How Do I Clean Mica In Pegmatite And Quartz

Pegmatite

Pegmatites are unusually coarse-grained crystalline igneous rocks, usually of granitic composition and characterized by interlocking crystals several centimeters up to tens of meters in length.

From: Encyclopedia of Geology (Second Edition) , 2021

Volume 2

David London , in Encyclopedia of Geology (Second Edition), 2021

Introduction

Pegmatites are texturally circuitous igneous rocks marked by some combination of extremely large but variable crystal size, spatial zonation of minerals, prominent anisotropy of crystal orientations from the margins inwards, and skeletal, radial, or graphic (terms in italics are explained farther in the Glossary) intergrowth habits of crystals (London, 2008). Though any ane of these textural attributes might identify a rock as pegmatite, they commonly occur together, resulting in exceedingly circuitous stone fabric (Fig. 1). Pegmatites are found as segregations near the roofward contact of their source pluton, as dike swarms emanating from their plutons into the surrounding igneous and metamorphic rocks, and every bit planar to lenticular intrusive bodies whose sources are not exposed (Fig. 2). Whereas the common plutonic magmas tend to course large bodies of texturally and mineralogically compatible rock, their pegmatites are precisely the opposite: minor in book and texturally and mineralogically diverse in their internal fabrics.

Pegmatites are associated with virtually of the common plutonic igneous rocks, including gabbro and syenite, but the vast majority of them are granitic in composition for reasons that are explained below. The common pegmatites possess uncomplicated granitic compositions, consisting of subequal proportions of sodic plagioclase, potassic brine feldspar, and quartz. They comprise minor (few percent by volume) to accessory (< 1% by volume) amounts of micas, garnet, tourmaline, and apatite. Field measurements on thousands of mutual pegmatites evidence that their compositions prevarication shut to granitic liquid of minimum or eutectic limerick, meaning that the magma has been refined through fractional crystallization to the lowest-temperature liquid that is possible for the terminal environment of its crystallization. Even the well-nigh chemically refined and mineralogically diverse pegmatites, such equally the Tanco deposit, Manitoba, possess granitic compositions in the strict and formal sense (Stilling et al., 2006). The chemical affinity of pegmatites to their compositionally similar plutonic rocks underscores the fact that pegmatites are igneous in origin. Rocks that, by virtue of their compositions, could non have been liquids at plausible pressures and temperatures are, therefore, not pegmatites. Some like-actualization rocks may originate equally hydrothermal veins, or equally metasomatic replacements of prior rock, or they may represent cumulates from which residual melt has escaped.

This commodity is in reference to pegmatites of granitic composition, as these are by far the most abundant. However, the processes by which pegmatites grade in association with other plutonic igneous rocks are likely the aforementioned.

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Geochemistry of Mineral Deposits

R.L. Linnen , ... A.R. Chakhmouradian , in Treatise on Geochemistry (Second Edition), 2014

13.21.3.3.2 Peraluminous pegmatite-hosted deposits

Pegmatite-hosted Ta mineralization has been mined from peraluminous pegmatites in Canada (Tanco) and Commonwealth of australia (Greenbushes and Wodgina) in the past, only recently product has shifted to Brazil (Mibra) and Africa (notably Kenticha, Federal democratic republic of ethiopia, and pegmatite-derived placer deposits in the Autonomous Republic of the congo). Using the pegmatite classification system of Černý and Ercit (2005), the major Ta pegmatites are rare-element–Li subclasses, complex type pegmatites that belong to the LCT (Li–Cs–Ta) family. The Tanco pegmatite has been the subject of about scientific researches and has recently been summarized by Černý (2005). Tanco is a circuitous pegmatite with nine distinct zones that are crudely distributed in a concentric pattern that is interpreted to reverberate in crystallization. The nearly important units for Ta mineralization are the aplitic albite zone and the primal intermediate zone, although other units also incorporate Ta mineralization, in particular the lepidolite zone. More than detailed work on Tanco has focused on magmatic and metasomatic styles of mineralization at Tanco. Van Lichtervelde et al. (2006) studied one particular area of mineralization (the '26 H area') where the bulk of the mineralization was hosted by albite aplite and lower intermediate zones. Based on textural relationships, they concluded that the mineralization was primarily magmatic, a determination that is supported past an increase of the Ta/Nb ratio of columbite group minerals from the margin to the core of this pegmatite cell. They as well concluded that the variation of Mn/Fe values in columbite was controlled past silicate phases, notably tourmaline. An association betwixt metasomatic albite is observed elsewhere in the Tanco pegmatite and is described in other pegmatites (e.g., Kontak, 2006). A second metasomatic mode of mineralization is an association with muscovite replacement, termed 'MQM' (muscovite–quartz afterward microcline) at Tanco. Van Lichtervelde et al. (2007) completed a detailed report of this style of mineralization from the lower pegmatite zone at Tanco. Central textural observations were the complexity of the intergrowths several Ta oxide phases inside single grain aggregates and an association of these aggregates with other HFSE minerals, for example, zircon and apatite. These features led the authors to propose a magmatic–metasomatic origin for the mineralization, that is, replacement past a melt rather than a fluid phase. The largest Ta pegmatites in Australia, Greenbushes, and Wodgina, also belong to the LCT family, but lack the classic zonation seen elsewhere. Greenbushes is a spodumene pegmatite that consists of iv layers. The Ta mineralization is associated with a massive albite–quartz-rich unit, and, like Tanco, the Li is mined from a unlike unit (Fetherston, 2004; Partington et al., 1995). In the Wodgina surface area, Ta has been mined from 2 areas. The Mount Tinstone–Mount Cassiterite surface area consists of a swarm of albite–spodumene pegmatites (Fetherston, 2004), whereas, in the Wodgina surface area, Ta occurs in albite pegmatites that are interpreted to having been derived from the albite–spodumene pegmatites (Sweetapple and Collins, 2002). Less information has been published in international journals on African and Brazilian pegmatites, but mineral chemistry information are available for a number of African pegmatites because of the problem of 'blood coltan' (Melcher et al., 2008). One of the most important Ta pegmatites in Africa is Kenticha in Ethiopia. This is a complexly zoned spodumene subtype LCT pegmatite that Küster et al. (2009) grouped the zones into three units. Most of the Ta mineralization occurs in the upper zone, which as well contains most of the spodumene mineralization, and is thought to represent the most evolved unit (bottom-to-top crystallization; Küster et al., 2009). Other pegmatites in Africa include Morrua and Marrapino in Mozambique, which are deeply weathered, and the Democratic Republic of the congo contains many eluvial and alluvial placer deposits that are pegmatite-derived (Fetherston, 2004).

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GEMSTONES

C. Oldershaw , in Encyclopedia of Geology, 2005

Pegmatites

Pegmatites are intrusive igneous rocks. They produce a greater range of gemstones than whatsoever other rock type and accept also been the source of some of the largest gemstones ever mined. The large crystals form as the water-rich portion of a granite-similar molten rock is put nether increased pressure as it is squeezed into fractures in the surrounding rock. As the molten rock begins to solidify, the elements that it contains begin to crystallize. The largest gemstones and some quite rare gemstone varieties are found in precious stone pockets at the middle of the pegmatite, where they have formed from the hot concentrated mineral-rich fluid that was the last to crystallize ( Figure 6).

Pegmatites occur throughout the globe, but the largest gem-producing pegmatites are those of Minas Gerais, Brazil. Other pegmatite areas include the Pala area of San Diego County in California, the Nuristan expanse of Afghanistan, the Sverdlovsk region of the Urals, and the Altai region of north-western Cathay. Gems formed in pegmatites include topaz, tourmaline, kunzite, and members of the beryl family, such as the blue aquamarine and the pink morganite.

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Geological Setting of Amazonite

Mikhail Ostrooumov , in Amazonite, 2016

2.3.3 Amazonitic Pegmatites

Amazonitic pegmatites—one of the almost well-known and widespread genetic types of amazonite-containing rocks—are particular to all iii rare-metal-bearing granite formations. The mineralogical-geochemical features of such pegmatites, every bit well every bit the degree of the development of the amazonitization procedure in them, depends on their formational nomenclature, age, and formation depth.

In the alaskite germination, amazonite occurs in pegmatites quite rarely, and the intensity of amazonitization of potassium feldspars ranges from very weak in endocontact pegmatites (western Baikal region; Kazakhstan) to medium in exo-intrusive pegmatite veins (Canada and India). For the latter, which equally a dominion are embedded in various metamorphic rocks (gneisses, schists, and others), a visible connection with the granitoids sometimes observed in these districts has not been established. These pegmatites, having lentiform or stock form, are characterized past well-expressed zonality. Intensively occurring in the strongly differentiated pegmatite veins are the afterward processes of silicification and albitization, with which is connected the formation of accessory beryl, columbite-tantalite, samarskite, and other rare-metal minerals.

Granite plutons that enclose pegmatites of this formational blazon are composed of coarse- to medium-grained leucogranite rocks [4]. Pegmatite veins take a lenticular form; sometimes these are schlieren-blazon pegmatoid isolations invariably of small sizes (length of a few dozen meters, thickness of a few meters). They are weakly zoned, as expressed in the replacement from the contact of bodies toward their center of ii to 3 varieties by indistinctly exposed, only distinct textures (graphic, apographic, and block). The chief rock-forming minerals of pegmatites are microcline, pale-green amazonite, oligoclase, albite, and quartz.

Very rarely, insignificant amazonitization of potassium feldspar that encloses cavities with crystal fluorite and pure quartz is reported in miarolitic pegmatites located in crystal-pegmatite-begetting intrusions (Kazakhstan). Endocontact pegmatites were formed primarily in the Paleozoic and are distinguished past a dependence on germination depths of muscovite-topaz or biotite-fluorite (Ural) mineralization [47].

Amazonitic pegmatites of the subalkaline-leucogranite formation are not associated directly with granitoid plutons and are embedded in all manner of metamorphic rocks of Precambrian and more than rarely of Paleozoic age: granitogneisses, schists, amphibolites, quartzites, and others. Pegmatite bodies take dike-vein form, are of medium size (length, from a few hundred meters to several kilometers, thickness of several meters, in rare cases up to 10 m), and are weakly differentiated.

The mineral complex associated with green-yellowish and light-green amazonitic potassium feldspar is represented equally lepidolite, polychromatic tourmaline, and beryl, and rare tantalum-niobium oxides (Canada, Sweden, USA). In rare cases and in insignificant quantities, spodumene is noted hither, but, as mentioned already, amazonite is not typical for microcline-albite and albite pegmatites with lithium minerals (of sodium-lithium type).

Most interesting and of import in practical terms are amazonitic pegmatites of the alkali metal-granite formation. Characteristic for them are a wide and intensive development non only of amazonitization, merely also of other post-magmatic processes (albitization, greisenization, and ore formation). According to the data of I.V. Bel'kov and A.Ia. Lunts, pegmatite bodies with amazonite are localized predominantly in the far and near exocontacts of alkaline plutons and are confined to partially transformed element of group i dissolution or unaltered gneisses, schists, and other metamorphic rocks.

The most ancient amazonitic pegmatites of Precambrian age with rare-earth mineral paragenesis are known at present in many regions of the globe: in Russia on the Kola Peninsula and in eastern Siberia including the Baikal region, the USA, Nigeria, Mozambique, and elsewhere [seven,47] [7] [47] . The grade of these pegmatite bodies is most ofttimes lentiform-vein, and their length ranges from a few dozen to a few hundred meters, more than rarely up to 400 to 600 m, with thickness from a few meters upwards to 15 to 20 m in the burl of veins. Zonality in pegmatite bodies is expressed adequately weakly and is reported only in terms of the increase in size of individuals of stone-forming minerals in the direction from the selvage toward the center of veins and in the change in the same direction of the colour tone of potassium feldspar from gray and pink to bluish-green of various hues and saturation. Autonomously from microcline and amazonite, the principal minerals of pegmatites include albite and quartz, the secondary minerals include biotite, fluorite, magnetite, garnet, and the accessory minerals include gadolinite, tantalite-columbite, genthelvite, fergusonite, cyrtolite, and galena, and more rarely yttrialite, thorite, pyrochlore, samarskite, and beryl.

The early on to mid-Paleozoic amazonitic pegmatites are fairly close to those described in a higher place in terms of class, sizes, and internal structure, but they are singled-out in terms of their accessory mineralization: gadolinitic with beryl (Iakutiia, Russia; southern Norway) or merely beryllic (western Baikal region and eastern Saiian, Russia; Poland).

Amazonitic pegmatites of belatedly Paleozoic age associated with the alkaline-granite germination are known in Russia in the Ural and in Tuva, as well every bit in Republic of madagascar and in the United states of america. Characteristic for these are platy and lentiform forms of bodies, curt length (as a rule, of several dozen meters) and thickness (upwards to 5 or 10 m). Pegmatite veins are differentiated, and their larger role is occupied past zones of graphic and pegmatoid texture, which sometimes incorporate large cavities with crystals of feldspars, quartz, topaz, and several other minerals. Rock-forming minerals of these pegmatites are represented by microcline, amazonite, albite, and quartz; the secondary minerals are micas; and the accessory minerals are garnet, topaz, beryl, phenakite, columbite, fergusonite, samarskite, helvite, and thorite.

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Volume one

Cahit Helvaci , in Encyclopedia of Geology (Second Edition), 2021

Magmatic Sources

Pegmatites and contact-metamorphic rocks contain assemblages of diverse boron-containing minerals, such equally datolite, ludwigite, paigeite, and tourmaline. These correspond concentrations of boron that relate more than or less directly to the crystallization of an intrusive granitic magma. Analyses evidence that granites boilerplate almost x ppm boron, with a few exceptions ranging upwards to 300 ppm. However, boron does not readily enter into the crystal structures of the common rock-forming minerals; hence, when magma crystallizes, the boron is thought to concentrate in the residual water which may be subsequently released. The combination of high temperatures (300–400 °C) and fluids nether high pressure at an intrusive contact could also extract some boron from the adjacent country rocks. These borate skarn deposits, some of which are associated with iron ores and magnesium deposits of commercial grade, are mined in both eastern Russian federation and People's republic of china (Figs. 1 and 2).

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Geochemistry of Mineral Deposits

A. Audétat , J.B. Lowenstern , in Treatise on Geochemistry (Second Edition), 2014

xiii.half-dozen.6.5 Pegmatites

Many pegmatites are associated with mineralization of Nb, Ta, Sn, Zr, Hf, and REE and/or gemstones (see Capacity 13.21 and thirteen.23). The common presence of large, well-preserved fluid and melt inclusions in pegmatite minerals has led to a huge body of dominantly Russian literature. General aspects of pegmatite formation have been discussed in London (2008), whereas a review on the salient features of melt and fluid inclusions tin can be found in Thomas et al. (2006b). Bachelor evidence suggests that the magmatic-to-hydrothermal development of pegmatites is very complex and usually involves multiple types of silicate melts and aqueous fluids that either coexist with each other or continuously grade into each other (cf. Section 13.half-dozen.v.ane ). Hither, the authors focus on a few selected studies that provide information on the metallic content of pegmatitic liquids.

Kovalenko et al. (1996) studied exceptionally well-preserved melt inclusions in topaz from the gem pegmatite fields in Volhynia. They found that these melts were trapped at 650–700 °C/280–300 MPa and coexisted with a single-phase, aqueous fluid of ~xviii wt% NaCl_equiv salinity. SIMS analyses of homogenized melt inclusions revealed high concentrations of Rb (~ 2000 ppm), Cs (~500 ppm), and Be (~300 ppm). The presence of columbite, cassiterite, wolframite, uraninite, graphite, and monazite inclusions on the aforementioned growth zones as the melt inclusion provides unambiguous proof for a magmatic origin of these minerals.

Evidence for farthermost degrees of cook fractionation and associated enrichment in ore-forming elements in melt inclusions from the Sn–W-mineralized Ehrenfriedersdorf pegmatite, Frg, was reported by Webster et al. (1997), Rickers et al. (2006), Thomas et al. (2011), and Borisova et al. (2012). According to SIMS, LA-ICP-MS and Synchrotron 10-ray fluorescence (XRF) analyses, blazon B melt inclusions incorporate 0.one–0.5 wt% SnO_two, 0.half-dozen–vi.9 wt% P₂O₅, 0.1–0.nine wt% Cs₂O, 2.6–6.2 wt% F, 1.0–4.7 wt% B₂O₃, iv.3–6.7 wt% Cl, and 0.ii–ii.8 wt% BeO.

Even more extreme degrees of cook fractionation are indicated by melt inclusions studied from the tourmaline-rich gem pegmatites of Malkhan, Russian federation (Peretyazhko et al., 2004). These melts were trapped at 570–615 °C and 100–300 MPa and coexisted with an aqueous fluid containing 4–eight wt% NaCl_equiv and 12–16 wt% H₃BO₃. The melt independent 58 wt% SiO_two, 2.five wt% B₂O_iii, 2.7 wt% F, and ~ half-dozen–12 wt% H₂O and extremely high concentrations of Cs_iiO (4–5 wt%), Ta (0.6 wt%), Nb (0.1 wt%), and Be (0.1 wt%).

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High-Tech Metals in Finland

O. Sarapää , ... T. Al-Ani , in Mineral Deposits of Republic of finland, 2015

Somero-Tammela Re Pegmatites

The Somero-Tammela RE pegmatite area in the Häme belt, southern Finland, is 400 km ² in total size and comprises at least 56 complex pegmatites enriched in Li, Nb, Ta, Be, Sn, Cs, P, and B. The Häme chugalug is equanimous of mafic volcanic rocks and mica schists into which syntectonic gabbro, diorite, granodiorite, tardily-tectonic microline granite, and finally LCT pegmatites dikes accept intruded (Alviola, 2003; Ahtola, 2012). RE pegmatites include lithium silicates and phosphates such as cookeite, elbaite, heterosite-siclerite, lepidolite, lithiophilite, petalite, spodumene, triphylite, and Li-Fe-micas (Vesasalo, 1959; Alviola, 1993).

The largest and best-known Li pegmatites are the Hirvikallio petalite pegmatite and the Kietyömäki spodumene pegmatite. Hirvikallio was drilled by GTK in 1958 and afterwards studied by Lohja Oy/Partek Oy in 1974–1996. The dike is 170 m long, v–25 m wide, and contains 0.2 Mt with i.eight wt% LiO_ii to the depth of 50 chiliad. The Hirvikallio petalite pegmatite occurs in a weakness zone along the contact betwixt mica schists and amphibolites (Vesasalo, 1959). Petalite contains 4.74 wt% Li₂O and a very low fe content of 0.01 wt% Fe_twoO_iii. The Kietyönmäki dike swarms were drilled past GTK in 1987–1988. Petalite occurs only in 1 dike; elsewhere it has completely been converted to spodumene and quartz by hydrothermal amending (Alviola, 1993). The main dike contains 0.4 Mt with 1.5% Li_iiO, 0.016% Sn, 0.003% Ta. It is highly probable that several undiscovered RE pegmatites nevertheless occur in the Somero-Tammela area.

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Volume 5

Rolf L. Romer , Michel Pichavant , in Encyclopedia of Geology (2d Edition), 2021

Abstruse

Rare-metal granites and pegmatites are highly evolved rocks that form in a wide range of different tectonic settings. Ore element associations may vary widely, depending on source rocks, conditions of source rock melting, extent of fractionation, and weather of cook-hydrothermal transitions. The range of textural variation and of associated mineral deposits largely depend on local constraints at the level of emplacement of these highly fractionated granites. For Sn, West, Ta(-Nb) and Li specific rare metallic granites, the protoliths are dominantly sediments, characterized by low Ca and Na contents, and for this reason they are commonly referred to as "S-blazon" granites. The predominance of Sn over W or Li-Cs-Ta in mineral deposits related to these granites reflects dissimilar melting weather in the source region and partitioning of these elements at the melt-hydrothermal transition. Subsequently the separation of fluid from the granite magma, Sn and W are transported in separate loftier temperature (250–450 °C) aqueous solutions whose physicochemical parameters command degradation mechanisms and make up one's mind the nature of the hydrothermal deposits that ultimately form (i.east., veins, greisen or skarn).

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Igneous Rocks

S.K. Haldar , Josip Tišljar , in Introduction to Mineralogy and Petrology, 2014

4.two.one.iii Shapes and Structures of Veins Igneous Rocks

At the stop of magmatic crystallization, i.east. pegmatite and pneumatolytic phase of crystallization, often magma penetrates into cracks in surrounding rocks of stony crust and crystallize in the grade of thin plates (dykes or sills) ( Fig. four.5). These are igneous rocks known as the veins rocks (Table 4.1). If the magma in pegmatite or pneumatolytic stage of crystallization is pushed parallel in-betwixt layers, information technology forms igneous body with the shape of saucer. It is known by the name sill or concordant intrusive sail (Fig. iv.5).

An important textural feature of the veins rock (aplite, pegmatites and lamprophyre, Table 4.i) is holocrystalline and microcrystalline in aplite and lamprophyre, macrocrystalline in pegmatites and oft with some giant crystal of bore upwards to several meters (Section four.three.3).

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MINERALS | Zeolites☆

Westward.Due south. Wise , in Reference Module in World Systems and Environmental Sciences, 2013

Late-stage crystallization and amending of pegmatitic bodies

Zeolites are common phases in the late stages of pegmatite crystallization. Early in the formation of a pegmatite dike, magmatic crystallization produces the bulk of the minerals, but equally the magma is depleted and the temperature decreases excess H _iiO forms a fluid phase. This fluid produces minerals at lower temperatures, many every bit amending products of earlier phases. Fantabulous examples of hydrothermal zeolite formation in pegmatite bodies are found in the Lovozero Massif, Kola Peninsula, Russia. Here, all of the pegmatite pods, lenses, pipes, and dikes are nepheline syenite. Some analcime may be magmatic in origin, but much of information technology, along with the very abundant natrolite, is of hydrothermal origin.

Zeolites too occur in vapor pockets late in the crystallization of granitic pegmatite dikes, mostly every bit a result of the alteration of feldspar either by remainder magmatic fluid or by introduced H₂O. Laumontite and stilbite are commonly precipitated along fractures or in miarolitic cavities. A well-known example is the granodiorite pegmatite dikes near San Piero in Campo on the island of Elba, Italia, where mordenite, dachiardite, stilbite, epistilbite, heulandite, and chabazite occur with pegmatite pocket minerals quartz, tourmaline, beryl, pollucite, and lepidolite.

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