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A study of ore and rock specimens from the Nkana mine, Northern Rhodesia Barker, Reginald Anthony 1951

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L£b hi  A STUDY OF ORE AND ROCK  '  Cap •  I  SPECIMENS FROM THE NKANA MINE, NORTHERN RHODESIA by  REGINALD ANTHONY BARKER  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE  i n t h e Department of GEOLOGY AND GEOGRAPHY  We a c c e p t t h i s t h e s i s as conforming t o t h e standard required  from c a n d i d a t e s f o r t h e  degree o f MASTER OF APPLIED SCIENCE.  Members o f t h e Department o f Geology.  THE UNIVERSITY OF BRITISH COLUMBIA May, 1951.  May 15,  1951.  Dr. H. C. Gunning, Head, Department of Geology and Geography, University of B r i t i s h Columbia, Vancouver, B. C.  Dear S i r : I take great pleasure i n submitting the following thesis, "A Study of Ore and Rock Specimens from the NKana Mine, Northern Rhodesia' , i n p a r t i a l fulfilment of the requirements of 1  the course leading to the degree of Master of Applied Science i n Geology at the University of B r i t i s h Columbia. Yours t r u l y .  R. A. BARKER  ABSTRACT  The ore and rock specimens which form the material f o r t h i s study are a c o l l e c t i o n sent by Mr. T. D. Guernsey, geologist for the Rhokana Corporation, Northern Rhodesia, to Dr. H. C. Gunning of t h i s Univ e r s i t y under whose d i r e c t i o n the present work was done. Owing to the lack of previous detailed work a microscopic investigation i s undertaken with no p a r t i c u l a r problem i n view, but with the hope that the accumulation of f a c t u a l evidence may  aid i n c l a r i f y i n g  the geological problems which have led to a d i v e r s i t y of opinion regarding the o r i g i n of these deposits. An h i s t o r i c a l sketch and a b r i e f d e s c r i p t i o n of the geological setting of the Rhodesian copper deposits i s given.  This information has  a l l been gathered from the available l i t e r a t u r e on the subject. acter and mineralogy  The  char-  of the ore deposits and relations to t h e i r northward  extensions i n Katanga, Belgian Congo are summarized. Descriptive notes, with interpretative remarks, of the l i t h o logy and ore mineralogy  of the NKana 'Ore Horizon' as determined by a  study.of the 38 specimens and over 30 t h i n sections, constitute a major portion of the paper. General theories of ore genesis and supporting g e o l o g i c a l evidences are summarized for the purpose of c l a r i f y i n g the issues i n v o l ved and to help i n the erection of a theory f o r the Rhodesian copper deposits.  Extant theories regarding these deposits are outlined and an  analysis and synthesis of the evidence gathered i n t h i s .investigation i s presented.  The framework of an epigenetic theory i s constructed but  mention i s made t h a t a m e t a - s y n g e n e t i c (metamorphic-sedimentary) o r i g i n f o r these d e p o s i t s i s a p o s s i b i l i t y . S u g g e s t i o n s f o r f u r t h e r r e s e a r c h both i n the f i e l d and i n the l a b o r a t o r y are g i v e n i n the hope t h a t t h e y may d i r e c t i o n t o subsequent i n v e s t i g a t i o n s .  i n some way  lend  TABLE OF CONTENTS  t  Page INTRODUCTION  1  HISTORICAL SKETCH  4  PHYSICAL FEATURES  •  6  GEOLOGICAL SET-TING  - - 8  SEQUENCE OF EVENTS  16  THE ORE DEPOSITS  18  The Ores Comparison of the Rhodesia and Katanga Deposits  20 _____  - - 22  DESCRIPTIONS OF SPECIMENS FROM THE 'ORE HORIZON' AT NKANA MINE  23  DETAILS OF ORE MINERALOGY AT NKANA MINE . 39 ORIGIN OF THE ORES General Theories of Ore Emplacement 46 Geological Evidence - - - - - - ___ -48 A B r i e f R e c a p i t u l a t i o n of Theories of O r i g i n of the Northern Rhodesian Copper Deposits - - 49 Evidence gathered i n t h i s Study - - _ _ _ - _ - _ 51 ' Summation and Suggestions f o r Further Research - - - - - - - - - - - - - - - - - - -55 Concluding Remarks - - - - - - - - _ _ _ _ .59 BIBLIOGRAPHY 1  60 ILLUSTRATIONS  Figure I  _ Location Map  Figure I I - Geological Map Figure I I I - Cross-section - NKana Mine  4a 8a 18a  INTRODUCTION  The ore and r o c k specimens which form the m a t e r i a l f o r t h i s study were s u p p l i e d by Mr. T. D. Guernsey, g e o l o g i s t f o r the Rhokana C o r p o r a t i o n , N o r t h e r n  Rhodesia.  This c o l l e c t i o n ,  comprising  r e p r e s e n t a t i v e s o f the v a r i o u s l i t h o l o g i c u n i t s o f the 'Ore  Horizon'  at  NKana Mine, c o n t a i n s 3# i n d i v i d u a l samples: a t l e a s t two  specimens  of  each type  o f ore a r e p r e s e n t . I t was i n d i c a t e d by Mr. Guernsey t h a t a l t h o u g h  the NKana  Mine had been i n o p e r a t i o n f o r a number o f y e a r s , no d e t a i l e d s t u d i e s of  the ores had been made.  A c a r e f u l search o f the a v a i l a b l e l i t e r -  a t u r e r e v e a l e d t h a t although much work had been done and much had been w r i t t e n d u r i n g the f i r s t y e a r s  ( c a . 1930)  o f the development o f these  d e p o s i t s , n o t h i n g had been p u b l i s h e d i n r e c e n t y e a r s . t h e r e f o r e , t h a t a g e n e r a l study o f these  I t was  felt,  specimens might a i d i n the  -2-  e l u c i d a t i o n of the problem o f g e n e s i s o f t h e copper ores o f one most important  copper d i s t r i c t s i n the I t was  of the  world.  r e a l i z e d t h a t the l a c k o f i n t i m a t e knowledge o f  these d e p o s i t s on the p a r t o f the w r i t e r and the members o f the  Depart-  ment o f Geology a t t h i s U n i v e r s i t y would p r o v i d e a s e r i o u s l i m i t a t i o n to  the g e n e r a l i n t e r p r e t a t i o n of the i n f o r m a t i o n g a i n e d d u r i n g the i n -  v e s t i g a t i o n and the c o r r e l a t i o n o f t h i s i n f o r m a t i o n w i t h t h a t g a i n e d the f i e l d  by o t h e r w r i t e r s . No  of  in  s p e c i f i c problem was  c o n s i d e r e d as the immediate .object  the study a t the o u t s e t , because i n f a c t no s p e c i a l problem was  once a p p a r e n t .  There had  been and  at  s t i l l i s a d i v e r s i t y of o p i n i o n r e -  g a r d i n g the o r i g i n o f the copper d e p o s i t s , but because o f t h e i r s i z e c o n t i n u i t y t h e r e has been no p r a c t i c a l n e c e s s i t y f o r a f u l l of  t h e i r mode o f o r i g i n .  c h a l l e n g e and  a fertile  and  understanding  However, the d e p o s i t s p r o v i d e a t once both field  a  o f i n v e s t i g a t i o n t o the students o f ore  genesis. Because o f the d i s s e m i n a t e d  nature  o f the ore i t was  t h a t t h i n s e c t i o n s and the p e t r o g r a p h i c microscope o f f e r e d the means o f s t u d y i n g both the ores and the host r o c k s . t h i r t y t h i n s e c t i o n s and  felt  best  Consequently,  s e v e r a l p o l i s h e d s e c t i o n s were prepared  over  f o r ex-  amination. The  study was  conducted under the d i r e c t i o n o f Dr. H.  Gunning, t o whom the c o l l e c t i o n o f specimens o r i g i n a l l y had To him and  the w r i t e r wishes t o extend  encouragement tendered  C.  been s e n t .  h i s warmest a p p r e c i a t i o n f o r a d v i c e  throughout the course  o f i n v e s t i g a t i o n . Other  -3-  members o f t h e Department o f Geology were e x t r e m e l y h e l p f u l both d i r e c t l y and i n d i r e c t l y .  To D r s . L . Dolar-Mantuani and K. C.  McTaggart p a r t i c u l a r l y t h e w r i t e r  extends g r a t e f u l acknowledgement  f o r many h e l p f u l s u g g e s t i o n s and s i n c e r e l y r e g r e t s  t h a t the l i m i t a t i o n  o f time made i t i m p o s s i b l e t o undertake a l l t h e p o s s i b i l i t i e s f o r i n vestigation.  Acknowledgement i s a l s o made o f t h e work o f Mr. J . A.  Donnan who prepared a l l the t h i n s e c t i o n s  used i n t h e s t u d y .  HISTORICAL SKETCH The Rhodesian Copper Belt parallels the northeastern border of Northern Rhodesia (see F i g . l ) and, together with i t s northern extensions i n the Province of Katanga i n the Belgian Congo, forms the most important single copper d i s t r i c t i n the world. The d i s t r i c t has come into such prominence since the turn of the present century.  Earliest production came from the deposit at BWana  MKubwa which had been known and worked by the natives before the advent of the white man.  Production here was sporadic during and after World  War I and i t was not u n t i l the 1920's that B r i t i s h and American i n t e r ests, provided with prospecting rights over large areas, f i r s t realized the magnitude and importance of the Rhodesian deposits. In an upland country, f a i r l y heavily wooded and with very deep regolith, the surface expression of these enormous deposits was p r a c t i c a l l y non-existant; no great copper stained outcrops or gossans advertised the extent and teaor of the copper-bearing sediments, ,, though i t was early noted that straight treeless avenues through the forest ("copper dambds") indicated the presence of hidden copper. Because of f a i r l y simple structural conditions i t was not long before wide-spaced d r i l l holes had, at a number of places, outlined large and r i c h orebodies, and production commenced i n the early 1930's. Since then the eight proved deposits, consolidated into four operating units, Roan Antelope, Rhokana, NChanga, and M u f i l i r a , have rapidly assumed a position as the greatest single copper d i s t r i c t i n the world as the following figures of reserves amply i l l u s t r a t e .  Mine or D i s t r i c t  Percent Copper  Rhokana Nkana North Orebody Nkana South Orebody Mindola Orebody Totals  s  3.23 2.78 3.67  Reserves (millions of tons)  3.37  33 20 57  Roan Antelope  3.26  95  NChanga  4.66  141  Mufulira  3.85  148 3.86  Totals (Note:  110  494  These figures are taken from the Minerals Yearbook-1948, and estimates have probably increased since then.) Total annual production of copper from these mines i n recent  years has been about  350,000  short tons. With the expansion of treat-  ment f a c i l i t i e s and improvement i n r a i l and labour conditions this figure w i l l doubtless show a considerable increase within the next few years.  -6-  PHYSICAL FEATURES The copper region l i e s i n a part of the Central African Plateau. This f a i r l y recently uplifted peneplane stands at an elevation of about 4,000 feet and i t s gently undulatory surface i s modif i e d by shallow stream depressions and occasional monadnocks of older crystalline rocks.  Relief i s nowhere greater than 1000 feet.  Forests cover the land but these consist of f a i r l y widely spaced trees with scanty intervening underbrush. Accordingly, crosscountry travel i s r e l a t i v e l y simple. Outcrop i s scarce since the products of-decomposition  and  disintegration have accumulated as a deep regolith; i n many places the s o i l and clay residuum reaches- depths of from 25 to 35 feet, grading downwards into badly decomposed rock.  S o i l cover over easily weathered  gabbros and dolomites reaches 100 feet. Though lying close to the equator the region, because of i t s elevation, enjoys a very pleasant climate. R a i n f a l l of 40 to 50 inches comes between November and A p r i l while i n the dry season (winter) sunshine prevails and the nights are cool. The Rhodesian copper belt i s drained by the Kafue River and i t s tributaries, a part of the Zambesi system. Bateman (1930)" " states 1  that the Kafue apparently follows i t s pre-uplift course and crosses the region without regard to hardness ot structure of the underlying rocks. As seen i n Figure 1 the drainage has developed a dendritic pattern and there are many swamps, particularly at the headwaters of tributary streams. 1. Figures i n parentheses refer to the bibliography at the end of this paper.  - 7 -  The boundary between Northern Rhodesia and the province of Katanga i n the Belgian Congo follows the very low divide between the Kafue and Congo drainages.  -8-  GEOLOGICAL SETTING (Fig.2) The copper ores are found i n a group of sedimentary rocks appearing now as synclines which s t r i k e , and plunge s l i g h t l y , i n a northwesterly direction.  In Rhodesia the anticlines have been removed  during peneplanation, but northwards i n Katanga where the folding was more intense, the folds are expressed topographically as successions of nearly p a r a l l e l strike ridges. Bateman's interpretation of the region i s given below (Bateman,- 1930, p.414): "The Rhodesian section with i t s simple open folds and minor faulting represents the eroded f o o t h i l l region of an ancient mountain structure. The Katanga section l i e s nearer the axis of this old mountain range, of which only the roots are l e f t . Here the folds are closed and overturned; faults are numerous; and successive nappes of older strata of the Serie des Mines formation are thrust above the younger Kundelungu beds". Anton Gray (Gray, 1930) correlated the copper-bearing sediments of Katanga and Rhodesia and proposed a nomenclature for the sedimentary Systems of the region.  The table below follows that of Gray  (1930, p.788) but includes intrusive rocks as given by Bateman (1930), Jackson (1932(2)), and Gray (1932)  O  "  G  REFERENCE  Q  |  |  u ><Ff  Middle  \ B*iana  Mkubrsa  Series  Lower- . '*a".  ore  horizons,  boulder  Qasernant  conglomerate  rocks  Qabbro •  ) ,•  •  *>  |~~~>- I  Granite Geological  CX-^ MUSI  boundaries  '~  C. <j COLO  G I (-A.L.  C D£PT  /^f.  LT NCHANC,A  OMlfJf  THE NORTHERN RHODESIAN COPPER BELT REDUCED FROM R.C.B.C. COMPILATION SHEET. Drawn Date  by O W M 30juf*B -i. I lo  Cop  500,000  ie  -c.-  TABLE OF FORMATIONS Katanga-Rhodesia Copper Belt  Permiar LJixrass: C  LUBILASH (Karoo) Unconformity ACID AND BASIC INTRUSIVES - Gabbro and diabase s i l l s and dykes - Younger Grey Granite - Younger Red Granite (NChanga)  iably Pre-C a  s  o  SYSTEM OF KATANG Serie kundelungi Mine,  UPPER KUNDELUNGU LOWER KUNDELUNGU  <u  to  0)  T3  MWASHIA UPPER ROAN  m  LOWER ROAN Unconformity  o  •otero2  •rl O  Archear  -op  GRANITIC INTRUSIVES - Muliashi porphyritic granite and gneiss - Older Grey Granite (MKushi gneissoid granite) (MKushi Granite-Gneiss) - Older Red Granite (NChanga) MUVA SYSTEM Unconformity  ...  LUFUBU SYSTEM (BASEMENT SCHISTS)  -10-  The following short descriptive notes on the rock units are taken from a number of authors, particularly from Jackson (1932(2)). LUFUBU SYSTEM  (BASEMENT SCHISTS)  These ancient metamorphosed sediments, now micaceous and c h l o r i t i c schists, are probably Archean i n age.  Their base i s not ex-  posed on the Central African Plateau, but they are doubtless several thousand feet thick. MUVA SYSTEM The metamorphic shales and sandstones of this system are seve r a l thousand feet thick and l i e unconformably above the Lufubu.  The  upper white quartzites of this series form well exposed ridges. GRANITIC INTRUSIVES Older Red Granite Jackson (1932(2)), pp. 489-94) includes a composite, red granitic stock at NChanga as both older and younger (Younger Red Granite) than the System of the Katanga, (see p. 14)). Older Grey Granite The MKushi gneissoid granite (Bancroft and P e l l e t i e r , 1929, • p. 6) i s identical with Jackson's (1932, p. 454) MKushi Granite Gneiss which consists "characteristically of gneissoid and quartzose adamellites, with porphyritic facies" and i s equivalent to Gray and Sharpstone's (1929, pp. 14-15) Older Grey Granite.  Jackson (1932(2), p. 455) doubts  whether these intrusives a r e , a l l pre-Katanga i n age stating that "There i s no essential mineralogical difference between the t y p i c a l MKushi granite-gneiss and the younger grey granites, and where the l a t t e r are  -11-  l o c a l l y gneissoid, any difference, either mineralogical or structural practically vanishes". On the other hand Gray (1930, p. 787) states that "Both these Systems (Muva and Lufubu) before the formation of the System of Katanga, were intruded by large masses of granite.  From these rocks  was derived the material of which the sediments of the System of the Katanga were formed". Jackson notes that t y p i c a l granitic pebbles of basal BWana MKubwa (Roan) are leucocratic granites, very low i n ferro-magnesian minerals f o r which the provenance i s unknown. Muliashi Porphyritic Granite and Gneiss This gneissose, strongly porphyritic, biotite-adamellite i s of l o c a l occurrence along the Muliashi River. SYSTEM OF THE KATANGA A synopsis of these sediments i s given below i n the comparative table drawn up by Gray (1930, p.791).  The following points i n respect to  nomenclature should be noted. 1.  The MWashia i s l o c a l l y (NKana) known as the Christmas  Series. 2.  The Serie des Mines (Katanga); the MWashia-Upper Roan-  Lower Roan (Rhodesian Selection Trust, Ltd.); and the UpperMiddle-Lower Bwana Mkubwa (Bancroft and P e l l e t i e r ) represent equivalent terminologies.  I  II  •12-  COMPARISON OF THE SYSTEM OF THE KATANGA IN KATANGA AND RHODESIA V i c i n i t y of Elizabethville - Du Bois System Lubilash  not present  unconformity  not present  System Katanga m.  Lower Kundelungu 1500 m. Feldspathic 0-30 Sandstone — Shales Calcareous — Sandstone Calcaire de 50-100 Kakontwe 0-50 Shales Grand Conglomerate 100-400 300-500 MWashia . Feldspathic 10-50 Quartzite Black Shale ) Green Dol. Shale) 200-4000 1-2 Chert and Jasper 1-2 Siliceous Oolites Dolomites of the Serie des Mines 200-400 (Base unknown)  System Lubilash  unconformity  System Katanga Upper Kundelungu 2000 —Shales, sandy ' 5-10 Calcaire Rose 0-10 Shales Petit Conglomerat 10-30  V i c i n i t y of Mufulira - Gray  Upper Kundelungu 2000 m, Arkose, "purple" Quartzite, Shales — Calcaire Rose Shales Petit Conglomerat Lower Kundelungu 2000 m, Feldspathic Sandstone Calc. sandy Shale Shales Kakontwe Limestone 100 Shales ) Basal Conglomerate) 150 MWashia 400-600 Feldspathic Quartzite 15 Black and Var. banded Shale, Ss. Chert and Oolites 5 Upper Roan Dolomite and d o l . -Shale with int'b'd. Sandstone Lower Roan 350 Int'b'd. Shale, Ss. Dolomite 175 Feldspathic Sandstone g r i t , conglomerate 175 unconformity MUVA SYSTEM  •13-  The beds of the System of the Katanga are unfossiliferous, hence no faunal dating has been possible.  Radioactivity determinations  (Bateman, 1930, p. 375) on the radium deposits of Chinkolobwe, Katanga (occurring i n beds of the Serie des Mines) give 610 m i l l i o n years, or pre-Cambrian, as the age of the ores. Bateman feels that the uranium and copper mineralization i n Katanga are of one age, and also that the copper of Northern Rhodesia i s the same age and therefore pre-Cambrian. Serie des Mines. Since this series w i l l be discussed i n more d e t a i l on subsequent pages, only brief notes w i l l be given here. The lower beds of the series, not exposed i n Katanga, are separated by a marked unconformity from the underlying Muva and Lufubu Systems.  The copper deposits of Katanga are found i n the basal MWashia  and Upper Roan, while those of Rhodesia are found i n the Lower Roan. Kundelungu Series The basal member, lying conformably above the Serie des Mines, i s composed of f l u v i o - g l a c i a l shales and conglomerates and i s called the " t i l l i t e of the Katanga".  Bancroft (Gray, 1930, p. 789)  found these beds over a greater area than the Serie des Mines, the basal conglomerate at places lying d i r e c t l y on the ancient schists and Gray states that "these beds represent, therefore, a transgressive overlap i n the sedimentation of the o r i g i n a l basin i n which the System of the Katanga was l a i d down". ACID AND BASIC INTRUSIVES  -14-  NChanga Red Granites Under this heading Jackson (1932 ( 2 ) , p. 489) describes a large composite granite stock at NChanga composed of red b i o t i t e adamellite-granite to red mierocline-alaskite, which he believes represents two ages, the Older Red Granite and the Younger Red Granite, older and younger respectively than the BWana MKubwa (Serie des Mines). Jackson also believes that the copper.ores of NChanga are genetically related to the Younger Red Granite. Younger Grey Granite This includes a widespread group of grey biotite-adamell i t e s , with quartz-diorite and granite facies which are intrusive into the basal members of the Lower Roan Series, and these together with the NChanga younger red granite, are believed to have been the source of copper mineralization of Northern Rhodesia and of the Katanga. Pegmat i t e and aplite dykes of the younger grey granite cut the Basement Schists, and the granite has, i n places, a garnetiferous contact aureole where i t intrudes the Basement Schists. Basic Intrusive Group The gabbros and norites of t h i s group occur chiefly as s i l l s of over a thousand feet i n thickness and are apparently the youngest intrusives.  The s i l l s on the whole conform to the structure of the  sediments, but i n places form irregular transgressive bodies.  They cer-  t a i n l y cut upper Serie des Mines beds and are probably younger than Kundelungu. Bancroft and P e l l e t i e r (Jackson, 1932 ( 2 ) , pp. 504-505) suggest that the Basic Intrusives may correspond broadly to the Keweenawan basic intrusives of the Canadian Shield.  -15-  LUBILASH SYSTEM This system consists of a basal g l a c i a l or fluvo-glacial conglomerate which i s overlain by sandstones, coal measures, variegated a r g i l l i t e s and shales, and upper f r i a b l e sandstones and lenticular conclomerates.  I t l i e s unconformably and almost horizontally upon the  Kundelungu and has been almost entirely removed from the area of the copper belt.  The system i s said to be Permian to Jurassic i n age and  i s correlated with the Karoo System of South A f r i c a .  SEQUENCE OF EVENTS The sediments of the Katanga System were l a i d down on an erosional surface formed of a basement complex of ancient schists and gneisses intruded by older granites. Subsequently, and possibly accompanied by intrusions of younger granites, the Katanga System was highly folded and faulted to the north i n Katanga but f a i r l y gently folded i n Northern Rhodesia. This l a t t e r folding produced a system of rather open synclines and anticlines with a regional northwesterly trend.  Those  writers who conceive of an epigenetic origin for the copper deposits relate the mineralization to the intrusions of the Younger Granites, but state that since the shape of some of the deposits was controlled by i t , the folding preceded the mineralization.  :.  The relation between the rather gentle folding i n Northern Rhodesia and the stronger overthrusts of Katanga i s aptly described by Douglas (1930, p. 337) who says: "An European p a r a l l e l may be drawn between the African structures and those of the Alps and Jura. The anticlines and synclines of the Jura can be likened to the similar folds i n Northern Rhodesia, while the nappes and thrust blocks of the Alps find their equivalent i n the Belgian Congo". Following the intrusion of the Younger Granites, which i n places domed the sediments, gabbroic and diabasic s i l l s and dykes were intruded, and are often found, according to Jackson, as the cores of synclines. The region was then base-leveled and the Permian to Jurassic beds of the Lubilash, or Karoo System were deposited.  These rocks have  subsequently been removed during further u p l i f t and peneplanation which has continued u n t i l recent times.  -17-  Bateman suggests (1930, p. 3&1-384) that there i s evidence that just before or since the latest u p l i f t , very arid climatic conditions prevailed i n the region.  The water table must have been very  deep since oxidation i s found to depths of 2000 feet (Gray, 1932, p. 323), and i t i s suggested that only during the very latest u p l i f t , to the present 4000 feet elevation, has the water table risen to within several tens of feet of the surface. A new cycle of erosion has commenced; the upland region i s i n the stage of extreme youth and many streams are beginning to entrench themselves i n their old courses.  -18-  THE ORE DEPOSITS Since many details of.the ore deposits, especially at NKana, w i l l be brought out i n a later section of this paper, a brief and general description w i l l be given here and a short comparison with the Katanga ores w i l l be made. As already indicated, the ores i n Northern Rhodesia usually occur i n the basal beds of the Lower Roan. The more common host beds are feldspathic, quartzites, shales, and dolomitic shales, though l o c a l l y talc-tremolite schists and schistose limestones may carry ore. At most mines the tabular orebodies extend through a very short s t r a t i graphic interval; however, at Mufulira for example, three d i s t i n c t and stratigraphically separated orebodies are present. In many of the deposits ore i s concentrated at drags or thickenings (Fig. 3) on the synclinal.limbs.  Thus both tabular and  roughly pipe-like orebodies are present, the former being by far the most important.  At Roan and NChanga the ore forms part of both limbs  of narrow pitching synclines and hence has a horizontal V-shape i n plan and a rough U-shape i n section.  At Mufulira and Nkana (Fig. 3) where  the deposits are on one synclinal limb only, they have the form of tabular bodies. From the epigenetic viewpoint several features seem to be responsible for ore localization:  the proximity of granitic intrusions  that supplied the metallizing solutions has been cited by a number of writers (Bateman, 1930, p. 411; Davidson,' 1931, p. 148; Jackson, 1932 (1), p. 256; Gray, 1932, p. 335). The position of the ores within the sediments i s apparently  -18a-  Figure 3  TOW  //oij/fjj L/a// /fry/ W / t - o r jSrotvf  rfpprox. Or* t-ior/z or?  3oo /Lev*/ £>a/orni/e  C/xrrfy /fry///,/* 3ar><Sec/ U//>;y e£>°Jor>,,/ir/Gr*y/?rf///rr'e  4SO  £>ar* 6r-<ry <*?ryi VA /«  600  /ho ItS*// Chrrp/orrr*r<r/*  rso  ,  000  /BSo  J4SO  /aso  '•9/0  2/*€>  Z370  TypiCAL SECTION-NORTH  OREBODY  Rhok a na Corpotat/or? -Nkan o M/ne Scale? i=4/6  -19-  the result of physical rather than chemical control since the ores occur i n beds of diverse chemical and mineralogical character. ' Thus permeability favoured the l a t e r a l progression of mineralization and Jackson (1932(1), p. 256) suggests that bending and fracturing of otherwise impermeable beds along the axes of minor folds rendered them especially favourable to entry by solutions. Another factor noted by several authors i s the control of s o l utions by overlying impervious beds. Gray, especially, points this out i n his description of the Mufulira Mine (Gray, 1932, pp. 335-336). Each of the three orebodies i s overlain by an impervious horizon and Gray states that "the stratigraphic position of the orebodies i s clearly due to the damming action of the dense and unfractured overlying beds". No large, cross-cutting, "feeder" faults or fracture zones are mentioned by any of the writers though Gray (1932, p. 335) states that "the solutions reached the sediments most probably through tension cracks i n the cooled granite margin, joint cracks i n the Muva schist and joints i n the basal Mine series quartzites i n a l l of which they formed sulphide bearing veins". Davidson (1931, p. 151) introduces the p o s s i b i l i t y of chemi c a l or mineralogical control when he mentions that the ore replaces the o r i g i n a l calcareous cement of the shaley host rock at Chambishi. As Lindgren (1933, p. 629) puts i t , "The persistance of the ore-bearing beds i s amazing". For example, along 42,000 feet of the north limb of the NKana syncline ore i s developed, with two interruptions, for something over 35,000 feet and extends to a depth of about 2400 feet.  This ore has a stratigraphic thickness averaging 30 to 40  -20-  feet which i s the order of magnitude for the whole d i s t r i c t .  Batemen  1942, p. 517) says, "At Roan Antelope the metallized bed laps around the nose of a plunging syncline and extends along both limbs for a t o t a l proven length of 5 miles and an indicated length of another 4 miles". The Ores. A feature of these copper ores i s their f a i r l y simple mineralogy.  Chalcopyrite, bornite, chalcocite, and c a r r o l l i t e or linnaeite  are the major sulphides which are, for the most part, f i n e l y scattered through the sediments. The sulphides are sometimes so minutely d i s seminated that a cursory examination does not detect their presence i n rock that i s classed as ore. Minor amounts of pyrite, hematite, and native copper make up the remainer of the metallic minerals but these have not the uniform distribution of the f i r s t named group. Oxidation products (excluding bornite and chalcocite) are numerous but are generally considered to be of minor importance though McKinnon (1943) writes:  "One-third, or more, of the copper mineral-  i z a t i o n i n these (NChanga) orebodies occurs i n the form of carbonates and oxides, ....". Cuprite, native copper, malachite, azurite, chrysocolla, tenorite, bieberite (CoS0^.7H20), limonite, goethite, jarosite, cornetite (Cu-^Og^CutOH^), libethnite (Cu-^Og.CutOH^), and manganese wad have been reported from the d i s t r i c t . The problem of hypogene versus supergene bornite and chalcocite has received much attention from the early workers. In the case of bornite, Gray, Bateman, and Davidson advocate  -21-  an hypogene origin for the major part of the bornite, while Bancroft and Jackson hold the supergene viewpoint.  A brief analysis of the  arguments presented leads the writer to believe that i n most instances bornite i s primary but that i n some cases much bornite may be supergene . The chalcocite problem has been very thoroughly dealt with by Bateman (1930, pp. 393-405) who concludes, contrary to the opinion of the resident geologists of the time, that "part, and perhaps the major part, of the Rhodesian chalcocite i s of hypogene o r i g i n and was formed at a temperature above 91°C. or possibly above 200°C". Gray, Bancroft, and Jackson hold that the majority of the chalcocite i s supergene. Bateman's extensive treatment of the chalcocite problem i s very impressive and, as with the bornite, the writer f e e l s , after a perusal of the l i t e r a t u r e , that though i n some places most of the chalcocite now appears supergene much of i t throughout the d i s t r i c t was o r i g i n a l l y introduced. It should be pointed out that since the relative amounts of copper sulphides d i f f e r somewhat from mine to mine i t i s d i f f i c u l t to generalize for the d i s t r i c t .  For example at Chambishi (Davidson, 1931,  p. 149) bornite i s the predominant sulphide, and "Bornite and chalcopyrite make up f u l l y 98 percent of the primary copper minerals so far ;  exposed", while at NChanga (Jackson, 1930, p. 2 6 l "chalcocite i s the most abundant sulphide copper ore-mineral", with bornite second i n importance and chalcopyrite occurring sparingly. In this l a t t e r case Jackson believes that the chalcocite i s predominantly supergene.  -22-  I t does not appear, upon c o n s i d e r a t i o n o f t h e whole  district,  t h a t secondary s u l p h i d e enrichment has p l a y e d a major r o l e i n the f o r mation o f t h e copper d e p o s i t s o f N o r t h e r n R h o d e s i a . Not a l l copper m i n e r a l i z a t i o n i s f o u n d ' i n t h e sediments. Chambishi  At  (Davidson, 1931, p . 151) t h e " g r a n i t e i t s e l f c a r r i e s t r a c e s o f  copper, and pegmatites and q u a r t z v e i n s t h a t come from i t a l s o c a r r y copper s u l p h i d e s " .  T h i s statement may be a p p l i e d t o a number o f mines  i n the d i s t r i c t .  Comparison  o f t h e Rhodesia and Katanga D e p o s i t s . (Gray, 1930, P» 801) In  t h e f i r s t p l a c e t h e o r e s o f Rhodesia and Katanga o c c u r a t  d i f f e r e n t s t r a t i g r a p h i c l e v e l s : t h e former i n t h e a r g i l l i t e s ,  shales,  and a r k o s e s o f the Lower Roan w h i l e the l a t t e r are found i n t h e d o l o m i t i c beds o f t h e Upper Roan and MWashia. Secondly the Katanga d e p o s i t s a r e a l l o x i d i z e d b o d i e s l y i n g c l o s e t o the s u r f a c e , w h i l e those o f Rhodesia, w i t h t h e e x c e p t i o n o f the  o l d BWana Mkubwa Mine, a r e s u l p h i d e d e p o s i t s t h a t go t o d e p t h . The reasons f o r t h e d i f f e r e n c e i n s t r a t i g r a p h i c  are  position  n o t p e r f e c t l y c l e a r but no doubt l o c a l s t r u c t u r a l c o n d i t i o n s ex-  e r t e d a primary c o n t r o l .  -23-  DESCRIPTIONS OF SPECIMENS FROM THE . 'ORE HORIZON AT NKANA MINE. 1  The following i s a generalized but f a i r l y t y p i c a l section of the Lower BWana MKubwa (Roan) Series as found at NKana Mine (after Guernsey, 1947). Top  Feldspathic Sandstones, quartzites, and a r g i l l i t e s  150 feet  Grey, well bedded, quartzose (Hanging Wall) a r g i l l i t e  25-35  "Ore Horizon"  3 O-40  Foot Wall Conglomerate  0-30  Feldspathic sandstones and t h i n sandy a r g i l l i t e s  50  "Lower" Conglomerate  40-50  Grey-brown, muddy, dolomitic sandstones  60-70  Hard, l i g h t , cross-bedded, f e l d spathic quartzites  up to  600  Basal conglomerate  up to  80  The following divisions of the "Ore Horizon" are also taken from Guernsey.  Although the horizon changes to some extent both along  the strike and with depth this i s a typical sequence at the North and Mindola Orebodies. Top 1. Hanging Wall A r g i l l i t e 2. 'Porous Sandstone' -banded, impure dolomite  5 feet  3. 'Cherty Ore' -hard, fine grained argillite  9  -24-  4.  'Banded Ore' -interbedded grey a r g i l l i t e and white dolomite  6 feet  5. 'Low Grade A r g i l l i t e ' -grey, f a i r l y massive dolomitic a r g i l l i t e 6. 'Schistose Ore -schisted dolomite and dolomitic a r g i l l i t e  12  .  1  5  7. Foot Wall Conglomerate 8. Arkoses and A r g i l l i t e s -fejispathic sandstones and t h i n sandy a r g i l l i t e s In the following descriptions "N" refers to the North Orebody, "M" refers to the Mindola Orebody, and the numbers refer to the above beds of the Ore Horizon, 1. Hanging Wall A r g i l l i t e Megascopic The five specimens of t h i s bed show f a i r l y similar general features.  The rock i s dense, soft to rather hard, grey i n colour, and  has a slight to marked clay odour. Two of the specimens exhibit a lamellar structure manifested by dark and l i g h t colouring. have thicknesses measuring about L.mm. to, or represent, bedding.  The lamenae  and they are doubtless p a r a l l e l  One specimen (Ml-C) d i f f e r s somewhat from  the others i n that i t exhibits no laminations, i s harder, and i s speckled with very small flecks and blobs of c a r r o l l i t e and a l i t t l e bornite, which minerals also line numerous cavities averaging 3 or 4 mm. i n size. Guernsey states that this last i s not a t y p i c a l specimen. Microscopic Typically the rock consists of a mosaic or mat of quartz, feldspar, and sericite grains that average 0.02  mm. i n size.  Very  -25-  roughly these minerals are t o make q u a n t i t a t i v e  i n equal p r o p o r t i o n s though i t  estimates of the quartz.and  is usually i n small irregular grains no p o l y s y n t h e t i c t w i n n i n g . are  t w i n n e d arid t h e s e a r e  is  pleochroic, pale  o u t l i n e and s t a i n i n g dolomite;  rare  b i o t i t e , carbonate,  tan to colourless;  tourmaline grains  are  present  is  rock because i t contains c a n s u g g e s t no b e t t e r has  latter  feldspar  but grains  of  and t o u r m a l i n e .  i t is  be d e a l t  is  ragged  virtually  very small, greenish i n t e r p r e t e d as  authigenic  The d e t a i l s section.  p o s s i b l y not a v e r y precise  name f o r  p r a c t i c a l l y no c l a y m i n e r a l s , b u t t h e is  all  i n colour,  with i n a l a t e r  one t h a t  in  and out-  carrollite, bornite, chalcopyrite,  i n one o r t w o o f t h e s p e c i m e n s .  ore m i n e r a l occurrences w i l l "Argillite"  The relief  carbonate  shows t h a t  rims which are  V a r i a b l e , s m a l l amounts  and p y r i t e a r e  sericite  are  (Copper n i t r a t e )  o f t e n have t h i n c o l o u r l e s s growths.  slightly larger  difficult  a l b i t i c i n composition.  Minor constituents Biotite  feldspar.  t h a t have a n e g a t i v e  Some o f t h e  is  i n common u s a g e .  developed through diagenetic  of  this writer  Most probably  the  o r l o w grade metamorphic  processes subsequent t o the d e p o s i t i o n o f an o r i g i n a l l y  siliceous  argillite. 2.  W h i t e , R e d , o r Brown D o l o m i t e (misnamed " P o r o u s Three specimens  crystalline  carbonate  and b i o t i t e . native copper,  o f t h i s member p r e s e n t  aspect with scattered  and h e m a t i t e  a medium g r a i n e d  grains  The r e d c o l o u r a t i o n o f t h e r o c k s  is  Sandstone").  of quartz,  feldspar,  i m p a r t e d by  feldspar,  i n varying proportions.  An i l l - d e f i n e d  c o l o u r b a n d i n g , w h i c h may be e q u i v a l e n t t o b e d d i n g , i s l a y e r i n g of s i l i c a t e  and c a r b o n a t e  minerals.  d e r i v e d from a  -26-  Staining  shows t h a t  c a l c i t e but i n another case  (N2-B) a l l the carbonate  calcite  The f o u r t h s p e c i m e n ( M 2 - B ) o f t h i s g r o u p b e a r s n o t t h e  slight-  resemblance  present.  to the other three  grouped w i t h the  and t h e w r i t e r  "Cherty Ore" specimens.  Microscopic  feels  s h o u l d be be  consider-  purposes.  -  Under t h e m i c r o s c o p e t h e r o c k p r e s e n t s  a mosaic  t e r l o c k i n g g r a i n s w h i c h a v e r a g e a b o u t 0.5 mm. i n The c a r b o n a t e euhedral grains  are  Small subhedral  d o l o m i t e and l a r g e r i r r e g u l a r g r a i n s  referable  to orthoclase  and c l o u d y g r a i n s  r e p l a c e d by c a l c i t e  are  irregular  Some t w i n n e d  q u i t e c l e a r a n d may  to  calcite.  and m i c r o c l i n e forms  and s e r i c i t e .  a l b i t i c i n c o m p o s i t i o n , are  of closely i n -  size.  i s variable i n character.  Feldspar which i s  spar g r a i n s ,  that i t  Consequently i t w i l l  ed a p a r t of t h a t h o r i z o n f o r d e s c r i p t i v e  be  is  (M2-A) a p p r o x i m a t e l y e q u a l amounts o f  and d o l o m i t e a r e  est  i n one c a s e  feld-  therefore  authigenic. A s m a l l amount o f q u a r t z i n i r r e g u l a r i n t e r l o c k i n g g r a i n s  present  i n a l l the r o c k s .  Several of these grains  secondary outgrowths i n o p t i c a l  are  i n m i n o r amounts a r e  y e l l o w i s h c h l o r i t e , m u s c o v i t e and s e r i c i t e ,  a l t e r a t i o n products of the feldspars.  copper,  hematite,  and b o r n i t e a l l i n f a i r l y  The r o c k v a r i e s mitic limestone. most p r o b a b l e  have c l e a r l y d e f i n e d  continuity.  Other minerals present tite,  is  tan to green b i o -  and c l a y m i n e r a l s  M e t a l l i c m i n e r a l s are  which  native  s m a l l amount.  from an impure limestone t o an impure d o l o -  Some a u t h i g e n i c f e l d s p a r s  may be p r e s e n t  that the cloudy, i r r e g u l a r grains  but i t  of orthoclase  and  is  -27-  microcline are o r i g i n a l d e t r i t a l constituents. 3.  Cherty A r g i l l i t e or "Cherty Ore" . Megascopic Megascopically the nine specimens of this ore bed present  varied aspects. Colours are.predominantly.shades  of grey but two  specimens are brown and one i s black. Most of the specimens show l i g h t and dark laminations, these often containing ore minerals. The rocks are a l l very fine grained, dense i n fact, and i n most cases are quite hard, hence their "cherty" description. One of the dense brown specimens contains a one-half inch white lens p a r a l l e l to the laminations and also thin lacey veinlets or stringers cutting across the rock.  •" The black specimen (N3-D) previously referred to i s unique i n  the collection.  I t i s a dense black f i s s i l e rock cut by a number of quartz-  carbonate veinlets and lenses about 2 mm. i n width containing f a i r amounts of chalcopyrite. Most of these veinlets follow the f i s s i l i t y but several cut i t at high angles and some are irregular and curved. Varying amounts of c a r r o l l i t e , bornite, pyrite, and chalcopyrite are present i n a l l the specimens and are mainly distributed along the laminations but some sulphides appear as blobs and disseminations throughout the rocks. Microscopic The specimens, though d i f f e r i n g i n outward appearance, are quite similar mineralogically. Very fine grained quartz, feldspar, and sericite are the major constituents together with varying amounts of carbonate.  -28-  Quantitative estimates of quartz and feldspar are very d i f f i c u l t to make but i n general the feldspar i s at least equal i n amount to the quartz. Quartz, feldspar, and s e r i c i t e grains average about 0.02 mm. i n size but the ragged carbonate grains are usually about 0.1 mm. i n diameter. The very fine grained untwinned feldspar i s of indeterminate composition but because i t has negative r e l i e f i t i s probably either a potash feldspar or a l b i t e .  Some larger poysynthetically twinned grains  are usually present and these are a l b i t e .  Several altered and i r r e g u l a r  grains of orthoclase and microcline are also present. Much of the quartz exhibits s t r a i n shadows.  The s e r i c i t e and  other micas have a f a i r l y good preferred orientation p a r a l l e l to the megascopic lamellar structure. Minor though recurring constituents are b i o t i t e , tourmaline, and a few grains of zircon, c h l o r i t e , and epidote.  B i o t i t e and tour-  maline are both apparently allogenic though the l a t t e r , which i s normally green i n colour, i s often narrowly rimmed with colourless secondary outgrowths. The black f i s s i l e rock has s l i g h t l y d i f f e r e n t mineralogies! features.  I t i s almost wholly composed of white mica grains 0.02 to  0.03 mm. i n length and having an extremely good preferred o r i e n t a t i o n . Some very fine grained quartz occurs i n t e r s t i t i a l l y with the mica. The v e i n l e t s are composed of interlocking quartz and carbonate grains with i n t e r s t i t i a l chalcopyrite.  The black colouration i s produced by a good  deal of very f i n e l y divided black, opaque, carbonaceous m a t e r i a l . It i s rather d i f f i c u l t to apply a rock name to t h i s group of  specimens. Their present quartz, feldspar, sericite composition i s no doubt due i n some degree to the impress of conditions differing from those existing at the time of deposition though i t i s not l i k e l y that there has been much, i f any, material introduced. could possibly be authigenic (Gruner and Thiel,  Some of the feldspar  1937),  though here i t ex-  hibits no diagnostic features. An o r i g i n a l l y siliceous or feldspathic shale could have given rise to this rock under conditions of f a i r l y low grade regional metamorphism. For want of a better name and because of i t s outward appearance i t may be termed " a r g i l l i t e " . One or two of the specimens have a large content of carbonate. This i s assumed to be original calcareous material the grains of which having acquired an irregular shape through r e c r y s t a l l i z a t i o n . The black rock with the marked f i s s i l i t y , though very different megascopically from the other specimens i s , nevertheless, minerallogica l l y quite similar. 4.  I t i s probably best called a black f i s s i l e shale.  'Banded Ore' - banded white dolomite and grey a r g i l l i t e . Megascopic This i s t y p i c a l l y a grey to white, f i n e l y crystalline to dense,  rather soft laminated rock.  The laminations vary from paper-thin to sev-  e r a l millimeters i n thickness, the grey laminae being thicker and denser and the white ones thinner and f i n e l y c r y s t a l l i n e .  The lighter c r y s t a l -  l i n e material i s carbonate, staining indicating that i t i s mostly dolo-. mite. Ore minerals, bornite, chalcopyrite, a very l i t t l e c a r r o l l i t e , and possibly some chalcocite, are distributed i n thin layers paralleling the lamellar structure. Some sulphides are disseminated through the rock,  -30-  and i n specimen N4-A much bornite occurs i n t h i c k e r l e n t i c u l a r masses and i n i r r e g u l a r blobs associated w i t h coarse quartz and c a l c i t e . Microscopic I r r e g u l a r and anhedral grains of dolomite, averaging about 0.1 mm. i n s i z e , comprise the major p o r t i o n of these specimens.  Varying  amounts of i r r e g u l a r feldspar and quartz g r a i n s and i n some cases a l i t t l e s e r i c i t e are the other important constituents.* The carbonate i s doubtless an o r i g i n a l c o n s t i t u e n t ; the grains may p o s s i b l y have assumed t h e i r present i r r e g u l a r o u t l i n e s through some recrystallization.  In one specimen (N4-B) they are somewhat elongate  owing presumably t o deformation.  Specimen M4-A contains anhedral t o sub-  hedral dolomite c r y s t a l l s enclosed i n i r r e g u l a r and cloudy c a l c i t e g r a i n s . Many of the t h i n sections contain much (up t o 30 o r 40 percent) feldspar.  This occurs i n i r r e g u l a r i n t e r l o c k i n g grains of which some are  potash i n composition but many of which are p o l y s y n t h e t i c a l l y twinned plagioclase.  I t i s b e l i e v e d that most of t h i s l a s t i s a l b i t e but that  i s by no means proven.  Inclusions of carbonate are very common but the •  feldspar g r a i n s are otherwise quite c l e a r .  Other evidence i s not appar-  ent, consequently i t cannot be s a i d whether the f e l d s p a r i s a l l o g e n i c or authigenic.  Quartz has much the same occurrence as the feldspar but there  i s much l e s s of i t . The micas, b i o t i t e , muscovite, and s e r i c i t e , are on the whole of quite minor amount.  In one case small elongate b i o t i t e f l a k e s make up  15 o r 20 percent of the t h i n s e c t i o n and i n s e v e r a l cases a good d e a l of s e r i c i t e I s present.  The b i o t i t e f o r the most part has a d e t r i t a l aspect  but i n one specimen (M4-A) very i r r e g u l a r and roughly equidimensional  -31-  b i o t i t e s c a l e s have every appearance o f being  endogenic.  V e r y " s m a l l amounts of d e t r i t a l t o u r m a l i n e and a p a t i t e i n one o r two  occur  of the specimens.  T h i s rock appears "Cherty A r g i l l i t e " .  t o be a v e r y d o l o m i t i c phase o f the p r e v i o u s  Dolomite  g r a i n s u s u a l l y . f o r m i n g 50 p e r c e n t o r more  o f the r o c k s permits the use of the r o c k name " d o l o m i t e " .  The  darker  l a m i n a t i o n s are f e l d s p a r , q u a r t z , and minor s e r i c i t e so i t can p o s s i b l y be s a i d the r o c k c o n s i s t s o f a r g i l l a c e o u s and d o l o m i t i c l a y e r s .  Actually  the m i n e r a l o g i c s e g r e g a t i o n i s not as c l e a r as t h i s l a s t statement  might  imply so t h a t a l a m i n a t e d a r g i l l a c e o u s , o r q u a r t z o - f e l d s p a t h i c , f i n e g r a i n e d d o l o m i t e might p r e s e n t a c l e a r e r d e s c r i p t i o n o f t h i s  5.  'Low  rock.  Grade A r g i l l i t e '  Megascopic The  specimens of t h i s bed are f a i r l y u n i f o r m i n c o l o u r , t e x -  t u r e , and a l l outward appearances.  They are s h a l e y o r a r g i l l a c e o u s  ap-  p e a r i n g r o c k s , u n i f o r m l y dark g r e y i n c o l o u r , f a i r l y s o f t but compact, and have p a r t i n g or bedding are d e f i n e d i n one  o r two  h y d r i t e and i n another  p l a n e s one o r two  cases by t h i n (1 mm.)  inches apart.  These  last  l a y e r s o f gypsum o r  an-  case by a s i m i l a r l y t h i n l a y e r o f f i n e white c a l -  c i t e very f i n e l y speckled'with  biotite.  Very c l o s e s c r u t i n y r e v e a l s the presence  of rare small blobs  and l e n s e s o f c h a l c o p y r i t e and b o r n i t e , the l a t t e r o f t e n h a v i n g a  little  f i n e grained quartz i n a s s o c i a t i o n .  Microscopic  -  The major m i n e r a l s of t h i s r o c k , q u a r t z , f e l d s p a r ,  biotite  and muscovite form a r a t h e r u n i f o r m textural features. ing  i n t e r l o c k i n g mosaic w i t h no s p e c i a l  The q u a r t z and f e l d s p a r t o g e t h e r ,  i n grains  s l i g h t l y l e s s than 0.1 mm. i n s i z e , make up about 50 p e r c e n t  averago f the  r o c k and t h e remainder i s m o s t l y b i o t i t e and muscovite o r s e r i c i t e ,  with  a d d i t i o n a l s m a l l amounts o f carbonate (3 o r 4 p e r c e n t ) , c h l o r i t e , and anhydrite. The and  quartz  and f e l d s p a r form a background o f s m a l l  irregular  i n t e r l o c k i n g g r a i n s which a r e d i f f i c u l t t o d i s t i n g u i s h f o r q u a n t i -  tative estimations.  Some f e l d s p a r g r a i n s a r e twinned and those g r a i n s  measured a r e a l b i t e ; many g r a i n s a r e untwinned and because t h e y appear t o have n e g a t i v e few  r e l i e f may be e i t h e r a l b i t e o r a potash f e l d s p a r .  A  s m a l l and r a t h e r rounded g r a i n s o f b o r n i t e a r e s c a t t e r e d i n the r o c k  section. Argillite  seems t o be a f a i r name f o r t h i s r o c k .  At places  i t may be d o l o m i t i c but t h e specimens a v a i l a b l e t o t h e w r i t e r do n o t c o n t a i n d o l o m i t e as a major c o n s t i t u e n t . One  o f t h e specimens o f t h i s group (M5-C) i s c u t , a t an angle  o f about 40 degrees t o t h e bedding ( ? ) , by an o n e - h a l f v e i n , which has bleached  i n c h wide  quartz  t h e r o c k f o r d i s t a n c e s up t o one i n c h from t h e  vein.  A little  little  c h a l c o p y r i t e and b o r n i t e occur i n t h e d r u s y p a r t s o f t h e v e i n .  6.  c a l c i t e c o a t s the q u a r t z  ' S c h i s t o s e Ore  c e n t r a l l y i n t h e v e i n and a v e r y  1  Megascopic The  specimens o f t h i s bed are c h a r a c t e r i z e d by g r e y t o g r e y i s h  white and white b a n d i n g .  I n t h e two specimens which are " s c h i s t o s e " t h e  -33-  bands,  one-quarter  defined.  t o one i n c h i n w i d t h ,  The g r e y b a n d s a r e  fine grained b i o t i t e . is  sugary  are  These  layers  grade i n t o o t h e r s  scarcer  but of l a r g e r  q u i t e w h i t e and i n t h e M i n d o l a specimens quartz,  not  sharply-  dense and d e r i v e t h e i r c o l o u r m a i n l y f r o m v e r y  and t h e b i o t i t e i s  anhydrite,  f o r t h e most p a r t  and w h i t e d o l o m i t e .  a mottled or patchy appearance.  they are  i n which the  grain.  texture  Other layers  composed o f v i o l e t t i n t e d  In places the banding gives  Specimen M6-B c o n t a i n s  way  o f f i n e t o medium g r a i n e d p u r p l i s h a n h y d r i t e , w h i t i s h  mite,  quartz,  either  and i r r e g u l a r s t r i n g s  A little Orebody  scattered  It  is  dolo-  bounded on  rock.  b o r n i t e and c h a l c o c i t e o c c u r i n the  North  specimen.  Microscopic  -  D o l o m i t e and v a r y i n g amounts tuents  of b i o t i t e .  s i d e by d a r k t o l i g h t g r e y f i n e g r a i n e d  to  a two-inch white  l a y e r composed a little  are  of the  and f e l d s p a r  "schistose"  specimens.  are the minor  of grains  that  p e a r s t o be o f p r i m a r y o r i g i n . slightly  smaller i n size,  concentrated row bands are  are  averaging  quartz,  chlorite,  is  scattered  d o l o m i t e and i t  orientation.  and a r e  ap-  shreds,  among t h e . d o l o m i t e g r a i n s  good p r e f e r r e d  about  "close-  0.3 mm. i n d i a -  Y e l l o w i s h b i o t i t e s c a l e s and  o f t e n i r r e g u l a r and d i s c o n t i n u o u s  and  also  These  nar-  sometimes  composed  one-half the average g r a i n s i z e .  f o r the o r i g i n of the b i o t i t e i s  "interstitially"  about  a l l the carbonate  i n bands where i t has  o f b i o t i t e and d o l o m i t e g r a i n s evidence  of  consti-  s u b h e d r a l and a n h e d r a l o u t l i n e s i n a  packed" t e x t u r a l arrangement Staining indicates  S m a l l amounts  the major  constituents.  The d o l o m i t e h a s  meter.  of b i o t i t e are  not c l e a r  a n d w i t h no g o o d r e p l a c e m e n t  and t h o u g h i t  The  occurs  f e a t u r e s i t may n o t be  an  -34-  o r i g i n a l constituent. Feldspar grains vary both i n s i z e and composition.  Large  i r r e g u l a r orthoclase grains are crammed w i t h i n c l u s i o n s of carbonate and b i o t i t e .  Smaller i r r e g u l a r twinned and untwinned grains of a l b i t e  are f a i r l y c l e a r .  Quartz grains are u s u a l l y f a i r l y small and i r r e g u l a r .  The f i n e grained p o r t i o n o f one of the specimens i s composed of quartz, carbonate, and b i o t i t e i n roughly equal proportions. Small i r r e g u l a r g r a i n s of bornite and c h a l c o c i t e occur sparingly. The evidences f o r deformation are not apparent and there i s some doubt as t o whether the rock has been " s c h i s t e d " t o any great extent . 7.  Foot Wall Conglomerate. The specimens of t h i s bed are d i v i s i b l e i n t o three groups each  e x h i b i t i n g d i s t i n c t i v e p e t r o l o g i c a l characters. One group, i n c l u d i n g specimens N7-C, and M7-A, C, and D, i s grey-white i n colour and though t y p i c a l l y conglomeratic i n aspect has a "welded" appearance.  Larger rounded and subrounded pebbles, of one  inch or so i n size and c o n s i s t i n g mostly of quartz and chert, are quite scarce.  Most of the rock c o n s i s t s of small (averaging about 1 cm.) an-  gular fragments of quartz and white p l a g i o c l a s e f e l d s p a r i n a grey iceous matrix.  sil-  Femic minerals, which together with f i n e g r a i n s i z e im-  part the dark colour, include b i o t i t e and muscovite. One specimen, M7-A, contains some v i o l e t t i n t e d g r a i n s of anhydrite.  Another, N7-C, i s speckled w i t h small masses of p y r i t e .  -35-  M i c r o s c o p i c c h a r a c t e r s were o n l y observed The  on specimen  t h i n section contains f e l d s p a r of several v a r i e t i e s - orthoclase,  m i c r o c l i n e , and a l b i t e - t o t a l l i n g about 50 o r 60 p e r c e n t , and c o m p r i s i n g 25 o r 30 p e r c e n t of the s e c t i o n . of  N7-C.  biotite  ( c a . 5%)  a p a t i t e , and  The  remainder  i s made up  and minor amounts o f c h l o r i t e , carbonate,  zircon,  pyrite.  I t appears  t h a t t h e r e has been e x t e n s i v e r e c o n s t i t u t i o n  p o s s i b l y metasomatism a c t i v e i n the f o r m a t i o n o f t h i s r o c k . potash f e l d s p a r s , as w e l l as c o n t a i n i n g s e r i c i t e and  clay  Two  l a r g e r twinned  s m a l l ( l e s s t h a n 0.1  mm.)  c l e a r untwinned g r a i n s w i t h n e g a t i v e  T h i s l a t t e r type may  be o f a u t h i g e n i c o r i g i n .  The  larger  t y p e s of  (An. 5),  p l a g i o c l a s e are p r e s e n t :  73;  Goldschmidt,  l a r g e r grains of a l -  1916,  pp. 124-25; Grubenmann and N i g g l i , 1924,  evidence of replacement the evidence i s not  origin.  B i o t i t e may  and  relief.  "chessboard" o r " s c h a c h b r e t t " t e x t u r e which i s t a k e n  some ( G i l l u l y , 1933, pp. 68, Becke, 1913,  grains of a l b i t e  The  and  alterations,  have been r e p l a c e d by q u a r t z o f the f i n e g r a i n e d v a r i e t y .  bite exhibit  quartz  pp. 68,  71,  by  78,  86;  pp. 435-36) t o be  replace other minerals  clear.  I t might be suggested t h a t t h i s grey conglomerate  has been de-  r i v e d from the O l d e r Gray G r a n i t e s , but because no specimens of t h i s ter  but  lat-  rock a r e a v a i l a b l e t o him t h i s i s pure c o n j e c t u r e on the p a r t of the  writer. The second group of Foot W a l l Conglomerate specimens i n c l u d e s N7-A  and  group.  B which are more t y p i c a l l y sedimentary  t h a n those o f the  first  These are t h o r o u g h l y i n d u r a t e d r o c k s but t h e y do not a t a l l have  the welded appearance of the f i r s t g r o u p .  L a r g e r (1  t o 2 cm.)  rounded  -36-  quartz and chert pebbles and smaller (less than 1 mm.),  angular, red-  dish potash feldspar fragments are embedded i n a sandy and clayey cement which i s s l i g h t l y calcareous. Microscopically the specimens are f a i r l y similar.  Feldspar, including microcline, orthoclase, and a l b i t e ,  and quartz are the major minerals with small amounts of b i o t i t e , chlorite, muscovite and carbonate.  A few d e t r i a l tourmaline grains are also present.  The boundaries of the strained quartz grains are minutely scalloped by narrow bands of authigenic (?) albite (?). The larger feldspars contain much sericite and clay alteration. Obviously the grey conglomerates have been subjected to an higher grade of metamorphism than the buff or pink rocks whose characters may have been derived from purely diagenetic processes. The f i n a l group of the foot Wall Conglomerate types i s represented by one specimen, M7-B.  This rock i s a f a i r l y porous polymictic  conglomerate. Rounded to sub-angular pebbles are one-half to one inch i n size and range i n composition from dense chert and clear quartz, to red, medium grained "granite", and to f i n e l y c r y s t a l l i n e , calcareous, b i o t i t i c , and c h l o r i t i c (possibly serpentinous) dark fragments.  The  cementing or matrix material consists of medium to fine grained quartz, pink potash feldspar, and biotite at least partly held together i n a rather porous mass by powdery c a l c i t e .  A 2mm.  quartz veinlet cuts through  the specimen. No suggestion can be given by the writer for the provenance of this rock but i t i s obviously quite different from that of the other representatives of the Foot Mall Conglomerate. It i s suspected that although this Foot Wall Conglomerate  •37-  may, as a conglomerate facies, be persistent over large areas, the det a i l s of i t s l i t h o l o g i c character, with respect to both components and induration or metamorphosm, vary considerably i n a l o c a l sense. 8.  "Kegelspathic Sandstones and thin sandy A r g i l l i t e s " or Arkoses and A r g i l l i t e s Megascopic The three specimens of t h i s bed d i f f e r somewhat i n outward  appearance but are apparently quite similar i n overall mineralogic composition.  A l l are reddish or pinkish i n colour and of medium or fine  grain. Specimen N8-A i s a f a i r l y fine grained compact rock consisting predominantly of pink feldspar and quartz and containing several wavy, very t h i n dark bands which consist of specular hematite.  Specimen N8-B  though mineralogically similar, i s banded with pinkish quartzo-feldspathic layers alternating with dark fine grained siliceous bands up to 5 mm. i n width*  The layers tend to have rather irregular surfaces and the dark  colour i s apparently the result of a lack of pink feldspar and a s l i g h t l y smaller grain size rather than an increase i n dark mineral content. Specimen M8-A has a rather porous texture and i s composed predominantly of angular pink feldspar grains about 1 mm. i n size.  Angular and rounded  quartz and chert fragments occur here and there as do dark b i o t i t i c and c h l o r i t i c masses. The rock also contains a very thin dark lens of fine grained specular hematite. Microscopic The rock sections are composed almost wholly of quartz and feldspars i n about equal proportions and averaging about 1 mm. i n size.  -38-  The quartz has rounded to sub-rounded outlines which are scalloped i n detail.  Most of the quartz grains exhibit strain shadows. The larger  grains of feldspar are mostly orthoclase and microcline usually containing a good deal of clay alteration.  The matrix material consists of an  intimate mixture of very small (o.05 mm. or less) grains of quartz and feldspar.  The l a t t e r shows negative r e l i e f but only rarely polysynthetic  twinning, and i s quite clear. Varying but small amounts of carbonate, b i o t i t e , muscovite, chlorite, tourmaline, and anhydrite are also present. As noted previously minor amounts of specular hematite produce t h i n darkish layers i n parts of the rocks. Feldspathic sandstones, or arkoses are appropriate names for these rocks.  Textures are apparently due to diagenesis and no obvious  metamorphic effects are apparent. The fine grained quartz-feldspar cementing material may have derived i t s present character from some compaction and possible reconstitution subsequent to deposition.  Microcline  has clear secondary outgrowths which may be termed "pressure microcline" and fine grained feldspar produces, by replacement, the scalloped borders on quartz grains and may therefore be authigenic.  The other minerals,  including tourmaline, exhibit no features that would class them as other than d e t r i t a l fragments. Specimen M8-A can possibly best be described as a "decomposed" granite, i . e . a sedimentary rock formed of the products of a rapidly weathered granite, which products have undergone l i t t l e or no transportation and have formed a rock l i t t l e different, from the parent.  -39-  DETAILS OF ORE MINERALOGY AT NKANA MINE  General Statement Copper mineralization, according to Guernsey (1947), has been found i n the 'Ore Horizon' and to a minor extent i n the Hanging Wall strata, along both limbs of the syncline but, to date, mining has been done only along a part of the East limb where the South, North, and Mindola Orebodies are located. The 'Ore Horizon' i s continuous between them but i s poorly mineralized at two or more l o c a l i t i e s along the outcrop. Guernsey makes the following statements concerning the ore minerals and their occurrences. "The dominant ore minerals are chalcopyrite, bornite, chalcocite, and c a r r o l l i t e . Pyrite i s present at some l o c a l i t i e s where chalcopyrite i s the principal ore mineral. Bornite and chalcocite are important below the zone of oxidation but tend to decrease down the dip. The decrease i s not uniform throughout and i s evidently conditioned, to some extent, by the structure and porosity of i n d i v i dual members of the 'Ore Horizon'. Chalcocite and native copper extend to a depth of at least 2370 feet at the north end of the North Orebody. The l a t t e r , i n thin sheets and small irregular aggregates, i s generally restricted to the 'Porous Sandstone' but has been noted near the foot w a l l . Minor malachite staining has been observed at a depth of 1810 feet i n this section. The sulphides occur principally as disseminations throughout the 'Ore Horizon' strata and, to a lesser extent, as clots, aggregates and vein-like aggregates with carbonates and quartz. Throughout the North and Mindola Orebodies the so called 'Cherty Ore' i s generally richest i n copper, while the 'Low Grade A r g i l l i t e ' i s the poorest. The cobalt-copper sulphide C a r r o l l i t e i s most often concentrated i n the copper members of the 'Ore Horizon , - the 'Cherty Ore' and the Porous Sandstone'". 1  1  Because of the disseminated character of the ore minerals, t h i n sections and the petrographic microscope offered the best means of studying mineralogic relationships and consequently very l i t t l e polished section work was undertaken.  -40-  D e t a i l s o f ore m i n e r a l o c c u r r e n c e s w i l l be discussed, under the v a r i o u s members o f the 'Ore H o r i z o n ' . 1.  Hanging W a l l  Argillite.  C a r r o l l i t e , b o r n i t e , c h a l c o p y r i t e , and p y r i t e a r e found i n s m a l l amounts i n t h i s bed. C a r r o l l i t e  ( i n specimen Ml-C) i s p r e s e n t  both as d i s s e m i n a t i o n s and i n c a v i t i e s from 1 t o 5 o r 6 mm.  i n diameter.  E u h e d r a l , s u b h e d r a l , and i r r e g u l a r g r a i n s from 0 . 2 t o 0 . 4 mm. meter, and l a r g e r masses up t o 3 mm.  i n dia-  i n s i z e a r e found throughout the  specimen. B o r n i t e forms t h i n r i m s on the c a r r o l l i t e and i s d i s s e m i n a t e d as i n d i v i d u a l g r a i n s from 0 . 1 t o 0 . 2 mm.  i n size.  The s m a l l amount o f  c h a l c o p y r i t e i s a s s o c i a t e d r i w i t h , and r e p l a c e s t o some e x t e n t , t h e c a r r o l l i t e and i s i t s e l f p a r t i a l l y r e p l a c e d by b o r n i t e . . P y r i t e , i n g r a i n s from 0 . 0 1 t o 0 . 0 5 mm. masses a v e r a g i n g 0 . 3 mm.  i n s i z e and a l s o i n cubes and i r r e g u l a r  i n s i z e , i s thoroughly disseminated  throughout  some o f t h e specimens. The g r a i n s i z e o f t h e p y r i t e bears a d i r e c t r e l a t i o n t o the g r a i n s i z e o f t h e r o c k m i n e r a l s w i t h which i t o c c u r s : c o a r s e r g r a i n s o f p y r i t e a r e found i n c o a r s e r p o r t i o n s o f the r o c k and f i n e r g r a i n e d p y r i t e with f i n e r g r a i n e d r o c k m i n e r a l s .  I t i s f a i r l y c e r t a i n that  p y r i t e r e p l a c e s r o c k m i n e r a l s because t h e l a r g e r masses o f p y r i t e  con-  t a i n i n c l u s i o n s o f both b i o t i t e and f e l d s p a r though no p r e f e r e n c e f o r any one m i n e r a l s p e c i e s i s a p p a r e n t .  There i s some tendency  f o r small  p y r i t e g r a i n s t o be o r i e n t e d i n " s t r i n g s " p a r a l l e l t o the l a m i n a t i o n s i n t h e r o c k but m i c r o s c o p i c a l l y no s t r u c t u r a l o r m i n e r a l o g i c a l c o n t r o l can be d i s c e r n e d .  -41-  C a r r o l l i t e , bornite, and chalcopyrite have features similar to those of the pyrite, with the difference that the grain size of the rock does not control the size of the sulphides.  The sizes of the c a r r o l -  l i t e grains and masses are much larger than those of the surrounding rock minerals.  Irregular c a r r o l l i t e masses, rimmed by bornite and p a r t i a l l y  replaced by chalcopyrite, contain inclusions of carbonate, feldspar, and white mica, and apparently replace rock minerals although, as with the pyrite, no metamorphic or hydrothermal effects connected with sulphide emplacement can be recognized.  I t i s suggested that the sulphides may  have replaced carbonate preferentially but this i s merely an impression and conclusive proof i s lacking. 2.  'Porous Sandstone' Native copper and hematite are the metallic minerals found i n  t h i s bed and although they can be discerned with the naked eye nothing concerning t h e i r relationships to other minerals can be determined. The t h i s sections reveal that the native copper, which occurs as dusty fragments and shapeless masses often a millimeter or so i n size, has a very marked a f f i n i t y for feldspar grains.  The l a t t e r are so thoroughly cram-  med with copper that r e l i c t polysynthetic twinning i s barely perceptible. Although i t i s sometimes found between carbonate grains the copper prac0  t i c a l l y never i s included i n them. Powdery red hematite, sometimes impossible to distinguish from the copper, appears to line minute fractures and cleavage cracks as well as outline the carbonate grains. Why the copper has such preference for the feldspar and at the same time such disdain for the carbonate i s rather inexplicable i n the writer's opinion.  The copper i s probably of secondary o r i g i n and i t s  42-  reduction may have been brought about by the- hematite.  I f such i s the  case then the present position of the copper has been controlled by the position of the hematite.  Thus the copper followed the hematite and now  appears as coatings on the rock minerals and f i l l s the interstices between them. 3.  "!Cherty Ore' The sulphides, c a r r o l l i t e , bornite, chalcopyrite, and pyrite,  are found i n varying quantities, never more than several percent of the t o t a l rock mass, i n the specimens of this ore bed. In general the sulphides are oriented along laminations or bedding (?) planes but this i s by no means always so.  In many instances  small blobs and masses are scattered through the rock seemingly without regard to structure.  There are rare cases i n which the ore minerals are  located along cross-cutting fractures but because these structures are very infrequent that type of occurrence i s similarly uncommon. No obvious mineralogic controls of ore emplacement are apparent i n the thin sections with the exception that the size of the sulphide grains i s clearly a direct function of the size of the rock minerals. The sulphides a l l occur as irregular masses that doubtless replace rock minerals, as evidenced by inclusions of feldspars, carbonate, tourmaline, quartz, and even rock fragments. If there i s any preferential replacement i t i s of carbonate; but the writer doubts whether this could be proven s t a t i s t i c a l l y or otherwise. C a r r o l l i t e i s invariably confined to coarser layers within the rocks. Chalcopyrite, bornite, and pyrite although often concentrated  in layers are also very thoroughly disseminated. The range of grain size i s quite large.  Carrollite aver-  ages about 1 mm. i n size; bornite, chalcopyrite, and pyrite range from less than 0 . 0 5 mm. to over o.l mm. i n diameter. Very noticeable are the lack of hydrothermal type alterations or the association with the sulphides of "gangue" minerals.  I t i s possible  that some of the coarser grained feldspars and carbonates may have originated with the ore solutions but no evidence can be put forth to substantiate such a proposition. L,  'Banded Ore' The occurrences of the ore minerals i n this bed are much the  same as i n preceding horizons. of c a r r o l l i t e are the sulphides.  Bornite and chalcopyrite and a rare grain For the most part these minerals, as  strings of grains and elongate irregular masses, are situated along lamination or bedding planes.  Some smaller grains are disseminated.  In one  specimen (N4-A), i n which the lamellar structure i s not as clearly defined, larger and more irregular masses of bornite with a l i t t l e chalcopyrite are present, i n one place as i n t e r s t i t i a l masses associated with quite coarse and interlocking quartz and carbonate grains. Microscopic s i m i l a r i t i e s to other occurrences are also noticeable.  Some of the larger masses of bornite and chalcopyrite (from 0 , 1 to  2 mm, i n size) contain inclusions of carbonate, b i o t i t e , white mica, and feldspar.  Thus the sulphides assuredly replace rock minerals but at the  same time the sulphides are moulded to some extent around the rock mineral;, grains i n which manner they have acquired quite irregular outlines. Again, as before, the ore minerals are larger and more numerous  -44-  i n c o a r s e r p o r t i o n s o f the rock and  s m a l l e r i n f i n e r p o r t i o n s as  by s c a t t e r e d specks of b o r n i t e 0 . 0 5  mm.  size.  No  'Low  emplacement.  Grade A r g i l l i t e ' Ore m i n e r a l s  1 mm,  i n s i z e i n rock of s i m i l a r g r a i n  a l t e r a t i o n s or gangue m i n e r a l i n t r o d u c t i o n can be a t t r i b u t e d to  the s u l p h i d e  5,  evidenced  are p r a c t i c a l l y i m p e r c e p t i b l e  l e n s of c h a l c o p y r i t e occurs i n one  e l s e can be seen with the naked Two  i n t h i s bed.  of t h e specimens but  A  nothing  eye.  t h i n s e c t i o n s r e v e a l the presence of s m a l l ( 0 , 1  to  0,3  mm..), r a t h e r r o u n d i s h g r a i n s o f b o r n i t e v e r y s p a r s e l y s c a t t e r e d through the r o c k s . e r a l s and  These g r a i n s are somewhat l a r g e r than the e n c l o s i n g rock minhave no apparent replacement r e l a t i o n s w i t h them.  In f a c t  the  method of emplacement of the s u l p h i d e g r a i n s i s r a t h e r p u z z l i n g .  6,  'Schistose  Ore'  The The  two  M i n d o l a specimens c o n t a i n no s u l p h i d e s whatsoever.  North Orebody specimen c o n t a i n s b o r n i t e and  p o s s i b l y some c h a l c o c i t e  i n very s m a l l i r r e g u l a r masses s c a t t e r e d through the c o a r s e r p o r t i o n s o f the  rock. In t h i n s e c t i o n the m e t a l l i c m i n e r a l s  those a l r e a d y d e s c r i b e d .  Some l a r g e r ( l mm.  are no d i f f e r e n t from  or so) i r r e g u l a r aggregates  are found i n the c o a r s e r p o r t i o n s of the rock and  a v e r y few  g r a i n s are s c a t t e r e d through the f i n e r p o r t i o n s .  In p l a c e s r e d powdery-  hematite o u t l i n e s the rock  7,  Foot W a l l  smaller  minerals.  Conglomerate.  Only one  of the specimens o f t h i s member c o n t a i n s any  sulphide  -45-  mineralization.  The matrix of specimen N7-C, one of the "welded" appear-  ing rocks, contains about 1 percent of pyrite as small ( l mm. or less) scattered irregular blobs. The thin section shows that the pyrite encloses small grains of b i o t i t e , white mica and feldspar. No structural controls, preferential replacement, or alteration effects are apparent. 8,  Arkoses and A r g i l l i t e s The specimens of the member contain no sulphides. The only  metallic mineral present i s a small amount of specular hematite which, i n two arkosic specimens forms very thin, wavy, and discontinuous layers. This iron mineral i s very fine grained and i t s i d e n t i f i c a t i o n i s based on i t s appearance both i n hand specimens and i n thin sections and on the fact that chemical tests detected only iron and no other metallic element. In the thin section the hematite appears as small fragments and irregular masses (less than 0.5 mm. i n size) scattered through the fine matrix mate r i a l of the rock. How this hematite came to i t s present position i s a perplexing problem. The grains are most certainly arranged i n a linear or planar pattern but the continuation of a controlling structure i s not to be seen i n the hand specimens, which are, i n one case at least, apparently quite structureless.  Nor can any structure be seen i n the thin section. Large  grains of kaolinized feldspar cut across the band formed by the metallic grains and certainly no structure crosses the feldspar. There does not seem, therefore, any reason for supposing that this material has been i n troduced; i n fact i t i s more probable that i t was deposited contemporaneously with the other d e t r i t a l mineral fragments.  -46-  ORIGIN OF THE ORES  This section of the paper w i l l be devoted to: a brief review of general theories of ore genesis; a recapitulation of prevalent theories concerning the Northern Rhodesian copper ores; a summation and interpretation of evidence gathered i n this study; and suggestions f o r further work which may help i n the elucidation of the genesis of the copper ores. General theories of ore emplacement. It i s not the object of the following remarks to present a c r i t i c a l review of the details of various theoretical concepts respecting the origin of ore deposits. I t i s hoped that a brief summary of theories w i l l aid i n the direction of thought: the case for any theory must be b u i l t upon a foundation of numerous pieces of factual evidence which have been put together i n such a way that the strongest possible structure results.  Facts may be related one to another i n many ways but  there i s assuredly only one way which i s right: this then i s the ultimate truth. The f i r s t step towards the attainment of the truth i s the accumulation and analysis of the factual evidence; the second i s the synthesis of this evidence.  I t i s therefore necessary to know what  evidence to accumulate and what the synthesis i s l i k e l y to produce. Theories of ore genesis may be broadly cast into three groups: 1.  Epigenetic - ore deposits of later origin than the rocks among which they occur.  2.  Syngenetic - ore deposits formed contemporaneously with  -47-  the enclosing rocks; for the present purpose two subdivisions may be made: i. ii.  Deposits i n sedimentary rocks, Deposits i n plutonic rocks.  In the following discussion the term syngenetic w i l l be restricted to deposits i n sedimentary rocks. 3.  Meta-syngenetic - ore deposits resulting from the metamorphism of pre-existing deposits.  These theories have three essential factors i n common: a source of material; a means of transport of material; a s i t e and a means of deposition of material. Epigenetic theories of ore genesis presuppose a previous accumulation of materials at depth i n a reservoir of some sort. These materials must now rise to the scene of deposition and obviously two factors are essential.  F i r s t l y there must be some means of access to the site of  deposition and secondly the materials must be i n a condition of 'potential mobility'.  There must of course be a suitable site for the re-accumulation  of the upward migrating material and a means of deposition (a physical or chemical process). Pre-existing rocks provide the source of materials for syngenetic (sedimentary) theories of ore genesis.  These materials are trans-  ported to the s i t e of accumulation or deposition by surface agencies: water, wind, and i c e . The site i s obviously a sedimentary channel or basin and the means of deposition may be physical or chemical or both. Meta-syngenetic theories of ore genesis include the middle ground between epigenetic and syngenetic theories. The elucidation of  -48-  meta-syngenetic ores i s fraught with complexities, as i s that of their counterparts i n petrology, the metamorphic rocks. Geologic evidence. The support of any theory w i l l be based upon geologic evidence. Where w i l l this evidence be found and what w i l l be i t s nature? Epigenetic deposits Because a source at depth has been postulated some evidence of this magmatic source may be discovered or possibly induced.  These questions  must be answered: Are possible source rocks close at hand? Can these rocks be identified as source rocks?  Evidence w i l l be provided by ore-bearing  plutonic rocks, or by plutonic rocks which are obviously the parents of ore-bearing veins. Closely related to the source i s the means of access.  Along  which paths were the materials brought to their present resting place? Such features as major faults or shear zones, secondary or subsidiary faults and fractures, and small to very small scale openings w i l l be looked for to answer this question. As a corollary of the preceding question comes the next question:  I f pathways are present do they bear the imprint of the materials  which used them? Ore minerals themselves, or exotic minerals, or transformations of pre-existing minerals w i l l provide an answer to this query. Finally:  What i s the site of deposition and what were the  means of deposition? The growth of minerals i n open spaces, the f i l l i n g of cracks, the replacement of pre-existing minerals and similar features which point to the ore minerals as 'late-comers w i l l help to elucidate 1  the problem posed by this question.  -49-  A lack of evidence for epigenjis leads naturally to a syngenetic conception. If no plutonic source, no tectonic structural controls, and no alterations or mineralogical replacements can be discerned then obviously the foundation has been laid for the erection of a syngenetic theory. Upon this foundation evidence relating the ores to purely sedimentary phenomena may be built. Such facts as stratigraphic layering of ore, detrital characteristics of ore minerals, and the presence, either actual or inferred, of precipitating agents may be used. The middle ground provided by the meta-syngenetic theory is very difficult to map, depending on the extent to which the processes responsible for transformation have been effective.  At one extreme the  over-print of metamorphic effects will be very light and relict sedimentary features will still be apparent.  At the other extreme the sedimen-  tary deposit will be so thoroughly transformed that no original features remain and the deposit is now indistinguishable from an epigenetic one. The reader is referred to a recent paper by Backlund (1950) for a more extensive treatment of this last extreme viewpoint. A brief recapitulation of theories of origin of the Northern Rhodesian Copper Deposits. Some reference to theories of origin has already been made in an early part of this paper, (p. 18). Both syngenetic and epigenetic theories have been proposed for these copper ores but only the latter is dealt with to any extent in the literature.  In fact the only literature available to the writer  proposes and cites evidences for epigenetic theories.  Schneiderhohn (1931)  50-  i s the only author known to this writer who has upheld the syngenetic concept. His work was done very early i n the history of the development of the deposits and forms a part of a larger part of a work on South Africa.  Schneiderhohn's theory was doubtless based upon the large extent  and bedded nature of the deposits and also upon the apparent lack of hydrothermal alterations. Much evidence has been put forward by proponents of epigenetic theories.  Some of this may be open to question but the following tabu-  lation gives an indication of the type and extent of evidence that has been cited. 1.  Proximity of Younger Granites (source rocks) and ore bearing strata.  In places these granitic rocks are said to  cut the ore horizons. 2.  Copper i s found i n the granite, i n fissures i n the Basement Schists, i n joints i n the basal Mine series quartzi t e s , and in veins in the ore horizon i t s e l f (Gray, 1932, p.  3.  Ore  329),  is found i n beds of diverse mineralogical and chemical  composition: a physical control i s indicated, 4.  The ores are confined to beds which are, or have been quite permeable. Permeability of beds has been increased by folding and consequent re-arrangement.  5.  The ores have been localized by the damming action of impermeable sedimentary horizons.  6.  The ore has migrated from one horizon to another through openings i n impermeable beds.  -51-  7.  The o r e m i n e r a l s  r e p l a c e rock m i n e r a l s .  Ore r e p l a c e s  the o r i g i n a l c a l c a r e o u s cement o f t h e o r e h o r i z o n (Davidson, 8.  Presence  1931,  151).  p.  o f the h i g h temperature m i n e r a l , t o u r m a l i n e , and  o t h e r m i n e r a l s such as white mica, c o l o u r l e s s c h l o r i t e , and secondary  f e l d s p a r s which have been i n t r o d u c e d by t h e  ore s o l u t i o n s .  The i n t r o d u c t i o n o f q u a r t z and carbonate  m i n e r a l s and the a s s o c i a t i o n o f o r e m i n e r a l s w i t h  this  'gangue'. 9. 10.  S u l p h i d e s o r i e n t e d a l o n g s c h i s t o s i t y show no e l o n g a t i o n . The m a j o r i t y o f t h e c h a l c o c i t e was formed above 91°C.  or  p o s s i b l y above 200°C. 11.  The shape o f t h e d e p o s i t s i s p a r t l y c o n t r o l l e d by t h e f o l d i n g : t h e o r e m i n e r a l i z a t i o n i s l a t e r than t h e f o l d i n g .  Some remarks c o n c e r n i n g  these evidences and t h e i r i n t e r p r e -  t a t i o n w i l l be made a f t e r t h e ensuing p r e s e n t a t i o n o f evidences  gathered  d u r i n g the study o f t h e specimens.  Evidence  gathered  i n this  study.  I t i s c e r t a i n l y not p o s s i b l e t o base a c o m p l e t e l y t h e o r y o f g e n e s i s upon t h e evidence as t h i s .  Nevertheless  detailed  accumulated i n an i n v e s t i g a t i o n  such  i f answers t o c e r t a i n q u e s t i o n s a r e forthcoming  the e r e c t i o n o f a t h e o r y may be f a c i l i t a t e d o r a t l e a s t the s e a r c h o f evi d e n c e may be g i v e n  direction.  L o g i c a l l y the f i r s t question i s : minerals  c o n c e n t r a t e d and what reasons  ore i n these beds?  In what beds a r e t h e o r e  can be g i v e n f o r t h e occurrence o f .  Guernsey (1947) states that the 'Cherty Ore' i s richest i n copper while the 'Low Grade A r g i l l i t e ' i s the poorest, and also that c a r r o l l i t e i s most often concentrated i n the 'Cherty Ore' and the 'Porous Sandstone'. These statements are borne out by the collection of specimens. The 'Cherty Ore' member carries the largest quantity of sulphides and the 'Porous Sandstone' and 'Banded Ore' carry less, but nevertheless important, quantities. Other beds contain very minor amounts of sulphide minerals: the Hanging Wall A r g i l l i t e contains a l i t t l e carroll i t e , bornite, chalcopyrite, and pyrite; the 'Low Grade A r g i l l i t e ' has a few scattered grains of bornite and chalcopyrite; the 'Schistose Ore' contains a l i t t l e bornite; the Foot Wall Conglomerate contains a l i t t l e pyrite; the Arkoses and A r g i l l i t e s contain no sulphides. What are the features of the major ore beds? Marked d i f f e r ences i n mineralogical composition are at once apparent. The 'Cherty Ore* horizon i s a dense, f a i r l y hard a r g i l l i t e , i n places containing small amounts of carbonate. The 'Banded Ore' i s an argillaceous dolomite and the 'Porous Sandstone' i s an impure limestone or an impure dolomitic limestone.  Obviously the presence of sulphides i s not a direct function of  the composition of the rocks. Presumably then the presence of ore i n these beds may i n some way be connected with their physical characteristics.  What physical char-  acters these beds might have i n common i s not readily imagined. If i t i s believed that ore minerals are deposited from hydrothermal solutions then permeability i s a factor to be considered.  The  writer cannot imagine that the primary or secondary (product of deformation) permeability of what i s now a very dense a r g i l l i t e can ever have  -53-  been greater than that of the other beds of the 'Ore Horizon '. Possibly 1  Mackay's (1946) 'principle of impedance' (essentially the 'hypo-filtration' or obstruction of 'ore radicles' but not of the 'carrier' solution: an osmotic process) may account for the preponderance of ore i n this dense horizon.  I t must be pointed out however that even i f this principle i s ap-  plicable here i t does not apply to other mines i n the d i s t r i c t whose major ore horizons d i f f e r , both chemically and physically, from this 'Cherty Argillite'.  Also inexplicable i s why the lower 'Low Grade A r g i l l i t e " of  similar physical and mineralogical character did not 'impede' the rising solutions before they progressed to the 'Cherty A r g i l l i t e * .  The writer can  produce no satisfactory explanation, following epigenetic theory and based on the chemical and nhysical character of the rocks, for the preponderance of ore i n this horizon. Perhaps the stratigraphic position of the ores may be attributed to features which are not a direct function of the character of the host rock.  This introduces the p o s s i b i l i t y of *damming' action. Rising s o l -  utions upon reaching an impervious horizon may be obstructed i n t h e i r vert i c a l progression and thereupon spread l a t e r a l l y along more permeable horizons.  This appears to be a p o s s i b i l i t y at NKana. The hanging wall of the  ore deposit i s formed by a f a i r l y massive a r g i l l i t e which has been mineralized to some extent near i t s base. The 'Low Grade A r g i l l i t e ' , near the foot wall of the 'Ore Horizon', may also have acted as a barrier because, though very sparsely mineralized i t s e l f , i t overlies the 'Schistose Ore' which i n places contains appreciable copper mineralization. Because only those evidences observable in the collection of specimens are being considered, the effect of faults and l i k e structures as possible 'localizers' of ore w i l l not be considered here.  The position of the ore minerals within the beds of the 'Ore Horizon' should be reviewed.  The sulphides, though disseminated to a  greater or lesser extent, are noticeably oriented along lamination planes. Presumably this might be an effect of hydrothermal processes.  I t i s pos-  sible that microstructures were formed along the lamination (bedding) planes during deformation and prior to or accompanying mineralization. These openings would provide pathways for the mineralizing solutions. Such openings may have been very small indeed but i t i s that they  than the pore spaces of the rock.  were l a r g e r  only  necessary  Cross-cutting  fractures are not at a l l common i n the ore beds but where they do occur they are found to be mineralized. The black f i s s i l e shale requires special comment. Conformable (with f i s s i l i t y ) and cross-cutting chalcopyrite bearing quartzcarbonate veins are a unique feature of this rock.  The origin of these  veins most assuredly conforms with epigenetic theory.  The cross-cutting  veins exhibit an interesting form. They are sinuous, a shape which i s interpreted by the writer as the result of nonaffine deformation along the f i s s i l i t y surfaces.  I f such i s the case then they were obviously  emplaced before or during the deformation which produced the f i s s i l i t y . What microscopic characters may be used as evidence? The size of sulphides i s goverened by the size of the enclosing rock minerals.  This morphological correspondence suggests replacement of the  rock minerals by the ore minerals. definitely occurred.  In the writer's opinion this has  Inclusions of s i l i c a t e and carbonate minerals i n  the sulphides i s evidence of this but i t must be admitted that a speci f i c example i n which sulphides could be 'seen' to replace other  -55-  minerals would be hard to find. At some places there i s doubtless an association of the ore minerals with quartz and carbonate, as witnessed by the veins i n the f i s s i l e shale. A similar association i s found along some of the lamination planes. But this i s by no means always the case. Many instances of sulphide occurrence without the association of these 'gangue' minerals have been noted and the writer would be loath to generalize that the ore minerals are always associated with quartz and carbonate, introduced or otherwise. Tourmaline occurs i n small quantity throughout the rocks of the 'Ore Horizon but every grain examined by the writer showed d e t r i t a l 1  characteristics, though some grains did have colourless rims which are interpreted as authigenic outgrowths.  Other minerals such as b i o t i t e ,  s e r i c i t e , chlorite, and feldspars may or may not be original sedimentary constituents but they certainly show no special relations to the ore minerals and are probably best attributed to diagenetic or low grade regional metamorphic processes. Summation and suggestions f o r further research. Enough data have been accumulated to form a basis f o r a theory of origin of these ores but i t i s clear that much of these data require re-examination and substantiation.  In the writer's opinion the evidence  most markedly points to an epigenetic theory. There are certainly too many c r i t e r i a f o r enigenesis to warrant an attempt to construct a syngenetic (sedimentary) theory. I t i s not proposed that any one fact or piece of evidence alone must support the theory: numerous relatable facts must be used.  -56-  Considering as factual a l l evidence that has been cited up to this point the case for epigenesis may be stated i n the following manner. There i s a source for the ore minerals i n the younger granites and these rocks exhibit evidence i n the form of copper mineralization that they were indeed source rocks,  Channelways bearing the imprint of metal-  l i z i n g solutions lead from the source rocks to the sites of deposition. The sites of deposition are provided by rocks more permeable than their neighbours and mineralogical relationships show that replacement of these rocks by the ore minerals did take place.  Barriers to r i s i n g solutions  were present and were effective i n concentrating the mineralization. The strength of a theory depends upon the strength of the e v i dence with which i t i s b u i l t .  How strong i s this evidence?  The writer  submits that his evidence i s strong enough to preclude a ourely syngenetic (sedimentary) theory. Because of his unfamiliarity with the d i s t r i c t the writer can scarcely c r i t i c a l l y review the evidence of other writers but doubt apparently exists (Brock, 1951) concerning the v a l i d i t y of some of the evidence and certainly much of i t i s not clear to the writer. There seems to be some doubt extant concerning both the proximity of granite rocks to ore deposits and their authenticity as source rocks.  Though the problem i s not quite clear to the writer the d i s t i n -  ction between 'older' and 'younger' granites i s apparently sometimes d i f ficult.  Jackson considers that the 'younger* granites are indeed the  source rocks but nevertheless admits (1932(2)), p. 455) that: "There i s no essential mineralogical difference between the typical MKushi granite-gneiss(Older Grey Granite) and the younger grey granites, and where the l a t t e r are l o c a l l y gneissoid, any difference, either mineralogical or structural  -57-  p r a c t i c a l l y vanishes'". Here then i s one  field  f o r f u r t h e r work: d e t a i l e d  f i e l d map-  p i n g and e s p e c i a l l y d e t a i l e d p e t r o g r a p h i c work would d o u b t l e s s a i d i n the e l u c i d a t i o n o f the problem  o f the  granites.  I t s h o u l d be i n t e r j e c t e d here t h a t the w r i t e r r e a l i z e s w e l l the d i f f i c u l t i e s  full  o f d e t a i l e d f i e l d mapping i n a r e g i o n such as  this  where o u t c r o p s a r e s c a r c e and where much i n f o r m a t i o n i s d e r i v e d from p l o r a t o r y ' p o t - h o l i n g ' through deep overburden.  Nevertheless a  awareness o f the type o f evidence b e i n g sought w i l l  complete  l e a d t o a more  and c r i t i c a l a n a l y s i s o f a l l a v a i l a b l e i n f o r m a t i o n and i t i s w i t h thought  ex-  thorough this  i n mind t h a t these remarks are made. Doubtless a r e s u l t o f the l a c k o f o u t c r o p i s the p a u c i t y o f  knowledge o f f a u l t i n g i n the d i s t r i c t . f a u l t i n g i s undoubtedly  Jackson  (1932(2)) remarks t h a t  p r e s e n t t o a c o n s i d e r a b l e e x t e n t i n the NChanga  a r e a but few outcrops render the d i s c o v e r y and s o l u t i o n o f the r e s u l t s o f t e c t o n i s m a most d i f f i c u l t  task.  I t i s most p r o b a b l e t h a t i n an a r e a which  i s a p a r t o f a r e g i o n o f the w o r l d i n which enormous v e r t i c a l are commonplace and i n which t e c t o n i c doming o f sediments some l a r g e s c a l e f a u l t i n g i s p r e s e n t . problem for  displacements  i s known t o e x i s t ,  F a u l t s have a p p a r e n t l y p r e s e n t e d  to m i n i n g o p e r a t i o n s but a knowledge o f them i s c e r t a i n l y  the u n d e r s t a n d i n g of 'why  necessary  the ore i s where i t i s * .  C r e s t s o f l a r g e and s m a l l drag f o l d s have been c i t e d as of  no  o r e a c c u m u l a t i o n thus i n f e r r i n g t h a t f o l d i n g preceded  mineralization.  The w r i t e r does not doubt the p r o b a b i l i t y o f t h i s but i t i s apparent c o n c e n t r a t i o n s o f o r e i n such p l a c e s may  loci  that  have been produced m e c h a n i c a l l y .  A c l o s e examination might s u b s t a n t i a t e one o r o t h e r o f these  possibilities.  -58-  A more thorough  examination  o f what has been termed the  'sites  o f d e p o s i t i o n ' i s o b v i o u s l y n e c e s s a r y and i n t h i s r e s p e c t the w r i t e r sugg e s t s t h a t w i t h t h i s an examination especially f r u i t f u l .  of ' s i t e s o f n o n - d e o o s i t i o n ' would be  I t i s noted t h a t a l o n g the e a s t l i m b o f the NKana  s y n c l i n e f o r example t h a t the 'Ore H o r i z o n ' i s " p o o r l y m i n e r a l i z e d a t o r more l o c a l i t i e s a l o n g the o u t c r o p " (Guernsey, t i g a t i o n to determine  the reasons  for this  1947).  two  S u r e l y an i n v e s -  'poor' m i n e r a l i z a t i o n would  answer some o f the problems o f ' r i c h ' m i n e r a l i z a t i o n .  There a r e a l s o  p l a c e s i n the copper d i s t r i c t where lower members of the Mine S e r i e s have been e x p l o r e d and found u n m i n e r a l i z e d ,  A d e t a i l e d p e t r o g r a p h i c study o f  these beds, a l o n g the l i n e s o f the p r e s e n t i n v e s t i g a t i o n , and  comparison  o f f i n d i n g s w i t h those r e s u l t i n g from the study of m i n e r a l i z e d beds would y i e l d much i n f o r m a t i o n .  Perhaps the problem o f whether c e r t a i n m i n e r a l s  t o u r m a l i n e , b i o t i t e , w h i t e mica, c h l o r i t e , and f e l d s p a r s - a r e the o f metamorphic ( i n c l u d i n g d i a g e n e t i c ) o r 'hydrothermal' answered.  processes  -  products c o u l d be  Comparative chemical a n a l y s e s o f c e r t a i n rocks i n which m i n e r a l  g r a i n s a r e too s m a l l f o r o p t i c a l i d e n t i f i c a t i o n i s a suggested The p o s s i b i l i t y o f these d e p o s i t s b e i n g o f  approach.  meta-syngenetic  o r i g i n has been omitted p u r p o s e l y from the p r e c e d i n g d i s c u s s i o n s .  The  w r i t e r f e e l s t h a t owing t o the c o m p l e x i t i e s i n v o l v e d the b e s t approach to the f o r m u l a t i o n o f a t h e o r y o f o r i g i n f o r these d e p o s i t s l i e s i n an attempt able.  to c o n s t r u c t an e p i g e n e t i c t h e o r y u s i n g the i n f o r m a t i o n now A t the same time the p o s s i b i l i t y o f meta-syngenesis must be  i n mind i n o r d e r t h a t no p i e c e of u s e f u l evidence i s o v e r l o o k e d . morphic p r o c e s s e s a c t i n g on an o r i g i n a l l y sedimentary  availkept  I f meta-  d e p o s i t have p r o -  ceeded to the e x t e n t t h a t some ' m i g r a t i o n ' o f ore m i n e r a l s o r r e c o n s t i -  -59-  tution of the whole mieral aggregate has occurred then c r i t e r i a for either epigenesis or meta-syngenesis would i n general be similar or indistinguishable. Theory would diverge however when the problems of source and of access of material to sites of deposition were considered.  Thus i f no  rocks could be found and proven to be source rocks and i f no pathways were found to lead from these sources to the ore deposits then the origin of a deposit exhibiting 'replacement' features might be explained i n terms of meta-syngenetic theory.  The writer i s quite aware that such i s a possib-  i l i t y i n the Rhodesian Copper Deposits. Concluding remarks. The writer lays no claim that the results of his study have clearly indicated the processes which formed the NKana copper deposit. Nor does he claim that, using the material available, the p o s s i b i l i t i e s for investigation have been exhausted.  Many more facts can doubtless be  gleaned from the specimens. Both sulphide and s i l i c a t e mineral i d e n t i f i cations and relations leave much room for further work.  Statistical  methods could be employed, with a good chance of success, to determine whether or not ore minerals have replaced any rock mineral species preferentially or whether there i s any special association of non-sulphides with the ore minerals. However, the writer feels that because no previous laboratory type work had been done (or at least has been published) on Nkana deposits a coverage of the whole problem at a more general l e v e l has been more v a l uable than i f an attempt had been made to treat exhaustively a specific problem at a more detailed l e v e l .  CD  BIBLIOGRAPHY  BACKLUND, H.G.,  "The Actualistic Principle i n Geological Research", reprint from Fran filosofiens och forskningens f a i t , Nya ron inomskilda vetenskaper, University of Uppsala, 1950.  Bancroft, J.A, & P e l l e t i e r , R.A., "Notes on the General Geology of Northern Rhodesia", Min. Mag., v o l . 41, pp. 369-72, v o l . 42, pp. 47-50. 117-120, 180-82, 1929 & 1930.  Bastin, E.S.,  Bateman, A.M.,  " C r i t e r i a of the Age Relations of Minerals", Ec. Geol. v o l . 2 6 , pp. 5 6 1 - 6 1 0 , 1 9 3 1 . "The Ores of the North Rhodesian Copper Belt", Ec. Geol. v o l . 25, pp. 365-418, 1930.  "Economic Mineral Deposits", John Wiley & Sons, Inc., New York, 1942. Becke, F.,  "Sur Physographie der Gementeile der Krystallinen Schiefer", K.K. Akad, Wiss., Mat.-Naturwiss. Klasse, Denkschr, Bond 75, 1913.  Boswell, P.G.H.,  Brock, B.B., Davidson, D.M.,  "On the Mineralogy of Sedimentary Rocks", Thomas Murby & Co., London, 1933. (excellent annotated bibliography). Personal Communication, 1951. "Geology and Ore Deposits of Chambishi, Northern Rhodesia", Ec. Geol. v o l . 2 6 , 1931.  Douglas, D.V.,  "Observations on the Geology and Mines of the Belgian Congo", Min. Mag. v o l . 4 2 , PP. 337-48, 1930.  •  Cr  Gilluly, J.,  "Replacement Origin of the Albite Granite near Sparta, Oregon", U.S.G.S, Prof. Pap. 175-C, 1933.  Gray, A.,  "The Correlation of the Ore-bearing Sediments of the Katanga and Rhodesian Copper Belt", Ec. Geol. vol. 25, pp. 783-804, 1930. "Mufulira Copper Deposit, Northern Rhodesia", Ec. Geol. v o l . 27, pp. 315-343, 1932. & Parker, R.J., "The Copper Deposits of Northern Rhodesia", E. & M.J. vol'. 128, 1929. & Sharpstone, D.C., "An Outline of the Geology of the Nkana Concession and Roan Angelope Mine", Min. Mag. v o l . 42, pp. 180-82, 1930.  Grubenmann & N i g g l i , "Die Gesteins metamorphose, I, Berlin, 1924. Gruner, J.W. & Thiel, G.A., "The Occurrence of fine grained Authigenic Feldspar i n Shales and S i l t s " , Amer. Miner, v o l . 22, pp. 842-847, 1937. Grim, R.E., Bray, R.H., & Bradley, W.F., "The Mica i n Argillaceous Sediments", Amer. Miner, v o l . 22, p. 813, 1937. Heald,  M.T.,  Guernsey,  T.D.,  Jackson, J.A.C.  "Authigenesis i n West Virginia Sandstone", Jour, of Geol., v o l . 58, 1950. "A Short Summary of the Geology, NKana Mine", Rhokana Corporation Ltd., 1947. (1) "Ores of NChanga Mine and Extension", Ec. Geol. v o l . 27, 1932. (2) "The Geology of the NChanga D i s t r i c t , Northern Rhodesia", ".J.G.S. vol 88, pp. 443-515, 1932.  Krynine, P.D.,  "Arkose Deposits of the Humid Tropics", Amer. Jour. S c i . , ser, 5, v o l . 29, 1935. "Paleogeographic and Tectonic Significances of Arkoses", G.S.A. B u l l . , abstract, v o l . 52, 1941.  Lindgren, W.,  "Mineral Deposits", McGraw-Hill, New York, 1933.  Mackay, R.A.,  McKinnon, D.,  Murray-Hughes, R.,  "The Control of Impounding Structures on Ore Deposition", Ec. Geol. v o l . 41, 1946, Private Report, NChanga Consolidated Copper Mines Ltd., Dec. 8, 1948. "Geology of part of Northwestern Rhodesia", with petrographical notes by A.A. Fitch, Q.J.G.S., v o l . 85, pp. 109-63, 1929.  Oosterbosch, R.,  Pettijohn, F.J.,  Robert, M,,  "Copper Mineralization i n the Fungurume Region, Katanga", Ec. Geol. v o l . 46, 1951. "Sedimentary Rocks", Harper & Bros., New York, 1949. "An Outline of the Geology and Ore Deposits of Katanga, Belgian Congo", Ec. Geol. vol 26, pp. 531-39, 1931.  Rove, O.N.,  Tester & Atwater,  Turner, F.,  "Some Physical Characteristics of Certain Favourable and Unfavourable Ore Horizons", Ec. Geol. v o l . 42, 1947. "Occurrence of Authigenic Feldspar i n Sediments", Jour. Sed. Petrol, v o l , 4, 1934. "The Mineralogical and Structural Evolution of the Metamorphic Rocks", Mem. 30, G.S.A., 1948,  Schneiderhohn, H,, "Mineralische Bodenschatze im Sudlichen Afrika", Berlin, 1931. Studt,  F.E.,  "The Geology of Katanga and Northern Rhodesia", Geol. Soc. of S. A f r i c a , V o l . 12, 1913.  

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