Ridley Abstract 1

W. Ian RIDLEY, Byron R. BERGER, Carol, A. FINN, Trude V. V. KING, Frederick E. LICHTE, Wayne, C. SHANKS III, Mineral Resource Surveys Program, USGS, Denver, CO 80225, Brenda HOUSER and Floyd GRAY, USGS, 210 E. 7th Street, Tucson, AZ 85742

Porphyry copper-style deposits and other types of hydrothermal mineralization have been emplaced along regional fault systems within the Santa Cruz Drainage Basin. The dominant structural trends are coincident with present-day hydraulic conductivity. High metal concentrations in Nogales city water and elevated metal concentrations in Tucson storage basin water suggest groundwater quality is affected by metals associated with hydrothermal mineralization.

Re-requisites to estimating the availability of chemicals to the regional surface and groundwater systems include:

the nature of fractures in the subsurface,
fracture interconnectivity and transmissivity,
sub-surface structure,
detailed knowledge of alteration,
distribution of mineralization,
alteration and ore mineralogy,
crystallographic siting of potentially toxic elements and their solubility,
surface mineral distribution, and
sources of dissolved ions.

In order to better understand the geologic factors that contribute to the quality of water entering the drainage basin we have initiated an interdisciplinary evaluation that incorporates economic geology, structural geology, sedimentology, geophysics (potential fields and remote-sensing), trace element and stable isotope geochemistry, and geochemical/hydrological modeling. The Patagonia Mountains, in the south-eastern part of the Santa Cruz Drainage Basin, is the site of a pilot study where extensive and intensive hydrothermal activity has altered and mineralized rocks within the Sonoita Creek drainage sub-basin. The area includes acid-sulfate alteration, Cu-Pb-Zn-Ag-Au mineralization, mine dumps, and mill tailings. We will describe the water quality implications resulting from our interdisciplinary studies of the geologic characteristics of the Santa Cruz Drainage Basin.

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Contributions of Mineralization And Metal Mining To The Santa Cruz River Drainage Basin. Southern Arizona: Evaluation of Geological Geologic Factors