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Tertiary Mineral Deposits of Vancouver Island
DAVID J. T. CARSON, Geologist, Noranda Exploration Company, Ltd., Toronto, Ont.
ABSTRACT INTRODUCTION The metalliferous deposits of Vancouver Island have generally been assigned to the Mesozoic "Coast Range DURING THE COURSE OF A METALLOGENIC STUDY of Van Orogeny." However, a metallogenic study by the writer couver Island sponsored by the Geological Survey of has revealed that several important classes are early or middle Tertiary. Included are porphyry cop'pers, and gold Canada (Carson, 1968), the writer found that many quartz, arsenic and copper-arsenic veins. of the mineral deposits generally believed to have The porphyry coppers and many gold-quartz veins are formed during the Mesozoic "Coast Range Orogeny" within and adjacent to Oligocene-Eocene quartz diorite are of early to middle Tertiary age. intrusive complexes. Arsenic and copper-arsenic veins have a close spatial relationship to sills and laccoliths of The previously recognized Tertiary deposits are Oligocene dacite porphyry which intrude the late Creta near Sooke (Clapp and Cooke, 1917; Fyles, 1949) and ceous Nanaimo Group. Other deposits of demonstrable Tertiary age include a Mount Washington (Carson, 1960). The deposits of molybdenum stockwork related to a relatively potassic these two areas are in rocks of Tertiary (Sooke) and Eocene plug and a few small copper-skarn occurrences. late Cretaceous and Tertiary (Mount Washington) Some copper stockworks and a mercury deposit are prob ages. In most other areas of Vancouver Island, host ably also Tertiary. The copper deposits of previously recognized Tertiary rocks for the mineral deposits are late Paleozoic, Tri age are those of the Sooke area that occur in Eocene assic or Jurassic and, in almost all cases, the deposits basalts and Oligocene gabbros. were believed to have formed from solutions emanat ing from granitic intrusions emplaced during the "Coast Range Orogeny." The metallogenic project involved studies of both mineable deposits and "showings." They were classi fied on the basis of metal content, mineralogy, struc DAVID J. T. CARlSON received his B.Sc. in engineering geology from tures, host rocks and, where applicable, the petro Queen's University, his M.A.Sc. in graphy of related intrusions. Potassium-argon age de geology from the University of Brit terminations were very useful for indirectly dating ish Columbia and his Ph.D. from Car some deposits by yielding the ages of gangue min leton University, Ottawa. His thesis at Carleton involved a metallogenic erals or of related intrusions. The data for these age study of Vancouver Island, sponsored determinations have been published by the Geological by the Geological Survey of Canada. Survey of Canada (Wanless et al., 1967, 1968). The Dr. Carson has carried out geolog seven Tertiary determinations referred to in this ical mapping work and metallogenic studies with the GSC in Ontario and paper were made on single specimens of granitic in British Columbia. He then joined No trusions from widespread localities. The Tertiary age randa ,Exploration Company Limited in July, 1967, in of all seven intrusions is supported by chemical and British Columbia. In his present capacity as research petrographic data (Carson, 1968), and in two cases geologist, he is now working out of Toronto doing geolog ical work in Canada and the United States. the ages are confirmed by intrusive relationships. MANUSCRIPT SUBMITTED: on February 9, 1969. The writer would like to express much appreciation KEYWORDS: Mineral deposits, Tertiary deposits, Van to J. E. Muller of the Geological Survey of Canada, couver Island, Metallogenic stUdies, Porphyry copper de who is currently doing regional mapping on Vancouver posits, Gold-quartz veins, Arsenic mineralization, Copper deposits, Molybdenum deposits, Sooke copper deposits, Island, and who supplied geological information and Skarn deposits, Mercury deposits, Zeballos area, Mount aid in the field. E. Leigh Scales of Noranda Explora Viashington area. tion Company, Limited kindly prepared the figures for publication. C.I.M. TRAN'SACTIONS: Vol. LXXII, pp. 116-125, 1969. (/~~~:~j -1- C.· \j}) P;ROPERTY FIL~I n 1 .?-:C='f!\erCtr. /1'\ r~\. LEGEND 0 Au-Quartz Vein Tertiary Intrusion /'- limits of Known til As Vein .. (- ~ Cu-As Vein, Breccia -~ Possible Tertiary Intrusion / Tertiary Intrusivi Activity III HQ Breccia-FillinQ 81 Na-Hot SprinQ t1:1~) Tertiary Volcanic Rocks Cu Porphyry , 39 K- Ar AQe (Millions of Years.) • tJ. Cu-Sooke [J Cu Stockwork • Mo Stockwor k
I I:-:l I o 10 20 40 I ! I I MILES
Figure I.-Known and Probable Tertiary Mineral Deposits and Zones of Tertiary Intrusive Activity. (
" ARSENIC VEINS COPPER..ARSENIC DEPOSITS Two arsenic-carbonate veins, the Grizzly and Wolf Three distinguishing features of the two known deposits, occur on Vancouver Island (Figure 1). members of this class, Mt. Washington Copper and Neither has been mined, but the Grizzly has yielded Macmillan (Table I), are the copper-arsenic content, some native arsenic samples for mineralogical col the exotic mineralogy and their occurrence near the lections. Their main characteristics are given in unconformity between the Triassic Karmutsen basalts Table I. and late Cretaceous sedimentary rocks of the Nanaimo Both arsenic deposits are in steeply dipping brec Group. ciated fault zones and have close spatial relationships The Mt. Washington Copper orebody is a gently with Tertiary dacite porphyry sills or laccoliths in dipping tabular body of quartz and sulphides deposited truding sedimentary rocks of the late Cretaceous Na in a fault or sheeted zone. It partly follows the con naimo Group. Grizzly is Tertiary, because it occurs tact between Upper Cretaceous sedimentary rocks and in argillites assigned to the Nanaimo Group (Muller, a Tertiary dacite porphyry sill. Chalcopyrite is the 1964). Wolf (Figure 2) is probably Tertiary (Gun most important constituent of the ore, but the deposit ning, 1931) because of its spatial relationship to Ter contains numerous other minerals including chalco tiary dacite porphyry and its proximity to Mt. Wash stibite and the rare bismuth telluride, wehrlite (Table ington, which is the locus of much Tertiary mineral I). The copper-arsenic orebody is stratigraphically a ization (Carson 1960; 1968). few hundred feet above the Karmutsen-Nanaimo un-
Table I- Characteristics of Arsenic and Copper-Arsenic Deposits of Vancouver Island
Deposits Metals, M ineralo~y , Textures, Host Rocks, Alteration Structural Main Tenor Textures Physical Associated Controls References (important newly Forms Rocks reported minerals in bold face) ------~:__I--·----:--.,..--O:--~I-o;___---.----.-,.-I-.--~-_:__--.I~--·--_:___:__-_I-----_:__o:__--I_:__-.-.----._.---1------ARSENIC I As; negligible Native As, araeno Arsenopyrite Argillites of the Limited carbon Vertical fracture Laanela (1964) VEINS Au, Ag. pyrite, carbonate, stringers, dissem Nanaimo Gp., atization and si or fault with Muller (1964) quartz. inations and na Tertiary dacite licification of brecciated wall Grizzly tive As "kidneys" porphyry sills wallrocks. rocks. in veins up to 2' nearby. wide, 50' - 60' long.
As Realgar, arseno Realgar masses Andesite of Kar as for Grizzly Steeply-dipping Hurst (1927) pyrite; minor na up to 4' x 9", mutsen Fm. brecciated fault. Gunning (1931) Iwolf tive As; calcite, lenses of calcite NanaimoGp. quartz. up to 6' wide, sediments and stringers of ar Tertiary dacite senopyrite, all porphyry sill in steeply dip nearby. ping veins 2'-12' wide and 250' long. - __. ,-.--·---·---·--1------1------1 1--.--.-.--.-.---1 ,------COPPER Cu 1.40%; Abundant quartz Nearly-horizon Argillite and Intense silicifica Nearly flat-lying Carson (1960) ARSE