Hydrogeochemistry of porphyry-related solutes in ground and surface waters; an example from the Casino Cu–Au–Mo deposit, Yukon, Canada

Kidder, J.A.; McClenaghan, M B; Leybourne, Matthew I.; McCurdy, M W; Pelchat, P; Layton‐Matthews, Daniel; Voinot, Alexandre

doi:10.1144/geochem2021-058

Cited by 7 publications

(2 citation statements)

References 68 publications

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“…This study builds upon several recent investigations on metal(loid) hydrogeochemistry in the Dawson Range, west-central Yukon, Canada (Figure ). ,,, The study area features discontinuous permafrost and is contained within traditional territory of Tr’ondëk Hwëch’in and Selkirk First Nation. Its physiography, geology and permafrost coverage have been described elsewhere. ,,, Briefly, permafrost covers ∼60% of land area, with thicknesses ranging from >150 m near ridgetops to <30 m in valley bottoms .…”

Section: Methodsmentioning

confidence: 99%

Arsenic Mobilization from Thawing Permafrost

Skierszkan,

Schoepfer,

Fellwock

et al. 2024

ACS Earth Space Chem.

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Thawing permafrost releases labile organic carbon and alters groundwater geochemistry and hydrology with uncertain outcomes for the mobility of hazardous metal(loid)s. Managing water quality in thawing permafrost regions is predicated on a detailed understanding of the speciation and abundance of metal(loid)s in permafrost soils and porewaters produced during thaw, which remains limited at present. This study contributes new knowledge on the sources and fate of arsenic during the thaw of organic-rich permafrost using samples collected from a subarctic permafrost region associated with geogenic arsenic (Dawson Range, Yukon, Canada). Several permafrost cores and active-layer samples from this region were analyzed for their solid-phase and aqueous geochemical characteristics and their arsenic speciation. Porewaters were extracted from permafrost cores after thaw under anaerobic conditions for aqueous geochemical analyses. Bedrock samples from the field site were also analyzed for arsenic speciation and mineralogy. X-ray diffraction and X-ray near-edge spectroscopy (XANES) analyses of weathered bedrock upgradient of soil sampling locations contained arsenic(V) hosted in iron-(oxyhydr)oxides and scorodite. XANES and micro X-ray fluorescence analyses of permafrost soils indicated a mixture of arsenic(III) and arsenic(V), indicating redox recycling of arsenic. Soil-bound arsenic was colocated with iron, likely as arseniferous iron-(oxyhydr)oxides that have been encapsulated by aggrading permafrost over geologic time. However, permafrost thaw produced porewater containing elevated dissolved arsenic (median 40 μg L −1 , range 2−96 μg L −1 ). Thawed permafrost porewater also contained elevated dissolved iron (median 5.5 mg L −1 , range 0.5−40 mg L −1 ) and dissolved organic carbon (median 423 mg L −1 , range 72−3240 mg L −1 ), indicative of reducing conditions. This study highlights that arsenic can be found in reactive forms in permafrost soil, and that its thaw can release arsenic and iron to porewater and produce poor water quality.

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Section: Methodsmentioning

confidence: 99%

Arsenic Mobilization from Thawing Permafrost

Skierszkan,

Schoepfer,

Fellwock

et al. 2024

ACS Earth Space Chem.

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“…In addition to Snrich hematite, they recovered ferberite, hübnerite, bismuthinite, daubréeite, tetradymite, and goethite from the sample. The geochemistry of stream and groundwaters sampled in 2017 as part of the Geological Survey of Canada (GSC) study at Casino are reported in Kidder et al (2022).…”

Section: Surficial Geologymentioning

confidence: 99%

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

et al. 2023

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Case studies around porphyry Cu deposits in the glaciated regions of the Canadian Cordillera have identified the indicator mineral signatures of these deposits in till samples and demonstrated that these are useful methods for porphyry Cu exploration. This study applies the same indicator methods to stream sediment samples around the Casino calc-alkaline porphyry Cu-Au-Mo deposit in the unglaciated terrain of west-central Yukon, Canada. It is one of the largest porphyry Cu-Au-Mo deposits in Canada and is hosted in Late Cretaceous quartz monzonite and associated breccias. Bulk (8–16 kg) coarse-grained stream sediment samples were collected in creeks around the deposit, nearby porphyry Cu occurrences and background areas. The Casino deposit has an obvious indicator mineral signature in the <2-mm heavy (>3.2-specific gravity [SG]) and mid-density (2.8- to 3.2-SG) fractions of stream sediments that is detectable at least 18 km downstream and includes gold, chalcopyrite, tourmaline, molybdenite, sphalerite, jarosite, goethite, and pyrite. In contrast, not all of these mineralogically anomalous samples have corresponding anomalous geochemical signatures in the fine fraction. The porphyry indicator minerals identified in this study are similar to those reported for glaciated terrain with the addition of molybdenite and secondary minerals. Indicator mineral methods provide physical evidence of nearby mineralization and can be chemically analyzed to provide insights about the nature of the mineralizing system. Government and exploration surveys could benefit from the addition of indicator mineral methods to routine stream sediment sampling protocols in unglaciated regions of the Yukon and elsewhere globally where porphyry Cu exploration is conducted.

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