Mineralogy and silver distribution in argentiferous manganese ores from la encantada mines in Mexico
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abstract
Various Ag-Mn ore samples from La Encantada Mines in Mexico, were mineralogically characterized by XRD, SEM and TEM. The major minerals in the ore samples were found to be calcite (CaCO3), pyrosulite (MnO2), johannsenite (CaMn(Si2O6)), quenselite (2PbO Mn2O3 H2O), cerussite (PbCO3) and hematite (Fe2O3). TEM studies revealed no silver in the crystal lattice of the manganese oxides neither in their pores. SEM showed silver in the ore as native silver (Ag), acanthite (Ag2S), cerargyrite (AgCl), embolite (Ag(Cl,Br)) and freibergite ((Ag,Fe,Zn,Cu)12Sb2S13). These Ag minerals with a size of less than 5 μm were found to be occluded in the manganese oxides and hematite. Silver recovery by cyanide leaching was evaluated for the as-received ore samples and the samples free of carbonates, manganese oxide and iron oxides. The silver distribution in these mineral components of the ores was determined by selective leaching. Silver was found to be mostly distributed in manganese oxides with a lesser percentage in Fe2O3 and CaCO3. Very low silver recovery resulted from the as-received samples because of a high encapsulation level of the silver minerals in the manganese oxides and Fe2O3. Silver recovery significantly improved through fine grinding of the ore samples and dissolution of the manganese oxides from the samples.
