PRELIMINARY ENVIRONMENTAL GEOCHEMICAL EVALUATION OF THE MINE WASTE MATERIAL AT THE XICHU MINING DISTRICT, SIERRA GORDA NATURAL RESERVE, NORTHEAST GUANAJUATO STATE

The Xichu Mining District is located in the extreme northeast area of the Guanajuato State, central Mexico, in what is call the “Sierra Gorda”, which is a protected, natural reserve of the biosphere. The mining activity in this district started in the 1800´s and concluded by 1950. There are several dispersed ore deposits in the area, being the most important a polymetallic ore formed by the combination of epithermal veins and skarn type deposits hosted in upper Cretaceous calcareous rocks. The main ore minerals in the ore deposit are: galena (PbS) with some concentrations of silver (Ag), chalcopyrite (CuFeS), sphalerite (ZnS), and abundant pyrite (FeS) with some arsenic (As) and important concentrations of gold (Au). So, the elements mined were Zn, Cu, Pb, Ag and Au. The mines are located at the bottom of a deep valley with hills rising up to 1,000 meters from the valley floor. Several mine tailings, amounting some 800,000 tons of mine waste material are just deposited over the hills facing the valley. The risks of high mobility of heavy metals derived from the high metal content mine waste material into the environment poses a real treat to local population. We present in this work preliminary results of chemical analyses in mine tailings, sediments, soil, surface water and local plants (vegetation). The mine tailings present the following concentrations: As = 7,000 mg/kg, Cu = 977 mg/kg, Pb = 3,400 mg/kg, and Zn = 5,700 mg/kg. Our objective is to assess the environmental geochemical factors controlling mobility of heavy metals derived from the mine waste material and into the biosphere (sediments, soil and vegetation).