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Cache Creek group and contiguous rocks, near Cache Creek, B.C. 1982

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CACHE CREEK GROUP AND CONTIGUOUS ROCKS, NEAR CACHE CREEK, B.C. By KENNETH ROBB SHANNON B.Sc., UNIVERSITY OF BRITISH COLUMBIA, 1975 THESIS SUBMITTED IN PARTIAL FULFILLMENT, OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Geological Sciences) We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA APRIL, 1982 © KENNETH ROBB SHANNON In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of GEOLOGY The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 D a t e A P R I L 2 6 . 1 9 8 2 DE-6 (3/81) i i ABSTRACT The Cache Creek Group in the type area i s characterized by oceanic rocks such as r a d i o l a r i a n chert, fusulini'd limestone and pillow basalt. Three d i v i s i o n s have been made in the Cache Creek Group in t h i s study: 1) s t r u c t u r a l l y lowest i s the melange unit (which has been i d e n t i f i e d as a subduction complex); 2) an overlying greenstone unit; and 3) the Marble Canyon Formation. Emplacement of the Marble Canyon Formation and greenstone unit on the underlying melange unit i s believed to have occurred in the Early to Mid-Jurassic along a shallow dipping thrust f a u l t . This emplacement may have caused soft sediment deformation features in the Early to Mid-Jurassic Ashcroft Formation. F e l s i c volcanic rocks and associated t u f f s and v o l c a n i c l a s t i c sediments are found mainly along the east side of the Cache Creek Group. These f e l s i c rocks have been c a l l e d the Nicola(?) Group and based on l i t h o l o g i c a l c o r r e l a t i o n are of probable Late T r i a s s i c age. The Nicola(?) Group i s correlated both with the western belt of the Nicola Group as described by Preto (1977) and the P a v i l i o n beds as described by T r e t t i n (1961). Blocks of Nicola(?) Group t u f f s have been found in the Cache Creek Group melange u n i t . This indicates that in Late T r i a s s i c time the Cache Creek Group and Nicola(?) Group were adjacent to one another. Paleoenvironmental and geochemical evidence indicate an ocean island or platform depositional environment for the Cache Creek Group. Tropical shallow seas covered most of these islands. Lack of continental sediments indicates that the Cache Creek Group was distant from any major land masses. i v T a b l e of C o n t e n t s ABSTRACT i i ACKNOWLEDGEMENTS v i i INTRODUCTION 1 LOCATION AND ACCESS .3 PREVIOUS WORK 3 CACHE CREEK GROUP .7 I ) MELANGE UNIT .7 Ia) Bedded R a d i o l a r i a n C h e r t B l o c k s 11 l b ) L i m e s t o n e B l o c k s 14 I c ) G r e e n s t o n e B l o c k s 17 Id) N i c o l a ( ? ) G r o u p B l o c k s 17 AGE OF BLOCKS IN THE MELANGE UNIT 18 I I ) GREENSTONE UNIT 21 AGE OF THE GREENSTONE UNIT 29 I I I ) MARBLE CANYON FORMATION 29 AGE OF THE MARBLE CANYON FORMATION 33 IV) SERPENTINITE 34 CORRELATION OF UNITS 37 NICOLAC?) GROUP 38 I ) F E L S I C TUFF UNIT 38 I I ) VOLCANI C L A S T I C UNIT 39 AGE OF THE NI C O L A ( ? ) GROUP 41 ASHCROFT FORMATION 43 RED CONGLOMERATE SANDSTONE UNIT 45 CHERT PEBBLE CONGLOMERATE UNIT 46 AGE OF THE CHERT PEBBLE CONGLOMERATE UNIT 48 KAMLOOPS GROUP 48 STRUCTURAL GEOLOGY 50 STRUCTURAL STYLE OF INDUVIDUAL UNITS 50 PALEOENVIRONMENTAL RECONSTRUCTION 57 TECTONIC MODELS AND HISTORY 59 ECONOMIC GEOLOGY I 63 CONCLUSIONS 65 REFERENCES 69 V L i s t of Figures 1 . Map showing tectonostratigraphic b e l t s of B.C. 4 2. Map showing location of f i e l d area 5 3. General geology of f i e l d area, from Shannon, 1981 8 4. Summary stratigraphic column showing units in f i e l d area 9 5. Photomicrograph of r a d i o l a r i a n chert breccia, two km north of Cache Creek, B.C 13 6. Rotated limestone block in melange unit, on west side of Bonaparte River, Cache Creek, B.C 13 7. Isolated limestone block, on Bonaparte Reserve north of Cache Creek, B.C 16 8. Radial structures in limestone block to west of Boston F l a t s 16 9. Nicola(?) block from 3 km north of Cache Creek, B.C. Showing v o l c a n i c l a s t i c texture 19 10. Nicola(?) Group v o l c a n i c l a s t i c rock from v i c i n i t y of Woodburn Ranch ;....19 11. Cache Creek Group v o l c a n i c l a s t i c rock from 3 km northwest of Carguile 20 12. Photomicrograph of ashflow t u f f block in Cache Creek Group melange unit from near Boston F l a t s ......20 13. Photomicrograph showing augite phenocryst a l t e r i n g to glaucophane, from agglomerate block in melange unit 21 14. View looking eastward across Bonaparte Valley to the north of Cache Creek, B.C. Dashed l i n e indicates contact of melange unit with overlying greenstone unit 23 15. Basalt pillows in greenstone unit 3 km north of Carguile 24 16. Trace element geochemistry of Cache Creek Group greenstones 26 17. A l k a l i c to t h o l e i i t i c plot of Y/Nb, adapted from Pearce and Cann, 1973 27 18. Discrimination diagram, adapted from Pearce and v i Cann, 1973. F i e l d D = ocean island or continental basalt. F i e l d A+B = low potassium t h o l e i i t e s . F i e l d C+B = c a l c - a l k a l i basalt 28 19. Basalt v o l c a n i c l a s t i c rock with f u s u l i n i d s . The fusu l i n i d s are v i s i b l e as the round c l a s t s with dark spots radiating out from t h e i r centres. From west side of Hat Creek Valley to the south of Medicine Creek 32 20. Compound p i s o l i t i c texture in limestone from top of Cornwall H i l l s at south end of map area 32 21. Interbedded r a d i o l a r i a n limestone and tuff from near top of Cormwalls H i l l s 33 22. Serpentinite outcrop showing t y p i c a l recessive nature from south side of Scottie Creek 35 23. Nicola(?) v o l c a n i c l a s t i c rock from along the Hat Creek road approximately 8 km west of Carquile 42 24. Pavilion bed v o l c a n i c l a s t i c rock from along roadside approximately 6 km east of Big Bar 42 25. Ashcroft Formation conglomerate on the Bonaparte Reserve north of Cache Creek, B.C 44 26. Stereoplot of poles to bedding and f o l i a t i o n , Cache Creek Group, f o l i a t i o n ( + ), bedding(X) 52 27. Stereoplot of poles to bedding and f o l i a t i o n , Nicola(?) Group, f o l i a t i o n ( + ), bedding(X) 53 28. Tectonic model for Cache Creek Group 60 29. Geology of the Cache Creek area, B.C in -peeHeetSpecx^A 30. F o s s i l and Geological Station Map in pee-k-et Sj«e\aA Colled-1« vii ACKNOWLEDGEMENTS I would l i k e t o thank W.R. Danner and J i m Monger f o r i n v a l u a b l e a s s i s t a n c e i n the f i e l d and g u i d a n c e and encouragement d u r i n g w r i t i n g of t h i s t h e s i s . B i l l T r a v e r s p a r t i c i p a t e d i n numerous d i s c u s s i o n s of the t e c t o n i c h i s t o r y of the t h e s i s a r e a . Marc B u s t i n c o n t r i b u t e d h i s s k i l l s i n e d i t i n g as w e l l as g i v i n g a d v i c e on the s t r u c t u r a l s e c t i o n of the t h e s i s . A s s i s t a n c e w i t h m i c r o f o s s i l s was k i n d l y g i v e n by Mike O r c h a r d of the G e o l o g i c a l Survey of Canada. P e r m i s s i o n t o work i n a r e a s r e s t r i c t e d from p u b l i c a c c e s s was g r a n t e d by the Bonaparte I n d i a n Band and t h i s was g r e a t l y a p p r e c i a t e d . H e l p i n a v a r i e t y of c a t e g o r i e s was p r o v i d e d by the g r a d u a t e s t u d e n t s and t e c h n i c i a n s a t U.B.C., i n c l u d i n g Randy P a r r i s h , Graham N i x o n , E r n i e P e r k i n s , Ed Montgomery and many o t h e r s . F i n a n c i a l s u p p o r t was p r o v i d e d by U.B.C, G e o l o g i c a l Survey of Canada and B.C. Hydro;. t h i s s u p p o r t i s g r a t e f u l l y acknowledged. I would l i k e t o thank Hun Kim of B.C. Hydro f o r h i s s u g g e s t i o n s d u r i n g p r e p a r a t i o n of t h i s t h e s i s . 1 INTRODUCTION Considerable interest has been directed towards the Cache Creek Group because of the implied transport of stratigraphic terranes proposed by Danner (1970) and Monger and Ross (1971). Permian f u s u l i n i d s found in limestones of the Cache Creek Group are Tethyan in o r i g i n (Dunbar, 1932) with counterparts in the Permian of the Mediterranean sea area, Japan, Indochina and south China. Fusulinids in the Harper Ranch Assemblage 100 km to the east, in part of similar age, belong to a d i f f e r e n t and cooler water fauna and may have o r i g i n a l l y evolved a great distance from the Cache Creek fauna (W.R. Danner, pers comm, 1981). The more recent interpretation of features in the Cache Creek Group thought to be t y p i c a l of subduction complexes such as subduction melanges and associated island arcs has been made by W. Travers (1978). Subduction - of oceanic plates would provide a mechanism for the juxtaposition of the Cache Creek Group Tethyan f u s u l i n i d s and the Harper Ranch Assemblage subtropical f u s u l i n i d s . Preliminary discoveries of subduction complex features by W. Travers (1978) indicated the need for regional mapping of the Cache Creek Group and surrounding rocks at the type l o c a l i t y at Cache Creek, B.C. This thesis mapping i s a continuation of regional mapping done e a r l i e r to the south by Grette (1978) and Ladd (1979). To the east of the Cache Creek Group i s a package of f e l s i c volcanic rocks and immature c l a s t i c rocks with some s i l i c i f i e d sediments and minor limestone. These f e l s i c v o l c a n i c l a s t i c rocks have been dated as Late T r i a s s i c by Grette (1978) and Travers (1978) who correlated 2 them with the Nicola Group to the east. The present study suggests on the basis of s i m i l a r age and l i t h o l o g y that these f e l s i c v o l c a n i c l a s t i c rocks may be c o r r e l a t i v e with the Pa v i l i o n beds of T r e t t i n (1961). U n t i l the detailed stratigraphy of the Nicola Group i s known, the f e l s i c v o l c a n i c l a s t i c rocks w i l l be referred to as the Nicola(?) Group. Controversy has been generated over the o r i g i n of the Cache Creek Group and i t s mechanism of emplacement in models put forward by Monger (1977) and Travers (1978). Work to the south of this present study was undertaken by Grette (1978) and Ladd (1979) in an e f f o r t to solve some of these problems. Such problems include: 1) what was the environment of deposition of the Cache Creek Group; 2) regional structure and stratigraphy of the Cache Creek Group; 3) the nature of the r e l a t i o n s h i p between the Cache Creek Group and the Nicola (?) Group; and 4) the time of juxtaposition of the Cache Creek Group and Nicola(?) Group. The purpose of t h i s thesis was to try to provide answers to the above problems. A regional mapping project (1:50,000) was undertaken during the summer of 1980, near Cache Creek, B.C. and forms the basis of t h i s thesis. This project was part of regional remapping of the Ashcroft map area by the Geological Survey of Canada. Extensive sampling of limestones and cherts of the Cache Creek Group was undertaken in the hopes of providing more f o s s i l dates concerning the age of t h i s group. 3 LOCATION AND ACCESS The area mapped i s about 600 km2, extending from Ashcroft Manor on the south to 20 Mile House on the north and Hat Creek Valley on the west to Bonaparte Valley on the east (Fig. 2). The area l i e s on the western margin of the Intermontane Belt which consists mainly of unmetamorphosed to low-grade metamorphic sediments and volcanic rocks ranging in age from Mississippian to Recent (Monger, 1981). To the west across the Fraser River Fault system l i e s the Coast Plutonic Complex and to the east i s the high-grade metamorphic to igneous Omineca C r y s t a l l i n e Belt (Fig. 1). Access to the area i s good via Highways 1, 97 and 12, as well as by numerous logging and ranching roads. Some of the l a t t e r are only accessible by 4-wheel drive. New logging roads were being constructed in the area during t h i s study and furnished new and important outcrops. Much of the map area i s covered by overburden and the best exposures occur along road cuts and stream v a l l e y s . Outcrops are more e a s i l y seen at lower a l t i t u d e s because of the sparse plant cover of grass, sagebrush and cactus. Higher a l t i t u d e outcrops are obscured by forests of Ponderosa pine and Douglas f i r . PREVIOUS WORK A. Selwyn (1872) was the f i r s t to describe the geology of the study area and named the Cache Creek Group a f t e r the small v i l l a g e near the type l o c a l i t y . G. Dawson (1895a) made the f i r s t geological map of the area and divided the Cache Creek Figure 1. Map showing tectonostratigraphic belts of B.C. F i g u r e 2. Map s h o w i n g l o c a t i o n o f f i e l d a r e a 6 Group into a lower unit of sedimentary rocks and greenstone and an upper unit predominantly of limestone, which he c a l l e d the Marble Canyon Formation. G. Dawson's reconnaissance mapping was updated by D u f f e l l and McTaggart (1952) who divided the Cache Creek Group into an eastern, c e n t r a l and western b e l t . Most of the f e l s i c volcanic rocks and limestones along Highway 1 between Martel and Cache Creek were included with the Cache Creek Group by both Dawson (1895) and D u f f e l l and McTaggart (1952). These f e l s i c volcanic rocks were reassigned from the Cache Creek Group to the Nicola Group by Grette (1978), Travers (1978), and Ladd (1979). From f i e l d evidence Grette ( 1 978) and Travers ('1978) defined the Cache Creek-Nicola contact as a steeply west dipping NW-SE trending f a u l t . This r e l a t i o n s h i p was in agreement with work done by Ladd (1979) who also suggested the contact may be in part a thrust f a u l t with older Cache Creek rocks being emplaced on top of Nicola rocks. Paleontological and paleo-environmental studies of Cache Creek Group carbonate rocks in the type area have been c a r r i e d out by Danner (1966, 1968, 1976). W.R. Danner (pers comm, 1981) suggests that the Marble Canyon Formation i s composed of carbonate banks formed on a volcanic to sedimentary substrate in warm shallow t r o p i c a l waters. Ages of fu s u l i n i d s found in the Cache Creek Group in southern B r i t i s h Columbia range from Middle Pennsylvanian to Late Permian. A preliminary report on the regional geology has been published by Monger (1981) and ear l y results of th i s thesis project have been published by Shannon (1981). 7 CACHE CREEK GROUP Work completed during the summer of 1980 showed that the eastern and c e n t r a l belts of the Cache Creek Group in the type area, can be divided into three main d i v i s i o n s ; a melange unit, a greenstone unit and the Marble Canyon Formation. The greenstone unit and Marble Canyon Formation appear to overlie the melange unit possibly along a thrust contact. Serpentinite i s included as a fourth unit in the Cache Creek Group and is described separately although i t crops out in a l l d i v i s i o n s . Geology of the f i e l d area i s summarized in F i g . 3 and a s t r a t i g r a p h i c column indicating the r e l a t i o n s h i p s of the main litho l o g . i c a l units i s shown in F i g . 4. Below, each of the four d i v i s i o n s of the Cache Creek Group i s described separately s t a r t i n g with the lowest st r u c t u r a l unit. I) MELANGE UNIT Tectonic melanges are bodies of deformed rocks characterized by the inclusion of t e c t o n i c a l l y mixed fragments or blocks, which may range up to several kilometres in s i z e , in a pervasively sheared matrix (Hsu, 1968). Sedimentary melanges are sheared olistostromes or debris flows which include blocks fragmented and mixed by sedimentary processes that are now embedded in a pervasively sheared matrix (Hsu, 1974). The Cache Creek melange unit contains a variety of blocks in a pervasively sheared matrix. Except for the serpentinite bodies which are fa u l t c o n t r o l l e d , most of the blocks could have been emplaced by either tectonic or sedimentary processes. Evidence presented 8 [mm L E G E N D V V V [v V V V V KAMLOOPS GROUP (EOCENE) CHERT-PEBBLE CONGL. (L.-M. CRET.) ASHCROFT FM. (L. JURRASIC) NICOLA (?) GROUP (TRIASSIC) MARBLE CANYON FORMATION GREENSTONE UNIT MELANGE UNIT SERPENTINITE BEDDING, FOLIATION FAULT DEFINED, APPROX CONTACT DEFINED, APPROX . K M. 2 A S H C R O F T J S E C T I O N A - A 1 Figure 3. General geology of f i e l d area, from Shannon, 1981 9 Kamloops Group Chert Pebble Conglomerate Unit Marble Canyon Fm Greenstone Unit .Red Conglomerate Unit NicolaC?) Group Melange Unit F i g u r e 4. Summary s t r a t i g r a p h i c column showing u n i t s i n f i e l d a r e a 10 during description of the geology of the melange blocks indicates that both tectonic and sedimentary processes have been involved in the genesis of the melange unit. Best exposures of the melange unit are in the town of Cache Creek, on the west side of the Bonaparte River. Additional outcrops are found along the Bonaparte Valley extending from Ashcroft Manor to 20 Mile House; other exposures are in stream valleys such as along lower Hat Creek. Within the thesis area the melange unit i s exposed only in these topographically low regions. Natural outcrops of the melange unit may show only blocks as the recessive matrix usually i s not exposed. The melange unit comprises blocks of limestone, greenstone, radio l a r i a n chert, greywacke, gabbro, serpentinite and f e l s i c tuff breccia in a variably sheared matrix of carbonaceous a r g i l l i t e and p h y l l i t e . The blocks range in size from centimetres to hundreds of metres. Changes in the r e l a t i v e percentage of blocks versus matrix greatly a f f e c t the physical c h a r a c t e r i s t i c s of the melange. Where the melange i s predominantly a r g i l l i t e or p h y l l i t e with few blocks present, i t is highly sheared and bedding cannot normally be followed for more that a few metres. This i s a r e f l e c t i o n of the extreme incompetency of these rocks. As the proportion of chert or limestone blocks increases, the competency of the melange also increases and degree of shearing decreases. Large outcrops of ribbon chert or limestone are usually not extensively broken, although they may be deformed. Lit h o l o g i e s of blocks in the melange are rocks types common 11 in the Cache Creek Group but include some that are t y p i c a l of the NicolaC?) Group as well. Most of the blocks in the melange unit are r a d i o l a r i a n chert (>50%), with some limestone (5-20%) and minor greenstone, serpentinite and Nicola(?) Group blocks (5-15%). Numerous blocks of f e l s i c volcanic material' are present in the v i c i n i t y of Cache Creek but only appear occasionally elsewhere in the melange. Radiolarian chert normally occurs scattered randomly in the melange with a few blocks in excess of 100 metres across. When mapping in the melange, geological contacts could not be followed in a normal fashion because each block was not in s t r a t i g r a p h i c contact with other blocks. It i s d i f f i c u l t to determine i f a small outcrop i s in fact an outcrop or a recent s l i d e block because there i s no geological continuity between blocks, and units show up as scattered knobs topographically. The matrix of the melange unit i s formed of interbedded ribbon chert and a r g i l l i t e in varying proportions. Areas with mixed ribbon chert and a r g i l l i t e or a r g i l l i t e alone are quite incompetent and when deformed, become highly sheared. Areas with thick sequences of ribbon chert acted independently from the matrix because of their competence and formed blocks. Ribbon chert i s the most frequent type of block in the melange ahd often forms the bulk of the outcrop. Ia) Bedded Radiolarian Chert Blocks Colours of the ribbon cherts are variable although grey and black v a r i e t i e s probably form over 90% of the cherts. Red, 12 green, white and brown v a r i e t i e s are present, probably r e f l e c t i n g impurities such as iron and manganese. Ribbon chert commonly forms layers 1-5 cm thick separated by thin, argillaceous partings. On some of the larger r e l a t i v e l y undeformed blocks an e f f o r t was made to trace the extent of single beds l a t e r a l l y . After a few metres at best the chert bed would pinch out, as i s common for ra d i o l a r i a n chert (Danner, 1970a). Locally, the cherts contain abundant well preserved r a d i o l a r i a , usually seen as clear glassy spheres less than 0.5 mm in diameter. In most modern interpretations of the o r i g i n of ribbon chert, r a d i o l a r i a are thought to be the source of s i l i c a for the ribbon chert sequences (McBride and Folk,1979). Previously, subaqueous volcanic emanations were thought to provide the source of s i l i c a for the ribbon chert sequences (Davis, 1918). There i s s t i l l controversy as to the method of formation of the rhythmic layering in ribbon cherts. Current theories rely on an al t e r n a t i n g combination of t u r b i d i t e and pelagic deposition (McBride and Folk, 1979). Previous theories focused around diagenetic a l t e r a t i o n of the ribbon chert into bands (Davis, 1918). A chert breccia crops out two kilometres north of Cache Creek, above and to the west of Highway 97. The outcrop i s composed of sub-rounded to sub-angular chert c l a s t s , usually less than 2 cm in size in a matrix of chert (Fig. 5). Colours of the c l a s t s range from black to gray. This unit i s interbedded with r a d i o l a r i a n ribbon chert. The variety of chert 13 Figure 5. Photomicrograph of r a d i o l a r i a n chert breccia, two km north of Cache Creek, B.C. Figure 6 . Rotated limestone block in melange unit, on west side of Bonaparte River, Cache Creek, B.C. 14 c l a s t s in the breccia and the occurrence of other l i t h o l o g i e s such as limestone cobbles indicates that t h i s breccia unit might be a s l i d e breccia. The breccia unit i s only found in one other location in the study area and i s probably best explained by l o c a l i z e d submarine s l i d i n g . Limestone beds occasionally interbedded with the ribbon cherts and a r g i l l i t e are usually less than 1 metre thick. These limestone beds sometimes contain shallow water f o s s i l s such as f u s u l i n i d s , which indicate that either the r a d i o l a r i a n chert formed in shallow water, or the limestone beds were emplaced in the chert stratigraphy as t u r b i d i t e units. Some of the limestones appear to be composed of sorted c l a s t i c f o s s i l debris which would support -a t u r b i d i t e o r i g i n . Examples of these t u r b i d i t e limestones are found along the east side of the Bonaparte River 2 km northeast of 20 Mile House (station #4, Fi g . 30) and south of Cache Creek just to the west of Boston Fla t s (station #355, F i g . 30). Ib) Limestone Blocks Limestone blocks commonly are in tectonic contact with the melange (Fig. 6). However some blocks grade into the matrix of the melange over a distance of usually <1 metre. The gradat.ional contact appears to be developed as a progressive decrease in the amount of fine-grained carbonate away from the edge of the block into the matrix. A suggested i n t e r p r e t a t i o n of these gradational contacts i s that the limestone blocks are large s l i d e blocks which broke off in shallow water and s l i d to 15 the s i t e of deposition as coarse sediments with a fine grained carbonate cloud around them. In most cases t h i s gradational contact is not present because of la t e r tectonism of the melange. Another interpretation proposed by W.R. Danner (pers comm, 1981) i s that at least some of the limestone blocks are large in s i t u carbonate accumulations such as a l g a l mounds. The contacts of these mounds have been modified by l a t e r tectonism. Some of the limestones in the melange unit south of Cache Creek have finely laminated structures which have been interpreted as a l g a l laminations (Danner, 1976). Intensive r e c r y s t a l l i z a t i o n has o b l i t e r a t e d o r i g i n a l textures in many limestone blocks, leaving a grey and white, mottled, coarsely c r y s t a l l i n e rock with rare f u s u l i n i d s and c r i n o i d columnals. Limestone i s very resistant to weathering in the arid climate of i n t e r i o r B.C., and on highly eroded h i l l s i d e s i t may form the only outcrop (Fig. 7). Dolomite comprises up to 10% of some samples. A f e t i d , bituminous odor was noticed when the limestones were freshly broken. Some of the limestones in the melange south of Cache Creek e x i b i t a strange . columnar r a d i a l j o i n t i n g that morphologically looks similar to a spray of aragonite c r y s t a l s except the columns are in excess of 2 metres long in places and are composed of sparry c a l c i t e (Fig. 8). Cathode-luminescence was attempted to see i f zoning could be observed in a cross-section of the columns. Results showed no zoning although the limestone did fluoresce a l i g h t blue colour instead of the usual orange for c a l c i t e (Koop, 1981). The anomalous fluorescence may be related to some cation 16 I Figure 7. Isolated limestone block, on Bonaparte Reserve north of Cache Creek, B.C. Figure 8. Radial structures in limestone block to west of Boston F l a t s 17 impurity in the c a l c i t e structure (Koop, 1981). Ic) Greenstone Blocks Blocks of greenstone are not common in the melange unit. Blocks up to several tens of metres across were observed but most were less than ten metres in longest dimension. Colour of the greenstones i s usually dark green to almost black. T y p i c a l l y the blocks are amygdaloidal and some show pillow structures. Greenstones in the melange unit tend to be highly sheared and fresh surfaces are rare. C a l c i t e and quartz veins up to 10 cm thick commonly crosscut the blocks. Id) Nicola(?) Group Blocks Light green v o l c a n i c l a s t i c blocks occur scattered in the melange unit, mainly in the v i c i n i t y of Cache Creek, B.C. Such blocks are si m i l a r in appearance and compostion to rocks of the Nicola(?) Group which i s adjacent to the Cache Creek Group on the east. The l i g h t green v o l c a n i c l a s t i c blocks are s i l i c e o u s and contain a variety of c l a s t s including f e l s i c volcanics, quartz-eye porphyries, chert and fine-grained sedimentary rocks (Fig. 9). These v o l c a n i c l a s t i c blocks are similar to Nicola(?) Group rocks cropping out along the Bonaparte River south of Cache Creek, which contain c l a s t s of f e l s i c volcanic rocks, s i l t s t o n e and r a d i o l a r i a n chert (Fig. 10). Cache Creek Group v o l c a n i c l a s t i c rocks contain only mafic volcanic, and limestone 18 c l a s t s (Fig. 11). Some of the l i g h t green v o l c a n i c l a s t i c blocks have well developed welded ash flow t u f f textures (Fig. 12). Welded t u f f s have been found in the Nicola Group by McMillan (1978) although such rocks have not been reported in the Cache Creek Group. A l l the l i g h t green blocks contain p y r i t e , l o c a l l y up to several percent. Presence of p y r i t e i s c h a r a c t e r i s t i c of Nicola rocks (McMillan, 1974) whereas p y r i t e i s rare in the Cache Creek Group except within some ribbon cherts. The preceeding evidence strongly supports the c o r r e l a t i o n between the l i g h t green v o l c a n i c l a s t i c blocks in the melange unit and the Nicola(?) Group v o l c a n i c l a s t i c rocks. P a r t i a l a l t e r a t i o n to clays and c h l o r i t e has rendered some of the Nicola(?) rocks incompetent and they form recessive rubbly outcrops. The volcanic and sedimentary c l a s t s in these blocks range in composition from t u f f s and agglomerates to volcanic greywackes. One of these breccia t u f f s north of Cache Creek has developed rims of fibrous blue-lavender glaucophane around brown augite phenocrysts (Fig. 13). AGE OF BLOCKS IN THE MELANGE UNIT F o s s i l dates in the melange unit have been obtained from r a d i o l a r i a extracted from cherts and conodonts extracted from limestone blocks. The dates based on r a d i o l a r i a range in age from probable Early Permian (D. Jones, written communication, 1981, United States Geological Survey) up to Late T r i a s s i c (Travers, 1978). Ages of blocks of limestone in the melange are mostly Late Pennsylvanian to Early Permian based on conodonts F i g u r e 1 0 . N i c o l a ( ? ) Group v o l c a n i c l a s t i c rock from v i c i n i t y of Woodburn Ranch F i g u r e 12 . P h o t o m i c r o g r a p h o f a s h f l o w t u f f b l o c k i n Cache C r e e k G r o u p melange u n i t f r o m n e a r B o s t o n F l a t s 21 Figure 13. Photomicrograph showing augite phenocryst a l t e r i n g to glaucophane, from agglomerate block in melange unit (M. Orchard, written communication, 1981, Geological Survey of Canada). Therefore rocks in the melange unit appear to have been deposited between Late Pennsylvanian to Late T r i a s s i c time. Deposition ceased sometime in the Late T r i a s s i c as no younger Cache Creek Group rocks have been found in the melange unit. II) GREENSTONE UNIT The greenstone unit crops levels with best exposures River Valley e s p e c i a l l y on the out mainly at higher topographic along ridges above the Bonaparte west side north of Carquile. The 22 greenstone unit overlies the melange unit possibly along a r e l a t i v e l y shallow clipping thrust f a u l t (Fig. 14). Amygdaloidal basalt is the most common l i t h o l o g y ; i t has a d i s t i n c t i v e spotted look caused by small black spherical c h l o r i t e amygdules (<3 mm) in an aphanitic green matrix. Also common are v o l c a n i c l a s t i c rocks which appear to be debris flow deposits; usually c l a s t s are basalt and limestone. Degree of c l a s t rounding and size of fragments i s var i a b l e . These v o l c a n i c l a s t i c rocks probably formed by submarine slumping of flows, as evidenced . by poor sorting, lack of internal s t r a t i f i c a t i o n except for alignment of fragments, multimodal c l a s t size d i s t r i b u t i o n and abrasive rounding of some c l a s t s (Fisher, 1971). Other l i t h o l o g i e s include basalt breccia, pillowed basalt (Fig. 15) and aphanitic basalt. Microscopically the basalts commonly have abundant plagioclase phenocrysts ranging from 0.1 to >10 mm in length. Augite phenocrysts were also observed sometimes with a brecciated appearance. Amygdaloidal i n f i l l i n g s and a l t e r a t i o n products include c a l c i t e , pumpellyite, stilpnomelane, quartz and c h l o r i t e . The c h l o r i t e commonly i s a late stage mineral replacing c a l c i t e in some samples. Opaque minerals present include p y r i t e , hematite and magnetite(?). Minor ribbon chert and p h y l l i t e are also included in the greenstone unit. Limestone i s present as interpillow i n f i l l i n g s 'and c l a s t s in basalt tuff breccia. Approximately 3 km north of Carquile, interpillow limestones produced abundant f i s h teeth during processing for conodonts. The age of these teeth could Figure 14. View looking eastward across Bonaparte Valley to the north of Cache Creek, B.C. Dashed l i n e indicates contact of melange unit with overlying greenstone unit 24 Figure 15. Basalt pillows in greenstone unit 3 km north of Carquile not be determined and no conodonts were recovered. Major element geochemistry was not attempted on any samples as extensive a l t e r a t i o n made analyses suspect. Work done by others on the Cache Creek Group basalts in northern B.C., indicates that they straddle the a l k a l i n e - t h o l e i i t i c boundary (Souther, 1977). An e f f o r t to i d e n t i f y the o r i g i n a l tectonic setting of these rocks was made using immobile element geochemistry. Elements were chosen which are r e l a t i v e l y insensitive to a l t e r a t i o n processes; these include T i , Zr, Nb, and Y (Pearce and Cann, 1973). Results are presented in Fi g . 16. Levels of Nb and T i are substantially above normal ocean floor basalt and according to the Y/Nb r a t i o the samples plot mainly in the a l k a l i c to t r a n s i t i o n a l compositional f i e l d 25 (Fig. 17). When plotted on the discrimination diagram (Fig. 18), the samples f a l l mainly in the "within plate" or ocean i s l a n d f i e l d , except for sample 103 which appears to be d i s t i n c t l y d i f f e r e n t than the other samples. Sample 103 i s not anomalously enriched in Nb or T i and appears s i m i l a r to normal ocean f l o o r basalt. It i s the only sample from the melange unit; a l l the other samples were from the greenstone unit or the Marble Canyon Formation. This l i m i t e d evidence suggests that the Cache Creek Group greenstones may be of two d i s t i n c t types. The f i r s t type, enriched in Nb and Ti i s of the ocean i s l a n d v a r i e t y . The second type has normal amounts of Nb and T i as compared to the average of ocean floor basalts ( Fig. 16). Geochemical differences between Cache Creek greenstones of the greenstone unit and Marble Canyon Formation versus normal ocean floor basalts are also manifested mineralogically. Clinopyroxene phenocrysts are common in the Cache Creek Group greenstones and in some samples the clinopyroxenes predominate over plagioclase. This i s not t y p i c a l of normal ocean f l o o r basalt in which o l i v i n e and plagioclase are dominant, with rare clinopyroxene ( S h i l l i n g , 1973). S h i l l i n g suggests that clinopyroxene-rich basalts are related to hot spot a c t i v i t y in the underlying mantle. 26 SAMPLE Nb(ppm) T i ( p p m ) Y(ppm) Z r ( p p m ) MVS-80-3a 4 8 2 17 100 26 172 MVS-80-22 37 15200 32 142 MVS-80-43a 29 17500 19 99 MVS-80-103 8 6800 38 25 MVS-80-171 77 28200 45 276 MVS-80- 19 l b 27 16800 42 111 CACHE CREEK GREENSTONE MEAN 38 16933 34 138 OCEAN-FLOOR BASALT MEAN 5 8350 30 92 OCEAN ISLAND BASALT MEAN 32 16250 29 115 ( P e a r c e and Cann, 1973) ( V a l u e s a r e + maximum o f 10%, S t a n y a H o r s k y , p e r s comm, 1981) Figure 16. Trace element geochemistry of Cache Creek Group greenstones 27 TRANSITIONAL T u r i t C 1 1 T 1 „ - ALKALIC — T H O L E I I T I C • Carlsberg Ridge(OF)- Palmer Ridge (OF)- Hawali (01)- Cache Creek*-*—• • • • i 0 Z Madelra(OI)- F l o r e s ( O l ) ' i 1 1 i r—i—r—i—i 1 r——r—r——i 1—i i r 0.1 I 1 0 Y/Nb Figure 17. A l k a l i c to t h o l e i i t i c plot of Y/Nb, adapted from Pearce and Cann, 1973 28 Ti/ I 00 Y.3 Figure 18. Discrimination diagram, adapted from Pearce and Cann, 1973. F i e l d D = ocean island or continental basalt. F i e l d A+B = low potassium t h o l e i i t e s . F i e l d C+B = c a l c - a l k a l i basalt 29 AGE OF THE GREENSTONE UNIT Dating the greenstone i s d i f f i c u l t because of r a r i t y of f o s s i l s . F u s u l i n i d limestone c l a s t s in a basalt v o l c a n i c l a s t i c rock 3 km northwest of Carquile have been assigned an Early to Mid-Permian age by W.R. Danner (pers comm, 1981). A single conodont fragment found in a limestone c l a s t in basalt 5 km south of Cache. Creek has been i d e n t i f i e d as Upper Permian by M. Orchard (written communication, 1981). These two dates suggest that the greenstone unit was l i k e l y deposited in the Permian. I l l ) MARBLE CANYON FORMATION The Marble Canyon Formation crops out mainly along the east side of Hat Creek valley and to the north in the Pavi l i o n Mountains. Areas underlain by the Marble Canyon Formation can be distinguished on a i r photographs by the prominent white limestone c l i f f s which the unit tends to form. Caves and sinkholes and some tufa springs are found in the Marble Canyon Formation and are a r e f l e c t i o n of i t s importance in the l o c a l groundwater c i r c u l a t i o n . The Marble Canyon Formation as described by D u f f e l l and McTaggart (1952) i s predominantly limestone with less than 10% andesite, chert and a r g i l l i t e . However new exposures along logging road cuts in the area mapped as Marble Canyon Formation indicate that the amount of material other than limestone i s 30 s u b s t a n t i a l l y greater than 10%. Except for l o c a l areas that are almost a l l limestone such as the top of Cornwall H i l l s , Whiterock C l i f f s and Marble Canyon i t s e l f the Marble Canyon Formation i s composed of ba s a l t i c v o l c a n i c l a s t i c rocks, limestone beds, r a d i o l a r i a n chert, a r g i l l i t e and minor serpentine in decreasing order of abundance. Because of i t s resistance to weathering in t h i s area the limestone forms a higher percentage of natural outcrops, but in road-cuts i t can be seen that limestone forms less than 50% of the Marble Canyon Formation. The most common li t h o l o g y among the limestones i s a dark grey and white mottled variety which weathers l i g h t grey. It i s commonly cross-cut with coarsely c r y s t a l l i n e c a l c i t e veins up to several centimetres in width. Other v a r i e t i e s include tan limestone with black stringers (graphite?) and dolomitized limestone with small rhombs of white-orange dolomite (0.1-0.2 mm) forming up to 10% of the rock. Some limestone has been almost completely converted to dolomite. One of the more f o s s i l i f e r o u s rocks in the Marble Canyon Formation i s a c l a s t i c rock with fragments of greenstone, micrite, f u s u l i n i d s , c r i n o i d columnals and other f o s s i l debris in a fine grained tuffaceous(?) matrix (Fig. 19). Occasionally these c l a s t i c rocks are found interbedded with r a d i o l a r i a n chert (station #296, F i g . 30). It i s unusual to f i n d units with shallow water f o s s i l s such as fu s u l i n i d s interbedded with ra d i o l a r i a n chert. Abrasive rounding of some of the c l a s t s indicates transport of the f o s s i l debris to the s i t e of 3 1 deposition. Turbidite transport or debris flow of the shallow water f o s s i l s would provide a mechanism for their emplacement in supposed deeper water sediments. Another d i s t i n c t i v e unit in the Marble Canyon Formation i s an o o l i t i c to p i s o l i t i c limestone which i s best exposed on Cornwall H i l l s ( Fig. 20). Dolomitization has been highly se l e c t i v e in these rocks sometimes replacing the cores of the o o l i t e s and sometimes the edges or even a few selected bands in the o o l i t e . These limestones probably formed in shallow, warm and agitated seas, as these conditions are required for o o l i t e formation. As well as o o l i t i c limestone, outcrops of thin bedded ra d i o l a r i a n limestone and tuff are also found on Cornwall H i l l s ( Fig. 21). These rocks are interpreted as deep water facies because of the i r thin even bedding and lack of benthic organisms. Clasts of o o l i t i c limestone are found in the tuff interbeds of the ra d i o l a r i a n limestone sequence. The presence of shallow water o o l i t e c l a s t s in the deep water ra d i o l a r i a n limestone and t u f f indicates that the topgraphy on the seafloor must have been steep at t h i s l o c a l i t y . Steep topography would allow the shallow water o o l i t i c debris to s l i d e down into the rad i o l a r i a n limestone basin. 32 Figure 19. Basalt v o l c a n i c l a s t i c 'rock with f u s u l i n i d s . The fu s u l i n i d s are v i s i b l e as the round c l a s t s with dark spots radiating out from their centres. From west side of Hat Creek Valley to the south of Medicine Creek Figure 20. Compound p i s o l i t i c texture in limestone from top of Cornwall H i l l s at south end of map area 33 Figure 21. Interbedded r a d i o l a r i a n limestone and t u f f from near top of Cormwalls H i l l s AGE OF THE MARBLE CANYON FORMATION Fusulinids found previously in limestones of the Marble Canyon Formation in southern B.C., range in age from Mid-Pennsylvanian to late Permian (Danner and N e s t e l l , 1966). A Late Permian age was reported by Grette (1978) for fus u l i n i d s in the Marble Canyon Formation west of Venables valley and to the south of th i s map area. Ages in c o l l e c t i o n s made during t h i s study range from Early Permian to Middle Permian (W.R. Danner, pers comm, 1981). Samples were also processed for conodonts and ages determined range from probable Late Pennsylvanian to Late T r i a s s i c (M. Orchard, written communication, 1981). Two col l e c t i o n s of r a d i o l a r i a obtained from ribbon cherts in the Marble Canyon Formation near station #296 (Fig. 30) gave Early 3 4 Permian dates (D. Jones, written communication, 1981). W.R. Danner has c o l l e c t e d thin shelled Halobia l i k e T r i a s s i c pelecypods in limestones northwest of the lookout on Cornwall H i l l s (pers comm, 1981). Greenstone t u f f s on Cornwall H i l l s have been assigned an Early T r i a s s i c age on. the basis of conodonts in interbedded limestones (M. Orchard, written communication, 1981). These conodonts provide cl e a r evidence for the continuation of Cache Creek volcanism into the Early T r i a s s i c ; these are the youngest known Cache Creek Group volcanic rocks in the Canadian C o r d i l l e r a . Deposition of the Marble Canyon Formation was mainly during the Permian but extends from the Late Pennsylvanian to as young as the Late T r i a s s i c . In a regional perspective the Marble Canyon Formation appears to become progressively younger from northeast to southwest; most of the older Pennsylvanian to Early Permian limestones occur in the northeast, the Middle Permian i s in the c e n t r a l part of the map area and the Late Permian to T r i a s s i c is found to the southwest. IV) SERPENTINITE Serpentinite i s found as iso l a t e d outcrops in a l l the units of the Cache Creek Group. Normally there are abundant slickensided surfaces and fractures throughout the outcrops. Serpentinite usually crops out as a rubbly green talus slope 35 (Fig. 22) and commonly weathers recessively. Figure 22. Serpentinite outcrop showing t y p i c a l recessive nature from south side of Scottie Creek Colour varies depending on amount of f r a c t u r i n g . Highly fractured samples tend to be l i g h t green to almost white whereas fresher r e l a t i v e l y unfractured serpentine i s dark green to almost black. Cross-cutting zones of white serpentinite a l t e r a t i o n products are quite common. North of 16 Mile d i o r i t e dykes cut through the serpentinites along an easterly trend. Chalcedony and c a l c i t e veins usually <3 cm thick are also quite common . in the serpentinites, often the chalcedony w i l l weather out in raised r e l i e f giving a coarse mesh texture to the outcrops. 36 A common a l t e r a t i o n product of the serpentinite bodies i s a quartz, carbonate and fuchsite (chromian-mica) rock which i s a d i s t i n c t i v e orange-white colour with bright green speckles of f u c h s i t e . The quartz-carbonate rock i s resi s t a n t to weathering and tends to form ridge outcrops or c i r c u l a r knobs. This rock may be erroneously i d e n t i f i e d as malachite stained gossan material and i s probably the quartz-carbonate with 2-3% chalcopyrite and malachite described by Ladd (1979) near Oregon Jack Creek (W. McMillan, pers comm, 1981) just to the south of the map area. Chromite was rarely observed in serpentinites in the f i e l d but in thin-section chromite occurs as small discrete brecciated c r y s t a l s disseminated throughout the serpentinite. The occurrence of serpentinite as a series of aligned bodies, together with i t s highly sheared nature and f a u l t bounded outcrop margins indicate that emplacement of the serpentinites was l i k e l y related to f a u l t a c t i v i t y . Most of the serpentinites are found along or near the Bonaparte Valley so probably t h i s was an area of high f a u l t a c t i v i t y . A recent discovery of serpentinites in the Marble Canyon Formation by H. Kim and A. Penner of B.C. Hydro was examined by the writer in January, 1981. It i s located along the east side of Hat Creek Valley to the south of Medicine Creek in a logging road cut. It i s variably sheared to fresh serpentinite in a sequence of limestone and basaltic v o l c a n i c l a s t i c rocks, t y p i c a l of the Marble Canyon Formation. This discovery means that the belt of serpentinite outcrops i s over 20 km wide. 37 CORRELATION OF UNITS Several outcrops in the f i e l d areas of Grette (1978) and Ladd(l979) were v i s i t e d so a c o r r e l a t i o n could be made with the d i v i s i o n s of the Cache Creek Group established in t h i s study. J. Grette divided the Cache Creek into three d i v i s i o n s , a lower c l a s t i c unit, a mafic volcanic unit and an upper c l a s t i c unit. J. Ladd divided the Cache Creek Group into a melange unit and the Marble Canyon Formation. Areas of greenstone were interpreted by Ladd (1979) as large blocks in the melange unit. The following c o r r e l a t i o n s are suggested: Cache Creek Group (Shannon,1981) (Grette,1978) (Ladd,1979) 1. Marble Canyon Fm—1. Upper C l a s t i c Unit 1. Marble Canyon Fm 2. Greenstone Unit 2. Mafic Volcanic Unit--2. Melange Unit 3. Melange Unit 3. Lower C l a s t i c Unit 3. Melange Unit 38 NICOLA(?) GROUP The Nicola(?) Group rocks are part of a package of f e l s i c volcanic rocks and sediments which have been dated as Late T r i a s s i c by . Grette(l978) and Travers(1978) and were correlated by them with the Nicola Group to the east. Similar rocks crop out immediately adjacent to the Guichon Batholith and are found as far south as Merritt (W.R. McMillan, pers comm, 1981 and Morrison, 1980). Rocks c a l l e d Nicola(?) Group in th i s study are correlated with other Nicola Group rocks to the east s t r i c t l y on l i t h o s t r a t i g r a p h i c grounds. Mapping was not s u f f i c e n t l y d e t a i l e d to outline the d i s t r i b u t i o n of sub-units in the Nicola(?) Group rocks, but for desc r i p t i v e purposes the Nicola(?) Group was divided into a f e l s i c t u f f unit and a v o l c a n i c l a s t i c unit. I) FELSIC TUFF UNIT Best exposures of the f e l s i c t u f f unit are to the north of Cache Creek on Cattle Valley Ridge and also to the south of Red H i l l along Highway 1. The f e l s i c t u f f unit consists mainly of a l i g h t green tuff with augens of quartz, plagioclase and chert in an aphanitic mica-chert matrix. Undulatory extinction was evident in some of the quartz grains. Extensive r e c r y s t a l l i z a t i o n has changed the chert grains to metamorphic quartz patches with highly sutured boundaries. Late stage carbonatization has replaced up to 15% of the rock with c a l c i t e . 39 Thinly laminated limestones up to several metres thick are found with these rocks. Abundant c r i n o i d columnals were observed in these limestones which are dark grey on a fresh surface and weather a l i g h t grey to white. Included within t h i s unit are minor amounts of coarser v o l c a n i c l a s t i c debris. II) VOLCANICLASTIC UNIT The main exposures of the v o l c a n i c l a s t i c unit are southwest of McLean Lake and along the Hat Creek road (station #19, Fig . 30). The v o l c a n i c l a s t i c unit i s c h a r a c t e r i s t i c a l l y blue green in colour and includes both p y r o c l a s t i c and e p i c l a s t i c rocks (mostly l a p i l l i t u f f s and volcanic sandstones, F i g . 23). A c h a r a c t e r i s t i c of the l a p i l l i t u f f s i s their f e l s i c nature; quartz "eyes" are very common and s i l i c i f i c a t i o n i s extensive. Chlo r i t e , pumpellyite and stilpnomelane are found as a l t e r a t i o n and replacement products. The blue green colour of the rocks i s due to the extensive c h l o r i t i z a t i o n . Clast l i t h o l o g i e s include amygdaloidal volcanic rocks, chert, fine-grained sediments, f e l s i c i n t r u s i v e rocks and limestone. P y r i t i z a t i o n i s very common in t h i s unit with 1-3% pyrite in most samples. E p i c l a s t i c rocks become more dominant higher in the Nicola(?) section and at the contact with the overlying Jurassic sediments the Nicola(?) i s e n t i r e l y sedimentary (Travers, 1978, Woodburn Ranch). The change in the Nicola(?) from dominantly volcanic to sedimentary i s re f l e c t e d in deposition of immature 40 volcanic sandstones, s i l t s t o n e and minor claystone in the upper Nicola(?) section. Rocks of the Pavi l i o n beds to the northwest (Trettin,1980) were examined in an e f f o r t to c o r r e l a t e N i c o l a C ? ) strata west to the Fraser River. Near Big Bar, along the Fraser River about 50 km northwest of Cache Creek, green volcanic sandstones were sampled. Colour, c l a s t l i t h o l o g y and amount of s i l i c i f i c a t i o n and p y r i t i z a t i o n were very s i m i l a r to Nicola(?) rocks cropping out south of Cache Creek (Fig. 24). Conodonts recovered from nearby limestone interbeds gave a Late T r i a s s i c age (M. Orchard, written communication, 1981), which i s the same age as the Nicola(?) Group rocks. Because of these s i m i l a r i t i e s the Nicola(?) rocks have been correlated with the Pa v i l i o n beds. The c o r r e l a t i o n of Nicola(?) rocks and the P a v i l i o n beds i s s i g n i f i c a n t as i t extends the area of f e l s i c v o l c a n i c l a s t i c rocks west as far as the Fraser River. No rocks of Nicola(?) a f f i n i t y have been found with the Marble Canyon Formation or greenstone unit of the Cache Creek Group between Big Bar and Cache Creek. F e l s i c v o l c a n i c l a s t i c blocks in the Cache Creek Group melange unit have been corr e l a t e d with the Nicola(?)Group. The main points of t h i s c o r r e l a t i o n are as follows: 41 NICOLA(?) GROUP CACHE CREEK GROUP FELSIC VOLCANICLASTIC VOLCANICLASTICS VOLCANICLASTICS BLOCKS IN MELANGE 1. diverse l i t h o l o g y 1. basalt, limestone 1. diverse l i t h o l o g y including s i l t s t o n e c l a s t s only. including s i l t s t o n e f e l s i c volcanics and f e l s i c volcanics and chert. chert. 2. contains f e l s i c 2. contains no f e l s i c 2. contains f e l s i c volcanic units such volcanic rocks. volcanic units such as ash flow t u f f s as ash flow t u f f s and quartz-eye and quartz-eye porphyries. porphyries. 3. ubiquitous p y r i t e 3. p y r i t e i s rare. 3. p y r i t e i s present in t h i s unit ranging in a l l blocks from 1-3%. usually >2%. The above comparison suggests that the f e l s i c v o l c a n i c l a s t i c blocks are part of the Nicola(?) package and not the Cache Creek Group. The occurrence of Nicola(?) blocks in the Cache Creek melange unit i s s i g n i f i c a n t . Such a re l a t i o n would suggest that the Nicola(?) rocks were being deposited into the Cache Creek melange unit as i t was forming. AGE OF THE NICOLA(?) GROUP No diagnostic f o s s i l s were found in any units of the Nicola(?) Group in the thesis area. Thinly bedded limestones on Cat t l e Valley Ridge to the north of Cache Creek produced abundant f i s h teeth during conodont processing but no conodonts were found. Ammonite f o s s i l s found in Nicola(?) sediments southeast of Cache Creek are dated as Late T r i a s s i c (Travers,1978). A Late T r i a s s i c age based on conodonts i s Figure 23. Nicola(?) v o l c a n i c l a s t i c rock from along the Hat Creek road approximately 8 km west of Carquile Figure 24. P a v i l i o n bed v o l c a n i c l a s t i c rock from along roadside approximately 6 km east of Big Bar A3 reported for Nicola limestones by Grette (1978). Volcanic rocks dated by Rb-Sr (Grette,1978) indicated a Late T r i a s s i c age as well. Limestones of the P a v i l i o n beds which are correlated with the Nicola(?) rocks have produced Upper T r i a s s i c conodonts (M. Orchard, written communication, 1981). Nicola(?) Group rocks represent a period of extensive Late T r i a s s i c volcanism with marine limestones present l o c a l l y . Extensive erosion during the Late T r i a s s i c produced the volcanic sediments predominating in the upper part of the Nicola(?) Group. ASHCROFT FORMATION North of the Bonaparte Indian Reserve within the Cache Creek Group i s a large area of brown to grey conglomerate and s i l t s t o n e . Some areas of fi n e r grained sediment show a weak f o l i a t i o n . No f o s s i l s were found in these rocks but on l i t h o l o g i c a l grounds they are correlated with the Lower Jurassic Ashcroft Formation as described by Travers (1978) in the v i c i n i t y of Ashcroft, B.C. Outcrops of well f o l i a t e d s i l t s t o n e and sandstone with no conglomerate, which occur to the northwest of 20 Mile House extending to Clinton are t e n t a t i v e l y correlated with the Ashcroft Formation. Clasts in the conglomerate on the Bonaparte Indian reserve 44 are extremely variable in size although usually not exceeding 10 cm in diameter. Clast l i t h o l o g i e s are mostly intermediate to f e l s i c intrusive rocks, quartz-feldspar porphyries and argillaceous sediments with minor gray m i c r i t i c limestone and mafic volcanic rocks (Fig. 25). Well rounded c l a s t s indicate that the conglomerate i s quite mature but some of the argillaceous sediment c l a s t s are quite angular; perhaps they were incorporated into the conglomerate close to the depositional s i t e . Sand size matrix material usually exceeds Figure 25. Ashcroft Formation conglomerate on the Bonaparte Reserve north of Cache Creek, B.C. 10% of the rock and appears to be mostly quartz. Cross-cutting c a l c i t e stringers are common. 45 S i l t s t o n e and minor a r g i l l i t e interbedded with the conglomerate have l o c a l l y developed slaty cleavage. Sometimes this f o l i a t i o n i s perpendicular to bedding but usually i t i s subparallel. Elsewhere in the map area outcrops of Ashcroft Formation are mainly s i l t s t o n e and sandstone with no conglomerate. F o l i a t i o n i s usually present at low angles to bedding. An outcrop of Ashcroft Formation sandstones and si l t s t o n e s along Lower Hat Creek is s t r a t i g r a p h i c a l l y underneath Nicola(?) f e l s i c volcanics and sediments. A single tops determination on Nicola(?) s i l t s t o n e s indicates that the unit i s right side up, t h i s would place T r i a s s i c rocks on Jurassic rocks. The most l i k e l y cause of such a st r a t i g r a p h i c anomaly i s that the Jurassic rocks have been faulted into place against the Nicola(?). RED CONGLOMERATE SANDSTONE UNIT A few outcrops of red conglomerate and sandstone are v i s i b l e along and north of the lower Hat Creek Road. Clast lithology i s quite variable including limestone, chert, green to white f e l s i c volcanic rocks, argillaceous sediments, serpentine and quartz, usually in a sparry white c a l c i t e cement. Clasts are subrounded to subangular and range up to 20 cm across. Abundant bright red c l a s t s are d i s t i n c t i v e and include 46 s i l t s t o n e , jasper and red chert. An outcrop close to the Marble Canyon Formation on the Hat Creek Road contains f u s u l i n i d limestone c l a s t s ; another about 4 km west of Carquile contains abundant chromite-serpentine c l a s t s . The c o r r e l a t i o n between Cache Creek bedrock type and c l a s t l i t h o l o g y in the conglomerate, the poorly sorted coarse nature of the deposits, presence of minor crossbedding and the limited extent of the unit a l l indicate an a l l u v i a l fan depositional environment for the conglomerate unit (Friedman and Saunders, 1978). Age of the red conglomerate sandstone unit i s unknown although i t appears to underlie a mid- Cretaceous chert pebble conglomerate at station #271 (Fig. 30). CHERT PEBBLE CONGLOMERATE UNIT A chert pebble conglomerate unit i s found along Lower Hat Creek. Outcrops continue both to the south and north along s t r i k e . G. Dawson (1895a) mapped the chert pebble conglomerate unit as the Coldwater Formation of Oligocene age. Subsequent workers assigned a Tertiary or Eocene age to the Coldwater, including D u f f e l l and McTaggart (1952) and Church (1975). Although sandstones and conglomerates are the main l i t h o l o g i e s in the unit i t also contains minor s i l t s t o n e layers. The most common c l a s t l i t h o l o g y in the conglomerates i s grey to 47 black chert pebbles (usually >50%) which contain v i s i b l e r a d i o l a r i a . Other c l a s t s include aphanitic volcanic rocks, argillaceous sediments,, high grade metamorphic rocks (with sutured quartz grains) and d i s t i n c t i v e f e l s i c t u f f s and ash. A high l e v e l of maturity i s indicated by the preponderance of well rounded chert and quartz c l a s t s , usually less than 3 cm in diameter. Incompetent rounded white ash c l a s t s found throughout t h i s unit are anomalous in such a mature sediment. Likely volcanism during the Cretaceous which produced the Spences Bridge Group to the south and west has contributed ash to the chert pebble conglomerate. The conglomerate i s often cemented with sparry c a l c i t e composing up to 5% of some samples. In thin-sec t i o n i t can be seen that thin Fe-oxide rims have formed around many c l a s t s , probably as a result of a l t e r a t i o n from groundwater flowing through th i s permeable unit. Most of the sandstones are composed c h i e f l y of small chert grains and quartz fragments. Tops structures such as truncated crossbedding indicate that the beds are right side up. Paleoenvironmental i n d i c a t o r s include mostly planar and massive bedding with l i t t l e cross-bedding; thick layers of coarse . sediments and sand with l o c a l f i n i n g upward sequences; large carbonized logs up to 60 cm in diameter; an absence of fine grained sediments and lack of marine f o s s i l s . These are in d i c a t i v e of braided r i v e r deposits (Friedman and Saunders, 1978). 48 AGE OF THE CHERT PEBBLE CONGLOMERATE UNIT Previously these continental rocks were assigned an Te r t i a r y age based on l i t h o l o g i c a l c o r r e l a t i o n (Dawson, 1895, D u f f e l l and McTaggart, 1952 and Church, 1975). Palynomorphs c o l l e c t e d at station #280 (Fig. 30) were examined independantly by G. Rouse (University of B.C.) and W.S. Hopkins (Geological Survey of Canada) and assigned a Late Albian or Cenomanian age. Correlation with the Eocene Coldwater Group and the Eocene Hat Creek rocks i s therefore i n v a l i d . The chert pebble conglomerate unit i s probably c o r r e l a t i v e with the Pasayten Group to the south (Monger, 1981). KAMLOOPS GROUP The Kamloops Group consists mainly of agglomerates, lahars and vesicular basalt and andesite. The lahars have sub-angular to sub-rounded c l a s t s which can exceed 30 cm in diameter set in a fine grained s i l t y matrix. Clast l i t h o l o g i e s include l i g h t coloured andesite and dacite and black glassy basalt. The Kamloops Group crops out mainly to the east of the Bonaparte Valley but also' occurs as i s o l a t e d knobs scattered throughout the map area. This is the youngest unit in the map area and has been assigned an Eocene age by Church (1975) based on 49 radiometric dating. - A prominent basalt outcrop north of the Oregon Jack Creek road and west of the road leading up to the Cornwall H i l l s f o r e s t r y lookout has a K-Ar age of 48 Ma (W.R. Danner, pers comm, 1980). Chalcedony and minor opal v e i n l e t s commonly cross-cut the volcanic units and vuggy c a v i t i e s l i n e d with small c r y s t a l s of quartz and c a l c i t e are common. Some of the volcanic units are f a i r l y incompetent and north of Carquile a few large caves were observed in c l i f f s of Kamloops Group volcanic rocks. Large areas of white r h y o l i t e cropping out northwest of McLean Lake and north of White Rock c l i f f s are also included in the Kamloops Group and have been dated as Eocene (51 Ma) by Church (1979). Tuffs and ash units containing c l a s t s of serpentinite were found in the Kamloops Group in some outcrops to the northeast of the Bonaparte Indian Reserve. Minor sandstones and s i l t s t o n e s are also found in the Kamloops Group. Kamloops Group rocks unconformably o v e r l i e Cache Creek Group greenstones at #265 (Fig. 30) but in some places they are in fa u l t contact. 50 STRUCTURAL GEOLOGY There are two dominant s t r u c t u r a l trends in the map area, the oldest s t r i k e s 140 degrees and p a r a l l e l s the s t r i k e of much of the C o r d i l l e r a . It i s r e f l e c t e d by an elongate d i s t r i b u t i o n of map units (see F i g . 3). A pronounced feature associated with t h i s trend i s a f o l i a t i o n reconized in most pre-mid- Cretaceous rocks. The younger s t r u c t u r a l trend s t r i k e s northeast and i s re f l e c t e d by numerous linear r i v e r valleys and lakes. These two dominant s t r u c t u r a l features are truncated by a later one that s t r i k e s north. These north s t r i k i n g structures are thought to have controlled the development of Eocene basins in the map area which formed in grabens (eg. Hat Creek, Church, 1975). Reactivation of fa u l t s has occured throughout the region as evident from the fault juxtaposition of older rocks such as the Cache Creek Group against younger rocks such as the chert pebble conglomerate and Kamloops Group. Faulted contacts appear to be ch a r a c t e r i s t i c of the units in t h i s region and extensive fa u l t i n g has led to the development of isolated f a u l t bounded blocks. STRUCTURAL STYLE OF INDUVIDUAL UNITS A penetrative deformation, recognized by a micaceous f o l i a t i o n and shear fabric has af f e c t e d both Cache Creek and 51 Nicola(?) Group rocks. A planar f o l i a t i o n c o n s i s t i n g of aligned argill a c e o u s partings i s seen in r a d i o l a r i a n cherts, elsewhere the cherts may be highly brecciated as a r e s u l t of the extensive shearing. The absence of a pronounced planar mineral fabric within the Cache Creek Group limestones i s due mainly to a lack of platy mineral grains. Whilst f u s u l i n i d s within the limestone near the Marble Canyon entrance are d i s t o r t e d , most of the s t r a i n e f f e c t s have been destroyed as a res u l t of post- deformational r e c r y s t a l l i z a t i o n . A mylonitic fabric developed within Nicola(?) Group rocks is best seen in the quartz-eye t u f f unit on C a t t l e Valley Ridge, to the north of Cache Creek. Quartz augens (0.1-0.5 mm diam) showing undulatory extinction occur in an aphanitic matrix of s e r i c i t e and m i c r o c r y s t a l l i n e quartz which wraps around the quartz augens in a fla s e r texture. In both the Cache Creek Group and Nicola(?) Group f o l i a t i o n s are p a r a l l e l or sub-parallel to bedding and have a s t r i k e d i r e c t i o n of 140 degrees (Figs. 26 and 27). Minor exceptions to t h i s f o l i a t i o n orientation s t r i k e northeasterly, almost perpendicular to the major s t r i k e d i r e c t i o n . The general conformity of f o l i a t i o n to bedding i s best explained by the presence of large i s o c l i n a l f o l d s . This hypothesis i s supported by the o r i e n t a t i o n of bedding which i s predominantly steep and dips to the southwest except within anomalous zones in which the bedding usually dips northeast. These anomalous zones are interpreted to be s t r u c t u r a l l y located in the hinge zones of the large i s o c l i n a l folds. Large i s o c l i n a l folds (limb lengths in 52 Figure 26. Stereoplot of poles to bedding and f o l i a t i o n , Cache Creek Group, f o l i a t i o n ( + ) , bedding(X) 5 3 Figure 27. Stereoplot of poles to bedding and f o l i a t i o n , Nicola(?) Group, f o l i a t i o n ( + ) , bedding(X) 54 excess of 1 km) have been reported in the Marble Canyon Formation by T r e t t i n (1980) and W.B. Travers (pers comm, 1980). Slaty cleavage within the Early to Mid-Jurassic Ashcroft Formation also has a pronounced northwest-southeast s t r i k e , W. Travers (.1978) reported a modal value of 136 degrees s t r i k e and a southwesterly dip of 32 degrees. W. Travers also presents evidence of soft sediment deformation features in the Ashcroft Formation. These soft sediment features include lack of fractures in tight f o l d hinges and thin wispy pull-apart structures in sandstone layers. The presence of soft sediment deformation structures in the Ashcroft Formation indicates that formation of the 140 degree f o l i a t i o n occured when the sediments had not yet been l i t h i f i e d . In as much as the 140 degree f o l i a t i o n developed in mid-Jurassic strata and not in post-mid- Cretaceous strata, development of the 140 degree f o l i a t i o n must then be post-mid-Jurassic and pre-mid-Cretaceous. Soft sediment deformation structures in the Ashcroft Formation suggest that the deformation was close to mid-Jurassic time. Because of repeated r e a c t i v a t i o n of the fa u l t s the o r i g i n a l contacts between units have been modified (eg. the contact between the Cache Creek Group melange unit and the Nicola(?) Group). Clasts of presumably Cache Creek Group r a d i o l a r i a n chert are found in volcanic greywackes of the Nicola(?) Group south of Cache Creek. The presence of c l a s t s of Cache Creek rocks in Nicola(?) sediments indicates that the contact between the two units is probably an unconformity and at least l o c a l l y the Cache Creek melange rocks were being u p l i f t e d in T r i a s s i c 55 time. The best exposed contact i s a steep f a u l t on the Woodburn Ranch south of Cache Creek (Travers, 1978). Nicola(?) sedimentary, rocks probably have an unconformable relationship with the melange unit, but nowhere are they seen to occur unconformably on the greenstone unit or Marble Canyon Formation. The fact that the Nicola(?) Group rocks are not found unconformably with respect to the greenstone unit or Marble Canyon Formation i s a very s i g n i f i c a n t factor in tectonic modelling for the area. This aspect w i l l be covered in more d e t a i l in the chapter on tectonic h i s t o r y . The Nicola(?) Group-Ashcroft Formation contact appears to be a faulted one throughout most of the map area. North of the Bonaparte Indian Reserve steeply southwest dipping Nicola(?) strata abutt gently dipping Ashcroft conglomerates along a l i n e a r depression trending across the h i l l s i d e . This feature has a 140 degree trend and i s probably a f a u l t . Along the Hat Creek Road, near station #19 (Fig. 30) Nicola(?) rocks o v e r l i e Ashcroft s i l t s t o n e s and sandstones. D i f f e r i n g orientation of the units suggests a f a u l t contact. To the south Travers (1978) reported the contact both as an unconformity and as a thrust f a u l t , the thrusting post-dates the unconformity. Such complexly faulted i n t e r e l a t i o n s h i p s continue into Eocene time. At station #265 (Fig. 30) immature sandstones of the Eocene Kamloops Group unconformably o v e r l i e greenstones of the Cache Creek Group. About 3 km to the north the contact i s a v e r t i c a l f a u l t s t r i k i n g north-south which contains serpentine bodies cropping out along the contact. The varied nature of the 56 stratigraphic contacts r e f l e c t s the deformational history of thi s area between T r i a s s i c and Eocene time. 57 PALEOENVIRONMENTAL RECONSTRUCTION The association of r a d i o l a r i a n ribbon chert, pillowed basalt, gabbro, ultramafic rock and limestone suggest an oceanic environment for deposition of Cache Creek Group rocks. A varie t y of s p e c i f i c enviroments has been proposed including a mid-ocean ridge as well as volcanic seamounts (Monger, 1977). Geochemical evidence of high concentrations of Nb and Ti suggest an ocean island or continental environment (Pearce and Cann, 1973). The occurrence of abundant shallow water faunas such as f u s u l i n i d s and calcareous algae suggest a shallow marine environment. Together the geochemistry and paleontology suggest a large oceanic island or oceanic plateau environment as the most l i k e l y depositional s i t e . Shallow water indicators in the limestones such as f u s u l i n i d s , o o l i t e s and alg a l laminations show that most of the Cache Creek oceanic plateau must have been covered by shallow warm seas. Conditions were t r o p i c a l as i s supported by the growth of large f u s u l i n i d s which probably grazed on algae and other organic debris on carbonate banks (W.R. Danner, pers comm, 1980). Evidence for minor sub-areal exposure has been reported in the Cache Creek Group near Dease Lake,, B.C. (Morrow, 1967). This Cache Creek plateau was mainly composed of mafic volcanic and v o l c a n i c l a s t i c rocks and limestone. Intermixing of limestone and mafic volcanic rocks i s common in the Cache Creek Group in southern B.C. In northern B.C. the Cache Creek Group usually has d i s t i n c t areas of limestone and volcanic rocks with l i t t l e interbedding of the two (Monger, 1977 ) . 5 8 Both adjacent to and within the plateau were deeper water areas of pelagic deposition. A r g i l l i t e and chert were most common in these areas. Topographic r e l i e f on the plateau and i t s margins led to the sedimentation of both carbonate and chert debris-flow deposits into the surrounding pelagic sediments. From time to time large blocks of limestone were broken off the plateau and s l i d into the deeper water r a d i o l a r i a n chert and a r g i l l i t e sediments. Almost a l l the limestone blocks in the melange unit of the Cache Creek Group contain the same or similar Permian conodont fauna (M. Orchard, pers comm, 1981). The limestone blocks were probably dislodged by cataclysmic events such as hurricanes or earthquakes and emplaced as submarine talus and s l i d e deposits. A similar explanation for limestone blocks interbedded with r a d i o l a r i a n chert in the Cache Creek Group in northern B.C., has been proposed by J . Monger (1977). F e l s i c t u f f s , agglomerates and flows with some ba s a l t i c rocks characterize the lower Nicola(?) while the upper part i s mainly water-lain volcanic sediments (Travers, 1978). Limestones are found sporadically throughout the section and contain c r i n o i d s , brachiopods and other marine f o s s i l s . This sequence of rocks could have been deposited in a maturing island arc s e t t i n g , where extensive erosion occurs as volcanism wanes, as proposed by Travers (1978). Gra n i t i c rocks of the underlying comagmatic Guichon Batholith would provide the plutonic roots for the system (McMillan, 1976). 59 TECTONIC MODELS AND HISTORY A model has been developed in an e f f o r t to unite models put forth by previous authors (Monger, 1977), (Travers, 1978) and (Ladd, 1979) with new geological and paleontological information c o l l e c t e d in t h i s study. In the model proposed here the older rocks are divided into four groups. 4) Ashcroft Formation 3) Nicola(?) Group (Island Arc) 2) Greenstone Unit and Marble Canyon Formation (Oceanic Plateau) 1) Melange Unit (Subduction Complex) On F i g . 28 the oceanic plateau i s shown as approaching the arc. The plateau i s composed of the greenstone unit and the Marble Canyon Formation. Formation of a subduction complex occurs at the trench and occasional arc debris slumps out to the ocean; where i t i s incorporated into the ocean sediments and eventually the melange. Radiolarian chert and a r g i l l i t e scraped off the ocean floor are the main constituents of the melange in the subduction complex. Also included are blocks which have s l i d off the nearby plateau and minor volcanic and sedimentary rocks from the Nicola(?) island arc. Late T r i a s s i c Nicola(?) rocks and Early to Mid-Jurassic Ashcroft Formation sediments are deposited out over the melange. These rocks are represented by the Nicola(?) volcanic and sedimentary rocks south of Cache 60 S U B D U C T I O N P O S T M I D - J U R A S S I C Figure 28. Tectonic model for Cache Creek Group 61 Creek, west of McLean Lake and west of the Bonaparte Indian Reserve; and Ashcroft Formation rocks south of Cache Creek, west of the Bonaparte Indian Reserve and along the Lower Hat Creek road. The Ashcroft Formation i s composed mainly of eroded remanents of the extinct Nicola(?) islan d arc and associated plutonic basement. As the ocean plateau c o l l i d e s (Fig 28b) i t i s thrust up over the melange-arc unit for a minimum distance of 40 km, coming to a rest only a few kilometers from the b a t h o l i t h i c core of the island arc (Fig 28c). This obduction may be the source of the predominant 140 degree southwest dipping f o l i a t i o n common in the pre-mid-Cretaceous rocks throughout the map area. Early to Mid-Jurassic rocks overlying the Nicola(?) Group rocks are involved in t h i s deformation as discussed in the s t r u c t u r a l geology section. Because t h i s deformation has no obvious e f f e c t on the mid-Cretaceous chert pebble conglomerate unit i t must predate deposition of these rocks. Later block f a u l t i n g along the 140 degree and NS trends has brought a l l units into contact mainly along block boundaries. This e f f e c t has been quite dramatic west of Carquile in the chert pebble conglomerate unit. Rocks which o r i g i n a l l y were deposited in a broad f l a t r i v e r v a l l e y have now been t i l t e d into two opposing half-grabens. Along the upthrown center portion of the two half-grabens are discontinuous pods of serpentinite and rocks from the Nicola (?).Group and Ashcroft Formation. This block f a u l t i n g has continued u n t i l at least Eocene time as Kamloops Group rocks are l o c a l l y faulted against Cache Creek 62 Gr o u p r o c k s . 63 ECONOMIC GEOLOGY Metalli c mineral deposits in the map area include the Cache Creek, Scotty Creek, Ferguson Creek and Cornwall Creek chromite occurrences (Duff e l l and McTaggart, 1952). The chromite i s found as small pods and disseminations in serpentinites of the Cache Creek Group. Due to the e r r a t i c low-grade nature of much of the mineralization these occurrences have not been explored in recent years. The Maggie Mine i s a low-grade porphyry copper-molybdenum deposit with about 200 MT of reserves grading 0.4% copper equivalent (B.C. Dept of Mines, G.E.M., 1971, p 304), located about 3 km north of Carquile. Regional geochemical sampling for further examples of t h i s kind of mineralization have been ca r r i e d out by Bethlehem Copper and other companies but no new discoveries have been made. Small quartz veins in Cache Creek Group and Nicola Group rocks carry minor amounts of chalcopyrite, galena and sphalerite throughout the map area. South of Cache Creek near Boston F l a t s , ribbon chert blocks were found with malachite and azurite coating fracture surfaces. None of these small occurrences appear to be large enough to warrant furthur exploration. Altered serpentinites which form resistant outcrops of quartz, carbonate and fuchsite rock may be hosts to large- tonnage low-grade gold deposits. The association of quartz- carbonate rocks and gold deposits i s documented in recent l i t e r a t u r e (Boyle, 1980). A grab sample of quartz, carbonate and fuchsite rock from west of McLean Lake gave values of over 64 300 ppb Au and 18 ppm Ag. However mineralization i s e r r a t i c and nearby outcrops contained no gold or s i l v e r values. Detailed sampling over large areas of quartz, carbonate and fuchsite rock would have to be c a r r i e d out to locate gold and s i l v e r - r i c h zones. There i s good potential in the Nicola(?) Group rocks for volcanogenic massive sulphide deposits. Nicola(?) Group rocks 15 km south of Cache Creek at Red H i l l apparently contain massive chalcopyrite which appears volcanogenic in o r i g i n (Albrechtsons, 1981). New areas of Nicola(?) type rocks were discovered in the course of mapping for t h i s project; these could be examined for extensions of Red H i l l - t y p e massive sulphide mineralization. G. Dawson (1895) mentions reports of gold in the chert pebble conglomerate unit (Coldwater Formation) occuring as paleo-placer mineralization. Prospecting for t h i s kind of deposit could be done by regional geochemistry in areas of favourable stratigraphy. Special attention should be focused on coarse gravel deposits which may indicate channel bottoms and could contain placer accumulations of gold. Adjacent to the map area on the west i s Hat Creek Valley which contains one of the worlds thickest single deposits of coal . Estimates of t o t a l reserves have exceeded 10 B i l l i o n tons (H. Kim, pers comm, 1980). T e r t i a r y rocks with comparable stratigraphy were not found in the map area so the p o t e n t i a l for coal deposits of the same type i s very low. 65 CONCLUSIONS 1. The Cache Creek Group rocks of the eastern and central belts in southern B.C. ( D u f f e l l and McTaggart, 1952), can be divided into a lower melange unit and a s t r u c t u r a l l y overlying greenstone unit and Marble Canyon Formation. 2. Thinly laminated c h e r t - a r g i l l i t e of the melange unit i s interpreted as representing a deeper water environment because of lack of carbonate (except as blocks) and evidence of pelagic sedimentation(radiolaria and thin rhythmic bedding of a r g i l l i t e between chert l a y e r s ) . Limestone blocks in the melange unit contain f u s u l i n i d s and a l g a l structures indicating shallow water provenance. Greenstone blocks in the melange unit contain c l a s t s of f u s u l i n i d limestone as well as in t e r p i l l o w carbonate (but no deeper ,water c h e r t - a r g i l l i t e ) , indicating deposition of the greenstone in r e l a t i v e l y shallow water. Therefore the melange probably formed by blocks of shallow water faci e s rocks s l i d i n g into deeper water where deposition of chert and a r g i l l i t e was predominant. A term for melange formed in t h i s manner would be talus melange. Olistostrome would imply sedimentary transport of the c h e r t - a r g i l l i t e matrix which does not appear to have occured. Later tectonism has sheared the melange unit and caused rotation of blocks in the melange. 3. Limited geochemical evidence from immobile elements such as Nb, Y and T i indicates that the Cache Creek greenstones formed pa r t l y in an in t r a - p l a t e ocean plateau environment (Pearce and Cann, 1973). Most greenstones in the Cache Creek Group in southern B.C. are highly enriched in Nb and Ti compared 66 to normal ocean floor basalts. Values up to 77 ppm Nb and 276 ppm T i were recorded. One sample of greenstone had concentrations of Nb and Ti similar to ocean floor basalts i n d i c a t i n g that there may have been more than one magma source for the Cache Creek Group greenstones. A modern analogue for t h i s environment i s Iceland ( S c h i l l i n g , 1973). Most of the rocks were a l k a l i c to t r a n s i t i o n a l and not t h o l e i i t i c according to the Y/Nb ratios(Pearce and Cann, 1973). 4. Discovery of probable Nicola(?) rocks apparently occurring as blocks in the Cache Creek Group melange unit has several implications. F i r s t , the Cache Creek Group and Nicola(?) Group were juxtaposed by Late T r i a s s i c time and the Nicola(?) was shedding d e t r i t u s into the Cache Creek melange. As the Nicola(?) blocks contain glaucophane they presumably have been subjected to pressure and temperature conditions similar to the rest of the melange which i s reported to contain blue amphiboles (Grette, 1978). Since the Nicola(?) blocks have developed blueschist mineralogy they could not have been introduced into the melange unit as l a t e r f a u l t s l i c e s . 5. Radiolarian chert c l a s t s found in the Nicola(?) greywackes along the Bonaparte River south of Cache Creek are probably derived from Cache Creek Group cherts and provide furthur evidence that the two units were together by Late T r i a s s i c time. This i s disputed by W.R. Danner who maintains the r a d i o l a r i a n c l a s t s may have come from cherts in the Nicola(?) Group. Radiolarian cherts are not presently known to occur in the Nicola(?) Group. Since Cache Creek Group 67 radiolarian cherts are as young as Late T r i a s s i c (Travers, 1978), the p o s s i b i l i t y exists that Nicola(?) Group ra d i o l a r i a n cherts may be discovered. 6. Superposition of the predominantly Permo-Triassic Marble Canyon Formation-greenstone unit and the Permo-Triassic melange unit i s probably along a large shallow-dipping thrust f a u l t . Minimum displacement can be estimated by measuring from the furthest west Cache Creek melange type rocks (along the Fraser River near Moran) to the easternmost edge of the greenstone unit north of Cache Creek; t h i s provides a figure of at least 40 km displacement. T r e t t i n (1980) has proposed the existence of si m i l a r f l a t l y i n g thrust f a u l t s in the Cache Creek Group in the Marble Range to the north. An alte r n a t i v e explanation suggested by J. Monger (pers comm, 1981) i s that the areas of greenstone and limestone which appear to ov e r l i e the melange unit are enormous blocks. If t h i s i s true then Nicola(?) Group rocks should be found s i t t i n g unconformably above the greenstone unit and Marble Canyon Formation because Nicola(?) Group blocks are found in the melange unit. However no Nicola(?) rocks are observed on the Marble Canyon Formation or the greenstone unit. 7. Radiolarian chert c l a s t s presumably derived from the Cache Creek Group melange unit rocks are found in Nicola(?) greywackes south of Cache Creek. However no limestones of Cache Creek Group o r i g i n have been found in these rocks (W.R. Danner, pers comm, 1981), which indicates that the melange unit was in contact with the Nicola(?) Group in the Late T r i a s s i c but the 68 Marble Canyon Formation was not. The lack of Marble Canyon Formation debris in the Nicola(?) Group provides further support to the suggestion that the Marble Canyon Formation and greenstone unit were emplaced in their p o sition a f t e r deposition of the Nicola(?) volcanic greywackes. 69 REFERENCES Albrechtons, E.A. (1981) The geology of the S i l i c a Claim Group, Red H i l l area, near Ashcroft, B.C. Unpublished BSc. Thesis, Lakehead University, Thunder Bay, Ontario, 56p. Boyle, R.W. (1980) The geochemistry of gold and i t s deposits. Geological Survey of Canada, B u l l e t i n 280, 584p. Church, B.N. (1975) Geology of the Hat Creek Coal Basin. B.C. Mi n i s t r y of Mines and Petroleum Resources, Geology in B r i t i s h Columbia, p G99-G118. Church, B.N. (1979) Combustion metamorphism in the Hat Creek area, B r i t i s h Columbia. Canadian Journal of Earth Sciences, V 16, p 1882-1887. Danner, W.R. and N e s t e l l , M.K. (1966) Biostratigraphy of the Cache Creek Group, Pennsylvanian-Permian, in the type area, B r i t i s h Columbia, Canada. (ABSTRACT) Geological Society of America Annual Meeting in San Francisco, p 49-50. Danner, W.R. (1968) The Cache Creek Complex in Southern B r i t i s h Columbia and northern Washington. (ABSTRACT) Geological Association of Canada Annual Meeting in Vancouver, B r i t i s h Columbia, p 10-11. Danner, W.R. (1970) Paleontologic and stratigraphic evidence for and against sea floor spreading and opening and clo s i n g oceans in the P a c i f i c northwest. Geological Society of America, (Abstract), C o r d i l l e r a n Section Annual Meeting, p84-85. Danner, W.R. (1970a) Cherts and Jaspers of the Western C o r d i l l e r a n Eugeosyncline of Southwestern B r i t i s h Columbia and Northern Washington. West Commemoration Volume, New Delhi, India, p534-553. Danner, W.R. (1976) Limestones of southwestern B r i t i s h Columbia. Proceedings of Eleventh I n d u s t r i a l Minerals Forum. Special Publication, Montana Bureau of Mines and Geology, No. 74, p 171-176. Davis, E.F. (1918) The Radiolarian Cherts of the Franciscan Group. Publication of the University of C a l i f o r n i a , B u l l e t i n , V 11, No 3, p235-432. Dawson, G.M. (1895) Report on the area of the Kamloops map- sheet, B r i t i s h Columbia. Geological Survey of Canada,. Annual Report, V 11, p 3B-427B. Dawson, G.M. (1895a) Kamloops Sheet, B r i t i s h Columbia. 7 0 Geological Survey of Canada, Map 556. D u f f e l l , S. and McTaggart, K.C. (1952) Ashcroft Map-Area, B r i t i s h Columbia. Geological Survey of Canada, Memoir 262, 122p. Dunbar, CO. (1932) Neoschwagerina in the Permian faunas of B r i t i s h Columbia. Transactions of the Royal Society of Canada, Third Series, V 26, Sec. 4, p 45-49. Fisher, R.V. (1971) Features of coarse-grained, high concentration f l u i d s and t h e i r deposits. Journal of Sedimentary Petrology, V 41, p 916-927. Friedman, G.M. and Saunders, J.E. (1978) P r i n c i p l e s of Sedimentology, John Wiley and Sons, United States, 729p. Grette, J.F. (1978) Cache Creek Group and Nicola Group near Ashcroft, B r i t i s h Columbia. University of B r i t i s h Columbia, Unpublished MSc. Thesis, 88p. Hsu, K.J. (1968) P r i n c i p l e s of melanges and t h e i r bearing on the Franciscan-Knoxvilie paradox. Geological Society of America B u l l e t i n , V 79, No. 8, p 1063-1074. Hsu, K.J. (1974) Modern and Ancient Geosynclinal Sedimentation; problems of p a l i n s p a s t i c reconstruction. Society of Economic Paleontologists and Mineralogists, Special Publication No. 19, p 321-333. Koop, O.C. (198 1 ) Cathodeluminescence Petrography. Journal of Geological Education, V 29, p 108-113. Ladd, J.H. (1979) Mesozoic overthrusting of oceanic crust in south-central B r i t i s h Columbia. Cornell U n i v e r s i t y , Unpublished MSc. Thesis, 96p. McBride, E.F. and Folk, R.L. (1979) Features and o r i g i n of I t a l i a n r a d i o l a r i t e s deposited on continental c r u s t . Journal of Sedimentary Petrology, V 49, No. 3, p 837-868. McMillan, W.J. (1974) Stratigraphic section from the Jurassic Ashcroft Formation and T r i a s s i c Nicola Group contiguous to the Guichon B a t h o l i t h . B.C. Ministry of Mines and Petroleum Resources, Geological Fieldwork, p 27-34. McMillan, W.J. (1977) Promontory H i l l s . B.C. Ministry of Mines and Petroleum Resources, Geological Fieldwork, p 31-36. McMillan, W.J. (1978) Nicola Project-Merritt Area. B.C. Ministry of Mines and Petroleum Resources, Geological Fieldwork, p 41-46. M i a l l , A.D. (1978) Li t h o f a c i e s types and v e r t i c a l p r o f i l e models ( 71. in braided r i v e r deposits: a summary. F l u v i a l Sedimentology, Canadian Society of Petroleum Geologists, Memoir 5, p 597-604. Monger, J.W.H. and Ross, C A . (1971) D i s t r i b u t i o n of fusulinaceans of the Canadian C o r d i l l e r a : a plate-tectonic model. American Journal of Science, V 272, p 259-278 Monger, J.W.H. (1977) Upper Paleozoic rocks of the western Canadian C o r d i l l e r a and their bearing on Co r d i l l e r a n evolution. Canadian Journal of Earth Sciences, V 14, p1832-1859. Monger, J.W.H. (1981) Geology of parts of western Ashcroft map area, southwestern B r i t i s h Columbia. Geological Survey of Canada, Current Research, Part A, Paper 81-1A, Report 24. Monger, J.W.H. et a l (1981) C o r d i l l e r a n cross-section, Calgary to V i c t o r i a . F i e l d t r i p hand-out for Geological Association of Canada Annual Meeting in Calgary, May 1981. Morrison, G.W. (1980) Stratigraphic control of Cu-Fe skarn ore, d i s t r i b u t i o n and genesis at Craigmont, B r i t i s h Columbia. Canadian Mining and Metallurgical B u l l e t i n , V 73, p 109-123. Morrow, D.W. (1967) The environment of deposition of a Permian limestone, Dease Lake area, B.C. University of B r i t i s h Columbia, Unpublished BSc. Thesis Pearce, J.A. and Cann, J.R. (1973) Tectonic setting of basic volcanic rocks determined using trace element analyses. Earth and Planetary Science Letters, V 19, p 290-300. Preto, V.A. (1977) The Nicola Group: Mesozoic volcanism related to r i f t i n g in southern B r i t i s h Columbia. Geological Association of Canada, Special Paper 16, p 39-58. S c h i l l i n g , J.G. (1973) Afar mantle plume: rare earth evidence. Nature, Physical Science, V 242, p 2-5 Selwyn, A.R.C. (1872) Journal and report of preliminary, explorations in B r i t i s h Columbia. Geological Survey of Canada, Report of progress for 1871-1872, p 16-72. Shannon, K.R. (1981) The Cache Creek Group and Contiguous rocks near Cache Creek, B r i t i s h Columbia. Geological Survey of Canada, Paper 81-1A, p 217-221. Souther, J.G. (1977) Volcanism and tectonic environments in the Canadian C o r d i l l e r a - a second look. Geological Association of Canada, Special Paper 16, p 3-24. T r e t t i n , H.P. (1961) Geology of the Fraser Valley between L i l l o o e t and Big Bar Creek. B.C. Department of Mines and Petroleum Resources, B u l l e t i n 44, I09p. 72 T r e t t i n , H.P. (1980) Permian rocks of the Cache Creek Group in the Marble Range, Clinton area, B r i t i s h Columbia. Geological Survey of Canada, Paper 79-17, 17p. Travers, W.B. (1978) Overturned Nicola and Ashcroft strata and the i r r e l a t i o n to the Cache Creek Group, southwestern Intermontane Belt, B r i t i s h Columbia. Canadian Journal of Earth Sciences, V 15, p 99-116.

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