GEOLOGY

Geology (from Greek γη- (ge-, "the earth") and λογος (logos, "word", "reason")) is the science and study of the Earth, its composition, structure, physical properties, history and the processes that shape it. It is one of the Earth sciences. Geologists have helped establish the age of the Earth at about 4.6 billion (4.6x109) years, and have determined that the Earth's lithosphere, which includes the crust, is fragmented into tectonic plates that move over a rheic upper mantle (asthenosphere) via processes that are collectively referred to as plate tectonics. Geologists help locate and manage the earth's natural resources, such as petroleum and coal, as well as metals such as iron, copper, and uranium. Additional economic interests include gemstones and many minerals such as asbestos, perlite, mica, phosphates, zeolites, clay, pumice, quartz, and silica, as well as elements such as sulfur, chlorine, and helium. Astrogeology refers to the application of geologic principles to other bodies of the solar system. However, specialised terms such as selenology (studies of the Moon), areology (of Mars), etc., are also in use. The word "geology" was first used by Jean-André Deluc in the year 1778 and introduced as a fixed term by Horace-Bénédict de Saussure in the year 1779. An older meaning of the word was first used by Richard de Bury. He used it to distinguish between earthly and theological jurisprudence.

Contents 1 History

2 Important principles of geology 3 Fields or related disciplines

4 Regional geology 4.1 By Nations

5 Planetary geology 6 See also

7 External links History In China, the polymath Shen Kua (1031 - 1095) formulated a hypothesis for the process of land formation: based on his observation of fossil shells in a geological stratum in a mountain hundreds of miles from the ocean, he inferred that the land was formed by erosion of the mountains and by deposition of silt. The work on rocks Peri lithon by Theophrastus, a student of Aristotle, remained authoritative for millennia. Its interpretation of fossils was not overturned until after the Scientific Revolution. It was translated into Latin and the other languages of Europe such as French. Georg Bauer (Georg Agricola), a physician, summarised the knowledge of mining and metallurgy in 1556. Georg Agricola (1494-1555) wrote the first systematic treatise about mining and smelting works, De re metallica libri XII, with an appendix Buch von den Lebewesen unter Tage (Book of the Creatures Beneath the Earth). He covered subjects like wind energy, hydrodynamic power, melting cookers, transport of ores, extraction of soda, sulfur and alum, and administrative issues. The book was published in 1556. Nicolaus Steno (1638-1686) is credited with the law of superposition, the principle of original horizontality, and the principle of lateral continuity: three defining principles of stratigraphy.

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By the 1700s Jean-Etienne Guettard and Nicolas Desmarest hiked central France and recorded their observations on geological maps; Guettard recorded the first observation of the volcanic origins of this part of France. James Hutton recorded his Theory of the Earth in the 1788 Transactions of the Royal Society of Edinburgh, later called uniformitarianism. William Smith (1769-1839) drew some of the first geological maps and began the process of ordering rock strata (layers) by examining the fossils contained in them. James Hutton is often viewed as the first modern geologist. In 1785 he presented a paper entitled Theory of the Earth to the Royal Society of Edinburgh. In his paper, he explained his theory that the Earth must be much older than had previously been supposed in order to allow enough time for mountains to be eroded and for sediment to form new rocks at the bottom of the sea, which in turn were raised up to become dry land. Followers of Hutton were known as Plutonists because they believed that some rocks were formed by vulcanism which is the deposition of lava from volcanoes, as opposed to the Neptunists, who believed that all rocks had settled out of a large ocean whose level gradually dropped over time. In 1811 Georges Cuvier and Alexandre Brongniart published their explanation of the antiquity of the Earth, inspired by Cuvier's discovery of fossil elephant bones in Paris. To prove this, they formulated the principle of stratigraphic succession of the layers of the earth. They were independently anticipated by William Smith's stratigraphic studies on England and Scotland. Sir Charles Lyell first published his famous book, Principles of Geology, in 1830 and continued to publish new revisions until he died in 1875. He successfully promoted the doctrine of uniformitarianism. This theory states that slow geological processes have occurred throughout the Earth's history and are still occurring today. In contrast, catastrophism is the theory that Earth's features formed in single, catastrophic events and remained unchanged thereafter. Though Hutton believed in uniformitarianism, the idea was not widely accepted at the time. Plate tectonics - seafloor spreading and continental drift illustrated on relief globe of the Field MuseumBy 1827 Charles Lyell's Principles of Geology reiterated Hutton's uniformitarianism, which influenced the thought of Charles Darwin. 19th Century geology revolved around the question of the Earth's exact age. Estimates varied from a few 100,000 to billions of years. The most significant advance in 20th century geology has been the development of the theory of plate tectonics in the 1960s. Plate tectonic theory arose out of two separate geological observations: seafloor spreading and continental drift. The theory revolutionised the Earth sciences. The theory of continental drift was proposed by Alfred Wegener in 1912 and by Arthur Holmes, but wasn't broadly accepted until the 1960s when the theory of plate tectonics was developed. Important principles of geology There are a number of important principles in geology. Many of these involve the ability to provide the relative ages of strata or the manner in which they were formed. The Principle of Intrusive Relationships concerns crosscutting intrusions. In geology, when an igneous intrusion cuts across a formation of sedimentary rock, it can be determined that the

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igneous intrusion is younger than the sedimentary rock. There are a number of different types of intrusions, including stocks, laccoliths, batholiths, sills and dikes. The Principle of Cross-cutting Relationships pertains to the formation of faults and the age of the sequences through which they cut. Faults are younger than the rocks they cut; accordingly, if a fault is found that penetrates some formations but not those on top of it, then the formations that were cut are older than the fault, and the ones that are not cut must be younger than the fault. Finding the key bed in these situations may help determine whether the fault is a normal fault or a thrust fault. The Principle of Inclusions and Components states that, with sedimentary rocks, if inclusions (or clasts) are found in a formation, then the inclusions must be older than the formation that contains them. For example, in sedimentary rocks, it is common for gravel from an older formation to be ripped up and included in a newer layer. A similar situation with igneous rocks occurs when xenoliths are found. These foreign bodies are picked up as magma or lava flows, and are incorporated, later to cool in the matrix. As a result, xenoliths are older than the rock which contains them. The Principle of Uniformitarianism states that, the geologic processes observed in operation that modify the Earth's crust at present have worked in much the same way over geologic time. A fundamental principle of geology advanced by the 18th century Scottish physician and geologist James Hutton, is that "The Present is the Key to the Past." In Hutton's words: "the past history of our globe must be explained by what can be seen to be happening now." The Principle of Original Horizontality states that, the deposition of sediments occurs as essentially horizontal beds. Observation of modern marine and nonmarine sediments in a wide variety of environments supports this generalisation (although cross-bedding is inclined, the overall orientation of cross-bedded units is horizontal). The Principle of Superposition states that, a sedimentary rock layer in a tectonically undisturbed sequence is younger than the one beneath it and older than the one above it. Logically a younger layer cannot slip beneath a layer previously deposited. This principle allows sedimentary layers to be viewed as a form of vertical time line, a partial or complete record of the time elapsed from deposition of the lowest layer to deposition of the highest bed. The Principle of Faunal Succession is based on the appearance of fossils in sedimentary rocks. As organisms exist at the same time period throughout the world, their presence or (sometimes) absence may be used to provide a relative age of the formations in which they are found. Based on principles laid out by William Smith almost a hundred years before the publication of Charles Darwin's theory of evolution, the principles of succession were developed independently of evolutionary thought. The principle becomes quite complex, however, given the uncertainties of fossilisation, the localisation of fossil types due to lateral changes in habitat (facies change in sedimentary strata), and that not all fossils may be found globally at the same time. Economic geology Economic geology is concerned with earth materials that can be utilized for economic and/or industrial purposes. These materials include precious and base metals, nonmetallic minerals, construction-grade stone, petroleum minerals, coal, and water. The term commonly refers to metallic mineral deposits and mineral resources. The techniques employed by other earth science disciplines (such as geochemistry, mineralogy, geophysics, and structural geology) might all be used to understand, describe, and exploit an ore deposit.

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Economic geology is studied by and practised by geologists, however it is of prime interest to investment bankers, stock analysts and other professions such as engineers, environmental scientists and conservationists because of the far-reaching impact which extractive industries have upon society, the economy and the environment.

Contents 1 Mineral resources

2 Ore geology 3 Coal and petroleum geology

4 Reference 5 See also

Mineral resources See main article: Mineral resource classification Mineral resources are concentrations of minerals which are of note for current and future societal needs. Ore is classified as mineralisation economically and technically feasible for extraction. Not all mineralisation meets these criteria for various reasons. The specific categories of mineralization in an economic sense are: mineral occurrences or prospects which are of geological interest but may not be economic interest mineral resources, include those which are potentially economically and technically feasible, and those which are not ore reserves, must be economically and technically feasible to extract Ore geology Geologists are involved in the study of ore deposits, which includes the study of ore genesis and the processes within the Earth's crust which 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 utilises geochemistry prospecting, drilling and resource esimation via geostatistics to quantify economic ore bodies. The ultimate aim of this process is mining. Mineral resource classification From Wikipedia, the free encyclopedia Jump to: navigation, search Mineral resource classification involves organizing information on ores and other current or future economically important mineral deposits as a guidance for governmental and industrial planning. Mineral resources are concentrations of minerals which are of note for current and future societal needs. Ore is classified as mineralisation economically and technically feasible for extraction. Not all mineralisation meets these criteria for various reasons. The specific categories of mineralization in an economic sense are:

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mineral occurrences or prospects which are of geological interest but may not be economic interest mineral resources, include those which are potentially economically and technically feasible, and those which are not ore reserves, must be economically and technically feasible to extract The common terminology for mining, ie "ore deposit" by definition must have an 'ore reserve', and may or may not have additional 'resources'. Classification, because it is an economic function, is governed by statutes, regulations and industry best practice norms. There are several classification schemes worldwide, however the Canadian CIM classification (see NI43-101) and the Australiasian Joint Ore Reserves Committee Code (JORC Code) are the general standards.

Contents 1 Mineral occurrences, prospects

2 Mineral resources 3 Mineral reserves

4 Further information Mineral occurrences, prospects These classifications of mineral occurrences are generally the least important and least economic. They included are all known occurrences of minerals of economic interest, including obviously uneconomic outcrops and manifestations. However, these are often mentioned in a company prospectus because of "proximity"; a concept that something valuable may be found near these occurrences because it has been in the past due to a similar geological environment. Often, such occurrences of mineralisation are the peripheral manifestations of nearby ore deposits. "Ore deposit" is a term applied specifically to those economic mineral occurrences which could be mined at a profit after consideration of all factors impacting a mining operation. Mineral resources Mineral resources are those economic mineral concentrations which have undergone enough scrutiny to quantify their contained metal to a certain degree. None of these resources are ore, because the economics of the mineral deposit may not have been fully evaluated. Indicated resources are simply economic mineral occurrences which have been sampled (usually by drilling) to a point at which an estimate of their contained metal and grade has been made. Generally this is very approximate and subject to sampling errors and uncertainties. Measured resources are indicated resources which have undergone enough further sampling that a 'competent person' (which is defined by the norms of the relevant mining code; usually a geologist) has declared them to be an acceptable estimate of the grade, tonnage and occurrence of the mineral occurrence. Resources may also be portions of a mineral occurrence which are attached to reserves, but are not sufficiently drilled out to qualify as Reserve status too deep to economically extract too deep to technically extract too low of grade to economically or technically extract contaminated, or refractory in nature have not yet met all of the criteria for Reserve status

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Mineral reserves Mineral reserves are the resources which are known to be economically feasible for extraction. Reserves are either 'Probable Reserves or Proven Reserves, in a similar manner to resources, above. Generally the conversion of resources into reserves requires; knowledge of the geology of the deposit sufficient that it is predictable and verifiable consideration of metallurgy, including plans for extraction, mineral processing calculation and design of open pit or underground mine plans based on ore models quantification of geotechnical risk; basically, managing the geological faults, joints and fractures in the ground so the mine does not collapse consideration of technical risk; essentially, statistical and variography to ensure the ore is sampled properly scrutiny of the assay data to ensure the accuracy of the information supplied by the laboratory This is required because ore reserves are bankable. Essentially, once a deposit is brought up to reserve status, it is an economic entity and an asset upon which loans and equity can be drawn - generally in order to pay for its extraction (hopefully, at a profit).

Ore

Iron ore (Banded iron formation)

Manganese ore

Lead ore

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Gold ore

An ore is a volume of rock containing components or minerals in a mode of occurrence which renders it valuable for mining. An ore must contain materials which are:

• valuable • in concentrations which can be profitably mined • able to be extracted from waste rock by mineral processing techniques.

Ore deposits are mineral deposits defined as being economically recoverable. Mineral deposits may include those bodies of mineralisation which are uneconomic resources, of too low a grade or tonnage or technically impossible for extraction of the contained metal.

What is valuable to mine is generally considered in terms of purely economic considerations. However, cultural, strategic or social goals of nations, tribes and individuals may render economically unfeasible bodies of rock valuable for extraction, for instance ochre, some clays and ornamental stones which are of religious, cultural or sentimental value to a population. Here, value is placed on the rock in non-economic terms.

Ore is thus an economic entity, not a physical entity. Fluctuations in commodity prices will determine what rock is considered valuable and hence ore, and what rock is not valuable and is considered waste. Similarly, the costs of extraction may fluctuate, for example with fuel costs, rendering mining unprofitable and turning ore into waste.

The grade or contained 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 weighted against the contained metal value of the rock and a 'cut-off grade' used to define what is ore and what is waste.

Ore minerals are generally oxides, sulfides, silicates, or native metals that are not commonly concentrated in the Earth's crust. The ores must be processed to extract the metals 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.

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Exploration geophysics

Exploration geophysics is the applied branch of geophysics which uses deep and primarily near surface methods to probe or image the earth. This is for obtaining information relevant to hydrocarbon or mineral extraction, engineering, and geological studies.

This includes the following popular techniques:

Seismic methods Magnetotellurics Electromagnetic

Radio (e.g., ground penetrating radar) Electrical resistivity techniques

Induced Polarization (IP) Magnetic Gravity

Geodetic Remote Sensing

Geophysics, the study of the earth by quantitative physical methods, especially by seismic reflection and refraction, geodesy, gravity, magnetic, electrical, electromagnetic, and radioactivity methods. It includes the branches of: Seismology (earthquakes and elastic waves) Gravity and geodesy (the earth's gravitational field and the size and form of the earth) Atmospheric science, which includes: Atmospheric electricity and terrestrial magnetism (including ionosphere, Van Allen belts, telluric currents, Radiant energy, etc.) Meteorology and Climatology, which both involve studies of the weather. Aeronomy, the study of the physical structure and chemistry of the atmosphere. Geothermometry (heating of the earth, heat flow, volcanology, and hot springs) Hydrology (ground and surface water, sometimes including glaciology) Physical oceanography Tectonophysics (geological processes in the earth) Exploration and engineering geophysics Geophysical Engineering Geodesy

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