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TitleGeochemistry of mine waters draining a low-sulfide, gold-quartz vein deposit, Bralorne, British Columbia
AuthorDesbarats, A JORCID logo; Parsons, M BORCID logo; Percival, J BORCID logo; Beauchemin, SORCID logo; Kwong, Y T J
SourceApplied Geochemistry vol. 26, 2011 p. 1990-2003,
Alt SeriesEarth Sciences Sector, Contribution Series 20100459
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia
Lat/Long WENS-123.0000 -122.5000 51.0000 50.7500
Subjectsgeochemistry; environmental geology; hydrogeology; environmental studies; environmental impacts; environmental analysis; groundwater; groundwater pollution; water analyses; water quality; water geochemistry; Bralorne Mine; Pioneer Mine
Illustrationslocation maps; histograms; plots; tables
ProgramEnvironmental Geoscience
Released2011 12 01
AbstractThe Bralorne and Pioneer mines, now inactive, produced over 4 million ounces of Au from an orogenic lode Au deposit located on the eastern edge of the Coastal Mountains of SW British Columbia. Between 2007 and 2009, drainage from a recently developed exploration adit was investigated in order to better understand and anticipate potential environmental management issues associated with the development of this type of deposit in the future. Portal discharge rate and specific conductance were monitored continuously over a 14-month period during which 36 water samples were collected. Additional samples were collected from flooded workings within the adit. Concentrations of As and Sb at the portal range as high as 1738 and 316 lg/L, respectively, while those in the mine pool reach 3304 and 349 lg/L, respectively. Effluent chemistry is mildly alkaline (pH = 8.7) and is dominated by Na, Ca, Mg, HCO3 and SO4. Geochemical inverse modeling of effluent composition indicates weathering of albite (2515 kg/a), ferroan dolomite (718 kg/a), pyrite (456 kg/a), arsenopyrite (23 kg/a) and stibnite (2 kg/a). Modeled sulfide reaction coefficients, normalized by their corresponding host rock concentrations, suggest that oxidation of arsenopyrite is 25 times slower than that of pyrite whereas oxidation of stibnite is 1.5 times faster. Oxidative dissolution of arsenopyrite and stibnite releases 10.6 kg/a of As and 1.1 kg/a of Sb of which 57% and 46%, respectively, are sorbed to ferrihydrite and gibbsite on the bed of the shallow channel through which the mine pool drains to the portal. Although mass balance calculations predict the formation of sufficient ferrihydrite to sorb 100% of the As dissolved in the mine pool, this attenuation process was ineffective possibly because the precipitated sorbents settled to the bottom of the water column or because of competition for sorption sites from Ca and HCO3. The dissolved Sb/As molar ratio in portal effluent (0.082) is much greater than the Sb/As ratio of the mineralization (0.002) because of slower arsenopyrite oxidation and somewhat lesser sorption of Sb.

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