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Geochemistry of Altered Rock, Mineral Deposits, and Surface and Ground Water Resources

Task Objectives

Mercury mines and other sites were evaluated for stable isotopic studies.

There are potential human health and BBNP ecosystem environmental problems related to: 1) hydrothermal alteration related to ore deposits and volcanic rocks, 2) natural and anthropogenic surface and groundwater contamination, 3) metals in hot springs, and 4) metals in locally-derived airborne dust. Several of these have been identified as key environmental concerns for BBNP. In the broad Trans-Pecos region that includes BBNP and adjacent areas of Chihuahua and Coahuila, Mexico, extensive deposits of Hg, Ag, Zn, Pb, and Be are located. Contaminants such as Hg, Se, and As are present in soils and surface and groundwater. F- and U-rich mineralized rock is present locally.

As part of this task, the USGS has worked with NPS, USGS, and academic scientists to (1) obtain a comprehensive understanding of metal sources and transport in past hydrothermal systems related to volcanism and/or ore-forming processes, (2) study sources and dispersion of metals in surface waters, groundwater, and presently active geothermal waters, and (3) evaluate transfer of metals to dust, soil, and stream sediment. USGS objectives were to survey potential sources of metals and other elements in the surficial environment by determining the distribution of mineralizing systems and past hydrothermal activity related to volcanism. Trace element and isotopic studies were used to understand sources and evolution of surface and ground water, and geothermal water in BBNP. Transfer of elements from mineralized sources into surface and ground water, dust, soil, and stream sediment was studied to understand potential affects on the BBNP ecosystem. Uptake of potentially toxic elements by plants and animals, and the use of stable isotopes to track such processes were also evaluated.

Highlights and Key Findings

Several samples of bear hair were analyzed for C, N, and S isotopes and for concentrations of several trace elements. Results of the analysis of bear hair and interpretation of possible contaminant sources were described in USGS Circular 1327.

In addition, several spring water samples collected in BBNP were dated by the ³He/³H method and results from this study were also presented in USGS Circular 1327.

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