2010 GSA Denver Annual Meeting (31 October –3 November 2010)
424 Thursday, 4 November 2010
7:15 AM-3:00 PM, Colorado Convention Center: Lobby B

Estimating Natural Background Groundwater Chemistry, Questa Molybdenum Mine, New Mexico

Primary Leader: Philip L. Verplanck
Leader(s): Geoffrey S. Plumlee, D. Kirk Nordstrom, Bruce M. Walker
Field Trip Description: This two-and-a-half day field trip is an overview of a USGS project that estimated pre-mining groundwater chemistry at the Questa Molybdenum mine. The deposit is one of a series of Climax-type porphyry molybdenum systems occurring along the Red River, New Mexico. Natural acid weathering of the sulfide-mineralized rocks produced a series of erosional scars and associated debris fans feeding these mineralized rocks, their weathering products, and acidic waters into the Red River. New Mexico State regulations require that groundwater-quality standards be met at mine closure unless it can be shown that pre-mining contaminant concentrations exceeded them. Because of intense debate among stakeholders regarding pre-mining standards, the New Mexico Environment Department and Chevron Mining Inc. agreed that the USGS should determine pre-mining groundwater quality at the Questa mine. The USGS investigation utilized detailed knowledge of a proximal natural analog site and applied an interdisciplinary approach to infer pre-mining conditions. Characterization included environmental geology, AVIRIS remote sensing, mineralogy, groundwater–surface water interactions with mass balances, and chemical evolution in a debris-fan aquifer. This trip will include a surface tour of the Questa mine and key locations in the erosion scar areas and along the Red River. The trip will provide participants with a detailed understanding of processes that influence pre-mining environmental baselines in mineralized areas and estimation techniques for determining pre-mining baseline conditions using an interdisciplinary approach linking geology, geophysics, geochemistry, remote sensing, geomorphology, and hydrology. The trip will include several slightly to moderately strenuous hikes. Overnight lodging will be in Taos.
Field Trip will span: 2 days
Sponsor(s): US Geological Survey; Chevron Mining, Inc

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