Environmental controls on water quality: Case studies from Battle Mountain mining district, north-central Nevada

The environmental controls on water quality were the
focus of our study in a portion of the Battle Mountain mining
district, north-central Nevada. Samples representing areas
outside known mineralized areas, in undisturbed mineralized
areas, and in mined areas were chemically and isotopically
analyzed. The results are related to geologic, hydrologic, and
climatic data.
Streams in background areas outside the mineralized
zones reflect normal weathering of volcanically derived rocks.
The waters are generally dilute, slightly alkaline in pH, and
very low in metals. As these streams flow into mineralized
zones, their character changes. In undisturbed mineralized
areas, discharge into streams of ground water through hydrologically
conductive fractures can be traced with chemistry
and, even more effectively, with sulfur isotopic composition
of dissolved sulfate. Generally, these tracers are much more
subtle than in those areas where mining has produced adits and
mine-waste piles. The influence of drainage from these mining
relicts on water quality is often dramatic, especially in unusually
wet conditions.
In one heavily mined area, we were able to show that
the unusually wet weather in the winter and spring greatly
degraded water quality. Addition of calcite to the acid, metalrich
mine drainage raised the stream pH and nearly quantitatively
removed the metals through coprecipitation and (or)
adsorption onto oxyhydroxides.
This paper is divided into four case studies used to
demonstrate our results. Each addresses the role of geology,
hydrology, mining activity and (or) local climate on water
quality. Collectively, they provide a comprehensive look at the
important factors affecting water quality in this portion of the
Battle Mountain mining district.