Servolab Science News N°2: The Gold Association

ABSTRACT

A mineralogical association of gold (Au) was established in three (3) geological samples from the southeastern area of the Bolivar state, Venezuela, using a sequential open-vessel acid digestion process with 1.00 mol/L hydrochloric acid (HCl); concentrated nitric acid (HNO3) and aqua regia (HCl:HNO3, 3:1). The percentage of Au recovery in each extracted fraction was estimated by flame atomic absorption spectrometry (FAAS). The HCl fraction did not show the presence of Au; while in the HNO3 fraction the recovery was in the order of 12.38% for zone 1; 0.87% for zone 2 and 4.00% for zone 3. Through the identification of the mineralogical phases by X-ray diffraction (XRD) of the original samples, it was established that approximately 50.00% of the samples corresponded to ferro-dolomite. The analysis of the solid residues obtained from each digestion determined that this mineral together with calcite react with HCl (present in zone 3) and with HNO3 react pyrite and chlorite-serpentine; remaining unreacted the silicates: quartz, albite, muscovite, microcline and orthoclase, which, as expected, did not react in aqua regia either. By scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS), the distribution of the minerals in the samples under study could be established and correlated with the XRD results. The studies carried out established that most of the Au in the studied areas are found, mostly, associated with the silicate phases.

Key words: Gold, sequential extraction, acid digestion, acid digestion