Geochemistry and mineralogy of Au-tailings from Tlalpujahua-El Oro mining district, Mexico, and their environmental impact implications

The tailing dumps of the mining district of Tlalpujahua and El Oro (DIMITO) were stacked on the active drainage system and covering a basement consisting of carbonaceous limestones and shales +/- andesites, which constitute the host rock of the epithermal Au vein-type deposit. This geomorphological setting shows deep channels and gullies of erosion and it has been estimated a loss of material > 27-34 % of its original volume. We present mapping of five tailing dumps that were placed similar to 68 year ago as well as the mineralogical and geochemical characterization of 12 profiles and 48 samples. Tailings are essentially siliceous-calcareous slime with clasts. Their pH is slightly alkaline from 7.5 to 8.5 and they show low conductivity < 80 mu S/cm. They are constituted by abundant quartz (>= 53-68 %), lithics (7-20 %), calcite (>= 12 %), silicates (9-11 %), Fe-Ti oxides (>= 2-3 %) and sulphides and sulphosalts (<= 2 %). Bulk compositions are characterized by SiO2 (56-92 %), Al2O3 (>15-13 %), CaO+MgO (>= 5-11 %), Fe-tot (<= 3-5 %), S (0.3-0.91 %), and C (3.4-6.1 %). DIMITO tailings show values of Au (1.2-1.61 g/ton), Ag (28.1-46.8 g/ton), Pb (53.3-145.2 g/ton) and Zn (155.9-354.5 g/ton), suggesting that they could still have some economic recovering. In relation to the concentrations of the potentially toxic elements, the values of Sb (27.3-72.2 g/ton) significantly exceed high risk of the LMP (WHO, 2015), and a dozen samples of Pb and Zn and As (25.2-40.5 g/ton) show higher values than low-risk of the LMP. However, these values are scattered and random in each profile, so its toxic potential is discussed based on its mineralogical-geochemical correlation and its potential mobility. In order to estimate the acid-base accounting (ABA) of the DIMITO, we carried out a mathematical model based from the Gauss-reduction normalization of the geochemical data and their relationships with normative mineralogy. We found that the mineralogy represents a powerful proxy for the diagnostic of the toxic potential of the waste mines and that in general the tailings show not risk of acide mine drainage generation. However, we discuss the environment impact of the tailing dumps and the relationships with the actual land use of the DIMITO.