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.

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.

Description and analysis of the geology of quartz veins containing gold ores in the Yukon Territory.

The Hunker Creek area is located 30 km southeast of Dawson City, Yukon. Gold and sulphide-bearing quartz veins (MINFILE 115O 067, 068) crosscut metamorphic rocks of the Klondike Schist. The veins are enclosed by envelopes of sericitic (inner) and propylitic (outer) alteration. Locally, carbonatization occurs between propylitized and sericitized rocks. Three stages of vein mineralization can be distinguished:: (1) quartz, carbonates, gold, arsenopyrite, pyrite, pyrrhotite, chalcopyrite, and galena; (II) quartz, carbonates, chalcopyrite, sphalerite, tetrahedrite, freibergite, polybasite, 'polyargyrite', argentite, pyrostilbnite and galena; (III) quartz and gold. Fluid inclusion data indicate that stage I minerals precipitated from hydrothermal solutions containing CO2. Homogenization temperatures range from 260° to 390°C. Stage II aqueous fluid inclusions homogenize between 190° and 260°C. Stage III inclusions homogenize between 120° and 210°C. Salinities of the three stages range from 0 to 7.2 wt-% NaCl equiv. and show no significant changes with time. It is suggested that stage I mineralization was initiated by unmixing of an original single-phase H2O and CO2 bearing fluid, and that subsequent hydrothermal evolution was controlled mainly by decreasing temperature.

This study describes the structural evolution of the Klondike Schist and the structural setting of mineralized mesothermal veins from which over 500 tonnes of placer gold has been derived. The Klondike Schist was emplaced as a series of thrust slices on top of a structural stack that includes at least three additional thrust slices. A distinctive set of mesoscopic structures, particularly a set of recumbent folds, formed during thrust emplacement. These folds have a general southeast trend, and deform thrust-emplaced ultramafic rocks. Underlying thrust panels contain folds that resemble these thrust-related structures, but have a consistent northeast trend. The Klondike Schist may have been rotated about a vertical axis during the latter stages of thrusting along phacoidal cleavage zones. Extensional sites in post-thrust kink folds and faults host mesothermal gold veins. Hence, gold mineralization postdated thrust stacking. Normal faults offset mesothermal veins, and host late-stage hydrothermal alteration zones.

A detailed methodology has been devised and tested for establishing metal zoning patterns in and about oreshoots within the plane of Ag-Pb-Zn veins of the Keno Hill - Galena Hill mining camp, Yukon, using whole rock vein geochemistry of run-of-mine samples. These ideal metal distribution patterns are easily interpretable in more classical zoning terms as mineral distribution patterns. To establish a zoning model samples that span a wide range of grades are rearranged in order of decreasing silver contents. The resulting "rearranged" profiles for other elements are then evaluated relative to silver. Computer-based curve fitting methods are useful means of generalizing these "rearranged" metal profiles. The foregoing procedure has been used to develop a general model for the Keno Hill - Galena Hill camp based on analytical results from 3 main deposits (Keno, Husky, No Cash) including 6 veins. Essential character of the model is embodied in analyses of Ag, Pb, Zn, and Ca and the Zn/Ag ratio. Additional but in cases ambiguous detail is added to the model by Hg, and Co and/or Ni analyses. These elements allow vein mineralogy to be monitored in a quantitative manner and provide a practical zoning model that can be used as an exploration, tool in evaluating underground workings for proximity to oreshoots in the more than 60 deposits known in the camp. A companion study involving whole rock K-Ar age determinations of small stockwork zones adjacent to Ag-Pb-Zn veins indicated an age of mineralization of about 87±2 Ma. for the Ag-Pb-Zn veins.

The Flex Gold-Silver deposit is a multiple vein epithermal system found within the Mount Nansen precious metal trend. High-grade gold and silver values are associated with north-northwesterly trending, sulphide-rich quartz veins that infill structures associated with regional shearing. BYG has stripped and mapped the deposit to prepare advanced exploration and mining design plans. The mineralization is typically epithermal with extensive wall rock alteration including argillic and phyllic zones. Gold - silver values occur with sulphide-rich quartz veins, breccia veins, and silicified zones. Gold values up to 34 grams per tonne and silver values up to 1416 grams per tonne were obtained from the sulphide-rich veins.

The upper Sixtymile River area is located approximately 128 km west of Dawson City, Yukon. Lithology in this area consists of Precambrian to Paleozoic metamorphic rocks, Paleozoic ultramafic rocks, Middle Jurassic pegmatite and aplite dykes, Late Cretaceous porphyritic dykes and volcanic rocks with intercalated sedimentary rocks, Quaternary alkaline basaltic dykes and Quaternary alluvial sediments. Gold bearing, mesothermal quartz-(carbonate)-sulphide veins which trend NNE-SSW are hosted by metamorphic rocks north and south of Sixtymile River. The mesothermal quartz-(carbonate)-sulphide veins are surrounded by successive envelopes of sericitic, K-feldspar and propylitic alteration. Two stages of vein mineralization are recognized in the northern part of the area, and three stages are recognized in the south part. In the northern veins, pyrite, arsenopyrite, pyrrhotite and quartz are intergrown and formed first. These minerals are fractured and healed by second stage minerals, which include galena, sphalerite, chalcopyrite, pyrite, carbonate and minor quartz. Stage I mineralization in the southern veins is represented by quartz, and pyrite containing inclusions of other sulphides. Stage II is the main stage of precious metal enrichment, represented by arsenopyrite and galena which contain tetrahedrite, miagyrite and polybasite exsolutions. Stage I and II minerals are tectonically fractured, and healed by pyrite, sphalerite, chalcopyrite, freibergite and quartz of stage III. In both vein systems, gold enrichment is associated with arsenopyrite and silver enrichment is associated with galena. The evolution of hydrothermal fluids in the northern area is characterized by decreasing temperature (330°C to 280°C), salinity (12.8% wt.-% to 6 wt.-% NaCI equiv.), oxygen activity (log a(O2) = -30 to log a(O2) = -35), and sulphur activity (log a(S2) = -10 to log a(S2) = -12), as well as a slight increase in pH range (from >3.1 - <5.2 to >3.3 - <5.4). In the southern vein system the fluid evolution characterized by a decrease in temperature (330°C to 150°C), salinity (18.3 wt.-% to 10 wt.-% NaCI equiv.), oxygen activity (log a(O2) = -29 to log a (02) = - 52), and sulphur activity (log a(S2) = -9 to log a(S2) = -18, as well as a slight increase in pH range (>3.2 - <5.3 to >4.1 - <5.9). The following conclusions can be drawn about the fluid composition and mineral enrichment process in the fossil geothermal system of the Sixtymile River area. Deep seated fluids which circulated in the metamorphic rocks were characterized by high temperatures (above 300°C), high salinities (about 18 wt.-% NaCI equiv.) and pH values between 3.1 and 5.2. These fluids are similar to alkaline chloride fluids of active geothermal systems. Arsenic was transported as H3AsO3°-complex, gold as Au(HS)2- and lead, zinc, iron, copper as MeCl2° complexes. The first stage mineralization resulted from reaction of this deep-seated fluid with the wall rock. Second and third stage mineralization is believed to result from the mixing of two fluids with different physico-chemical characteristics.

Marble, calc-silicate rock and pelitic layers of the Ram Creek assemblage surrounding the Dan Zn (± Cu-Pb-Ag) occurrence display ample evidence of a monocyclic structural evolution with three main events of progressive deformation (D1-D3). These events developed a tightly folded package of west-northwest-trending tectonites. Primary planar structures (S0) generally lie sub-parallel to two tectonic foliations (S1 and S2), which dip shallowly to steeply southwest. Inter-foliation slip (D3) resulted in a transverse, sub-vertical foliation (S3) that dips generally shallowly to moderately north. Cross-sections based on new mapping and fold analysis indicate that similar folds containing stratabound zinc-sulphide mineralization should be present south of the Dan occurrence, as part of regional north-northeast-verging folds or a thrust-fault-repeated succession.

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.