Abstract

Temperature logs at 18 drill-holes in the four large Roadside rock piles at the molybdenum mine near Questa, NM, allow the fitting of equations representing heat transfer to temperature data, providing estimates of vertical and horizontal flow. From first-order approximations, the analyses indicate considerable fluid flow and heat transfer by advection, which is consistent with previous models. Because the rock piles are typically water unsaturated (liquid not encountered in the rock pile at drill-holes above the Red River), and because vapors are observed coming from the ground surface at some locations, most of the fluid flux in the rock piles is likely gas phase. Temperature logs at the 18 sites and sample characterizations at many of the sites indicate that pyrite oxidation may often occur preferentially over a depth interval of ∼10–20 m, which is at depths of ∼⅓ to ⅔ of the depth of the drill-hole. Flows deduced from the T logs indicate that 1) pyrite oxidation is an important driver of present flow; 2) large amounts of air flow occur in the rock piles, consistent with necessary oxygen for pyrite oxidation; 3) present-day three-dimensional flows are possible in the rock piles; 4) thermal conditions in the rock piles are very heterogeneous; and 5) flow patterns are complicated and may vary with time. Temperature increases of 2–20°C are noted near the water table at the base of the rock piles in a few wells, indicating advection of heat from the rock pile and possible deep pile fluid circulation.

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