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.

URL: https://geoscience.data.qld.gov.au/dataset/cr120222 Prior to the granting of EPM18548 to Byerwen Coal, no previous metals exploration activity had been undertaken within the permit area. EPM18548 is considered prospective for a variety of mineralisation styles. Work in the current reporting period included further geological review of EPM18548 incorporating the information from the 2017-18 sampling work. As a result of the review a total of 14 subblocks were identified as having limited prospectivity and relinquished, effective 10 April 2019.

In 2010-11, Yukon Geological Survey awarded a contract to NEW ERA Engineering Corporation of Whitehorse to undertake a study of recent developments in gravity gold recovery techniques. In partial fulfillment of the contract, Randy Clarkson attended the Gravity Gold 2010 Optimizing Recovery Conference in Ballarat, Australia, and presented the following report and recommendations at the Yukon Placer Workshop in November 2010.

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EBA Engineering Consultants Ltd. has prepared this report, based on literature review, to provide information to assist the Yukon mining industry in remediating environmental problems caused by acid rock drainage (ARD) with its associated heavy metals contamination. There are three main sections to this review. First, the history of ARD is presented. Second, the chemistry and microbiology of ARD and the treatments that are used worldwide, with emphasis on cold climate treatments, are reviewed. Finally, we present the most promising technologies developed in temperate regions, that could be tested under typical Yukon conditions. This is the main challenge given the short growing season and cold temperatures. Acid mine drainage is caused by oxidization of metal ores, containing sulphur and metal sulfides found in coal. There are three steps in this process. First, oxygenated water, from rain, for example, oxidizes metal sulfides producing acidic water and ferrous iron. When the water becomes moderately acidic, a number of bacteria can assist in further oxidization and increase the acidification of the drainage water. Finally, when the water reaches a pH of 3.5, an iron bacterium, Thiobacillus ferroxidans, can further dissolve metal sulfides, such as pyrite, producing ferric hydroxide, which can smother vegetation. Also, the sulphuric acid is acutely toxic. Heavy metals that are toxic, are also present in the ARD. Some common treatments for ARD identified by EBA including neutralizing the acidity of water using limestones, minimizing water contact with metal sulfides, or using organic amendments to bind with heavy metal contaminated waters. Important developments in using natural wetlands for ARD, have taken place in the late 1990s, which have identified that anaerobic (oxygen free conditions) are important in treating ARD. High sediment loads in streams have been found to limit neutralization by coating carbonates and decreasing microbial reduction of metal, as well as preventing metal uptake by vegetation.

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 report reviews methods and criteria for placer mining settling pond design. The mining and processing of placer gold generates wastewaters containing high concentrations of fine sand, silt and clay. Reduction of sediment discharges is required primarily to minimize impacts of sediment and turbidity on the aquatic environment and fish. Sediment discharge control to avoid sedimentation of water supply intakes of downstream mining operations and to allow recycling of process water in water short areas are secondary factors.