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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
Rocks exposed to meteoric waters at or near the Earth’s surface undergo chemical weathering of mineral constituents in the form of dissolution and leaching, hydrolysis and oxidation, and commonly these reactions are combined. The extent to which rocks are chemically weathered depends predominantly on the parent rock composition, climate and time. The resultant weathered rock is termed regolith. Ore deposits formed as a result of chemical weathering are called supergene. Supergene ore deposits develop either as: Residual (in situ) oresPrecipitation from shallow groundwatersSupergene enrichment Chemical weathering is enhanced in areas that have humid climates, which results in weathering to considerable depths and the production of a later-ite profile (Figure 1.11). The profile comprises several subhorizontal layers that reflect increasing intensity of hydrolysis, oxidation and dissolution of soluble minerals towards the surface. These processes cause enrichment of certain elements and depletion of others.
Function and status of structural geology in the Resource industry
Published in Australian Journal of Earth Sciences, 2023
Many, but not all, mineral deposit types are epigenetic and hence structurally controlled. Best known are lode gold deposits, and this epigenetic control extends to others such as basin Pb–Zn deposits (Keays et al., 1989; Sangster, 1996). Many mineral deposits that may be regarded syngenetic are controlled by structures, mostly high-level faults, such as epithermal and volcanogenic massive sulfides (Sibson, 1987; Vearncombe et al.,1998). Deposits such as Archean Ni, which are largely syngenetic volcanic, can show significant structural modification and in some cases upgrading (Perring, 2015). Iron ores are largely sedimentary syngenetic but with significant structural modification and fault–fracture controls on supergene upgrading (Angerer et al., 2017; Thorne et al.,2017). The orthodox ‘magma-syngenetic’ deposits such as porphyry Cu–Mo–Au are structure-controlled hydrothermal veins in solid brittle (cooled) intrusive host (Phillips et al., 2023; Piquer et al., 2021; Skarmeta, 2021). Structure is the major control, and structural geology an essential tool for finding, assessing and mining these deposits.
Review of Fracturing Techniques (Microwaves, High-Voltage Pulses, and Cryogenic Fluids) for Application as Access Creation Method in Low-Permeability Hard Rocks for Potential in situ Metal Recovery
Published in Mineral Processing and Extractive Metallurgy Review, 2023
Sahar Kafashi, Laura Kuhar, Andrej Bóna, Aleksandar N. Nikoloski
In tropical environments, gold may be leached from surface deposits by a fluid that descends through the material below and is then redeposited at an Eh or pH interface. Likewise, copper is leached during the oxidation of porphyry deposits near the surface, transported in descending fluids and reprecipitated as a chalcocite blanket at the Eh boundary. Such processes, which are termed ‘supergene enrichment’ by geologists, are a natural form of ISR. Supergene processes include the majority of meteoric water circulation (i.e. water derived from precipitation) with concomitant oxidation and chemical weathering (O’Gorman et al. 2004). The descending meteoric waters oxidize the primary (hypogene) sulfide ore minerals and redistribute the metallic ore elements. Metals that have been leached from the oxidized ore are carried downward by percolating groundwater and react with hypogene sulfides at the supergene-hypogene boundary. Examples are the strongly oxidized leached cap at Bisbee, Arizona or strongly oxidized leach caps developed in volcanoes that overlie the Porphyry Copper deposit at Red Mountain, Santa Cruz County, Arizona (Briggs, 2013).
Phanerozoic history of the Pilbara region: implications for iron mineralisation
Published in Australian Journal of Earth Sciences, 2022
C. S. Perring, J. M. A. Hronsky, M. Crowe
The Phanerozoic history of the Pilbara region provides important context for understanding iron-ore mineralisation because the majority of current iron-ore resources, namely the martite–goethite (M-G) and channel-iron deposit (CID) ores, formed during this period (see Danisik et al., 2013; Ramanaidou et al., 2019; Vasconcelos et al., 2013). Moreover, the genesis of both ore types was driven by near-surface geological processes (e.g. Morris & Ramanaidou, 2007; Perring et al., 2020). These processes fundamentally relate to sediment deposition and the downward infiltration of surface-derived water to produce both the regolith and supergene ore deposits. In turn, the two primary large-scale drivers of these surficial processes are the geodynamics of the craton and the paleoclimate.