The Ketza River gold deposits, in central Yukon, are gold-bearing, massive sulphide mantos and chimneys in Lower Cambrian limestone. Mining is presently confined to oxidized portions of the deposits. The deposits are bounded on three sides by silver-rich veins. Metal zoning corresponds to a pronounced domal uplift that is thought to be related to a buried Cretaceous intrusion. The zoning may partly reflect stratigraphic control, but distance from the buried intrusion is considered the prime control.

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The Ketza River polymetallic mineral deposits are situated in the Pelly Mountains, Central Yukon Territory. The deposits were mined for gold from 1988 to 1990, producing 400 tomes of oxide ore per day over that period. The Ketza River deposits are hosted by lower Paleozoic sedimentary strata of the parautochthonous Cassiar Terrane. The main host to economic mineralisation is a lower Cambrian, massive, areheocyathid-bearing limestone, which outcrops over much of the Ketza River area. Four styles of mineralisation are recognised within the Ketza River deposits. Type I mineralisation occurs in the centre of the area and consists of argillite-hosted, Au- quartz-sulphide veins. Sulphide mineralogy is mainly arsenopyrite and pyrite. Type II mineralisation consists of limestone-hosted, massive sulphide mantos and chimneys. The principal sulphide mineralogy of the mantos is pyrrhotite-arsenopyrite-pyrite-chalcopyrite, with quartz and calcite gangue. Gold is present within the arsenopyrite and pyrite. Type III mineralisation consists of limestone-hosted, quartz-sulphide veins and mantos. Mineralogy is similar to the Type II mineralisation, but contains a higher proportion of gangue. Type IV mineralisation consists of Ag-Pb veins. These veins are hosted by a variety of lithologies and represent the outermost extent of Ketza River mineralisation. Sulphide mineralogy is galena-sphalerite-pyrite, with siderite, calcite and quartz gangue. Oxidation of sulphides in parts of the Ketza River area is deep and pervasive. Areas of oxidation show increased gold grade and were the focus for mining. Oxidation occurs in the heavily fractured central area of the mineralisation, and along the Peel Fault, which extends from the centre of mineralisation towards the east. Light stable isotope studies indicate that the main mineralising fluid was of meteoric origin (delta (18)Ofluid = 10 per mil, delta Dfluid = -165 per mil). This fluid had evolved in delta (18)O by interaction with Cassiar Terrane rocks before mineralisation occured. Fluid flow in the limestones was pervasive, and produced a large, approximately 75km(2), (18)O depletion halo around the deposits. The later oxidising fluid was also of meteoric origin (delta (18)Ofluid = 18 per mil) but shows no evidence of interaction with the sedimentary pile. Fluid inclusion microthermometry suggests that the temperature of formation of the deposit was around 325 degrees C, at pressures above 600 bars. The mineralising fluid contained approximately 11 mole% CO2+ or -CH4, and 5 equivalent weight% NaCI.

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Conglomerates belonging to the Indian River formation (IRF), south of the Klondike goldfield, have recently become the focus of exploration activity owing to their potential as hosts for paleoplacer gold derived from the Klondike. However, textures within the conglomerate have been interpreted as indicative of hydrothermal activity, and the possibility exists of in situ epithermal gold. Paleocurrents in conglomerates indicate dominant transport from the southeast, incompatible with gold transport from the Klondike. Gold grains from unconsolidated conglomerate at Montana Creek reveal an epithermal signature (20-50% Ag, 0.3 to 3% Hg and opaque inclusion suite containing complex polymetallic sulphotellurides and sulphosalts), distinct from the signature of placer and lode sources in the central and southern Klondike (12-20% Ag, Hg absent and opaque inclusion suite of simple base metal sulphides). Gold grain morphology and alteration textures within unconsolidated conglomerates suggests that Montana Creek gold is derived from in situ epithermal mineralization related to that previously reported at Eureka Dome.

Diamond placer occurrences are historically reported in Yukon and in the adjacent areas of British Columbia and Alaska (Casselman and Harris, 2002) and are generally recovered during clean-ups on placer gold mining operations. While three stones from Crooked Creek in Alaska have been scientifically confirmed and described (Forbes et al., 1987), the same cannot be said of the Yukon diamond placer occurrences. In the Yukon, reports of a diamond discovery initiated sampling for diamond-indicator minerals that subsequently returned neither diamonds nor their indicators (chrome-diopside, pyrope-garnet, picro-ilmenite). Furthermore, none of the known ultramafic rocks, diatremes of ultramafic-alkaline volcanic rocks nor high-pressure eclogites in Yukon and Alaska have been proven to be diamond-bearing. Alluvial diamonds are present along the West Coast in Oregon and California (Hausel, 1994) and exploration of diamond placers in California produced several hundred stones, including high-quality gems. However, all of these aforementioned occurrences lack diamond-indicator minerals common for cratonic diamond deposits, and no igneous diamond-bearing rocks are known in the area. Therefore, the placer occurrence of diamonds in Yukon as well the Pacific Coast remains enigmatic.

Results of a study to determine the origin of alteration in the Plio-Pleistocene White Channel sediments and bedrock using field observations, mineralogical and geochemical analysis. The study was coordinated with a sedimentological study of the White Channel gravel by S.R. Morison in 1985. A copy of this thesis is available at the EMR library – TN414.C32 Y86. This thesis is available online at https://doi.org/10.7939/R32F7JW6S.

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