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Ore is natural rock or sediment that contains one or more valuable minerals concentrated above background levels, typically containing metals, that can be mined, treated and sold at a profit. The grade of ore refers to the concentration of the desired material it contains. The value of the metals or minerals a rock contains must be weighed against the cost of extraction to determine whether it is of sufficiently high grade to be worth mining and is therefore considered an ore. A complex ore is one containing more than one valuable mineral.
In geology, a placer deposit or placer is an accumulation of valuable minerals formed by gravity separation from a specific source rock during sedimentary processes. The name is from the Spanish word placer, meaning "alluvial sand". Placer mining is an important source of gold, and was the main technique used in the early years of many gold rushes, including the California Gold Rush. Types of placer deposits include alluvium, eluvium, beach placers, aeolian placers and paleo-placers.
Phosphorite, phosphate rock or rock phosphate is a non-detrital sedimentary rock that contains high amounts of phosphate minerals. The phosphate content of phosphorite (or grade of phosphate rock) varies greatly, from 4% to 20% phosphorus pentoxide (P2O5). Marketed phosphate rock is enriched ("beneficiated") to at least 28%, often more than 30% P2O5. This occurs through washing, screening, de-liming, magnetic separation or flotation. By comparison, the average phosphorus content of sedimentary rocks is less than 0.2%.
Ultramafic rocks are igneous and meta-igneous rocks with a very low silica content, generally >18% MgO, high FeO, low potassium, and are composed of usually greater than 90% mafic minerals. The Earth's mantle is composed of ultramafic rocks. Ultrabasic is a more inclusive term that includes igneous rocks with low silica content that may not be extremely enriched in Fe and Mg, such as carbonatites and ultrapotassic igneous rocks.
In soil science, podzols are the typical soils of coniferous or boreal forests and also the typical soils of eucalypt forests and heathlands in southern Australia. In Western Europe, podzols develop on heathland, which is often a construct of human interference through grazing and burning. In some British moorlands with podzolic soils, cambisols are preserved under Bronze Age barrows.
Carbonatite is a type of intrusive or extrusive igneous rock defined by mineralogic composition consisting of greater than 50% carbonate minerals. Carbonatites may be confused with marble and may require geochemical verification.
A soil horizon is a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features, mainly colour and texture. These may be described both in absolute terms and in terms relative to the surrounding material, i.e. 'coarser' or 'sandier' than the horizons above and below.
Porphyry copper deposits are copper ore bodies that are formed from hydrothermal fluids that originate from a voluminous magma chamber several kilometers below the deposit itself. Predating or associated with those fluids are vertical dikes of porphyritic intrusive rocks from which this deposit type derives its name. In later stages, circulating meteoric fluids may interact with the magmatic fluids. Successive envelopes of hydrothermal alteration typically enclose a core of disseminated ore minerals in often stockwork-forming hairline fractures and veins. Because of their large volume, porphyry orebodies can be economic from copper concentrations as low as 0.15% copper and can have economic amounts of by-products such as molybdenum, silver, and gold. In some mines, those metals are the main product.
Various theories of ore genesis explain how the various types of mineral deposits form within Earth's crust. Ore-genesis theories vary depending on the mineral or commodity examined.
Heavy mineral sands are a class of ore deposit which is an important source of zirconium, titanium, thorium, tungsten, rare-earth elements, the industrial minerals diamond, sapphire, garnet, and occasionally precious metals or gemstones.
The theory of biorhexistasy describes climatic conditions necessary for periods of soil formation (pedogenesis) separated by periods of soil erosion. Proposed by pedologist Henry Erhart in 1951, the theory defines two climatic phases: biostasy and rhexistasy.
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.
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.
A polymetallic replacement deposit, also known as carbonate replacement deposit or high-temperature carbonate-hosted Ag-Pb-Zn deposit, is an orebody of metallic minerals formed by the replacement of sedimentary, usually carbonate rock, by metal-bearing solutions in the vicinity of igneous intrusions. When the ore forms a blanketlike body along the bedding plane of the rock, it is commonly called a manto ore deposit. Other ore geometries are chimneys and veins. Polymetallic replacements/mantos are often stratiform wall-rock replacement orebodies distal to porphyry copper deposits, or porphyry molybdenum deposits. The term manto is derived from the Spanish word manto, meaning "mantle" or "cloak".
Illuvium is material displaced across a soil profile, from one layer to another one, by the action of rainwater. The removal of material from a soil layer is called eluviation. The transport of the material may be either mechanical or chemical. The process of deposition of illuvium is termed illuviation. It is a water-assisted transport in a basically vertical direction, as compared to alluviation, the horizontal running water transfer. The resulting deposits are called illuvial deposits. Cutans are a type of illuvial deposit.
The Canadian System of Soil Classification is more closely related to the American system than any other, but they differ in several ways. The Canadian system is designed to cover only Canadian soils. The Canadian system dispenses with the sub-order hierarchical level. Solonetzic and Gleysolic soils are differentiated at the order level.
In pedology, leaching is the removal of soluble materials from one zone in soil to another via water movement in the profile. It is a mechanism of soil formation distinct from the soil forming process of eluviation, which is the loss of mineral and organic colloids. Leached and eluviated materials tend to be lost from topsoil and deposited in subsoil. A soil horizon accumulating leached and eluviated materials is referred to as a zone of illuviation.
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.
Mount Ngualla, often referred to simply as Ngualla, is a collapsed volcano located in the remote south west of Tanzania. It is approximately 200 km north of the Mbeya township.
Regolith-hosted rare earth element deposits are rare-earth element (REE) ores in decomposed rocks that are formed by intense weathering of REE-rich parental rocks in subtropical areas. In these areas, rocks are intensely broken and decomposed. Then, REEs infiltrate downward with rain water and they are concentrated along a deeper weathered layer beneath the ground surface.
References
- ↑ "Glossary of Soil Science Terms". Soil Science Society of America. Archived from the original on 2006-09-27. Retrieved 2006-11-10.
- ↑ "Glossary of Terms". PhysicalGeography.net. Retrieved 2006-11-11.
- Gupta, Chiranjib Kumar (2002) Chemical Metallurgy: Principles and Practice, Wiley, ISBN 3-527-30376-6
- Cronan, David Spencer (1999) Handbook of Marine Mineral Deposits, CRC Press, ISBN 0-8493-8429-X
- Swiecki, Rafal (2006) Eluvial Placers Accessed 18 April 2006
- Van Hees, Edmond H., (2002) Supergene Phosphate Enrichment in Carbonatite-Derived Eluvial Sediments: Agrium Phosphate Mine, Kapuskasing, Ontario, Canada, The Geological Society of America (GSA) abstract. Archived 2016-10-21 at the Wayback Machine Accessed 18 April 2006
