Abstract
We report results of a detailed indicator mineral and geochemical study of the Casino calc-alkaline porphyry Cu-Au-Mo deposit in the unglaciated terrain of west-central Yukon. It is one of the largest and highest-grade porphyry Cu-Au-Mo deposits in Canada and is hosted by Late Cretaceous quartz monzonite and associated breccias. At 22 sites, a large (10-14 kg) stream-sediment sample, streamwater and stream silt samples were collected to compare geochemical and heavy mineral signatures. The Casino deposit has an obvious indicator mineral signature in the less than 2 mm heavy (>3.2 specific gravity (SG)) and mid-density (2.8-3.2 SG) fractions of stream sediments that is detectable at least 14 km downstream and consists of, in order of effectiveness, gold>chalcopyrite>molybdenite>sphalerite >jarosite>goethite>pyrite. Similar indicator mineral patterns occur in creeks downstream of other local porphyry occurrences (i.e. Cockfield, Zappa). The geochemical signature of the deposit is best defined by Ag, As, Au, Bi, Cd, Cu, Fe, Mn, Mo, Pb, U, and Zn in the less than 0.177 mm fraction of stream sediment and Cd, Co, Cu, Mo, Pb, Re, and Zn in stream water. Governments and exploration companies will benefit from adding indicator mineral sampling to routine stream-sediment sampling protocols during geochemical surveys in which detailed follow up during the same season is impossible.
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