WEATHERING PROCESSES, OXIDE MINERALOGY, AND TRACE-ELEMENT ADSORPTION AT DAVIS PYRITE MINE, ROWE, MASSACHUSETTS

Davis Mine in Rowe, MA operated from 1882 until 1911, producing pyrite from a mineralized zone in the Ordovician Hawley Formation. This unit is in the Berkshire Mountains of western Massachusetts, and consists of gneiss, schist, and amphibolite, all metamorphosed to lower amphibolite grade. The ore body contains granular pyrite, with associated chalcopyrite, pyrrhotite, sphalerite, and galena. Since the time of the mine collapse in 1911, acidic drainage has been transporting sulfate, iron, and trace metals from the exposed tailings piles in surface runoff and groundwater. Mineralogical studies of the waste-rock piles piles document intense weathering, typified by destruction of secondary aluminosilicates and the formation of soluble acidic sulfates such as jarosite and hydrobasaluminite. The bed of the effluent stream is coated by the oxidation products of the sulfides with colors ranging from yellow to red-brown. Samples were collected along the length of the effluent stream and separated into silt- and clay-size fractions via sieving and centrifugation. The clay size fraction was analyzed via X-ray diffraction. In general, despite the change in color of the precipitated minerals, goethite (FeOOH) remains the dominant iron mineral along the length of the effluent stream. Small amounts of ferrihydrite were detected in more distal areas. Nevertheless, the composition of the adsorbed cations changes downstream. In upstream areas of Davis Mine Brook, which receives the mine effluent, Pb is the dominant trace element on Fe-oxide coatings even though Pb has a negligible concentration in the water. However, farther downstream Al becomes the dominant adsorbed species followed by Pb and Zn. These results indicate that downstream mineralogical differences are not a factor in the adsorption of trace elements from stream water, but rather they reflect progressive changes in fundamental chemical processes.