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Mineral exploration
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
Gossans are weathered varieties of rocks that contain substantial amounts of sulphide minerals such as matrix or massive sulfides. Gossans that are a product of weathering of iron-rich sulfides such as pyrite generally contain hematite, goethite, jarosite, whereas gossans that are a product of weathering of iron-poor sulfides such as galena and sphalerite tend to be siliceous. Gossans have typical fabrics such as boxwork and colloform, which allows their discrimination from other ferruginous regolith. Multi-element geochemistry of gossans is required as both target and pathfinder elements can be variably depleted in gossans due to intense leaching. The multi-element suites for various mineralisation types were tabulated by Taylor and Thornber (1992) and the use of multivariate statistical analysis techniques such as stepwise discriminant analysis are best suited to gossan geochemistry. The identification of gossans near or at the surface has led to the detection of several base metal deposits such as Broken Hill and Mt. Isa. Although gossans are less likely to be detected close to surface nowadays in exploration surveys, gossans may still be recognised in moderate to deeper transported cover via drilling.
Underground hard rock (metal/non-metal) mining
Published in A.J.S. (Sam) Spearing, Liqiang Ma, Cong-An Ma, Mine Design, Planning and Sustainable Exploitation in the Digital Age, 2023
A.J.S. (Sam) Spearing, Liqiang Ma, Cong-An Ma
During early prospecting and exploration in the field, geologists often look for specific indicators such as: Rust (Gossan) – Rust-coloured rocks or soil are one of the best indications of mineralization. Rust is caused by iron, which may indicate the presence of other metallic minerals. A variety of rust-coloured minerals exist. Copper sulphide is identified by green or blue stain, nickel sulphide by a pale green stain and uranium minerals may weather to bright yellow, orange or green stains.Quartz – Most sulphide mineral deposits are associated with quartz veins. Unless visible, gold and silver cannot be definitely determined without an assay test, but other metals such as copper, lead and zinc may be identified without an assay.Dykes – These are long thin bodies of igneous rock that, while in a molten state, flowed into cracks in older rocks. They stand out from the rock they flowed into and frequently contain or are associated with valuable minerals.Shear zones – A shear zone is a place of weakness or a break in the earth's crust through which mineralized solutions may have been channelled. From the air, they appear as long depressions or lines. Since they often contain quartz veins, they are a likely location of metallic minerals.
Integration of SPOT-5 and ASTER satellite data for structural tracing and hydrothermal alteration mineral mapping: implications for Cu–Au prospecting
Published in International Journal of Image and Data Fusion, 2018
Reyhaneh Ahmadirouhani, Mohammad-Hassan Karimpour, Behnam Rahimi, Azadeh Malekzadeh-Shafaroudi, Amin Beiranvand Pour, Biswajeet Pradhan
Iron oxide/hydroxide minerals, such as goethite, limonite, haematite and jarosite tend to have spectral absorption features in the visible to middle infrared from 0.4 to 1.1 μm of the electromagnetic spectrum (Sabins 1999). Iron oxides (gossan) are one of the important mineral groups that are associated with hydrothermally altered rocks. ASTER band 1 and 3 absorption features detect mainly Fe-oxides (Di Tommaso and Rubinstein 2006). Phyllic zone is characterised by illite/muscovite (sericite), which yields an intense Al-OH absorption feature cantered at 2.20 μm, coinciding with ASTER band 6. The argillic zone includes kaolinite and alunite, which collectively displays a secondary Al-OH absorption feature at 2.17 μm that correspond with ASTER band 5. The mineral assemblages of the propylitic zone include epidote, chlorite and calcite, which all exhibit Fe-Mg-OH and CO3 absorption features situated in the 2.35 μm, which coincide with ASTER band 8 (Mars and Rowan 2006, 2010, 2011, Rowan et al. 2006).
Geological setting of the Moorowie Formation, lower Cambrian Hawker Group, Mt Chambers Gorge, eastern Flinders Ranges, South Australia
Published in Australian Journal of Earth Sciences, 2020
T. J. Mount, J. B. Jago, N. R. Langsford, C. R. Dalgarno
Gossan species include the normal secondary malachite, azurite, cuprite, botryoidal chrysocolla and limonitic boxworks after chalcopyrite and other sulfides, while associated minerals may include milky quartz, colloform-to-crystalline calcite, siderite, pyrolusite, galena (some deformed), and possible cerussite, with specular hematite and slickensides in faults. The megabreccias of Unit 9 host minor disseminations of chalcopyrite and copper carbonates, with a highly selective silicification of some limestone boulders of greater purity that has proceeded along joints and faults.