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The Sn-W sulphide mineralizations of the southern end of the Villar del Ciervo granite; western Salamanca province, Spain.
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
R.M. Reguilón Bragado, A. Martín-Izard, A. Aguiar Ramos
The veins are mainly composed of quartz, with tourmaline, and smaller amounts of chlorites and, occasionally, feldspars, muscovite and fluorite as gangue minerals and Sn and W minerals (Cassiterite, wolframite and scheelite), sulphides (arsenopyrite, pyrrhotite, pyrite, marcasite, chalcopyrite, sphalerite, and bismuthinite) and native bismuth among the ore minerals. Finally, there are alteration minerals (scorodite, covellite and Fe and Ti oxides).
Our Earth, its minerals and ore bodies
Published in Odwyn Jones, Mehrooz Aspandiar, Allison Dugdale, Neal Leggo, Ian Glacken, Bryan Smith, The Business of Mining, 2019
Odwyn Jones, Mehrooz Aspandiar, Allison Dugdale, Neal Leggo, Ian Glacken, Bryan Smith
Hydrothermal activity involves the passage of aqueous solutions containing dissolved metallic elements through rocks. These fluids are derived either from depth (magmatism and/or metamorphism) or surface (meteoric, oceanic or connate–pore waters). Fluids derived from depth are sourced at pressures equal to lithostatic pressure but are overpressured with respect to fluids derived from the surface (e.g. groundwater) which have pressures close to hydrostatic. Fluid migration through rocks is enhanced by micro fracturing along grain boundaries in response to the pressure of the fluid. Fluids derived from depth tend to migrate upwards whereas those derived from the surface migrate laterally or convect. Products of hydrothermal fluid flow include hydrothermal alteration, veins and breccias. Hydrothermal alteration results in a change of chemical composition and mineralogy of the rock as a result of fluid interaction with existing minerals. The amount and nature of hydrothermal alteration depends on the permeability of the rock, existing mineralogy and the composition of the fluid. Veins develop as a result of fracturing of the rock due to either deformation or overpressured fluid. The opening of the fracture enables fluid to flow into the open space, which can trigger the crystallisation of certain minerals such as quartz and carbonate from solution. Breccias result when the pressure of the fluid exceeds lithostatic pressure, which can result in an explosive release of pressure and boiling of the fluid. Metallic elements dissolved within the fluid will precipitate either as a result of chemical reactions between the fluid and existing minerals or physical changes in the fluid in response to temperature or pressure fluctuations. Commonly ore deposits formed as a result of hydrothermal activity evolve over an extended time frame, sometimes in the order of > 100 million years. Hydrothermal ore deposits represent the most diverse style of mineralisation due to the variations in host rock lithology, metamorphic grade and degree of deformation and fluid composition.
Petroleum Geochemical Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
Sulfate ions (SO4)2– are represented by a structure in which four oxygen atoms occupy four corners of a tetrahedron with one sulfur atom at the center. This is similar to silicate ion (SiO4)4–. But the sulfate minerals do not undergo polymorphism or polymerization (repeated units of (SO4)–2 to form macromolecules, as silicate minerals do. The sulfate ion remains as a single unit. It is unable to form rings, sheets or frame networks as SiO44– ions do. The sulfate mineral is formed by any one of the following phenomena. Oxidation of sulfide (S2–) minerals and subsequent deposition as sulfate, during underground geo-thermodynamic circulation of formation water containing sulfide ions. Oxidation of minerals containing sulfide radicals, for example iron sulfide, to sulfate minerals in subsurface conditions.Water-soluble alkali or alkaline earth sulfates crystallize upon complete vaporization of sea water, forming solid sulfate deposits. The sulfate mineral is formed as evaporite deposits as hydrothermal veins in rock. A vein is a distinct sheet of crystallized mineral within rock. A vein is formed when a dissolved mineral is precipitated.With limited supply of water, a saturated solution of sulfate is formed, which is known as bittern or brine solution. Subsurface flowing water with soluble sulfate reacts with calcium ions in mud, clay and limestone to form metallic sulfate minerals such as alabaster, plaster of paris and gypsum (CaSO42H2O) minerals.‘Anhydrite mineral’ is a sulfate mineral chemically known as anhydrous calcium sulfate (CaSO4). The anhydride mineral deposit occurs in sedimentary strata from which sea water has been evaporated.
Accumulation and bioaccessibility of toxic metals in root tubers and soils from gold mining and farming communities in the Ashanti region of Ghana
Published in International Journal of Environmental Health Research, 2022
Godfred Darko, Samuel Adjei, Marian Asantewah Nkansah, Lawrence Sheringham Borquaye, Kwadwo Owusu Boakye, Matt Dodd
The study was carried out in four cluster communities (Figure 1) in the Ashanti Region of Ghana, namely; Akumadan (7°23ʹ45.72”N; 1°57ʹ14.08”W), Amansie Central (6°27ʹ47.70”N; 1°53ʹ15.92”W), Offinso (7°18ʹ17.71”N; 1°47ʹ34.22”W), Konongo (6°37ʹ29.80”N; 1°12ʹ26.37”W). The economy of Ashanti region (found in the southern part of Ghana) is driven primarily by extraction and processing of a diverse range of ores (including gold, manganese, and bauxite) and agricultural commodities (such as cocoa, coffee) and tuber crops such as yam, cassava and sweet potatoes (Darko et al. 2014). Gold mining began in the region more than 123 years ago, in 1897 (Mensah et al. 2020) when it was originally known as the Ashanti Mine. The veins consist mainly of quartz with carbonate minerals, green sericite, carbonaceous partings and metallic sulfides and arsenides of Fe, As, Zn, Au, Cu, Sb, and Pb (Dzigbodi-Adjimah 1993). Whereas Akumadan and Offinso are farming communities, Konongo and Amansie are well-noted artisanal gold mining areas where the artisanal activities are scattered all over the place.
Selecting support pillars in underground mines with ore veins
Published in IISE Transactions, 2020
Levente Sipeki, Alexandra M. Newman, Candace A. Yano
Our work was motivated by mining contexts in which the ore is concentrated in a system of very long, thin veins containing rock with high ore density, as is common for gold, silver, lead, zinc, nickel, and iron ore. Unlike mineral deposits involving soft substances such as coal, which are usually flat-lying, veins arise in hard rock and generally span a substantial vertical distance due to the way in which the deposits formed. For example, gold is deposited in the rock by the intrusion of hydrothermal solutions. The ore can nevertheless be extracted via the top-down open-stope mining method, under which the extraction progresses layer-by-layer in the downward direction, and on each layer in the mine, the extraction process creates open stopes (areas of void) while unextracted material provides structural integrity. For such a setting, mining companies conceptually divide the vein and the surrounding rock into three-dimensional rectangular blocks on the various layers; the pattern of blocks is generated by industry-standard design software. The mine design specifies which blocks should be extracted and processed into salable ore, thus creating open stopes, and which should be left behind as part of a pillar to provide geotechnical structural stability. We consider the problem of designing the high-level extraction plan (without detailed sequencing) for a mine in which top-down open-stope mining is used to extract the ore from hard rock. The typical objective is to maximize profit subject to geotechnical structural stability constraints. We call this the pillar selection problem. The resulting extraction plan is also useful for making decisions concerning mine infrastructure and equipment.
A review of the current state of knowledge on gold mineralisation in Benin Republic, West Africa
Published in Applied Earth Science, 2019
Fatchessin Bruno Adjo, Anthony Temidayo Bolarinwa, Luc Adissin Glodji, Franck Wilfried Nguimatsia Dongmo, Jerry Olugbenga Olajide-Kayode
In the basement (Bembèrèke, Djougou and Dunkassa Sheets) the quartz veins are also associated with tectonic zones. The proximity of the quartz veins and granitic masses is visible, and the veins often appear in the contact zones of granite with the surrounding formations. Thus, the emplacement of granitic masses plays a fundamental role in the formation of quartz veins especially in the zones of tectonic dislocation, which is in agreement with the study of Woodward (1993). The close connection between the quartz veins and the granite suggests that they are hydrothermal veins resulting from the injection of hydrothermal solutions related to granites in the fractured zones.