Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
DSpace
UBCV
McDougall, James John
Master of Science - MSc
University of British Columbia
The regional geology of the McDame Area is described briefly and a detailed description of the "Contact Group" mineral claims within this area is presented. The "Contact" vein deposit described herein is apparently unique, as far as geological literature is concerned, in its primary mineral associations. This vein, in a contact-metamorphic environment, possesses the form and textural characteristics of a mesothermal deposit. Typical high, medium and low temperature minerals are present in relationships that suggest unbroken deposition in the vein and a genetic relation to both the associated intrusive and related pyrometasomatic deposits. The occurrence and origin of native sulfur, wad, and hydrocarbon in the vein are discussed. Alabandite (MnS), which is a common constituent, is classified, on grounds of ex-solution phenomena, as having crystallized at temperatures greater than those previously assigned to it. The role of manganese in this deposit is given special attention. The conclusion is reached that the Contact Vein was formed at shallow depth under conditions of high but rapidly falling temperature and locally high pressure. Accordingly, it illustrates telescoping within the mesothermal-pyrometasomatic range of physical conditions.
I THE TELESCOPED SILVER-LEAD-ZINC DEPOSITS of the CONTACT GROUP MINERAL CLAIMS, Cassiar D i s t r i c t , B.C. By James John McDougall A thesis submitted i n p a r t i a l f u l f i l m e n t of the requirements f o r the degree of Master of Science, i n the Department of Geology and Geography We accept this thesis as conforming to the standard required from candidates for the degree of Master of Science Members of the Department of Geology and Geography "The University of B r i t i s h Columbia A p r i l 1953 Abstract The regional geology of the McDame Area i s des-cribed b r i e f l y and a detailed description of the "Contact Group" mineral claims within this area i s presented. The "Contact" vein deposit described herein i s apparently unique, as far as geological l i t e r a t u r e i s concerned, i n i t s primary mineral associations. This vein, i n a contact-metamorphic environment, possesses the form and t e x t u r a l c h a r a c t e r i s t i c s of a mesothermal deposit. Typical high, medium and low temperature minerals are present i n relationships that suggest unbroken deposition i n the vein and a genetic r e l a t i o n to both the associated i n t r u s i v e and rela t e d pyrometasomatic deposits. The occurrence and o r i g i n of native s u l f u r , wad, and hydrocarbon i n the vein are discussed. Alabandite (MnS), which i s a common constituent, i s c l a s s i f i e d , on grounds of ex-solution phenomena, as having c r y s t a l l i z e d at temperatures greater than those previously assigned to i t . The role of manganese i n thi s deposit is given special attention. The conclusion i s reached that the Contact Vein was formed at shallow depth under conditions of high but rapidly f a l l i n g temperature and l o c a l l y high pressure. Accordingly, i t i l l u s t r a t e s telescoping within the mesothermal-pyrometasomatic range of physical conditions. T a b l e o f C o n t e n t s C h a p t e r 1 I n t r o d u c t i o n P a g e G e n e r a l S t a t e m e n t 1 L o c a t i o n a n d A c c e s s i b i l i t y 1 P o p u l a t i o n a n d I n d u s t r y . . . 3 C l i m a t e a n d V e g e t a t i o n 4 D r a i n a g e 5 P h y s i c a l F e a t u r e s 5 G l a c i a t i o n 6 P r e v i o u s W o r k 6 A c k n o w l e d g m e n t s . 8 C h a p t e r 2 G e n e r a l G e o l o g y o f t h e A r e a R e g i o n a l S e t t i n g : 9 S e d i m e n t a r y R o c k s . . . . 9 I n t r u s i v e R o c k s . . . . . . . . 11 .Me t a m o r p h i c Roc k s 13 M i n e r a l Depos i t s 21 C h a p t e r 3 C o n t a c t G r o u p M i n e r a l C l a i m s I n t r o d u c t i o n 21 G e n e r a l G e o l o g y 22 I n t r u s i v e R o c k s 22 S t r u c t u r e 24 O t h e r M i n e r a l D e p o s i t s B i s m u t h i n i t e - Q u a r t z V e i n 27 P y r r h o t i t e - S k a r n D e p o s i t 31 C a l c i t e V e i n 33 C h a p t e r 1+ C o n t a c t M a i n V e i n P a g e G e n e r a l E n v i r o n m e n t , F o r m a n d D i m e n s i o n s ..34 D y k e s A s s o c i a t e d .^38 W a l l R o c k A l t e r a t i o n ...39 M i n e r a l o g y . . . P r i m a r y M i n e r a l s N o n - m e t a l l i e s -..40 M a g n e t i t e .41 M o l y b d e n i t e ....42 P y r i t e 42 A r s e n o p y r i t e ..42 S p h a l e r i t e 43 A l a b a n d i t e a n d t h e R o l e o f ' M a n g a n e s e 44 P y r r h o t i t e .53 C h a l c o p y r i t e ....56 G a l e n a . 56 S i l v e r 57 T e t r a h e d r i t e . . . . . . . . . . . . 57 B i s m u t h i n i t e . . . .• .58 P y r a r g y r i t e . . . 58 N a t i v e A n t i m o n y 59 Unknown " C " ( D y s c r a s i t e ?) ..60 . U n k n o w n " F n .62 M a r c a s i t e . . . 62 S e c o n d a r y M i n e r a l s N a t i v e S u l f u r 63 Wad ...65 H y d r o c a r b o n 67 C h a p t e r 5 Summary a n d C o n c l u s i o n s C o n t a c t V e i n 68 R e l a t i o n o f C o n t a c t V e i n . t o P y r r h o t i t e D e p o s i t . . 7 2 C o n c l u s i o n 76 B i b l i o g r a p h y 77 L i s t of I l l u s t r a t i o n s Page Plate I.... Inclusion i n Cassiar Granite 12 II....As above 13 III.... .Alteration i n Contact Hornfels 20 V....Fault i n Contact Limestone... 25 VI....Lower Portion Contact Main Vein 26 VII....Lower Vein-Contact Mineral Vein 36 VIII....Ex-solution Intergrowth, Alabandite i n Sphal...46 IX....Ex-solution Intergrowth, Pyrrhotite i n Alaban . . 5 3 a X.... Native Antimony i n Galena 59 XIa... .Dyscrasite (?) i n Galena.. 61 Xlb.... As above 6lA XII.. ...Marcasite Showing Colloform' Bands 61B •Figure 1....Cross Section - Contact Vein Area. 24b l a . . . Pyroxene-Hornfels Facies Diagram .18 2....Paragenesis - Quartz-Bismuthinite Vein....28b 3....Paragenesis - Pyrrhotite-Skarn Deposit....28b 1 5... .Paragenesis, Contact Vein 40b 5 a . . .Rods of Pyrrhotite i n Zns, PbS, and MnS . . .54 7 . . . . Graph - S i l v e r vs Lead, Zinc and Manganese 5.6b 8... .'Dyscrasite (?) i n Galena 5'6b 9 . ..> S o l i d Solution Data for the Systems MnS-ZnS and Mns-Fe]__xS 46a 10....Comparison, Contact Vein to Pyrrhotite Deposit.. :. 73a Map I....McDame Area - . - • . (Pocket) Map II....Contact Group (in Pocket) 1 THE TELESCOPED SILVER-LEAD-ZINC DEPOSITS of the CONTACT GROUP MINERAL CLAIMS Cassiar D i s t r i c t , B. C. Chapter 1 INTRODUCTION General Statement This report contains a b r i e f geological description of that part of the Cassiar Mountains within the McDame Map Area of northern B r i t i s h Columbia and a detailed description of the mineral deposits of the Contact Group Mineral Claims located within this area. The writer spent the f i e l d seasons, of 1950 and 1951 i n the McDame Area i n the employ of the Geological Survey of Canada. During the course of this work several i n t e r e s t i n g problems arose concerning these mineral deposits. In 1952 a week was spent i n examining and mapping the deposits i n greater d e t a i l than previously. Related laboratory work was car r i e d out at the University of B r i t i s h Columbia during the f a l l and winter sessions of 1951-52 and 1952-53. Location and A c c e s s i b i l i t y The Contact Group mineral claims are i n the McDame 2 Map Area of north central B r i t i s h Columbia. As defined by the Geological Survey of Canada, t h i s area is bounded by la t i t u d e s 59 and 60 degrees north and longitudes 128 and 130 degrees west. (See Map 1) Pr i n c i p a l settlements i n or serving the area include Lower Post, B. C , at the junction of the Dease and Liard Rivers, and Watson Lake, Yukon Territory, a few miles to the northwest. Both are served by the Alaska Highway which cuts across a small portion of the McDame Map Area. Distances from Dawson Creek (Mile 0) along the Alaska Highway are 620 miles to Lower Post and 635 miles to Watson Lake. Mileage to Whitehorse from Dawson Creek i s 918. Watson Lake a i r p o r t i s 8 miles northwest of Watson Lake and is served by a branch road. This a i r p o r t i s a scheduled stop of Canadian P a c i f i c A i r l i n e s and i s a Royal Canadian Ai r f o r c e base. Charter planes of land and water type are also available. This service i s maintained by Mr. Dalzielse of Watson Lake. Access to the central part of the area and p a r t i -c u l a r l y the l o c a l i t y to be discussed i s now gained by a 70 mile road which leaves the Alaska Highway near Mile 6A-8 and runs southerly to the former Moccasin Mines placer camp on McDame Creek. The road forks at this point, one fork going downstream about 11 miles to the now abandoned McDame Post at the junction of McDame Creek with Dease River, and the other going upstream about 18 miles to McDame Lake. From Snow Creek,, some 13 miles along this l a t t e r road from Moccasin 3 Mines, a 10-mile road connects with "Cassiar"*, a recently-constructed mining camp of Cassiar Asbestos Corporation on Troutline Creek to the northwest. A three to four mile road connects the raining camp'with the asbestos deposit to the north. This road runs less than a mile to the east of the Contact Group Mineral Claims which are ea s i l y v i s i b l e from i t . Pack and game t r a i l s provide access to most of the remote points. Several lakes suitable for use by pontoon-equipped a i r c r a f t occur scattered throughout the d i s t r i c t . (See Map 1) Population and Industry Placer gold deposits were discovered in. the Cassiar D i s t r i c t i n about 1872 and about $5,000,000 worth of gold was recovered up to 1923 (Hanson and McNaughton, 1936, p.12). About $1,500,000 of this value was recovered from Mc.Dame Creek (Ibid p.12). Value of placer since "then has been n e g l i g i b l e . Lode Gold deposits received notice i n 1934 when a one-ton shipment containing 4 ounces of gold was made. However, due to the shallowness and i r r e g u l a r i t y of these deposits, they have not proved economic as yet. No further shipments of ore were reported from the area u n t i l the advent of the Alaska Highway made the area more accessible. In 1947-48 Moccasin Mines Limited constructed the road from the Highway already referred to. Dredging operations ceased i n 1949 a f t e r a season of poor recovery (Hemsworth, 1950, p.A197). Following the discovery, during the 1949 f i e l d season, of a deposit of high * U n o f f i c i a l name 4 grade chrysotile asbestos on a t r i b u t a r y of Troutline Creek, and i t s ultimate purchase by Con West Exploration Limited i n the late summer of 1950, the area took a new lease on l i f e . At the present time a crew.of several hundred men i s engaged i n the construction of mine and m i l l f a c i l i t i e s at Cassiar p r i o r to expected production of commercial asbestos i n 1953. Climate and Vegetation Physiographically the area i s situated i n the Central Plateau and Mountain area of B. C. (Bostock, 1948, p.45). P r e c i p i t a t i o n i n this region i s approximately 25 inches per annum. The summer r a i n f a l l i s not heavy, but i s consistent, occurring mostly i n the mountains during late afternoon. The snowfall i s l i g h t with about a four foot average i n the v a l l e y s . The extreme winter temperature averages about 20° below zero (Mandy, 1 9 3 5 , p. B13). In 1950 and 1951 the snow had melted i n the main valleys and south facing h i l l s i d e s by mid-June but d i d not leave most of the other slopes u n t i l mid-July. The f i r s t permanent snow occurs i n the valleys during October, although t h i s i s subject to much variance. There are no g l a c i e r s i n the area although semi-permanent "snow caps" are common. During the summer months daytime temperatures are moderate and nights are cool. Tree l i n e occurs at about 4 5 0 0 f e e t . Spruce and jackpine are the p r i n c i p a l forest vegetation, the former reaching 18 inches in diameter i n some of the main valley bottoms. Natural feed-grass i s p l e n t i f u l and appears i n 5 quantity along r i v e r banks and i n v a l l e y bottoms within three weeks of the melting of the snow. The Contact Group claims, which occur between 5>000 and 6,500 feet, are barren except for small amounts of bunch-grass. Drainage The drainage pattern of the area i s indicated on Maps 1 and 2 (pocket). A l l streams shown i n f u l l l i n e are persistent. A l l streams i n the area are incorporated i n A r c t i c drainage. Asbestos* Creek flows v i a Troutline and McDame and Dease River into Liard River. Asbestos Creek originates i n several smaller t r i b u t a r i e s as shown on the map. One of these p e r s i s t e n t t r i b u t a r i e s i s i n part sub-terranean. Each of the streams shown i s large enough to supply water f o r diamond d r i l l i n g . Physical Features The Contact claims are in the Cassiar Mountains, which, as designated by Bostock (Bostock, 1948, p.43), l i e within the Central Plateau and Mountain Area of B. G. The Cassiar Mountains r i s e from the Dease and Liard plains i n the east and merge some 50 miles to the west with the Kawdy Plateau, a subdivision of Stikine Plateau. These mountains stretch northwest along the west side of the Rocky Mountain trench which i s occupied here by the Liard River. The Cassiar Batholith forms their backbone. Several peaks of about 7500 feet elevation occur in the area, but the general ^ U n o f f i c i a l name for creek l o c a l l y known as "Third North Fork o f Troutline Creek". 6 summit l e v e l i s about 6500 feet. The maximum r e l i e f , which i s along the Dease v a l l e y , i s about 4900 feet. Generally the g r a n i t i c and volcanic peaks produce a much more rugged t e r r a i n than the sedimentary rocks. Maximum r e l i e f i n the v i c i n i t y of the Contact Group claims i s about 3600 feet. The' peaks here are rugged and large talus areas characterize the lower slopes. Most of the mountain valleys are U shaped and are d r i f t f i l l e d . G l a ciation The Pleistocene ice-sheet i s reported to have moved north i n the McDame Creek area (Hanson and McNaughton, 1936, p.3). Preliminary investigation, primarily of g l a c i a l e r r a t i c s a l l of which occur below 6500 feet elevation, i n -dicate an easterly movement as well. Extensive felsenmare deposits are common i n the higher elevations. Previous Work George M. Dawson and R. G. McConnel c a r r i e d out a reconnaissance survey of the geology along the Dease River i n 1887. Various engineers of the B. C. Department of Mines have v i s i t e d the McDame Creek placers from time to time. J. T. Mandy examined lode gold deposits near McDame Lake for this department i n 1935 and 1937 (Mandy, 1935, pp. B13-B22). George Hanson and D. A. McNaughton mapped a southern portion of the area i n 1935 (Hanson and McNaughton, 1936, p.12). Leo Price began mapping the McDame area proper i n 1949 for the Geological Survey of Canada. This work was continued during 1950, 1951, and 1952 by H. Gabrielse whom the writer 7 assisted i n the f i e l d during the f i r s t two seasons. B. T. 0 f Grady carried out a general survey of the asbestos area during 1950 (0 TGrady, 1950, pp. A207-214). This was followed i n 1951 by a detailed examination of the asbestos deposit by J. W. McCammon (McCammon, 1951, pp. 209-214). A report on the mineralogy of the Contact Group Mineral Claims was pre-pared by E. H. Kohse during 1952 (Kohse, 1952). No other work on the area has been published. Reports on nearby areas which may be used for regional c o r r e l a t i o n have been published by the following: To the west — K. DeP. Watson and W. M. Mathews (Watson and Mathews, 1944). To the south and southwest — W. A. Johnston (Johnston, 1925, pp.33-74) and F. A. Kerr (Kerr, 192 5, pp. 75-99). To the southeast — M. Y. Williams (Williams, 1944). To the north C. S. Lord (Lord, 1944). Acknowl edgmen t s The writer wishes to express his appreciation to Dr. Gunning and the present members of the s t a f f of the Department of Geology and Geography for co-operation and h e l p f u l suggestions received and e s p e c i a l l y to Dr. R. M. Thompson for -the numerous X-Ray determinations; to Mr. J. Donnan f o r help i n preparing thin and polished sections; to J. S. Soles, X-Ray Assistant;' and to Dr. R. Delavault f o r carrying out several chemical determinations. Thanks are also expressed to Messrs.. W. Puritch and G. Davis, co-owners of the Contact Group, and to Dr. W. V. Smitheringale for courtesies received during the course of the f i e l d work. The writer i s indebted to Mr. H. Gabrielse, Geological Survey of Canada, for permission to publish parts of the information contained herein. 9 Chapter 2 General Geology of the Area As no s a t i s f a c t o r y geological report has yet been published on the McDa'me Area, only an outline of the general geology w i l l be presented here. Regional Setting The Contact Mineral Claims enclose an area of metamorphosed Paleozoic sediments and i n t r u s i v e Cassiar granite. (See Map 1). These sediments, which are a part of the l o c a l Dease Series, are overlain by sediments and volcan-ic s belonging to the McLeod Series. Despite the large areas of sedimentary rock exposed, f o s s i l s are rare and s t r a t i -graphic c o r r e l a t i o n further complicated by complex structures. Sedimentary Rocks The Dease Series The Dease Series i s comprised of north-westerly trending bands of Paleozoic sedimentary rocks lying between the Rocky Mountain Trench to the east and the Cassiar Bath-o l i t h to the west. This conformable series i s composed largel y of limestones and dolomites with lesser amounts of quartzite, shale, a r g i l l i t e , and chert. The base of the Dease Series has not been determined. Several thousand feet of u n f o s s i l i f e r o u s shales, quartzites, and limestones occur s t r a t i g r a p h i c a l l y below Lower Cambrian shales and a part of pre Cambrian time'may be represented here. 10 Mid Devonian limestones and shales form the uppermost members of the wholly sedimentary Dease-Series. Within the l i m i t s described some 30,000 feet of sedi-ments have been measured. However, r e p e t i t i o n by large scale regional f a u l t i n g and other s t r u c t u r a l complexities, as evid-enced by obvious r e p e t i t i o n s and the fact that Lower Cambrian horizons are known to overlie Mid-Paleozoic horizons, invalidate t h i s f i g u r e . A true thickness of about 20,000 feet i s probably more nearly correct. S t r u c t u r a l l y t h i s s e r i e s consists of several broad, open fo l d s with axes trending northwesterly and plunging gently to the southeast; where i n near contact with the Cassiar Bath-o l i t h , the strata dip to the east at unusually steep angles. The McLeod Series The McLeod Series, i s a somewhat poorly defined, com-plex assemblage of volcanics, a r g i l l i t e s , quartzites, limestones, and u l t r a basic rocks comprising the uppermost horizons i n the area. Interbedded andesitic (?) volcanics and a r g i l l i t e s at i t s base o v e r l i e , with apparent conformity, the Mid Devonian top of the Dease Series. The o v e r a l l geological age of t h i s series i s as yet unknown. Upper Mississippian f o s s i l s have been co l l e c t e d i n the limestone member(s). Elsewhere in the series a l a t e Paleozoic age i s suggested by poorly preserved f o s s i l s representing rugose cor a l s . •* Personal communication with H. Gabrielse, 1952. ** Personal communication with H. Gabrielse,1953• 11 Restricted to thi s series or i t s immediate lower contact are long narrow s i l l - l i k e bodies of serpentine, some of which contain c h r y s o t i l e asbestos. Maximum thickness of the McLeod Series, which i s preserved only i n the s y n c l i n a l areas bordering the batho-l i t h , i s estimated to be about 1 5 , 0 0 0 feet. Intrusive Rocks Intrusive rocks i n the area include, the Cassiar Batholith with several related stocks, and ultrabasic s i l l s and dykes now altered l a r g e l y to serpentine. A p l i t e , pegmatite, and basalt dykes are found l o c a l l y i n the area under discussion. The Cassiar Batholith, which trends northwest i n this area, has the composition and texture of a true granite and possesses many porphyritic and pegmatitic phases. The porphyritic phase i s characterized by large f l e s h colored orthoclase c r y s t a l s i n a groundmass of f a i r l y coarsely c r y s t a l l i n e quartz, oligoclase (Ab75 A n 2 5 ) and orthoclase. Accessory minerals include b i o t i t e and apatite. Small amounts of muscovite, sphene, and c a l c i t e are also present. The pegmatitic segregations occupy areas of several square miles. These and related pegmatite dykes are characterized by the presence of muscovite f l a k e s , about 1 - 1 / 2 inches across or l e s s , and spessartite* garnet. Often the large pinkish orthoclase c r y s t a l s of the coarsely porphyritic phases have a white rim. These are * Possibly raanganiferous almandite. 12 composed mainly of quartz and a sodic plagioclase. Micro-sco p i c a l l y , zonal growth i s evident near the extremities of the orthoclase c r y s t a l s . Inclusions are common i n granite of this type. One such dark colored i n c l u s i o n appears to be an amygdaloidal quartz-free volcanic. Somewhat rounded c r y s t a l s of pinkish to flesh-colored orthoclase, similar to that of the enclosing granite, are scattered through the i n c l u s i o n (Plate I and I I ) . It appears that this orthoclase, which i s not found i n the matrix of the inclusion, has developed by some replacement process. Plate 1. Inclusion of Cassiar Porphyritic Granite. L i g h t colored m i n e r a l i s o r t h o c l a s e . Note amygdaloidal (?) texture. 13 P l a t e I I . I n c l u s i o n i n C o n t a c t G r a n i t e The c o m p o s i t i o n s o f t h e s t o c k s a r e u n k n o w n , b u t t h e y a p p e a r more b a s i c t h a n t h e b a t h o l i t h a n d h a v e l i t t l e o r no f r e e q u a r t z . M e t a m o r p h i c R o c k s I n t r o d u c t i o n M o s t s e d i m e n t a r y r o c k s o f t h e a r e a a p p e a r t o h a v e u n d e r g o n e m i l d r e g i o n a l m e t a m o r p h i s m w i t h t h e p r o d u c t i o n o f a r g i l l i t e s , s l a t e s a n d r o c k s o f c o m p a r a b l e g r a d e . The m a j o r i t y o f t h e f o s s i l s h a v e b e e n o b l i t e r a t e d . T h e r m a l m e t a m o r p h i s m i s w e l l m a r k e d i n t h e s e d i m e n t a r y r o c k s n e a r t h e i r c o n t a c t w i t h t h e C a s s i a r B a t h o l i t h . T h i s e f f e c t h a s b e e n s t u d i e d o n l y i n t h e a r e a e n c l o s e d b y t h e C o n t a c t G r o u p , b u t i s , h o w e v e r , b e l i e v e d t o b e r e p r e s e n t a t i v e o f t h e c o n t a c t 14 zone as a whole. Hornfelses and metamorphosed limestones are well represented. Subdivisions of the metamorphic rocks of the Contact Group area are plotted on Map 11 (Pocket). These members have been designated by the author the Leopard Hornfels, the Black Hornfels, and the Marmorized Limestone. Hornfelses Hornfelses are defined by Turner and Verhoogen (Turner and Verhoogen, 1951, pp.444) as being products of thermal metamorphism i n which structure i s t y p i c a l l y grano-b l a s t i c ' ( h o r n f e l s i c ) . The rock i s usually very tough. Diagnostic mineralogical c h a r a c t e r i s t i c s may include the presence of c e r t a i n metamorphic minerals that are almost e n t i r e l y r e s t r i c t e d to t h i s type of rock and various assembl-ages of which are representative to some degree of the thermal metamorphic history of the rock. Eskola enunciated the idea of metamorphic f a c i e s , an i n d i v i d u a l of which includes a l l rocks, of any chemical composition, which have reached chemical equilibrium during metamorphism under a p a r t i c u l a r set of physical conditions. Modifications and additions p a r t i c u l a r l y by Goldschmidt, (Ibid p.441.•.quoting Goldschmidt) T i l l e y , ( T i l l e y , 1924) and Turner, (Turner and Verhoogen, 1951, p.^434) have resulted i n well defined f a c i e s and sub f a c i e s which are i n d i c a t i v e of the degree of metamorphism undergone. The hornfelses of the Contact area are weakly f o l i a t e d and thus do not show the t y p i c a l i s o t r o p i c character 15 of most hornfelses. An alternative name such as s l a t e , etc., would not, however, be appropriate for t h i s group of rocks. Bedding of these sediments has persisted throughout metamor-phism. These rocks, because of t h e i r toughness, have e f f e c t -i v e l y resisted forces which deformed the limestone member. The unmetamorphosed equivalents of these hornfelses have not been found. Leopard Hornfels This member, of unknown thickness, overlies the Black Hornfels. and underlies an extensive unmapped sequence of meta-sediments. This hornfels, so named because of i t s black and white spotted appearance, exhibits i n d i v i d u a l beds which may be as much as several feet i n thickness'but aver-ages about f i v e inches. This tough, 'grayish-green to black rock i s composed of f i n e grained c o r d i e r i t e , orthoclase, quartz, and b i o t i t e . . Minor amounts of p y r i t e , tourmaline, epidote, white mica, sphene, and c l i n o z o i s i t e are present. The spotted appearance i s caused by spherical to lense-like biotite-poor segregations of c o r d i e r i t e grains. The assemblage c o r d i e r i t e , K feldspar, and b i o t i t e would assign the rock t o Eskola's Pyroxene-Hornfels Facies, which, as interpreted by Turner and Verhoogen, (Ibid.p.441) "includes products of high termperature contact metamorphism, c h a r a c t e r i s t i c a l l y developed i n the innermost zone of meta-morphic aureoles surrounding plutonic intrusions i n f o l d -mountain regions. Moderately high, but not extreme, pressure 1 6 and s t r e s s of low magnitude, i n s u f f i c i e n t t o cause apprec-i a b l e deformation, are c h a r a c t e r i s t i c . " The composition o f the assemblage l i e s above the a n o r t h i t e - h y p e r s t h e n e l i n e on Goldschmidt's ACF diagram ( F i g . l a ) and i s probably i d e n t i c a l to a m o d i f i c a t i o n (IA) proposed by T i l l e y ( T i l l e y , 1 9 2 4 ) which i n c l u d e s c o r d i e r i t e , b i o t i t e , o r t h o c l a s e , and q u a r t z . ("A" on diagram). As such i t would probably be the metamorphic e q u i v a l e n t of an "aluminous" iron-magnesium b e a r i n g s h a l e or a f e r r u g i n o u s magnesian a r g i l l i t e . A A n d a l u s i t e F i g . l a .. Fyroxene-Hornfels F a c i e s . Probable compositions of Contact H o r n f e l s Assemblages shown. Green H o r n f e l s This member, composed o f very t h i n , l i g h t b l u i s h -gray, l i g h t brown, blac k , and green bands of v a r i o u s horn-f e l s i c assemblages, u n d e r l i e s the c r y s t a l l i n e limestone w i t h which i t i s i n f a u l t c o n t a c t . I t i s cut o f f to the west by 17 granite and i s at l e a s t several hundred feet thick. The bluish-gray and green bands are almost c h e r t - l i k e i n appear-ance. The darker bands are often discontinuous and have the appearance of bars p a r a l l e l to the bedding and to the more continuous l i g h t e r colored horizons. • The thickest bands, which are about two inches, are composed of i r r e g u l a r l y a l t e r n a t i n g assemblages of: (a) mass-ive l i g h t brown garnet with diopside and c a l c i t e ; (b) K f e l d -spar, c o r d i o r i t e and b i o t i t e ; and (c) diopside with K f e l d -spar. Other assemblages may be present but were not ident-i f i e d . Magnetite tourmaline, clino.zoisite, white mica, sphene, and c h l o r i t e are present i n small amounts. The garnet (grossularite) - diopside r e l a t i o n (a) again f i t s Goldschmidt's Pyroxene-Hornfels Facies (Fig. la) and i s i n d i c a t i v e of the Thermally metamorphosed equivalent of a calcareous to dolomitic shale. Assemblage (b) i s s i m i l a r to that already assigned to T i l l e y ' s IA sub-facies. Assemblage C apparently represents a rock i n which ir o n was absent and calcium, magnesium, potassium, s i l i c a and alumin-ium were present. This member contains bedding f a u l t s which are p a r t i c u l a r l y evident near the Contact Fault. Here the f a u l t surfaces, when not i n contact, are often l i n e d with small c a l c i t e c r y s t a l s . Black Hornfels The Black Hornfels i s i n part similar to the Green Hornfels, but i s characterized by the presence of large 18 amounts of b i o t i t e which give i t the black color. The out-crops of this member are limited by talus and i t s eastern contact i s not exposed; i t s boundaries, as plotted, are lar g e l y hypothetical. Thus i t may contain other rock assemblages. V i o l e t to blackish c o r d i e r i t e i s recognizable megascopieally i n t h i s rock as i t i s i n the Leopard Hornfels. L i t t l e , i f any, garnet i s present although small amounts of diopside are found.in various bands lacking i n c o r d i e r i t e . Orthoclose and quartz are also widespread and small amounts of magnetite and other u n i d e n t i f i e d minerals are present. This member, because of the large percentage of b i o t i t e present, i s not as tough or as re s i s t a n t to weathering as the preceding members. It has numerous bedding f a u l t s , one of which i s occupied by a pegmatite dyke (N.1520 E.1020).* Marmorized Limestone This member, about 150 feet thick, i s the r e s u l t of thermal metamorphism of a r e l a t i v e l y pure limestone. Its eastern contact i s exposed only i n the southern part of the map area and i t s western edge i s i n f a u l t contact with the Green Hornfels already described. Its general a t t i t u d e i s sim i l a r to that of the other meta-sediments of the area. The milky-white, r e c r y s t a l l i z e d c a l c i t e grains comprising most of this nearly massive body impart to i t a medium grained "sugary" texture not unlike that of coarsely ground commercial rock s a l t . Size of the i n d i v i d u a l grains * Co-ordinates refer to Map 11 i n pocket* 1 9 i s constant, ranging from 1/8 to 1/4 inches i n diameter over a l l areas exposed. Twinning i s readily v i s i b l e i n the hand specimens and exceptionally well shown when viewed microscopi-c a l l y . Despite the f a c t that t h i s member has undergone much f a u l t i n g and slumping, i t has r e s i s t e d weathering more e f f e c t -i v e l y than the hornfelses and stands as a wall where the l a t t e r i s not v i s i b l e , The f a c t that this c r y s t a l l i n e aggregate appears loosely coherent and porous on the surface i s misleading. Ac-t u a l l y the fresh material i s f a i r l y impermeable to l i q u i d s and porosity i s low. * These properties may have been import t'ant i n c o n t r o l l i n g "mineral deposition and w i l l be discussed l a t e r . Near the eastern unexposed contact the i n d i v i d u a l beds are thin ( 1 / 2 to 4 inches) and are often interbedded with equally thin h o r f e l s i c horizons. The limestone at i t s southern-most extension i n the Contact area i s very thinbedded (about 1/2 inch t h i c k ) , and has a decided wafer-like appearance. In the v i c i n i t y of the Contact vein i t i s more massive and indivi-* dual beds are d i f f i c u l t to d i s t i n g u i s h . Introduction of Material Introduction or migration of material following thermal metamorphism, apart from mineral deposits, has taken i place throughout most of the metaosediments. C a l c i t e , p y r i t e , quartz, epidote, and a c t i n o l i t e are common i n v e i n l e t s i n the hornfelses where they may e i t h e r cut or p a r a l l e l the bedding. Well formed c a l c i t e c r y s t a l s up to l / 2 inch i n * Observed during attempted l i q u i d impregnation during manufacture of th i n sections, 20 diameter l i n e bedding plane f a u l t surfaces i n the hornfels west of the Contact Fault, and minute c a l c i t e veinlets occur i n most of the hornfelses of the area. Small pyrite segregations occur along c e r t a i n beds of the Leopard Hornfels. Veinlets of a c t i n o l i t e and quartz are common i n the thin banded rocks where they are usually surrounded by a pronounced leached and s i l i c i f i e d zone. Such an example i s shown by plate 111 (IV) Plate 111 Al t e r a t i o n Zone Surrounding A c t i n o l i t e -C a l c i t e Veins i n Contact - type Hornfels Series of dark, disconnected but p a r a l l e l bars, as seen i n cross section, are c h a r a c t e r i s t i c of many of the 21 hornfelses. These bars have been formed by leaching, around crosscutting v e i n l e t s of t h i s type, of the b i o t i t e which i s the dark constituent i n these biotite^diopside-quartz assemblages. Quartz i s abundant i n these "leached" areas, and iron minerals are absent in d i c a t i n g a thorough leaching of i r o n . Mineral Deposits The locations of mineral deposits, other than those of the Contact Group, are shown on Map 1. Production has been attained only from the gold placer and the asbestos deposits. Except for a small amount of work done on several gold-quartz veins, (Mandy, 193 5» pp.B13-B22) lode deposits have had no detailed examinations to date. Of special i n t e r e s t to this thesis are the deposits on Marble Creek, several miles south of the Contact Group area. These veins are s i m i l a r i n many respects to the main deposit under discussion here. The Contact Group Mineral Claims Introduction This group of s i x claims, which were staked by William Puritch and Gerald Davis, of McDame Lake, are shown on Maps 1 and 11, Due to the large areas of talus and the rugged topography, prospecting of the group has been d i f f i c u l t and thus a minimum of work has been done on i t . Deposits around which these claims were staked include quartz veins i n the granite, pyrrhotite replacement deposits i n the meta-* sediments. A l l deposits are represented within the l i m i t s of 22 one mineral claims and with re l a t e d features are incorporated i n one Map (Map 11 - i n pocket). General Geology On the Contact claims a tongue-like body composed of the hornfelses and c r y s t a l l i n e limestone already described projects into the Cassiar Batholith (See Map 1)» These metamorphosed sedimentary rocks are on the steep easterly-dipping limb of a large southeasterly plunging syncline com-? posed of Dease and McLeod Series rocks. The formations are overlain by about 5000 feet of Dease Series sediments and their metamorphic equivalents' that terminate with probable Mid-Devonian limestone underlying the base of the McLeod formations, * Intrusive Rocks Intrusive bodies i n the claim area include the Cassiar Batholith and a p l i t e , basalt, and pegmatite dykes. The granite represented here i s the coarse porphy« r i t i c type which i n l o c a l areas contains the white rimmed orthoclase c r y s t a l s already mentioned. The granite has under-gone l i t t l e i f any visible- a l t e r a t i o n although the actual contact with the sediments i s obscured i n most places. Inclusions such as those shown i n Plate 1 are common. Aplite i n t r u s i v e s i n the area include s i l l s , dykes,, and i r r e g u l a r f i n g e r - l i k e bodies ranging i n thickness from four inches to four feet. As these are r e s t r i c t e d to the poorly exposed limestone member they have not been traced f o r any great distance. These white bodies are si m i l a r i n com-* # Personal communication, March 1953, with H. Gabrielse, Geologist mapping McDame area f o r Geological Survey of Canada. 23 po s i t i o n and contain quartz, a l b i t e , (An8) and orthoclase. Apatite, s e r i c i t e , hornblende, and b i o t i t e occur i n small amounts. These medium to fine-grained rocks are found i n the marmorized limestone. They appear to exhibit a s l i g h t decrease in grain size near t h e i r contacts but the c r y s t a l l i n e limestone country rock i s not altered. However, one of these bodies p a r a l l e l s a 20 foot thick, sharp-walled skarn "vein" (N 2600-W 1650) consisting of brown massive garnet, c a l c i t e , quartz, epidote, p y r i t e , and hematite. The v e r t i c a l , s i l l -l i k e body, about four feet thick, appears between t h i s skarn and the normal wall rock on i t s south.side. No d i r e c t evidence i s present by which age r e l a t i o n s can be determined. This "vein" i s conformable with the enclosing rocks which i n t h i s case s t r i k e about 30 degrees west of the average s t r i k e of the limestone elsewhere i n the area. This skarn body thus appears to represent an impure limestone bed which has under* gone pyrometasomatism d i r e c t l y connected with the a p l i t e s i l l or s t r u c t u r a l channel ways now occupied by i t . This horizon was not noted elsewhere i n the limestone sequence 0 The Contact main vein i s cut by a four inch a p l i t e dyke (N 1900-W 2170) which on f i r s t inspection appears to be l a t e r than the mineral deposit. However, t h i s could not be proven because of the eroded nature of the contacts. Two hornblende-basalt dykes, each about a foot i n width, appear to be r e l a t e d to the mineral deposit. Like the a p l i t e s , these black, fine grained dykes are found only.in the marmorized limestone. These show a c h i l l e d edge but <• : 2 4 have not altered the wall rock. The lower dyke seems to r e t a i n i t s c h i l l e d edge against the mineral vein which i t appears to cut. Mineralogically these dykes are composed of labradorite x (An60), and hornblende with minor amounts of augite, b i o t i t e , •vand m e t a l l i c s . Both dykes s t r i k e northwest and dip.steeply to the south. A small, coarse textured pegmatite dyke, about two inches i n thickness, occupies a bedding plane i n the Black Hornfels (N 1520«E 1020), This body contains pure and except t i o n a l l y well developed c r y s t a l s of red spessartite garnet and black tourmoline ( s c h o r l i t e ) . Large l/2 inch r a d i a t i n g clusters of white mica are a d i s t i n c t i v e feature. Apatite, Potash, feldspar, quartz, a l b i t e , and several u n i d e n t i f i e d minerals are also present. According to generally accepted terminology, t h i s pegmatite should be classed as complex. Samples of t h i s pegmatite are not radioactive. Structure Structural features of the area include widespread f a u l t i n g and folding of the limestone member and f a u l t i n g of the hornfelses. These members s t r i k e north-south and dip 70° to the east away from the granite, A- hypothetical E^W«cross section (Fig. 1) near the contact vein suggests the possible r e l a t i o n s of the meta-sediments to the i n t r u s i v e . Proximity to t h i s i n t r u s i v e i s suggested only by the presence of a p l i t e and pegmatite dykes i n the sediments. Faults and folds e x i s t i n the. meta-sediments and Elev, F i g . 1 PROBABLE STRUCTURE SECTION ALONG LINS X-Y OF CONTACT GROUP GEOLOGICAL MAP. 6 3 0 0 J S c a l e : 1 IN. TC 200 FT. LEGEND F T / 1 CASSIAR GRANITE • GREEN HORNFELS MARL!. LI&IEST0N2 BLACK HORNFELS z APLITE D Y K E BASALT DYKE &. FAULT 25 especially within the more homogeneous c r y s t a l l i n e limestone member. In this member a complicated series of small scale f a u l t s , with related drag folds and fractures, combined with l a t e r slumping and f r o s t heaving, produce a very complicated structure and make interpretation a d i f f i c u l t task. Many of these f a u l t s are excessively complex, as shown by Plate V» Here a massive marmorized limestone body i s brought into contact with a thin-bedded limestone sequence i n much the same way as the bow of a ship which has ploughed into the p i l e s of a wharf. Fault movement which occurred i n the hornfelses seems to have been taken up along many of the bedding planes, minor f o l d i n g or f r a c t u r i n g of these more r e s i s t a n t rocks i s uncommon. Recent slumping along shear or f a u l t planes has resulted i n the formation of several narrow "crevasses" i n 26 the lime horizon. One of these, where exposed, has an a t t i -tude remarkably similar to that of the Contact vein and shows poorly developed drag folds on the sides of the crevasse. Plate VI. Lower Portion of Contact Main Vein i n Marmorized Limestone. Looking west. Vein Walls, which appear i r r e g u l a r because of coloration by manganese and i r o n oxides, are outlined. 27 Major f a u l t s , as shown on the claim map, include the one marking the Marmorized Limestone - Green Hornfels contact. This w i l l be r e f e r r e d to as the "Contact Fault." This i s apparently a pre-ore gravity f a u l t although, l a t e r movement may have occurred along i t . An "offshoot" of t h i s f a u l t i n the marmorized limestone i s the fracture now occupied by the Contact vein. The actual f a u l t did not occupy the exact contact but apparently has wandered i n places so as to include the outer few feet of the hornfels horizon. The f a u l t zone i s largely obscured by a wall marked t a l u s - f i l l e d depression i n which the f a u l t foot wall i s v i s i b l e but the hanging wall eroded away. Scarps and indentations, presumably the r e s u l t of f a u l t i n g and weathering, cut across the limestone and hornfels to the south of the Contact Vein #; Talus also covers most of this area, * Nothing i s known of the upper or eastern limestone contact except at i t s southernmost ex-tension where i t i s l a r g e l y obscured by metasomatism,. Description of other Mineral Deposits. These deposits w i l l be discussed b r i e f l y as they have features in common with those of the s i l v e r - l e a d - z i n c deposit to be discussed. Paragenetic sequence within these deposits i s i l l u s t r a t e d by F i g . 2, (a) Bismathinite - Quartz Vein This quartz vein i s i n the porphyritic granite immediately south-east of the skarn deposit. (N 500 - E 1500) The vein walls are poorly defined and i n most cases, on the weathered surface at least, the quartz, which comprises * Float i n t h i s area i s s l i g h t l y mineralized. most of the vein, appears to be gradational into the granite. This may constitute s i l i c i f i c a t i o n s of the wall rock. The vein strikes northerly and apparently dips easterly into the mountain at varying but low angles. The true width of the vein, because of gradational and erosional features, i s d i f f i c u l t to ascertain but probably varies between f i v e and f i f t e e n f e e t . The exceptionally rugged nature, of the topography has prevented i t s outcrops being r e a d i l y traced along the surface for more than 100 feet. However, s i m i l a r quartz veins were discovered intermittently for about 1500 feet along str i k e to the South, * These, however, are d i f f erent:mineralogically. The mineralogy of the vein i s quite simple and consists of euhedral crystals of p y r i t e , bismuthinite, and cos a l i t e occupying drusy c a v i t i e s , up to l/2 inch i n diameter, i n the r e l a t i v e l y coarsely c r y s t a l l i n e cloudy quartz. The bismuthinite and c o s a l i t e do not form more than one percent of the volume of the ye in-* Chalcopyrite occupies small fractures i n the bismuthinite. (See F i g . 2 f o r paragenesis, etc.) The quartz, which shows well developed c r y s t a l terminations i n the c a v i t i e s , has numerous microscopic f l u i d i nclusions which possess no ov e r a l l o r i e n t a t i o n . Well preserved quartz molds with thin walls are common i n the c a v i t i e s . The shape of these s i l i c e o u s c e l l s , squarish to rectangular, indicates the former presence of pyrite and possibly bismuthinite* The quartz of these molds appears to * Personal communication with Mr. G. Davis & W. Puritch, McDame Lake, B.C.-P I G . 2 P A R A G E N E S I S . . . . Q U A R T Z - B I S M U T H I N I T E V E I N D e t e n u , QUARTZ L + x x x x x 1,2 S C H E E L I T E S- X X X X 1,2,4 P Y R I T E S XXXX 2 B I S M U T H I N I T E s - XXXX 2,3 C O S A L I T E N- XXXX 2,3' C H A L C O P Y R I T E N. XXXX 2 B I S M I T E XXXX 2 L I M O N I T S • XXXX ' 2 M O L Y B D E N I T E S XXXX 2 B I O T I T E S XXXX 1,2 M O L Y B D I T E s" XXXX 2 UNKNOWN " A " S - T T T T 2,3 F i g . 3 P A R A G E N E S I S . . . . P Y R R H O T I T E - S K A R N D E P O S I T B B 0 S W r a G A R N E T ( s i Mn) XXXX XXXX 1,2, 1, 3 2 D I O P S I D E E P I D O T E XXXX X x X X 1 1 UNKNora -g- O L I T E , P Y R R H O T I T E . x x x x x XXXX i : i , 3 2 P Y R I T E XXXX 2 C H A L C O P Y R I T E XXXX 2 S P H A L E R I T E XXXX 2 C A L C I T E • i , 2 & A R C A S I T E 2 L I M O N I T E XXXX i , 2 K E Y . • F I G S . 2,3i&5. A p p r o x i m a t e % o f T o t a l V e i n M a t e r i a l (volume) L . . +15$, M. .5-15#f S . . l - 5 % , N . . l % . { + ) : : § £ § § t e r D E T E R M I N A T I O N ^ D e t ) ( 1 ) . . O p t i c a l , ( 2 ) . . P h y s . & C h e m . P r o p e r t i e s ( 3 ) X - R a y Powder G r a i n S I a e . . l mu to l & m } ° ' (4)Speotograph. be continuous with that of the main body i n d i c a t i n g an overlap during sulphide deposition. Scheelite i s present as buff colored lumps up to one inch i n diameter i n the quartz and i s unrelated to the drusy c a v i t i e s . Molybdenum, antimony, zinc, : and s i l v e r are indicated by spectographic an a l y s i s . Mineralogically and s t r u c t u r a l l y this vein would probably best f i t Lindgren's mesothermal c l a s s i f i c a t i o n . A s t r i k i n g feature of t h i s deposit i s the development and persistence of large amounts of lemon colored bismite (I^O^ - H£0?) on the steep h i l l s i d e below the deposit. Here t h i s secondary oxide, derived from the bismuthinite, imparts a d i s t i n c t i v e yellow color to several thousand square feet of granite t a l u s . Small amounts of intermixed limonite give i t an orange coloration i n part. Similar quartz veins are reported to occur intermittently along s t r i k e to the south f o r several thousand feet or more. Samples from such a deposit about 1500 feet i n t h i s d i r e c t i o n show the quartz to be lacking drusy c a v i t i e s . Radiated aggregates of molydbenite c r y s t a l s are found i n the quartz and are unaccompanied by other sulphides. A small amount of b i o t i t e i s present. The molydbenum oxide molybdite (MQO^ or, according to Dana, probably FegO^ « 3M o0 3 ~ Bh^O), i s present on the weathered surfaces. I f free of intermixed limonite, the i r o n of which may have been derived from pyrite ... now completely oxidized, the molybdite has a yellowish color s i m i l a r to that of the bismite. 31 Pyrrhotite - Skarn Deposit This deposit, i n the most southerly extension of the sedimentary tongue referred to previously, i s near an i n d i s t i n c t granite contact which i s between the quartz vein f i r s t described and the main contact vein to the north. Intense metasomatism, following thermal metamorphism, has occurred with both the hornfelses and the c r y s t a l l i n e lime-stone of t h i s tongue having been effected, but to d i f f e r e n t degrees. The Black Hornfels, which was not v i s i b l y meta-somatized near i t s contact with the granite some 500 feet to the north, has at t h i s southern contact been appre-ci a b l y altered. This difference may be due i n part to the presence i n the south of more susceptible beds previously unrecognized i n this poorly defined Black Hornfels. The hornfelsic horizon, although s t i l l possessing pre-metamorphic bedding attitudes, i s l a r g e l y replaced i n an i r r e g u l a r area (See Map 11) by coarse textured skarn consisting c h i e f l y of weakly radiating c l u s t e r s of brown scapolite and large i n d i v i d u a l garnets which occupy cert a i n bedding planes i n the more limy rocks. These garnets, which w i l l be referred to as "barnacle" garnets because of their i n d i v i d u a l i t y and apparent base-like attachment to the "footwall" of the beds as seen on weathered surfaces, are noticeably twinned and zoned. In thin sections the zoned portions are often strong-l y anisotropic to the extent of exhibiting a poorly defined b i a x i a l interference f i g u r e . In composition t h i s garnet i s probably andradite and i s s l i g h t l y manganiferous. The zoning and manganese content are important properties i n distinguishing t h i s metasomatic garnet from the non-manga-niferous g r o s s u l a r i t e of the hornfelses. Besides the garnet and scapolite, small amounts of diopside, c a l c i t e , quartz, epidote, tremolite (?) and an un i d e n t i f i e d z e o l i t e (?) are present. Small v e i n l e t s of p y r i t e , quartz, c a l c i t e , and disseminated grains of pyrrhotite together with several unidentified s i l i c a t e s (?) constitute the remainder of this assemblage. The pyrrhotite body i s associated with the metamorphic s i l i c a t e s but i s r e s t r i c t e d to the marmorized limestone. Where exposed on the side of a c l i f f t h i s brownish black deposit i s Well defined as a massive replace-ment body, squarish i n outline, which seems to have eaten i t s way from below to within a few feet of the present surface where i t was suddenly arrested. This upper k n i f e -l i k e contact could be depicted as a near horizontal plane about 15 feet wide, perpendicular to the attitude of the limestone horizon above. No s t r u c t u r a l control i s evident and t h i s deposit would not out crop i f the present surface were continuous and the c l i f f non-existent. A point worthy of note here i s that t h i s upper marmorized limestone has not been altered i n any recognizable form near the replace-ment sulphide body and i n t h i s respect i s quite unlike that surrounding the contact vein which occurs nearby i n th i s same limestone. This sulphide body i s less sharply defined on the sides and seems to grade rapid l y on the east to the skarn already described, and on the west to t h i n bedded wafer-like sequences of barnacle garnet and c r y s t a l l i n e limestone. The southern or lower extent i s obscured by talus. Coarse grained pyrrhotite, largely altered to marcasite, constitutes about 75% of the body. About lJt% chalcopyrite i s present. Minute sphalerite blebs i n the chalcopyrite are believed by Kohse (Kohse, 1952) to be re-presentative of ex-solution. Pyrite i s present i n small amounts. The pyrrhotite i s magnetic and s l i g h t l y n i c k e l -i f e r o u s . Notable for i t s absence i n t h i s i r o n r i c h pyro-metasomatic deposit.is the oxide magnetite which occurs i n abundance i n the nearby Contact vein. Although magnetite may occur at depth, i t i s held that sulfur was present i n excess during t h i s mineralization and the i r o n oxide either could not form, or i f i t did, was replaced by l a t e r pyrrho-t i t e . The non-metallics consist c h i e f l y of coarse grained c a l c i t e and smaller amounts of diopside and garnet. The grain size and the well-developed twinning of the c a l c i t e are s i m i l a r to that of the c r y s t a l l i n e limestone. C a l c i t e Vein Other deposits of i n t e r e s t on the Contact Group are small i r r e g u l a r veins of coarsely c r y s t a l l i n e , cloudy c a l c i t e i n the marmorized limestone. One of these contains small amounts of azurite but no metallic mineral has been noticed. 3 4 Chapter 4 The Contact Sulphide Vein Environment, Form and Dimensions: This deposit i s about 1200 feet to the north of and i n the same marmorized limestone member as the pyrrhotite replacement body. The nearest granite exposure i s about 300 feet to the west. As shown on Map 11 the Contact sulphide deposit i s a vein i n an horizon of Paleozoic c r y s t a l l i n e limestone. This limestone i s overlain and underlain by thin-bedded thermally metamorphosed sediments. The whole assemblage i s bounded on the west and south by coarse porphyritic granite of the Cassiar Batholith. Thus t h i s vein occupies a po s i t i o n s i m i l a r to that of many pyrometasomatic deposits. The upper vein, as shown on the map, i s exposed along s t r i k e f o r s l i g h t l y more than 100 feet h o r i z o n t a l l y . This involves a v e r t i c a l range of approximately 100 feet as the h i l l s i d e slopes to the east at about 4 5 degrees. The down-hill or eastern extension i s obscured by ta l u s . The western or upper boundary i s defined by the Contact f a u l t and the Green Hornfels. The vein increases i n width as the upper contact i s neared. Thus a true width of about three feet near the "base" increases to about f i v e feet near the upper contact. Near t h i s upper l i m i t the vein shows a d i s t i n c t i v e bend to the south. It st r i k e s on an average approximately east-west and dips about 80 degrees to the south. The s t r i k e i s perpendicular to that of the en-closing c r y s t a l l i n e limestone beds. The r i c h e s t part of the vein i s the widest portion, namely the 20 feet nearest the upper contact. I t i s i n t h i s portion that the high temperature non-metallic gangue minerals are most common. A s i x inch vein which st r i k e s northerly from the larger vein i s shown on Map 11 and f i g u r e 4. It i s exposed continuously f o r about 30 feet. Beyond th i s the rock i s disrupted and the vein can.not be traced through i t with certainty. However, the presence along s t r i k e of s i m i l a r l y mineralized f l o a t and altered wall rock, which i s usually associated with the vein, suggests i t s contin-uation for at l e a s t another 20 feet. The dip of t h i s " s t r i n g e r " vein has not been determined but i t appears to be steep. The lower vein i s exposed intermittently on the talus-laden h i l l s i d e below and to the north-east of the upper vein. It appears to occupy a bedding f a u l t i n a c r y s t a l l i n e limestone-hornfels sequence which here s t r i k e s north 40 to 60 degrees east and dips about 70 degrees to the south. 36 Where exposed on the surface the vein i s about one foot wide. (See plate V l l below). This lower deposit has not been examined i n d e t a i l . Plate V l l . Lower Vein of Contact Mineral Claim - looking west. 37 The walls of the upper vein appear very i r r e g u l a r on f i r s t inspection (See plate VI) but t h i s i s due mainly to di s c o l o r a t i o n of the limestone by manganese and i r o n oxides. Structural conditions i n these rocks have been described already and features responsible f o r the l o c a l i -zation of the upper Contact vein discussed. Evidence suggests replacement and f i s s u r e f i l l i n g by ore solutions along "channelways" formed by movement occurring along the Contact Fault. Direct evidence of replacement i s absent i n the upper vein but i s evident i n the related s t r i n g e r vein where the mineralization was less concentrated and carbonates s i m i l a r to the wall rock are the major constituent. The r e l a t i o n of the lower to the upper vein i s not known. The former p a r a l l e l s and seems to replace along the bedding of the sediments while the l a t t e r cuts, across i t at a high angle. The lower deposit could have been formed by a s t r u c t u r a l d e f l e c t i o n i n the course of the mineralizing solutions which formed the upper vein or could have been formed independently. Influence of Wall Rock on Deposition The f a v o r a b i l i t y f o r mineral deposition expressed by the coarsely c r y s t a l l i n e , limestone member was probably due to i t s b r i t t l e character, which caused i t to fracture r e a d i l y under stress, and to the reducing or n e u t r a l i z i n g action of the carbonate wall rock on mineralizing solutions. The Green Hornfels, on the other hand, did not possess these properties and was veined and replaced only s l i g h t l y . Dykes Closely associated i n space with these deposits are the basalt and a p l i t e dykes shown on Map 11 and Fig.4> and previously described. Neither dyke can be traced f o r any distance because of the highly disrupted nature of the rocks along s t r i k e . The lower basalt dyke could con-ceivably be related to the upper by f a u l t i n g . Evidence such as t h e i r s i m i l a r i t y i n composition, attitude, and size i s suggestive. A talus f i l l e d depression c o r r e c t l y situated to outline such a f a u l t i s shown on Plate V l l . Structure of the Upper Vein Coarse banding p a r a l l e l to the vein walls i s cha r a c t e r i s t i c of t h i s main vein. Megascopically the bands consist of alt e r n a t i v e sequences, 1/4 to l/2 inch wide, of the more common sulphides-galena, sphalerite, pyrrhotite, etc. There are no vugs or openings i n t h i s vein which i s made up la r g e l y of metallic minerals. 3 9 Wall Rock A l t e r a t i o n Dolomitization of the pure c r y s t a l l i n e limestone wallrock i s a r e a d i l y recognizable feature of the Contact upper vein. Areas of t h i s buff brown a l t e r a t i o n roughly p a r a l l e l both walls of the vein, where exposed, at an average distance of about two feet where gradation to the coarser grained limestone i s quite rapid. The a l t e r a t i o n appears to be lacking i n places, e s p e c i a l l y near the lower (eastern) part of the vein; however i n other areas i t may penetrate the c r y s t a l l i n e limestone f o r about f i v e feet (See sketch-map, F i g . 4)- No d i r e c t r e l a t i o n appears to e x i s t between the width of the vein and the width of the a l t e r a t i o n . Thus the small, sparsely mineralized stringer vein has an aureole comparable i n size to that of the main vein. Close examination of t h i s a l t e r a t i o n reveals the following: (a) Dolomite and c a l c i t e are present i n about equal amounts. (b) The grain size i s about l/20th inch, or about 1 / 3 as coarse as the containing c r y s t a l l i n e limestone. (c) Small, scattered euhedral magnetite c r y s t a l s are found i n the dolomitized wallrock but are.absent i n the adjoining limestone. Small amounts of white mica are present. Age r e l a t i o n s suggested by the above are uncertain. The r e s t r i c t i o n , to the dolomitized portion, of the octa-hedral magnetite c r y s t a l s suggests that t h i s magnetite mineralization was controlled by some condition p r e v a i l i n g at the time, Dolomitization appears to have been the only c o n t r o l l i n g condition and as such may have been able to pre-pare the physically poor limestone for veining and re-placement by mineral solutions. Mineralogy The o v e r a l l appearance of the primary minerals studied i n polished section i s that of a complex, dissemi-nated mixture i n which the late minerals provide a matrix for the e a r l i e r . Typical high and low temperature minerals occur side by side. Thus within the area of a one inch square section up to 18 d i s t i n c t i v e primary metallic minerals have been recognized. Fracturing and re l a t e d veining of e a r l i e r formed minerals i s not common although there i s much evidence of replacement. Extensive overlapping and complicated exsolution within the sulphide minerals during deposition i s evident. Paragenesis, grain size, amount, and method of determination of the minerals are presented i n tabular form i n F i g . 5' Non-Metallic Gangue Minerals Non-metallic gangue comprises l e s s than ten per cent by volume of the upper vein. The chief con-sti t u e n t s , c a l c i t e , quartz, and rhodonite, are di s t r i b u t e d through the deposit. Some of the c a l c i t e i s r e l i c and some i s l a t e r than the sulphides. Quartz and rhodonite preceded the sulphides. Small but well-formed FIG. 5 # f PARAGENESIS...CONTACT VEIN DEPOSIT Max Grain, (see Fig.2 f o r key) 1c M .ze 11 (n ft Det. m Diopside N+ X X X o 1 Orthoclase N XXX o 1,2 Mg. Tourmaliiije X X X 0 1 White Mioa N* X X X 0 1 B i o t i t e N X X X 0 1 U^r«l¥?e(?) X X X 0 1 Mn. Garnet N . . ? . X X X < » 1,2 Rhodonite N + X X X o 1,2 Quartz S- xxxx ( i 1 Magnetite L xxxx 0 2,3,4 Molybdenite N- XX 0 2 P y r i t e M .XXX 0 2 P y r r h o t i t e M .xxxx..xxxx a 2,3 Arsenopy.riteN + . X X X 0 2 Sphalerite I xxxx 0 1,2,3 Alabandite M .xxxx... 0 2,3 ChaloopyriteN + xxxx ( > 2 Galena L xxxx ( '2,3,4 TetrahedriteS- xxxx c » 2,3 Dysorasite N+ xxxx 0 2,3 Native Antimgh f' xxxx q 2,3 BismuthiniteN xxxx. •Q 2 Native S i l v e ^ _ . X X 2 P y r a r g y r i t e N . X X X . 2 Marcasite M . . X X X 2 C a l c i t e S xxxxx 2 Wad N + X X X 1,2 43 1,2,3 Native Sulfur. X X X . Limonite N X X X . , 2 HydrozinciteN X X X . . ' 2 Unknown n p n N- X X . 2,5 #.. i/!ay be"inclusions" 41 manganiferous garnets have been found near the limestone wallrock i n the upper vein. Fine-grained gangue-like material, p a r t l y re-placed by sulphides, i s present near the upper or western extremity. This rock i s composed.of orthoclase, quartz, tourmaline, b i o t i t e , white mica, pyroxene, garnet and an uni d e n t i f i e d fibrous mineral. Texturally and mineralogi-c a l l y i t i s not much unlike the nearby hornfels and may represent an inc l u s i o n or a pseudomorphous replacement of such. The wall rock to the south i s limestone; that to the north has been removed by surface erosion, but judging by the talus present was limestone also. Unlike the horn-f e l s e s examined, which contained minute amounts of schor-l i t e , t h i s rock has a r e l a t i v e l y high percentage (3%?) of a yellowish pleochroic tourmaline believed to be the magnesian variety dravite. Along with garnet t h i s tour-maline appears to vein the remaining assemblages. Me t a l l i c Minerals Maximum grain s i z e , paragenesis, quantity, and method of determination of these minerals i s given i n tabular form (Fig. 5). Magnetite (Fe-^ 0^) Magnetite i s a common constituent of the vein deposit and was the e a r l i e s t metallic mineral deposited. It occurs invariably as small disseminated, well-formed octahedral c r y s t a l s surrounded by sulphides. It also i s found i n the dolomitized limestone wallrock. 42 The mineral i s strongly manganiferous, contain-ing between 10 and 15 per cent manganese. About 0.2 per cent t i n i s also present. No t i n or manganese minerals have been recognized within the magnetite grains and i t i s assumed these elements exi s t i n s o l i d solution i n the magnetite. Spectographic analyses reveal the presence i n trace amounts of copper, magnesium, zinc and boron. The magnetite has not been fractured or percep-t i v e l y altered. Molybdenite (Mo S 2) Molybdenite i s present i n minute amounts. It occurs i n pyrrhotite which appears to have replaced i t i n part. Pyrite (Fe S 2) Pyrite i s present i n a l l mineral deposits of the Contact Group. In the main vein i t occurs as coarsely banded aggregates or as disseminated subhedral cubic grains c l o s e l y associated with the pyrrhotite. It has been replaced i n very small amount by marcasite but contains no i n -clusions. Average grain size i s about 5 mm. Arsenopyrite (FeAsS) Arsenopyrite i s a minor constituent of the vein. It occurs as well formed laths or diamonds up to 600 microns across, surrounded by other sulphides, namely sphalerite and galena, which have replaced i t i n part. The mineral has been fractured i n several instances and veined by l a t e r sulphides. 43 Sphalerite (ZnS) Sphalerite i s abundant i n most parts of the Con-tact vein and forms up to 25 per cent of the content i n places. It i s di s t r i b u t e d i n the deposit as massive seg-regations, banded lenses, and i n d i v i d u a l blebs i n other sulphides. The brownish-black mineral exhibits a reddish-brown i n t e r n a l r e f l e c t i o n under oblique arc l i g h t , i n -d i c a t i n g a high iron content. Manganese i s present i n small amounts i n the sulphide. Inclusions of chalcopyrite and alabandite are common. The chalcopyrite has exsolved from s o l i d solution as evidenced by long rows of chal-copyrite blebs and exsolution to the rims. Well defined twinning resembling that of plagioclase feldspar i s common. Rods of pyrrhotite are widely dispersed through the sphal-e r i t e , as they are through alabandite and galena. A l t e r a t i o n products include fluorescent hydro-z i n i c i t e and minute amounts of zinc carbonate. Small lemon yellow stains on sphalerite were investigated f o r the presence of cadmium which i s known to occur i n trace amounts. Only zinc was detected microchemically, however, and,it was concluded that the stains, which occurred i n c a l c i t e , were probably due to yellow willemite or native s u l f u r . This p a r t i c u l a r assemblage did not fluoresce under u l t r a - v i o l e t lamp but elsewhere i n the specimens the d i s t i n c t i v e bright green, fluorescence suggestive of willemite was noticed. 44 Alabandite and the Role of Manganese Alabandite (MnS) occurs i n small amounts both i n the main vein and i n the f l o a t of the lower p i t . I t i s most abundant near the western l i m i t of the main vein where i t may constitute up to 10 per cent of the sulphides. This mineral i s r e l a t i v e l y rare, having been reported with ce r t a i n t y i n about 20 l o c a l i t i e s i n the world. The en-vironments i n which i t occurs i n these l o c a l i t i e s are re-markably si m i l a r to one another. This has l e d several authors to regard alabandite as a mineral often t y p i c a l and p r a c t i c a l l y r e s t r i c t e d to such deposits. The alabandite environment of the Contact vein agrees i n general with that of the other deposits but has important differences. Chief among these are i n f e r r e d temperatures of deposition and certain mineral associations. ' I n polished section the mineral i s most r e a d i l y distinguished from sphalerite, with which i t i s intimately associated i n t h i s deposit, by i t s l i g h t bluish-gray color and i t s i n s t a n t almost violent reaction to hydrochloric acid during which large amounts of H^S gas are evolved. The c h a r a c t e r i s t i c greenish streak and i n t e r n a l r e f l e c t i o n of alabandite were not noticed to any recognizable extent, possibly due to a high iron content. The mineral takes a very smooth pol i s h , lacks signs of twinning or cleavage, i s unfractured and unaltered. It contains exsolution i lamellae of pyrrhotite and appears to be i t s e l f i n part an exsolution product i n sphalerite. 45 Alabandite i s r e s t r i c t e d in t h i s occurrence to an intimate association with sphalerite and less commonly galena. This close association has not been reported i n other deposits, although ZnS i s present i n 9 out of 13 deposits studied i n d e t a i l . (Hewett and Rove, 1930, pp.36-56.) The mineral appears to have been ex-solved from extensive s o l i d solution i n sphalerite (Plate. V l l l ) . C r i t e r i a , as suggested by Edwards (Edwards, 1947, pp.37-5&) for detection • of ex-solution textures, are present as follows: (1) Alabandite shows l i t t l e evidence of replacement and where present as rounded blebs shows mutual boundaries with the sphalerite. (2) Oriented d i s t r i b u t i o n and emulsion textures are common. (3) Sharp, smooth boundaries are always present. (4) There is no widening at the junctions of Ala-bandite lamellae. (5) Crystals are generally single. (6) Within l i m i t s , there i s a f a i r l y even d i s t r i b u t i o n through the host. Further: "Composition and c r y s t a l structures of the minerals must be such that s o l i d solution i s fea s i b l e at high temper-atures. I f the diameter of the solute and solvent atoms d i f f e r by less than 15 percent, extensive s o l i d solution can occur. The valence of the two metal atoms involved must be sim i l a r . The tendency to form intermediate compounds i s the stronger, the more ele c t r o p o s i t i v e the one element and the more electronegative the other. Oriented intergrowth i s favored by s i m i l a r i t y of chemical composition of the two minerals and by the surfaces i n contact possessing planes of sim i l a r atomic spacing. This spacing should not vary by more than 10 percent." The q u a l i f i c a t i o n s that alabandite f u l f i l l s these demands may r e a d i l y be seen by r e f e r r i n g to Fig . 9-46 Plate V l I I . Ex-solution Intergrowth, Alabandite i n Sphalerite. 46a F i g . 9 . Table showing date for f e a s i b i l i t y of s o l i d solution i n the Systems ZnS - Mns and Mns - Fen „s. Property Alabandite Sphalerite % D i f f . Pyrrhotite %Di. Cf. Mn Xn Element Mn Zn Fe Composi-t i o n MnS ZnS F e l - x s Valence 2 2 — 2- - -Atomic Radii 1.37A* 1 .33A* 11% 1.24A* 9.8 6 . 8 Crystal Struct-ure Isometric hexoctahe-dral Isometric ' hexoctahe-d r a l Dihexagonal dipyramidal Ao 5.214A* 5.400A' Co 5.680A* 47 Kroger (Kroger, 1939, p.4#2) has carried out the only-experiments recorded involving s o l i d solution of sphalerite and alabandite. Mixed orange-red crystals of ZnS and MnS . were.obtained by heating a mixture of the two substances i n KCI at a temperature of 1180°C. These mixtures contained a l l molecular percentages of MnS up to 52 percent. The mixed cr y s t a l s were of the wurtzite or zinc-blende type, according to the temperature of formation when the Mn content was low. When a high percentage of the Mn was present, the cr y s t a l s were always of the wurtzite type. The only recorded occurrence of alabandite i n natural s o l i d solution i s reported by Schneiderhohn and Ramdohr (Schneiderholn and Ramdohr, 1931, p.101) who i n f e r unmixing of pyrrhotite in a sample of alabandite from B o l i v i a . Small idiomorphic grains of pyrrhotite are arranged along the . ( I l l ) planes of the alabandite. Indirect evidence i s present by which a minimum temperature requirement f o r s o l i d solution involving alaban-dite may be determined. Unmixing of alabandite i n sphalerite has been in f e r r e d . A myriad of minute blebs of chalcopyrite dispersed through the sphalerite i s strongly suggestive of ex-solution. Edwards, (Edwards, 1947, p.79) quoting other authors, states that a temperature i n excess of 350° G i s necessary f o r such a s o l i d solution to develop. There i s no evidence to indicate more than one period of sphalerite mineralization, yet else-where unmixing of alabandite i n sphalerite also appears well 48 developed. Thus a temperature of formation approximately that indicated for the chalcopyrite-sphalerite r e l a t i o n i s suggested. Alabandite i s believed to be the source of both the manganese oxides and the native sul f u r found as secondary-minerals in the Contact vein. This w i l l be discussed under appropriate headings. Of the ' 1 3 major alabandite deposits examined i n d e t a i l , the following minerals were present or absent as follows: 13 deposits Contact Vein Sphalerite Absent i n 4 Present Galena n H 4 n Pyrite tt tt 1 n Chalcopyrite tt tt 7 tt Tetrahedrite n tt 9 tt Pyrargyrite " tt 11 tt Bournonite tt ft 12 Absent Tellurides tt tt 12 tt Quartz n tt 2 Present C a l c i t e tt tt 6 tt Dolomite tt tt 11 ?t S i d e r i t e it tt 10 Absent Rhodochrosite tt tt 1 tt Rhodonite tt ft 8 Present Some conclusions reached i n the study of these deposits were as follows: (1) In deposits containing alabandite, s i l v e r i s the most valuable mineral. (2) A r e l a t i v e l y young age for alabandite deposits (late Mesozoic or Tertiary) i s probable. (3) The deposits are epithermal and formed near the surface. (4) The proportion of sulphides to gangue i s low i n a deposit uniformly y i e l d i n g alabandite. Hewett and Pardee, (Hewett and Perdee, 1 9 3 3 , p p . 6 7 1 - 6 8 2 ) a f t e r studying most of the American occurrences of t h i s hypogene manganese mineral have also concluded that: ( 1 ) Manganese minerals tend to show a consistent zonal d i s t r i b u t i o n and are concentrated i n an outer zone with preference to the int r u s i v e centre i n each d i s t r i c t . ( 2 ) In t y p i c a l l y hypothermal and pyrometasomatic deposits minerals with a high manganese content are lacking, - except possibly when manganese occurs with s i d e r i t e . ( 3 ) Rhodochrosite and alabandite are character-i s t i c a l l y epithermal. (4) Rhodonite i s t r a n s i t i o n a l epi-to mesothermal. ( 5 ) Rhodonite-alabandite relations are obscure. With the above f o r comparison, a c r i t i c a l examin-ation may now be made of the manganese environment i n the Contact vein. S i l v e r i s the most valuable metal i n the Contact vein and i n several s i m i l a r manganese bearing deposits to the south on Marble Creek. These appear to represent the highest s i l v e r concentrations known i n the McDame area. Manganese i s not believed to occur i n recognizable amounts i n deposits other than these veins i n limestone near the Batholithic contacts. The s i l v e r i n these manganese-rich veins i s present i n d i r e c t l i n e a r r e l a t i o n to the lead content and shows no r e l a t i o n to the manganese or zinc present. (See F i g . 7 , page 5 6 a ) . A r a t i o of 1 . 5 ounces of 50 s i l v e r to each percent of lead i s nearly constant for the deposit. The sphalerite i s s l i g h t l y manganiferous but the galena i s not. Thus the manganese i s an associate of the s i l v e r bearing minerals but not d i r e c t l y related to them. Most recorded alabandite occurrences have either been i n Tertiary i n t r u s i v e s or i n sediments within a mile of t h e i r contacts. The age of the Cassiar Batholith i s not known other than that i t i s not older than Jurassic (Hansen and McNaughton, 1936, p.10). On the other hand volcanic cinder-cones of Pleistocene age are present i n the Eagle-McDame area to the south. Basaltic dykes are known to cut these cones and to cut granite (Ibid. p.11). There i s a p o s s i b i l i t y that some of the stock-like bodies of the area are a c t u a l l y l a t e r than the batholith. The exceptionally coarse porphyritic granite body, which seems to bulge out to the immediate southwest of the Contact vein and which con-tains the bismuthinite deposit, has not been proven to be continuous with the main b a t h o l i t h . Thus intrusions of l a t e r granite may have occurred along this pre-existing b a t h o l i t h i c contact. This manganese mineralization then cannot be proven to be non-Tertiary. That such deposits are near surface i n o r i g i n i s i n d i r e c t agreement with this thesis. However, exception i s taken to the epithermal c l a s s i f i c a t i o n of such deposits. Paragenetic and s o l i d solution evidence which has been present-ed here indicates a temperature of formation of the alabandite 51 above 350° C* and thus well above that of a t y p i c a l epithermal mineral. However, mineralization i n the Contact vein i s believed to represent a special set of conditions governed by an exceptionally steep temperature gradient dur-ing which overlapping i n the paragenetic sequence i s apparent. A l l stages i n the arrested d i f f u s i o n of the ex-solution bodies to the grain boundaries of the host are evident. Further complication has been added by the extensive replacement des-cribed. Thus i t i s conceded that some of the alabandite, e s p e c i a l l y the small amounts associated with the galena, may or may not be of epithermal o r i g i n . Alabandite i s not common i n deposits i n calcareous sediments and the chemistry of deposition i n a carbonate environment may be quite d i f f e r e n t than that encountered elsewhere. The low proportion of sulphide to gangue i n a deposit uniformly y i e l d i n g alabandite does not hold for the Contact vein where the sulphides outnumber the gangue, i n -cluding magnetite, by more than two to one. The zonal d i s t r i b u t i o n of the manganese minerals may be s i g n i f i c a n t i n the study of t h i s deposit wherein a case i s presented f o r a genetic and time r e l a t i o n with the pyrometasomatic pyrrhotite deposit. Manganese i s present as a major constituent i n the garnet of the pegmatite associated with the Cassiar i n t r u s i v e and i s a minor constituent i n the * Based on the chalcopyrite-alabandite ex-solution phenomena. 52 garnet of the pyrometasomatic deposit s i m i l a r l y associated. It does not appear i n quantity, however, u n t i l an "outer" zone such as that occupied i n part by the Contact vein i s reached. This i s w e l l within the one mile l i m i t postulated by Hewett and Rove. In the vein i t i s a minor constituent i n the magnetite, garnet, and sphalerite, and a major con-st i t u e n t i n the rhodonite and alabandite. Hewett and Rove conclude that minerals with a high manganese content are lacking i n t y p i c a l pyrometasomatic and hypothermal deposits. The Contact deposit i s not t y p i c a l of either of these. However, the exact connotation of "high manganese content'? i s uncertain. Certainly the magnetite, which contains between 10 and 15 percent manganese, i s of high temperature o r i g i n , as are the garnets which occur i n the pegmatites and contain manganese as an e s s e n t i a l compon-ent,. Manganese, however, i s not e n t i r e l y lacking i n other high temperature associations. It i s an important c o n s t i t -uent of f r a n k l i n i t e , a high temperature mineral which i s found at Franklin Furnace. Lindgren considered t h i s deposit pryo-metasomatic. The Bluebell mine i n the Kootenay D i s t r i c t of B r i t i s h Columbia i s e s s e n t i a l l y of the pyrometasomatic type, but contains much Knebelite, a manganese o l i v i n e . * There i s no evidence to indicate that included manganese could have appreciably lowered the temperatures at which the magnetite was deposited i n the Contact vein. * Personal communication with H.C.Gunning, U.B.C. Department of Geology, 1953-53 Pyrrhotite (Fe]__xS) This mineral i s abundant i n the main deposit as granular masses often somewhat banded,-and as i n d i v i d u a l grains or rods. It has been replaced, to a large extent, by marcasite which appears as well developed colloform bands or as c h a r a c t e r i s t i c composite- lamellae which are a r e f l e c t i o n of the fracture pattern or parting of the pyrrhotite (See PI. XII). The pyrrhotite, i n general, i s present i n an environment complicated by extensive overlapping, replace-ment and s o l i d solution. Two v a r i e t i e s and generations of pyrrhotite are recognized; one magnetic, the other non-magnetic. The magnetic variety, e a r l i e r formed, i s that found as the more massive or banded type l a r g e l y replaced by marcasite. It i s very si m i l a r to the pyrrhotite of the skarn deposit already described. It has been replaced by sphalerite and galena. The non-magnetic variety i s more complex. Its f a i l u r e to be attracted by a strong permanent magnet may be due to the presence of a small amount of manganese which could dampen this property i n much the same manner as i t does i n s t e e l . This variety i s usually present i n a manganese-rich environment. Small rods o f t h i s second generation pyrrhotite appear dispersed i n the lead, zinc, and manganese s u l -phides. Concentrations suggestive of ex-solution are 54 noticeable i n the l a t t e r sulphide and have been discussed. Often these rods cut across boundaries from one of these sulphides into the other. Thus galena-sphalerite, sphaler-ite-alabandite, and galena-alabandite appear bridged by these rods. Occasionally, as shown by the following diagram (Fig. 5A) groups of these rods, although enclosed i n several minerals, possess a common orientation. It may be argued that the pyrrhotite i s present as a mineral which had replaced the other three sulphides. However i t i s very un l i k e l y that c r y s t a l or cleavage planes are present which exactly coincide i n these sets of adjacent minerals. These planes, common to both sulphides, would be a necessary q u a l i f i c a t i o n i n this case as there are no signs of fr a c t u r -ing or rela t e d veining in the minerals under discussion. r~200mu—i Fig. 5A, Composite Drawing of Rods of Pyrrhotite i n Galena, Sphalerite and Alabandite 55 The only plausible way to account for the d i s t r i b u t i o n and orientation of these rods would be by ex-solution of the pyrrhotite i n one of the sulphides and extensive replacement of i t by the others. During t h i s replacement the rods were not affected and appear as bridges where the l a t t e r process was arrested i n an area which included a part of them. Sphalerite was the e a r l i e s t mineral formed i n t h i s case and as such the pyrrhotite must have ex-solved from i t . Solid solution of these two minerals i s e n t i r e l y f e a s i b l e as shown by Figure 9 (Page 46a) and as discussed i n the section on alabandite. Lath-like bodies of pyrrhotite, arranged i n what appears to be the (111) planes of alabandite, were noticed i n several samples (See Plate LX). Ex-solution intergrowth of t h i s type but involving sphalerite and pyrrhotite has not been observed. The rods of pyrrhotite, believed to have been ex-solved from the e a r l i e r sphalerite, are i n a l l cases . well dispersed through the sphalerite and no concentration such as that seen in the alabandite occurs. Thus s t a t i s t i c -a l l y the pyrrhotite appears to have ex-solved d i r e c t l y from the alabandite and i s not a r e l i c l e f t over from the replacement of sphalerite as was the rod-like form. Ex-solu-tion of pyrrhotite i n alabandite has been reported by Schneiderhohn and Ramdohr and has been discussed under the "Alabandite" heading. 56 Small i r r e g u l a r bodies of pyrrhotite appear to have replaced ex-solution lamellae of alabandite (Plate VIII) and as such would of course be l a t e r than the alabandite. However a d i s t i n c t c h a r a c t e r i s t i c of t h i s deposit i s the complicated ex-solution, replacement and overlapping undergone during mineral deposition. Discrepancies, such as those noted with the pyrrhotite, would help rather than hinder the thesis that t h i s vein i s a telescoped deposit characterized i n a large part by complications such as those mentioned. Chalcopyrite (CuFe S 2) This mineral i s sparingly present i n the Contact vein deposit. It i s seldom recognizable megascopically but under the microscope i s seen as small blebs i n the sphalerite and occasionally the pyrrhotite. Some ex-solution i n the sphalerite i s in f e r r e d from the t y p i c a l orientation of minute blebs i n and rim segregation to the sphalerite grains. This evidence of ex-solution indicates a temperature of formation of 350/400°C (Hanson and McNaughton, 1936, p.10) (.Edwdt. Galena (PbS) Galena i s probably the most abundant sulphide i n the deposit. It appears as medium grained massive segrega-tions, as a constituent of the coarse bands p a r a l l e l to the walls of the vein, as disseminated bodies usually i n the sphalerite, or more commonly as a matrix cementing dissemin-ated magnetite and e a r l i e r sulphides. Numerous inclusions are common i n the "matrix type". Intimately associated with the galena i n t h i s group F i g . 7. G r a p h . . S i l v e r y s L e a d , Z i n c , & M a n g a n e s e C o n t e n t i n C o n t a c t D e p o s i t . S I L V E R OZ 60 5 & ~ 30__ 20. 10 0 L e a d 0 10 20 3< % L E A D , Z I N C , & M A N G A N E S E . ^ > ? C M . . " C N a t i v e <^ S i l v e r i ~* g a l e n a c l e a v a g e ^ o i t s . / TE N a t i v e A n t i m o n y ^ ^ 1 F i g . 8. P r e f e r r e d O r i e n t a t i o n o f U n k n o w n " C " ( d y s c r a s i t e ) i n G a l e n a . 57 are the sulpho s a l t s such as pyrargyrite, bismuthinite and tetrahedrite. Native antimony and s i l v e r are also present, as are several unindentified minerals one of which appears to be a variety of dyscrasite. As can be seen r e a d i l y on the graph which com-pares lead content to s i l v e r values (Fig. 7) the r e l a t i o n i s almost l i n e a r . A r a t i o of about 1.5 ounces of s i l v e r to each per cent of lead i s constant for the deposit. This i s , of course, explained by the r e s t r i c t i o n to the galena of the s i l v e r bearing minerals mentioned. Much of the galena, e s p e c i a l l y that with a high content of included minerals, has a reddish iridescent tarnish. This tarnish i s probably caused by secondary man-ganese minerals developed from the small amounts of a l a -bandite present i n t h i s type of galena. S i l v e r (Ag) Minute blebs and prisms, usually only a few microns i n size, of a very white, apparently i s o t r o p i c mineral are present i n most of the galena. Etch te s t s , to-gether with properties mentioned, suggest native s i l v e r . The bodies are too small to permit posi t i v e i d e n t i f i c a t i o n . Gold i s present i n trace amounts. Tetrahedrite (3Cu 2 S. Sb2S-j) Tetrahedrite, which i s present i n small amounts, i s r e s t r i c t e d to the galena* It occurs as rounded blebs up to one millimeter i n diameter or as arm-like bodies a few hundred microns or more i n length. These l a t e r forms (See Plate X) tend to occur around the edges of i n d i v i d u a l galena grains which can be distinguished by the change i n orientation of the cleavage p i t s . The regular d i s t r i b u t i o n , through most of the galena, of these bodies i s suggestive of an exsolution intergrowth although the boundaries are not sharp. This form i s i t s e l f intergrown with small amounts of grayish anisotropic mineral which resembles a ruby s i l v e r . The blebs, and to some extent the arm-like bodies, have been replaced i n part by pyrargyrite, native antimony, and a mineral resembling dyscrasite. Bismuthinite ( B i 2 S^) Bismuthinite i s r e s t r i c t e d i n i t s few occurrences to the massive galena i n which i t attains i t s usual fibrous, somewhat columnar c r y s t a l outline. Simultaneous deposition with the galena i s indicated. Maximum grain dimension i s about 300 microns. Pyrargyrite (3Ag 2 S.SbjpS-j) Pyrargyrite i s present i n minor amounts as small elongated bodies up to 300 microns i n length, which have replaced tetrahedrite and galena. Another ruby-silver mineral i s probably present i n the arm-like bodies of tetrahedrite but has not been i d e n t i f i e d as the amount present i s small. Pyrargyrite i s not believed to be present i n s u f f i c i e n t amount to account for the s i l v e r values inherent i n the galena. 59 Native Antimony (Sb) Blebs and c r y s t a l l i n e forms of native antimony are present i n small amounts i n the galena. That showing c r y s t a l form i s seldom over 100 microns i n i t s greatest dimension but the formless blebs have a range up to 600 microns. The mineral i s creamish-yellow and i s s l i g h t l y sec-t i l e . Grains similar i n appearance to the antimony r e a d i l y develop a brownish tarnish. Several of these grains, which were believed to possess either arsenic or s i l v e r as agents which would precipitate tarnishing, were examined by means of X-Ray powder photographs. The pattern obtained did not coincide exactly with that of any known mineral, but was reasonably close to that of a variety of dyscrasite (Ag-jSb). Antimony appears to have replaced i n part both tetrahedrite and the non-magnetic variety of pyrrhotite, (See plate X). PLATE X Native Antimony i n Galena Note tarnished portion of antimony (or dyscrasite?) Sb-£, tetrahedrite rims (?) TeT, and unknown "C" G. 60 Cross sections of the i n d i v i d u a l antimony cr y s t a l s are usually poorly defined hexagons although rhombs and i r -regular prismatic bodies are occasionally present. Exsolution i s not i n f e r r e d . Antimony i s usually considered an epithermal mineral and i t s occurrence i n t h i s deposit does not suggest otherwise. It has been reported by Warren (Warren, 1948, p.83) to be associated'with hessite and p y r i t e at P e l l a i r e Mines, Taseko Lake area, B.C. Mineral "C" Close examination of most of the galena of the Contact vein revealed many minute, silver-white, c r y s t a l l i n e forms of a, mineral which could not be i d e n t i f i e d with certainty. As seen i n cross-section, these consist of near perfect or modified diamonds, rhombs, t r i a n g l e s , squares, i hexagons and rectangles and as such are probably represen-t a t i v e of an orthorhombic or rhombohedral system. Some of these appear i n the creamish colored antimony and are rea d i l y distinguished from i t by the d i s t i n c t i v e "whiter than galena" color (See plate X). The mineral has the same hardness as the galena. It i s quite strongly anisotropic, exhibiting brown to yellow to greenish-blue p o l a r i z a t i o n colors, and does not tarnish. X-Ray and etch tests were not very successful because of the minute s i z e , (less than 50 microns) of the c r y s t a l s , but did suggest, however, that the mineral f e l l i nto the complicated antimony-dyscrasite group. 6 1 Preferred orientation i n the crystallographic directions of the galena i s well developed and i s a clue toward i d e n t i f i c a t i o n . One edge of any c r y s t a l examined i s always p a r a l l e l to one side of the cleavage p i t triangles of the enclosing galena grain (See Plate XIA and F i g . 8 ) . When viewed i n cross sections cut p a r a l l e l to one of the cube faces the forms are s l i g h t l y modified cubes and rectangles (See Plate Xlg). This orientation i s thought to be the re-su l t of unmixing from s o l i d solution i n galena. As such the faces of the c r y s t a l s i n contact should possess planes of similar atomic or ionic spacing. Edwards (Edwards, 1 9 4 7 , P » 5 7 ) , quoting Gruner, states, "that the l i n e a r differences i n spacing of the atoms (or ions) of the element i n the two planes i n which the c r y s t a l s meet requires not to exceed 1 0 per cent of the spacing of the larger of the two struc-tures present". Plate XIA. Preferred Orientation of Unknown "G" i n Galena. Oblique section. Plate XIB. Unknown "C" (dyscrasite)? i n Galena. Exsolution intergrowth i n crystallographic planes of galena. Section cut p a r a l l e l to cube face. Inked crosses indicate c r y s t a l l o -graphic d i r e c t i o n shown elsewhere. 1mm Plate XII. Colloform Banded Marcasite. 62 In t h i s case then the unknown mineral should possess a unit c e l l with dimensions of 5 .93A 0 (± 10%). Dyscrasite, with dimensions Co - 5.225 A°, would be near the extreme l i m i t - between 10 and 11 per cent. Dyscrasite, showing some c r y s t a l form, i s often present i n galena as noted by Edwards (1947). Unknown Mineral "F" This mineral occurs i n the galena as arm-like bodies si m i l a r to the tetrahedrite already described. (See Plate X). It resembles tetrahedrite i n color, hardness, and etch tests, but on close examination appears to be, i n part at l e a s t , anisotropic. The p o l a r i z a t i o n colors are similar to those of pyrargyrite. X-Ray powder photographs of the minute amounts obtainable gave a simple, apparently cubic pattern which i s not d i s t i n c t i v e of any mineral. An intergrowth of tetrahedrite and a ruby s i l v e r should produce a complex pattern. Marcasite (Fe S 2) Marcasite i s common but r e s t r i c t e d i n i t s oc-currence to the pyrrhotite which i t has c l e a r l y replaced. This replacement i s widespread and has resulted i n well developed composite lamellae of marcasite. Colloform banding i s exceptionally well developed near the pyrrhotite. The other iron minerals present, magnetite and p y r i t e , appear l i t t l e effected by the mar-casi t e . Where a nucleus i s present associated with the colloform bands, i t i s always pyrrhotite. Galena seems to have acted as an armour i n pro-tecting small amounts of pyrrhotite enclosed i n i t . The age of the marcasite i s not known. I t i s c l e a r l y older than the limonite and manganese oxides as these secondary minerals have penetrated the colloform bands. None of the sulphides have done t h i s however. Thus i t is either a late hypogene or an early supergene mineral. Similar marcasite i n the skarn deposit i s considered secon-dary. Secondary Minerals Native Sulfur (S) Native sulfur i s present i n small amounts i n the Contact vein. The yellow mineral can be seen i n minute fractures which occur i n the sulphides through most of the vein. The sulfur i s r e a d i l y detected i n a l l instances by heating the sample s l i g h t l y . Molten sulfur oozes from the minute fractures and w i l l burn i f ignited. Characteristic sulphurous fumes are rea d i l y recognized. These are also evolved during the cutting of specimens with a diamond saw. The following o r i g i n i s i n f e r r e d : Native sulfur has apparently been formed i n the vein under a special set of conditions wherebyvmanganese and iron sulphides were a v a i l a b l e . Alabandite, which i s noted for i t s extreme i n s t a b i l i t y under acid conditions, was r e a d i l y attached by acids formed during the oxidation of pyrite or pyrrhotite according to the equation: (1) FeS 2 4 70 * H20. Fe S0 4 * H2S04, 9 ) . 64 The acid solutions then reacted r e a d i l y with the alabandite to evolve H^S gas: (2) H 2S04 •* MnS H 2S * MnS04 The MnS04 solutions moved downward and l a t e r a l l y , p r e c i p i -t a t i n g manganese at the limestone walls by reaction with the Ca CO3 r e s u l t i n g i n the various Mn oxides (See under "Wad"). At the same time the H2S, which i s acrelativelyr.unstable compound, reacted with the a i r to form native s u l f u r . In aqueous solution native s u l f u r i s displaced by dissolved oxygen according to the reaction: (3) 2H2S + 0 2 2H20 * 2 3 . Unlike the manganese oxides, the native sul f u r so formed should not be r e s t r i c t e d to any p a r t i c u l a r part of the vein, providing pyrite and alabandite are available - a f a c t borne out by examination. However, i t should not be assumed that the re-agents or reactions involved are as r e s t r i c t e d or as simple as infe r r e d . For instance by a second feas i b l e process the ferrous sulphate and sulphuric acid, formed by the o r i -ginal oxidation of the p y r i t e (Hanson and McNaughton, 1936, p. 12),, may react with a d d i t i o n a l oxygen and produce the f e r r i c s a l t Fe 2 (SO^)^. This s a l t i s a strong oxidizing agent and would r e a d i l y attack any of the sulphides remaining. By a reaction similar to (2) and (3), native s u l f u r would be obtained. (Lihdgren, 1933, p.829). Thus a loosely coherent block of native s u l f u r , found occupying a rectangular mineral mold i n scapolite-garnet skarn near the granite contact, i s probably i n d i c a t i v e of derivation from the p y r i t e . No 6 5 manganese sulphide i s known to occur here. Indeed both of the above mentioned processes may have occurred i n the Contact Vein with the manganese oxides being a r e a d i l y ac-counted f o r end product. Although s i m i l a r s u l f u r occurrences are not rare, p a r t i c u l a r l y i n American deposits, they have seldom been re-ported i n B r i t i s h Columbia. The sulfurous fumes have never b&en so r e a d i l y detected i n the course of preparing hundreds of thin and polished sections of oxidized p y r i t e - s p h a l e r i t e specimens i n the laboratory at the University of B r i t i s h Columbia. * Thus the s i m i l a r l y rare manganese sulphide, by s t a t i s t i c a l evidence as w e l l as chemical, probably played a major r o l e i n the formation of native s u l f u r i n t h i s deposit. Manganese Oxides (Wad) Manganese oxides are r e a d i l y recognized i n the Contact deposit by the shiny black and iridescent colors they impart to the 1 vein material and surrounding rock. Ex-amination of the deposit i s made somewhat d i f f i c u l t by t h i s o v e r a l l coloration. The only concentrations of this wad are near.the hanging w a l l . (See F i g . 4) Here several lenses of t h i s highly porous, sponge-like material, which are about f i v e or more feet i n length, and up to three inches i n width, occupy positions p a r a l l e l to the walls of the vein. Thin section examination of t h i s wad revealed * Personal communication .. Mr. J. Donnan, laboratory technician. U.B.C. 66 numerous, extremely fine grained, colorless aggregates. These consist of quartz, carbonate, and a feldspar believed to be a potash variety. These aggregates, which are up to f i v e millimeters across, are surrounded by and included i n well-developed colloform bands of manganese and iron oxides. Spectographic examination of a mixture containing these inclusions revealed the presence, besides manganese and i r o n , of zinc and sodium as major constituents and magnesium and s i l i c a as minor constituents. Traces of arsenic, copper, cadmium, lead, s i l v e r and t i n are also present. A l l of these elements, with the exception of sodium, are present i n the unoxidized portions of the vein. In a l l cases the iron r i c h oxide seems to have deposited before the hydrous manganese oxides although several cycles of deposition are indicated by the colloform bands. This i s i n keeping with the s o l u b i l i t y of manganese and iron sulphate solution (42). Alabandite i s believed to be the source of the manganese i n the wad. Manganese sulphide can be taken into solution much more readily i n d i l u t e HgSo^ than can the other possible sources of the manganese, namely the manganiferous magnetite and the rhodonite. The HgS evolved during the action of HgSo on alabandite was probably the major source of the native sulfur now found i n the Contact deposit. The manganese i n the r e s u l t i n g sulphate solution, however, could not be precipitated u n t i l these solutions had been neutralized. This seems to have been accomplished by reactions with the 67 carbonate w a l l rock as shown by the position of the wad lenses. The vein has remarkably few non-metallic gangue minerals, c a l c i t e included, thus p r e c i p i t a t i o n by reaction within the vein was very li m i t e d . The absence of rhodochrosite (MnCo-j) i n an environment containing abundant manganese and carbonate i s notable. Of the 13 alabandite deposits examined i n d e t a i l , * rhodochrosite was absent i n only one. It was a primary mineral i n a l l cases. To quote Savage (Savage, 1936) with regards to secondary rhodochrosite: " I t i s l i k e l y that MnCo^ can be preci p i t a t e d only from neutral or s l i g h t l y a l k a l i n e solutions and would not be found i n an oxidizing ore body." Hydrocarbon i n the Contact Vein An unidentified high grade hydrocarbon i s present i n small amounts i n the porous and permeable wad described' above. This hydrocarbon, which i s not derived from coal or l i g n i t e * apparently accumulated i n the pore space of the wad. No attempt can be made here to account f o r i t s presence other than to mention possible o r i g i n s . These i n -clude: (1) A d i s t i l l a t e r e s u l t i n g from the metamorphism of p etroliferous limestone. (2) Introduction or formation during igneous a c t i v i t y . ^Personal communication with Dr. R. E. Delavault, Research Chemist, U.B.C., 1953 68 (3) Animal secretions. The wad has many inclusions, but none of these suggests evidence of organic l i f e ( i . e . , h a i r or other re-mains commonly associated with gophers or marmots, etc.) However, the high sodium content of the wad, as indicated by spectographic analysis, may be suggestive of such an o r i g i n . Hydrocarbon has not been reported i n the rocks of the McDame Area. Chapter 5 Summary and Conclusions Regarding the Mineralogy of the Contact Vein and Related Deposits Contact Vein The mineral r e l a t i o n s and assemblages of the Contact vein and t h e i r i n t e r p r e t a t i o n and c l a s s i f i c a t i o n are complex. F i r s t , an assumption i s made that mineralization occurred within one general period. Except i n small amounts of the arsenopyrite, there has been a minimum of fracturing of the e a r l i e r formed minerals as would be the case, for instance, i f the vein "opened" allowing a l a t e r period of mineralization. The l a t e r minerals, p a r t i c u l a r l y the galena and i t s associates, appear throughout the vein as well as forming, with the e a r l i e r minerals, an i n t e g r a l part of the coarsely banded assemblage. The fact that d i s t i n c t stages 69 of deposition are recognized i n no way implies an interrup-t i o n of deposition. The obvious overlapping, p a r t i c u l a r l y of pyrrhotite and alabandite, and the occurrence, within areas o f a square inch or l e s s , of p r a c t i c a l l y a l l the primary m e t a l l i c minerals represented i n the deposit, are in d i c a t i v e of deposition with-i n a comparatively short time. Perhaps the best evidence that the lower tempera-ture minerals were not deposited during a l a t e r period i s that exhibited by the s i x inch stringer vein. This strikes normal to the main vein and can be traced for at l e a s t 30 feet. I t consists largely of magnetite grains i n a matrix of carbonate gangue s i m i l a r i n grai n size and c r y s t a l form to that of the wall rock and as such seems to be of a replacement o r i g i n . Galena and sphalerite are again present i n small amounts and the grains are disseminated as are those of magnetite. There i s no str u c t u r a l or t e x t u r a l evidence to indicate that these miner-a l s , which are of r e l a t i v e l y l ate age i n the main vein, entered along s t r u c t u r a l channelways that were riot present when the mag-net i t e was deposited. The constant association o f magnetite and the late.sulphides i n similar deposits on Marble Creek, and the absence of deposits containing these sulphides alone, are suggestive of a single mineralizing period. The presence of manganiferous magnetite and garnet with the l a t e r manganese minerals rhondonite and alabandite i s ind i c a t i v e of a common o r i g i n . However, the occurrence and d i s t r i b u t i o n of manganese along the eastern contact of the 70 Cassiar Batholith, i n the McDame Area at le a s t , i s suggestive of a metallogenic province. Included i n t h i s , besides the sulphide deposits, are the spessartite bearing pegmatite dykes and phases of the Batholith, the manganiferous garnet of the pyrometasomatic deposits, and possibly the rhodonite associated with the McLeod volcanics. In such a province, manganese mineralization, although suggestive of common or i g i n , could occur at d i f f e r e n t times. The above considerations seem to lead l o g i c a l l y to the conclusion that deposition i n the Contact deposit occurred during one general period. The conditions under which the deposition took place are l a r g e l y r e f l e c t e d by the mineralogy of thi s vein and of nearby deposits believed to be rela t e d to i t . The association of usually t y p i c a l high temperature minerals, such as garnet, magnetite, and pyrrhotite, with low temperature minerals such as alabandite, pyrargyrite, native antimony and possibly dyscrasite, i s in d i c a t i v e of telescoping. Edwards (Edwards, 1947, p.119) states that the presence of magnetite or pyrrhotite i n abundance i s evidence that deposition began a t a high temperature (of the order of 600°C). S i m i l a r l y the epithermal minerals present indicate a temperature below 200°C. A determination of the pressure existing at the time of the vein formation i s d i f f i c u l t to determine. Probably the garnet indicates i n i t i a l l y high pressures. I f the magnesian tourmaline could, be proved g e n e t i c a l l y related 71 to the vein material i t would also be suggestive. However, pressures must have f a l l e n o f f quite rapidly to permit a rapid decrease i n temperature as indicated by telescoping. The mineralogy of the neighbouring deposits, which are believed to be g e n e t i c a l l y related to the vein, i s sug-gestive of high temperature and pressure. The presence of garnet and tourmaline i s accepted as i n d i c a t i v e of high pressures of formation. The tourmaline-s p e s s a r t i t e - r i c h dyke, previously described, i s present under conditions similar to that of the Contact vein. S i m i l a r l y the related skarn deposits contain abundant garnet and scapolite and pressures and temperatures were s t i l l high enough to allow extensive replacement of the previously thermally metamorphosed rock. The a p l i t e dykes may be further in d i c a t i o n that pressures were not low preceding formation of the Contact deposit. Possible minimum cover during the i n t r u s i o n of. the ba t h o l i t h i n t h i s area include some 15,000 feet of sedi-mentary and volcanic rock. However, the contorted nature and steep dip of these rocks would prevent a determination of previously p r e v a i l i n g hydrostatic pressure. That pressure and temperature were i n i t i a l l y high during the formation of the Contact vein has been indicated. The telescoping involved required a rapid lowering of temperature; a condition which would not have occurred under a large hydrostatic pressure. The decrease i n temperature can r e a d i l y be at t r i b u t e d to shallow depth, but the i n i t i a l l y high pressure can not be so 72 explained. The best solution to this problem would be that the pressures were only l o c a l l y high. The impervious horn-f e l s e s , overlying the deposits, could act as a near-surface cap rock under which pressures due to mineralizing f l u i d s or gases could conceivably be b u i l t up. Under such conditions the v o l a t i l e constituents of the pegmatites, the skarn, and the vein would be retained and be represented i n the r e s u l t -ing mineral assemblages. Garnets could form. Under these conditions of low hydrostatic pressure fractures or tensional openings could exist and the pegmatite and a p l i t i c magma force t h e i r way into them. The vuggy quartz-bismuthinite vein i n the intrusive i t s e l f could be formed under these pressure conditions as could the pyrrhotite deposit. As temperatures were necessarily lowered, ore bearing solutions which had passed through magnesian bearing rock, were able to react with c r y s t a l l i n e limestone r e s u l t i n g i n dolomitization and the deposition, as temperature decreased, of oxides and sulphides. In summary, the whole process of mineralization i n this area, as evidenced by the telescoping i n the Contact vein, appears to have occurred under conditions of high but rapidly f a l l i n g temperatures and l o c a l l y high pressure. Relation of the Contact Vein to the Pyrometasomatic Pyrrhotite Deposit Some s t r i k i n g mineralogical s i m i l a r i t i e s e x i s t between the vein and the t y p i c a l pyrometasomatic pyrrhotite 73 replacement deposit. These, together with other s i m i l a r i t i e s , are shown i n tabular form (Fig. 10). Graton (Graton, 1931, p.184) i n r e f e r r i n g to hypo-thermal 'veins, asks the question: "Is i t not time to regard the Contact-metamorphic deposits frankly as an i n t e g r a l component of the hypothermal group, of which they represent a well i n d i v i d u a l i z e d subdivision c h i e f l y because of the special nature of the wall rock involved?" I f this were answered i n the af f i r m a t i v e , the Contact vein, although more mesothermal i n character than hypothermal, would s t i l l be considered "Contact Metamorphic" because of the wall rock involved. This vein, however, has several c h a r a c t e r i s t i c s which are not too common i n t y p i c a l contact metamorphic (or more r i g h t l y pyrometasomatic) deposits. These differences are indicated by Fig. 10. Chief of these i s the dolomitized wallrock. Alte r a t i o n involving dolomitization has seldom been reported as a feature of pyrometasomatic deposits i n limestone. This may be due to the lack of attention paid i t or mistaking the aureole for o r i g i n a l country rock. However, i n view of the f a c t that a great deal of work has been done on such deposits, i f i t were' common i t would probably have received more attention than i t has. This a l t e r a t i o n i s more commonly present around lower temperature hydrothermal veins. However, i n B r i t i s h Columbia's Salmo d i s t r i c t , such dolomitization does occur. Here the Emerald, H.B., and Jackpot properties, which have pyrometasomatic F i g . 10 - Table Comparing Contact Vein to Pyrrhotite Deposit PROPERTY PYRRHOTITE PYROMETASOMATIC DEPOSIT CONTACT MAIN VEIN Occurrence & Association In marmorized limestone c l i f f within 200 f t . of granite, surrounding rocks intensely ska r n i f i e d (garnet,diopside, scapolite, epidote, etc. In the same marmorized lms within 300 feet of nearest granite. Nearest gran-i t e along s t r i k e of lms and Contact Fault-800 f t . , - surrounding rocks hornfelses, - a p l i t e and basalt dykes cl o s e l y associated. Shape & * Size Massive, rectangular .. exposed 15 x . 30 feet - sharp contact with lms .. gradational into surrounding skarn. Vein .. Exposed on 45° h i l l s i d e .. exposed intermittently for 300 feet .. longest exposure 150 f t . slope d i s t . -width - 1 to 5 f t . . . Av. 3.5 f t . Primary Minerals Common to Both Deposits Magnetic Pyrrhotite - la r g e l y altered to marcasite. Chalcopyrite .. sphalerite . . p y r i t e .-. c a l c i t e .. manganiferous garnet . (native s u l f u r , secondary, present i n small amount.) i Minerals Deficient Oxides (magnetite..non-magnetic pyrrhotite..rhodonite. Minerals l a t e r than sphalerite i n paragenetic sequence of contact vein Scapolite, epidote, diopside. Metallic Content of Deposit (Vol) 60% 90% Texture & Structure Massive replacement - pyrrhotite coarse grained, - non-metallics.. medium grained Replacement arid f i s s u r e f i l l i n g ... coarse banding p a r a l l e l to walls of vein metal l i e s medium grained", .. non-metallics. .fine Wallrock A l t e r a t i o n of Lms. None Irregular - dolomitization. 74 minerals i n t h e i r gangue, have extreme dolomitization assoc-iated with t h e i r ores.* There i s no d i r e c t evidence on which to base an age r e l a t i o n o f the two deposits. C a l c i t e and quartz have veined the sulphides of both. The intensity of marcasite development i n each i s noteworthy. I f t h i s marcasite were proven hypogene, an acid condition during l a t e stage deposition would probably have been common to both. Chalcopyrite and sphalerite are believed to have existed i n s o l i d solution i n both, although the hosts have interchanged. The manganese content indicates a genetic r e l a t i o n s h i p . I n i t i a l temperatures of formation of the vein, as witnessed by the abundant magnetite, could well have been within the range of that p r e v a i l i n g i n the pyrrhotite deposit. Refringent garnet i n the l a t t e r indicates that a temperature of 800° C. was not exceeded, as above t h i s value garnet becomes i s o t r o p i c . Lindgren states that associations s i m i l a r to those of the pyrrhotite deposit indicate a temperature perhaps of from 400° to 600 QC. Certain mineral assemblages known to be unstable above certain temperatures would probably be the best such i n d i c a t i o n , but as yet these have not been apparent i n t h i s deposit. The thermally metamorphosed sediments i n which both deposits occur were shown to belong to the Pyroxene-Hornfels f a c i e s . Turner and Verhoogen suggest temperatures as low as 700° f o r t h i s development and assume a r e l a t i v e l y high press-ure. However, this metamorphism has no d i r e c t r e l a t i o n to the metasomatism which may have occurred much l a t e r i n geological time. * Personal communication ... Dr. H.C. Gunning, Dep't Geology, U.B.C., 1 9 5 3 -75 Lindgren believes that such metamorphic deposits could form within 1000 feet of the e x i s t i n g surface and are not necessarily deep-seated. Thus the pyrometasomatic phyrrhotite deposit, i f closely related in o r i g i n to the Contact vein, need i n no way d i s t r a c t from the conclusion that the vein formed near surface. 76 Conclusion The conclusion i s reached that the -Contact vein, characterized by a wide range of minerals complexly related, was formed at shallow depth under conditions of l o c a l l y high pressure and steep temperature gradient, and as such repre-sents a "telescoped" deposit. 77 Bibliography (1) Bostock,W.S.(1948), "Physiography of the Canadian C o r d i l l e r a with Special Reference to the Area North of the F i f t y - f i f t h P a r a l l e l , " G.S.C. Memoir 247. (2) Edwards, A.B. (1947), "Textures of the Ore Minerals," Austr.I.M.M. (3) Graton,L.C. (1931), "The Hydrothermal Depth Zones," Ore Dep. West. States, A.I.M.E. 1933* (4) Hanson, G. and McNaughton,D.A.(1936), "Eagle-McDame Area, Cassiar D i s t r i c t , B.C." G.S.C. Mem. 194-•',.. (5) Hemsworth, F.J.(1950), Ann. Rept., Minister of Mines, B.C., 1950. (6) Hewett, D.F., and Rove, O.N.(1930), "On the Occurrence of Alabandite," Econ. Geol. Vol.25. (7) Hewett,D.F., and Pardee,J.T. (1933), "Manganese i n Western Hydrothermal Ore Deposits," Ore Dep. West. States,A.I.M.E. (1933). (8) Johnston,W.A.(1925), "Gold Placers of Dease Lake Area, Cassiar D i s t r i c t , B.C." G.S.C. Sum. Dept. 1925. (9) Kerr, F.A. (1925), "Dease Lake Area", Cassiar D i s t r i c t ; B.C.,"(G.S.C. Sum Rept.,Pt.A, 1925. (10) Kohse,E.H.(1952), "A Study of the Contact Group Miner-a l s , " unpublished Rept., U.B.C. Dept. of Geol.,1952. (11) Kroger,F.A.(1939), "Formation of S o l i d Solution i n the System ZnS-2nS, "Zeite. B r i s t . 1939, Vol. 100, 1939. (Quoted from "Mineral Abstracts," Vol.7, 1938-40.) (12) Lindgren,W. (1933), "Mineral Deposits," McGraw-Hill, N.Y., 4th E d i t . (13) Lord, G.S. (1944), "Geological Investigations along the Alaska Highway between Watson Lake and Te s l i n River, Yukon and B.C.," G.S.C* Pap.44-25 (1944). (14) McCammon,J.W.(1951), Ann. Rept., Minister of Mines, B.C. 1951. (15) Mandy,J.T. (1935), Ann Rept., Minister of Mines, B.C., 1935. (16) 0'Grady,B.T. (1950), Ann Rept., Minister of Mines,B.C., 1950. 78 (17) Rasor, G.A. (1939), "Mineralization at Tombstone," Arizona," Econ. Geol. Vol.31, 1936. (18) Savage, W.S. (1936), "On the Deposition of Manganese and Iron Oxides," (19) Schneiderhb*hn, H. , and Ramdohr, P. (1931)," Lehrbuch der Ersmikroskopie ,11, B e r l i n , Geb. Borntraeger, 714. (20) T i l l e y , C.E. (1924) /'Contact Metamorphism i n the Comrie Area of the Perthshire Highlands," Geol. Soc. London Quart. Jour., Vol. 80. (21) Turner, F.C. and Verhoogen, J. (1931); "Igneous and Metamorphic Petrology," McGraw-Hill, 1st E d i t . (22) Warren, H.V. (1948), "Mineralogical Notes on Ore Minerals from Western Canada,". Abstract - Univ. of Toronto Studies, Geol. Series No. 52, 1948. (23) Watson, K. DeP., and Mathews, N.H. (1944), "The Tuya-Teslin Area," B u l l , No. 19, B.C. Dept. of Mines. (24) Williams, M.Y. (1944), "Geological Investigations along the Alaska Highway from Fort Nelson, B.C., to Watson Lake, Y.T.," G.S.C. Paper 44-28, (1944). 130" Y U K O N T E R R I T O R Y - i I i . i • I . , • I , 50' =1= 1 0 ' 30' 20' 10' 129° SO' 40' 30' M l ' 10' 128° 60° MAP 1 Mo DAME AREA B . C . Scale t 1 t 506,880 or 8 miles to 1 i n c h t Approximate Magnetic Declination, t 33*30 E . Geology approximate o n l y . . a f t e r G.S.C. IEGEND r%n. . MesozoicC ?) C a s s i a r E a t h o l i t n . <Sc Related i n t r u s i v e s Meao-Paleozoic McLeod S e r i e s . . mainly v o l c a n i c s , a r g i l l i t e s , c £ L m s . .»• Paleozoic Dease Series, .mainly 1ms., do l . , & q t z s ... U l t r a - b a s i c rocks, mostly s e r p e n t i n i z e d ... Mineral L o c a l i t y (1) Au placer,(2)Au-qtz lode ,(3)Ag-Pb-Zn,(4)Pb-Ba, ( 5)Cu£6)Zn. ... Lake suitable f o r a i r c r a f t , Bedding Attitude •.. Fault R E F E R E N C E Boundary: provincial Main highway Secondary road Trail Settlement. Trading post Tr. • Wireless station with call letters »}-| VY2V| Rapids and falls =s===t:^fc==s:=: Height in feet (approximate) 6230 Contours (approximate) — Marsh or swamp - Jit" " Glacie, 132" 128° Index to adjacent sheets MAP IE: G E O L O G Y OF THE CONTACT GROUP M INERAL ' C L A I M S L I A R D M.D. B.C. sc A L E M N . T O 200 F T . 200 400 Uj LEGEND G R A N I T E CASSIAR BATHOLIi A P L I T E D Y K E P E G M A T I T E 5 H B A S A L T D Y K E L E O P A R D H O R N F E L S B L A C K H O R N F E L S M A R M . L I M E S T O N E G R E E N H O R N F E L S 3 0 0 C L N . APPROXIMATE M A G N E T I C D E C L I N A T I O N 3 3 ° 3 0 ' E A S T 0 E 0 L 0 6 Y BY J .MCDOUGALL! 1 9 5 1 - 5 2 , C A R T O G R A P H Y BY AIR PHOTO I N T E R P R E T A T I O N AND C O M P A S S TR IANGU ILAT ION S U R V E Y . 5 K A R N - G A R N E T , S C A R , | E B I S M U T H - Q U A R T Z V E I N M O L Y B D E N I T E - Q U A R T Z V E I N O P Y R R H O T I T E DEPOSI "CONTACT" MAIN VEIN S T A L U S H O U T C R O P E l B E D D I N G - I N C L I N E D , V E R T . -A F A U L T A P P R - O X I M A T E A S S U M E D APPROX. DEF INED G3 G E O L O G I C A L B O U N D A R Y EH PIT O M I N E R A L C L A I M P O S T GRID 5 0 0 FT. CONTOUR INT. 100 FT.
Thesis/Dissertation
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Geological Sciences
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Graduate
The telescoped silver-lead-zinc deposits of the contact group mineral claims, Cassiar district, B.C.
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