The Cash porphyry copper-molybdenum deposit, Dawson Range, Yukon Territory

CIM Bulletin, Vol. 74, No. 833, 1981

W.D. SINCLAIR, Geological Survey of Canada, Ottawa, Ontario, R.J. CATHRO, Archer, Cathro and Associates Ltd. Vancouver, British Columbia, E.M. JENSEN, Amoco Canada Petroleum Co. Ltd. Calgary, Alberta

The Cash is one of the largest porphyry copper-molybdenum deposits found in Yukon to date. It is 80 km northwest of Car-macks, within the unglaciated portion of the Dawson Range, and is associated with the Big Creek fault, an important tectonic feature. Part of the mineralized zone is blanketed by up to 70 m of alluvial drift. The remainder is covered by a relatively thin residual soil layer. The mineralized zone, however, was not detected by conventional stream-sediment sampling because pathfinder elements, such as Cu and Mo, have not been geochemically dispersed into the main drainage system. The deposit was discovered by a combination of soil analysis and inspection of rock fragments from small pits.Twenty widely spaced, shallow drill holes have outlined an area over 2700 m long and 550 to over 1000 m wide that grades more than 0.1% copper equivalent (% CuE= % Cu + (5x% MoSJ). Two smaller zones grading over 0.4% copper equivalent occur within the larger area. The limits of the widest end of the deposit have not been delineated.The Cash deposit is fairly typical of high-level, calc-alkaline porphyry copper-molydenum occurrrences in the Canadian Cordillera (cf. CIM Special Volume 15) and is representative of most prospects in the Dawson Range. It is associated genetically with a subvolcanic complex of small, irregular stocks and dykes of feldspar porphyry and related breccias of Late Cretaceous age. Copper and molybdenum sulphides occur along fractures, in quartz veinlets and disseminated in feldspar porphyry and in older metasedimentary and intrusive rocks. Higher-grade zones of copper and molybdenum have associated potassic alteration. Phyllic alteration is, in part, superimposed on potassic alteration. Argillic alteration occurs locally.This paper describes the history of the discovery and the geochemical and geophysical characteristics, together with the regional geology, and the nature and distribution of the host rocks, hypogene mineralization and hydrothermal alteration.

Keywords: Cash deposit, Copper, Molybdenum, Dawson Range, Yukon, Porphyry deposits, Geochemical exploration, Soil analysis, Alteration.