The Brewery Creek mine is a bulk tonnage gold deposit located 57 km east of Dawson City, in central Yukon, within the foothills of the Ogilvie Mountains along the northeastern boundary of the Tintina Trench. High-level fracture-controlled gold mineralization is hosted within Cretaceous monzonite sills and Devonian Earn Group siliciclastic rocks of the Selwyn Basin. Structural controls include northeast and southeast sub-vertical shears bounded by moderately south-dipping, southeasterly-extending listric normal faults; listric faulting and sill emplacements are localized along pre-existing graphitic thrust faults. Gold occurs as sub-micron particles in solid solution with pyrite and arsenopyrite as growth bands around larger sulphide grains that are disseminated within fine quartz veinlets. The open-pit heap leach operation produces 75,000 - 80,000 ounces annually, with a stripping ratio of 1.5:1 and a cash cost of US$200/oz or less. The mineable reserves at the end of 1997 stood at 13.3 MT @ 1.44 gpt (613,000 oz).

A reconnaissance-level study of post-mining hydrogeochemical conditions was carried out at the Brewery Creek gold deposit within the Tintina Gold Province. The deposit is characterized byepizonal mineralization with a consistent arsenic-gold-mercury-antimony geochemical signature. Surface discharges and seeps in the area are naturally alkaline (pH=7.6-8.2), Ca-HCO3 ¯-SO4²¯ waters. Upstream from the recognized mineralization, waters contain <3 ¿g/L As and <1 ¿g/L Sb. Water samples immediately downstream from the ore bodies show maximum concentrations of 18 ¿g/L dissolved and 47 ¿g/L total arsenic, and 18 ¿g/L dissolved and 21 ¿g/L total antimony. Two kilometres below the mineralization, on lower Laura Creek, arsenic concentrations are diluted to background levels of <3 ¿g/L, and antimony levels are still slightly elevated at 9-10 ¿g/L. Comparison with hydrogeochemical data from Donlin Creek, an undeveloped epizonal deposit in Alaska, indicates that elevated concentrations of a few tens of ¿g/L arsenic and antimony are typical of waters draining such gold systems, regardless of their state of development. In addition to their usefulness for the construction of geoenvironmental models, these data also provide information for establishing exploration programs utilizing water sampling.

The Grew Creek epithermal gold-silver deposit in southeast Yukon (MINFILE 105 K 009) is hosted by Eocene volcanic and sedimentary rocks deposited in a pull-apart basin within the Tintina Fault Zone. Flow rhyolites forming a dome in the Tarn Zone area, 1.5 km east of Grew Creek, pass westward into a succession of rhyolitic ignimbrites and air fall tuffs, exposed along Grew Creek and in the Main Zone, 500 m west of Grew Creek. These rhyolitic rocks are faulted against fluvial sediments to the north, along the W-E Fault, and basaltic rocks to the west. In the Main Zone, the volcanics, sediments, and the W-E Fault all dip steeply to the north. The gold-silver mineralization forms an elongate tabular zone within the rhyolitic tuffs. The zone strikes parallel to the W-E Fault and dips vertically or steeply to the north. The eastern end of the mineralized zone is defined by a decrease in grade, whereas the western end is faulted off against the basaltic rocks. Within the zone, stockwork veins and hydrothermal breccias contain assemblages which include quartz, adularia, carbonates, quartz peudomorphous after calcite, pyrite, marcasite, and traces of arsenopyrite, chalcopyrite, acanthite, electrum, silver selenides, galena, and sphalerite. There is good correlation between gold and silver in drill core assays, with a gold::silver ratio of around 1::4 for the ore grade mineralization. The mineralization is strongly anomalous in arsenic and mercury, but there is only a weak correlation of mercury with gold and silver, with most high values for mercury lying above the gold-silver zone and associated with the W-E Fault. Arsenic conccentrations are elevated over much of the area but there is no statistical correlation with the locally high concentrations of gold or silver. Outcropping rhyolitic rocks are hydrothermally altered to intermediate argillic and advanced argillic assemblages, whereas subsurface rhyolitic rocks are altered to quartz-adularia or illite-quartz assemblages adjacent to veins, and to illite-quartz-adularia ± carbonate elsewhere. Advanced illite-quartz-adularia ± carbonate alteration is accompanied by an increase in Na2O and decreases in TiO2, CaO and Al2O3. Basalts are altered to carbonate-chlorite (propylitic) assemblages, accompanied at an advanced stage by a slight increase in CaO and decreases in K2O, Na2O, SiO2, and Al2O3. Mineralization postdated tilting of the host pyroclastic and sedimentary rocks. Episodic fault movements in the Tintina Fault Zone structurally focused the hydrothermal fluids by providing locally high secondary permeability, whereas the high primary permeability of the rhyolitic tuffs promoted the development of stockwork veins and breccias. The absence of significant alteration and mineralization in the sediments suggests that a partly welded and intensely altered tuff unit, along the footwall of the W-E Fault, acted as an aquiclude, confining the hydrothermal fluid within the rhyolitic tuffs. Intense pyritic alteration of this unit and high concentrations of mercury in the vicinity of the W-E Fault form pyrite and mercury zones north of the mineralization.

The Brewery Creek property is a low grade oxide gold deposit hosted by syenitic intrusive rocks in the south Klondike area. The deposit apears to be structurally controlled by a low angle fault which may be part of the Tintina fault system. Drilling to date has proved up several million tonnes of mineralization grading approximately 2.5 g/t Au.

Brewery Creek is a bulk tonnage gold deposit 76 km east of Dawson. The economically important intrusive bodies are the semi-conformable sills of quartz monzonite which intrude into upper Road River and lower Earn Group (dominantly clastic sedimentary) strata. Low angle faults, inferred to be thrust faults, appear to have controlled the emplacement of the Cretaceous quartz monzonite sills which host most of the gold mineralization.

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Grew Creek epithermal gold prospect, in south-central Yukon Territory, is adjacent to and southwest of the Robert Campbell Highway, halfway between the communities of Ross River and Faro. The prospect is within the Tintina Trench, which from Late Cretaceous to Tertiary time was a zone of major right lateral movement that juxtaposed the Cambrian and Ordovician slate and phyllites of the Pelly-Cassiar Platform (to the southwest) against rocks of the Anvil Allochthon (to the northeast). Grew Creek rocks are mid-Eocene based on K-Ar dates of basalt of 51.4 ±1.8 Ma and 50.7 ±1.8 Ma and pollen spores in volcaniclastic rock dated at 56 to 46 Ma. Felsic volcanic and volcaniclastic rocks were overlain by a sequence of interbedded coarse clastic sediments, basaltic flows, and basaltic volcaniclastic rock. Late Tertiary uplift and faulting resulted in graben formation and consequent preservation of Eocene rocks in a structurally complex graben bounded to the south by the Grew Creek fault and to the north by the Danger Creek fault. Mineralization at Grew Creek occurs at the tip of a westwardly pointing wedge of dominantly felsic, crystal lithic lapilli tuff. The zone of precious metal deposition is truncated to the northeast by steeply dipping clastic sediments and to the southwest by the Grew Creek Fault. Gold, electrum, pyrite, and silver selenide were identified in a high grade sample from the discovery outcrop. Alteration at Grew Creek is both surficial and hydrothermal. Surficial alteration is ubiquitous, pervasive, and characterized by mixed-layer clays and carbonates. Hydrothermal alteration, responsible for the gold-silver mineralization is closely associated with rhyolitic dykes and is of three types:: silicic, acid sulphate, and argillic acid sulphate. K-Ar dating of sericite indicates hydrothermal alteration is mid-Eocene (51.5 ±1.8 Ma and 47.0 ±1.7 Ma) and synchronous with deposition of the volcanics. Quartz associated with mineralization at Grew Creek is enriched in heavy oxygen isotopes. A deep magmatic source for the mineralized fluids is one explanation for this enrichment.

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Auriferous sheeted quartz veins and silicified shear zones occur along the margins and within adjacent hornfels zones of mid-Cretaceous Tombstone intrusions near the head of Clear Creek in the central Yukon. The lodes are the source for more than 120,000 ounces of downstream placer gold production. These lodes contain variable amounts pyrrhotite, pyrite, and arsenopyrite, with less abundant scheelite - alkali-feldspar, muscovite, biotite and tourmaline are common gangue phases. Grab samples of mineralization often contain gold grades in excess of 1 ounce per ton. Gold-to-silver ratios vary most commonly from 1:1 to 5:1. Gold-rich quartz veins cut all stocks, adjacent hornfels and associated lamprophyre dykes commonly contain greater than 1% arsenic. Bismuth, and less consistently tungsten and stibnite, characterize many of the most highly mineralized veins within and surrounding the stocks. Quartz veins along the intrusive-metasedimentary rock contact around the Pukelman stock are also enriched in lead and silver. R-mode factor analysis of multi-element geochemical data for 111 gold- and sulphide-bearing rock samples indicates that there are two geochemically distinct metal suites in the Clear Creek occurrences. The first is characterized by As-Au-Bi ± Sb, Te ore-related mineral association, which is typical of many intrusion-related deposits in the Tombstone gold belt. Less consistently, anomalous concentrations of Ag, Co, Cu, Fe, and Mo occur within these auriferous rocks. The second metal factor is defined by Ag-Bi-Pb ± As, Au and Te. It characterizes metalliferous vein samples that have uncommonly low Au: Ag ratios and may represent a second hydrothermal episode. Tungsten shows little consistent correlation with the metalliferous veins in either element suite.

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.