Summary

Description

Hardrock mining for gold and other metals is proposed for the Kensington Mine, located on Lynn Canal in Southeast Alaska, approximately 45 miles north of Juneau. The adjacent Jualin Mine is in the exploration phase. Over a tenyear period, various scenarios have been proposed for the Kensington Mine, including the cyanidation process to extract gold from crushed orebearing rock, a tailings pond for tailings disposal above anadromous fish streams, mixing zones for excess tailings water into fresh andor marine waters, dry upland tailings storage, and most recently, submarine tailings disposal, and onsite process water treatment. The Kensington Mine is located adjacent to marine waters that support large numbers of migratory waterfowl, salmon, and herring. There are few baseline data on metals in local organisms available to compare with later monitoring data if this and other mines become operational. The object of this study is to produce a set of data to be used as a predevelopment baseline for metal and cyanide concentrations in sediments and biota from potentially affected areas near Kensington and adjacent mining properties. Marine sediment was collected in 1994 from two coastal locations and blue mussels Mytilus trossulus were taken from six locations adjacent to the Kensington Mine site. Total metals and cyanide analyses were done for all samples. Dolly Varden Salvelinus malma and prickly sculpin Cottus asper were collected from Sherman and Sweeny Creeks, which flow through the Kensington Mine site. Metal concentrations in sediments mean concentrations in ppm dry weight DW: As 9.65, Cd 0.1, Cr 24.41, Cu 43.94, Hg 0.027, Ni 17.75, Pb 6.07, Zn 47.24 were comparable to other Southeast Alaska locations that have not been affected by human activities. Cyanide concentrations mean of 0.07 ppm DW were close to the level of detection in all marine sediment samples. Metal concentrations in blue mussels were also comparable to those in mussels from other Southeast Alaska locations with the exception of cadmium. Cadmium concentrations mean of 9.95 ppm DW were higher than any concentrations previously reported from Southeast Alaska mussels. Composite samples of Dolly Varden and sculpin arsenic concentrations 1.88, 1.37 ppm DW, respectively were higher than expected when compared to fish from other Southeast Alaska locations, but reflect naturally high arsenic levels reported in water from Sweeny and Sherman Creeks collected by Coeur Alaska. Other freshwater fish metal concentrations were similar to those reported in previous baseline studies from Southeast Alaska. These data will provide partial baseline data prior to any mine development.