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).

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.

The Brewery Creek gold mine (13.3 Mt @ 1.44 g/t Au) is a bulk tonnage, heap leach operation located 57 km east of Dawson City, Yukon. The deposit lies on the northeastern side of the Tintina Fault and within Selwyn Basin. Gold mineralization is hosted by intrusions of the mid-Cretaceous Tombstone Plutonic Suite (TPS), and Silurian to Carboniferous clastic metasedimentary rocks of the Steel Formation and Earn Group. The sedimentary rocks are faulted and variably folded, however they display poor cleavage development. The TPS intrusions are also faulted and contain rafts of argillaceous sedimentary rock. No regional ductile fabrics were observed to crosscut the intrusions. Five phases of intrusion have been recognized; these are `raft monzonite, feldspar porphyry (FP1), biotite monzonite, a second phase of feldspar porphyry (FP2), and a pyroxenite. The most important feature at Brewery Creek is a linear zone of monzonite intrusions, faulting and mineralization termed the Reserve trend. This zone trends west-northwest and has a moderate dip to the south. A number of stages and orientations of faulting have been identified along the Reserve trend; lithological relationships suggest a substantial amount of vertical movement occurred post-TPS emplacement and pre- to syn-mineralization.

This study was first conceived as an attempt to document the processes undertaken for the Brewery Creek Mine (referred to as Brewery Creek in this report) in the Yukon Territory and provide a description of the lessons learned from this process. The hope is that this report will be used in the future as a tool for regulatory authorities, assessors, resource development companies, and First Nations for analyzing and planning resource development projects. This report provides an analysis of some of the aspects of the first heap leach mine north of 600 from planning through to post-closure monitoring, start to finish by comparing expectations and predictions versus reality and the lessons learned through the entire process.

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.

Placer gold in the Clear Creek drainage basin is found in a variety of gravel deposits, each of which is associated with a specific geological setting. The schematic profile of Clear Creek drainage basin illustrates the distribution of these gravel deposits, and indicates both known deposits and favourable sedimentologic conditions for placer mineral accumulation. Known placer gold deposits include creek and gulch placers, as well as preglacial fluvial gravel or buried channels. Favourable placer deposit settings include alluvial fans, gravelly sediments similar to the Pliocene (?) White Channel gravel of the Klondike area, and specific glacially derived sediments. This paper describes each of the above placer deposit settings, and outlines the associated stratigraphy and sedimentology of placer gold deposits.

In order to determine which shrub species might be useful in revegetating Yukon mine sites at the time of closure, eleven species of shrubs were transplanted at three open disturbed sites at the Brewery Creek Mine in the Central Yukon in the fall of 2000. These sites included a steep north-facing slope, a steep south-facing slope, and a lower nearly level area. All three of these areas had been recontoured and seeded in 1996-97, and there was a thick growth of grasses and clovers at the time the shrubs were planted in 2000. To determine if this thick growth interfered with the survival of the newly planted shrubs, the grasses and clover were first removed from one-half of each of the test plots. Six years after the shrubs were planted, it appears that black spruce and Alaska birch are the most successful species transplanted on the north-facing site, trembling aspen and Alaska birch the most successful on the south-facing site, and dwarf birch, prickly rose and trembling aspen the most successful on the nearly level site. The planting of willow stem cuttings was not successful. After six years, the previously cleared half of each plot was once again covered with a thick growth of seeded and naturally occurring plant species. The clearing of vegetation before the transplanting of shrubs does not appear to have much of an effect on the ultimate survival and growth of the transplanted shrubs.

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