A dike or dyke, in geological usage, is a sheet of rock, formed in a fracture in a pre-existing rock body. Dikes can be either magmatic or sedimentary in origin. Magmatic dikes form when magma flows into a crack solidifies as a sheet intrusion, either cutting across layers of rock or through a contiguous mass of rock. Clastic dikes are formed. An intrusive dike is an igneous body with a high aspect ratio, which means that its thickness is much smaller than the other two dimensions. Thickness can vary from sub-centimeter scale to many meters, the lateral dimensions can extend over many kilometres. A dike is an intrusion into an opening cross-cutting fissure, shouldering aside other pre-existing layers or bodies of rock. Dikes are high-angle to near-vertical in orientation, but subsequent tectonic deformation may rotate the sequence of strata through which the dike propagates so that the dike becomes horizontal. Near-horizontal, or conformable intrusions, along bedding planes between strata are called intrusive sills.
The term "sheet" is the general term for both sills. Sometimes dikes appear in swarms, consisting of several to hundreds of dikes emplaced more or less contemporaneously during a single intrusive event; the world's largest dike swarm is the Mackenzie dike swarm in Canada. Dikes form as either radial or concentric swarms around plutonic intrusives, volcanic necks or feeder vents in volcanic cones; the latter are known as ring dikes. Dikes can vary in texture and their composition can range from diabase or basaltic to granitic or rhyolitic, but on a global perspective the basaltic composition prevails, manifesting ascent of vast volumes of mantle-derived magmas through fractured lithosphere throughout Earth history. Pegmatite dikes comprise coarse crystalline granitic rocks - associated with late-stage granite intrusions or metamorphic segregations. Aplite dikes are sugary-textured intrusives of granitic composition; the term "feeder dike" is used for a dike. Magma flowed along out of the dike formed another feature.
In contrast to magmatic dikes, a sill is a magmatic sheet intrusion that forms within and parallel to the bedding of layered rock. Sedimentary dikes or clastic dikes are vertical bodies of sedimentary rock that cut off other rock layers, they can form in two ways: When a shallow unconsolidated sediment is composed of alternating coarse grained and impermeable clay layers the fluid pressure inside the coarser layers may reach a critical value due to lithostatic overburden. Driven by the fluid pressure the sediment forms a dike; when a soil is under permafrost conditions the pore water is frozen. When cracks are formed in such rocks, they may fill up with sediments; the result is a vertical body of sediment that cuts through a dike. Batholith Ring dike Fissure vent – Linear volcanic vent through which lava erupts Laccolith Runamo – A cracked dolerite dike in Sweden, for centuries held to be a runic inscription interpreted as a runic inscription. Dike swarm Sill
Phlogopite is a yellow, greenish, or reddish-brown member of the mica family of phyllosilicates. It is known as magnesium mica. Phlogopite is the magnesium endmember of the biotite solid solution series, with the chemical formula KMg3AlSi3O102. Iron substitutes for magnesium in variable amounts leading to the more common biotite with higher iron content. For physical and optical identification, it shares most of the characteristic properties of biotite. Phlogopite is an important and common end-member composition of biotite. Phlogopite micas are found in igneous rocks, although it is common in contact metamorphic aureoles of intrusive igneous rocks with magnesian country rocks and in marble formed from impure dolomite; the occurrence of phlogopite mica within igneous rocks is difficult to constrain because the primary control is rock composition as expected, but phlogopite is controlled by conditions of crystallisation such as temperature and vapor content of the igneous rock. Several igneous associations are noted: high-alumina basalts, ultrapotassic igneous rocks, ultramafic rocks.
The basaltic occurrence of phlogopite is in association with picrite basalts and high-alumina basalts. Phlogopite is stable in basaltic compositions at high pressures and is present as resorbed phenocrysts or an accessory phase in basalts generated at depth. Phlogopite mica is a known phenocryst and groundmass phase within ultrapotassic igneous rocks such as lamprophyre, kimberlite and other sourced ultramafic or high-magnesian melts. In this association phlogopite can form well preserved megacrystic plates to 10 cm, is present as the primary groundmass mineral, or in association with pargasite amphibole and pyroxene. Phlogopite in this association is a primary igneous mineral present because of the depth of melting and high vapor pressures. Phlogopite is found in association with ultramafic intrusions as a secondary alteration phase within metasomatic margins of large layered intrusions. In some cases the phlogopite is considered to be produced by autogenic alteration during cooling. In other instances, metasomatism has resulted in phlogopite formation within large volumes, as in the ultramafic massif at Finero, within the Ivrea zone.
Trace phlogopite, again considered the result of metasomatism, is common within coarse-grained peridotite xenoliths carried up by kimberlite, so phlogopite appears to be a common trace mineral in the uppermost part of the Earth's mantle. Phlogopite is encountered as a primary igneous phenocryst within lamproites and lamprophyres, the result of fluid-rich melt compositions within the deep mantle; the largest documented single crystal of phlogopite was found in Lacey mine, Canada. Similar-sized crystals were found in Karelia, Russia. Deer, W. A. R. A. Howie, J. Zussman, Rock-forming minerals, v. 3, "sheet silicates", p. 42–54 Spencer, Leonard James. "Phlogopite". In Chisholm, Hugh. Encyclopædia Britannica. 21. Cambridge University Press. P. 447
Iron oxide or ferrous oxide is the inorganic compound with the formula FeO. Its mineral form is known as wüstite. One of several iron oxides, it is a black-colored powder, sometimes confused with rust, the latter of which consists of hydrated iron oxide. Iron oxide refers to a family of related non-stoichiometric compounds, which are iron deficient with compositions ranging from Fe0.84O to Fe0.95O. FeO can be prepared by the thermal decomposition of iron oxalate. FeC2O4 → FeO + CO2 + COThe procedure is conducted under an inert atmosphere to avoid the formation of ferric oxide. A similar procedure can be used for the synthesis of manganous oxide and stannous oxide. Stoichiometric FeO can be prepared by heating Fe0.95 O with metallic iron at 36 kbar. FeO is thermodynamically unstable below 575 °C, tending to disproportionate to metal and Fe3O4: 4FeO → Fe + Fe3O4 Iron oxide adopts the cubic, rock salt structure, where iron atoms are octahedrally coordinated by oxygen atoms and the oxygen atoms octahedrally coordinated by iron atoms.
The non-stoichiometry occurs because of the ease of oxidation of FeII to FeIII replacing a small portion of FeII with two thirds their number of FeIII, which take up tetrahedral positions in the close packed oxide lattice. Below 200 K there is a minor change to the structure which changes the symmetry to rhombohedral and samples become antiferromagnetic. Iron oxide makes up 9% of the Earth's mantle. Within the mantle, it may be electrically conductive, a possible explanation for perturbations in Earth's rotation not accounted for by accepted models of the mantle's properties. Iron dissolved in groundwater is in the reduced iron II form. If this groundwater comes in contact with oxygen at the surface, e.g. in natural springs, iron II is oxidised to iron III and forms insoluble hydroxides in water. Iron oxide is used as a pigment, it is FDA-approved for use in cosmetics and it is used in some tattoo inks. It can be used as a phosphate remover from home aquaria. Http://webmineral.com/data/Wustite.shtml
An ore is an occurrence of rock or sediment that contains sufficient minerals with economically important elements metals, that can be economically extracted from the deposit. The ores are extracted from the earth through mining; 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 oxides, silicates, or native metals that are not concentrated in the Earth's crust, or noble metals 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. An ore deposit is an accumulation of ore; this is distinct from a mineral resource. An ore deposit is one occurrence of a particular ore type.
Most ore deposits are named according to their location, or after a discoverer, or after some whimsy, a historical figure, a prominent person, something from mythology or the code name of the resource company which found it. Ore deposits are classified according to various criteria developed via the study of economic geology, or ore genesis; the classifications below are typical. Mesothermal lode gold deposits, typified by the Golden Mile, Kalgoorlie Archaean conglomerate hosted gold-uranium deposits, typified by Elliot Lake, Ontario and Witwatersrand, South Africa Carlin–type gold deposits, including. Volcanic hosted massive sulfide Cu-Pb-Zn including. Stratiform arkose-hosted and shale-hosted copper, typified by the Zambian copperbelt. Stratiform tungsten, typified by the Erzgebirge deposits, Czechoslovakia Exhalative spilite-chert hosted gold deposits Mississippi valley type zinc-lead deposits Hematite iron ore deposits of altered banded iron formation Sudbury Basin nickel and copper, Canada The basic extraction of ore deposits follows these steps: Prospecting or exploration to find and define the extent and value of ore where it is located Conduct resource estimation to mathematically estimate the size and grade of the deposit Conduct a pre-feasibility study to determine the theoretical economics of the ore deposit.
This identifies, early on, whether further investment in estimation and engineering studies is warranted and identifies key risks and areas for further work. Conduct a feasibility study to evaluate the financial viability and financial risks and robustness of the project and make a decision as whether to develop or walk away from a proposed mine project; this includes mine planning to evaluate the economically recoverable portion of the deposit, the metallurgy and ore recoverability and payability of the ore concentrates, engineering and infrastructure costs and equity requirements and a cradle to grave analysis of the possible mine, from the initial excavation all the way through to reclamation. Development to create access to an ore body and building of mine plant and equipment The operation of the mine in an active sense Reclamation to make land where a mine had been suitable for future use Ores are traded internationally and comprise a sizeable portion of international trade in raw materials both in value and volume.
This is because the worldwide distribution of ores is unequal and dislocated from locations of peak demand and from smelting infrastructure. Most base metals are traded internationally on the London Metal Exchange, with
Carbonatite is a type of intrusive or extrusive igneous rock defined by mineralogic composition consisting of greater than 50% carbonate minerals. Carbonatites may require geochemical verification. Carbonatites occur as small plugs within zoned alkalic intrusive complexes, or as dikes, sills and veins, they are exclusively associated with continental rift-related tectonic settings. It seems that there has been a steady increase in the carbonatitic igneous activity through the Earth's history, from the Archean eon to the present. Nearly all carbonatite occurrences are subvolcanic intrusives; this is because carbonatite lava flows, being composed of soluble carbonates, are weathered and are therefore unlikely to be preserved in the geologic record. Carbonatite eruptions as lava may therefore not be as uncommon as thought, but they have been poorly preserved throughout the Earth's history. Carbonatite liquid compositions are more alkaline than what is preserved in the fossil carbonatite rock record as composition of the melt inclusions shows.
Only one carbonatite volcano is known to have erupted in historical time, the active Ol Doinyo Lengai volcano in Tanzania. It erupts with the lowest-temperature lava in the world, at 500–600 °C; the lava is natrocarbonatite dominated by gregoryite. The magmatic origin of carbonatite was argued in detail by Swedish geologist Harry von Eckermann in 1948 basen on his study of Alnö Complex, it was however the 1960 eruption of Ol Doinyo Lengai in Tanzania that led to geological investigations that confirmed the view that carbonatite is derived from magma. Carbonatites are rare, peculiar igneous rocks formed by unusual processes and from unusual source rocks. Three models of their formation exist: direct generation by low-degree partial melts in the mantle and melt differentiation, liquid immiscibility between a carbonate melt and a silicate melt, extreme crystal fractionation. Evidence for each process exists. Carbonatites were thought to form by melting of limestone or marble by intrusion of magma, but geochemical and mineralogical data discount this.
For example, the carbon isotopic composition of carbonatites is mantle-like and not like sedimentary limestone. Primary mineralogy is variable, but may include natrolite, apatite, barite, ancylite group minerals, other rare minerals not found in more common igneous rocks. Recognition of carbonatites may be difficult as their mineralogy and texture may not differ much from marble except the presence of igneous minerals, they may be sources of mica or vermiculite. Carbonatites are classed as calcitic sovite and alvikite facies; the two are distinguished by minor and trace element composition. The terms rauhaugite and beforsite refer to dolomite- and ankerite-rich occurrences respectively; the alkali-carbonatites are termed lengaite. Examples with 50–70% carbonate minerals are termed silico-carbonatites. Additionally, carbonatites may be either enriched in magnetite and apatite or rare-earth elements and barium. Natrocarbonatite is made up of two minerals and gregoryite; these minerals are both carbonates in which sodium and potassium are present in significant quantities.
Both are anhydrous, when they come into contact with the moisture in the atmosphere, they begin to react quickly. The black or dark brown lava and ash erupted. Carbonatite is composed predominantly of carbonate minerals and unusual in its major element composition as compared to silicate igneous rocks because it is composed of Na2O and CaO plus CO2. Most carbonatites tend to include some silicate mineral fraction. Silicate minerals associated with such compositions are pyroxene and silica-undersaturated minerals such as nepheline and other feldspathoids. Geochemically, carbonatites are dominated by incompatible elements and depletions in compatible elements; this together with their silica-undersaturated composition supports inferences that carbonatites are formed by low degrees of partial melting. A specific type of hydrothermal alteration termed fenitization is associated with carbonatite intrusions; this alteration assemblage produces a unique rock mineralogy termed a fenite after its type locality, the Fen Complex in Norway.
The alteration consists of metasomatic halos consisting of sodium rich silicates arfvedsonite and glaucophane along with phosphates and other iron and titanium oxides. Associated igneous rocks include ijolite, teschenite, phonolite, shonkinite, silica undersaturated foid-bearing pyroxenite, nepheline syenite. Carbonatites are associated with undersaturated igneous rocks that are either alkali, ferric iron and zirconium-rich agpaitic rocks or alkali-poor, FeO-CaO-MgO-rich and zirconium-poor miaskitic rocks; the Mount Weld carbonatite is unassociated with a belt or suite of alkaline igneous rocks, although calc-alkaline magmas are known in the region. The genesis of this Archaean carbonatite remains contentious as it is the sole example of an Archaean carbonatite in Australia. Carbonatite is known to form in association wit
A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption. A maar characteristically fills with water to form a shallow crater lake which may be called a maar; the name comes from a Moselle Franconian dialect word used for the circular lakes of the Daun area of Germany. Maars are shallow, flat-floored craters that scientists interpret as having formed above diatremes as a result of a violent expansion of magmatic gas or steam. Maars range in size from 60 to 8,000 m from 10 to 200 m deep. Most maars have low rims composed of a mixture of loose fragments of volcanic rocks and rocks torn from the walls of the diatreme. Maar lakes referred to as maars, occur when groundwater or precipitation fills the funnel-shaped and round hollow of the maar depression formed by volcanic explosions. Examples of these types of maar are the three maars at Daun in the Eifel mountains of Germany. A dry maar results when a maar lake dries out, becomes aggraded or silted up. An example of the latter is the Eckfelder Maar.
Near Steffeln is the Eichholzmaar which has dried out during the last century and is being renaturalised into a maar. In some cases the underlying rock is so porous. After winters of heavy snow and rainfall many dry maars fill and temporarily with water; the largest known maars are found on the Seward Peninsula in northwest Alaska. These maars range in size from 4,000 to 8,000 m in diameter and a depth up to 300 m; these eruptions occurred in a period of about 100,000 years, with the youngest occurring about 17,500 years ago. Their large size is due to the explosive reaction that occurs when magma comes into contact with permafrost. Hydromagmatic eruptions are explosive when the ratio of water to magma is low. Since permafrost melts it provides a steady source of water to the eruption while keeping the water to magma ratio low; this produces the explosive eruptions that created these large maars. Examples of the Seward Peninsula maars include North Killeak Maar, South Killeak Maar, Devil Mountain Maar and Whitefish Maar.
Maars occur in western North America, Patagonia in South America, the Eifel region of Germany, in other geologically young volcanic regions of Earth. Elsewhere in Europe, La Vestide du Pal in the Ardèche department of France provides a spectacular example of a maar visible from the ground or air. Kilbourne Hole and Hunt's Hole, in southern New Mexico near El Paso, are maars; the Crocodile Lake in Los Baños in the Philippines was thought of as a volcanic crater is a maar. The notorious, carbon dioxide-saturated Lake Nyos in Africa is another example. An excellent example of a maar is Zuni Salt Lake in New Mexico, a shallow saline lake that occupies a flat-floored crater about 6,500 ft across and 400 ft deep, its low rim is composed of loose pieces of basaltic lava and wall rocks of the underlying diatreme, as well as random chunks of ancient crystalline rocks blasted upward from great depths. Maars in Canada are found in the Wells Gray-Clearwater volcanic field of east-central British Columbia and in kimberlite fields throughout Canada.
A notable field of maars is found in the Pali-Aike Volcanic Field in South America. And in the Sudanese Bayuda Volcanic Field; the Auckland volcanic field in the urban area of Auckland, New Zealand has several maars, including the accessible Lake Pupuke in the North Shore suburb of Takapuna. One of the most notable craters misidentified. In the Volcanic Eifel there are about 75 maars; these include water-filled maar lakes. Both types, lake-filled maars and dry maars, are typical of the Volcanic Eifel; the last eruptions took place at least 11,000 years ago and many maars in the Eifel are older. For this reason many are heavily eroded and their shapes and volcanic features are not as obvious as those of more recent or active maars elsewhere in the early; the maars of the Eifel are well preserved. In the Eifel and Volcanic Eifel there are numerous dry maars: Mosbrucher Weiher Booser Doppelmaar Dreiser Weiher Dürres Maar Duppacher Weiher Geeser Maar Eckfelder Maar Eigelbacher Maar Hitsche Maar Immerather Risch Gerolsteiner Maar Schalkenmehrener Maar E Schönfelder Maar Steffelner Laach or "Laach Maar" Dehner Maar Walsdorfer Maar Wollmerather Maar The following volcanic features are colloquially referred to as a "maar" or "maar lake", although they are not speaking, maars: Windsborn Crater Lake and Hinkelsmaar in theManderscheid Volcano Group near Bettenfeld, crater lakes of the Mosenberg Laacher See near Maria Laach, lake in a caldera
Lamprophyres are uncommon, small volume ultrapotassic igneous rocks occurring as dikes, laccoliths and small intrusions. They are alkaline silica-undersaturated mafic or ultramafic rocks with high magnesium oxide, >3% potassium oxide, high sodium oxide and high nickel and chromium. Lamprophyres occur throughout all geologic eras. Archaean examples are associated with lode gold deposits. Cenozoic examples include magnesian rocks in Mexico and South America, young ultramafic lamprophyres from Gympie in Australia with 18.5% MgO at ~250 Ma. Modern science treats lamprophyres as a catch-all term for ultrapotassic mafic igneous rocks which have primary mineralogy consisting of amphibole or biotite, with feldspar in the groundmass. Lamprophyres are not amenable to classification according to modal proportions, such as the system QAPF due to peculiar mineralogy, nor compositional discrimination diagrams, such as TAS because of their peculiar geochemistry, they are classified under the IUGS Nomenclature for Igneous Rocks separately.
For example, the TAS scheme is inappropriate due to the control of mineralogy by potassium, not by calcium or sodium. Mitchell has suggested that rocks belonging to the "lamprophyre facies" are characterized by the presence of phenocrysts of mica and/or amphibole together with lesser clinopyroxene and/or melilite set in a groundmass which may consist of plagioclase, alkali feldspar, carbonate, melilite, amphibole, perovskite, Fe-Ti oxides and glass. Classification schemes which include genetic information, may be required to properly describe lamprophyres. Rock considered lamprophyres are part of a "clan" of rocks, with similar mineralogy and genesis. Lamprophyres are similar to kimberlites. While modern concepts see orangeites and kimberlites as separate, a vast majority of lamprophyres have similar origins to these other rock types. Mitchell considered the lamprophyres as a "facies" of igneous rocks created by a set of conditions. Either scheme may apply to some, but not all and variations of the broader group of rocks known as lamprophyres and melilitic rocks.
Leaving aside complex petrogenetic arguments, it is fair to say that the essential components in lamprophyre genesis are. Rock considered lamprophyres to be derived from deep, volatile-driven melting in a subduction zone setting. Others such as Mitchell consider them to be late offshoots of plutons, etc. though this can be difficult to reconcile with their primitive melt chemistry and mineralogy. Lamprophyres are a group of rocks containing phenocrysts of biotite and amphibole, pyroxene, but not of feldspar, they are thus distinguished from the porphyries and porphyrites in which the feldspar has crystallized in two generations. They are dike rocks, occurring as dikes and thin sills, are found as marginal facies of plutonic intrusions, they are dark in color, owing to the abundance of ferro-magnesian silicates, of high specific gravity and liable to decomposition. For these reasons they have been defined as a melanocrate series. Biotite and amphibole are panidiomorphic. Feldspar is restricted to the ground mass.
In many lamprophyres the pale quartz and felspathic ingredients tend to occur in rounded spots, or ocelli, in which there has been progressive crystallization from the margins towards the center. These spots may consist of quartz and feldspar. A central area of quartz or of analcite represents an original miarolitic cavity infilled at a period; the presence or absence of the four dominant minerals, plagioclase and hornblende, determines the species: Minette contains biotite and orthoclase. Kersantite contains plagioclase. Vogesite contains orthoclase. Spessartite contains plagioclase; each variety of lamprophyre may and does contain all four minerals but is named according to the two which predominate. These rocks contain iron oxides, sometimes sphene and olivine; the hornblende and biotite are brown or greenish-brown, as a rule their crystals when small are perfect and give the thin section views an recognizable character. Green hornblende occurs in some of these rocks. Augite exists as euhedral crystals of pale green color zonal and weathering.
Olivine in the fresh state is rare.