Economic geology

Economic geology is concerned with earth materials that can be used for economic and/or industrial purposes. These materials include precious and base metals, nonmetallic minerals, construction-grade stone, petroleum, natural gas, coal, and water. Economic geology is a subdiscipline of the geosciences; according to Lindgren (1933) it is “the application of geology”. Today, it may be called the scientific study of the Earth's sources of mineral raw materials and the practical application of the acquired knowledge.[1] The term commonly refers to metallic mineral deposits and mineral resources. The techniques employed by other earth science disciplines (such as geochemistry, mineralogy, geophysics, petrology and structural geology) might all be used to understand, describe, and exploit an ore deposit.

Economic geology is studied and practiced by geologists. Economic geology may be of interest to other professions such as engineers, environmental scientists, and conservationists because of the far-reaching impact that extractive industries have on society, the economy, and the environment.

Arandis Mine quer
An open pit uranium mine in Namibia

Purpose of studies

The purpose of the study of economic geology is to gain understanding of the genesis and localization of ore deposits plus the minerals associated with ore deposits.[2] Though metals, minerals and other geologic commodities are non-renewable in human time frames, the impression of a fixed or limited stock paradigm of scarcity has always led to human innovation resulting in a replacement commodity substituted for those commodities which become too expensive. Additionally the fixed stock of most mineral commodities is huge (e.g., copper within the earth's crust given current rates of consumption would last for more than 100 million years.[3] Nonetheless, economic geologists continue to successfully expand and define known mineral resources.

Mineral resources

Mineral resources are concentrations of minerals significant for current and future societal needs. Ore is classified as mineralization economically and technically feasible for extraction. Not all mineralization meets these criteria for various reasons. The specific categories of mineralization in an economic sense are:

  • Mineral occurrences or prospects of geological interest but not necessarily economic interest
  • Mineral resources include those potentially economically and technically feasible and those that are not
  • Ore reserves, which must be economically and technically feasible to extract

Ore geology

Citrobacter freundii
Citrobacter species can have concentrations of uranium in their bodies 300 times higher than in the surrounding environment.

Geologists are involved in the study of ore deposits, which includes the study of ore genesis and the processes within the Earth's crust that form and concentrate ore minerals into economically viable quantities.

Study of metallic ore deposits involves the use of structural geology, geochemistry, the study of metamorphism and its processes, as well as understanding metasomatism and other processes related to ore genesis.

Ore deposits are delineated by mineral exploration, which uses geochemical prospecting, drilling and resource estimation via geostatistics to quantify economic ore bodies. The ultimate aim of this process is mining.

Coal and petroleum geology

Mudlogging
Mud log in process, a common way to study the lithology when drilling oil wells.
See main articles Coal and Petroleum geology

The study of sedimentology is of prime importance to the delineation of economic reserves of petroleum and coal energy resources.

See also

References

  1. ^ Pohl, W.L., 2011. Economic Geology, Principles and Practice: Metals, Minerals, Coal and Hydrocarbons – an Introduction to Formation and Sustainable Exploitation of Mineral Deposits. 663 Pages, Wiley-Blackwell, Oxford.
  2. ^ J. M. Gilbert and C. F. Park, Jr., 2007, The Geology of Ore Deposits, 985 pages, Waveband Press, Long Grove, IL
  3. ^ J.E. Tilton, 2010, "Is Mineral Depletion a threat to sustainable mining?", Society of Economic Geologists Newsletter, No. 82
Banded iron formation

Banded iron formations (also known as banded ironstone formations or BIFs) are distinctive units of sedimentary rock that are almost always of Precambrian age.

A typical banded iron formation consists of repeated, thin layers (a few millimeters to a few centimeters in thickness) of silver to black iron oxides, either magnetite (Fe3O4) or hematite (Fe2O3), alternating with bands of iron-poor shales and cherts, often red in color, of similar thickness, and containing microbands (sub-millimeter) of iron oxides.Some of the oldest known rock formations (having formed ca. 3,700 million years ago), are associated with banded iron formations. Banded iron formations account for more than 60% of global iron reserves, and can be found in Australia, Brazil, Canada, India, Russia, South Africa, Ukraine, and the United States.

Boxwork

In geology, boxwork can have two possible meanings. In cave geology, boxwork is an uncommon type of mineral structure, or speleogen (similar to a speleothem, but formed by erosion rather than accretion), occasionally found in caves and erosive environments. In mining geology, boxwork refers to quartz-lined cavities retaining the shape of the dissolved ore minerals in gossans.

Earth materials

Earth materials include minerals, rocks, soil and water. These are the naturally occurring materials found on Earth that constitute the raw materials upon which our global society exists. Earth materials are vital resources that provide the basic components for life, agriculture and industry. Earth materials can also include metals and precious rocks.

Eluvium

In geology, eluvium or eluvial deposits are those geological deposits and soils that are derived by in situ weathering or weathering plus gravitational movement or accumulation.

The process of removal of materials from geological or soil horizons is called eluviation or leaching. There is a difference in the usage of this term in geology and soil science. In soil science, eluviation is the transport of soil material from upper layers of soil to lower levels by downward precipitation of water across soil horizons, and accumulation of this material (illuvial deposit) in lower levels is called illuviation. In geology, the removed material is irrelevant, and the deposit (eluvial deposit) is the remaining material. Eluviation occurs when precipitation exceeds evaporation.

A soil horizon formed due to eluviation is an eluvial zone or eluvial horizon. In a typical soil profile, the eluvial horizon refers to a light-colored zone located (depending on context and literature) either at the lower part of the A horizon (symbol: Ae) or within a distinct horizon (E horizon) below the A, where the process is most intense and rapid. Yet some sources consider the eluvial zone to be the A horizon plus the (distinct) E horizon, as eluviation technically occurs in both.

The strict eluvial horizon (E horizon) is typically light gray, clay-depleted, contains little organic matter and has a high concentration of silt and sand particles composed of quartz and other resistant minerals.

Eluvial ore deposits are those such as tungsten and gold placer deposits formed by settling and enriched by the winnowing or removal of lower density materials. Diamonds within yellow ground (weathered portions of kimberlites) may be considered to be eluvial deposits. Cassiterite and columbite-tantalite deposits also occur as residual or eluvial concentrations. The Pitinga tin deposit in Brazil, an eluvial deposit, is one of the largest tin mines in the world. Weathering supergene enrichment of an apatite rich carbonatite in Ontario has produced a significant eluvial phosphate ore deposit.

Exploration geophysics

Exploration geophysics is an applied branch of geophysics and economic geology, which uses physical methods, such as seismic, gravitational, magnetic, electrical and electromagnetic at the surface of the Earth to measure the physical properties of the subsurface, along with the anomalies in those properties. It is most often used to detect or infer the presence and position of economically useful geological deposits, such as ore minerals; fossil fuels and other hydrocarbons; geothermal reservoirs; and groundwater reservoirs.

Exploration geophysics can be used to directly detect the target style of mineralization, via measuring its physical properties directly. For example, one may measure the density contrasts between the dense iron ore and the lighter silicate host rock, or one may measure the electrical conductivity contrast between conductive sulfide minerals and the resistive silicate host rock.

Geobotanical prospecting

Geobotanical prospecting refers to prospecting based on indicator plants like metallophytes and the analysis of vegetation. For example, the Viscaria Mine in Sweden was named after the plant Silene suecica (syn. Viscaria alpina) that was used by prospecters to discover the ore deposits.A "most faithful" indicator plant is Ocimum centraliafricanum, the "copper plant" or "copper flower" formerly known as Becium homblei, found only on copper (and nickel) containing soils in central to southern Africa.In 2015, Stephen E. Haggerty identified Pandanus candelabrum as a botanical indicator for kimberlite pipes, a source of mined diamonds.The technique has been used in China since in the 5th century BC. People in the region noticed a connection between vegetation and the minerals located underground. There were particular plants that throve on and indicated areas rich in copper, nickel, zinc, and allegedly gold though the latter has not been confirmed. The connection arose out of an agricultural interest concerning soil compositions. While the process had been known to the Chinese region since antiquity, it was not written about and studied in the west until the 18th century in Italy.

Geology of Egypt

The geology of Egypt includes rocks from Archaean - early Proterozoic times onwards. These oldest rocks are found as inliers in Egypt’s Western Desert. In contrast, the rocks of the Eastern Desert are largely late Proterozoic in age. Throughout the country this older basement is overlain by Palaeozoic sedimentary rocks. Cretaceous rocks occur commonly whilst sediments indicative of repeated marine transgression and regression are characteristic of the Cenozoic Era.

Gold mining

Gold mining is the resource extraction of gold by mining.

Jackson School of Geosciences

The Jackson School of Geosciences at The University of Texas at Austin unites the Department of Geological Sciences with two research units, the Institute for Geophysics and the Bureau of Economic Geology.

The Jackson School is both old and new. It traces its origins to a Department of Geology founded in 1888 but became a separate unit at the level of a college only on September 1, 2005. The school's formation resulted from gifts by the late John A. and Katherine G. Jackson initially valued at $272 million. The school's endowment as of December 31, 2015 is $442.3 million.Dr. Sharon Mosher is the Dean of the Jackson School of Geosciences.

Land rehabilitation

Land rehabilitation is the process of returning the land in a given area to some degree of its former state, after some process (industry, natural disasters, etc.) has resulted in its damage. Many projects and developments will result in the land becoming degraded, for example mining, farming and forestry.

Lode

In geology, a lode is a deposit of metalliferous ore that fills or is embedded in a fissure (or crack) in a rock formation or a vein of ore that is deposited or embedded between layers of rock.

The current meaning (ore vein) dates from the 17th century, being an expansion of an earlier sense of a "channel, watercourse" in late Middle English, which in turn is from the 11th-century meaning of lode as a ‘course, way’.The generally accepted hydrothermal model of lode deposition posits that metals dissolved in hydrothermal solutions (hot spring fluids) deposit the gold or other metallic minerals inside the fissures in the pre-existing rocks. Lode deposits are distinguished primarily from placer deposits, where the ore has been eroded out from its original depositional environment and redeposited by sedimentation. A third process for ore deposition is as an evaporite.

A stringer lode is one in which the rock is so permeated by small veinlets that rather than mining the veins, the entire mass of ore and the enveined country rock is mined. It is so named because of the irregular branching of the veins into many anastomosing stringers, so that the ore is not separable from the country rock.One of largest silver lodes was the Comstock Lode in Nevada, although it is overshadowed by the more recently discovered Cannington Lode in Queensland, Australia. The largest gold lode in the United States was the Homestake Lode. The Broken Hill Lode in South Australia is the largest lead-zinc lode ever discovered.

Mineralization (geology)

In geology, mineralization is the deposition of economically important metals in the formation of ore bodies or "lodes" by various process.

The first scientific studies of this process took place in the English county of Cornwall by J.W.Henwood FRS and later by R.W. Fox, FRS.The term can also refer to the process by which waterborne minerals, such as calcium carbonate (calcite), iron oxide (hematite or limonite) or silica (quartz), replace organic material within the body of an organism that has died and was buried by sediments.Mineralization may also refer to the product resulting from the process of mineralization. For example, mineralization (the process) may introduce metals (such as iron) into a rock. That rock may then be referred to as possessing iron mineralization.

Ore

An ore is a natural occurrence of rock or sediment that contains sufficient minerals with economically important elements, typically metals, that can be economically extracted from the deposit. The ores are extracted at a profit from the earth through mining; they are then refined (often via smelting) to extract the valuable element or elements.

The ore grade, or concentration of an ore mineral or metal, as well as its form of occurrence, will directly affect the costs associated with mining the ore. The cost of extraction must thus be weighed against the metal value contained in the rock to determine what ore can be processed and what ore is of too low a grade to be worth mining. Metal ores are generally oxides, sulfides, silicates, or native metals (such as native copper) that are not commonly concentrated in the Earth's crust, or noble metals (not usually forming compounds) such as gold. The ores must be processed to extract the elements of interest from the waste rock and from the ore minerals. Ore bodies are formed by a variety of geological processes. The process of ore formation is called ore genesis.

Petroleum geology

Petroleum geology is the study of origin, occurrence, movement, accumulation, and exploration of hydrocarbon fuels. It refers to the specific set of geological disciplines that are applied to the search for hydrocarbons (oil exploration).

Placer deposit

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, and paleoplacers.

Placer materials must be both dense and resistant to weathering processes. To accumulate in placers, mineral particles must be significantly denser than quartz (whose specific gravity is 2.65), as quartz is usually the largest component of sand or gravel. Placer environments typically contain black sand, a conspicuous shiny black mixture of iron oxides, mostly magnetite with variable amounts of ilmenite and hematite. Valuable mineral components often occurring with black sands are monazite, rutile, zircon, chromite, wolframite, and cassiterite.

Platinum group

The platinum-group metals (abbreviated as the PGMs; alternatively, the platinoids, platinides, platidises, platinum group, platinum metals, platinum family or platinum-group elements (PGEs)) are six noble, precious metallic elements clustered together in the periodic table. These elements are all transition metals in the d-block (groups 8, 9, and 10, periods 5 and 6).The six platinum-group metals are ruthenium, rhodium, palladium, osmium, iridium, and platinum. They have similar physical and chemical properties, and tend to occur together in the same mineral deposits. However they can be further subdivided into the iridium-group platinum-group elements (IPGEs: Os, Ir, Ru) and the palladium-group platinum-group elements (PPGEs: Rh, Pt, Pd) based on their behaviour in geological systems.The three elements above the platinum group in the periodic table (iron, nickel and cobalt) are all ferromagnetic, these being the only known transition metals with this property.

Prospecting

Prospecting is the first stage of the geological analysis (second – exploration) of a territory. It is the physical search for minerals, fossils, precious metals or mineral specimens, and is also known as fossicking.

Prospecting is a small-scale form of mineral exploration which is an organised, large scale effort undertaken by commercial mineral companies to find commercially viable ore deposits.

Prospecting is physical labour, involving traversing (traditionally on foot or on horseback), panning, sifting and outcrop investigation, looking for signs of mineralisation. In some areas a prospector must also make claims, meaning they must erect posts with the appropriate placards on all four corners of a desired land they wish to prospect and register this claim before they may take samples. In other areas publicly held lands are open to prospecting without staking a mining claim.

Salt evaporation pond

A salt evaporation pond is a shallow artificial salt pan designed to extract salts from sea water or other brines. Natural salt pans are geological formations that are also created by water evaporating and leaving behind salts. Some salt evaporation ponds are only slightly modified from their natural version, such as the ponds on Great Inagua in the Bahamas, or the ponds in Jasiira, a few kilometres south of Mogadishu, where seawater is trapped and left to evaporate in the sun.

The seawater or brine is fed into large ponds and water is drawn out through natural evaporation which allows the salt to be subsequently harvested.

The ponds also provide a productive resting and feeding ground for many species of waterbirds, which may include endangered species. The ponds are commonly separated by levees. Salt evaporation ponds may also be called salterns, salt works or salt pans.

Vein (geology)

In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation. The hydraulic flow involved is usually due to hydrothermal circulation.Veins are classically thought of as being the result of growth of crystals on the walls of planar fractures in rocks, with the crystal growth occurring normal to the walls of the cavity, and the crystal protruding into open space. This certainly is the method for the formation of some veins. However, it is rare in geology for significant open space to remain open in large volumes of rock, especially several kilometers below the surface. Thus, there are two main mechanisms considered likely for the formation of veins: open-space filling and crack-seal growth.

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