Magmatic and structural controls on the development of. Discuss the mechanisms by which crystal fractionation could occur in. Magmatic ore deposits, also known as orthomagmatic ore deposits, are deposits within igneous rocks or along their contacts in which ore minerals crystallised from a melt or were transported in a melt. An ore deposit formed by magmatic segregation, generally in mafic rocks and layered intrusions, as crystals of metallic oxides or from an immiscible sulfide liquid. The best candidates for magmatic differentiation processes to form the footwall deposits of the south range are at little stobie, lindsley, the creighton 126 ore body, creighton deep, crean hill, mckim, and perhaps parts of the garson mineral system details are provided in chapter 4. Magmatic ore deposits in layered intrusionsdescriptive. Ore deposits produced by magmatic segregation, with special. Other articles where magmatic segregation is discussed. About 7% of chromite ore production goes to the refractory industry. Mineral deposits in new zealand whose origin can be ascribed to primary magmatic segregations are associated with maficultramafic complexes related to two orogenic episodes which took place during palaeozoic and mesozoic times. One is ophiolitic and has podiform chromite mineralisation presumably formed below a spreading ridge. This material then cooled to form a variety of intrusive and extrusive igneous rocks.
Magmatic segregation geology britannica encyclopedia britannica. The mineralogical nature of the ores is dependent on a number of factors. Mineral deposits in new zealand whose origin can be ascribed to primary magmatic segregations are associated with maficultra mafic complexes related to two orogenic episodes which took place during paleozoic and mesozoic times. Much more uncommon than maficultramafic magmatic ore deposits. Some ore deposits have such an intimate association with igneous rocks that a common heritage can be inferred. Discrimination between magmatic and hydrothermal nicu. The principal styles of mineral deposit which have formed by magmatic segregation are listed in. These magma bodies are traditionally considered to be longlived and dominated by melt.
When the mineral content present in magma crystallizes, it sinks down and settles at the bottom of magma chamber as it is denser than the magma. The relative roles of magmatic segregation, volcanic exhalation and regional metamorphism in the. In between, the strain rate leading to melt segregation through fluid. Ore deposits produced by magmaticsegregation, with special reference to. Through the magmatic segregation process, one or more minerals are concentrated locally during the cooling of magma. The formation temperature of different magmatic deposits varies from 1500c to 300c. The absolute concentrations of pge in sulfides from different deposits vary over a range of five orders of magnitude, whereas those of other chalcophile elements vary by factors of only 2 to 100. The porphyry cu deposit is flanked out ward and upward by a characteristic suite of deposit types. Segregation of ore metals between magmatic brine and vapor. Magmatic segregation deposits may also form by crystallization of residual magmas.
Magmatic nickelcopperplatinum group element deposits. The formation of valuable minerals in magma that is cooling is. Lode deposits of the area can be divided into several deposit types. As early crystallizing minerals form from magma, they incorporate certain elements, some of which are metals.
Pdf how do metals escape from magmas to form porphyrytype. Magmatic segregation is a general term referring to any process by which one or more minerals become locally concentrated segregated during the cooling and crystallization of a magma. Primary magmatic segregation deposits in new zealand. Economic geology principles and practice metals, minerals, coal and hydrocarbons introduction to formation and sustainable exploitation of mineral deposits, walter l. Magmatic deposits article about magmatic deposits by the. Geological association of canada mineral deposits division special publication 5, 205222. Layered, ultramafic to mafic intrusions are uncommon in the geologic record, but host magmatic ore deposits containing most of the worlds economic concentrations of platinumgroup elements pge figs. All these suggestions are compliant with previous conclusions from the xray luminescence of feldspar on common source of the novosibirskob area granitoids formation boroznovskaya et al. Magmatic sulfide ore deposits are products of natural smelting. Vertically extensive and unstable magmatic systems. Magmatic intrusions result in partitioning of elements and contamination of the melt by assimilation of the host rock. Mineral deposit formation of mineral deposits britannica. Lkind of deposits lalmost all chromite deposits are magmatic segregation in ultrabasic rocks.
Clair state university of iowa this work has been identified with acreative commons public domain mark 1. Mineral deposits form because some medium serves as a concentrating and transporting agent for the ore minerals, and some process subsequently causes the transporting agent to precipitate, or deposit, the minerals. The successive alteration zones porphyry deposits magmatic, potassic. However, some of the mineralization in some deposits e. Magmatic origin of giant kirunatype apatiteironoxide. Ore deposits produced by magmatic segregation, with special reference to the nickel ores of the sudbury district, ontario stuart st. Magmatic segregation can also take place as a result of the separation of sulphide and silicate liquids. These deposits vary in shape and occur in igneous rocks that are related to them in origin. Lall economic deposits of chromite are in ultrabasicrocks and are either stratiform in layered intrusions 98% of worlds chromite resources or podiform. Iv chromiteplatinumgroup element magmatic deposits giorgio garuti encyclopedia of life support systems eolss electroplanting, and pharmaceutics. Gravitation segregation of sulphur result in sulfide ore to form at the bottom of the melt. Sulfidesilicate textures in magmatic nicupge sulfide. A mafic magma without a high enough o2 for early crystallization of feti oxide minerals would produce enrichment of iron and titanium in the residual magma.
No layering due to 100 higher mew, also due to lower density differences between minerals. Rogers, of the leland stanford university, california, have issued a small volume in the university series of publications entitled a study of the magmatic sulfid. Pge deposits are believed to have formed by segregation of immiscible sulfide melts andor alloys from maficultramafic magmas in dynamic magmatic systems such as lava channels, feeder dikes, and magma chambers. The relationship between hot springs and epithermal veins. Hawaiian islands it is widely understood that volcanoes can have short and longterm effects on the atmosphere, hydrosphere, and biosphere. Cornwall geological survey bulletin 1223 geology, resources, and reserves of nickel sulfide and nickeliferous. Niggli classification niggli considered only mineral deposits related to magmatic processes the deposits formed under high temperaturehigh pressure, deep seated conditions are termed as plutonic, or intrusive. Most major magmatic cunipge sulphide deposits are thought to have formed by segregation of an immiscible sulphide melt from a silicate host magma, in response to processes such as magma mixing, rapid cooling, differentiation, and contamination. Curich magmatic nicupge deposits top magmatic deposit producers 20072008 simexmin 2014 symposium may 14, 2014 deposit location operators cu pa tonnes cu grade norilsk taimyr peninsula, russia norisk nickel 364,400 2. It is also possible to produce this type of ore through the meteorite impacts, riftcontinental flood basaltassociated sills and dykes, volcanic flows and troctolite intrusions. With theriseof manydeveloping nations, the worlds need for metal deposits increased rapidly in. Representatives of magmatic concentration are many and widespread, but the. Form, distribution, textures and timing of segregation of nicupge sulfide.
Magmatic deposits deposits of minerals formed deep in the earths crust during the solidification and crystallization of basic or alkaline magma containing high concentrations of valuable minerals. Some geologists favor the theory of magmatic segregation, that is, that the ironnickelcopper sulfides separated. Lightfoot5, nadya krivolutskaya6, bo wei7 6 1csiro mineral resources, perth, australia. Rocks formed as a result of magmatic segregation are called magmatic cumulates. The relative roles of magmatic segregation, volcanic exhalation and. The processes of formation of mineral deposits are grouped. Magmatic segregation is an oreforming process, in which the valuable minerals are concentrated by settling them out from cooling magma. Some of these minerals are extremely rare and almost never encountered in common rocks, an example being alloys of the platinum metals. Magmatic sulfiderich nickelcopper deposits related usgs. Exploration for magmatic nicupge sulphide deposits. The magmatic deposits are classified into two major groups, viz.
Magmatic nicupge deposits in magma plumbing systems. The rocks that are formed as a result of magmatic segregation are called magmatic cumulates. The metal content of the sulphides is governed by the concentration of the metals in the silicate host magma, the sulphide meltsilicate melt. Kaneko encyclopedia of life support systems eolss size and richness to constitute valuable mineral deposits such as chromium, platinum and ree. Some of the commonly formed mineral deposits formed due to magmatic segregation are iron, granite, aluminum, diamond, chromite, and platinum. In many cases it can be confirmed by a study of field relationships, from ore textures and from the results of experimental petrology that the ores have segregated during the crystallization of a magma. A magmatic model for the origin of large salt formations stef heerema large formations of rock salt are found on every continent around the world. Ore deposits formed by gravity settling due to magmatic. The three most crucial factors for the formation of large and superlarge magmatic sulfide deposits are. Magmatic differentiation an overview sciencedirect topics.
These maficultramafic complexes are essentially of two types. When magma rises along a deep fault and pours out on the earths surface, it is termed lava. Magmatic ore deposits are derived from accumulations of crystals of metallic oxides, or immiscible sulfide, or oxide liquids that formed during the cooling and crystallization of magma, typically with mafic to ultramafic compositions. Examples of concentrating and transporting agents are groundwater, seawater, and magma. Magmatic cumulates magmatic segregation is a general term referring to any process by which one or more minerals become locally concentrated segregated during the cooling and crystallization of a magma. Introduction ore deposits are crustal concentrations of useful elements that can be exploited at a pro.
Chromite occurs in the host rock as masses, lenses, and dissemination. Chromite and magnetite are ore minerals that form in. A magmatic ore deposit is an accumulation of magmatic minerals. A magmatic model for the origin of large salt formations. Magmatic sulfide deposits containing nickel ni and copper cu, with or without.
Oil and gas are often associated with salt deposits, which can rise kilometers above the top of the main underground salt body. The defining characteristic of igneous rocks is that at one time they were molten and part of magmas or lavas. Sulphide and silicate liquids are immiscible meaning they do not mix, so droplets of iron, copper, nickel and platinum sulphides that form at high temperatures and are denser than the surrounding silicate liquid magma sink to the base of the intrusion to form a cumulate layer, where they. This theory is contested by some geologists, however, particularly for deposits in several of the larger districts.
Magmatic segregation deposits of chromite download. Mcqueen crc leme, australian national university, canberra, act 0200 and school of rehs, university of canberra, act 2601. Platinumgroup elements pge are mined predominantly from deposits that have formed by the segregation of molten ironnickelcopper sulfides from silicate magmas. It is less widely recognized that the environment around a volcano affects the magmatic. A magma is a body of molten rock that occurs below the surface of the earth.
General model of a zoned magmatic hydrothermal system showing poten tial linkages between a porphyry cu deposit centered on a composite porphyry intru sion at depth adapted from sillitoe, 1993. These crystals may settle onto the bottom of the intrusion, concentrating ore minerals there. Shallow magma chambers either erupt as volcanoes or solidify as intrusive magma bodies. Type deposits of iron, chromium, aluminum, and diamond that. Magmatic ore deposits chapter 2 ore deposit geology.
Name 5 processes that might cause the chemical composition of a magma to change. The analytical data emphasize the importance of magmatic vapor and vapor condensate as oreforming solutions and suggest that brinevapor separation may be an important mechanism of base and precious metal segregation in hightemperature hydrothermal systems. Ore deposits produced by magmatic segregation, with. The common association of pges with sulfide minerals is a result of processes of magmatic and sulfide liquid segregation and fractionation. These include direct magmatic segregation or crystallization, magmatic hydrothermal replacement and hydrothermal precipitation in the sense of.
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