MINERALOGY AND BIOACCCESSIBILITY FROM THE LARGEST HISTORICAL PORPHYRY CU TAILINGS OF THE SONORAN DESERT, NORTHWESTERN MEXICO

Nacozari de García city, located in the second most important porphyry Cu district in Mexico, contains the largest historical mine tailings in Sonora. These mine tailings (MT-I, MT-II, and MT-III) and street dust were chosen to perform mineralogical and bioaccessible (gastrointestinal and lung) studies in the 250 and 10 μm fractions. X-ray diffraction analysis in mine tailings and street dust samples determined the presence of silicates that were most likely derived from surrounding lithologies. The main secondary minerals identified in the mine tailings were jarosite and gypsum, which indicate advanced oxidation processes. Efflorescent minerals identified were chalcanthite and hexahydrate (MT-I), szomolnokite and poitevinite (MT-II), and halotrichite (MT-III); these minerals were developed because of the semi-arid conditions. The highest elemental concentrations corresponded to efflorescent crusts (Al = 55,584 μg/g; Mn = 36,619 μg/g; Cu = 90,366 μg/g; Zn = 35,391 μg/g; and Cd = 137 μg/g), followed by the 10 μm fraction of mine tailings (Al = 19,651 μg/g; Mn = 914 μg/g; Cu = 5,626 μg/g; Zn = 936 μg/g; Cd = 3.2 μg/g). Efflorescent crusts displayed the highest bioaccessible concentrations in the simulated fluids: gastric (Cu=100,356 μg/g), intestinal (Cu= 1,046 μg/g), Gamble solution (Mn= 28,210 μg/g), and artificial lysosomal fluids (Cu=74,131 μg/g). The findings confirm the health and environmental risk posed by efflorescent minerals from historic mine tailings in semi-arid regions.