Concentrations of Cu, Ba and as In Sediments and Their Association with the Presence of Mines In Northeast Chihuahua

Concentration of three elements in northeast Chihuahua were spatially analyzed to determine (a) background levels in areas unaffected by mineral deposits, (b) natural background concentrations near mineral deposits, and (c) anomalous values. Arroyos in this area reflect natural conditions since they drain desert land that is devoid of industrial or agricultural wastes, leaving mining as the only additional source of contaminants besides outcrops' weathering. Analyzes were conducted using 1,016 arroyo sediment geochemical data from SGM (Servicio Geologico Mexicano) plus 11 river sediment samples collected by the authors. The spatial distribution of As, Ba, and Cu concentrations were plotted to show their geographical association to mineral deposits containing barite, Pb-Zn-Cu sulfides and Mn-oxides. The background values were determined using values below the 80 percentile (813 data points). For values >80 percentile associations to the mines were sought, while anomalous values were identified as those higher than the mean plus two standard deviations. A proximity to the mines was able to explain anomalous concentrations for all three elements and also for As and Ba values of areas near mineral deposits (values higher than the 80 percentile). In contrast, the Cu pattern of concentrations of values higher than the 80 percentile was not associated with known mines as 98.5% of the data points plotted in the southern part of the study area. Background values and concentration patterns may be used to monitor effects of ongoing and future increase in mining, agricultural and urbanization activities.