ENVIRONMENTAL GEOCHEMISTRY OF AREAS ASSOCIATED WITH ABONDONED COPPER-SULFIDE MINES, PRINCE WILLIAM SOUND, ALASKA

Abandoned copper mines exist throughout certain regions of Prince William Sound, Alaska. Approximately 5,800,000 tons of high-grade copper sulfide ore were extracted and shipped from seven different deposits during 1897-1930. Of these the Beatson deposit on Latouche Island (southwest) was the largest and today has the most volume of waste rock remaining on site. Other sites of interest to this study are the Ellamar and Threeman mines. Massive sulfides and associated waste rock piles are exposed to conditions of oxidation by meteoric and seawater at or near the surface along or close to shorelines at the mine sites. In the case of the Beatson site the waste piles are not directly in contact with seawater due to several meters of uplift that occurred during the 1964 Alaskan Earthquake. In contrast, at the Ellamar and the Threeman sites the waste rock piles are exposed to seawater interaction mostly at high tide. Oxidation of the remaining sulfide bearing material is occurring at all sites resulting in the release of acidic water containing elevated concentrations of various metals including iron, aluminum, copper, lead, zinc, among others. The magnitude and extent of the acid- and metal-rich effluent varies based on differences in the mineral content of waste material and the hydrology of each site. Shallow groundwater samples range in pH from 3.0 to 5.5 and surface waters are mostly circum-neutral. Iron oxyhydroxides have been identified as secondary mineral phases in most environments and they contain elevated concentrations of associated heavy metals. Autosamplers and dataloggers were utilized at the Beatson site in order to try to understand longer term variations in surface water flow and chemical composition. In addition, massive microbially-mediated precipitation of iron oxides is occurring at some of the sites. There are distinctive Leptothrix colonies at the Beatson site and other types of bacteria associated with acidic conditions and the presence of sulfur and iron at other sites.