Effects of waste deposit geometry on the mineralogical and geochemical composition of mine tailings.

The study tailing pond shows a particular geometry resulting from the tailings stockpiles deposited onto the northern part of the beach. This generated three types of superficial waste: (i) tailings of the stockpiles (A-type) (pH=2.2-2.6; soluble fraction average - SF=14.2%), subjected to intense oxidation and evaporation; (ii) tailings of the lowlands of waste, characterized by low oxidation and no evaporation (B-type) (pH=2.7-3.1; SF=7.7%); (iii) salt crusts (C-type) (pH=2.6-3.5; SF=81.5%), formed by the evaporation of leachates accumulated in stagnant pools. Principal Component Analysis (PCA) showed the following sequences of secondary minerals precipitation: A-type waste (I - ferricopiapite, rozenite, ferrihydrite; II - jarosite, coquimbite); B-type (I - Fe oxyhydroxides; II - jarosite, butlerite); C-type (I - ferrihydrite, rozenite; II - alunogen, hexahydrite, epsomite). PCA also revealed that the abundance of Al (1-10% AlO in A and B wastes; 1-5% in C waste) is particularly controlled by primary silicates and clay minerals. Iron (11-23% FeO in A and B wastes; 5-10% in C waste) is almost exclusively related to pyrite, ferrihydrite, and goethite. Moreover, Zn and Cd were collected by halotrichite, rozenite, jarosite, ferricopiapite, and apjohnite, whereas the clay minerals seem to trap selectively Cu, Pb and As in their structure.