambrian leads.  Why the data should f a l l on two apparently distinct lines i s not  clear, but there is a weak relationship between age of host rock and isotope composition.  Leads in Aldridge rocks f a l l on either line; those  in Creston rocks l i e on the lower line; those in upper Purcell strata l i e on the upper line. confidently.  These relationships can not be interpreted  Curiously, the P b  208  /Pb  201+  (fig. 2.7) plot also shows two  distinct lines, but the mineral deposits show different groupings from those of f i g . 2.6 (compare Midway, Palmyra, Leader on both graphs). That the anomalous lines do not pass through the cluster of old leads (fig. 2.7) i s evidence that the younger leads are due to growth in various U/Pb environments, rather than to simple mixing of old leads with a single widespread radiogenic lead (see Kanasewich, 1968). The slopes of least-squares lines through  Mesozoic-Cenozoic  52  leads are given i n table 2.IV with computed ages of commencement of growth of the radiogenic component.  These ages were calculated assuming  two stage development i n which growth was terminated by mineralisation at 100 MY.  Table 2.IV  Two-stage model ages for Mesozoic-Cenozoic leads from Purcell Supergroup rocks.  Deposits  Slope  ti(calculated)  t2(assumed)  Lower Line Midway, Leader, Pitt Creek, B i r d i e l , Anderson, Palmyra, L i l y May Extension  0.094 ± 0.011  1,470 ± 230 MY  100 MY  0.094 ± 0.006  1,470 ± 130 MY  100 MY  Upper Line Dan Howe, Polaris, Rose Pass, Lockhart Creek, Warhorse, Mineral King, Paradise  The computed t j , usually interpreted as the age of the source rocks, i s i n good agreement with the inferred age of older Purcell strata. The agreement i s less impressive than i t appears, however, since selection of lines i s somewhat subjective.  Further comments on the Mesozoic-Cenozoic  leads are made in section 2.4.  2.5 COMPARISON WITH GALENA LEADS FROM BELT SUPERGROUP ROCKS IN NORTHWESTER U.S.A.  Sixty-six lead isotope analyses of galenas in Beltian sediments of N.W. Montana and N. Idaho have been reported recently by Zartman and Stacey (1971). The region studied by Zartman and Stacey i s shown as f i g . 2.14 and their isotopic results as f i g . 2.15.  53  In major aspects, the isotopic compositions of Belt galenas are very similar to those of Purcell galenas, but there are fine-scale differences.  Furthermore, there are features of Belt leads which were  either not discussed by Zartman and Stacey, or which can be interpreted in alternative ways. The possibility that any interpretable differences between the two sets of analyses are of instrumental origin is remote, since they are of similar precision (la<0.1%) and are referred to a common standard (Broken H i l l Standard). Late Precambrian  Leads  Zartman and Stacey (1971) stated that the uniformity of the Late Precambrian leads over a large region was a good indication that the calculated single-stage ages of 1.2 - 1.5 BY were reasonable estimates of the time of mineralisation.  The absence of this lead from  rocks younger than the Belt, and the Precambrian ages of uraninite associated with lead mineralisation in faults at Coeur d'Alene were mentioned as evidence that the deposits probably formed during or soon after sedimentation. The resemblance of the elongate array shown by the Precambrian leads ( f i g . 2.15)  to a two-stage, short-period anomalous lead line was  discussed and they calculated an "instantaneous" age (ti=t ) of 1.3 2  from the slope of this array.  As an alternative, a t\ of 1.7 BY  assumed and an age of mineralisation ( t ) of 825 MY was 2  BY  was  calculated.  They stated that the source of the Coeur d'Alene lead remained a matter of speculation.  Introduction of lead as a chemical precipitate  during sedimentation, or from the mantle/lower crust along major fracture systems were offered as possible explanations of the isotopic similarity  I IT*  116*  115*  114"  EXPLANATION  Basalt of Columbia Plateau  Foult Boshed where approximately located. Arrows snow relative direction of displacement. Age of mrnerotizotion (based on lead isolopes) Mesozoic or Cenozoic. Numerals refer to groupings m Table 3.  Vtrtcowic rocks end continental sedimentary rocks Lorqety endesite, lotite, and bosalt flows  J  e Lflle Precambrian  <  Granitic rocks Largely gronodiorite ond quartz monzonite  Sedimentary rocks Largely Combrion quartzite, shale, and limestone; includes some rocks of younger Paleozoic age in Washington Hign-g/oo* met amorphic rocks Age varied ond uncertain. Strotigraphic position uncertain  F i g . 2.14  Region studied by Zartman and Stacey (1971). Taken from p. 858 and 859 of t h e i r paper.  II Windermere series of Canada Coarse conglomerate, phyllite.ond greenstone  Belt Supergroup Subdivided where possible into three units: upper, Missoula Group (Libby and Striped Peok Formation); middle, Waiioce Formation ond Ravalli Group (St. Regis, Revett, ond burke Formations); lower, Prichard Formation  55  40.00  35.001  L—I—1—L  15.60  i—i—i—i—I—i—i—i—r  °- 15.40  ceo 15.20 16.00  J  i  i  i_  i  i  i  17.00  Pb  i 18.00 206 204  J  I  I L_  I  I  L  _l  19.00  I  I  L. 20.00  / p b  Lead isotopic composition "of galenas from Belt Supergroup rocks in northwestern Montana and northern Idaho. Solid symbols: late Precambrian deposits (symbol with star represents Sullivan Mine, British Columbia, from Cooper, Reynolds, and Richards. 1969); open symbols: Mesozoic or Cenozoic deposits. Anomalous lead lines (with numbered arrows) shown for the 4 groupings given in Table 3. Primary growth curves are those of Stacey, Delevaux, and Ulrvch (1969) using their curve A for the P b ^ / P b vs. P b ^ / P b " diagram. 2 0 4  F i g . 2.15  3  Lead isotope results of Zartman and Stacey (1971). from p. 851 of their paper.  Taken  56  of the leads.  Although they considered i t unlikely, Zartman and Stacey  could not dismiss the possibility that some deposits of the Precambrian group were emplaced in Phanerozoic times by remobilisation of Precambrian galena. The present writer has already argued that the late Precambrian lead of galena deposits in Purcell rocks may have been leached from surrounding strata and deposited from connate brines and this explanation i s extended to the old Belt leads.  This same explanation has been pre-  viously argued by others, including Hershey (1913, 1913a), Davidson (1967), and Sorenson (1972), but i t has been less popular than other views, for example that the lead and other metals of the Coeur d'Alene d i s t r i c t came from underlying granitic rocks (Ransome and Calkins, 1908) or a deepseated (sub-crustal?) source (Hobbs and Fryklund, 1968). In contrast to old Purcell leads, which are confined to Aldridge rocks, the old Belt leads are found in Pre-Ravalli, Ravalli and Piegan rocks ( f i g . 2.16).  The leads in Pre-Ravalli rocks are considered  separately from the others because, in the U.S.A., Pre-Ravalli leads seem to be different in compositional trend from leads i n the younger Precambrian rocks, and because in Canada old Purcell leads are a l l in Pre-Ravalli rocks. Pre-Ravalli  leads These leads are identified in f i g . 2.17, a composite plot of  Belt-Purcell leads of the late Precambrian group.  Least-squares lines  through Beltian Pre-Ravalli leads, through Purcell Pre-Ravalli leads and through the combined data are shown in table 2.V along with calculated ages of the source rocks.  in  Fig. 2.16  Plot of P b / P b v. P b / P b for analyses of Purcell galena leads (table 2.1) and Belt galena leads (Zartman and Stacey, 1971; their tables 1 and 2). The key identifies the host rock. The growth curve i s drawn for (U /Pb ) - 9.09. present 207  20l+  206  20lt  238  20lt  Fig. 2.17  Plot of Pb /Pb * v. P b / P b for the "late Precambrian group" of galena leads in Purcell rocks (table 2.1) and In Belt rocks (Zartman and Stacey, 1971; p. 852 and p. 854). The symbols identify the host rock of the galena deposit. 207  2()l  206  20,+  *  R— 16-2  16-3  16-4  Ravalli  A  host  A  rock  _l_ 16-3  ,206/„. 204  Fig. 2.18 Belt-Purcell leads of the late Precambrian group plotted above are s p l i t arbitrarily into three sets and these are plotted on the accompanying map using the same symbols. A correlation between isotopic composition and geographic location is suggested. Data from Zartman and Stacey (1971, p. 852, 854) and table 2.1 (this thesis).  VO  60  Table 2.V  Isochron slopes and two-stage ages for Pre-Ravalli leads  Host Rock  Data Points  Belt (Prichard F.)  Slope (±la) (York, 1969)  t (BY) (calculated) 2  ti (BY) (assumed)  14  0.246 ( ±0.023)  2.64  ± .19  1.3  F.)  33  0.244 (± 0.009)  2.62  ± .08  1.3  Combined Belt-Purcell  47  0.261 ( ±0.006)  2.76  ± .05  1.3  Purcell (Aldridge  It was suggested i n section 2.3 that the immediate source of the late Precambrian leads in Purcell rocks was the lower Purcell sediments and that the "age of source rocks" calculated from the galenas was minimum age of the source of these sediments.  the  Results of calculations  based on a modified "frequent mixing model" were presented to show that this interpretation was a reasonable possibility.  The age calculated  above (2.6 to 2.8 BY) for the source of the Pre-Ravalli leads is therefore interpreted in the same way,  that i s as a minimum age for the  source rocks of Pre-Ravalli sediments. There is a small, real,difference between the leads from Purcell and Belt rocks ( f i g . 2.17), as f i r s t suggested by Cannon and others (1962).  This difference i s shown on f i g . 2.18, where the  isotopic composition of Precambrian galena leads in Pre-Ravalli and Ravalli rocks is shown to become, in general, less radiogenic to the south.  This geographic variation may be due to regional differences  in the isotopic composition of extractable lead in the sediments.  In  section 2.3, a model was proposed for Purcell leads in which 5% of extractable lead in the sediments was supposed to be 2.7 BY old lead in feldspars, quartz, etc. eroded from rocks which were not greatly affected  61  by the 1.7 BY orogeny.  If a larger percentage of such lead was present  In the source region of Belt sediments than that of Purcell sediments, this would easily account for the regional difference i n galena leads. Significantly, basement rocks east of the site of Purcell sedimentation are about 1.7 BY old (Burwash and others, 1962), whereas basement rocks exposed near the southern part of the Belt-Purcell basin (fig. 2.1) are about 2.6 BY old and perhaps older ( G i l e t t i , 1968; King, 1969).  As an  example of the possible effect of this difference i n age of the adjacent  Fig. 2.19  Large circles represent the compositions of 50 hypothetical leads after five stages of evolution in various U/Pb environments since 3.0 BY, with mixing at 1.3 BY. For the large open circles, 5% of 2.7 BY lead has been added; for the large striped circles, 10% of 2.7 BY lead has been added. The solid dots are measured Purcell leads (table 2.1), the small circles are Belt leads (Zartman and Stacey, 1971). Growth curve i s the primary growth curve of Stacey and others (1969), for (Tj238/p 204) 9. now b  =  09>  62  source regions assume the "frequently mixed model" calculated for Purcell leads i n section 2.4 i s applicable to Belt leads, except for addition of 10% of 2.7 BY old lead for Belt leads instead of 5% for Purcell leads. Isotope ratios calculated on this basis are compared with measured ratios from leads in Purcell and Belt rocks in f i g . 2.19 and there i s a gross resemblance of the two patterns.  It is suggested, therefore, that  regional variation in galena leads in Belt-Purcell sediments reflect differences in extractable lead in sediments from one end of the basin to the other.  In turn, these differences could reflect differences in  the age of the source rocks. Ravalli  and Piegan leads Interpretation of Ravalli-Piegan leads i s complicated by the  fact that some Ravalli leads are indistinguishable from Pre-Ravalli leads. With some reservations, Ravalli leads are included with the Piegan leads, most of which are clearly different from Pre-Ravalli leads.  The slope  of a least-squares line through the Ravalli and Piegan leads is 0.121 0.008, quite different from leads in the older rocks. of choices of t j and t  2  ±  There are a number  that could f i t both this slope and the geological  evidence,and three of these are summarised in the diagram below (fig.  Case (A) Case (B)  t  1  = 1.7 BY (assumed)  t  ti = 1.3 BY (assumed)  Case (C) t! - 1.2  • (±0.1) = t  t  2  2  = 0.6  2.20)  (±0.2) BY  = 1.1 (±0.2) BY  2  TIME Fig. 2.20  Diagram showing three possible interpretations of the slope for old Ravalli-Piegan leads.  63  For case A, t i was chosen to be 1.7 BY because this i s the approximate age of nearby Hudsonian basement rocks.  Older ages for t i  could be assumed, but t then becomes younger and the scatter of the 2  points could be expected to be greater, a point made by Zartman and Stacey (1971) in a similar calculation. Case B represents a model where radiogenic lead developed in Belt sediments between 1.3 and 1.1 BY is mixed with remobilised lead of the older 1.3 BY mineralisation. younger than 1.3 BY are chosen for t j then t case C, t j = t . 2  2  becomes older u n t i l , as in  Case C represents a model where radiogenic lead pro-  duced in Belt sediments at 1.2 BY i s mixed with leads of the 1.3 mineralisation. tion.  If ages  BY  The age 1.2 BY is the oldest possible time of mineralisa-  In both cases  B and C upward remobilisation of Pre-Ravalli leads  i n late Precambrian time i s implied.  The writer prefers case B because  i t i s most consistent with the origin proposed for the Pre-Ravalli leads, but there is l i t t l e practical difference between case B and C. There may be a correlation between the two ages (1.3 and 1.1  BY)  of mineralisation inferred above from lead isotope data and the two older Rb/Sr ages obtained from Beltian sediments by Obradovich and Peterman (1968).  This correlation i s shown i n a diagrammatic way in f i g . 2.21  where ages obtained from whole-rock Rb/Sr isochrons are compared with those obtained by galena lead isochrons. Obradovich and Peterman (1968) interpreted their Rb/Sr data as ages of sedimentation with 200 MY-long periods of non-deposition between them but they were unable to cite f i e l d evidence of such long time breaks. The writer's interpretation, based on lead isotopes in mineral deposits, is quite different in viewpoint.  The lead ages have been related to min-  64  eralisation events involving circulation of connate brine, metamorphism, and Precambrian faulting and these events are believed to have taken place within sediments deposited without major breaks, but probably with numerous diastemic intervals.  It seems possible that the Rb/Sr ages are  not ages of sedimentation but are instead ages of the same hydrothermal events that the lead i s thought to date.  Pb  Rb/Sr  Time 10 yr. 9  0-8 "  0-9 10 11 CL.  sedimentation event  hydrothermal event  sedimentation event  hydrothermal event  1-2 1-3  UJ CO  t^-^-^HKr-I-I!i  t  1-4 1-5 1-6 1-7 1-8 1-9 20  Fig. 2.21  Zoo  >-  oc  U  Hi!+  Comparison of Rb/Sr dating of Beltian sediments by Obradovich and Peterman (1968) with the lead isotope interpretation of the "old" Belt-Purcell galenas given in this thesis.  Mesozoic-Cenozoic  Leads  Zartman and Stacey (1971) concluded that the isotopic composition  65  of their Mesozoic-Cenozoic group of leads (fig. 2.15) was largely controlled by heterogeneity in the basement rocks. They grouped leads of four different geographic areas (fig. 2.14) and calculated source-rock ages (t^) of 1.6 and 1.5 BY for the two western groups (3 and 4), and 2.7 and 2.8 BY for the two eastern groups (1 and 2), assuming a t 100 MY.  2  of  They pointed out that these were the two ages of major tectonism  known from the crystalline basement rocks, although they recognised that the slopes they used for the calculations were not firmly established. Zartman and Stacey emphasised a geographic grouping of samples. It i s noted here that a crude relationship of composition to stratigraphy also exists.  In f i g . 2.22 a l l the Mesozoic-Cenozoic leads in Pre-Ravalli  rocks are compared to those in Ravalli and younger rocks and a rather ill-defined grouping i s seen.  Although this grouping i s not clear, the  distribution Is somewhat like that for the Precambrian leads, suggesting that the older pattern could have influenced or controlled the compositions of the Mesozoic-Cenozoic leads.  Fig. 2.22 also illustrates one possible  way i n which the distribution of old leads could be reflected in the distribution of younger leads.  If this sort of evolution has occurred, ages  determined from the oversteepened slopes of the lines w i l l be slightly older than they should be.  Although i t is speculated from f i g .  2.22  that the Mesozoic-Cenozoic leads could be controlled by the older pattern found in the Precambrian leads, more information i s needed to test this "stratigraphic" alternative proposal to the very reasonable "basementcontrol" interpretation of Zartman and Stacey.  66  Pb  307  Pb  EVOLUTION FROM A LINEAR ARRAY  EVOLUTION  FROM TWO ARRAYS  KEY Q  PRE-RAVALLI  0  RAVALLI, POST—RAVALLI  Pbypb™ Fig. 2.22  The pattern of compositions which results from evolution (growth, mixing) from two arrays i s shown in the upper sketch. In the lower diagram, actual compositions from Belt-Purcell rocks are shown. It is suggested that the Mesozoic-Cenozoic leads could be controlled by the compositional pattern of the Precambrian leads.  67  2.6  SUMMARY  (1)  The main conclusions reached by Leech and Wanless (1962) in a  study of lead isotopes from galena deposits of the East Kootenay district have been confirmed by the analyses reported in this study.  The earlier  conclusions are as follows. (a)  Two main groups of lead isotopes exist:  variable, more radiogenic group.  a uniform group, and a  Leads of the uniform group have single-  stage ages in the range 1.2 - 1.4 BY; the others appear to be MesozoicCenozoic in age. (b)  Most of the large lead-zinc deposits of the region, many of them  stratiform, contain lead of the old, uniform group. Deposits containing Mesozoic-Cenozoic lead are small and occur i n veins.  The unimportant  veins in Moyie intrusions contain lead of the old, uniform group. (2)  The new analyses permit the following additional conclusions. (a)  The uniform "late Precambrian leads" form a short elongate array  resembling a multi-stage anomalous line.  If mineralisation was at 1.3  BY, the source rocks of the lead are 2.6 BY old (two-stage model). (b)  A correlation exists between the isotope ratios of the late Pre-  cambrian leads and geography, the least radiogenic leads being in the southern part of the East Kootenay d i s t r i c t . (c) lines.  The Mesozoic-Cenozoic leads appear to be related to two anomalous The groupings could be related to the host rocks, but this  relationship is not clear.  If mineralisation i s assumed to be at 100  MY,  the age of source rocks of the anomalous lead i s calculated to be about 1.5 BY.  It is therefore suggested that Mesozoic-Cenozoic leads came from  Purcell sediments and that they are the result of addition of radiogenic  68  lead (developed between about 1.5 BY and 100 MY) to lead resembling the late Precambrian group. (3)  The following conclusions can be drawn from a comparison of  leads in Purcell rocks with the analyses of leads in Beltian galenas reported by Zartman and Stacey (1971). (a)  Both sets of analyses show the same major features —  (1.2 - 1.5 BY) uniform group of leads and a young variable group.  an old  (Mesozoic-Cenozoic)  In both regions, the old leads are characteristic of  the principal lead-zinc mines. (b)  In Beltian sediments, lead of the old group i s found in rocks  as young as the middle Belt (Piegan Group), whereas in Purcell sediments a l l the deposits known to contain old lead are confined to the lowest Purcell (Aldridge Formation).  If isotope ratios of old leads i n Aldridge  rocks are combined with those of old leads in correlative Prichard rocks an age of about 2.7 BY can be estimated for the source rocks of the lead (assuming mineralisation at 1.3 BY).  A less certain anomalous line  through old leads in Ravalli-Piegan rocks suggests these leads were emplaced at about 1.1 (c)  BY.  If a l l the Mesozoic-Cenozoic leads from the Belt-Purcell basin  are considered together, a pattern grossly similar (though distorted) to the pattern of the old leads is seen,and i t is suggested that the compositional pattern of the old leads could have influenced or controlled that of the younger.  The distortion i s that expected by evolution of  lead isotopic compositions during the interval since the Precambrian mineralisations. (d)  A geographic pattern shown by isotope ratios of old Belt leads  69  is continuous with a geographic pattern shown by old Purcell leads i n Canada. (4)  In conclusion, the inferred history of the galena leads i n  Belt-Purcell sediments i s as follows. The old lead could have been derived from the Belt-Purcell sediments by circulating connate brines.  Thus, because the lead repre-  sents an average of a large volume of crustal rock and because i t i s well mixed during sediment transport and later during brine movement, the precipitated lead i s very uniform i n composition and has a singlestage age very close to the age of emplacement (believed to be about 1.3 BY).  Because of the slight variability i n extractable lead both regional-  ly and locally, these old leads retain faint evidence of the age of the 2.7+BY old source-rocks of the Belt-Purcell sediments — Shield.  the Canadian  The 2.7 BY age i s thus not interpreted as the age of  basement rocks.  underlying  There appear to be two groups of old leads, those i n  Pre-Ravalli rocks and those in overlying Ravalli and Piegan strata. It i s the leads in Pre-Ravalli rocks that contain evidence of the ancient source-rocks, and of a mineralisation event at 1.3 BY.  The old leads in  Ravalli-Piegan rocks could have been derived from growth of radiogenic lead i n Belt sediments between 1.3 and 1.1 BY, and by mixing of this lead with 1.3 BY old lead. The large concentrations  of lead and zinc that account for the  economic importance of the early mineralisation could be due to the opportunity  for wide-spread leaching of lead and zinc by a circulating  i n t e r s t i t i a l brine early in the history of the sediments.  Later restric-  tion of circulation to fault systems, and unavailability of large volumes  70  of fluid could account for the smaller size of the younger mineral deposits. Some of the interpretation offered here is admittedly speculative, and this i s partly due to a lack of c r i t i c a l , independent, local evidence of the age and origin of Belt-Purcell leads.  However, the general model  proposed i s consistent with recent investigations elsewhere of modern brines, some lead-zinc deposits and lead isotopes.  71  CHAPTER 3.  3.1  LEAD ISOTOPES FROM THE KOOTENAY ARC, BRITISH COLUMBIA  PREAMBLE  Analyses from a representative selection of the lead-zinc deposits of the Kootenay Arc have been reported by Sinclair (1966) and Reynolds (1967).  Most of this work has been repeated, however, and a  brief explanation of why this was done i s necessary. Sinclair (1964, 1966) made a detailed study of Kootenay Arc leads and found the isotopic ratios of a l l of them plotted on a single anomalous lead line.  Reynolds (1967), i n the course of a study of rock  leads and ore leads from the Nelson Batholith, reanalysed three of Sinclair's samples.  He found that these three samples and two additional  samples did not f i t Sinclair's line, but f e l l instead on a parallel anomalous line below i t (see f i g . 3.3).  Before any new work was done,  i t seemed essential to determine whether the slight difference between these lines was real.  Accordingly, most of the samples analysed by  Sinclair (1964), Reynolds (1967) and one sample of Kanasewich (1962) were reanalysed.  3. 2  These new analyses confirm that both anomalous lines are real.  OUTLINE OF THE GEOLOGY AND LEAD-ZINC ARC  MINERALISATION  OF THE KOOTENAY  Geology  Ross (1970), Yates (1970) and Fyles (1970) have given recent accounts of the geology of the Kootenay Arc.  The following outline i s  summarised mainly from Fyles (1970). The Kootenay Arc i s a curved structural belt (fig. 3.1) bounded  72  FIG. 3'1  The Kootenay Arc  mainly  I  after Fyles (1967, fig. 12; 1970, fig. IV-1]  Silver  Giant  &  Badshof-Reeves limestone ==Grnnitir  A  rocks  large deposi'f-more i/ian 50 * JO fc. Pb+Zn  ^Mineral  King  73  to the east by little-deformed Precambrian sediments of the Purcell Anticlinorium, and to the west by highly-deformed gneiss and schist of the Shuswap Metamorphic Complex.  The arc extends over 250 miles from near  Revelstoke (B.C.) where i t merges with the Shuswap terrain, into Washington State where i t i s covered by flood basalts of the Columbia Plateau. Rocks involved i n this structural belt are complexly deformed and variably metamorphosed sediments and volcanics of late Proterozoic to late Mesozoic age (fig. 3.2).  The succession i s essentially conformable, although a  late Palaeozoic disconformity and an early Mesozoic disconformity appear to be present, and others may exist.  An important lithologic marker i s  the Lower Cambrian Badshot-Reeves limestone which i s exposed i n a narrow belt i n the eastern part of the Arc (fig. 3.1).  To the east of this belt  rocks are generally older than the limestone unit, whereas to the west there i s a thick succession of younger sedimentary and volcanic rocks that includes rocks as young as Jurassic. Major deformation and metamorphism (locally to sillimanite grade) are known to have ceased before or during intrusion of the Nelson Batholith, which has a cooling age of 160 - 170 MY (Gabrielse and Reesor, 1964; Nguyen and others, 1968).  The exact timing of the polyphase  folding and metamorphism, however, i s in dispute (Ross, 1970; Wheeler, 1970).  The evidence does suggest that important deformation took place  both before and after deposition of the Upper Mississippian-Pennsylvanian Milford Group.  The main metamorphism i s considered to be early Mesozoic  by Wheeler and others (1972), and late Palaeozoic by Ross (1970). Jurassic to Middle Cretaceous granitic intrusions Include the Nelson and Kuskanax batholiths (fig. 3.1).  Small intrusions of Tertiary  74  monzonite,syenite and granite are found i n the southern part of the Arc. Widespread lamprophyre dikes cut a l l rocks.  EAST  WEST  INTERMEDIATE FLOW ROCKS <1 a.  a  INTERMEDIATE VOLCANIC BRECCIA  ft.At)  h°na  Fig. 3.2  Lead-Zinc  CONGLOMERATE  HI  QUARTZITE, SANDSTONE, SILTSTONE  PILLOW LAVA  SHALE .ARGILLITE.  QUARTZ-POOR PLUTONIC ROCKS.  HIGH GRADE METAMORPHIC ROCK  CARBONATES  QUARTZ-RICH PLUTONIC ROCKS.  MIGMATITIC GNEISS rVWv) UNCONFORMITY AND SCHISTS.  |v\/v\|DISCONFORMITY  Relationships of formations in the southern part of the Kootenay Arc. Taken from Monger and Preto (1972, p. 32).  Mineralisation Fyles (1966, 1967, 1970) has classified lead-zinc deposits of  the Kootenay Arc into two broad structural groups, one mainly concordant and the other mainly transgressive.  According to Fyles (1967, p. 69)  these structural groups are of significantly different ages, the concordant deposits being the older. Table 3.1 summarizes many details of  75  the deposits in the Kootenay Arc and i s taken from Fyles (1967). Concordant  deposits Deposits of the concordant group are the largest and most pro-  ductive.  They are older than the IJelson Batholith and may be older than  the regional metamorphism (Fyles, 1970; Muraro, 1966; Macdonald, 1970, in preparation).  In general, deposits of the concordant group are dis-  seminations of pyrite, sphalerite and galena, with or without pyrrhotite, in Cambrian carbonate rocks.  Fyles (1967) divided the concordant group  into three structural types. Metaline  type —  In unmetamorphosed dolomitised host; faulting  and brecciation important; gently folded. Salmo type —  In low grade regionally metamorphosed and dolomitised  host; complex penetrative deformation. Shuswap type —  In calcareous metasediments of medium to high  metamorphic grade; extensive and stratiform; complexly deformed. Transgressive  deposits  The transgressive deposits include fissure and replacement veins, both simple and complex.  They are generally richer in silver, lead and  zinc than are deposits of the concordant group (Fyles, 1966; SutherlandBrown and others, 1971) and Sinclair (1964) has shown that there are also distinct differences in the trace element content of galenas (notably Ag, Sb, TI, Sn, B i , Cu) of the two groups. Three once-important camps where mineralisation was of the transgressive type are Ainsworth (and Bluebell), Slocan City and Sandon, and at these camps mineralisation i s younger than a l l facies of Nelson plutonic rocks and younger than most of the widespread lamprophyre dikes  76  (Cairnes, 1934; Fyles, 1967).  In the Ainsworth and Bluebell areas  there i s a close relation between the orientation of veins and lamprophyric dykes and Fyles (1970) inferred from this that the mineralising process in these areas was connected with the magmatic activity. The lamprophyres have long been considered to be early Tertiary (e.g. Rice, 1941; Fyles, 1970)  on geologic grounds, and radiometric ages  of about 50 MY for several of these dykes in northeastern Washington (Yates and Engels, 1968)  and 49 MY for a dyke near Salmo (Macdonald, in  preparation) support this age assignment for most of the lamprophyres. Nguyen and others (1968), however, obtained a K/Ar age of 170 MY for a lamprophyre dike that cues the Nelson Batholith, and this suggests that a few older lamprophyres exist. Regarding a connection between Nelson granitic rocks and transgressive deposits, Fyles (1970, p. 52) concluded "The Nelson granitic rocks, which include Nelson and Kuskanax batholiths and a number of related stocks mainly in the southern part of the Arc, as now exposed, seem to have been incidental to the mineralization process.  Early  workers regarded these granitic rocks as the source of the lead and zinc, but detailed studies have not found evidence that any one deposit or group of deposits i s genetically related to a specific pluton."  3.3  PREVIOUS LEAD ISOTOPE STUDIES* Sinclair (1964, 1966)  summarised the scattered analytical work  on Kootenay Arc galenas prior to his study, the f i r s t detailed report of  ^Previous workers have used different values for the age of the earth and for primeval ratios. No modification of published ages has been made.  Deposit  Sulphides In Addition to Galena. Sphalerite, and Pyrite  Gangue  Structural Control of Orcbodies  Form of Ore bodies  Formation  Rock Types  Metamorphic Minerals  Grade and Type of Metamorphism  Ago  Met aline district.  Dolomite rock, calcite, quartz.  Irregular lowdipping tabular, sub bedded.  Adjustment related Upper Met&llne to regional faultlimestone. ing and fault zones.  Siltcifled dolomite breccia.  Chlorite, muscovite.  Low.gr ade regional Middle or late metamorphism. Cambrian.  Reeves MacDonald.  Pyrrhotite near lam rrophy re dykes.  Dolomite rock, calcite, minor bariie.  Elongate, troughlike, irregular in detail.  Steeply plunging isoclinal syncline.  Reeves limestone.  Dolomitized zone in limc>t>me in a sequence of phyllitcs and arpillites.  Muscovite, chlorite, chloritoid.  Low regional.  Jersty. H.B., Aspen, JackpoL  Pyrrhotite. arsenopyrite.  Dolomite rock, calcite, tremolite-talc and garneidiopside alterations.  Elongate bodies, low plunpe, irregular in detail.  Long dimension parallel to main fold axes.  Reeves limestone.  Dolomiiircd zones in limestone, in a sequence of phylhte. argillite, and hornfets near granitic : locks.  Biotite. garnet diopside, zoisite.  Duncan.  Pyrrhotite. chalcopyrite.  Dolomite rock, cherly dolomite, calcite.  Hlonpate bodies, low plunpe, irregular in detail.  Lonp dimension parallel to main fold axes.  Badshot limestone. Dolomitized and siliceous zones In limestone.  Bannockbum " Shells* Vein."  Tetrahedrite.  Calcareous quartziie.  Elorpate, low plunge.  Lonp dimension parallel to main fold axes.  Jordan River.  Pyrrhotite.  Calcareous schist, quartz, minor baiicc.  Bedded.  Ains worth Comp.  Pyrrhotite, chalcopyrite. arsenopyrite.  Quartz carbonates, fluorite.  Bluebell.  Pyrrhotite. chalcoryrite, arsenopyrite.  San don Camp.  Arsenopyrite, tetrahedrite, chalcopyrite, ruby silver.  ZLnctoo—Lucky lim.  Metal Ine type.  Lower Cambrian.  Pre-lamprophyre, during regional folding and metamorphism.  Salmo type.  Biotite grade regional, with superimposed contact metamorphism.  Lower Cambrian.  Pre-"granite" but some mineralization post contact metamorphism (11.B.J  Salmo type.  Biotite, chloritoid, garnet.  Biotite and garnet grades, repional metamorphism.  Lower Cambrian.  During regional folding and metamorphism.  Salmo type.  Uppermost Hamill Calcareous Group. quaruitc. phyllite, limestone.  Clorite. muscovite.  Low regional metamorphism.  Lower Cambrian.  During or after regional folding.  Salmo type.  Folded with the metamorphic sequence.  Shuswap metamor- Calcareous schists, phic complex. maiblc a-id quait.-ite.  Garnet sillimanite.  Hiizh-grnde regional metamorphism.  Uncertain.  Pre-metamorphism end folding.  Shuswap type.  Tabular.  Veins in normal faults.  Milford Group,  Limestones, mica and hornblende schists, quartzites.  Garnet, staurolite, biotite.  Biotite and garnet grades, regional metamorphism.  Late Palxozoic.  Post r.mprophyre, post foldint: and metnir.orphWrn. .  Vein type.  Quartz carbonates, limestone.  Irregular.  Replacement of limestone outward from fractures.  Badshot.  Crystalline limcstonej qiartzite, and schii-t.  Kyanitesilliminite.  High-grade regional metamorphism.  Lower Cambrian.  Post lamprophyre, post folding and metamorphism.  Fracture controlled replacement.  Quartz, sidcrite, calcite.  Tabular to irregular.  Veins in regional sbear-fauMs. Orrihoots strongly controlled by structure of wallrocks.  Slocan Group.  Dark-grcy argillitcs, siliceous and limy argillites.  Muscovite, chlorite, seiicite.  Low-grade regional metamorphism.  Trlasslc.  Late stages of folding; post lamprophyre, post Nelson.  Complex veinsystems.  Post lamprophyre.  Fracture controlled replacement.  Uncertain.  Complex shear zone.  Late stages of deformation(?), post lamprophyre.  Complex shear zone.  UD certain.  Complex shear zone.  Calcite, limestone, dolomite rock.  Irregular.  Replacement of limotoiic outward from fractures.  Lucky Jim limestone in Slocan Group.  Fine-grained limestone.  Muscovite.  Low-grade regional metamorphism.  Low-grade regional Triassic. and thermal metamorphism.  Chalcopyrite.  Sidcrite, quartz, calcite.  Lenses within a shear zone with steep plunge.  Irregularities In shear zone.  Slocan Group.  Slates, argillites, thin limestones.  Biotite.  Whitewater.  (1) Tetrahedrite, chalcopyrite. (2) Pyrrhotite, chalcopyrite.  (1) Sidcrite, quartz, (2) Magnetite, altered dyke rock.  Lenticular, modcrate plunge.  (1)  Irregularities within a shear zone. (2) Limestone replacement. (3) Replacement of a lamprophyre dyke.  Slocan Group.  (1) and (2) Limestone.  (1) and (2> Chlo- Low-grade rite • JU: covite. regional metamorphism.  (3) Lamprophyre dyke.  (3) Chrome mica.  Tetrahedrite, chalcopyrite, ruby silver.  Quartz, sidcrite.  Lenticular, iteep plunge.  Minor drag on shear zone.  Lardeau Group, Slates. Triune Formation.  Table 3.1  Classification  Uncertain.  Cork Province.  Silver Cup.  Age of Mineralization  Muscovite, chlorite, sidcrite, chrome mica.  Some important lead-zinc deposits of the Kootenay Arc.  Tri as sic.  Trlasslc.  Low-grade regional Mid Paleozoic plus Widespread hydro thermal alteration.  O O  s  CO  Taken from Fyles (1967; p. 66, 67).  rn </> 0)  3  78  lead isotope analyses from this region. From analyses of 16 representative lead-zinc deposits, Sinclair found a l l were related by a single anomalous lead line on a graph of P b  206  /Pb  201t  v. P b  207  /Pb  201t  .  From the  slope of this line, Sinclair calculated that the age of source rocks was 1,700 MY, assuming mineralisation was at about 170 MY.  He believed  the 1,700 MY age was too young for the source to be Hudsonian basement and suggested that lower Purcell rocks were a possible source of the radiogenic lead.  In Sinclair's view, the leads were the result of mixing  1,340 MY old (single-stage age) Sullivan-type lead with radiogenic lead developed i n lower Purcell sediments.  These mixed leads were considered  to have been emplaced during Middle Jurassic (approximately) mineralisation.  Sinclair (1966) did not find any correlation between isotopic  composition and size of deposit, type or age of wall-rock, or minor element content of galena. Reynolds (1967) analysed four galenas from deposits which he considered were "associated" with the Nelson Batholith, and lead from four samples of feldspar from the batholith i t s e l f .  A l l these leads and  some older analyses of Bluebell Mine galena (Kanasewich, 1962) plot on an anomalous line below Sinclair's (1966) line.  Furthermore, the line  determined by Reynolds did not pass through lead of Sullivan composition, for i t was parallel to Sinclair's line.  Reynolds suggested that the  source rocks for the anomalous leads might be Hudsonian in age, or perhaps a mixture of Hudsonian and lower Purcell rocks. He believed his analyses provided (Reynolds, 1967; p. 65)  for the f i r s t time, clear evidence  of a genetic relationship between ore deposits and granitic rocks." leads on the lower anomalous line were considered to be the result of  The  79  mixing of hypothetical 1,600 MY primary lead and radiogenic lead developed between 1,600 MY and 150 MY.  This interpretation is similar, although  more detailed, to that suggested by Kanasewich (1962), for Bluebell lead. Reynolds and Sinclair (1971) reinterpreted their combined data ( f i g . 3.3) and related the two anomalous lead lines to two geologically distinct groups of deposits.  Leads on the upper line (Sinclair's line)  are of the Salmo type, leads on the lower line (Reynold's line) are vein deposits spatially related to Nelson plutonic rocks.  The Salmo-type  deposits were regarded as the result of simple mixing of Sullivan-type lead and radiogenic lead derived from 1,530 MY old upper-crustal source rocks.  The model age of Sullivan lead was calculated to be about 1,200  MY, and i t was suggested i t might be a representative sample of average lead i n the surrounding rocks at that time.  The magma of Nelson plutonic  rocks and the ore fluids of the spatially related "Nelson" deposits were inferred to come from the same U/Pb source, probably the lower crust. Contamination of this ore fluid with radiogenic lead from 1,530 MY old upper crustal rocks was required by their model.  For purposes of calcula-  tion, Reynolds and Sinclair assumed that Sullivan lead could be included with the Kootenay Arc leads, that both anomalous lines had the same slope, and they used the value (0.0982 ± 0.0052) of the more precisely determined upper line.  They also assumed a time of mineralisation of  150 MY for a l l deposits. Ohmoto (1968) noted that a genetic link between lamprophyres and Bluebell ore had been suggested by several authors and he obtained four lead isotope analyses of Bluebell galena, and two analyses of rock leads from lamprophyre dikes for comparison.  Because the composition of  lead i n the ore and the dikes was different, Ohmoto suggested that the  80  Fig.  3.3  Plot of ore and rock leads from the Kootenay Arc, reported by Reynolds and Sinclair (1971, p. 261). Key:  O =  Salmo type deposits  • =  Slocan and Ainsworth deposits  A  =  • =  Bluebell analyses  (Kanasewich, 1962)  Feldspar lead, Nelson Batholith  ore  lead and lamprophyre lead did not share a common source. He concluded  (op.  cit.., p. 26) "The apparent anomalous age and the large variation of  the  isotopic composition of Bluebell galena suggest that, with respect  to the concentrations of Pb, U and Th and the i n i t i a l Pb isotope ratios, the  lead was derived either from a very heterogeneous source or two or  more homogeneous but different sources." In a later paper, Ohmoto (1971, p. 99) stated "The sulphur, salts, and metals were probably derived from the  thick sedimentary sequences which were present above the Bluebell  limestone during Tertiary times and/or from the sedimentary sequences east of the Kootenay Arc."  81  3.4  DISCUSSION OF NEW LEAD ISOTOPE DATA A l l analyses made by the writer are presented in tables 3.II  and 3.III.  Most sample locations are shown on f i g . 2.5.  A l l Kootenay  Arc samples analysed in the present study are plotted on f i g . 3.4  and  3.5. Reynolds and Sinclair (1971) have discussed the fact that leads ( f i g . 3.3) on their lower line ("Nelson leads") are geologically distinct from those on their upper line ("Salmo leads"). In their view, the isotopic distinction was due to association of Nelson leads with the Nelson Batholith and the lack of such an association ^or the Salmo leads. In contrast, the view advanced i n the following discussion is that the distinction i s primarily due to a difference in age of emplacement of the concordant and transgressive types of deposit. The new analyses listed in tables 3.II and 3.Ill and plotted in f i g . 3.4 clearly show that the geological distinction between deposits on the two anomalous lines is that the "concordant" deposits plot without exception  on the upper line, whereas the "transgressive"  deposits plot with only one exception (Spider) on the lower line.  These  two groups are now considered separately, and the results are later integrated. Concordant Group Deposits on the upper line (fig. 3.4) include not only the Salmo-type deposits as already demonstrated by Reynolds and Sinclair (1971), but a l l the analysed Shuswap and Metaline even the two  Metaline  type deposits also,  type deposits from the region east of the Kootenay  TABLE 3.II UBC No.  ISOTOPE COMPOSITIONS OF LEAD IN GALENA FROM CONCORDANT DEPOSITS, KOOTENAY ARC  NAME OF DEPOSIT  Pb  2 0 6  /Pb  2 0 l +  Pb  207  /Pb  201  *  Pb  2 0 8  /Pb  2 0 1 t  *REF.  HOST ROCK  METALINE TYPE 837 874 865 864  MONARCH SILVER GIANT? VAN STONE PEND OREILLE  18.165 18.258 19.390 19.486  15.637 15.653 15.791 15.789  38.727 38.310 39.890 39.922  Cathedral F. (Mid Cambrian) (1) Jubilee F. (Mid, Upper Cambrian) (2) Metaline F. (mid) (Mid Cambrian-Ord?) (3) Metaline F. (upper) (Mid Cambrian-Ord?)(4)  19.093 19.076 19.089 19.281 18.992 19.417 19.347 18.280  15.736 15.738 15.727 15.756 15.744 15.786 15.767 15.667  39.437 39.386 39.486 39.534 39.304 39.915 39.718 38.275  Reeves 1st. (L. Cambrian)  18.239 18.242 18.417 18.468 18.251 17.924  15.630 15.630 15.663 15.668 15.630 15.592  38.240 38.211 38.261 38.126 38.108 37.884  SALMO TYPE 300 285 286 866 284 307 291 318  JERSEY REEVES-MACDONALD H.B. RAINBOW JACKPOT DUNCAN LAKE SAL A MOLLIE MAC  Index F. (L. Cambrian-Ord.?)  (5) (5) (5) (5) (5) (6) (6) (7)  Badshot 1st. (L. Cambrian)  (8)  Badshot 1st.? (L. Cambrian)  (9) (9) (9) (9)  it  II  II  ti ii  II  II  II  Badshot 1st. (L. Cambrian) II  II  SHUSWAP TYPE 854 855 856 857 858 859  WIGWAM WIGWAM COTTONBELT RUDDOCK CREEK RIVER JORDAN RIVER JORDAN  *REF. (1) Ney (1957) (2) Hedley (1949) (3) Cox (1968)  (4) McConnel and Anderson (1968) (5) Fyles and Hewlett (1959) (6) Fyles (1964)  II  II  II  II  II  II  (7) Fyles and Eastwood (1962) (8) Thompson (1969) (9) Fyles (1970a)  83  TABLE 3.Ill UBC No.  ISOTOPE COMPOSITIONS OF LEAD IN CALENA FROM TRANSGRESSIVE DEPOSITS, KOOTENAY ARC  NAME OF DEPOSIT  rb^/Ph '* 2 0  Pb^/Ph  2 0 1 1  Pb^/Pb '' 2 0  HOST ROCK  **REF.  AIliSWOFTH CA!-3>  226 315 316 314 910 911 S08 898 909 901  BLUEBELL* TRIUMPH NICOLET HIGHLANDER NO. 1 HIGHLAND SILVER HOARD SILVER GLANCE KOOTENAY FLORENCE MONTEZUMA*  17.481 17.537 17.570 17.556 17.768 17.534 17.793 17.489 17.463 17.583  15.488 15.506 15.502 15.511 15.530 15.498 15.522 15.486 15.488 15.507  37.961 38.224 38.205 38.248 38.344 38.253 38.298 37.994 37.969 38.244  Bluebell 1st.- Badshot 1st. (L. Cambrian) (1) Milford Croup (Miss-Penn) (2) (2) " Nelson granite (M. Juras.) (2) if (2) " .Kaslo Group (L. Trias.) (2) " (2) (2) " .Kaslo Group (L. Trias.) (2) Slocan Group (U. Trias-L. Jurassic) (3)  18.630 18.969 18.721 18.878 18.851 19.141 18.889 18.705 18.815  15.614 15.657 15.635 15.642 15.647 15.679 15.661 15.632 15.641  38.932 38.965 38.970 39.072 39.046 38.927 38.715 38.971 39.155  Nelson granite (Mid. Jurassic)  18.703 18.725 18.668 18.923 18.712 18.744 18.708 18.898 18.800 18.794 18.790 18.762 18.741 18.747 18.623 18.743 18.778 18.719 . 18.752  15.631 15.649 15.635 15.664 15.647 15.633 15.628 15.664 15.656 15.635 15.640 15.649 15.633 15.644 15.618 15.634 15.633 15.624 15.639  39.018 39.071 39.026 38.747 39.053 39.050 39.032 39.045 38.844 39.041 39.010 38.959 39.039 39.021 39.055 38.974 39.032 38.995 39.032  Slocan Group (U. Trias.-L. Jurassic)  18.733 18.989 19.225 19.157 19.322 19.114  15.644 15.675 15.695 15.732 15.710 15.696  38.873 38.776 39.482 39.260 39.269 38.845  SLOCAI1 CTTX CA1-IP  867 869 868 870 871 877 295 903 902  SILVER LEAF CORONATION ENTERPRISE OTTAWA ARLINGTON CHAPLEAU SCRAKTON* KALISPELL LITTLE TIM  " " "  " , quartzite Sediment in Nelson granite Nelson granite  (3) (3) (4) (4) (3) (4) (4) (3) (4)  SAIIDON CAMP  878 879 880 881 882 883 884 887 894 895 896 899 904 905 906 907 912 294 900  RUTH-HOPE SILVERSMITH STANDARD KOLLY HUGHES VAN ROI PAYNE VULTURE NOBLE 5 WHITEWATER CORK PROVINCE* UTICA INDEX* BOSUN IVANHOE CALIFORNIA FISHER MAIDEN LUCKY JIM VICTOR DUBLIN QUEEN  II  Nelson granite Slocan Croup  " II  it  n ti  " tt  " it  ti  Nelson granite Slocan Croup II  it  (5) (5) (4) (4) (4) (5) (3) (3) (6) (4) (4) (4) (4) (5) (3) (3) (6) (5) (3)  MISCELLANEOUS  863 886 317 875 897 860  RED ROCK YMIR MOONSHINE SPIDER SILVER CUP ELSIE  *Not in the main canp area **References: (1) Shannon (1970) (2) Fyles (1967) (3) Cairnes (1935) (4) Little (1960)  (5) (6) (7) (8)  Reeves 1st. (L. Cambrian) Ymir Gp. •= Slocan Gp. (U. T r i . - L . Juras.) Badshot 1st. (L. Cambrian) 7 Triune F. (Ord.?) (Carb-Permian?)  Hedley (1952) Hedley (1947) Fyles and Hewlett (1959) Cockfleld (1936)  (9) (10) (11) (12)  Fyles (1964) Eastwood and Peck (1956) Fyles and Eastwood (1962) Campbell (1963)  NOTE: References given are not necessarily the most recent or most complete available.  (7) (8) (9) (10) (11) (12)  15-Br  Fig. 3.4  Plot of Pb /Pb v. P b / P b Growth curve i s for (U /Pb *) 207  20lt  206  238  201+  201  for a l l the Kootenay Arc data listed i n tables 3.II and 3.III. . - 9.09.  Fig. 3.5  Plot of P b / P b v. P b / P b for a l l the Kootenay Arc data listed in tables 3.II and 3.III. Growth curve i s for (Th /Pb ) = 39.60. present 208  2014  206  232  20l+  2Qlt  86  Arc (Silver Giant, Monarch). A l l of the concordant deposits are in rocks of known (Salmo type, Metaline type) or inferred (Shuswap type) Cambrian age (Fyles, 1967, 1970a).  Although as a group the concordant deposits possess  unifying geologic characteristics and appear relatively old (Fyles, 1967), there i s no certainty that they are a l l of the same age (Weissenborn and others, 1970).  However, the strong isotopic relationship f i r s t demonstra-  ted by Sinclair (1964) can be regarded as evidence of a common age and i t i s assumed for present purposes that a l l the concordant deposits are approximately the same age, although interpretation of the lead isotopes would not be greatly influenced by a range in age of perhaps 200 MY. The absolute age of the concordant deposits i s not certain. Salmo type deposits seem to predate the Nelson Batholith (minimum age 170 MY) and are as old as,or older than, metamorphism and deformation of their host rocks (Fyles, 1967).  Muraro (1966) argued that in the Salmo  type deposits the sulphides have undergone the same deformation as the host rocks and he considered that the deposits of Metaline d i s t r i c t represented the closest approach to the original Salmo deposits. From a detailed study of the deformation of the main Salmo type deposits, Macdonald (in preparation) has come to a similar conclusion. Stratigraphic controls for deposition of metals of concordant deposits of every type have been noted by a number of writers and there is the possibility that metal emplacement occurred soon after sedimentation, although not necessarily i n the form of ore deposits. Thus Fyles (1970) noted that Cambrian sedimentary processes could have been important in controlling the regional distribution of metals now in Salmo deposits,  87  although in his view the main Salmo mineralisation accompanied and followed folding.  Whishaw (1954) suggested from limited geochemical  analyses that black a r g i l l i t e of Cambrian age could have been the source of lead in the Jersey deposit, a Salmo type deposit in the underlying Cambrian limestone.  In a discussion of regional aspects of Shuswap type  deposits, Fyles (1970a, p. 44) concluded "Thus the concordant lead-zinc deposits of the Shuswap Complex appear to have formed along specific stratigraphic horizons at various levels in the sedimentary sequence before intense folding and metamorphism." For the little-deformed deposits of Metaline  district,  possibly precursors of Salmo and Shuswap type deposits, McConnel and Anderson (1968) suggested that lead might have been introduced during sedimentation and diagenesis and later remobilised to a limited extent, perhaps during intrusion of the Kaniksu Batholith. For the same district Addie (1970) favoured control of pyrite deposition, at the time of sedimentation, by facies changes in the carbonate host rocks, but "much later" introduction of lead.  Evans and others (1968) studied trace elements  and sulphur isotopes from some western Canadian lead-zinc deposits, including the Monarch (table 3.II) and Kicking Horse ore-bodies Metaline  type).  (both  They proposed that the metals in a l l the deposits they  studied were precipitated from connate brines, and that the sulphur was derived from H 2 S associated with petroleum and natural gas  accumulations.  Ney (1957) and Sangster (1970) have commented on the location of the Monarch and Kicking Horse deposits close to a very rapid carbonate-shale facies change —  at the "Kicking Horse Rim" of Aitken (1971).  From the above i t seems that the age of concordant mineralisation  88  must l i e between the age of sedimentation of the Cambrian host rocks and the age of intrusion of the Nelson Batholith.  For this reason, several  possible mineralisation ages have been assumed in the calculations summarised i n table 3.IV.  Table 3.IV  Two-stage model ages for concordant deposits, upper anomalous line on f i g . 3.4. (Slope 0.119 ± 0.004) t i (calculated)  t 2 (assumed)  1.86 ± .08 BY  200 MY  1.78 ± .06 BY  350 MY  1.72 ± .06 BY  450 MY  Changing the assumed age of mineralisation ( t 2 ) does not have an important effect on the calculated t j , and in a l l cases the source of the anomalous lead can be interpreted to be rocks of Hudsonian age (about 1.6 - 1.9 BY).  The slope of the line determined in this study is slightly  but significantly steeper than that obtained by Reynolds and Sinclair (1971) , and this accounts for the difference in the calculated ages of source rocks. The age of source rocks calculated by Reynolds and Sinclair (1971) was 1,530 MY, just young enough to be lower Belt-Purcell sediments, but the older ages obtained here suggest these sediments were not involved. Transgressive  Group  The transgressive deposits are younger than Nelson plutonic rocks and seem to be younger than a widespread suite of lamprophyres (Fyles, 1967; 1970).  As previously discussed, most of the lamprophyres  89  seem to be T e r t i a r y .  Because the lamprophyre  dikes were fractured, o f f -  set and altered during the episode of transgressive m i n e r a l i s a t i o n , the transgressive deposits must be Eocene or younger.  I t i s therefore  d i f f i c u l t to see how these leads could bear any r e l a t i o n s h i p to hydrothermal f l u i d s accompanying Middle J u r a s s i c Nelson plutonic rocks, as Reynolds and S i n c l a i r (1971) i n f e r r e d . The lower (transgressive) anomalous lead l i n e i s made up mainly of samples from three mining camps, Ainsworth (and B l u e b e l l ) , Slocan C i t y , and Sandon.  Slopes of the short l i n e s through these separate data sets,  and the longer l i n e through the combined data are given i n table 3.V.  Table 3.V.  Slopes of least-squares l i n e s through transgressive group leads (the lower anomalous lead l i n e on f i g . 3.4). No. of Samples  Slope  19  0.124  + 0.027  Slocan C i t y  9  0.115  + 0.019  Ainsworth (+ B l u e b e l l )  9  0.118  + 0.025  41  0.116  + 0.003  Mining Camp  Sandon  Combined data f o r lower l i n e  (± l a )  Slopes of a l l these three sets are the same w i t h i n the quoted uncertainties and the slope f o r the combined data i s therefore used i n the c a l c u l a t i o n which follows.  Assuming a two-stage model and mineralisa-  t i o n (t£) at 50 MY, the beginning of the second stage i s calculated to be 1.90 ± 0.05 BY.  This age i s interpreted as the age of the source of the  anomalous leads and i s consistent with the age of Hudsonian rocks of the  90  Canadian Shield, although i t i s older than the mean K/Ar Hudsonian age of 1,735 Evolution  MY (Stockwell, 1970). of Lead Isotopes in the Kootenay Arc  It is concluded above that the two isotopically distinct groups of deposits correspond to the two structural groups of Fyles (1967). These two groups represent two different periods of mineralisation, apparently separated in time by 100 to 500 MY.  From geological relation-  ships neither mineralisation seems related to hydrothermal fluids accompanying intrusion of Nelson plutonic rocks, for one group is too young, the other too old. Since the slopes of the two lines are the same within experimental error, both groups of deposits incorporate a variable amount of essentially identical radiogenic lead component, as originally proposed by Reynolds and Sinclair (1971).  From the slopes of the lines and  assumed ages of mineralisation, the source of the anomalous component i s calculated here to be 1.7 - 1.9 BY old source rocks.  This anomalous  component could have been introduced from underlying Hudsonian basement, but this i s not necessary to the interpretation of the lead isotopes, since, i f the Phanerozoic sediments of the Kootenay Arc were derived from Shield rocks of Hudsonian age, the sediments could also supply the anomalous component. Because the lines are parallel, they incorporate the same radiogenic lead component and, for exactly the same reason, they do not incorporate lead of the same i n i t i a l composition.  It is not possible to  determine the i n i t i a l isotopic compositions with any certainty, and three possibilities are offered instead.  A minimum of two leads is required  91  MODEL 2  A A—-A  16  18  P0 /Pb M6  Fig. 3 . 6  Sketches of three models which show different "non-anomalous" components (A,B,C) for Kootenay Arc leads. Solid triangles represent "concordant" leads, open triangles represent "transgressive" leads.  92  to form a linear array, and in a l l cases one of these leads i s assumed to be of shield derivation as discussed above. Possible compositions for the other lead, loosely termed the "non-anomalous component", are shown on f i g . 3.6. Source of non-anomalous component Model 1. (A) upper line (B) lower line  Model 2. (A) upper line  (B) lower line Model 3. (A) upper line (B) lower line  (see f i g .  3.6)  Purcell lead of "late Precambrian group". Unradiogenic lead, possibly from a low U/Pb source (lower crust?). Perhaps associated with Eocene magmatic activity. 1.6 - 2.0 BY (approx.) source rocks with "appropriate" lead composition (e.g. an old "primary" lead). 1.6 - 1.9 BY source rocks with "appropriate" lead composition. Average lead in local sediments, extracted at some time between 200 and 450 MY. Average lead i n sediments and other rocks in the area at 50 MY. Special explanation needed for Ainsworth (and Bluebell) deposits(C).  Model 1 incorporates ideas proposed by Sinclair (1964), Reynolds (1967) and Reynolds and Sinclair (1971), although i t i s modified in two ways. F i r s t l y , the Nelson Batholith i s not considered directly related to leads on the lower line, both because the batholith i s too old, and because some feldspar leads from the batholith which were measured by Reynolds (1967) are more radiogenic than the "transgressive" ore leads (especially Ainsworth lead).  Secondly, Sullivan-like lead i t s e l f i s not considered  involved i n the upper line, but the general class of old Belt-Purcell leads might be.  Reynolds and Sinclair (1971) have discussed the possibil-  ity of a low U/Pb source linked with igneous rocks.  93  Model 2 requires hypothetical primary leads or very unradiogenic leads, for which no evidence has been found.  Reynolds (1967) postulated that  lead of composition B was a component of rock-lead from the Nelson Batholith and lead of some ore deposits. Model 3 i s based on the assumption that local country rocks could be the source of the non-anomalous component of the concordant leads. Well-mixed lead from surrounding sediments could provide lead of composition A, similar to a primary lead (see chapter 1).  Lead i n Shuswap deposits  might be representative of this lead component.  The same sediments could  also be the source of the anomalous component, i f leaching removed variable amounts of radiogenic lead. A l l the concordant leads are related by straight lines that pass through the least-radiogenic Shuswap group on both f i g . 3.4 and 3.5, providing evidence that concordant leads are the result of simple mixing of variable proportions of a single radiogenic component with a non-radiogenic component (see Kanasewich, 1968). It i s supposed that leaching of lead and emplacement of concordant deposits occurred early i n the history of the Kootenay Arc, before or during the f i r s t deformation i n Palaeozoic time. In Eocene times, another average of lead in country rocks, including the Nelson Batholith, Slocan Group sediments, etc., might give composition B.  Again the average lead is close to the primary growth  curve, and has a single-stage model age of about -300 MY.  It i s normal  for Phanerozoic primary lead ores to have calculated single-stage ages too young by 100 to 200 MY (e.g. Stacey and others, 1969).  Imperfect  mixing of lead Isotopes could explain the slight scatter of Slocan City and Sandon leads.  94  The origin of Ainsworth (and Bluebell) leads and their relation to Slocan City/Sandon lead must be considered enigmatic at present.  The  unradiogenic composition of Ainsworth leads probably reflects the unradiogenic composition of their source.  The two most obvious sources of  unradiogenic lead are high grade metamorphic rocks that have lost radiogenic lead or young intrusions that have penetrated uranium-depleted Precambrian rocks (Doe, 1968; Doe and others, 1968; Zartman and Wasserburg, 1969; Moorbath and others, 1969). possible.  In the Ainsworth area both sources are  L i t t l e can be said about the nearby metamorphic rocks as  sources of lead, but there i s some evidence against derivation of lead from the same source as the most closely associated igneous rocks, the lamprophyre dikes.  For example, Ohmoto and Rye (1970) found that the  water of inclusion fluids i n late (post-sulphide) minerals of the Blueb e l l deposits was meteoric, not magmatic. Also, one analysis of rock-lead in a lamprophyre dike near Bluebell mine is move radiogenic than lead i n Bluebell galena (Ohmoto, 1968).  The writer has no ready explanation for  Ainsworth and Bluebell leads. There are shortcomings i n a l l the simple models discussed above, but the writer prefers model 3 for the following reasons. (1)  It i s consistent with views expressed earlier on the origin of  lead-zinc deposits i n sediments (see chapters 1 and 2), that i s , the lead could be derived from sediments by connate brines and could approximate a primary lead.  Shuswap leads and Slocan City/Sandon leads are regarded  in a general way as the Palaeozoic and Cenozoic equivalents, respectively, of the late Precambrian group of Belt-Purcell leads. (2)  It i s conservative, that i s , only normal crustal processes acting  95  on normal crustal materials are required. (3)  Both anomalous and non-anomalous components can be derived from  the same local source. (4)  The correlation between geology and isotopic composition is clear  and the fact that the concordant deposits are older than the transgressive deposits i s fully accounted for i n this model.  If compositions A and B  of f i g . 3.6 are those of average crustal leads, and i f any significance can be placed on their single-stage ages, the calculated time gap between A and B is about 300 to 600 MY.  This gap i s regarded as the expression  of the difference i n age between concordant and transgressive periods of mineralisation.  3.5 LEAD ISOTOPE ZONING IN SANDON, SLOCAN CITY, AND AINSWORTH CAMPS District-wide zonal patterns for the distribution of minerals and metals (e.g. f i g . 3.7) have been reported for Sandon, Slocan City and Ainsworth camps (Sinclair, 1967; Orr, 1971; Orr and Sinclair, 1971; Davidson, 1972).  An attempt was therefore made to look for d i s t r i c t -  wide zonation of lead isotopes in these areas.  Zonation of lead isotopes  has been found elsewhere, both on the scale of a single crystal of galena (Austin and Slawson, 1961; Cannon and others, 1963) and on a regional scale (Heyl and others, 1966; Brown, 1967; Slawson and Austin, 1962). If regional zoning patterns reflect the movement of hydrothermal f l u i d , perhaps outward from a centre as Sinclair (1967) suggested for Sandon camp, then this fluid could scavenge lead from country rocks during their passage.  The original isotope composition of lead i n the fluid  96  ZINC X  an  RU / RG  t  Computer contoured plot of average zinc grades for 92 deposits, Computer-contoured map of Au/Ag ratios (multiplied by 1000) Slocan camp. Deposit locations are shown by solid triangles, for 43 deposits, Slocan City camp. Deposit locations are shown by solid triangles.  Fig. 3.7  Two examples of zonal patterns. (1971).  Taken from Orr and Sinclair,  w i l l then be progressively changed en route to depositional sites of the lead.  A number of models can be imagined in which leaching and mixing  processes w i l l result in a zonal distribution of isotopes, and one of the simplest of these is illustrated in f i g . 3.8.  97  ground  surface  contour lines joining deposits of equal Pb isotope ratio  \ country rock 204  I ,  ore  'feed deposit  fluid  "FOSSIL" CIRCULATION SYSTEM  CIRCULATION SYSTEM  Fig. 3.8  ^  \  Ptf7Pb -?9-5 O  /  Sectional sketch showing a simple model to explain lead isotope zonation i n mineral deposits by addition of lead from country rocks to lead in a circulating fluid.  The ore fluid (fig. 3.8) i s indicated to contain lead with an assumed original P b  206  /Pb  20lf  ratio of 18.6, and during circulation of  this fluid, rocks containing lead with a ratio of, say, 19.5 are traversed. Leaching of this rock-lead changes the isotopic composition of the ore f l u i d , the amount of change depending on the proportions of the original and leached components.  The amount of leachable lead may be simply  related to the volume of rock traversed, and thus to distance outward from the centre of the circulation system.  Since the same quantity of  98  ore f l u i d may traverse progressively greater volumes of rock for the same radially-outward distance, the rate of change of composition outward distance w i l l not be linear.  with  If the system does not change  greatly with time, lead in galena deposits w i l l show the sort of patterns sketched in f i g . 3.8.  Two important features of the hypothetical  sections shown are the concentric pattern of equi-ratio contours and the progressively closer spacing of these contours outwards from the centre.  The model shown i s not unique, however, and other models  relating compositional changes to time or to decreasing availability of leachable lead (e.g. Slawson and Austin, 1962; Sinclair and Walcott, 1966) could be proposed. Considering leads in the three Kootenay Arc camps under discussion, i t i s interesting to note f i r s t of a l l the remarkable isotopic uniformity of leads within the same camp (table 3.III).  This observation  implies that the ore fluid was isotopically rather uniform over an area the size of the camp, that i s , the scale on which the ore fluid existed i s revealed by the distribution of lead isotopic compositions.  Despite  this similarity of isotope ratios in deposits of the same camp, i t appears that zoning of isotope ratios i s present in the Slocan City, Sandon and Ainsworth areas. the ratio P b  206  In each case, the zoning is best shown by contouring  /Pb  201t  —  that i s , a directly measured quantity.  Some  details of the patterns obtained follow. Slocan City and Sandon Camps  Although Slocan City and Sandon camps are sometimes considered as separate entities, the lead isotope data from these camps suggests that they are parts of a single metallogenic region and are products of  99  Fig. 3.9  Contoured P b / P b ratios for Slocan City and Sandon data (table 3.III). Geology after Caimes (1934) and L i t t l e (1960). Two samples (901 and 887) do not f i t the contours. 206  201+  100  a single episode of mineralisation. This conclusion i s supported by the pattern of contours drawn for Pb ^ /Pb 2  camps ( f i g . 3.9).  6  201t  ratios of samples from the two  This pattern is like the idealised sketch of f i g . 3.8  and a correspondence with the simple model already outlined i s therefore suggested.  The westerly trough of low Pb  206  /Pb  20tt  , the more closely  spaced contours towards the periphery, and the assymetry are noteworthy features.  An interpretation according to the simple model proposed  i s that ore fluids rising near the western trough carried lead with Pb /Pb * ratio of about 18.6 206  201  (or less) and that this fluid leached  lead from Slocan Group sediments and from Nelson plutonic rocks. leachable lead composition  The  i s assumed to be more radiogenic than the  ore fluid lead, but i t s composition  is unknown. However, leads in four  samples of feldspar from the Nelson Batholith (Reynolds, 1967) have p 206/ b  P b  20»t  r  a  t  i  o  s  i  nt  he range 18.93 - 19.33, and the existence of  some leachable lead more radiogenic than the least radiogenic galena lead measured (18.6) i s therefore established. of rocks and feldspars  In any case, acid-leaching  in the laboratory (e.g. Doe and others,  1966;  Catanzaro and Gast, 1960) often yields a more radiogenic lead in the leach solution than the total lead and this could also account for an increase in radiogenic lead in the ore fluid. One consequence of the interpretation outlined above is that i t suggests that the difference in metal values (Cairnes, 1934;  Little,  1960) between Sandon camp (Pb - Ag, Ag - Pb - Zn) and Slocan City camp (Ag - Pb - Zn, Ag - Au, Au - Ag) are the result of different proportions of elements being leached from different wall rocks by a single widespread ore f l u i d .  101  Nelson granite Slocan Group Kaslo Group Milford Group • Lardeau Group Hamill Group  Fig. 3 . 1 0  Contoured Pb /Pb * ratios for analyses of samples from Ainsworth camp (table 3 . I I I ) . Geology after Fyles ( 1 9 6 7 ) . 206  201  102  Ainsworth Camp  It can be seen from f i g . 3.9 that leads of Ainsworth camp do not f i t the pattern for Slocan City and Sandon leads.  Only nine samples  were analysed from this camp, insufficient to define any pattern that may exist but enough to suggest a weak correlation between the isotope contours (fig. 3.10) and the strike of the three major vein systems described by Fyles (1967).  The major vein systems shown give a good  indication of the changing attitude of mineralised fractures from south to north in Ainsworth camp (Fyles, 1967; his f i g . 8).  It is suggested,  therefore, that the isotope contours simply reflect movement of ore fluid preferentially along, rather than across, the vein systems.  3.6  POSSIBLE RELATIONSHIPS BETWEEN KOOTENAY ARC LEADS AND LEAD IN PURCELL ROCKS  As has been shown, there are three distinct families of lead isotopes in southeastern British Columbia (a)  Leads in Purcell rocks  (b)  Leads in "concordant" ore deposits of the Kootenay Arc  (c)  Leads in "transgressive" ore deposits of the Kootenay Arc  Leads of the same family seem to be related, but there is no evidence of a direct isotopic relationship between families.  In particular, the  leads in Purcell rocks cannot be shown to have any genetic connection with the concordant or transgressive deposits of the Kootenay Arc.  In  f i g . 3.11, the three families noted above are represented by compartments and two extreme possible relationships between the families are shown. In one case, the whole system is open to lead, in the other, each compart-  103  ment i s closed.  In the absence of contrary evidence, i t seems that the  closed compartment scheme i s most applicable to leads of southeastern  B.C.  Cambrian — Jurassic sequence Purcell Windermere sediments  crystalline basement  open  Fig. 3.11  system  Diagrammatic illustration of two extreme possibilities for relationships between the three main families of leads (A,B,C,)  The above conclusion has an important bearing on the question of the source of lead in deposits of Precambrian to Tertiary age in southeastern British Columbia. There are three main explanations for the sources of this lead: (a)  There was an enrichment of lead in Purcell sediments during sedi-  mentation in Precambrian times.  This lead was remobilised from Purcell  rocks during deformation, erosion or igneous activity and formed the galena deposits of the Kootenay Arc. (b)  There is an enrichment of lead in the mantle or lower crust in  southeast B.C. which has persisted since Precambrian times.  This deep-  seated enrichment has supplied most of the metals in deposits of Precam-  104  brian to Tertiary age in both the East Kootenay d i s t r i c t and the Kootenay Arc. (c)  The number of lead-zinc deposits in southeastern B.C. could be  due to a repetition of processes capable of extraction and concentration of lead from surrounding rocks.  Sediments might be the source, connate  waters (including water evolved during metamorphism) the agent of extraction and concentration.  No absolute regional enrichment in crust or  mantle (as in (a) or (b)) i s necessary. To the writer, the evidence for (a) is not convincing, but this explanation must remain a possibility.  The second explanation, (b),  i s d i f f i c u l t to assess because of lack of data, but from previous discussion i t seems unlikely that the mantle was a source of lead.  The  writer favours the third explanation, which has already been discussed in chapters 1 and 2. Thus, the source of lead in the abundant lead-zinc deposits ih southeastern B.C. and adjoining parts of the northwestern U.S.A. is considered to be the thick successions of fine-grained sediments derived from the shield.  Major lead-zinc deposits in other parts of the world,  for example, Australia (King, 1965), are also associated with sequences of fine-grained sediments, and the idea that such sediments could be the source of lead in ore deposits certainly i s not  new.  There may, however, be an indirect relationship between the three "families" of leads.  If the leads come from sediments, and i f  the sediments come from the shield, leads of the three families should show some sign of a common source.  In fact, ages calculated for these  source rocks from the lead isotope compositions of Kootenay Arc and  105  Purcell galenas do coincide with important ages known from the shield. Although the age of source rocks calculated from Purcell data (2.6 - 2.7 BY) i s different from that calculated from Kootenay Arc data (1.7 - 1.9 BY), this difference i s not inexplicable.  For example, the age difference  could reflect simply a difference i n provenance of sediments, or a difference in level of erosion of the shield, the deeper levels exposed in Palaeozoic and later times having been more thoroughly homogenised by the 1.7 BY Hudsonian Orogeny. According to the above argument, large lead-zinc deposits i n thick fine-grained sediments eroded from the Canadian Shield could be  KEY  15C-  it Shuswap # Pine Point V Anvil  160  Fig. 3.12  170  A comparison of isotope ratios of samples from Anvil Range (table 4.1 ), Pine Point (Cumming and Robertson, 1969, p. 731), and Shuswap deposits (table 3.II).  106  indirectly related throughout western Canada.  Furthermore, distant  deposits of the same age should have a close isotopic resemblance, i f they have the same source.  For example, a resemblance of lead isotope  ratios might be expected for the concordant deposits of the Kootenay Arc, the Anvil Range deposits (chapter 4 ) , and the Pine Point ore-body (Beales and Jackson, 1968; Cumming and Robertson, 1969).  A compositional simi-  l a r i t y between some of these deposits i s shown in f i g . 3.12.  Only further  work w i l l determine, however, whether lead isotope relationships of the sort suggested above do exist throughout the Canadian Cordillera.  3.7  SUMMARY  Analyses by Sinclair (1964) and by Reynolds (1967) of lead . isotopes in mineral deposits of the Kootenay Arc were repeated and the earlier results found to be essentially correct.  In particular, the  repeated analyses and analyses of new samples confirm the existence of two parallel anomalous lines which seem related to two geologically different types of deposits.  The slopes of the anomalous lines are  slightly steeper than previously reported, however, and i t is therefore suggested that the source of the anomalous lead was 1.6 - 1.9 BY Hudsonian rocks, not 1.53 BY old rocks as suggested by Reynolds and Sinclair (1971). The two geological groups of Kootenay Arc lead-zinc deposits proposed by Fyles (1967) correspond in detail to the two isotopic groups of leads; the concordant deposits plot on the upper line, transgressive deposits plot on the lower.  It is proposed that the two anomalous lines  represent two periods of mineralisation that differ in age by 100 to 500 MY, an interpretation that i s consistent with geological evidence.  The  107  older deposits are those of the concordant type and these are interpreted to be average lead from lower Palaeozoic sediments mixed with variable amounts of an anomalous component derived from the same sediments, or perhaps from underlying Hudsonlan? basement.  The transgressive deposits  probably were emplaced i n Tertiary times and their-lead isotope composition could also be the result of mixing of "average crustal lead" with an anomalous component from surrounding country rocks.  There i s insuf-  ficient information to satisfactorily account for the origin of lead in deposits of Ainsworth camp (and Bluebell). The Pb  206  /Pb  201t  ratios of galena leads from Sandon and Slocan  City camps show a zonal pattern.  This pattern i s somewhat elongated in  a NE-SW direction, i s assymetric and shows an increase in Pb outward from a centre east of Slocan Lake.  206  /Pb  201t  It can be accounted for by  changes i n the composition of lead i n an ore fluid due to progressive leaching of lead of a different composition from country rocks during fluid circulation, although this explanation i s not unique.  108  CHAPTER 4.  LEAD ISOTOPES FROM THE ANVIL RANGE, YUKON TERRITORY  4.1 INTRODUCTION Three large lead-zinc deposits were discovered in the Anvil Range area of central Yukon Territory (fig. 1.1) between 1953 and  1966,  and the largest of these (Faro) is now an important producing mine. A l l three occurrences are stratiform pyritic lead-zinc deposits in Proterozoic or Cambrian phyllite and schist.  Eighteen drill-core samples from  these deposits were analysed for their lead isotope composition, and the most interesting feature of this work is the small but regular variation i n composition between deposits.  This variation could be related to  progressive regional metamorphism of the host rocks.  4.2  OUTLINE OF THE GEOLOGY AND LEAD-ZINC MINERALISATION OF THE ANVIL RANGE  Geology The following i s summarised mainly from a preliminary account (Tempelman-Kluit, 1968) of a detailed study of the ore deposits and geology of the Anvil Range.  Except for sampling the ore deposits, the  writer has not worked in the f i e l d in this area and discussions with Dr. Tempelman-Kluit on his unpublished  findings have been invaluable.  Anvil Range consists of an axial granitic core (Anvil Batholith) of mid-Cretaceous age flanked by late Proterozoic and Palaeozoic strata (fig. 4.1).  The stratigraphic sequence includes two regional  unconformities, one beneath Devonian-Mississippian beneath Pennsylvanian-Permian volcanic rocks.  strata and the other  Principal rock-types  and  LEGEND Isograd  Biotile  Garnet  S'auroMe U-Y '  Foliation  -q—  Bedding  -  Fault «•* i76.75»  Sulphide deposit : U.B.C. sample numbers 4  #  t N  KEY K  ] Granodiorite.  TR P. PN  ] Conglomerate. | S{  DM  ±2000'  Volcanics. chert, serpent.+3B0Q"  ] Clastic rocks.  ±1000'  SD Limestone, sandstone.  OS  i? F/G. 4-7  |  1 Slate  |  | JL^ '^ff ^nist.  400'+  Ph  )  <JWf.  50-150'  on  marble.  6000'+?  ?  Geological map of Anvil Range. After Tempelman-Kluitf 1968. pp. 46-47 )  Milts  110  lead-zinc deposits drawn to a common scale and orientation. Sites of the analysed samples listed i n table 4.1 are indicated by the numbered dots.  Ill  thicknesses of units are indicated i n f i g . 4.1, and i t may be noted that sediments and metasediments dominate the pre-Pennsylvanian succession, whereas basic volcanics dominate the Pennsylvanian-Permian sequence. Movement on faults in the Tintina Trench, a regional lineament that here forms the valley of the Pelly River, occurred in Early Triassic and later times in this area (Tempelman-Kluit, 1972). Lead-Zina  Mineralisation  A l l three of the major sulphide deposits (Swim, Vangorda, Faro) occur in the lowest part of a thick p h y l l i t i c to schistose unit that probably is of Cambrian or late Proterozoic age.  These metasediments,  which are intensely deformed, are overlain at one locality by OrdovicianSilurian graptolitic slate which is only weakly deformed.  Because de-  formation of the ore deposits is similar to that of the host rock, i t can be argued that the mineralisation is older than the weakly deformed Ordovician-Silurian slates —  that i s , the ore deposits were probably  emplaced in late Proterozoic to Ordovician time. Each of the main deposits consists of about 50% sulphides, characteristically with a granular texture.  Quartz and pyrite are the  main constituents, other important minerals being sphalerite, galena, pyrrhotite, chalcopyrite and marcasite, in decreasing order of abundance. The sulphide bodies are tabular (fig. 4.2, 4.3), roughly conformable to a pervasive transposition foliation, and are elongate parallel to linear structural features in the host rocks. up to 300' thick surround the deposits.  Envelopes of bleached phyllite According to Tempelman-Kluit  (pers. comm.) the form, setting, mineralogy and metal content of the deposits are very similar to deposits of the "stratiform type" discussed  112  by Stanton (1958, 1960). Unpublished analyses of sulphur Isotopes (D*F. Sangster, pers. comm.) are similar to the sulphur isotope ratios reported for a number of stratiform lead-zinc deposits by Stanton and Rafter (1966)  VERTICAL LONGITUDINAL SECTION THROUGH CENTRE PARO DEPOSIT  JVOC  Scale of feet VERTICAL CROSS-SECTION NEAR CENTRE OF FARO DEPOSIT  VERTICAL CROSS-SECTION NEAR KV END OF FARO DEPOSIT NE 4000  Massive and banded sulphide* |V.1 Disseminated sulphides  Locally graphitic biotit. chlorite cuartx phyllite 'Bleached** phyllite  I * ' \ Chlopitic tuffaceoua greenstone | * . [ Brecciated tuffaceoua greenstone J  A  fry?J Qusrtx diorite VERTICAL CROSS-SECTIONS FARO DEPOSIT  Fig. 4.3  Vertical cross sections of Faro deposit. Taken from TempelmanKluit (1968, p. 50). Sections of Swim and Vangorda deposits are somewhat similar but lack the greenstones and the quartz diorite (Tempelman-Kluit, 1968, p. 51).  The metamorphic grade of the host rock increases (from Swim to Faro) as follows: Swim  phyllite  Vangorda .... schistose phyllite Faro  schist  quartz-muscovite-chlorite-graphite quartz-muscovite-chlorite-biotite quartz-muscovite-biotite (andalusite, granet, staurolite)  113  Tempelman-Kluit (1970) has shown that accompanying this increase in metamorphic grade are increases in grain size of both silicates and sulphides, a relationship that he suggests i s a result of progressive regional metamorphism of the sulphide deposits.  Stratigraphic relationships f i x  the age of metamorphism as definitely pre-Devonian, and probably preOrdovician.  In Tempelman-Kluit's view, the parallel increases i n degree  of deformation, i n metamorphic grade, and i n sulphide grain size are evidence that metamorphism and deformation affected pre-existing bodies.  sulphide  He suggests that the deposits were emplaced i n approximately  their present concentrations during or soon after deposition of the Proterozoic-Cambrian  host rocks.  These rocks were originally carbonaceous  s i l t s with intercalated tuffs of intermediate composition.  Tempelman-Kluit  (pers. comm.) emphasises the strong similarities between the three deposits, the evidence that they are older than deformation and metamorphism, and the variation i n the effects these processes have had upon them.  4.3  DISCUSSION OF LEAD ISOTOPE DATA  A l l the isotope analyses reported i n table 4.1 are plotted on figs. 4.4 and 4.5. Sample locations are shown on plans of the ore deposits (fig. 4.2) or on the regional geological map (fig. 4.1). Leads from Faro, Vangorda and Swim deposits approximate primary lead (for c r i t e r i a see Kanasewich, 1968; Stacey and others, 1969). Single-stage model ages calculated from the average isotopic composition of each deposit range from 150 MY for Faro to 175 MY for Swim (225 MY for Sea 754), an insignificant difference. It is well known (e.g. Stacey and others, 1969; Richards, 1971) that such single-stage ages are unreli-  114 TABLE 4.1 UBC No.  LEAD ISOTOPE ANALYSES, ANVIL RANGE GALENAS  LOCATION D r i l l hole (footage)  Pb /Pb 20k  Pb /Pb 20**  Pb208 /Pb201+  18.349 18.354 18.374 18.365 18.370 18.368 18.346 18.401 18.392  15.662 15.672 13.672 15.668 15.667 15.657 15.670 15.683 15.672  38.326 38.332 38.374 38.345 38.358 38.312 38.321 38.409 38.401  18.365 18.346 18.351 18.356 18.351  15.676 15.668 15.662 15.662 15.668  38.334 38.273 38.272 38.315 38.309  18.336 18.338 18.346 18.341  15.659 15.666 15.664 15.669  38.273 38.293 38.297 38.309  18.486 18.224  15.668 15.635  38.457 38.142  19.230 19.217  15.725 15.724  39.325 39.293  206  207  FARO DEPOSIT (NTS/105K 62°22*N, 133°22'W) 772 753 752 809 810 811 812 813 755  66-10 66-15 66E1 66-33 67-34 67-4 67-26 67-27 Coarse h mile  (571-577) (307-311) (182-191) (370-384) (400-408) (464-465) ( 78- 80) (115-117) galena in pod E. of mine  VANGORDA DEPOSIT (NTS/105K 62°14'N, 133°13'W) 818 816 771 815 757  33 81 72 56 26  (245-270) (413-415) ( 38- 42) ( 95-115) (220-235)  SWIM DEPOSIT (NTS/105K 62°13'N, 133°02'W) 822 820 819 821  A30 A28 A24 A29  (480) (255) (176) (141)  SEA DEPOSIT (NTS/105K 62°11'N, 132°54'W) 823 754  2 (222) (Late vein) 2 (232)  VEINS IN ANVIL BATHOLITH 758 876  NTS/105K 62°19'N, 133°5'W NTS/105K 62°22'N, 133°8'W  Galena samples were taken from typical massive or banded pyritic ore, except for 755, 823 and the two veins i n the Anvil Batholith.  115  able i n detail, especially for deposits of Phanerozoic age.  Emplacement  ages of Phanerozoic stratiform leads are consistently older than their single-stage model lead ages, by about 100 to 400 MY (e.g. see table 6 of Stacey and others, 1969).  On this empirical basis, i t seems likely  thai: the age of emplacement of the Anvil ore bodies is also older than their single-stage ages indicate. From the age discrepancies mentioned above i t is suggested that their true emplacement age may l i e between the approximate limits 250 to 600 MY.  As previously stated (section 4.2)  geological relationships seem to indicate emplacement of the sulphide deposits between 450 and 800 MY  ago.  Analyses of samples from Swim, Vangorda and Faro deposits are very similar, but there is a slight change in Pb /Pb * ratios from 206  Swim (lowest ratio) to Faro (highest).  201  This pattern was f i r s t suggested  by some early imprecise analyses ( f i g . 4.6a)  and was later confirmed  by more numerous and more precise measurements ( f i g . 4.6b).  The slight  progressive change in isotopic composition parallels the changes i n metamorphic grade, in sulphide and s i l i c a t e grain size, and in degree of deformation referred to earlier (section 4.2).  Some of these relation-  ships are shown in f i g . 4.7 along with the change in tonnage of combined lead and zinc of the three deposits.  Because the only obvious feature  to which the isotopic variation can be related is the increase in intensity of deformation and metamorphism, i t i s suggested that a genetic  connection  could exist between the metamorphism and the ore deposits. A possible explanation of the nature of this connection follows. As previously argued (chapters 1 and 2) primary lead might be simply average lead from thick sequences of fine-grained sediments.  The easily  FIG. 4-4  Fig. 4.4 Fig. 4.5  Plot of P b / P b curve is for (Th  v. P b / P b /Pb ) „ present Plot of P b / P b v. P b / P b curve is for (U /Pb ») present 208  207  20l+  232  201+  238  206  201t  for a l l Anvil Range leads listed i n table 4.1. Growth = 39.60.  206  20l+  for a l l Anvil Range leads listed i n table 4.1. Growth 9.09 ± 0.06.  20l+  20l  fc  117  removable lead i s leached from the sediments by connate brine, from which i t can then be deposited by a variety of mechanisms.  If the evolv-  ing connate brine s t i l l exists during the onset of regional metamorphism i t might be capable of leaching greater amounts of lead from the rocks as the temperature of the brine rises and recrystallisation proceeds (see chapter 2).  In the laboratory, leaching of sediments with hot  water (Hart and Tilton, 1966) or hydrochloric acid (Doe and others, 1966), and volatilisation of lead in feldspars (Sinha, 1969) usually, but not invariably, releases a more radiogenic lead than the total lead.  These  experiments suggest the possibility of removing different compositions of lead depending on the conditions under which leaching occurs.  As  discussed in chapter 2, the reason for this probably is that leads of different compositions occupy sites of different availability in the same rock. From the above discussion i t i s proposed that the Anvil leads could represent lead stripped from surrounding fine-grained sediments by a connate brine at the onset of regional metamorphism in Cambrian or early Ordovician times.  The amount and isotopic composition of the  leached lead might have been dependent on both the character of the brine (e.g. temperature, salinity) and the availability of lead i n the sediments. Where metamorphism of the rocks was most intense, the greatest amount and the most radiogenic lead would have been released, thus accounting for the increase in size and i n radiogenic lead content of the deposits with increasing metamorphic grade.  The isotopic pattern shown (fig.  4.6)  for the three large deposits suggests that in rocks of lower metamorphic grade than at Swim deposit, an even less radiogenic lead than Swim might  118  FIG. 4-6a 757)  /  s  /O \J  15-64 18*35  15*68  Pb  18*37  18*39  18-41  18*43  KEY FARO  VANGORDA SWIM  18*45  FIG. 4-6b  207  Pbi 304 15*66  15-64 18*32  I  18-34  18-36  18*38  18*40  Pb  18*42  Pb 204  Fig. 4.6a  Plot of P b / P b v. P b / P b f o r some e a r l y a n a l y s e s (on an o l d e r mass s p e c t r o m e t e r ) o f l e a d s from Swim, Vangorda and Faro d e p o s i t s . These a n a l y s e s , w h i c h a r e n o t n o r m a l i s e d t o t h e Broken H i l l S t a n d a r d , were d i s c a r d e d .  F i g . 4.6b  Plot ofP b / P b v. P b / P b f o r t h e a n a l y s e s o f Swim, Vangorda and F a r o samples l i s t e d i n t a b l e 4.1.  2 0 7  2 0 7  2 0 l t  2 0 t t  2 0 6  2 0 6  2 0 l +  2 0 1 t  119 6-0  1 0 tons 6  4-0-  COMBINED Pfa + Zn TONNAGE  20-  3-0-  mm. 20  MEAN GRAIN SIZE OF COARSE  PYRITE 10-  mm. 02  MEAN GRAIN SIZE OF ORE  SULPHIDES 01  0-3  mm. 0-2  MEAN GRAIN SIZE OF HOST-ROCK SILICATES 01  206 204  ^Pb  18-360  MEAN LEAD  18-350  ISOTOPE RATIO 18-340  • increasing' —  SWIM Fig. 4.7  • metamorphic -  grade-  +  VANGORDA  FARO  Some features of Anvil Range deposits which show increases with increasing metamorphic grade (Swim to Faro). Grain size data from Tempelman-Kluit (1970). Isotope data from table 4.1. Tonnage of lead and zinc: Faro, Findlay (1969); Vangorda, Chisholm (1957); Swim, Northern Miner (March 9, 1967, p. 5).  120  be expected.  A sample of disseminated  galena from the stratiform Sea  prospect was analysed, where the host rocks are perhaps of slightly lower grade than at Swim deposit.  Significantly, this lead is the  least radiogenic of the four deposits.  Perhaps disseminated lead from  the Sea prospect i s similar to the average composition of easily leachable lead i n the sediments prior to their modification by progressive metamorphism. If lead i n the four deposits mentioned above is derived from surrounding sediments, and i f compositional differences are due to addition of variable amounts of radiogenic lead to an i n i t i a l  composition  like that of the Sea deposit, i t should be possible to calculate the age of the source of radiogenic lead.  This age should be either the i n i t i a l  age of the source rocks for the sediments, or the age of last thorough isotopic homogenisation of the source rocks.  It was suggested i n chapter  ? tht.t parts of the Canadian Shield, the main source of the late Proterozoic-Cambrian sediments of the Anvil Range, were as old as 3.5 BY. Ages of 2.7 BY were calculated from Precambrian lead in Purcell sediments, and ages of 1.7 - 1.9 BY from Kootenay Arc deposits.  Therefore, ages similar  to either of these results might be expected from Anvil Range leads, since the sediments are believed to have the same eastern shield source. In table 4.II, the model age of the source rocks of Anvil Range deposits is calculated to be 2.7 to 2.9 BY. The line i s obviously very short, and the uncertainty i n age i s large. Two analyses (758, 876) from small veins in the roof of Anvil Batholith are interesting because the lead isotope ratios are very d i f ferent from those of lead of the main deposits (see figs. 4.4, 4.5).  121  This dissimilarity can be interpreted as evidence that the Anvil Batholith has no genetic relationship with the principal stratiform sulphide deposits, the conclusion reached on geological grounds (section 4.2)  by  Tempelman-Kluit.  Table 4.II  Age of source rocks of sedimentary host of Anvil Range stratiform deposits (assuming a two-stage model).  Deposits  Slope  Sea 754, Swim, Vangorda,  0.202 ± 0.036  Faro (19 analyses in a l l )  ti  (calculated)  2.9 ± 0.3  BY  2.7 ± 0.4  BY  t£ (assumed)  0 MY 500  MY  A "modified sedimentary" origin for Anvil Range leads is not a new idea.  Gabrielse (1969) discussed geologic relationships of base-  mstal deposits in the northern Canadian Cordillera and showed that the principal occurrences (many of them vein deposits) were almost invariably in Lower Cambrian strata.  Furthermore, the mineralisation in these strata  seemed restricted to the westerly fine-grained facies ( f i g . 4.8). Gabrielse pointed out the significance of this relationship both to exploration and to concepts of ore genesis, and suggested two different explanations. (1)  Derivation of metals from late Proterozoic-early Cambrian sedi-  ments, the last important contribution of elastics to the Cordilleran Geosyncline from the craton. (2)  Deposition of metals from thermal springs associated with deep  fractures of early Cambrian age.  122  The interpretation offered for lead isotope data from the Anvil Range i s i n accord with Gabrielse's f i r s t explanation.  Fig. 4.8  Relation of occurrence of base-metal deposits of northern B.C. and southeastern Yukon to facies of Lower Cambrian and Eocambrian strata. Taken from Gabrielse (1969, p. 28). Faro, Vangorda, Swim shown as stars, other deposits as dots.  123  4.3  SUMMARY  (1)  Lead isotope ratios of the known stratiform lead-zinc deposits  of the Anvil district are nearly identical.  Because this lead approxi-  mates "primary" lead, the source could be the surrounding late Proterozoic - Cambrian metasediments. (2)  The surrounding sediments were derived from the Canadian Shield  and i t i s possible to calculate the age of this sediment source from the lead now i n the ore deposits.  This (imprecise) age i s about 2.7 -  2.9 BY, which suggests that the source area was affected (lead homogenised?) during the Kenoran Orogeny. (3)  A slight variation in P b  206  /Pb  20lf  ratios of the four analysed  deposits appears to be related to variation in metamorphic grade of the host rocks, higher ratios being associated with higher grade.  It i s  Therefore suggested that mineralisation was going on during the earliest stages of metamorphism.  Continuing metamorphism and deformation subse-  quently modified the sulphide deposits prior to Ordovician-Silurian time, according to Tempelman-Kluit (pers. comm.).  124  CHAPTER  5.1  5.  SUMMARY  PURCELL  LEADS  New lead isotope analyses confirm the findings of Leech and Wanless (1962) that isotope r a t i o s of galena leads i n P u r c e l l rocks  fall  i n t o two d i s t i n c t groups; a uniform, less radiogenic group and a v a r i a b l e , more radiogenic group.  The uniform group, which includes many of the  large s t r a t i f o r m deposits, seems to represent a widespread and economically important episode of lead-zinc m i n e r a l i s a t i o n 1.2 to 1.4 BY ago ( s i n g l e stage age).  The v a r i a b l e leads were probably  emplaced during the Mesozoic  or Cenozoic and they are found i n small vein deposits. On a p l o t of P b  2 0 7  /Pb  2 0 1 t  v. P b  2 0 6  /Pb  2 0 l  \ the uniform  form a short elongate array, l i k e that expected from imperfect  leads averaging  of c r u s t a l leads, and i t i s suggested, therefore, that they are average leads leached from the enclosing lower P u r c e l l s t r a t a by coiiiiate b r i n e . I f t h i s lead was deposited as galena 1.3 BY ago, the source rocks of the uniform group of leads are about 2.6 BY o l d (two-stage model).  The P u r c e l l  sediments, considered to be the immediate source rocks of the lead, are derived from the Canadian Shield, where ages as o l d as 2.6 BY and older are known. Although extraction of lead i n lower P u r c e l l sediments by connate brines i s a reasonable  p o s s i b i l i t y , convincing independent evidence  e i t h e r f o r or against i t i s l a c k i n g . evidence,  In the absence of such independent  the uniformity of the Precambrian leads, and c o r r e l a t i o n s  between i s o t o p i c composition  and factors such as geography, stratigraphy  and s i z e of deposit are considered  to support  the hypothesis  of a "modified  125  sedimentary" origin for the lead. The simplest explanation for the isotopic composition of the Mesozoic-Cenozoic leads i s that they were formed i n the Purcell sediments by addition of radiogenic lead to trace leads of the uniform Precambrian group.  Calculations based on a two-stage model with mineralisation at  100 MY indicate that the source rocks for these leads are about 1.5 BY old.  This age i s consistent with the age of lower Purcell sediments. The writer proposes that the uniform, late Precambrian leads  of the Belt Supergroup (Zartman and Stacey, 1971) could have had a similar origin to the uniform, late Precambrian Purcell leads.  5. 2  KOOTENAY ARC LEADS Lead isotopes from throughout the Kootenay Arc plot on two  parallel anomalous lines, as f i r s t discussed by Reynolds and Sinclair (1971).  In this thesis, these two isotopic groups are shovr. to correspond  In detail to the two geological groupings of Kootenay Arc lead-zinc deposits proposed by Fyles (1967); structurally concordant deposits plot on the upper line, transgressive deposits plot on the lower line.  The  separation of the lines can be explained as the result of a difference in age of 100 to 500 MY (approximately) between the two principal mineralisations, and this explanation is consistent with geological observations. Both groups of deposits contain lead derived from 1.7 - 1.9 BY old rocks, and i t i s suggested that sediment eroded from Hudsonian (1.7 BY) basement or perhaps underlying Hudsonian basement are the most likely sources of this lead. Contours of P b  206  /Pb  20tt  ratios of samples from Slocan City and  126  Sandon camps show a simple zonal pattern in which ratios increase outward from a single centre.  A model that could account for this pattern i s one  in which the isotopic composition of lead in hot rising fluid is progressively changed by leaching more radiogenic rock-lead during circulation. It is suggested that the repeated lead-zinc mineralisation in southeastern B.C. could be partly due to recurrent deposition of thick sequences of fine-grained sediment that served as source rocks for the lead and zinc now in the ore deposits.  5.3  ANVIL  RANGE  LEADS  The composition of lead isotopes from four geologically alike stratiform deposits of the Anvil Range (Y.T.) are very similar, and approximate primary leads with single-stage model ages of 150 - 225  MY.  The late Proterozoic to Cambrian metasediments which are the host rocks for the deposits are suggested as a possible source of the metals.  On  this assumption, the age of the source of the sediments can be calculated from the galena leads to be 2.7 - 2.9 BY (two-stage model). This age i s consistent with the oldest ages reported from the Canadian Shield, the probable source of the sediments. A slight variation in lead isotope ratios between the three main lead-zinc deposits seems to be related to variations in metamorphic grade of the host rocks, and i t is suggested that metamorphism and mineralisation overlapped.  The deposits were recrystallised and deformed  as metamorphism (Cambrian-Ordovician?) proceeded.  127  REFERENCES  Aalto, K.R. (1971) Glacial marine sedimentation and stratigraphy of the Toby Conglomerate (upper Proterozoic), southeastern British Columbia, northwestern Idaho and northeastern Washington. Can. J. Earth Sci. 8, 753-787. Addie, G.G. (1970) The Metaline d i s t r i c t , Pend Oreille County, Washington. In Lead-zina deposits in the Kootenay Arc, northeastern Washington and adjacent British Columbia (editor A.E. Weissenborn), pp. 65-78. State of Wash. Dept. Nat. Resources, Div. Mines & Geol. Bull. 61, 123 p. Aitken, J.D. (1971) Control of lower Palaeozoic sedimentary facies by the Kicking Horse Rim, southern Rocky Mountains, Canada. Bull. Can. Pet. Geol. 19, 557-569. Armstrong, R.L. (1968) A model for the evolution of strontium and lead isotopes in a dynamic earth. Rev. Geophys. 6_> 175-199. Austin, C F . and Slawson, W.F. (1961) Isotopic analyses of single galena crystals: a clue to history of deposition. Am. Mineral. 46, 1132-1140. Bally, A.W., Gordy, P.L. and Stewart, G.A. (1966) Structure, seismic data, and orogenic evolution of southern Canadian Rocky Mountains. Bull. Can. Pet. Geol. 14, 337-381. Beales, F.W. and Jackson, S.A. (1968) Pine Point: A stratigraphical approach. Can. Inst. Min. Met. 61, 867-878. Billings, G.K., Kesler, S.E. and Jackson, S.A. (1969) Relation of zincrich formation waters, northern Alberta, to the Pine Point ore deposit. Econ. Geol. 64, 385-391. Bishop, D. , Morris, H.C. and Edmunds, R.F. (1970) Turbidites and depositional features in the lower Belt-Purcell Supergroup (abs.). Geol. Soc. Am. Abs. with Programs. 2_, 497. Blenkinsop, J. (1972) Computer-assisted mass spectrometry and its application to rubidium-strontium geochronology. Ph.D. thesis, Univ. of B.C., 109 p. Brown, J.S. (1965) Oceanic lead isotopes and ore genesis. 60, 47-68.  Econ. Geol.  Brown, J.S. (1967) Isotopic zoning of lead and sulfur in Southeast Missouri. In Genesis of stratiform lead-zinc-barite-fluorite deposits (editor J.S. Brown), pp. 410-426. Econ. Geol. Monograph 3, 443 p.  128  Burwash, R.A., Baadsgaard, H. and Peterman, Z.E. (1962) Precambrian K-Ar dates from the western Canada sedimentary basin. J. Geophys. Res. 67, 1617-1625. Cairnes, C E . (1934) Slocan mining camp, British Columbia. Can. Memoir  Geol. Surv.  173, 137 p.  Calmes, C E . (1935) Descriptions of properties, Slocan Mining Camp, British Columbia.  Geol. Surv. Can. Memoir  184, 274 p.  Campbell, R.B. (1963) Adams Lake. Geol. Surv. Can. Map 48 - 1963. Cannon, R.S., Pierce, A.P. and Antweiler, J.C. (1971) Suggested uses of lead isotopes in prospecting. In Geochemical exploration (editor R..W. Boyle), pp. 457-463. Can. Inst. Min. Met. Special Vol. 11, 594 p. Cannon, R.S., Pierce, A.P., Antweiler, J.C. and Buck, K.L. (1962) Lead isotope studies in the northern Rockies, U.S.A. In Retrologic Studies:  A Volume in Honor of A.F. Buddington  H.L. James and B.F. Leonard), pp. 115-131.  (editors A.E.J. Engel,  Geol. Soc. Am.. 660 p.  Cannon, R.S., Pierce, A.P. and Delevaux, M. (1963) Lead isotope variation with growth zoning i n a galena crystal. Science, 142, 574-576. Catanzaro, E.J. (1968) The interpretation of zircon ages. In Radiometric Dating for Geologists (editors E.I. Hamilton and R.M. Farquhar), pp. 225-258. Interscience Publishers, London. 506 p. Catanzaro, E.J. and Gast, P.W. (1960) Isotopic composition of lead in pegmatitic feldspars. Geochim. Cosmochim. Acta 19, 113-126. Chisholm, E.O. (1957) Geophysical exploration of a lead-zinc deposit in Yukon Territory. In Methods and case histories  geophysics  in mining  (editor J.P. DeWet), pp. 269-277. Sixth Commonwealth  Mining and Metallurgical  Congress, 359 p.  Chow, T.J. and Johnstone, M.S. (1963) Lead isotopes i n the sediments of Hudson Bay and Baltic Sea (abs.) Trans. Am. Geophys. Union 44, 890-891. Chow, T.J. and Patterson, CC. (1962) The occurrence and significance of lead isotopes i n pelagic sediments. Geochim. Cosmochim. Acta 26, 263-308. Clark, A.L. (1971) Stratabound copper sulfides i n the Precambrian Belt Supergroup, northern Idaho and northwestern Montana, U.S.A. In IAGOD volume: IMA-IAGOD Meetings '70 (editor Y. Takeuchi), 261-267. Soc. Mining Geol. Japan Special Issue 3, 500 p.  pp.  Clark, S.H.B. (1971) Structure and metamorphism i n a high-grade Precambrian terrane in northern Idaho (abs.). In Metamorphism in the Canadian Cordillera, pp. 8-9. Geol. Assoc. Can. Cordilleran gramme and abstracts, 33 p.  Section,  pro-  129  Cockfield, W.E. (1936) Lode gold deposits of Ymlr-Nelson area, British Columbia.  Geol. Surv. Can. Memoir  191, 78 p.  Cooper, J.A., Reynolds, P.H. and Richards, J.R. (1969) Double-spike calibration of the Broken H i l l Standard lead. Earth Plan. Sci. Letters 6^, 467-478. Cox, M. (1968) Van Stone mine area (lead-zinc), Stevens County, Washington. In Ore Deposits  of the United States,  1933-1967 (editor J.D. Ridge)  Vol. 2, pp. 1511-1519. Am. Inst. Min. Met. & Pet. Eng. Inc., New York. 1880 p. (Vol. 1 & 2). Cumming, G.L. and Robertson, D.K. (1969) Isotopic composition of lead from the Pine Point deposit. Econ. Geol. 64, 731-732.  Dahlstrom, CD.A. (1970) Structural Geology i n the eastern margin of the Canadian Rocky Mountains. Bull. Can. Pet. Geol. 18, 332-406. Davidson, C F . (1967) Contributed remarks to discussion of paper by F.W. Beales and S.A. Jackson entitled Precipitation of lead-zinc ores in carbonate reservoirs as illustrated by Pine Point ore f i e l d , Canada. Trans. Inst. Min. Met. 76, B132-B134. Davidson, R.A. (1972) A computer-oriented analysis of metal production from Ainsworth mining camp, southeastern B.C. B. App. Sci. thesis,  Univ. cf B.C., 60 p.  Degens, E.T. and Ross, D.A. (1969) Editors, Hot Brines and Recent Heavy Metal Deposits in the Red Sea. Springer-Verlag, New York. 600 p. Doe, B.R. (1968) Lead and strontium isotopic studies of Cenozoic volcanic rocks i n the Rocky Mountain region - a summary. Quart. Colorado School Mines  ^3, 149-174.  Doe, B.R. (1970) Lead Isotopes.  Springer-Verlag, New York.  137 p.  Doe, B.R.-, Hedge, C E . and White, D.E. (1966) Preliminary investigation of the source of lead and strontium in deep geothermal brines underlying the Salton Sea geothermal area. Econ. Geol. (sl 462-483. t  Doe, B.R. , T i l l i n g , R.I., Hedge, C E . and Klepper, M.R. (1968) Lead and strontium isotope studies of the Boulder Batholith, southwestern Montana. Econ. Geol. 63, 884-906. Douglas, R.J.W. (1970) Introduction. In Geology and economic minerals of Canada (editor R.J.W. Douglas), pp. 2-6. Geol. Surv. Can. Economic Geol. Report 1, 838 p.  Dozy, J.J. (1970) A geological model for the genesis of the lead-zinc ores of the Mississippi Valley, U.S.A. Trans. Inst. Min. Met. 79, B163-B170.  130  Duncan, J.F. and Thomas, F.G. (1967) g-decay of radioactive lead tetramethyl. J. Inorg. Nuc. Chem. 29_, 869-890. Dunham, K.C. (1970) Mineralization by deep formation waters: Trans. Inst. Min. Met. Jl> B127-B136. Eastwood, G.E.P. and Peck, J.W. Reports, 99-105.  a review.  (1956) Spider. B.C. Dept. of Mines Ann.  E l l i s , A.J. (1970) Present day hydrothermal systems and mineral exploration. In Mining and petroleum geology (editor M.J. Jones), pp. 211-240. Proa. 9th Commonwealth Min. & Met. Congress 1969. vol. 2, 774 p. Evans, T.L., Campbell, F.A. and Krouse, H.R. (1968) A reconnaissance study of some western Canadian lead-zinc deposits. Econ. Geol. 63, 349-359. Findlay, D.C. (1969) The mineral industry of Yukon Territory and southwestern district of Mackenzie, 1968. Geol. Surv. Can. Paper 69-55, 71 p. Freeze, A.C. (1966) On the origin of the Sullivan orebody, Kimberley B.C. In Tectonic history and mineral deposits of the Western Cordillera (editors H.C. Gunning and W.H. White), pp. 263-294. Can. Inst. Min. Met. Special Vol. 8, 353 p. Fyles, J.T. (1964) Geology of the Duncan Lake area, British Columbia. B.C. Dept. Mines & Pet. Resources Bull. 49, 87 p. Fyles, J.T. (1966) Lead-zinc deposits in British Columbia. In Tectonic history and mineral deposits of the Western Cordillera (editors H.C. Gunning and W.H. White), pp. 231-237. Can. Inst. Min. Met. Special Vol. 8, 353 p. Fyles, J.T. (1967) Geology of the Ainsworth-Kaslo area. B.C. Dept. Mines & Pet. Resources Bull. 53, 125 p. Fyles, J.T. (1970) Geological setting of the lead-zinc deposits in the Kootenay Lake and Salmo areas of British Columbia. In Lead-zinc deposits in the Kootenay Arc, northeastern Washington and adjacent British Columbia (editor A.E. Weissenborn), pp. 41-53. State of Wash. Dept. Nat. Resources, Div. Mines & Geol. Bull. 61, 123 p. Fyles, J.T. (1970a) The Jordan River area near Revelstoke, British Columbia. B.C. Dept. Mines & Pet. Resources Bull. 57, 64 p. Fyles, J.T. and Eastwood, G.E.P. (1962) Geology of the Ferguson Area, Lardeau d i s t r i c t , British Columbia. B.C. Dept. Mines & Pet. Resources Bull. 45, 92 p. Fyles, J.T. and Hewlett, C.G. (1959) Stratigraphy and structure of the Salmo lead-zinc area. B.C. Dept. Mines Bull. 41, 162 p.  131  Gabrlelse, H. (1969) Lower Cambrian strata and base metals. Western Miner 42(2), 22-28. Gabrielse, H. (1972) Younger Precambrian of the Canadian Cordillera Am. J. Sci. 272, 521-536. Gabrielse, H. and Reesor, J.E. (1964) Geochronology of plutonic rocks in two areas of the Canadian Cordillera. In Geochronology in Canada (editor F.F. Osborne), pp. 96-138. Roy. Soc. Can. Special Pub. 8, 156 p. Gale, N.H., Arden, J. and Hutchison, R. (1972) Uranium-lead chronology of chondritic meteorites. Nature 240, 56-57. Gast, P.W. (1967)  Isotope geochemistry of volcanic rocks. In Basalts:  The Poldervaart  Treatise  on Rocks of Basaltic  Composition  H.H. Hess and A. Poldervaart), Vol. 1, pp. 325-358. New York. 432 p. (Vol. 1).  (editors  Interscience,  G i l e t t i , B.J. (1968) Isotopic geochronology of Montana and Wyoming. In Radiometric  Bating for Geologists  Farquhar), pp. 111-146.  (editors E.I. Hamilton and R.M.  Interscience Publishers, London, 506 p.  Goldich, S.S., Baadsgaard, H., Edwards, G. and Weaver, C E . (1959) Investigations in radioactivity-dating of sediments. Am. Assoc. Pet. Geol. Bull.  43, 654-662.  Goldich, S.S., Hedge, C E . and Stern, T.W. (1970) Age of the Morton and Montivideo Gneisses and related rocks, southwestern Minnesota. Geol. Soc. Am. Bull.  81, 3671-3696.  Halsted, R.E. and Nier, A.O. (1950) Gas flow through the mass spectrometer viscous leak. Rev. Sci. Inst. 21_, 1019-1021. Hamilton, E.I. (1965) Applied Geochronology. Academic Press, London & New York. 267 p. Harrison, J.E. (1972) Precambrian Belt basin of northwestern United States: i t s geometry, sedimentation, and copper occurrences. Geol. Soc. Am. Bull.  83, 1215-1240.  Harrison, J.E. and Grimes, D.J. (1970) Mineralogy and geochemistry of some Belt rocks, Montana and Idaho. U.S. Geol. Surv. Bull. 1312-0, 49 p. Harrison, J.E., Kleinkopf, M.D. and Obradovich, J.D. (1972) Tectonic events at the intersection between the Hope Fault and the Purcell Trench, northern Idaho.  U.S. Geol. Surv. Prof. Paper 719, 24 p.  Hart, S.R. and Tilton, G.R. (1966) The isotope geochemistry of strontium and lead in Lake Superior waters. In The earth beneath the continents (editors J.S. Steinhart and J.S. Smith), pp. 127-137. Am. Geophys. Union Monograph 10, 663 p.  132  Hedley, M.S. (1945) Geology of the Whitewater and Lucky Jim mine areas, Slocan d i s t r i c t , British Columbia. B.C. Dept. Mines Bull. 22, 45 p. Hedley, M.S. (1949) A204.  Silver Giant.  B.C. Dept. Mines Ann. Reports, A200-  Hedley, M.S. (1952) Geology and ore deposits, Sandon area, Slocan Mining camp. B.C. Dept. Mines Bull. 29, 130 p. Helgeson, H.C. (1967) of hydrothermal barite-fluorite Geol. Monograph  bilicate metamorphism in sediments and the genesis solutions. In Genesis of stratiform lead-zincdeposits (editor J.S. Brown), pp. 333-342. Econ. 3, 443 p.  Helgeson, H.C. (1968) Geologic and thermodynamic characteristics of the Salton Sea geothermal system. Am.J. Sci. 266, 129-166. Hershey, O.H. (1913) Origin of lead, zinc, and silver i n the Coeur d'Alene - I. Mining & Scientific Press 107, 489-494. Hershey, O.H. (1913a) Origin of lead, zinc, and silver i n the Coeur d'Alene - II. Mining & Scientific Press 107, 529-533. Heyl, A.V., Delevaux, M.H., Zartman, R.E. and Brock, M.R. (1966) Isotopic study of galenas from the upper Mississippi Valley, the I l l i n o i s Kentucky, and some Appalachian Valley mineral d i s t r i c t s . Econ. Geol. 61, 933-961. Hobbs, S.W. and Fryklund, V.o. (1968) The Coeur d'Alene d i s t r i c t , Idaho. In Ore Deposits of the United States, 1923-1967 (editor J.D. Ridge), Vol. 2, 1417-1435. Am. Inst. Min. Met. & Pet. Eng. Inc., New York. 1880 p. (Vol. 1 & 2). Hobbs, S.W., Griggs,.A.B., Wallace, R.E. and Campbell, A.B. (1965) Geology of the Coeur d'Alene d i s t r i c t , Shoshone County, Idaho. U.S. Geol. Surv. Prof. Paper 478, 139 p. Houtermans, F.G., Eberhardt, A. and Ferrara, G. (1964) Lead of volcanic origin. In Isotopic and Cosmic Chemistry (editors H. Craig, S.L. Miller and G.J. Wasserburg), pp. 233-243. North-Holland Publ. Co., Amsterdam. Huebschman, R.P. (1972) Correlation and environment of a key interval within the Precambrian Prichard and Aldridge formations, IdahoMontana-British Columbia. M.Sc. thesis, Univ. of Montana, 66 p. Hunt, G. (1962) Time of Purcell eruption i n southeastern British Columbia and southwestern Alberta. Alta. Soc. Pet. Geol. J. 10_, 438-442. I l l i n g , L.V. (1967) Discussion of paper by F.W. Beales and S.A. Jackson entitled Precipitation of lead-zinc ores in carbonate reservoirs as illustrated by Pine Point ore f i e l d , Canada. Trans. Inst. Min. Met. 76, B130-B131.  133  Jackson, S.A. and Beales, F.W. (1967) An aspect of sedimentary basin evolution: The concentration of Mississippi Valley-type ores during late stages of diagenesis. Bull. Can. Pet. Geol. 15, 383433. Kanasewich, E.R. (1962) Quantitative interpretation of anomalous lead isotope abundances. Ph.D. thesis, Univ. of B.C. 187 p. Kanasewich, E.R. (1968) The interpretation of lead isotopes and their geological significance. In Radiometric Dating for Geologists (editors E.I. Hamilton and R.M. Farquhar), pp. 147-223. Interscience Publishers, London. 506 p. Kanasewich, E.R. (1968a) Precambrian Rift: deposits. Science 16JL, 1002-1005.  genesis of strata-bound ore  King, H.F. (1965) Lead-zinc ore deposits of Australia. In Geology of Australian Ore Deposits (editor J. McAndrew), pp. 24-30. Eighth Commonwealth Min. Met. Cong. Vol. 1, 547 p. King, P.B. (1969) The tectonics of North America — A discussion to accompany the tectonic map of North America, Scale 1:5,000,000. U.S. Geol. Surv. Prof. Paper 628, 94 p. Knight, C L . (1957) Ore genesis — 52, 808-817.  the source bed concept.  Kollar, F. (1960) The precise intercomparison Ph.D. thesis, Univ. o f B.C. 107 p.  Econ. Geol.  of lead isotope  ratios.  Krauskopf, K.B. (1956) Factors affecting the concentrations of thirteen rare metals in sea^water. Geochim. Cosmochim. Acta 9_, 1-32B. Krauskopf, K.B. (1967) Source rocks for metal-bearing fluids. In Geochemistry of Hydrothermal Ore Deposits (editor H.L. Barnes), pp. 1-33. Holt, Rinehart and Winston, Inc., New York. 670 p. Krauskopf, K.B. (1971) The source of ore metals. Acta 35, 643-659.  Geochim. Cosmochim.  Leech, G.B. (1958) Fernie map-area, west half, British Columbia. Surv. Can. Paper 58-10, 40 p.  Geol.  Leech, G.B. (1960) Fernie (west half) Kootenay d i s t r i c t , British Columbia. Geol. Surv. Can. Map 11 - 1960. Leech, G.B. (1962) Metamorphism and granitic intrusions of Precambrian age i n southeastern British Columbia. Geol. Surv. Can. Paper 62-13, 8 p. Leech, G.B. (1963) Ages of regional metamorphism of the Aldridge Formation near Kimberley, B.C. (Preliminary report) In Age determinations and geological studies (including isotopic ages - Report 4) pp. 132-135. Geol. Surv. Can. Paper 63-17, 140 p. 3  134  Leech, G.B. and Wanless, R.K. (1962) Lead isotope and potassium-argon studies in the East Kootenay district of British Columbia. In Petrologic Studies: A Volume in Honor of A.F. Buddington (editors A.E.J. Engel, H.L. James and B.F. Leonard), pp. 241-279. Geol. Soc. Am. 660 p. Leigh-Smith, A. and Richardson, H.O.W. (1935) Interchange of heavy atoms in organo-metallic methyls. Nature 135, 828-829. L i t t l e , H.W. (1960) Nelson map-area, west half, British Columbia (82 F W%). Geol. Surv. Can. Memoir 308, 205 p. L i t t l e , H.W. (1970) Economic minerals of Western Canada. Metallic Deposits. In Geology and economic minerals of Canada (editor R.J.W. Douglas), pp. 494-517. Geol. Surv. Can. Econ. Geol. Report 1, 838 p. Long, A., Silverman, A.J. and Kulp, J.L. (1960) Isotopic composition of lead and Precambrian mineralization of the Coeur d'Alene d i s t r i c t , Idaho. Econ. Geol. 55, 645-658. Macdonald, A.S. (1970) Structural environment of the Salmo type lead-zinc deposits. In Lead-zinc deposits in the Kootenay Arc, northeastern Washington and adjacent British Columbia (editor A.E. Weissenborn), pp. 55-64. State of Wash. Dept. Nat. Resources, Div. Mines & Geol. Bull. 61, 123 p. Macdonald, A.S. (in preparation) Deformation and metamorphic features of the Salmo zinc-lead deposits. Ph.D. thesis, Univ. of B.C. McConnel, R.H. and Anderson, R.A. (1968) The Metaline d i s t r i c t , Washington. In Ore Deposits of the United States, 1933-1967 (editor J.D. Ridge), Vol. 2, 1461-1480. Am. Inst. Min. Met. & Pet. Eng. Inc., New York. 1880 p. (Vol. 1 & 2). McDowell, F.W. and Kulp, J.L. (1969) Potassium-argon dating of the Idaho batholith. Geol. Soc. Am. Bull. 80, 2379-2382. McMannis, W.J. (1963) LaHood Formation — a coarse facies of the Belt Series in southwestern Montana. Geol. Soc. Am. Bull. J^L* 407-436. Mitchell, R.H. and Krouse, H.R. (1971) Isotopic composition of sulfur and lead in galena from the Greenhow-Skyreholme area, Yorkshire, England. Econ. Geol. 66^ 243-251. Monger, J.W.H. and Preto, V.A. (1972) Geology of the southern Canadian Cordillera. Guidebook for excursion A03-C03. 24th Int. Geol. Cong. Montreal, Quebec. 87 p. Monster, J. (1972) Homogeneity of sulfur and carbon isotope ratios S V s and C / C in petroleum. Am. Assoc. Pet. Geol. Bull. 56, 941-949. 3  13  12  3 2  135  Moorbath, S., Welke, H. and Gale, N.H. (1969) The significance of lead isotope studies i n ancient, high-grade metamorphic basement complexes, as exemplified by the Lewisian rocks of northwest Scotland. Earth Plan. Sci. Letters J5, 245-256. Muffler, L.J.P. and Doe, B.R. (1968) Composition and mean age of detritus of the Colorado River Delta i n the Salton Trough, southeastern California. J. Sed. Pet. 38, 384-399. Muraro, T.W. (1966) Metamorphism of zinc-lead deposits of southeastern British Columbia. In Tectonic history and mineral deposits of the Western Cordillera (editors H.C. Gunning and W.H. White), pp. 239-247. Can. Inst. Min. Met. Special Vol. 8, 353 p. Murthy, V.R. and Patterson, C C . (1962) Primary isochron o:Z zero age for meteorites and the earth. J. Geophys. Res. 67_, 1161-1167. Ney, C S . (1957) Monarch and Kicking Horse Mines. In Structural Geology of Canadian Ore Deposits, Vol. II, 143-152. 6th Commonwealth Mining and Metallurgical Congress, Canada. 524 p. Nguyen, K.K., Sinclair, A.J. and Libby, W.G. (1968) Age of the northern part of the Nelson Batholith. Can. J. Earth Sci. 5_, 955-957. Noble, E.A. (1963) Formation of ore deposits by water of compaction. Econ. Geol. 58, 1145-1156. Obradovich, J.D. and Pet erman, Z.E. (1968) Geochronology of the Belt Series, Montana. Can. J. Earth Sci. 5_, 737-747. . . Ohmoto, H. (1968) The Bluebell Mine, British Columbia, Canada I and II). Ph.D. thesis, Princeton Univ.  (Parts  Ohmoto, H. (1971) Fluid inclusions and isotope study of the lead-zinc deposits at the Bluebell Mine, British Columbia, Canada. In IAGOD Volume: IMA-IAGOD meetings '70 (editor Y. Takeuchi), pp. 93-99. Soc. Mining Geol. Japan Special Issue 2, 193 p. Ohmoto, H. and Rye, R.O. (1970) The Bluebell Mine, British Columbia. I. Mineralogy, paragenesis, fluid inclusions, and the isotopes of hydrogen, oxygen, and carbon. Econ. Geol. 65_, 417-437. Orr, J.F.W. (1971) Mineralogy and computer-oriented study of mineral deposits in Slocan City Camp, Nelson Mining Division, British Columbia. M.Sc. thesis, Univ. of B.C. 143 p. Orr, J.F.W. and Sinclair, A.J. (1971) A computer-processible f i l e for mineral deposits i n the Slocan and Slocan City areas of British Columbia. Western Miner 44(4), 22-34. Ostic, R.G., Russell, R.D. and Stanton, R.L. (1967) Additional measurements of the isotopic of lead from stratiform deposits. Can. J. Earth Sci. 4_, 245-269.  136  Oversby, V.M. (1970) The isotopic composition of lead in iron meteorites. Geochim. Cosmochim. Acta  34, 65-75.  Posepny, F. (1902) Genesis of ore deposits. York. 2nd ed., 806 p.  Am. Inst. Min. Eng., New  Price, R.A. (1962) Fernie map-area, east half, Alberta and British Columbia.  82 G E h  Geol. Surv. Can. Paper  61-24, 65 p.  Price, R.A. (1964) The Precambrian Purcell System in the Rocky Mountains of southern Alberta and British Columbia. Bull. Can. Pet. Geol. 12, 399-426. Ransome, F.L. and Calkins, F.C. (1908) The geology and ore deposits of the Coeur d'Alene d i s t r i c t , Idaho. U.S. Geol. Surv. Prof. Paper 62, 203 p. Reesor, J.E. (1957) The Proterozoic of the Cordillera i n southeastern British Columbia and southwestern Alberta. In The Proterozoic in Canada (editor J.E. G i l l ) , pp. 150-177. Roy. Soc. Can. Special Publication  2. 191 p.  Reesor, J.E. (1958) Dewar Creek map-area with special emphasis on the White Creek Batholith, British Columbia. Geol. Surv. Can. Memoir 292, 78 p. Reid, R.R. and Greenwood, W.R. (1968) Multiple deformation and associated progressive polymetamorphism in the Beltian rocks north of the Idaho batholith, Idaho, U.S.A.  23rd Intemat.  Geol. Cong. Prague 4_, 3  75-87. Reid, R.R., Greenwood, W.R. and Morrison, D.A. (1970) Precambrian metamorphism of the Belt Supergroup in Idaho — Discussion. Soc. Am. Bull. 81, 915-917. Reynolds, P.H. (1967) A lead isotope  Ph.D. thesis, Univ. of B.C.  study of ores and adjacent  Geol.  rocks.  94 p.  Reynolds, P.H. and Sinclair, A.J. (1971) Rock and ore-lead isotopes from the Nelson Batholith and the Kootenay Arc, British Columbia, Canada. Econ. Geol.  66_, 259-266.  Rice, H.M.A. (1937) Cranbrook map-area, British Columbia. Geol. Surv. Can. Memoir  207, 67 p.  Rice, H.M.A. (1941) Nelson map-area, east half, British Columbia. Geol. Surv. Can. Memoir  228, 86 p.  Richards, J.R. (1962) Isotopic composition of Australian leads 2. Experimental procedures and interlaboratory comparisons. J. Geophys. Res. 62, 869-884.  137  Richards, J.R. (1971) 66, 425-434.  Major lead orebodies —  mantle origin?  Econ. Geol.  Roedder, E. (1967) Environment of deposition of s t r a t i f o r m ( M i s s i s s i p p i Valley type) ore deposits, from studies of f l u i d i n c l u s i o n s . In Genesis of stratiform lead-zinc-barite-fluorite deposits (editor J.S. Brown), pp. 349-362. Econ. Geol. Monograph 3, 443 p. Rogers, J.J.W. and Adams, J.A.S. (1969) Thorium. In Handbook of Geochemistry (editor K.H. Wedepohl), I I - l , 90-B-l to 90-N-l Springer Verlag, B e r l i n . Ross, C P . (1970) The Precambrian of the United States of America: northwestern United States — the Belt Series. In The Precambrian (editor K. Rankama), Vol. 4, 145-251. Interscience, New York. 288 p. Ross, D.A. (1972) 1455-1456.  Red Sea hot brine area:  Revisited.  Science  175,  Ross, J.V. (1970) S t r u c t u r a l evolution of the Kootenay Arc. In Structure of the southern Canadian Cordillera (editor J.O. Wheeler), pp. 5365. Geol. Assoc. Can. Special Paper 6, 166 p. R u s s e l l , R.D. (1956) Interpretation of lead isotope abundances. In Nuclear Processes in Geologic Settings, pp. 68-78. Proc. 2nd Conference, 1955. NAS-NRC Publ. 400. R u s s e l l , R.D. (1963) Som^ iccent researches on ..lead isotope abundances. In Earth Science crd Meteoritics (editors J . Geiss and E.D. Goldberg), pp. 44-73. North-Holland Publ. Co., Amsterdam. 312 p. R u s s e l l , R.D. (1972) Evolutionary model f o r lead isotopes i n conformable ores and i n ocean volcanics. Rev. Geophys. & Space Phys. 10, 529-549. R u s s e l l , R.D. and B e l l i s , E.J. (1971) Mass spectrometer power supplies using a s i l i c o n controlled A.C. switch. Mass Spectrometry 19, 37-47. R u s s e l l , R.D., Blenkinsop, J . , Meldrum, R.D. and M i t c h e l l , D.L. (1971) On-line computer assisted mass spectrometry for geological research. Mass Spectrometry 19_, 19-36. R u s s e l l , R.D., Kanasewich, E.R. and Ozard, J.M. (1966) Isotopic abundances of lead from a "frequently-mixed" source. Earth Plan. Sci. Letters 1, 85-88. Ryan, B.D. and Blenkinsop, J . (1971) Geology and geochronology of the H e l l r o a r i n g Creek Stock, B r i t i s h Columbia. Can. J. Earth Sci. j3, 85-95.  138  Sangster, D.F. (1970) Metallogenesis of some Canadian lead-zinc deposits in carbonate rocks. Proo. Geol. Assoa. Can. 22.* 27-36. Sangster, D.F. (1971) Sulphur isotopes, stratabound sulphide deposits and ancient seas. In IAGOD Volume: IMA-IAGOD meetings '70 (editor Y. Takeuchi), pp. 295-299. Soo. Mining Geol. Japan Special Issue 3. 500 p. Schofield, S.J. (1915) Geology of the Cranbrook map area, British Columbia. Geol. Surv. Can. Memoir 76, 245 p. Shannon, F.G. (1970) Some unique geological features at the Bluebell Mine, Riondel, British Columbia. In Lead-zinc deposits in the Kootenay Arc, northeastern Washington and adjacent British Columbia (editor A.E. Weissenboru), pp. 107-120, State of Wash. Dept. Nat. Resources, Div. Mines & Geol. Bull. 61, 123 p. Shaw, D.M. (1957) Comments on the geochemical implications of lead isotope dating of galena deposits. Econ. Geol. 5_2, 570-573. Simons, J.H., McNamee, R.W. and Hurd, CD. (1932) The thermal of tetramethyllead. J. Rhys. Chem. 36_, 939-948.  decomposition  Sinclair, A.J. (1964) A lead isotope study of mineral deposits Kootenay Arc. Ph.D. thesis, Univ. of B.C. 257 p.  in the  Sinclair, A.J. (1966) Anomalous leads from the Kootenay Arc, British Columbia. In Tectonic history and mineral deposits of the Western Cordillera (editors H.C. Gunning and W.H. White), pp. 249-262. Can. Inst. Min. Met. Special Vol. 8, 353 p. Sinclair, A.J. (1967) Trend surface analysis of minor elements i n sulfides of the Slocan mining camp, British Columbia, Canada. Econ. Geol. 62, 1095-1101. Sinclair, A.J. and Walcott, R.I. (1966) The significance of Th/U ratios calculated from west-central New Mexico multi-stage lead data. Earth Plan. Sci. Letters 1, 38-41. Sinha, A.K. (1969) Removal of radiogenic lead from potassium feldspars by volatilization. Earth Plan. Sci. Letters ]_, 109-115 Slawson, W.F. and Austin, C F . (1962) A lead isotope study defines a geological structure. Econ. Geol. 5_7, 21-29. Slawson, W.F., Kanasewich, E.R., Ostic, R.G. and Farquhar, R.M. (1963) Age of the North American crust. Nature 200, 413-414. Slawson, W.F. and Russell, R.D. (1967) Common lead abundances. In Geochemistry of Hydrothermal Ore Deposits (editor H.L. Barnes), pp. 77-108. Holt, Rinehart and Winston, Inc., New York. 670 p.  139  Small, W.D.  (1968)  leads.  Cordilleran  geochronology deduced from hydrothermal  Ph.D. thesis, Univ. of B.C., 97 p.  Smith, A.G. and Barnes, W.C. (1966) Correlation of and facies changes in the carbonaceous, calcareous, and dolomitic formations of the Precambrian Belt-Purcell Supergroup. Geol. Soc. Am. Bull. 77, 1399-1426. Sorenson, A.H. (1972) Age and Mode of Origin  Deposits. Idaho.  of the Coeur d'Alene Ore  Carlton Press, Inc., New York. 85 p.  Stacey, J.S., Delevaux, M.H. and Ulrych, T.J. (1969) Some triple-filament lead isotope ratio measurements and an absolute growth curve for single-stage leads. Earth Plan. Sci. Letters j6, 15-25. Stacey, J.S., Moore, W.J. and Rubright, R.D. (1967) Precision measurement on lead isotope ratios: preliminary analyses from the U.S. Mine, Bingham Canyon, Utah. Earth Plan. Sci. Letters 2, 489-499. Stacey, J.S., Zartman, R.E. and Nkomo, I.T. (1968) A lead isotope study of galenas and selected feldspars from mining districts in Utah. Econ. Geol.  63^, 796-814.  Stanton, R.L. (1958) Abundances of copper, zinc and lead i n some sulfide deposits. Joum. Geol. 66, 484-502. Stanton, R.L. (1960) General features of the conformable " p y r i t i c " orebodies. Part I - f i e l d association. Trans. Can. Min. Met. Bull. 63, 22-27. Stanton, R.L. and Rafter, A.T. (1966) The isotopic constitution of sulphur i n some stratiform lead-zinc sulphide ores. Minerdlium Deposita 1, 16-29. Stanton, R.L. and Russell, R.D. (1959) Anomalous leads and the emplacement of lead sulfide ores. Econ. Geol. 5_4, 588-607. Stewart, J.H. (1972) I n i t i a l deposits in the Cordilleran Geosyncline: evidence of a late Precambrian (850 m.y.) continental separation. Geol. Soc. Am. Bull.  83, 1345-1360.  Stockwell, CH. (1970) Geology of the Canadian Shield (Introduction). In Geology and Economic Minerals of Canada (editor R.J.W. Douglas), pp. 44-54. Geol. Surv. Can. Economic Geol. Report 1, 838 p.  Sutherland-Brown, A., Cathro, R.J., Panteleyev, A. and Ney, C S . (1971) Metallogeny of the Canadian Cordillera. Can. Inst. Min. Met. Bull. 64, 37-61. Swanson, CO. and Gunning, H.C. (1945) Geology of the Sullivan Mine. Trans. Caft. Inst. Min. Met. 48, 645-667.  140  Tatsumoto, M. (1966) Isotopic composition of lead in volcanic rocks from Hawaii, Iwo Jima and Japan. J. Geophys. Res. 2i> 1721-1733. Tempelman-Kluit, D.J. (1968) Geologic setting of the Faro, Vangorda and Swim base metal deposits, Yukon Territory (105 K). Geol. Surv. Can. Paper 68-1(A), 43-52. Tempelman-Kluit, D.J. (1970) The relationship between sulfide grain size and metamorphic grade of host rocks in some strata-bound pyritic ores. Can. J. Earth Sci. 7_, 1339-1345. Tempelman-Kluit, D.J. (1972) Evidence for timing and magnitude of movement along Tintina Trench (abs.). In Faults, fractures, lineaments and related mineralization in the Canadian Cordillera, p. 39. Geol. Assoc. Can. Cordilleran Section Program. 43 p. Thode, H.G., Monster, J. and Dunford, H.B. (1958) Sulfur isotope abundances in petroleum and associated materials. Am. Assoc. Pet. Geol. Bull. kl 2619-2641. y  Thompson, R.I. (1969) Wigwam property. In Geology, exploration, and mining in British Columbia 1969, pp. 339-340. B.C. Dept. of Mines and Pet. Resources. 466 p. Tilton, G.R., Patterson, C.C., Brown, H. Inghram, M., Hayden, R., Hess, D. Larsen, E. , Jr. (1955) Isotopic comp->Fition and distribution of lead, uranium, and thorium in a Precauibrian granite (Ontario). Geol. Soc. Am. Bull. 66, 1131-1148. Tooms, J.S. (1970) Review of knowledge of metalliferous brines and related deposits. Trans. Inst. Min. Met. j[9, B116-B126. Ulrych, T.J. (1960) The preparation of lead tetramethyl for mass spectrometer analysis. M.Sc. thesis, Univ. of B.C. 31 p. Vine, J.D. and Tourtelot, E.B. (1969) Geochemical investigations of some black shales and associated rocks. U.S. Geol. Surv. Bull. 1314-A, 43 p. Vine, J.D. and Tourtelot, E.B. (1970) Geochemistry of black shale deposits — A summary report. Econ. Geol. 6\5, 253-272. Wanless, R.K., Loveridge, W.D. and Mursky, G. (1968) A geochronological study of the White Creek batholith, southeastern British Columbia. Can. J. Earth Sci. 5_, 375-386. Wanless, R.K., Stevens, R.D., Lachance, G.R. and Edmonds, CM. (1967) Age determinations and geological studies. K-Ar isotopic ages, report 7. Geol. Surv. Can. Paper 66-17, 120 p. Wanless, R.K., Stevens, R.D. , Lachance, G.R. and Edmonds, CM. (1968) Age determinations and geological studies. K-Ar isotopic ages, report 8. Geol. Surv. Can. Paper 67-2 (Part A), 141 p.  141  Wanless, R.K., Stevens, R.D., Lachance, G.R. and Rimsaite, R.Y.H. (1965) Age determinations and geological studies. Part 1 — isotopic ages, report 5. Geol. Surv. Can. Paper 64-17 (Part 1), 126 p. Wedepohl, K.H. (1956) Unterschungen zur geochemie des bleis (in German). Geochim. Cosmochim. Acta 10, 69-148. Wedepohl, K.H. (1971a) Zinc and lead in common sedimentary rocks. In Zinc dispersion in the Wisconsin zinc-lead d i s t r i c t by Lavery, N.G. and Barnes, H.L. Econ. Geol. 66, 226-242. Wedepohl, K.H. (1971) "Kupferschiefer" as a prototype of syngenetic sedimentary ore deposits. In IAGOD Volume: IMA-IAGOD meetings '70 (editor Y. Takeuchi), pp. 268-273. Soc. Mining Geol. Japan Special Issue 3, 500 p. Weichert, D.H., Russell, R.D. and Blenkinsop, J. (1967) A method for d i g i t a l recording of mass spectra. Can. J. Phys. ^5_, 2609-2619. Weiss, A., and Amstutz, G.C. (1966) Ion-exchange reactions on clay minerals and cation selective membrane properties as possible mechanisms of economic metal concentration. Mineralium Deposita 1_, 60-66. Weissenborn, A.E., Armstrong, F.C. and Fyles, J.T. (1970) Introduction. In Lead-zinc deposits in the Kootenay Arc northeastern Washington and adjacent British.Columbia (editor A.E. Weissenborn), pp. 1-4. State of Wash. Dept. Nat. Resources, Div. Mines & Geol. Bull. 61, 123 p. s  Wheeler, J.O. (1970) Summary and discussion. In Structure of the southern Canadian Cordillera (editor J.O. Wheeler), pp. 155-166. Geol. Assoc. Can. Special Paper 6, 166 p. Wheeler, J.O., Campbell, R.B., Reesor, J.E. and Mountjoy, E.W. (1972) Structural style of the southern Canadian Cordillera. Guidebook for excursion A-01 and X-01, 24th International Geological Congress, Montreal, Quebec. 118 p. Whishaw, Q.G. (1954) The Jersey lead-zinc deposit, Salmo, B.C. Geol. 49, 521-529.  Econ.  White, D.E. (1965) Saline waters of sedimentary rocks. In Fluids in Subsurface Environments (editors A. Young and J.E. Galley), pp. 342-366. Am. Assoc. Pet. Geol. Memoir 4, 416 p. White, D.E. (1968) Environments of generation of some base-metal ore deposits. Econ. Geol. 63, 301-335. Whittles, A.B.L. (1964) Trace lead isotope studies with gas-source mass spectrometry. Ph.D. thesis, Univ. of B.C. 204 p. Williamson, J.H. (1968) Least-squares f i t t i n g of a straight line. Phys. 46, 1845-1847.  Can. J.  142  Yates, R.G. (1970) Geologic background of the Metaline and Northport mining d i s t r i c t s , Washington. In Lead-zinc deposits in the Kootenay Arc, northeastern Washington and adjacent British Columbia (editor A.E. Weissenborn), pp. 17-39. State of Wash. Dept. Nat. Resources, Div. Mines & Geol. Bull. 61, 123 p. Yates, R.G. and Engels, J.C. (1968) Potassium-argon ages of some igneous rocks i n northern Stevens County, Washington. In Geological Survey Research 1968, pp. D242-D247. U.S. Geol. Surv. Prof. Paper 600-D, 268 p. York, D. (1969) Least squares f i t t i n g of a straight line with correlated errors. Earth Plan. Sci. Letters .5, 320-324. York, D. and Farquhar, R.M. (1972) The Earth's Age and Geochronology. Pergamon Press. 178 p. Youden, W.J. (1951) Statistical Methods for Chemists. Sons, Inc., New York. 126 p.  John Wiley and  Zartman, R.E. and Stacey, J.S. (1971) Lead isotopes and mineralization ages in Belt Supergroup rocks, northwestern Montana and northern Idaho. Econ. Geol. 66_, 849-860. Zartman, R.E. and Wasserburg, G.J. (1969) The isotopic composition of. lead in potassium feldspars from some 1.0-b.y. old North American igneous recks. Geochim. Cosmochim. Acta ^3, 901-942.  APPENDIX NOTES ON SAMPLES, ANALYTICAL METHODS, AGE CALCULATIONS, PRECISION AND CONTAMINATION  A . 1 SAMPLES The writer spent two summers (1968, 1969) in the field i n the East Kootenay district of British Columbia, and  during this time most  of the analysed galenas from deposits in Purcell Supergroup rocks were collected.  Discussions with R.G. Gifford were helpful in selection of  these samples.  Several samples were obtained from R.G. Gifford, Dr.  G.B. Leech and from the collection of the Geological Sciences Centre of the University of British Columbia.  Drill-core samples from Sullivan  Mine were made available by Dr. H.C. Morris and were selected with the assistance of F.R. Edmunds. The writer has not worked in the f i e l d i n the Kootenay Arc or in the Anvil Range.  Samples from the Kootenay Arc were obtained from  Dr. A.J. Sinclair, Dr. J.T. Fyles, A.S. Macdonald, J.F.W. Orr, B. Price and from the collections of the UBC Geological Sciences Centre.  All  samples from the Anvil Range were collected by the writer except for one obtained from R.G. Chaplin and another supplied by G. Jilson.  Most of  the Anvil Range samples were taken from drill-core at Faro Mine, and at the Vangorda, Swim and Sea prospects.  These samples were made available by  Dr. A.E. Aho (Faro, Sea) and W.M. Sirola (Vangorda, Swim). The writer was assisted i n making these collections (in 1968) by Dr. D.J. Tempelman-Kluit.  A-2  A.2  ANALYTICAL METHODS A l l lead isotope analyses, including sample preparations,  were made by the writer, using a gas-source mass spectrometer and other f a c i l i t i e s of the Department of Geophysics and Astronomy of the University of British Columbia.  Samples were introduced as tetramethyl lead and the  trimethyl spectrum was measured (see Ostic and others, 1967). of typical spectra are shown in figs. A . l , A.2 and A.3.  Examples  The tetramethyl  lead was prepared by a Grignard reaction (Pb^+CR^MgBr) and was purified by a gas chromatographic method (see Ulrych, 1960; Sinclair, 1964). The mass spectrometer used in this study incorporates the analyser tube, magnet and Nier-type source of an older 90°-sector, 12 inch radius Instrument described in detail by Kollar (1960), but entirely new electronic supplies (Russell and B e l l i s , 1971). instrument are:  Some details of this  ion accelerating voltage 5 KV; spectrum is scanned by  variation of the magnetic f i e l d ; tungsten ribbon filament; electron energy about 120 ev; source s l i t 0.004", collector s l i t 0.020"; Faraday cup collector.  The instrument i s connected to an Interdata model 4  computer (Russell and others, 1971; Blenkinsop, 1972) which f i l t e r s d i g i t a l ion-current information and stores the filtered data and switch positions on magnetic tape using a program written by Dr. J. Blenkinsop. j  Final processing of data on the tape is done on an IBM Duplex 360/67 computer by a program written by Weichert (Weichert and others, 1967) and modified by Dr. R.D. Russell and Dr. J. Blenkinsop ( a l l of the Department of Geophysics and Astronomy). Electronic equipment for the mass spectrometer and the interface was constructed by E.J. B e l l i s , H. Verwoerd, and R.D. Meldrum, a l l of the  FIG. Al  Pb(CH J 3  4  Fig. A.l  Chart record of spectrum produced by electron bombardment (about 120 ev) of tetramethyl lead vapour. Principal ions responsible for each set of peaks are identified. Note mass scale below spectrum and the attenuation factors (in brackets). Fig. A.2  Chart record showing detail of peaks at masses 251 (mainly P b (CIi ) ) and 252 (mainly Pb " (CH X ). Resolution of the mass spectrometer i s about 460, peak shape is about 0.67 (10% value). The distance (dispersion) between the centres of the two ion beams which these peaks represent is about 0.05 inches. 2 0 6  +  3  2  7  +  3  3  3  FIG. A3  Fig. A. 3  j  P  Typical chart record of trimethyl lead spectrum. Attenuation factors, atomic mass numbers, time scale, and principal peak related to each of the four isotopes of lead are shown. The height of the largest peak (253 a.m.u.) corresponds to an ion current of about 5*10" amp. As well as being output in chart form, the spectrum i s digitised (5 readings/sec) and filtered to remove frequencies above about 0.6 hz. Four or five filtered readings are obtained on each peak top.  A-5  technical staff of the Department of Geophysics and Astronomy.  Dr.  R.D.  Russell was responsible for circuit design of the mass spectrometer; D.L. Mitchell and R.D. Meldrum designed the interface and associated control circuits. Isotope ratios were calculated from raw analyses in the following way. etc.  Samples were analysed i n the sequence shown below, where  represent separate analyses of sample A,B, etc. and  represent separate analyses of Broken H i l l Standard.  Si,S2,  , B i , etc.  etc.  Each analysis i s  based on measurements from five pairs (up- and down-mass) of spectra and took about one hour. Day 1 ^1^2*»•••••••>AjA2..........BjB2  Calculate mean of S S SsSu, calculate (S-A), (S-B) 1  2  Day 2 CC  838^  DD Calculate mean of  Day  SsS^Se,,  calculate (S*-c") , (S-D)  3  S S 5  EE  6  FF etc.  Absolute values were calculated for each sample (A,B,C, etc.) by addition of the true differences (S-A) , (S-B)', etc. to the absolute 1  value of the Broken H i l l Standard as reported by Stacey, Delevaux and Ulrych (1969) , that i s : ^ 2 0 6 ^ 2 0 4  =  1 6 > Q 0 7  p 207 b  / p b  20i4  =  1  5  <  3  9  7  p b  208  / p b  20<  +  =  35^75  A-6  A.3 CALCULATIONS For calculations of lead isotope ages, the decay constants in common use (e.g. see York and Farquhar, 1972) were employed (A238 x 10 y , X _ 9  - 1  ratios P b  206  2 3 5  /Pb  = 0.9722 20tt  x  10" y .  = 9.346, P b  9  207  -1  *232  /Pb  20l+  = 0.0499  x  10~ y ).  = 10.218, Pb  9  208  -1  /Pb  20I  =  0.1537  The primeval  \ = 28.963  (Oversby, 1970) and an "age of the earth" of 4.55 BY (Murthy and Patterson, 1962) were used where necessary.  These parameters are the same as those  used by Zartman and Stacey (1971), permitting the direct comparison of results in section 2.6.  Selection of a different "age of the earth" (e.g.  Cooper and others, 1969; 4.58 BY) w i l l significantly change some ages calculated i n this thesis but should have l i t t l e effect on the interpretations made. It i s not clear at the present time what the most appropriate value for the age of the earth i s (e.g. Gale and others, 1972). Slopes of anomalous lead lines were calculated by computer (program of Dr. R.D. Russell) using the least-squares method of York (1969), and assuming perfect positive correlation of errors i n x and y. As partial justification for using correlated errors, the correlation coefficient for the data of table A.II (n=39) i s +0.83 (95% limits 0.91).  0.70,  For slope calculations, analytical errors were uniformly assumed  (from inspection of data i n table A.I) to be 0.1% (la) for a l l lead isotope ratios, and standard errors of slopes (method of Williamson, 1968) which are quoted and used in age calculations are the 68% confidence level values. The goodness of f i t of lines was tested by determining the value of (S/n-2), where S i s the minimised quantity and n the number of points plotted (York, 1969).  In a l l cases (12), the value of (S/n-2) was less than 1.4, in 9  cases was less than 1.0, and no adjustment of slope errors was made.  A-7 TABLE A . I  U B C No.  rb  2 0 l  7rb"*  RF.n.ICATE ANALYSES  rb '/rb  U B C No.  T V ' / I V *  20  :oi  -  Pb'^/Pb  2 0  "  Pb  2 o e  /Pb  2 0  765  16.313 16.325  15.409 15.402  35.993 35.999  855  18.240 18.244  15.634 15.625  38.207 38.215  775  16.412 16.396 16.404 16.413  15.447 15.428 15.435 15.435  36.129 36.050 36.070 36.066  859  17.926 17.921  15.589 15.595  37.900 37.867  284  18.991 18.992  15.742 15.746  39.287 39.320  16.427 16.435  15.432 15.434  36.103 36.105  295  18.889 . 18.888  15.661 15.660  38.710 38.720  16.432 16.443  15.432 15.433  36.072 36.101  226  17.485 17.476  15.481 15.494  37.964 37.957  16.536 16.546 16.543  15.435 15.454 15.443  36.281 36.327 36.311  772  16.450 16.447  15.465 15.455  36.116 36.090  18.356 18.353 18.345 18.345 18.354 18.341  15.650 15.671 15.652 15.660 15.668 15.668  38.319 38.340 38.319 38.325 38.333 38.320  16.523 16.512  15.466 15.472  36.182 36.142  754  849  16.525 16.532  15.477 15.484  36.168 36.170  18.213 18.230 18.235 18.220  15.626 15.634 15.643 15.630  38.131 38.152 38.171 38.116  778  16.399 16.411  15.447 15.454  36.130 36.172  809  18.366 18.354 18.374  15.674 15.653 15.678  38.337 38.326 38.374  761  16.332 16.346  15.397 15.410  35.939 35.984  810  773  16.391 16.383 .16.392  15.435 15.414 -15.425  36.104 36.047 36.063  18.362 18.371 18.379 18.369  15.662 15.664 15.684 15.659  38.323 38.365 38.401 38.347  818 808  16.338 16.344  ID.AUD  18.369 18.361  15.684 15.668  38.347 38.321  15.407  35.970 35.991 822  762  16.327 16.336  15.401 15.411  35.968 36.002  18.336 18.336  15.655 15.662  38.253 38.293  819 759  17.275 17.263  15.529 15.534  37.085 37.106  18.342 18.350  15.655 15.672  38.285 38.308  820 300  19.093 19.092  15.743 15.792  39.454 39.419  18.341 18.335  15.666 15.666  38.299 38.287  821 768  18.788  15.638  38.778  18.337 18.347  15.664 15.673  38.301 38.316  18.795  15.637  38.777  769  851  852  8A6  847  Note 1.  Standard d e v i a t i o n s were c a l c u l a t e d i n the f o l l o w i n g way Set  Samples  W  W,,W ,  X  X,,X ,X,  Y  YI.YJ  Mean  2  2  Y  n  0  t 0.007(0.04%)  •  2a  ± 0.014(0.09%)  ± 0.017(0.11%)  Divisor  (W)-W*)  2  + (Wj-W*)  J  X*  (Xi-X*)  2  + (X -X*)  2  Y*  (Yi-Y*)  2  2  + (Y -Y*)  2  2  T o t a l o f above -  ±  0.022(0.06%)  ± 0.045(0.13%)  (Youden, 1951)  Calculate  W*  0.008(0.05%)  "  (n-1)  1 + (X3-X*)  2  2  +  "sum of s q u a r e s "  (Y "Y*) n  2  n-1  T o t a l o f above « "degrees o f  freedom"  sum of squares legrees of freedom Note 2 .  Of a t o t a l o f 79 a n a l y s e s done as checks o f p r e c i s i o n , a l l but 6 are g i v e n above; these b e i n g r e j e c t e d  as u n a c c e p t a b l e .  Note 3.  Each a n a l y s i s r e p o r t e d above i s c a l c u l a t e d from the mean o f 2 s e p a r a t e , of 4 s e p a r a t e c o n s e c u t i v e a n a l y s e s o f the s t a n d a r d .  Note 4 .  The p e r c e n t a g e s t a n d a r d d e v i a t i o n s were c a l c u l a t e d by comparing the s t a n d a r d d e v i a t i o n s w i t h the mean v a l u e s o b t a i n e d f o r the Broken H i l l S t a n d a r d , the sample w i t h the lowest r a t i o s measured l n t h i s study ( i . e . , these are maximum Z e r r o r s )  c o n s e c u t i v e a n a l y s e s as compared w i t h the mean  A-8 TABLE A . I I  MEASUREMENTS OF BROKEN HI LI. STANDARD, SET A. Pb  tober 8, 1971  c i l 1, 1972  H^MEAN  J C 6  /Pb  J 0  p 207  "  b  / p b  20»  Pb'c'/Pb  2 0  16.046 16.055 16.048 16.055 16.051 16.060 16.068 16.069 16.056 16.054 16.057 16.057 16.056 16.068 16.054 16.049 16.055 16.051 16.039 16.049 16.053 16.054 16.054 16.058 16.055 16.062 . 16.063 16.065 16.064 16.058 16.066 16.060 16.066 16.071 16.064 16.064 16.059 16.068 16.062  15.447 15.456 15.448 15.443 15.450 15.467 15.466 15.472 15.456 15.459 15.457 15.461 15.467 15.470 15.456 15.446 15.452 15.448 15.443 15.456 15.448 15.463 15.459 15.455 15.459 15.466 15.469 15.471 15.467 15.455 15.463 15.457 15.455 15.470 15.456 15.465 15.458 15.470 15.460  35.84 3 35.919 35.914 35.907 35.899 35.947 35.945 35.961 35.922 35.926 35.924 35.910 35.956 35.963 35.919 35.897 35.904 35.892 35.866 35.898 35.919 35.938 35.916 35.919 35.927 35.951 35.917 35.965 35.961 35.935 35.955 35.928 35.952 35.989 35.951 35.956 35.939 35.940 35.940  16.058  15.459  35.928  *  0  ± 0.007(0.05%)  ± 0.008(0.05%)  ± 0.029(0.08%)  20  ± 0.015(0.09%)  ± 0.017(0.11%)  ± 0.059(0.16%)  Note 1.  Above are a l l the analyses of UBC 001 done during the interval October 8, 1971 to A p r i l 1, 1972. Nearly a l l analyses interpreted in this thesis were run between these dates. The l i s t i n g i s consecutive.  Note 2 .  Calculation of standard deviation  Note 3.  Each analysis above i s the mean of two consecutive analyses. In calculating sample results, consecutive results shown above were paired, and this mean value of the standard was compared with the unknown sample analysis ( i t s e l f a mean of two analyses).  Note 4.  The above analyses show a change with time and the distribution of values i s not normal (is bimodal). As might be expected, the replicate sample analyses do not show this effect.  Note 5.  Because isotope ratios determined on a gas-source instrument depend on source conditions (e.g. electron voltage, magnetic f i e l d , etc.) as well as viscous/molecular flow fractionation, the mean value quoted i s not particularly significant. For example, another 6et of nine analyses gave the result ecu i P b / P b " =- 16.078 ?b /?b = 15.487 P b / P b * = 36.008 (±0.07%) (±0.12%) (±0.021%) r  2 0 6  2 0  A(X-X) V (n-1)  207  20h  2  2 0 8  2 0 1  where the errors are 2a values (corrected for the small number of samples). Nevertheless, published values for the Broken H i l l Standard and the two values given here are reasonably close to the ratios calculated (assuming fractionation) from the absolute ratios reported for this standard.  A-9  KEY (CRK K R Sm SDU S>K F Ka 0 SI 0  O  Cooper «nd others (1969) K o l l a r (1960) Richards (1962) S c u l l (1968) Stacey and others (1969) Stacey and others (1967) Farquhar (TorontoT Kanasewich (rue) Reported l n Ostlc (UBC) Slawson and Sinclair (UBC) R u s s e l l (1967) Ulrych (UBC) _  I n d i v i d u a l r e s u l t s , set~A  •y^rr.ean, s e t A •yk^iiean, note 5  This t h e s i s , p. A-8  Ct3 )SMR  /  15-500  Fractionated ratios  207  iSm  Pb  204  Pb  ±o-iz 15-400  Absolute ratios  I  16-000  Fig. A.4  I  16-100  P l o t o f mean v a l u e s o b t a i n e d by o t h e r w o r k e r s f o r t h e Broken H i l l Standard,and t h e r e s u l t s o f t a b l e A . I I . The e x p e c t e d ( f r a c t i o n a t e d ) r a t i o s were c a l c u l a t e d f r o m t h e two a b s o l u t e v a l u e s r e p o r t e d by S t a c e y and o t h e r s (1969) and Cooper and o t h e r s ( 1 9 6 9 ) , and i t was assumed t h a t gas f l o w i n t o t h e s o u r c e was v i s c o u s and f l o w o u t was m o l e c u l a r ( H a l s t e d and N i e r , 1950; W h i t t l e s , 1964).  A-10  A.4  PRECISION The precision of measurements reported i n this thesis i s fairly-  indicated by the two estimates of analytical uncertainty based on the replicate analyses in table A.I and A.II.  Because i t is d i f f i c u l t to  justify, very l i t t l e data were rejected (about 20 analyses out of 450), and then only where really necessary (e.g. blips on peak tops, circuit failures, etc.).  The replicate analyses were run concurrently with the  rest of the analyses.  A.5 CONTAMINATION The precautions taken against contamination during purification and analysis of samples are mentioned below, with some evidence to suggest these ^ere effective. Contamination  in the gas chromztograph  The chromatographic column used to separate tetramethyl lead from ether after the Grignard reaction was a pyrex h e l i c o i l (278 cm. x 7 mm.  I.D.) packed with 45/60 mesh Chromosorb W (AW, DMCS) coated with  20% dinonyl phthalate (HETP for  Pb^s)!,  = 0.5-1.1 cm.).  In normal use  the temperature was maintained at 75° and flow rates (N ) were 85-110 2  ml/min.  The materials used are relatively inert, the temperature i s low  relative to the decomposition temperature of tetramethyl lead (265°C; Simons and others, 1932), large samples (0.3-1.0 ml) containing about 0.1 ml, Pb(CH3)i were injected, and the column was flushed for a minimum of 4 t  hours at a flow rate of about 50 ml/min (12 l i t r e s of N ). 2  Samples that  A-ll  were known or suspected to be similar i n composition were processed i n groups and a separate column was used exclusively for samples of the Broken H i l l Standard.  The following experiment was done to test these  precautions. Two samples of a highly radiogenic galena lead (UBC 642 from the Siljan Ring, Sweden) and two samples of Broken H i l l Standard (001) were prepared and put through the column i n the same way as other samples and i n the sequence 642A, 001A, 642B, 001B.  If small amounts of 642  contaminate the succeeding 001 samples then the difference between these 001 samples and "uncontaminated" 001 w i l l give two estimates of the extent of contamination.  Sample  Pb  206  /Pb  201t  Pb  207  /Pb  201t  Pb  208  /Pb  Check 1.  001A  16.081  15.477  35.964  Check 2.  001B  16.085  15.456  35.952  Preceding analysis of "uncontaminated" standard sample  001*  16.062  15.460  35.940  201t  (001A - 001*)  + 0.019(0.12%)+ 0.017(0.88%)+ 0.022(0.16%)  (001B - 001*)  + 0.023(0.14%)- 0.004(0.21%)+ 0.012(0.09%)  Assuming that the differences (001A - 001*) represent an increment due to contamination by 642, the bracketed figures express the amount of contamination as a percentage of the difference i n ratios between 642 and 001. Because the difference between normal samples was always less than h of the difference between 642 and 001, the experiment  demonstrates  A-12  that contamination in the chromatographic column should be negligible. Contamination  in the mass  spectrometer  Because larger amounts of sample are handled i n the inlet system of the mass spectrometer than are admitted to the ion source, contamination i s most likely to arise in the inlet system - by sorption, or by trapping on reservoir walls by mercury or in valves (which are greaseless). Another possibility i s that lead deposited in the source or elsewhere by the thermal degradation of a previous sample of tetramethyl lead wil exchange with lead i n a new sample (Leigh-Smith and Richardson, 1935; Duncan and Thomas, 1967).  Flushing the system with a portion of the new  sample before analysis, keeping the source hot by leaving the filament on, allowing adequate pump-down time (normally more than 2 hours) between analyses, and running samples of similar composition i n groups are a l l useful precautions against contamination and were normal practice. The following test was done. Radiogenic sample 642 and the current standard (001) sample were analysed i n the following sequence:  642(a),  001(a), 642(b), 001(b), with the results shown below. Analysis  Pb /Pb *  642(a)  32.568  17.395  49.598  001(a)  16.069  15.458  35.927  642(b)  32.575  17.380  49.619  001(b)  16.055  15.461  35.953  206  20t  Pb  207  /Pb  20Jt  Pb  208  /Pb  201+  Difference between the two 642 analyses: 0.007 (0.02%)  0.015  (0.09%)  0.021  (0.04%)  Difference between the two 001 analyses: 0.014  (0.09%)  0.003 (0.02%)  0.026 (0.07%)  A-13  The results suggest that contamination i n the mass spectrometer can be kept to a negligible level.  The analyses of the Broken H i l l  Standard shown i n table A.II show no effects of contamination during routine work, and confirm this conclusion.  

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0302659/manifest

Comment

Related Items