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Ore mineralogy of the TV and Jeff volcanogenic massive sulfide deposits in northwestern British Columbia, Canada, The

Eck, Edgar Cole
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2023
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The precious metal-rich TV and Jeff volcanogenic massive sulfide deposits are located about ~10 km south of the world-class Eskay Creek deposit in the Iskut River area of northwestern British Colombia, Canada. The deposits are hosted by volcanic successions that form part of the Jurassic Hazelton Group. Drill core samples were collected from multiple holes intersecting the precious metal mineralization to identify the ore minerology, with particular emphasis being placed on the study of the mineralogical sequestration of the precious metals. A combination of reflected light microscopy, scanning electron microscopy, automated mineralogy, electron microprobe analysis, and laser ablation-inductively coupled plasma-mass spectroscopy was used to study the ore mineralogy. Paragenetic relationships in the ores show that three distinct stages can be distinguished ranging from pre-ore sulfide formation to metamorphic recrystallization. Pyrite is the most abundant sulfide phase at the TV and Jeff deposit occurring as framboidal pyrite, As-poor and As-rich subhedral to euhedral grains, porphyroblasts, and recrystallized pyrite grains affected by brittle deformation. The As-rich pyrite displays complex compositional zoning, with many of the zones containing small mineral inclusions. Brittle and ductile deformation are present in pyrite and base metal sulfides. Gold occurs as invisible Au in pyrite but also forms discrete grains of electrum. Silver is common as electrum and is present in a range of Ag-sulfosalts. The observed mineral association and generally low base metal grades at TV and Jeff suggests that precious metal enrichment at these deposits occurred at relatively low temperatures (<200°C). The mineral associations at TV and Jeff are distinct from other Au-rich volcanogenic massive sulfide deposits that are generally polymetallic in nature and have formed from hydrothermal fluids having higher temperatures.
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