CHEMICAL COMPOSITION OF WASTE ROCK DUMPS AND OTHER MINING-RELATED FEATURES ASSOCIATED WITH THE MOGOLLON MINING DISTRICT, NEW MEXICO

The Mogollon Mining District is a region of the Mogollon Mountains that was known for its gold and silver production. The subsequent mineralization brought hydrothermal alteration, depleting the surrounding country rock of Ca, Sr, and Na while enriching the rock in Ag, Au, K, and Rb. Economically-rich ore bodies are commonly found where Fanney Rhyolite is juxtaposed against the younger Mineral Creek Andesite. This study reports chemical analyses of composite dump, leachates, and host rock samples from mine sites near the Fanney Mine. The sampling effort was undertaken during reconnaissance geologic mapping in an attempt to characterize the economic value of mine waste and determine the environmental impact of the tailings. Thirty individual samples were collected and mixed from tailings along. An additional 10 sites were collected for individual analysis and are combined with 15 samples of altered and unaltered host-rock material. Here, we make general observations and preliminary assessment of the tailing pile and surrounding host rock.

All samples were analyzed by inductively coupled plasma mass spectrometry at Missouri State University using an Agilent 7900 ICP-MS. All samples were analyzed for 14 REEs & Ba, Th, Nb, Y, Hf, Ta, U, Pb, Rb, Cs, Sr, Sc, Zr, Ag, Au, As, K, Na and Cu. Elemental analysis of the composite dump sample were analyzed four times with various aliquots of material. Host-rock and individual site samples were each analyzed once. Each host rock and the composite sample was leached with nitric acid for 24, 26 and 48 hours each. Element concentrations vary within the pile and between the host-rocks. We suggest this is likely due to the degree of alteration in the host-rock. Highly contrasting geochemical signatures occur for two samples collected from the same waste-rock dump at the Fanney mine near Mogollon, New Mexico illustrating the heterogeneous nature waste dump rocks.