Characterization of Pathfinders and Indicators of Gold

Sammanfattning: Research on natural minerals and their chemical bonding to economically critical raw materials is a viable industrially relevant research area due to its increasing demand. Meeting demands requires fast, robust, and efficient techniques to explore new ore deposits and continuous operation of active mines as well as recycling. One of the most critical metals is gold which occurs in three main types of ore deposits: i) hydrothermal quartz veins and related deposits in metamorphic and igneous rocks; ii) volcanic-exhalative sulfide deposits, and iii) consolidated to unconsolidated placer deposits. Gold is commonly found as disseminated grains in quartz veins in pyrite and other sulfides or as rounded grains, flakes or nuggets in deposits in riverbanks, in contact with metamorphic or hypothermal deposits (e.g., skarns) or epithermal deposits such as volcanic fumaroles. Pathfinder elements and indicator minerals provide means to explore large areas for their potential mineral commodities such as gold, diamond, base metals, platinum group of elements, and rare earth elements by narrowing the search area to reduce exploration costs. The recent technological advancement in obtaining rapid geochemical results using field portable analytical devices as alternatives to the old approach where collected field samples are carried to the laboratory calls for further investigation to explore other techniques in mineral and metal exploration.In this Thesis, I investigate the properties of artisanal small-scale gold mining concentrate, outcrop, bulk Au, and drill hole samples from the Kubi Gold Project of the Asante Gold Corporation near Dunkwa-on-Offin in the Central Region of Ghana with a materials science perspective. X-ray diffraction (XRD) is used to identify SiO2 (quartz), Fe3O4 (magnetite), garnet, pyrite (FeS2), periclase (MgO), arsenopyrites, pyrrhotite, biotite, titanium oxide, and Fe2O3 (hematite) as the main indicator minerals in the mining site with less significant contributions from chalcopyrite, iridosmine, scheelite, tetradymite, gypsum, and a few other sulfates. X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) indicate that Fe, Ag, Al, N, O, Si, Hg, C, Ba, P, Ca, Mg, Na, Mn, Cl, S, K, and Ti are important host elements that form alloys with Au or are inherent in the sediment at the concession site. The results also indicate that Si and Ag are in strong co-occurrence with Au due to their eutectic qualities, while N, C, and O occur due to their attraction to Si. Also, the XPS results indicate that the relationship between Au and pathfinder elements or indicator minerals depends on the d-orbital of Au and other elements that possess octahedral or tetrahedral geometry to split into two states, eg and t2g that can acquire either higher or lower energy depending on the geometry and are responsible for the covalent, metallic, and ionic states of Au with other ligands. From the air anneal furnace (AAF) and differential scanning calorimetry (DSC), I investigated the transformations in quartz and pyrite minerals that alter to hematite minerals. The quartz samples are observed to transform from α-quartz to β-quartz and finally to cristobalite while the pyrite transforms to magnetite and later to hematite. These findings suggest that during the hydrothermal flow regime impurity materials are trapped by voids and faults and can be altered at different depositional stages by oxidation and reduction processes. Results from the scanning electron microscopy (SEM) revealed the presence of carbonates in fracture zones in the quartz, pyrite, and almandine-type garnet mineral in gabbroic rocks.The findings indicate that, from the top of the oxide zone, grains within sediments are seen to be controlled by quartz, and hematite, the bedrock consists of pyrite and pyrrhotite, and the orebody contains garnet, arsenopyrite, periclase, and biotite as pathfinder minerals within the concession area. Therefore, the Au mineralogy of the alluvial environment that is mined by artisanal small-scale miners is traced from the chemical weathering reaction of garnet minerals from the orebody that produces fractions of other indicator minerals as by-products in the Kubi mining area. These findings also indicate that primary geochemical dispersion evolving from the crystallization of magma and hydrothermal liquids are the main attributes and constitute the identification of indicator minerals and pathfinding elements in this mineralogical study area.Furthermore, the findings suggest that XRD, XPS, TEM, and EDX could be combined in other mineralogical laboratories to aid in identifying indicator minerals of Au and the location of ore bodies, to increase the knowledge in this field, and reduce environmental and exploration costs.