In ore deposit geology, supergene processes or enrichment are those that occur relatively near the surface as opposed to deep hypogene processes. Supergene processes include the predominance of meteoric water circulation (i.e. water derived from precipitation) with concomitant oxidation and chemical weathering. The descending meteoric waters oxidize the primary (hypogene) sulfide ore minerals and redistribute the metallic ore elements. Supergene enrichment occurs at the base of the oxidized portion of an ore deposit. 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. The reaction produces secondary sulfides with metal contents higher than those of the primary ore. This is particularly noted in copper ore deposits where the copper sulfide minerals chalcocite (Cu2S), covellite (CuS), digenite (Cu18S10), and djurleite (Cu31S16) are deposited by the descending surface waters. [1]
All such processes take place at essentially atmospheric conditions, around room temperature (25 °C) and standard atmospheric pressure (1 atm). [2]
Distinct zones of supergene processes can be identified at various depths. From the surface down they are the gossan cap, leached zone, oxidized zone, water table, enriched zone (supergene enriched zone) and primary zone (hypogene zone). [3]
Pyrite (FeS2) has oxidised to form goethite (FeO(OH)) and limonite (FeO(OH)·nH2O), [2] which form a porous covering over the oxidized zone known as a gossan cap or iron hat. [4] Prospectors use gossan as an indication of ore reserves.
Groundwater contains dissolved oxygen and carbon dioxide. As it travels downwards it oxidizes primary sulfide minerals, concomitant with forming sulfuric acid and solutions of oxidized metals. [5] For example, groundwater commonly interacts with pyrite (FeS2) to form an oxidized iron (FeO(OH)) and sulfuric acid (H2SO4), portrayed in the idealized chemical reaction below (intermediate steps omitted):
An intermediate in this process is ferric sulfate (Fe2(SO4)3), which oxidizes pyrite and other sulfide minerals. [6]
Above the water table the environment is oxidizing, and below it is reducing. [7] Solutions traveling downward from the leached zone react with other primary minerals in the oxidised zone to form secondary minerals [5] such as sulfates and carbonates, and limonite, which is a characteristic product in all oxidised zones. [3]
In the formation of secondary carbonates, primary sulfide minerals generally are first converted to sulfates, which in turn react with primary carbonates such as calcite (CaCO3), dolomite (CaMg(CO3)2) or aragonite (also CaCO3, polymorphic with calcite) to produce secondary carbonates. [4] Soluble salts continue on down, but insoluble salts are left behind in the oxidised zone where they form. Examples of insoluble salts that are commonly found in the oxidized zone include lead precipitates like anglesite (PbSO4) and pyromorphite (Pb5(PO4)3Cl); copper precipitates like malachite (Cu2(CO3(OH)2), azurite (Cu3(CO3)2(OH)2), and cuprite (Cu2O); and smithsonite (ZnCO3). [3] [7]
At the water table the environment changes from an oxidizing environment to a reducing one. [7]
Copper ions that move down into this reducing environment form a zone of supergene sulfide enrichment. [3] Covellite (CuS), chalcocite (Cu2S) and native copper (Cu) are stable in these conditions [7] and they are characteristic of the enriched zone. [3]
The net effect of these supergene processes is to move metal ions from the leached zone to the enriched zone, increasing the concentration there to levels higher than in the unmodified primary zone below, possibly producing a deposit worth mining.
The primary zone contains unaltered primary minerals. [5]
Chalcopyrite CuFeS2 (primary) readily alters to the secondary minerals bornite Cu5FeS4, covellite CuS and brochantite Cu4SO4(OH)6. [5]
Galena PbS (primary) alters to secondary anglesite PbSO4 and cerussite PbCO3. [2] [5]
Sphalerite ZnS (primary) alters to secondary hemimorphite Zn4Si2O7(OH)2.H2O, smithsonite ZnCO3 and manganese-bearing willemite Zn2SiO4. [2] [5]
Pyrite FeS2 (primary) alters to secondary melanterite FeSO4.7H2O. [5]
If the original deposits contain arsenic and phosphorus bearing minerals, secondary arsenates and phosphates will be formed. [5]
The word supergene is derived from the Latin root super meaning 'above' and the Greek root -gene ( -γενής ) meaning 'born' or 'produced'. The terms supergene and hypogene refer to the depth at which they occur.
Bioleaching is the extraction or liberation of metals from their ores through the use of living organisms. Bioleaching is one of several applications within biohydrometallurgy and several methods are used to treat ores or concentrates containing copper, zinc, lead, arsenic, antimony, nickel, molybdenum, gold, silver, and cobalt.
Extractive metallurgy is a branch of metallurgical engineering wherein process and methods of extraction of metals from their natural mineral deposits are studied. The field is a materials science, covering all aspects of the types of ore, washing, concentration, separation, chemical processes and extraction of pure metal and their alloying to suit various applications, sometimes for direct use as a finished product, but more often in a form that requires further working to achieve the given properties to suit the applications.
Chalcopyrite ( KAL-kə-PY-ryte, -koh-) is a copper iron sulfide mineral and the most abundant copper ore mineral. It has the chemical formula CuFeS2 and crystallizes in the tetragonal system. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mohs scale. Its streak is diagnostic as green-tinged black.
Bornite, also known as peacock ore, is a sulfide mineral with chemical composition Cu5FeS4 that crystallizes in the orthorhombic system (pseudo-cubic).
Chalcanthite (from Ancient Greek χάλκανθον (khálkanthon), from χαλκός (khalkós) 'copper' and ἄνθος (ánthos) 'flower, bloom') is a richly colored blue-green water-soluble sulfate mineral CuSO4·5H2O. It is commonly found in the late-stage oxidation zones of copper deposits. Due to its ready solubility, chalcanthite is more common in arid regions.
Chalcocite, copper(I) sulfide (Cu2S), is an important copper ore mineral. It is opaque and dark gray to black, with a metallic luster. It has a hardness of 2.5–3 on the Mohs scale. It is a sulfide with a monoclinic crystal system.
Covellite is a rare copper sulfide mineral with the formula CuS. This indigo blue mineral is commonly a secondary mineral in limited abundance and although it is not an important ore of copper itself, it is well known to mineral collectors.
Kambalda type komatiitic nickel ore deposits are a class of magmatic iron-nickel-copper-platinum-group element ore deposit in which the physical processes of komatiite volcanology serve to deposit, concentrate and enrich a Fe-Ni-Cu-(PGE) sulfide melt within the lava flow environment of an erupting komatiite volcano.
Digenite is a copper sulfide mineral with formula: Cu9S5. Digenite is a black to dark blue opaque mineral that crystallizes with a trigonal–hexagonal scalenohedral structure. In habit it is usually massive, but does often show pseudo-cubic forms. It has poor to indistinct cleavage and a brittle fracture. It has a Mohs hardness of 2.5 to 3 and a specific gravity of 5.6. It is found in copper sulfide deposits of both primary and supergene occurrences. It is typically associated with and often intergrown with chalcocite, covellite, djurleite, bornite, chalcopyrite and pyrite. The type locality is Sangerhausen, Thuringia, Germany, in copper slate deposits.
Gaspéite, a very rare nickel carbonate mineral, with the formula (Ni,Fe,Mg)CO3, is named for the place it was first described, in the Gaspé Peninsula, Québec, Canada.
Kambaldaite, NaNi4(CO3)3(OH)3·3H2O, is an extremely rare hydrated sodium nickel carbonate mineral described from gossaniferous material associated with Kambalda type komatiitic nickel ore deposits at Kambalda, Western Australia, and Widgie Townsite nickel gossan, Widgiemooltha, Western Australia.
Violarite (Fe2+Ni23+S4) is a supergene sulfide mineral associated with the weathering and oxidation of primary pentlandite nickel sulfide ore minerals.
Polydymite, Ni2+Ni23+S4, is a supergene thiospinel sulfide mineral associated with the weathering of primary pentlandite nickel sulfide.
Concrete degradation may have many different causes. Concrete is mostly damaged by the corrosion of reinforcement bars due to the carbonatation of hardened cement paste or chloride attack under wet conditions. Chemical damage is caused by the formation of expansive products produced by chemical reactions, by aggressive chemical species present in groundwater and seawater, or by microorganisms Other damaging processes can also involve calcium leaching by water infiltration, physical phenomena initiating cracks formation and propagation, fire or radiant heat, aggregate expansion, sea water effects, leaching, and erosion by fast-flowing water.
Saprolite is a chemically weathered rock. Saprolites form in the lower zones of soil profiles and represent deep weathering of the bedrock surface. In most outcrops, its color comes from ferric compounds. Deeply weathered profiles are widespread on the continental landmasses between latitudes 35°N and 35°S.
In ore deposit geology, hypogene processes occur deep below the Earth's surface, and tend to form deposits of primary minerals, as opposed to supergene processes that occur at or near the surface, and tend to form secondary minerals.
Rampgill mine is a disused lead mine at Nenthead, Alston Moor, Cumbria, England UK Grid Reference: NY78184351
Polymetallic ores or multimetal ores are complex ores containing a number of chemical elements, among which the most important are lead and zinc. In addition, polymetallic ores can contain copper, gold, silver, cadmium, sometimes bismuth, tin, indium and gallium. The main minerals that form polymetallic ores are galena, sphalerite, to a lesser extent pyrite, chalcopyrite, arsenopyrite, cassiterite. They are most commonly formed from sulfides but also include oxides.
Chvilevaite (Russian: чвилеваи́т, чвилёваи́т, in its own name) is a rare hydrothermal polymetallic mineral from the class of complex sulfides, forming microscopic grains in related minerals, its composition is a rare combination of alkali (combining lithophile) and chalcophile metals — sodium ferro-sulfide, zinc and copper with the calculation formula Na(Cu,Fe,Zn)2S4, originally published and confirmed as Na(Cu,Fe,Zn)2S2.