What was the groundwater quality before mining in a mineralized region? Lessons from the Questa project

Abstract

The U.S. Geological Survey, in cooperation with the New Mexico Environment Department and supported by Molycorp, Inc (currently Chevron Minerals), has completed a 5-year investigation (2001)(2002)(2003)(2004)(2005)(2006) to determine the pre-mining groundwater quality at Molycorp's Questa molybdenum mine in northern New Mexico. Current mine-site ground waters are often contaminated with mine-waste leachates and no data exists on premining ground-water quality so that pre-mining conditions must be inferred. Ground-water quality undisturbed by mining is often worse than New Mexico standards and data are needed to help establish closure requirements. The key to determining pre-mining conditions was to study the hydrogeochemistry of a proximal natural analog site, the Straight Creek catchment. Main rock types exposed to weathering include a Tertiary andesite and the Tertiary Amalia tuff (rhyolitic composition), both hydrothermally altered to various degrees. Two types of ground water are common in mineralized areas, acidic ground waters in alluvial debris fans with pH 3-4 and bedrock ground waters with pH 6-8. Siderite, ferrihydrite, rhodochrosite, amorphous to microcrystalline Al(OH)3, calcite, gypsum, barite, and amorphous silica mineral solubilities control concentrations of Fe(II), Fe(III), Mn(II), Al, Ca, Ba, and SiO2, depending on pH and solution composition. Concentrations at low pH are governed by element abundance and mineral weathering rates. Concentrations of Zn and Cd range from detection up to about 10 and 0.05 mg/L, respectively, and are derived primarily from sphalerite dissolution. Concentrations of Ni and Co range from detection up to 1 and 0.4 mg/L, respectively, and are derived primarily from pyrite dissolution. Concentrations of Ca and SO4 are derived from secondary gypsum dissolution and weathering of calcite and pyrite. Metal:sulfate concentration ratios are relatively constant for acidic waters, suggesting consistent weathering rates, independent of catchment. These trends, combined with lithology, mineralogy, and mineral solubility controls, provide useful constraints on pre-mining ground-water quality for the mine site where the lithology is known.

Effects and quantification of acid runoff from sulfide-bearing rock deposited during construction of Highway E18, Norway

“…It has long been known that CoS 2 and NiS 2 have the same crystal structure as pyrite and the solid substitution of Co and Ni in pyrite is common and covers a wide range, usually with Co>Ni but with many exceptions (Fleischer, 1955). Lab studies on the leachability of Co and Ni are not known to the authors but in a study on natural acid rock drainage in New Mexico a similar strong linear correlation was found between Co and Ni with a ratio of 0.42 (Nordstrom, 2008). Further, it was possible to show that the Co/Ni ratio in these acid waters was similar to the Co/Ni ratio in the pyrite.…”

Environmental and health hazards associated with exploration of barite from Bukkuyum (Zamfara State), Nigeria

“…Both the runoff of this water as well as the accumulation of this water in mining pits is of possible environmental concern. These issues must be addressed within the context of the environmental requirements in place in the jurisdiction within which the mining occurs (Siegel, 2002;Nordstrom, 2008;Oden, 2012). This paper is aimed at characterizing Barite from Bukkuyum local government area of Zamfara state of Nigeria, with the objective of giving adequate information of the environmental and health hazards associated with it exploration base on the findings of these characteristics which is a function of its geological origin.…”

Groundwater Quality

“…As no data existed about pre-mining ground-water quality, premining conditions had to be inferred to help establish closure requirements. Useful information was obtained from the geochemistry survey together with lithology, mineralogy, and mineral solubility controls (Nordstrom, 2008). An investigation showed that soil and groundwater were contaminated by untreated effluents from industries in Katedan Industrial Development Area, India.…”