Geochemical Characterization of Coexisting Precipitates and Waters From High-Sulfidation Epithermal Gold Deposits

Abstract

Water management and treatment at closed mine sites have become primary concerns for mining companies due to their costly nature, potential commitment of decades of water treatment, and impact on the environment. The long-term objective of this research investigates methods of extracting metals from acid mine waste in order to minimize the environmental impact of the drainage and decrease the financial burden on mining companies. However, understanding the mechanism of element mobility in mine waste requires a comprehensive assessment of the composition of the water and co-existing minerals at studied mines El Indio, Lagunas Norte and Pierina, which is the primary goal of this thesis. No study has previously provided a detailed analysis of the secondary precipitates at these mines or their role in storing trace elements.Water samples were analyzed by inductively coupled mass spectrometry and inductively coupled optical emission spectrometry. Coexisting mineral samples were characterized using an environmental scanning electron microscope, X-ray diffraction and synchrotron-based microanalysis. The pH of waters is acidic with values of 2.24 to 4.5. Major elements in waters include Ca, Al, Fe and SO4; minor elements include Cu, Mg, Mn, Zn, K, Na and trace elements consisted of As, Co, Ni, Sr, Pb and Cd. This study has identified previously unreported phases that may be placed into 3 broad groups: 1) hydrous Na-, Mg-, Ca, Cu-and other metal-sulfates such as blodite group minerals, hexahydrite and gypsum 2) Fe-oxides, oxyhydroxides and oxyhydroxysulfates such as ferrihydrite, goethite, scorodite and jarosite 3) other metal-rich, poorly crystalline Al phases. Synchrotron microanalysis has shown that these minerals sequester Cu, Mn, Zn, Cd, As, Ni and other trace elements. This research has improved the understanding of the mobility of elements by identifying the trace elements associated with minerals and by characterizing the relationship between chemistry of precipitates and solution. The occurrence of secondary precipitates stands as evidence purporting that sulfide oxidation at these mine sites is ongoing. Barrick Gold Corporation can consider capturing the sulfate-rich secondary precipitates by mechanically enhanced pond-evaporation and precipitation of efflorescent salts, methods which may allow to efficiently capture elements of interest.

Plant-minerals-water interactions: An investigation on Juncus acutus exposed to different Zn sources

“…After five months of plant-mineral-water interaction, XRD analysis did not show any bulk mineralogical variation between the initial substrates and the rhizospheres for both the CW and the ZnW (Table 2), but dissolution-precipitation reactions were active as demonstrated by the formation of efflorescent salts on the substrate surface. Gypsum and hexahydrite occurred as byproduct of sulfide mineral oxidation (Jambor et al, 2000;Manoukian, 2016). In our substrate samples, XRD analysis did not show sulfide phases but, probably, they were present below the detection limit of 1% by volume.…”