Elucidating Pathfinding Elements from the Kubi Gold Mine in Ghana

Abstract

X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) are applied to investigate the properties of fine-grained concentrates on artisanal, small-scale gold mining samples from the Kubi Gold Project of the Asante Gold Corporation near Dunwka-on-Offin in the Central Region of Ghana. Both techniques show that the Au-containing residual sediments are dominated by the host elements Fe, Ag, Al, N, O, Si, Hg, and Ti that either form alloys with gold or with inherent elements in the sediments. For comparison, a bulk nugget sample mainly consisting of Au forms an electrum, i.e., a solid solution with Ag. Untreated (impure) sediments, fine-grained Au concentrate, coarse-grained Au concentrate, and processed ore (Au bulk/nugget) samples were found to contain clusters of O, C, N, and Ag, with Au concentrations significantly lower than that of the related elements. This finding can be attributed to primary geochemical dispersion, which evolved from the crystallization of magma and hydrothermal liquids as well as the migration of metasomatic elements and the rapid rate of chemical weathering of lateralization in secondary processes. The results indicate that Si and Ag are strongly concomitant with Au because of their eutectic characteristics, while N, C, and O follow alongside because of their affinity to Si. These non-noble elements thus act as pathfinders for Au ores in the exploration area. This paper further discusses relationships between gold and sediments of auriferous lodes as key to determining indicator minerals of gold in mining sites.

Chemical bonding and valence states in Au-associated host minerals

“…These minerals consist of elemental components that form part of the mineral complexes and are believed to bond metallically, covalently, or form an alloy with gold. The chemical bonding and valence states of gold in the host minerals provide insights into the nature of gold mineralization and the mechanisms involved in the formation of gold deposits [30]. The ndings suggest that the oxidation state of Au is either Au 0 , Au 1+ , or Au 3+ depending on the speci c gold deposit and mineral composition.…”

“…On the other hand, the Au + 3 auric ion type bonds covalently and ionically, and as such, gold (III) ions form stable complexes with C, N, P, S, and O-donor ligands [30,31]. The average Au-S bond in pyrite (FeS 2 ) is 2.18-2.40 Å in agreement with literature [7], and the average Au-O bond in quartz (SiO 2 ) is 1.67-1.70 Å in agreement with the literature value of 1.67 Å [31] as listed in Table II.…”

Optical and electronic properties of pyrite

“…The hybridization between Fe 3d and S 3p states, creates a charge transfer excitation from the completely lled Fe 3d-t 2g orbitals to the empty Fe 3d-e g antibonding states. Therefore, a shift in the binding energy (E b ) along the e g states of empty orbitals will covalently bond to other ligands due to σ interactions [30][31][32]. Thus, by understanding the conductivity of surface and bulk conditions from the optical and electrical characterization of FeS 2 , it should be possible to improve the electrical properties for PV applications.…”

Characterization of Pathfinders and Indicators of Gold

“…From geological, geochemical, and mineralogical perspectives, it is essential to study the chemical bonding, flow mechanism, phase transformation, and transport properties of minerals to understand the efficiency of heat transfer and thermal structure of the earth's mantle as well as the dynamics and evolution of Earth and other terrestrial planets. To date, there have not been such studies on the Kubi concession, and this research aims to increase the knowledge of the rheological properties (material deformation), thermo-chemical structure, the kinetics of phase transformation, and thermal conductivity of minerals in this study area [16].…”