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.

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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Gold mineralization at the Mt. Skukum deposit occurs in nearly vertical quartz-carbonate veins which crosscut flat-lying andesites with a NNE trend. The mineralized veins represent the second stage of a two stage hydrothermal system, the first of which resulted in emplacement of thin chalcedonic veinlets. These two stages of veins are probably indicative of an evolving hydrothermal fluid rather than being representative of two separate events. Vein emplacement is one of the latest of a series of events which began with volcanism, producing felsic and andesitic volcanic rocks which overlie basement in this area. Subsequent periods of tectonism produced large faults along which rhyolitic dykes were emplaced. Continued tectonism resulted in reactivation of old faults along which andesitic and dacitic dykes were injected, crosscutting rhyolite dykes in many cases. As volcanic activity waned, the faults remained active, leaving zones of high permeability which acted as conduits for the still active hydrothermal circulation. Veins appear to have been emplaced at low temperature in a circulating hydrothermal system driven by a heat source at depth associated with dykes present in the area. Circulating hydrothermal fluids may have leached gold from the surrounding andesitic volcanics during propylitization. Permeability may have been controlled by faulting, brecciated flow tops and bottoms, and lapilli tuff horizons. Gold was precipitated in highly permeable conduits, such as the Main Fault Zone and breccia bodies.

The Stewart River map area (115 O&N) is the most important historic and current placer gold producing region in the Yukon. Unfortunately, the historic placer-gold deposits are becoming depleted, and more efficient mining of existing deposits and exploration for new deposits must be encouraged. Although placer deposits in the Klondike district are well described and their origin is quite well understood, placer deposits in the remaining part of the Stewart River map area have not been so well documented. The purpose of the Stewart River placer project is to describe and document the geology of known placer deposits, to interpret the formation of the placer deposits, and to relate the geology of the placer deposits to the regional surficial and bedrock geology. The objectives of the project are to aid in the exploration and mining of placer deposits by providing a comprehensive and up-to-date placer geoscience database. The utility of the placer database is that it can be used to construct placer deposit models (general summaries of given placer settings). These models then serve as predictors for future placer exploration and mining. Fieldwork for the project began in 1998 and will be completed in 2001; results of the project will be published in a final report and a resource appraisal map for placer gold.

Detailed exploration conducted during 2006 in the western part of the Skukum Creek deposit has revealed new structural, mineralogical and geochemical features. The deposit incorporates a number of (at least six or seven) sub- parallel narrow mineralized zones, coincident with andesite-dacite-rhyolite dyke swarms extending for at least 1 km along strike and for hundreds of metres down-dip. Various mineralized zones differ in size, structural setting, intensity and composition of mineralization, and, in total, form a large mineralized package more than 200 m wide, corresponding to a property- to district-scale fault zone extending for over 10 km and traced by a dyke belt. Significant potential exists for the exploration of these structures along strike and down-dip. The diamond drilling intersected numerous high-grade intercepts of gold and silver mineralization corresponding to the low-sulphidation sub-type of epithermal gold-silver deposits. However, strong enrichment in base metals (up to 25% of combined Zn+Pb+Cu) and arsenic suggests essential differences from typical epithermal mineralized systems.

The AurMac property, located 35 km north of Mayo in central Yukon, includes two metasedimentary rock-hosted gold deposits: the 6158 koz Au Powerline deposit and the 845 koz Au Airstrip deposit. Mineralization at the Powerline and Airstrip deposits is characterized by gold in sheeted quartz veins and mineralized skarn horizons, respectively. The AurMac deposits straddle the Robert Service thrust fault whereby the Powerline deposit is hosted in the Late Proterozoic to Cambrian Hyland Group hanging wall, and the Airstrip deposit is hosted in the Mississippian Sourdough Hill Member of the Keno Hill Quartzite footwall. Host rocks comprise siliciclastic metasedimentary rocks, variably calc-silicate–altered calcareous metasedimentary rocks and magmatic rocks. Magmatic rocks in the Powerline zone consist of foliated mafic horizons that are geochemically similar to Cambro-Ordovician magmatic rocks found in Hyland Group metasedimentary rocks in the McQuesten, Mayo, Clark Lakes and Hart River map areas. In the Airstrip zone, magmatic rocks include a steeply south-dipping, unfoliated, aplite dike. Evidence for intrusion-related gold mineralization at AurMac includes sheeted vein and skarn mineralization similar to the intrusionhosted, intrusion-related gold deposits at Dublin Gulch, as well as the presence of metamorphic porphyroblast assemblages that suggest contact metamorphism. These findings suggest potential for further discovery of mineralized intrusion-hosted zones on the AurMac property and sedimenthosted, intrusion-related gold deposits elsewhere in the region.

Kalzas, in central Yukon, is a porphyry-style stockwork and sheeted-vein wolframite deposit. Alteration includes a potassic core, a quartz-tourmaline-sericite zone and an outer quartz-sericite-pyrite zone, the latter in excess of 2 km in diameter. Wolframite is confined to the inner two zones, in an oval area 1500 m by 800 m. The wolframite is disseminated within the quartz-tourmaline stockwork and also occurs as coarse crystals in sheeted veins. Mineralization occurs within Neoproterozoic to Early Cambrian Hyland Group quartzites and phyllites, which are likely intruded at depth by a pluton, possibly of the Cretaceous Tombstone Suite. From 1981 to 1984, Union Carbide carried out mapping, soil and rock geochemistry, an airborne magnetometer survey, road building, trenching and drilling of two diamond drill holes. Results from Copper Ridge's 2001 sample program range from 0.3% WO3 to 0.5% WO3 over widths up to 70 m. They demonstrate the potential to define a signifi cant resource of surface-mineable tungsten mineralization at a grade of 0.4% WO3 or better. Drilling is required to confirm grade continuity at depth and along strike.

Significant economic concentrations of placer gold were first recognized in an intermediate level terrace near Dawson City in the late 1980's Regional surficial mapping has shown the distribution of many high level terraces of pre-Reid, Reid and McConnell age in central Yukon, but the relationship between economic gold concentration and terraces is not well understood. Sedimentological study of an intermediate level terrace near Dawson City suggests two river types have been dominant:: the first, a 'wandering gravel bed river' is characterized by moderate sinuosity, later accretion deposits, limited sand facies, and generally fine gravel; the second, 'proximal braided river' is characterized by multiple channels, very thick and crudely imbricate gravel, low bed relief, and a maximum particle size greater than the underlying wandering gravel bed river deposits. The gold-bearing 'wandering gravel bed river' assemblage is typical of present-day conditions with river processes dominated by lateral migration and high gravel transport rates through the system, conducive to heavy mineral concentration during an interglacial period. The 'proximal braided river' is characteristic of nearby glacial ice and rapid sedimentation resulting in poor heavy mineral concentration. The transition from a wandering gravel bed river to a proximal braided river is suggested to mark the onset of a pre-Reid glaciation in the Southern Ogilvie Mountains. The sedimentology of the intermediate terrace gravels suggests a geomorphic model which may be used for exploration of terrace placer deposits in central Yukon with a similar pattern of regional glaciation influencing terrace formation.

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