Evolution of the McLaughlin Gold Mine Pit Lakes, California

摘要

Cessation of open pit mining in 1996 at the McLaughlin hot-spring type gold deposit has resulted in the development of two pit lakes that will be managed as perimanent lakes with a total storage capacity of 10,000 acre-feet. The south pit lake developed from alkaline ground water infiltration and had an initial pH of 7.2. It contained high concentrations of boron and chloride, indicating that it consisted of a mix of meteroic and evolved connate waters. Numerous carbon dixoide gas vents were present initially in the shallow south pit lake, but as the pit lake increased in depth, gas venting ceased and carbon dioxide is retained in the lower layer of the chemically stratifed lake. Continued increase of dissolved carbon doixde in the lower layer increases the potential for a ilmnic eruption.