Downstream changes in antimony and arsenic speciation in sediments at a mesothermal gold deposit in British Columbia, Canada

• Published in: Applied geochemistry 2012-10, Vol.27 (10), p.1953-1965
• Main Authors: Beauchemin, Suzanne, Kwong, Y.T. John, Desbarats, Alexandre J., MacKinnon, Ted, Percival, Jeanne B., Parsons, Michael B., Pandya, Kumi
• Format: Article
• Language: English
• Subjects: absorption; antimony; arsenic; chemical speciation; detection limit; drainage; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Geochemistry; gold; iron; manganese; mineralization; oxidation; Pollution, environment geology; pyrites; sediments; spectroscopy; wetlands; X-radiation
• ISSN: 0883-2927; 1872-9134
• DOI: 10.1016/j.apgeochem.2012.04.003

► We study the mobility of antimony in the vicinity of a mesothermal gold deposit. ► Stibnite oxidizes faster than arsenopyrite. ► Secondary antimony species are dominantly associated with Fe-oxyhydroxides. ► Sb shows distinct oxidation reactions as compared to As under similar redox conditions. This study investigates Sb speciation in sediments along the drainage of the Upper Peter adit at the Bralorne Au mine in southern British Columbia, Canada, and compares the behavior of Sb with that of As. The Upper Peter mineralization consists of native Au in quartz-carbonate veins with 1wt.% sulfides dominated by pyrite and arsenopyrite although stibnite, the primary Sb-bearing sulfide mineral, can be locally significant. Dissolved Sb concentrations can reach up to 349μgL−1 in the mine pool. Sediments were collected for detailed geochemical and mineralogical characterization at locations along the 350-m flow path, which includes a 100-m shallow channel within the adit, a sediment settling pond about 45m beyond the adit portal and an open wetland another 120m farther downstream. From the mine pool to the wetland outlet, dissolved Sb in the drainage drops from 199μgL−1 to below the detection limit due to the combined effect of dilution and removal from solution. Speciation analyses using X-ray absorption near-edge structure (XANES) spectroscopy indicate that Sb(III)–S accounts for around 70% of total Sb in the sediments in the main pool at the far end of the adit. At a short distance (24m) downstream of the main adit pool, however, Sb(III)–O and Sb(V)–O species represent ⩾50% of total Sb in the bulk sediments, indicating significant oxidation of the primary sulfides inside the adit. Although Sb appears largely oxidized in the bulk samples collected near the portal, Sb(III)–S species are nevertheless present in the