Indicator-mineral signatures of the Casino porphyry Cu-Au-Mo deposit, Yukon

Abstract

This open file reports the results of an indicator mineral case study carried out around the Casino porphyry Cu-Mo-Au deposit in the unglaciated terrain of the west central Yukon. The research was part of the Geological Survey of Canada's (GSC) Targeted Geoscience Initiative 5 (TGI-5) Program. The purpose of the study was to test the use of indicator minerals as a porphyry Cu exploration tool in unglaciated terrain. At 22 sites around the deposit, a bulk stream sediment sample was collected to document the indicator mineral signature of the deposit. Steam water and stream silt samples were also collected at the same sites to compare geochemical to heavy mineral signatures. This open file presents indicator mineral abundance data for the bulk stream sediment samples. The Casino deposit has an obvious indicator mineral signature in the <2 mm heavy (>3.2 specific gravity (SG)) and mid-density (2.8-3.2 SG) fractions of stream sediments that consists of, in order of usefulness: gold>chalcopyrite>molybdenite>sphalerite>jarosite>goethite>pyrite that is detectable at least 14 km downstream. Similar indicator mineral patterns in other creeks indicate the presence of additional porphyry style mineralization nearby. Detailed characterization of the mineral chemistry of tourmaline and scheelite that is in progress will determine their suitability for porphyry Cu exploration in this unglaciated terrain. Government and exploration surveys will benefit from the addition of indicator mineral sampling to routine stream sediment sampling protocols.

Stream Sediment Indicator Mineral Signatures of the Casino Porphyry Cu-Au-Mo Deposit, Yukon, Canada

“…Table A1), similar to that reported for bedrock samples. Several 25-to 100-µm gold grains were recovered from mineralized, tourmaline-bearing Patton porphyry bedrock samples examined in this study (McClenaghan et al, 2020); this is similar to the gold grain size range (50-70 µm) reported by Huss et al (2013) for the hypogene zone. Chapman et al ( 2014) reported a broader size range (5-1,000 µm) in Casino bedrock samples.…”

“…Grain counts for selected indicator minerals are reported both in Table 3 and below as values normalized to 10 kg of <2-mm material to allow comparison between heavy mineral samples of different masses. Individual mineral distribution maps are included in McClenaghan et al (2020) and are summarized below. Unless otherwise stated, the results are for the 0.25-to 0.5-mm >3.2-SG fraction.…”

“…A total of 17 bedrock and 22 stream sediment heavy mineral samples were processed at Overburden Drilling Management Ltd. (ODM), Ottawa, Canada, to recover heavy mineral concentrates using methods described by McClenaghan et al (2020). Bedrock samples were broken apart using electric pulse disaggregation methods.…”

“…The 0.25-to 0.5-, 0.5to 1.0-, and 1.0-to 2.0-mm fractions of the nonferromagnetic >3.2-SG concentrate and the 0.25-to 0.5-mm fraction of the nonferromagnetic 2.8-to 3.2-SG fraction of each bedrock and stream sediment samples were examined by ODM using a binocular microscope; potential indicator minerals were visually counted, and selected grains were removed for chemical analysis. The mass of all fractions produced and abundances of indicator minerals in the bedrock and stream sediment samples, along with sample processing flow charts, are reported in McClenaghan et al (2020).…”