The Eocene Mt. Skukum gold-silver epithermal deposits are 65 km southwest of Whitehorse in the Yukon Territory. Veins are in nearly flat-lying Eocene andesitic volcanic rocks of the Mt. Skukum Caldera Complex, part of the Sloko Volcanic Province, which unconformably overlies the Mesozoic Coast Plutonic Complex and Paleozoic to Precambrian metamorphic rocks. Significant veins are contained in a regional halo of propylitic alteration centered on a graben in the southwestern corner of the Mt. Skukum Caldera Complex. Zones of steeply-dipping quartz-carbonate-sericite veins are associated with major faults and rhyolite dykes which bound blocks in the graben. Electrum and native silver form fine grains which average 15 to 20 microns and locally exceed 1 mm across, in veins containing only trave amounts of sulphides. Fliuid inclusions indicate that vein minerals were deposited from fluids averaging 313°C with an average salinity of 0.7 weight percent NaCl equivalent. Primary inclusions show that depositional fluids existed under two pressure regimes: one close to hydrostatic, the other approaching lithostatic. Both indicate deposition about 470 m below paleosurface. Oxygen and carbon isotope composition of minerals in the deposit and surrounding wall rocks indicate that depositional fluids were meteoric. Large depletions in O18 content of andesitic rocks in the deposit area indicate a minimum water: rock mass ratio of 0.81:1. Precious metals at the Mt. Skukum deposit were emplaced at relatively low temperature, near surface, by a meteoric water dominated hydrothermal system driven by heat from associated rhyolite dykes. Gold and silver were leached from andesitic and rhyolite stocks and volcanic rocks as well as metamorphic and granitic basement, and precipitated with quartz and carbonate in permeable conduits such as fault zones, and breccia bodies.

An interesting grassroots exploration prospect is associated with a Lower Cretaceous intrusive complex on the ridge north of Mt. Byng, 50 km northeast of Whitehorse. Brecciated quartz-carbonate veins which return sporadic high gold values are associated with north-trending rhyolite dykes and small stocks.

This property, which adjoins the Mt. Nansen property on the north side, is bisected by Discovery Creek, a significant placer gold producer. Two parallel zones of anastomosing quartz veins and porphyry dykes cut Cretaceous intrusive rocks and contain variable amounts of gold and silver over substantial widths. The two mineralized zones lie approximately on trend with the Brown-McDade and Webber-Huestis zones on the Mt. Nansen property to the south, and with gold and silver-bering veins on the Tawa property to the north. The mineralized zones are deeply oxidized, and the property appears to have good potential as a bulk tonnage low-grade oxide gold deposit.

The Mount Freegold district is an ideal natural laboratory to evaluate the structural and magmatic framework for porphyry, skarn and epithermal mineralization in the Dawson Range. The district is located within a major extensional relay zone of the Big Creek fault system, a regionally significant dextral strike-slip structure in which localized extension facilitated the emplacement of mid to Late Cretaceous magmatic rocks. New mapping defines a previously unrecognized granite pluton at Mount Freegold, as well as the ca. 77 Ma Stoddart pluton, which represents the magmatic roots of hypabyssal intrusive rocks at the Revenue Cu-Mo-Au-Ag deposit and Nucleus Au-Ag-Cu deposit. The relay zone in the Big Creek fault system is partly plugged by the ca. 70 Ma Seymour Creek stock, which is cut by a southern strand of the fault system. Episodic fault movement took place over a minimum 35 m.y. interval during which at least three distinct epochs of magmatic-hydrothermal mineralization occurred.

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In the eastern Ogilvie Mountains, geological mapping (1:50,000) was undertaken on map sheets 116A/10 and 11, which straddle the boundary between the Foreland and Omineca belts of the Cordilleran Orogen. The area is underlain by a diverse assemblage of epicontinental and miogeoclinal sediementary, and subordinate volcanic and intrusive rocks, ranging in age from Early Proterozoic to Triassic. These rocks represent most of the geological history of the northern Cordilleran miogeocline and its supracrustal basement.