Geological Implications of Regional Stream-Sediment Geochemical Data from South-Central British Columbia

CIM Bulletin, Vol. 71, No. 793, 1978

R. H. Wallis, Chief Geologist, and J. J. Brummer, Exploration Manager, Minerals Division, Canadian Occidental Petroleum Ltd., Toronto, Ontario, C. F. Gleeson, Consultant Geologist-Geochemist, C. F. Gleeson and Associates Ltd., Ottawa, Ontario

Weighted moving-average contour maps have been constructed for molybdenum, copper and zinc using 7850 stream-sediment samples from 5430 square miles (14,063 sq. kms) of south-central British Columbia. Regional trends for molybdenum and zinc are northeast, north and northwest and those for copper are north and northwest. These trends are interrupted by zones markedly low in metals. The metal-rich trends cross rocks of different lithology and age and thus appear to be structurally controlled. The northeast trend may have exerted control on metal distribution at two different times. The molybdenum trend passes through the Brenda mine, where it correlates with the northeast-trending stage 2A veins dated at 146 m.y. The molybdenum trend ends abruptly against a "Valhalla" pluton dated at 133 m.y. However, the zinc trend affects this pluton, and thus it appears that the northeast trend was reactivated in the late Cretaceous. Some of the most interesting north-south copper and molybdenum trends are within the Triassic Nicola volcanics, where they coincide with Preto's Central Belt. The regional sediment geochemical data suggest that the Central Belt may continue northward along the eastern side of the Guichon Creek valley. The contoured data indicate that the dominant control of regional metal distribution is by age and rock-type. The Triassic-Jurassic intrusions are characterized by high regional molybdenum content and by zoning patterns that are negative with respect to copper and zinc and positive with respect to molybdenum. The late-Cretaceous intrusions are characterized by high regional zinc content in the stream sediments. The Tertiary batholith can be distinguished by its low regional molybdenum values, relatively high copper content and positively zoned regional zinc distribution pattern. The southern outcrop area of pre-Mesozoic "Cache Creek" rocks is characterized by high regional copper, molybdenum and zinc contents in the stream sediments. These values are in marked contrast with the low values typical of the northern outcrop area. However, recent fossil evidence suggests that most of the northern area is, in fact, late-Triassic, Nicola Group, volcaniclastic sediments. This aug-gestion gains support from the geochemical contrast.
Keywords: Exploration, Geochemical exploration, Stream-sediment geochemistry, British Columbia, Moving-average techniques, Molybdenum, Copper, Zinc, Metal distribution, Mineralization.