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A study of the lead isotopic composition of galena at Manitouwadge, Ontario. Hayles, John Gordon 1973

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A STUDY OF THE LEAD ISOTOPIC COMPOSITION OF GALENA AT MANITOUWADGE, ONTARIO by JOHN GORDON HAYLES B.Sc, Queen's University, 1970 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the Department of GEOPHYSICS We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA March, 1973 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by the Head o f my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood t h a t c o p y i n g or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed w ithout my w r i t t e n p e r m i s s i o n . Department The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada (i) ABSTRACT Lead isotope compositions of galena from the Fox Creek Fault at Manitouwadge, Ontario form an anomalous l i n e a r array of values on a standard 2 0 7Pb/20''Pb vs. 2 0 6Pb/ 2 0-Pb p l o t and a 2 0 8Pb/ 2 0 , tPb vs. 2 0 6Pb/ 2 0 l 4Pb p l o t . The l a s t g e o l o g i c a l l y reasonable time for galena mineralization along the Fox Creek Fault i s during the Keweenawan age, 1100 m i l l i o n years ago. Using the slope of the anomalous lead l i n e and this time of 1100 m i l l i o n years as the time of f i n a l galena mineralization along the f a u l t gives an age of 2000 m i l l i o n years as the maximum. time of emplacement of uranium parent of the anomalous leads i n t o the crust. The corresponding Th/U r a t i o for the source of the anomalous leads i s 5.3. Lead isotope compositions of galena from the main ore zone at Manitouwadge are extremely homogeneous and do not show a l i n e a t i o n , other than along a 2 0 1*Pb error l i n e , which would indicate them as anomalous leads. I t i s improbable f o r the ore zone deposits to be as young as 2700 m i l l i o n years as required by T i l t o n and Steiger (1969) . In order to r e l a t e ore zone leads to Fox Creek Fault leads at l e a s t a three stage lead growth model i s required. Possibly no genetic r e l a t i o n exists between ore zone and Fox Creek Fault galenas analysed to date. Single galena c r y s t a l lead isotope variations should be studied i n d e t a i l within the Fox Creek Fault ( i i ) i t s e l f . Sulphur isotope studies may help to determine the r e l a t i o n between ore zone and f a u l t zone galena at Manitouwadge. 0 1 a ) TABLE OF CONTENTS ABSTRACT (i) LIST OF FIGURES ( i i i ) LIST OF TABLES (iv) ACKNOWLEDGEMENTS (v) CHAPTER I 1.1 Introduction 1 1.2 Geology 1 CHAPTER II 2 e l A n a l y t i c a l Procedures 7 2.2 Mass Spectrometry 8 CHAPTER III 3.1 A n a l y t i c a l Results and Interpretation 13 3.2 Summary 33 REFERENCES 36 APPENDIXES A. Ion Exchange Column Preparation 40 B. S i l i c a Gel - Lead Nit r a t e Loads 44 C. Pre c i s i o n and Double Spiking 46 ( i i i ) LIST OF FIGURES FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 6 Location map and geologic map of Manitouwadge, Ontario. (a) Example of a t y p i c a l l y stable lead i s o t o p i c i o n i z a t i o n at 1230 C. (b) Example of a p a r t i c u l a r l y unstable lead isotope i o n i z a t i o n using the s i l i c a g el procedure. Results of t h i s study, 2 0 7Pb/2("*Pb vs. 2 0 6Pb/20'*Pb compositions for galena from Manitouwadge, Ontario. Results of t h i s study, 2 0 8Pb/ 2 0 **Pb vs. 2 0 6Pb/ 2 0 **Pb compositions for galena from Manitouwadge, Ontario. 2 0 7 Pb/ 2 0 <t Pb vs 2 0 6, Pb/ 2 0 1 |Pb p l o t of lead isotope compositions of rocks and ores at Manitouwadge, Ontario and i t s environs. 20 S, 'Pb/^-Pb vs. 2 0 6Pb/ z o , ,Pb p l o t of lead isotope compositions of rocks and ores at Manitouwadge, Ontario and i t s environs. Page 2 11 15 16 26 27 (iv) LIST OF TABLES Page TABLE 1 The r e s u l t s of t h i s study of lead 13 isotope compositions of galena at Manitouwadge, O n t a r i o . TABLE 2 The normalized r e s u l t s of samples 24 analysed from i n and around the Manitouwadge area by O s t i c (1963), Doe, T i l t o n and Hopson (1965), Hart and T i l t o n (1966), and T i l t o n and S t e i g e r (1969) . (v) ACKNOWLEDGEMENTS The w r i t e r wishes to thank a l l those who contributed to the preparation of t h i s t h e s i s . The assistance of Drs. T. J . Ulrych, J . M. Ozard and R. D. Russell i s appreciated. Mrs. C. Curtis assisted the writer i n the laboratory i n many ways. Discussions with Mr. P. Le Couteur and Dr. J . Blenkinsop helped i n almost a l l phases of the the work. The mine s t a f f at the Geco mine, Mr. Unto J a r v i , Mr. Tim Bakker, Mr. Terry Williams, and Mr. Ross Weeks supplied samples and guided the author through much of the mine. Mr. Esko Autio, chief geologist at Willroy, donated the Willroy and Willecho samples analysed here. My wife typed t h i s t h e s i s . L a s t l y , I must thank Dr. W. F. Slawson who super- vised t h i s work. The study was supported f i n a n c i a l l y by a National Research Council of Canada grant to Dr. Slawson. - 1 - CHAPTER I 1.1 INTRODUCTION Manitouwadge i s about 165 miles east-northeast of Thunder Bay, Ontario and i s about 60 miles north of Lake Superior. The townsite i s about 40 miles by road north of Trans-Canada Highway #17 at Struthers, and i s served by spur l i n e s of both the Canadian National and Canadian P a c i f i c Railways. Manitouwadge has been an important metal producing, area since 1957. The Geco mine, owned by Noranda Mines Ltd., i s the largest deposit i n the area, and i n the 1957- 1971 period produced 639,630 tons of zinc, 377,830 tons of copper, 29,013,600 oz. s i l v e r , and minor lead and gold from 19,544,170 tons of ore. Reserves are about 30 m i l l i o n tons of 4.4% Zn, 2% Cu, and 1.8 oz. Ag. The i s o t o p i c composition of lead i n galena at Manitouwadge has been discussed i n s c i e n t i f i c l i t e r a t u r e since 1957. Frequently discussions on the age of the earth have centered around the lead i s o t o p i c composition at Manitouwadge. This thesis attempts to add i n s i g h t into the o r i g i n of Manitouwadge leads. 1.2 GEOLOGY Geology of the Manitouwadge area i s shown i n Figure 1 and has been described by E. G. Pye (1957) , E. H. M. Chown (1957), Brown et. a l . (1960) and Timms and I to I Figure 1 Geology of the iManitouwadge area modified a f t e r Pye (1957) and others. Locations of the Geco, Willroy, and Willecho mines are indicated by c i r c l e d numerals 1, 2, and 3, respectively. _ 3 _ Marshall (1959) . Manitouwadge l i e s within the Superior Province of the Canadian Shield as a roof pendent of metasedimentary- metavolcanic rocks surrounded by granites, granodiorites and migmatites. The metasedimentary-metavolcanic sequence i s of Keewatin age although i t s time r e l a t i o n s h i p with other Keewatin rocks of the Shield i s not known. The sequence forms a syncline with an axis trending 050° and plunging 15° to 20° to the northeast. Dips along the limbs of the syncline are steep. Relic bedding i s noticeable i n the metasediments and pil l o w structures can be found i n the metavolcanics. Tops i s not known due to high grade amphibolite facies metamorphism which occurred during the Kenoran Orogeny. This orogeny also obscured primary sedimentary structures and d i s t o r t e d the syncline. The s t r a t a are cut by pegmatite dikes and microgranodiorite dikes and s i l l s which possibly were intruded during l a t e phases of Kenoran Orogeny. The eight known orebodies i n the Manitouwadge area are hosted by a grey gneiss sequence thought to be sedimentary i n o r i g i n . This unit i s located toward the top or concave side of the plunging syncline, as depicted i n Figure 1. The major orogenic event i n t h i s area occurred 2700 m i l l i o n years ago as dated by Rb-Sr measurements according to T i l t o n and Steiger (1969) . Hanson et. a l . - 4 - (1971) also report Rb-Sr ages of 2700 m i l l i o n years for rocks from northern Minnesota, which i s within the same subprovince of the Canadian Shield as Manitouwadge. A swarm of northeast trending diabase dikes of probable Keweenawan age cut t h i s older deformed t e r r a i n . A major Keweenawan i n t r u s i v e complex i s located about 50 miles south-southwest of Manitouwadge, along the s t r u c t u r a l boundary between the Superior Province and Southern Province. An enormous amount of basic volcanism and diabase i n t r u s i o n occurred i n the Southern Province during the Keweenawan, which has been dated by Goldich et. a l . (1961) and the Geological Survey of Canada as occurring from 1200 to 900 m i l l i o n years ago. The in t r u s i v e s were emplaced early i n the evolution of the Southern Province, and are common i n the surrounding Archean t e r r a i n , Halls (1966) . Ore deposits at Manitouwadge are conformable within the metasediments and have been classed as copper- zinc type not unlike other ore deposits which occur i n an east-west b e l t across Ontario and part of Quebec. The Geco main zone and the Willroy #1 zone occur i n a muscovite- quartz s c h i s t along with some bands of iron formation. Iron formation completely encloses the other Willroy and Willecho orebodies. The orebodies are c l a s s i f i e d as replacement deposits by Pye (1957), with three modes of occurrence: (1) massive ore (2) lode f i s s u r e s and (3) disseminated ore. Pegmatite dikes have been replaced i n places by ore, which has been taken by many geologists to indicate that mineralization i s younger than pegmatite i n t r u s i o n . However, minor remobilization of ore could have occurred during the waining stages of the Kenoran Orogeny, and may be the cause of t h i s "replacement". S u f f e l et. a l . (1971) suggest t h i s l a t t e r view. Ore appears to be located i n long low-amplitude drag folds which possibly were formed during regional f o l d i n g . Galena samples were c o l l e c t e d during September of 1970 by the author from the Geco, Willroy and Wilecho ore zones. At both the Willroy and Geco zones galena appears to have been emplaced l a t e r than other sulphides, which i t often replaces. Galena constitutes less than one percent of the Geco ore, and occurs i n the massive ore and along fractures i n wallrock inclusions i n the massive ore, along fractures i n pegmatite dikes a s s i c i a t e d with disseminated ore, and associated with the Fox Creek Fault. Galena i n the Fox Creek Fault i s more abundant and occurs much larger c r y s t a l s than i n other parts of the mine. Fox Creek Fault galena i s usually associated with c a l c i t e which i s not common elsewhere at Geco. The Fox Creek Faul was ina c c e s s i b l e at the time of the author's v i s i t , and so samples of galena from there were donated from the Geco o f f i c e c o l l e c t i o n by Mr. T. Bakker and Mr. R. Weeks. Samples from the Willroy and Willecho mine were donated by Mr. E. Autio, the chief geologist. S u f f e l et. a l . (1971) point out that many c h a r a c t e r i s t i c s - 6 - of the Manitouwadge area are consistent with severe metamorphism. They note that the ore displays metamorphic granoblastic textures which indicates an o r i g i n p r i o r to metamorphism, possibly of sedimentary or submarine volcanic o r i g i n . The conformable nature of ore supports th i s hypothesis. Since grade of metamorphism i s high i n t h i s area i t seems unlilcely that the genesis of these orebodies w i l l ever be firmly resolved. The author favors a sedimentary o r i g i n . - 7 _ CHAPTER II 2.1 ANALYTICAL PROCEDURES The 13 galena-bearing samples analysed during t h i s study were i n d i v i d u a l l y crushed and galena was separated by hand, as much as possible. Approximately four grams of galena from each sample were placed i n 100 m i l l i l i t e r s of 6 molar hydrochloric acid, and held at about 60° C for about 6 hours. The r e s u l t i n g hot sol u t i o n containing lead chloride was then f i l t e r e d , and cooled to p r e c i p i t a t e lead chloride c r y s t a l s . A f t e r about 2 hours, r e s i d u a l l i q u i d was decanted, lead chloride c r y s t a l s were washed i n d i s t i l l e d water, dried i n a warm oven overnight and stored i n a clean b o t t l e . A 30 cm. long ion exchange column with a 100-200 mesh Dowex l x 8 chloride form exchange r e s i n was used to pur i f y the lead chloride since galena i n the samples was always associated with sulphides of i r o n , zinc and copper. This ion exchange p u r i f i c a t i o n i s based on a study by Kraus and Nelson (1955) with d e t a i l s given i n Appendix A. Af t e r p u r i f i c a t i o n , lead chloride was converted to c r y s t a l l i n e lead n i t r a t e which was stored. A de t a i l e d flow chart of the a n a l y t i c a l procedures i s given i n Appendix A. The s i l i c a gel-phosphoric acid method as des- cribed by Cameron et. a l . (1969) was used to make the lead analyses on a single outgassed filament of rhenium. - 8 - E s s e n t i a l l y t h i s method increases the i o n i z a t i o n e f f i c i e n c y of lead on a hot filament and can be used f o r very small (nanogram) masses of lead. Details of the s i l i c a gel procedure are given i n Appendix B. A double spike was used to correct for mass dependent f r a c t i o n a t i o n which occurs i n the source region of the mass spectrometer. The double spike used i n t h i s study was prepared by Mrs. C. C u r t i s , of th i s laboratory, from lead n i t r a t e standards supplied by the Oak Ridge National laboratory U.S.A. The double spike has been c a l i b r a t e d by Dr. J . M. Ozard, and by the author against the N.B.S. equal atom standard, SRM 982. C a l i b r a t i o n results are shown i n Appendix C. 2.2 MASS SPECTROMETRY The mass spectrometer used i n th i s study was a 12 inch, 90° sector, f i r s t order focusing, s o l i d source mass spectrometer as described by Russell et. a l . (1971) and Blenkinsop (1972). A d i g i t a l computer i s used on-line with the mass spectrometer as a standard feature at th i s lab to a s s i s t i n data reduction. Voltages proportional to the ion current flow at the c o l l e c t o r are measured d i g i t a l l y . This data i s f i l t e r e d giving peak heights above baseline heights which then i s converted by the computer to isotopic r a t i o s for each p a i r of spectra scanned and the res u l t s are recorded on a teletype. - 9 - The mass spectrometer chamber was reduced to a pressure of about 2><10 'millimeters of mercury, by an o i l d i f f u s i o n pump, a process requiring two hours a f t e r the sample had been inserted i n the source region. L i q u i d nitrogen was placed into a cold finger near the source, which further reduced the pressure, to about 0.5x10" millimeters of mercury. The magnet current supply and the high voltage supply were usually turned on and allowed to warm up f o r ten minutes before the filament current was turned on. The filament current was increased gradually from zero to around 1.8 amperes over f i v e minutes which brought the filament temperature to around 1000° C. as determined by an o p t i c a l pyrometer. Lead beams were large enough to give good p r e c i s i o n at about 1200° C. The ion current for the 2 0 l fPb peak must be greater than 10" 1 3 amperes to give s u f f i c i e n t p r e c i s i o n of isotope measurement, and temperatures were adjusted to achieve at l e a s t t h i s amount. Measurement of precise lead i s o t o p i c r a t i o s also requires a stable rate of i o n i z a t i o n i n the source region, because only one ion beam can be measured at a time. I f the i o n i z a t i o n i s unstable over the time the four beams of lead are scanned, meaningful i s o t o p i c r a t i o s could only be obtained by averaging many measurements. Speed and p r e c i s i o n of measurements of i s o t o p i c composition depend greatly on s t a b i l i t y of the rate of i o n i z a t i o n i n - 10 the source region. At normal operation temperatures of 1050o c . to 1300° C s i l i c a g el i s probably a l i q u i d upon the filament. The i o n i z a t i o n of lead atoms may take place as the atom evaporates from the filament or as the gaseous atom c o l l i d e s with the hot filament. No general theory exists to explain the sequence of events i n the thermal i o n i z a t i o n of an atom from a hot filament. The analyst must decide by t r i a l and error the optimum values of filament temperature, filament p o s i t i o n , and heating sequence which y i e l d precise analyses. Usually i o n i z a t i o n would be stable enough to begin measurement a f t e r 10 to 30 minutes of monitoring the beam at operation temperature. A t y p i c a l group of eight scans of a stable beam of sample 791 are shown i n Figure 2a. Even highly stable ion beams have some transients and an example can be seen at minute 62 on a 2 0"Pb peak. Measurements were continued for each sample u n t i l p r e c i s i o n was estimated to be approximately 0.05 percent. Scan records were edited of scans with obvious transients, 2 0 k such as on the Pb peak near minute 62 xn Figure 2a, before f i n a l reduction of data to a mean, standard deviation, and standard error of the mean for the isotope r a t i o s . A p a r t i c u l a r l y unstable beam, from sample 802, - 11 u o O 1 5 - 2 ° - 208 Pb peak \ a £ UJ a. E u o o CM 204 206 D O) 208 u_ I O N I Z A T I O N I N T E N S I T Y Pb x l O 1 3 P b i 2 0 7 P b x 3 x 1 0 ~ 1 3 Pb x 9 x 10 - 1 3 ampere ampere ampere I O N I Z A T I O N I N T E N S I T Y x 2 7 x l 0 ampere - 12 - i s shown i n Figure 2b. Af t e r about one hour of ion- i z a t i o n at normal run temperatures the beam i n t e n s i t y was s t i l l highly i r r e g u l a r . Figure 2b not only shows this i r r e g u l a r i t y , i t also shows a heating technique used to s t a b i l i z e beams. Often i f the ion beam i s unstable, increasing the filament temperature 200°- 300°C. for 2-3 minutes and then bringing i t back down increases the s t a b i l i t y . This p a r t i c u l a r run was unsuccessful, for when the beam f i n a l l y s t a b i l i z e d , the sample was too depleted to give a s u f f i c i e n t i o n i z a t i o n beam. - 13 - CHAPTER II I 3.1 ANALYTICAL RESULTS AND INTERPRETATION The r e s u l t s of t h i s study of the i s o t o p i c com- p o s i t i o n of galena at Manitouwadge, Ontario, are shown i n Table 1. Two samples from Manitouwadge were double spiked to c o r r e c t f o r mass-dependent f r a c t i o n a t i o n within the source region of the mass spectrometer. F r a c t i o n a t i o n c o r r e c t i o n s f o r the s i l i c a gel-phosphoric a c i d procedure used here were about 0.1 percent f o r the 2 0 6Pb/ 2 0 ,*Pb r a t i o ; t h i s was deemed i n s i g n i f i c a n t to the r e s u l t s of t h i s study and so f r a c t i o n a t i o n corrections have ignored. Double spike c a l i b r a t i o n and corre c t i o n s and r e p l i c a t e analyses of galena from Broken H i l l , the U.B.C. standard lead, are given i n Appendix C. S a m p l e * 0 6 p b 2 o <.pb 20 7 p b 2 0 ".Pb 2 0 8 p b 2 0 >.Pb 782 F o x C r e e k F a u l t 750 l e v e l 2 9 . 8 1 5 + . 0 1 7 * 17.481±.010* 46. 7 2 + . 0 3 * 783 F o x C r e e k F a u l t •p l e v e l 2 9.186+.007 17.389+.006 46.24 + .019 784 F o x C r e e k F a u l t 1000 l e v e l 31.72 +.013 17.817+.007 50.09+.016 785 F o x C r e e k F a u l t •p l e v e l 2 9.309+.009 17.403+.005 46.27+.016 786 F o x C r e e k F a u l t 250 l e v e l 32.10 +.002 17.868+.012 50.49+. 04 787 G e c o M a i n O r e 1129 l e v e l 1 3 . 1 9 2 + . 0 0 5 14.370+.007 32.98+.023 789 G e c o M a i n O r e 250 l e v e l 1 3.195+.006 14.377+.007 32.96+.017 790 G e c o M a i n O r e 2250 l e v e l 1 3.206+.006 14.394+.009 33.02+.025 791 G e c o M a i n O r e 2300 l e v e l 13.204+.004 14.384+.005 32.98+.019 800 G e c o M a i n O r e 550 l e v e l 1 3 . 1 8 4 + . 0 0 3 14.340+.003 32.86+.007 802 G e c o M a i n O r e ? l e v e l 1 3 .223+.006 14.382+.005 33.01+.030 805 W i l l r o y # 3 z o n e 13.182+.004 14 . 349+.004 32.91+.017 807 W i l l e c h o ( L u n e c h o ) m i n e 13.177+.005 14.359+.007 32.94+.018 * T h e ± f i g u r e s a r e s t a n d a r d e r r o r s o f t h e mean. Table 1 - 14 - The data of Tab l e 1 has been p r e s e n t l y g r a p h i c a l l y on F i g u r e 3 and F i g u r e 4, the 2 0 7Pb/ 2 ("*Pb vs 2 0 6Pb/ 2 ("*Pb p l o t and the 2 0 8 P b / 2 0 1 + P b v s . 2 0 e P b / 2 0 , > P b p l o t r e s p e c t i v e l y . A s i n g l e stage growth curve f o r l e a d , a f t e r Cooper e t . a l . (1969) has been added t o each F i g u r e . In F i g u r e 3, two d i s t i n c t l e a d i s o t o p i c p o p u l a t i o n s may be seen, one homogeneous c l u s t e r of valu e s below the growth cu r v e , which has been p l o t t e d a t a more d e t a i l e d s c a l e i n the F i g u r e , and another group which forms an anomalous l i n e a r a r r a y t o the r i g h t o f the growth c u r v e . Samples from the Fox Creek F a u l t a l l l i e along t h i s anom- alou s l e a d l i n e w h i l e ore zone samples from the Geco, W i l l r o y , and W i l l e c h o mines a l l have very c l o s e l y the same compos i t i o n . A 2 0 I*Pb e r r o r l i n e has been drawn through the ore zone l e a d c o m p o s i t i o n i n F i g u r e 3 and any d i f f e r e n c e s i n the ore zone l e a d composition probably may. be a s c r i b e d t o 2 0 1*Pb measurement e r r o r . A l e a s t square f i t l i n e , a f t e r York (1969)., has been f i t t e d to the l e a d compositions from the Fox Creek F a u l t and i s shown i n F i g u r e 3. T h i s b e s t f i t l i n e does not i n t e r s e c t w i t h i n e x p e r i m e n t a l e r r o r the ore zone l e a d c o m p o s i t i o n . F i g u r e 4 shows on the 2 0 8 P b / 2 0 , , P b v s . 2 0 6Pb/ 2 <"*Pb p l o t much the same r e l a t i o n s h i p s as t h a t shown on the 2 0 7Pb/ 2 0 1*Pb v s . 2 0 6 P b / 2 0 , | P b p l o t i n F i g u r e 3. The Fox Creek F a u l t leads form an anomalous l i n e a r a r r a y w h i l e the leads o f the main ore zones of the Geco, W i l l r o y , and 1 3.0 14.0 _ l I I L . U 16 18 20 2"2 206 /204 Pb/ Pb 24 2 6 2 8 30 32 Figure 3 2 0 7Pb/ 2 0 , ,Pb - 2 0 6Pb/ 2 0 1 ,Pb compositions for galena from Manitouwadge, Ontario. Growth curve after Cooper et. a l . (1969) labeled i n units of b i l l i o n s of years before; present. 54 3 3 . 6 2 0 6 / 2 0 4 P b / Pb Figure 4 2 0 8 Pb/ 2 0 1*Pb - 2 0 6Pb/ 2 0 4,Pb compositions for galena from Manitouwadge, Ontario. Growth curve a f t e r Cooper et. a l . (1969) labeled i n units of b i l l i o n s of years before present. - 17 - Willecho mines form a t i g h t c l u s t e r of values above the growth curve. A section of Figure 4 containing the ore zone leads has been plo t t e d at a more de t a i l e d scale and shows the i s o t o p i c compositions have a l i n e a t i o n along a 2 0 l*Pb error l i n e . A l e a s t square f i t l i n e , a f t e r York (1969) , through the Fox Creek Fault leads i s well defined on this p l o t which seldom shows i s o t o p i c r e l a t i o n s as well as the 2 0 7Pb/ 2 0 l>Pb vs. 2 0 6Pb/2("*Pb p l o t . The anom- alous l i n e i n this Figure 4 diverges even farther away from the ore zone lead composition than i n Figure 3. Problems presented by the i s o t o p i c composition of lead at Manitouwadge to previous interpreters may a s s i s t i n explaining the present r e s u l t s . At the University of Toronto, Russell and Farquhar (1957) made the f i r s t analyses of the lead i s o t o p i c com- p o s i t i o n of galena from Manitouwadge. They found that the lead composition of the main ore zone came from an environment of U-Th-Pb s i m i l a r but not equal to that of many conformable ore deposits. Stanton and Russell (1959) suggested that conformable ore deposits usually have a simple lead i s o t o p i c evolution model while leads from vein type environments have a more complex evolution. Galena leads at Manitouwadge however presented a problem to t h i s hypothesis because they were homogeneous and f i t Stanton's c l a s s i f i c a t i o n f o r conformable ore deposit and yet plotted below the simple - 18 _ model growth curve determined by many younger conformable deposits. Ostic (1963) discovered a highly anomalous lead composition within the Fox Creek Fault at Manitouwadge. This led to the suggestion by Slav/son et. a l . (1963) and Ostic et. a l . (1967) that the Manitouwadge ore zone i s part of an anomalous lead s u i t e d i r e c t l y related to the anomalous leads along the Fox Creek Fault. Ostic regarded the ore zone lead composition to be contaminated s l i g h t l y by anomalous leads s i m i l a r to that found along the Fox Creek Fault. A d i f f e r e n t i n t e r p r e t a t i o n of the lead i s o t o p i c composition at Manitouwadge was made by T i l t o n and Steiger (1965) and T i l t o n and Steiger (1969). Their argument i s s t r a i g h t forward. They postulated that the longer lead i s mobile i n the earth the better are i t s chances to com- bine with leads from other U-Th-Pb systems and so become anomalous. They thought best to base cal c u l a t i o n s of the age of the earth on very ancient lead mineralizations which may have had less chance for contamination. Manitouwadge was chosen as a s i n g l e example of an old mineralization and was combined i n a s i n g l e stage growth equation to c a l c u l a t e the age of the earth. T i l t o n and Steiger r e l y heavily on the observations by Pye (1957) that the ore zone mineralization must have been a f t e r emplacement of the Kenoran in t r u s i v e s which date by Rb-Sr at about 2700 m i l l i o n years. The earths age i s then - 19 - calculated as 4700 m i l l i o n years or about 200 m i l l i o n years older than previously calculated by Ostic et. a l . (1963). I t i s i n t e r e s t i n g to note that T i l t o n and Steiger ignore the possible anomalous nature of the ore at Manitouwadge as postulated by Slawson et. a l . (1963). (1963) and T i l t o n and Steiger (1965) and (1969) i s a difference i n views on the o r i g i n of the main ore zone deposits. The r e s u l t s of t h i s study l i s t e d i n Table 1 and shown on Figure 3 and Figure 4 have a d e f i n i t e bearing on the o r i g i n of the ore at Manitouwadge and may help to cl e a r up the above mentioned differences of opinion. Fault form a l i n e a r array as can be seen i n Figure 3 and Figure 4. The slope of the l i n e determined by these anomalous compositions may be used to determine the l a t e s t times of mineralization along the Fault zone. The times obtained i n t h i s analysis are independent of the number of mixing stages that the lead has gone through, Kanasewich (1962) and Kanasewich (1968). I f a three stage model i s assumed to represent the lead along the Fox Creek Fault and the slope of the anomalous l i n e i s R then: This difference of opinion between Slawson et. a l . The anomalous leads from within the Fox Creek R = 137.8 (e 1 (e X't 2 Xt 2 I f t 3 i s allowed to be zero which would correspond - 20 - to a t 3 mineralization yesterday, i t i s found that for a slope of 0.168±.003, on Figure 3, that tz must be 2580+50 m i l l i o n years. This age which coincides with the Kenoran Orogeny, would be the maximum time for emplacement of the uranium parent of the anomalous leads i n t o the crust. Another time l i m i t to mineralization may be obtained i f t 3 i s allowed to equal t 2 i n the equation above. This gives 1580+40 m i l l i o n years for the t 2 event. This time corres- ponds to the minimum time for uranium emplacement into the crust and i s also a maximum time for a f i n a l t 3 m i n e r a l i z a t i o n . This i n t e r p r e t a t i o n suggests a f i n a l mineralization along the Fault somewhere i n the time between the present and 1580 m i l l i o n years ago. A ge o l o g i c a l l y reasonable time for t h i s mineralization i s 1100 m i l l i o n years ago during the Keweenawan age. During the Keweenawan a vast amount of volcanism occurred i n the Southern Province of the Canadian Shield with a s t r u c t u r a l boundary about 50 miles south of Manitouwadge. Archean t e r r a i n surrounding the Southern Province was also r i d d l e d with dike swarms at t h i s time. Certainly temperatures necessary to mobilize galena solutions existed then, and may have caused mineralization along the Fox Creek Fault. Possibly the Fox Creek Fault i t s e l f i s a r e s u l t of c r u s t a l cooling a f t e r the Keweenawan i n t r u s i v e a c t i v i t y . A large diabase dike supposedly Keweenawan i n age l i e s p a r a l l e l to and 150 feet west of the Fox Creek Fa u l t . - 21 - If t 3 i s placed at 1100 m i l l i o n years, t 2 becomes 2000165 m i l l i o n years. The corresponding Th/U r a t i o for the source region of the anomalous leads i s then calculated as 5.3, Kanasewich (1962) . Some event that we do not know about may have caused the Fox Creek Fault galena mineralization, i n which case the above mentioned times are wrong. I t i s of l i t t l e use to theorize with so many unknowns. The lead i s o t o p i c composition of galena from within the main ore zone at Manitouwadge i s extremely homogeneous as may be seen on Figure 3 and Figure 4. The compositions show a spread along a 20''Pb error l i n e . I t i s not possible to d i s t i n g u i s h a pattern to these sample compositions which come from widely separated points along the ore zone. Galena lead from the main ore zone at the Geco mine i s indistinguishable from Willecho mine galena lead 7 miles ' away. Homogeneity i n lead i s o t o p i c composition i s one of the c h a r a c t e r i s t i c s of a primary lead as observed by Stanton, and Russell (1959) . Another c h a r a c t e r i s t i c of primary lead ores noticed by Stanton and Russell (1959) i s a conformable r e l a t i o n to i t s host rock. The ore zone deposits are d e f i n i t e l y conformable (see Figure 1) within the metasedimentary grey gneiss u n i t . The ore zone leads at Manitouwadge obey, as well as can be discerned, two of the c r i t e r i a of Stanton and - 22 - Russell (1959) for di s t i n g u i s h i n g a primary lead and yet these same leads p l o t well below the primary lead growth curve determined by many younger deposits. Primary growth curves of Ostic et. a l . (1967) and Cooper et. a l . (1969) have 2 3 8U/ 2 0 l*Pb rati o s of 8.94 and 8.79 respectively while the primary model 2 3 8U/ 2 0 1*Pb r a t i o for Manitouwadge i s well below these at 8.23. The ore zone i s o t o p i c composition at Manitouwadge i f "primary" i s c e r t a i n l y d i f f e r e n t from other primary lead systems. It i s not s u r p r i s i n g that T i l t o n and Steiger (1969) should postulate Manitouwadge ore zone lead as a true primary lead and use i t i n a single stage lead growth equation since the ore zone leads do have a gross s i m i l - a r i t y to other primary leads. T i l t o n and Steigers evid- ence for the ore to be 2700 m i l l i o n years old, post Kenoran i n t r u s i o n , i s not strong. Recent observations by Sangster .(1971) on sulphide s t a b i l i t y during metamorphism and observations by S u f f e l et. a l . (1971) of metamorphic textures within the Manitouwadge ore zone suggest a much older age to the ore zone than Kenoran. Therefore the ca l c u l a t i o n by T i l t o n and. Steiger placing the age of the earth at 4700 m i l l i o n years i s based on an age which i s much too young for the ore at Manitouwadge. Ore zone deposits at Manitouwadge are probably of sedimentary o r i g i n , abundant i r o n formation adjacent to the ore suggests a sedimentary environment as w e l l . Possibly the ore deposits r e s u l t from i s l a n d arc, submarine - 23 - volcanic type sources which deposited the volcanic rocks at Manitouwadge. In Figure 3 and Figure 4 as stated previously no difference can be seen between any of the samples taken from along the ore zone except differences due to 2 0 1*Pb error. I t i s apparent also from these Figures that the anomalous Fox Creek Fault leads are not simply re l a t e d to the lead isotope composition of the main ore zone. A two-stage mixing model would require ore zone lead com- p o s i t i o n to p l o t on the projection of the Fox Creek Fault anomalous lead l i n e . In order to r e l a t e these two com- positions g e n e t i c a l l y at l e a s t a three stage lead model must be employed. The ore zone lead composition must have existed within the f a u l t zone p r i o r to anomalous lead mineralization since the f a u l t o f f s e t s the Geco orebody 200 feet north on the eastern side. High l i n e a r i t y of lead isotope compositions from the Fox Creek Fault suggests a mixture of two f a i r l y homogeneous end members therefore, the ore zone lead would have had to be throughly mixed with some anomalous or primary lead and the f i n a l composition would then have to l i e somewhere on the extension of the anomalous lead l i n e . A 4 or 5 stage h i s t o r y of lead growth could be used to r e l a t e the ore zone i s o t o p i c composition to the f a u l t zone but too many unknowns e x i s t to do t h i s . The normalized results of samples analysed from i n and around the Manitouwadge area by Ostic ( 1 9 6 3 ) Doe, - 24 - T i l t o n , and Hopson (1965), Hart and T i l t o n (1966) and T i l t o n and S t e i g e r (1969) are presented i n Table 2. Sample 2 0 6 p b 2 0 7Pb 2 0 8Pb 20 wpb 2 0 tpb 20 '•Pb O s t i c (1963)* 33 2 V 7 i l l r o y mine, galena 13 .311 14. 423 33. 192 369 W i l l e c h o mine, galena 13 .316 14. 425 33. 257 370 Geco mine, galena 13 .319 14. 427 33. 233 372 Fox Creek F a u l t , galena 29 .785 17. 503 46. 883 Doe, T i l t o n and Hopson (1965)t KA 46 Echo T r a i l , Minnesota, f e l d s p a r 13 .572 14. 52 33. 06 KA 82 B i r c h d a l e , Minnesota, f e l d s p a r 13 .44 14. 48 33. 14 KA 249p Cusson, Minnesota, f e l d s p a r 13 .681 14. 58 33. 08 KA 356p Echo T r a i l , Minnesota, f e l d s p a r 13 .44 14. 53 KA 354 Ben I s l a n d , O n t a r i o , f e l d s p a r 13 .51 14. 57 33. 10 Hart and T i l t o n (1966)§ Lake Superior sediment t o t a l sample 20 .53 15. 87 40. 34 a c i d l e a c h 22 .84 16. 34 42. 86 water leac h 22 .48 16. 20 42. 34 T i l t o n and S t e i g e r (1969)t MG 4 8 Geco mine, galena 13 .26 14. 43 33. 39 MG 38 W i l l r o y mine, galena 13 .26 14. 46 33. 38 MG 19 f e l d s p a r 13 .63 14. 57 33. 39 MG 20 f e l d s p a r 13 .82 14. 59 33. 35 MG 41 f e l d s p a r 13 .80 14. 57 33. 35 MG 45 f e l d s p a r 13 .55 14. 64 33. 34 * Normalized to absolute values of Broken H i l l . R u s s e l l (unpublished) 16.009, 15.395, 35.70. t Normalized to absolute values of C.I.T. R u s s e l l (unpublished) 16.586, 15.425, 36.14. § Values not normalized. Table 2 The data from Table 2 above has been combined w i t h the new data reported i n Table 1 and has been p l o t t e d on conventional 2 0 7Pb/ 2 ( M tPb vs. 2 0 S P b / 2 0 " p b and 2 0 8Pb/ 2 0*Pb vs. 2 0 6Pb/ 2 0 l 4Pb plots i n Figure 5 and Figure 6 respectively. In each of these two Figures, only the new analyses for Fox Creek Fault leads reported i n Table 1 were used i n f i t t i n g the l e a s t square l i n e shown. In t h i s respect Figure 3 through Figure 6 are i d e n t i c a l . A sin g l e stage growth curve a f t e r Cooper et. a l . (1969) has been added to each p l o t . In Figure 5 the lead i s o t o p i c values f a l l i n two d i s t i n c t areas. One area i s below the sing l e stage growth curve and has been drawn at a more det a i l e d scale within the f i g u r e . Lead compositions within t h i s area are of two kinds, galena lead and feldspar lead. Galena lead com- positions reported by this study . (see also Figure 3 ) show a d e f i n i t e l i n e a t i o n along a 2 0 l*Pb error line-. Lead compositions for galena reported by Ostic (1963) and T i l t o n and Steiger (1969) do not f a l l s i g n i f i c a n t l y o f f t h i s error l i n e . Intralaboratory differences probably cause the spread of values shown here. The feldspar leads of T i l t o n and Steiger (1969) are from g r a n i t i c rocks and pegmatites associated with the Kenoran Orogeny from around Manitouwadge and from other Kenoran areas of Ontario and Minnesota. The feldspar leads show more scatter than the ore zone leads due to the wide area from which samples were taken, these leads also l i e beneath the growth curve. The second area of Figure 5 l i e s along a l i n e a r array Single Stage Growth Curve \ \ \ \ 1 4 ! 1 1 • 1 < r 1 * 1 — ~~ " I——" — 1 — " ~~~ ~~ * / + CP / * A •/ 204Pb • error line s . . . . . . • 1 1 3.0 1 4.0 Fox Creek Fault galena (This work) Ore Zone galena (This work) Ostic ( 1 9 6 J ) galena Ti Iton & Ste iger (1969) galen Ti Iton & Ste ige r (l 969) and Doe, Tilton & Hopson (1965) feldspar |ead Hart & Tilton (l 9 6 6 ) Lake Superior sediment 14 16 18 20 2 2 2 4 26 2 8 3 0 3 2 206Pb/204Pb F i g u r e 5 2 0 7Pb/ 2 0 1 ,Pb - 2 0 6 P b / 2 0 , , P b compositions of rocks and ores a t Manitouwadg On t a r i o and i t s e n v i r o n s . T h i s f i g u r e shows a l l p e r t i n e n t data t o date - 27 - 33.6 | 1 1 • 1 1 1 ' 1 r 2 0 6 P b / 2 0 4 P b Figure 6 2 0 8Pb/ 2 0*Pb - 2 0 6Pb/ 2 0 ,*Pb compositions of rocks and ores at Manitouwadge, Ontario and i t s environs. This figure shows a l l pertinent data to date. - 28 - of points to the r i g h t of the growth curve. The anomalous lead composition found by Ostic (1963) from the Fox Creek Fault l i e s close to the l i n e defined i n t h i s study. Possibly intralaboratory differences i f known, would bring t h i s composition down to coincide with the l i n e . Lake Superior sediment values of Hart and T i l t o n (1966) f a l l extremely close to the l i n e determined by the Fox Creek Fa u l t galenas. These values of Hart and T i l t o n (1966) have not been normalized to any absolute standard. Figure 6 i s the 2 0 8Pb/ 2 t M lPb vs. 2 0 6Pb/ 2 0 , ,Pb p l o t f o r the combined res u l t s to date on Manitouwadge and shows much the same r e l a t i o n as i n Figure 5. Three areas of lead isotope compositions may be found i n t h i s f i g u r e , one adjacent to the growth curve and two others which form d i s t i n c t l i n e a r arrays. The area adjacent to the growth curve shows the galena values of Ostic (1963), T i l t o n and Steiger (1969) and the new data of t h i s report scat- tered along a 2 0 1*Pb error l i n e . Feldspar leads i n t h i s f i g u r e show s i m i l a r v a r i a t i o n to the feldspar leads plotted on the 2 0 7Pb/ 2 C M tPb vs. 2 0 6Pb/ 2 0*Pb p l o t of Figure 5. Fox Creek Fault lead analysed by Ostic (1963) f a l l s on the l i n e determined by the new analyses although i t was not used to determine the l i n e shown here. In t h i s figure the values of Hart and T i l t o n (1966) from Lake Superior s e d i - ment form t h e i r own l i n e a r array well away from the anom- alous lead l i n e of the Fox Creek Fault samples. The l i n e determined by these sedimentary lead compositions passes - 29 - close to the general lead composition of Archean rocks and ores at Manitouwadge, Fox Creek Fault lead samples may not be at a l l related to the samples of the ore zone. The Geco ore i s primarily copper-zinc, and grades less than one percent lead. I t i s probable therefore that very l i t t l e of the ore zone lead exists i n the Fox Creek Fault zone. The f a u l t at the Geco mine consists of a breccia zone up to 80 feet wide and i s extremely wet underground. Pye (1957) states that post f a u l t p y r i t e , marcasite, and galena mineralization pos- s i b l y related to hot solutions caused by Keweenawan dike i n t r u s i o n has occurred within the f a u l t zone. The author has noticed that large galena c r y s t a l s seem to e x i s t i n the f a u l t zone in v a r i a b l y associated'with c a l c i t e , while ore zone galena c r y s t a l s are normally smaller, more d i s - seminated and associated with s i l i c a t e s or massive sulphides. No v a r i a t i o n of i s o t o p i c composition with depth i n the f a u l t seems to e x i s t . The author prefers a zero c o r r e l a t i o n model between the ore zone leads and the Fox Creek Fault leads analysed to date. The three or more stage mixing model required to r e l a t e the ore zone leads to the f a u l t zone leads appears complex. A complete i s o t o p i c homogenization of lead within the f a u l t zone, p r i o r to a f i n a l anomalous mineral- i z a t i o n as required by a multistage model appears less l i k e l y than a simple mineralization completely unrelated to the ore zone lead i s o t o p i c composition. - 30 - The r e s u l t s of Russell and Farquhar (1957) are of i n t e r e s t here although t h e i r analyses are from an older technological era and cannot be d i r e c t l y compared with any of the newer data presented here. Russell and Farquhar analysed galena from c e r t a i n f a u l t s cutting Keweenawan age rocks around Thunder Bay, Ontario, and found they were anomalous. The anomalous lead i s o t o p i c composition of galena from these f a u l t s formed a l i n e a r array very much the same as the Fox Creek Fault anomalous leads except the slope i s steeper (.186) on a 2 0 7Pb/ 2 0 l*Pb vs. 2 0 6Pb/ 2 0 l ,Pb p l o t . These anomalous leads were not simply rel a t e d to Keewatin type leads analysed by Russell and Farquhar from Steeprock Lake, Ontario, Sioux Lookout, Ontario and from Manitouwadge. This r e s u l t i s s i m i l a r to the new r e s u l t s reported here from within Manitouwadge 1s Geco mine i t s e l f . This s i m i l a r i t y strengthens the argument that the leads along the Fox Creek Fault are related to Keweenawan igneous a c t i v i t y . The r e l a t i o n of the Fox Creek Fault galenas to Keweenawan int r u s i v e s i s supported further by the lead i s o t o p i c composition of a Lake Superior sediment analysed by T i l t o n and Hart (1966). This sediment lead, although not normalized to absolute, plots extremely close to the anomalous l i n e determined by the Fox Creek Fault leads. Lake Superior i s to a large extent underlain and surrounded by Keweenawan i n t r u s i v e and volcanic rocks, Halls (1966 ).. - 31 - Estimates by White' (1966) place the t o t a l volcanic thickness i n parts of Lake Superior at greater than 30,000 feet. The sediment within Lake Superior must be influenced by the huge amounts of Keweenawan rocks around the lakes drainage basin, the s i m i l a r i t y of t h i s sediment lead to the lead along the Fox Creek Fault then may h i n t that f a u l t leads are of Keweenawan o r i g i n . I t would be i n t e r e s t i n g to i n t e n s i v e l y sample the galenas of the f a u l t zone to see i f and where the ore zone galenas might be contaminated with these anomalous leads. A lead i s o t o p i c composition for the Keweenawan volcanics would be of great use, and i n p a r t i c u l a r an i s o t o p i c analysis of lead from the large diabase dike 150 feet west of the Fox Creek Fault would also be i n t e r e s t i n g . A re-analysis of the Keweenawan galenas studied by Russell and Farquhar (1957) would also a s s i s t i n t e r p r e t a t i o n . Isotopic v a r i a t i o n s can possibly be found within s i n g l e c r y s t a l s of galena from within the Fox Creek Fault. I t would be i n t e r e s t i n g to knew whether lead emplaced by mineralizing solutions along the f a u l t have become more or less radiogenic with time; sing l e c r y s t a l studies should answer t h i s . Sulphur isotope studies may possibly show a difference i n source between ore and f a u l t zone galenas. Recent arguments by Richards (1971) and Le Couteur (1973) favour a source for primary lead of conformable ores within the crust i t s e l f . This requires a change of - 32 - view on .the words "primary lead", which i n t h e i r hypothesis i s a well-mixed lead from upper c r u s t a l sources. The simple explanation of a primary lead o r i g i n a t i n g from a homogeneous U-Th-Pb environment i n the mantle to being emplaced in t o the crust does not appear correct any more. They also suggest that connate brines within a sedimentary basin may act as the agent for both removal and p r e c i p i t a t i o n of ore metals and that t h i s brine s o l u t i o n can allow for the great mobility of lead necessary to produce a homogeneous i s o t o p i c composition. Perhaps the ore zone lead at Manitouwadge i s a c t u a l l y a primary lead formed i n a s i m i l a r method to those advanced by Richards (1971) and Le Couteur (1973). Previous interpretations of lead isotopes at Manitouwadge have neglected to state that Manitouwadge i s primarily a copper-zinc deposit with r e l a t i v e l y minor amounts of lead. This small amount of lead makes the. deposit vulnerable to the additions of small amounts of anomalous, multistage lead, early i n the sediments' h i s t o r y . This small smount of lead may also h i n t that the o r i g i n a l crust from which these sedimentary metals were derived was at an early stage i n i t s metallogenic evolution, with few lead minerals. - 33 - 3.2 SUMMARY The lead i s o t o p i c composition of galena from Manitouwadge, Ontario forms two d i s t i n c t populations. Galena leads from the main ore zone have a remarkably uniform lead isotope composition while galenas from within the Fox Creek Fault form an anomalous l i n e a r array of lead isotope compositions. Lead i s o t o p i c compositions of galena from the Fox Creek Fault form an anomalous lead l i n e on a standard 20 7 p b / 2 0 - p b v s > 2 0 6 p b / 2 0 i * p b p l Q t a n d a 20 8 p b / 2 0 H p b V £ , # 2 0 6Pb/ 2 0*Pb p l o t . Time l i m i t s obtained from the slope of the anomalous l i n e place 2580+50 m i l l i o n years as the maximum age of emplacement for the uranium parent of the anomalous leads into the crust. The minimum time for uranium emplacement i s 1580+40 m i l l i o n years which i s also a maximum time for f i n a l lead mineralization along the Fox Creek Fault. The l a s t g e o l o g i c a l l y reasonable time for galena mineralization along the Fault i s during the Keweenawan age, 1100 m i l l i o n years ago. Using t h i s time for f i n a l galena mineralization requires an age of 2000 m i l l i o n years for the time of uranium emplacement into the crust. The corresponding Th/U r a t i o f or the source of the anomalous component of leads along the Fox Creek Fault i s 5.3. Possibly the Fox Creek Fault i s i t s e l f a r e s u l t of Keweenawan igneous i n t r u s i v e a c t i v i t y . - 34 - The lead i s o t o p i c composition of lead i n galena sampled from the main ore zone does not show any l i n e a r trend, other along a 2 0 l*Pb error l i n e , that might support an argument to c l a s s i f y them as anomalous leads. The lead i s o t o p i c composition from the main ore zone plots below the single stage lead growth curve of Cooper et. a l . (1969) determined by many younger primary lead deposits. I t i s not yet resolved whether the ore zone leads are actu a l l y primary or anomalous. The ore deposits are probably much older than the 2700 m i l l i o n year age postulated by Pye (1957) and T i l t o n and Steiger (1969). Metamorphic textures i n the ores as observed by S u f f e l et. a l . (1971) support t h i s idea. Ore only occurs within metasedimentary rocks which does not appear to support a Kenoran Orogenic age of the ore as required by T i l t o n and Steiger (1969) . Possibly the ores are the r e s u l t of submarine volcanism and were deposited as a sediment i n an ancient ocean. Possibly a c r u s t a l averaging process s i m i l a r to those described by Richards (1971) and Le Couteur (1973) formed the ores at Manitouwadge. The ore zone lead isotope composition i s not related i n a simple fashion to the lead isotope composition along the Fox Creek Fault. At l e a s t a three stage mixing model i s required to r e l a t e ore zone leads to Fault zone leads. I t i s very possible that Fox Creek Fault leads sampled to date are not at a l l related to ore zone leads - 35 - since less than one percent of the ore i s lead at the Geco mine. Detailed studies of lead isotopes i n the Fox Creek Fault would be i n t e r e s t i n g . I t should be possible to f i n d ore zone leads contaminated by anomalous leads i n or near the Fault. Single c r y s t a l lead i s o t o p i c variations can possibly be measured from Fox Creek Fault galenas. I t would be i n t e r e s t i n g to know whether mineralizing solutions along the Fault have become more or less radiogenic with time. Lead isotope determinations of the large diabase dike 150 feet west of the Fox Creek Fault have not been done and are suspected by the author to be very s i m i l a r to the Fox Creek Fault leads. Sulphur isotope studies may be able to d i s t i n g u i s h between ore and f a u l t zone leads. - 36 - REFERENCES B l e n k i n s o p , J . (1972) . Computer-assisted mass spectrometry and i t s a p p l i c a t i o n t o r u b i d i u m - s t r o n t i u m geo- chronology. Unpublished Ph, D. t h e s i s , U n i v e r s i t y o f B r i t i s h Columbia. Brown, W. L. and Bray, R. C. E. and Mine S t a f f (1960) . The geology of the Geco mine. Can. Min. and Met. B u l l . , 63, 1. Catanzaro, E. J . , and Gast, P. W. (1960). I s o t o p i c com- p o s i t i o n o f l e a d i n pegmatite f e l d s p a r s . Geochim. Cosmochim. A c t a , 19, 113. Catanzaro, E. J . , Murphy, R. J . , S h i e l d s , W. R., and Garner, E. L. (1968). Absolute i s o t o p i c abund- ance r a t i o s of common, equal atom and r a d i o g e n i c l e a d i s o t o p e s s t a n d a r d s . J . Res. Nat. Bur. Stand., 72A, 261. Chown, E. H. M. (1957). Geology of the W i l l r o y P r o p e r t y . Unpublished M. A. Sc. t h e s i s , U n i v e r s i t y of B r i t i s h Columbia. Composton, W., and Oversby, V. M. (1969). Lead i s o t o p i c a n a l y s i s u s i n g a double s p i k e . J . Geophys. Res., 74, 4 338. Cooper, J . A., Reynolds, P. H., and R i c h a r d s , J . R. (1969) Double s p i k e c a l i b r a t i o n o f the Broken H i l l s t a n d a r d l e a d . E a r t h P l a n e t a r y S c i . L e t t e r s , 6, 46 7. D a l i w i t z , M. J . (1969). F r a c t i o n a t i o n c o r r e c t i o n s i n l e a d i s o t o p i c a n a l y s i s . Chemical Geology, 6, 311. Dodson, M. H. (196 3 ) . A t h e o r e t i c a l study of the use o f i n t e r n a l standards f o r p r e c i s e i s o t o p i c a n a l y s i s by the s u r f a c e i o n i z a t i o n t e c h n i q u e . J . S c i . Instrum., 40, 289. Doe, B. R., T i l t o n , G. R., and Hopson, C. A. (1965). Lead i s o t o p e s i n f e l d s p a r s from s e l e c t e d g r a n i t i c rocks a s s o c i a t e d w i t h r e g i o n a l meta- morphism. J . Geophys. Res., 70, 1947. G o l d i c h , W. W., N i e r , A. D. , Baadsgaard, H., Hoffman, J . II., and Krueger, H. W. (1961). The Precambrian geology and geochronology of Minnesota. Minn. Geo l . Survey B u l l . 41, 193p. - 37 - Graham, R„ A. F. (1967). Metamorphism of Willroy sulphide ore minerals by diabase dikes . Unpublished M. Sc, th e s i s , Univ. of Western Ontario. H a l l s , H. C. (1966). A review of Keweenawan Geology of the Lake Superior region. In: The earth beneath the continents, Am. Geophys. Union Geophys. Mon. Ser., No 10, 3. Hamilton, E. I. (1965). Applied Geochronology Academic Press, London - New York, 267p. Hanson, G. M., Goldich, S. S., Arth, J . G., and Yardley, D. H. (1971). Age of early Precambrian rocks of the Saganaga Lake—Northern Light Lake Area, Ontario—Minnesota. Can J . Earth S c i . , 8, 110. Hart, S. R., and T i l t o n , G. R. (1966). The isotope geo- chemistry of strontium and lead i n Lake Superior sediments and water. In: The earth beneath the continents, Am. Geophys. Union Geophys. Mon. Ser., 10 127. Kanasewich, E. R. (1962). Approximate age of tectonic a c t i v i t y using anomalous lead isotopes. Roy. Astron. Soc. Geophys. J . , 7, 15 8. Kanasewich, E. R. (1968). The i n t e r p r e t a t i o n of lead isotopes and t h e i r geological s i g n i f i c a n c e . In: Radiometric Dating for Geologists., Hamilton, E. I. and Farquhar, R. M. (eds.). Kraus, K. A. and Nelson, F. (1955). Anion exchange studies of f i s s i o n products. Proceedings International Conference on the Peaceful Uses of Atomic Energy. 7, United Nations, New York. Le Couteur, P. C. (1973). A study of lead isotopes from Min Mineral Deposits from Southeastern B r i t i s h Columbia and from the A n v i l Range, Yukon Te r r i t o r y , Unpublished Ph. D. t h e s i s , University of B r i t i s h Columbia. Mookherjee, A. (1970), Dykes, sulphide deposits and regional metamorphism: C r i t e r i a for determining t h e i r time r e l a t i o n s h i p . Mineral Deposita 5 pp. 120 - 144. Mookherjee, A. and Dutta, N. K. (19 70). Evidence for • i n c i p i e n t melting of sulphides along a dike contact, Geco mine, Manitouwadge, Ontario. Economic Geol., 65, 706. - 38 - Ostic, R. G. (1963). Isotopic i n v e s t i g i a t i o n of conformable lead deposits. Ph. D. Thesis, University of B r i t i s h Columbia. Ost i c , R. G., Russell, R. D., and Reynolds, P. H. (1963). A new c a l c u l a t i o n for the age of the earth from abundances of lead isotopes. Nature, 199, 1150. Ostic, R. G., Russell, R. D., and Stanton, R. L. (1967). Additi o n a l measurements of the i s o t o p i c composition of lead from strataform deposits. Can. J . Earth S c i . , 4,245. Pye, E. G. (1957). Geology of the Manitouwadge area. Ontario Dept. Mines Report, 66, 8. Richards, J . R. (1971). Major lead orebodies—Mantle Origin? Economic Geol., 66, pp. 425 - 434. Russell, R. D. and Farquhar, R. M. (1960). Lead Isotopes i n Geology, Interscience, New York. Russell, R. D. and Farquhar, R. M. (19 57). Anomalous leads from the upper Great Lakes region of Ontario. Transactions, Am. Geophys. Union 38, 552. Russell, 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 aeological research. Mass Spectroscopy, 19, 19. Russell, R. D. (1972). An evolutionary model for lead isotopes i n conformable ores and i n ocean vol c a n i c s . Rev. Geophys. and Space Phys. 10,529. Sangster, D. F. (1971). Metamorphism as an ore-forming process. Economic Geol., 66, 499. Slav/son, W. F., Kanaswich, E. R., Ostic, R. G., and Farquhar, R. M. (1963). Age of the North American crust. Nature, 200, 413. Stacey, J . S., Delevaux, M., and Ulrych, R. J . (1969). Some t r i p l e - f i l i m e n t lead siotope r a t i o measure- ments and an absolute growth curve for sing l e stage leads. Earth Planetary S c i . L e t t e r s , 6, 15. - 39 - S u f f e l , G. G., Hutchinson, R. W., and Riddler, R. H. (1971). Metamorphism of massive sulphides at Manitouwadge, Ontario, Canada. In: Soc. Mining Geol. Japan Spec. Issue 3, 235. T i l t o n , G. R. and Steiger, R. H. (1965). Lead isotopes and the age of the earth. Science, 150, 1805. T i l t o n , G. R. and Steiger, R. H. (1969). Mineral ages and i s o t o p i c composition of primary lead at Manitouwadge, Ontario. J . Geophys. Res., 74, 2118. Timrcs, P. D. and Marshall, D. (1959). The geology of the Willroy mines base metal deposits. Proc. Geol. Assoc. Canada, 11, 55. Ulrych, T. J . (1967). Oceanic basalt leads: A new i n t e r - pretation and an independent age for the earth. Science, 158, 252. White, W. S. (1966). Geologic evidence for Crustal structure i n the Western Lake Superior basin. In: The earth beneath the continents. Geophys. Mon. Ser., Am. Geophys. Union, 10, 28. Williamson, J . H. (1968). Least squares f i t t i n g of a s t r a i g h t l i n e . Can. J . Phys., 46, 1845. York, D. (1969). Least squares f i t t i n g of a s t r a i g h t l i n e with correlated e r r o r s . Earth Planetary S c i . L e t t e r s , 5, 320. York, D. and Farquhar, R. M. (1972). The Earths Age and Geochronology. Pergamon Press, Toronto. - 40 - APPENDIXES A. Ion exchange column p r e p a r a t i o n This i s a procedure suggested by Dr. U l r y c h at t h i s l a b , which i s modified from a procedure given i n Catanzaro and Cast (1960) . Figure A - l shows t h i s procedure. The m a t e r i a l s necessary f o r t h i s procedure are dowex (1x8, 100-200 mesh) r e s i n i n c h l o r i d e form, an i o n column, 1,5 molar reagent grade h y d r o c h l o r i c a c i d , and pure d i s t i l l e d water. The f i n e p a r t i c l e s were removed from about 100 grams of the r e s i n by mixing i t w i t h 100 m i l l i l i t e r s of 1,5 molar h y d r o c h l o r i c a c i d and pouring o f f the f i n e slower s e t t l i n g p a r t i c l e s . This was repeated about three times to remove most of the f i n e r e s i n p a r t i c l e s . A s l u r r y of r e s i n and 1.5 molar h y d r o c h l o r i c a c i d was then poured i n t o a c l e a n g l a s s i o n column and allowed t o s e t t l e to form a 28 to 29 centimeter le n g t h of r e s i n i n the column. The excess r e s i n was c a r e f u l l y poured out of the column. About 200 m i l l i l i t e r s of d i s t i l l e d water was then allowed to pass through the column fo l l o w e d by about 100 m i l l i l i t e r s of 1.5 molar h y d r o c h l o r i c a c i d . This prepares the r e s i n before i n t r o d u c t i o n of lead c h l o r i d e i n t o the column. Lead c h l o r i d e was d i s s o l v e d to s a t u r a t i o n i n 100 F I G U R E A - l SAMPLE PREPARATION FLOW CHART discard silicates 8 other sulphides STORE CRYSTALS ROCK S A M P L E goiena precipitate PbCl crystals decant liquid 4 wash crystals 1 R I N S E A L C O N O X + H 2 0 BATH 10% H N 0 3 BATH RINSE prepare column for new sample ION EXCHANGE COLUMN OOWEX IX 8 DESORB with pure H , 0 precipitate PbCl crystals DI RTY GLASSWARE S T O R E convert to P b [ N 0 3 ] 2 crystalline P D [ N 0 3 ] J in 20ml. I M . H N O , TAKE -003gm. Pb[N0 3 ] 8 + |Oml . 2(%) H N O j — SAMPLE READY LOAD F ILAMENT - 42 - m i l l i l i t e r s of 1„5 molar h y d r o c h l o r i c a c i d , and was poured i n t o the column. Lead ions would be s p l i t w i t h i n the r e s i n from c h l o r i n e and would adhere to the r e s i n . A f t e r t h i s a d s o r p t i o n phase the lead ions may be desorbed completely from the r e s i n i n e i t h e r 0 molar or 8 molar h y d r o c h l o r i c a c i d . For t h i s study 0 molar h y d r o c h l o r i c a c i d ( d i s t i l l e d water) was used f o r d e s o r p t i o n . The f i r s t 10 to 15 m i l l i l i t e r s of s o l u t i o n from the i o n column during d e s o r p t i o n w i t h d i s t i l l e d water does not c o n t a i n an a p p r e c i a b l e c o n c e n t r a t i o n of l e a d . The r e s u l t s of a short t e s t f o r lead i s given i n Table A - l . Approx. Time (minutes) Volume (ml.) pH Potassium Iodide Test 10 10 3.5 negative 20 20 3.5 p o s i t i v e 30 30 4.5 s l i g h t p o s i t i v e 40 40 5.0 negative Table A - l The second 20 m i l l i l i t e r s of s o l u t i o n u s u a l l y contains a high c o n c e n t r a t i o n of lead as determined by the potassium i o d i d e t e s t . Only t h i s concentrated lead s o l u t i o n was c o l l e c t e d . The column a f t e r l e a d d e s o r p t i o n i s then e l u t e d w i t h 200 m i l l i l i t e r s of pure d i s t i l l e d water f o l l o w e d by 100 m i l l i l i t e r s of 1.5 molar h y d r o c h l o r i c a c i d and the column i s ready f o r another sample. Care must be taken to wash the - 43 - sides of the column reservoir i n the d i s t i l l e d water phase to avoid contamination between samples. A t e s t was made for contamination between samples by passing a radiogenic Fox Creek sample through the ion column immediately p r i o r to Broken H i l l . The values for Broken K i l l were not affected as shown i n Table A-2. Column #1 Date Sample 2 0 6Pb "2 0 4 p b 2 0 7Pb 2 0 8Pb 2 0 "»Pb Feb. 28, 1972 786 Fox Creek Fault 32.10 17.893 50.52 Mar. 1, 1972 001 Broken K i l l 16.004 15.358 35.52 001 Broken H i l l (Russell) 16.009 15.395 35.70 001 Ave. of 6 15.991 15.367 35.58 Table A-2 - 44 - B. S i l i c a gel - Lead n i t r a t e loads The materials necessary for a s i l i c a gel lead n i t r a t e load are l i s t e d below: - outgassed rhenium filament - lead n i t r a t e s o l u t i o n ^ 300 p.p.m. i n 2% HN03 - clean pipettes - s i l i c a gel s o l u t i o n - phosphoric acid (reagent grade), 0.375 N. - filament block - a.c. current generator (1 watt peak power)" - a.c. voltmeter and ammeter The following procedure worked well i t was found, but variants on t h i s procedure may work as w e l l . The s i l i c a gel solution-suspension was agitated b r i s k l y and then l e f t to stand q u i e t l y for one to two minutes. A large drop was then removed with a clean pipette and placed on the filament. The filament was then heated slowly by passing an a l t e r n a t i n g current through i t of less than 1.0 ampere keeping a voltage of about 0.2 v o l t s . Best r e s u l t s occur at t h i s point i f the s i l i c a gel i s not allowed to lose a l l i t s water; heating was stopped when a translucent gel was v i s i b l e on the filament. One medium s i z e drop of lead n i t r a t e was then placed on the filament followed by a small drop of phosphoric acid, 0.375 N. The excess l i q u i d was evaporated from the filament with further heating at 1.0 amp, 0.2 v o l t s u n t i l the translucent gel mass appeared on the filament. I f a f a i r amount of s i l i c a gel was present on the filament then further heating could proceed. Often a small "capping" drop of gel was placed on top at t h i s stage to ensure enough g e l . The filament was next brought rapidly to a glowing red heat (about 1,8 amperes and 0.6 volts) for about 20 seconds and then allowed to cool. The mixture of g e l f lead n i t r a t e and phosphoric acid should turn white with i n i t i a l heating and may give o f f white smoke for a time. The sample i s now ready to be placed into the source assembly of the mass spectrometer. C. P r e c i s i o n and Double S p i k i n g R e p l i c a t e analyses of galena lead from Broken H i l l , the U.B.C. standard, are given i n Table C - l and shows good p r e c i s i o n . D i f f e r e n c e s between these values and absolute values f o r Broken H i l l as reported by Cooper e t . a l . (1969) or R u s s e l l (unpublished data) are not s i g n i f i c a n t to m a t e r i a l presented i n t h i s t h e s i s . Run 2 0 6Pb 2 0 7Pb 2 0 8Pb 2 0 X pb 20 <*Pb 2 0 i* pb 1 15.998 15.379 35.65 2 15.978 15.363 35.58 3 15.991 15.368 35.63 4 15.977 15.360 35.58 5 16.000 15.376 35.55 6 16.004 15.358 35.52 Mean 15.991 15.367 35.58 Standard E r r o r .005 .004 .019 Cooper e t c a l . 1969 16.003 15.390 35.66 R u s s e l l (unpublished) 16.009 15.395 35.70 Table C - l C a l i b r a t i o n of the U.B.C. 2 0 7 F b - 2 0"Pb double s p i k e was done agai n s t the N.B.S. equal atom standard S.R.M. 982 and i s shown i n Table C-2 below. The small f r a c t i o n a t i o n c o r r e c t i o n s shown i n Table C-2 are normal f o r s i l i c a gel-phosphoric a c i d procedures. - 47 - 2 0 6 p b 2 0 4Pb 2 0 7Pb 2 0 wpb 20 8 p b ToTpb Measured R a t i o Spike Corrected R a t i o .2765 .2766 9.512 9.520 .6049 .6065 Measured Ratio Spike Corrected R a t i o .2782 .2785 9.505 9.521 .6061 .6075 Average Corrected Ratio .2775 9.520 .6070 Table C-2 The r e s u l t s from double s p i k i n g tvzo Manitouwadge samples are shown i n Table C-3. Spike c o r r e c t i o n s seen here are not s i g n i f i c a n t to the iso t o p e d i f f e r e n c e s s t u d i e d i n t h i s t h e s i s and so have been ignored. Sample 2 0 6Pb 2 0 <*pb 2 0 7Pb 2 0 i* Pb 2 0 8Pb 2 0 4Pb 789 Measured R a t i o Spike Corrected R a t i o % d i f f e r e n c e 13.195 13.205 .08 14.377 14.393 0.11 32.96 33.01 0.15 786 Measured Ratio Spike Corrected R a t i o % d i f f e r e n c e 32.10 32.14 0.12 17.868 17.906 0.16 50.49 50.63 0.28 Table C-3

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