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Alteration in greisen-type granites develops through the progressive replacement of feldspars by potassic micas. Under the name 'greisen', quartz–muscovite assemblages display differences and include a variety of facies with variable relative proportions of quartz and muscovite. In principle, feldspar conversion to muscovite is written usually considering constant aluminium, and should result in a modal proportion of six quartz plus one muscovite. In Beauvoir greisens, which result from albite-rich granite, the relative proportion of quartz–muscovite is in favour of muscovite. Such a balance results from a reaction that implies imputs of potassium and aluminium, thus different from the classic one. The Q'-F' diagram provides a graphical solution for discriminating between reaction paths. A representative series of greisen data from the literature is compared in this diagram: Beauvoir B1 unit, Cligga Head, Cinovec, Panasqueira, Zhengchong, and Hoggar. [ABSTRACT FROM AUTHOR]

The Sn-W ore deposits in the Krupka surroundings are associated with greisens, which occur in the upper parts of Late Variscan granitoid intrusions. Fluid inclusions were studied in samples of quartz, cassiterite, apatite, fluorite, and topaz in greisenized granites, greisens, and hydrothermal veins with Sn-W mineralization. The greisenization process took place at temperatures 370–490 °C and pressures 155–371 bars, and associated fluids had predominantly low salinity and a low gas (CO2, N2 and CH4) content. The post-greisenization stage was connected with the formation of (i) low-salinity (0–8 wt. % NaCl eq.) fluid inclusions with homogenization temperatures <120–295 °C and (ii) high-salinity (18 to >35 wt. % NaCl eq.) fluid inclusions with homogenization temperatures 140–370 °C, often containing trapped crystals of quartz, topaz, and sulfides, or daughter crystals of salts and carbonates, which were identified by microthermometric measurements, electron microprobe analysis, and Raman spectroscopy. Analyses of fluid inclusion leachates have shown that Na and Ca chlorides predominate in fluids. According to hydrogen stable isotopes, the source of greisenizing and post-greisenizing fluids was not only magmatogenic but also meteoric water or fluids derived from sedimentary rocks. [ABSTRACT FROM AUTHOR]

Alteration in greisen-type granites develops through the progressive replacement of feldspars by potassic micas. Under the name ‘greisen’, quartz–muscovite assemblages display differences and include a variety of facies with variable relative proportions of quartz and muscovite. In principle, feldspar conversion to muscovite is written usually considering constant aluminium, and should result in a modal proportion of six quartz plus one muscovite. In Beauvoir greisens, which result from albite-rich granite, the relative proportion of quartz–muscovite is in favour of muscovite. Such a balance results from a reaction that implies imputs of potassium and aluminium, thus different from the classic one. The Q’-F’ diagram provides a graphical solution for discriminating between reaction paths. A representative series of greisen data from the literature is compared in this diagram: Beauvoir B1 unit, Cligga Head, Cinovec, Panasqueira, Zhengchong, and Hoggar.

The Mayo-Darley massif is an anorogenic complex of the Cameroon Line that has a mantle origin. Tin-bearing rocks were analyzed by ICP-AES and INAA analytical methods. The purpose of this work was to provide new geochemical data for the Mayo-Darley tin formation and to understand its petrogenesis and the origin of tin mineralization. The Mayo-Darley tin deposit is made up of tin-granite, and tin-greisen, greisenification was developed on the borders of quartz dykes. These rocks belong to the alkaline series and were classified into acid (SiO2 = 61.6%–73.8%; 65.4%–98% respectively) and basic (42.9%–47% SiO2) rocks. They showed enrichment in HSFE, LILE, Ga/Al and chondrite normalized REE patterns indicating LREE enrichment relative to HREE with a negative Eu anomaly, only sample SB8 of tin-granite showed Eu/Eu* = 1.11. Rocks display metaluminous, peralkaline, peraluminous, ferroan, high-K calc-alkaline to shoshonitic, alkalic to calcic affinity, and crystallized at 800 °C. The chemistry of this deposit reflects the primary composition of granite, quartz monzonite, gabbro, and foid gabbro. This complex experienced multi-stage sub-solidus hydrothermal fluid reactions and shows variable alteration of feldspars alkali mobility. The rocks are classified as A1-type granite, overlap with the OIB field, and were derived from a within-plate setting, similar to mantle non plume-derived magmas. The origin of tin mineralization in Mayo-Darley has a complex evolution, tin mineralization was derived from hydrothermal and hydrogenous metal-rich deposits and shows Sn–Hf–Zr and Sn–Tl–Nb association. These new data confirm the complexity of the Mayo-Darley tin complex and elucidate the origin of tin mineralization. [ABSTRACT FROM AUTHOR]

The Boam Li deposit in Uljin, South Korea, is a hard-rock Li deposit composed of albite-spodumene pegmatite and lepidolite-elbaite greisen. The timing of Li mineralization in the Boam deposit is poorly constrained due to a wide range of the mica K-Ar ages of the greisen from 176 to 127 Ma. We investigated the microstructure, mineral composition, and U-Pb age of zircons separated from the albite-spodumene pegmatite of the Boam Li deposit. Zircons are found as inclusions in spodumene and discrete grains intergrown with secondary albite, muscovite, columbite group mineral (CGM), microlite, and apatite, indicating that the zircon was saturated during the intrusion of pegmatite melt and subsequent greisenization of the Boam deposit. Most zircons have altered porous domains in cores mantled by overgrown rims with contrasting microstructures and chemical compositions. The porous domains in zircon cores contain Ca, Al, and Fe-bearing zircon solid solution, quartz, K-feldspar, muscovite, CGM, and microlite, which indicates pervasive alteration during greisenization. Higher U contents and Zr/Hf ratios of the core than the rim suggest that the melt from which the zircon cores crystallized was U-rich and less evolved. The overgrown rim domain with weak oscillatory zoning occurs in association with albite, muscovite, and apatite. Based on the microstructure and zircon compositions, we suggest that the SHRIMP U-Pb age of the zircons from the pegmatite indicates the timing of greisenization and Li mineralization in the Boam deposit. The zircon core and rim U-Pb isotope data constitute a single discordia line, yielding a weighted mean age of 172.4 ± 1.1 Ma (MSWD = 2.3). The age is consistent with the oldest mica K-Ar age of the lepidolite-elbaite greisen in Uljin. [ABSTRACT FROM AUTHOR]

Topazolite (greisen) is a rock formed essential by quartz and topaz, with accessory white mica, tourmaline, sulphides (molybdenite and arsenopyrite), wolframite and cassiterite. This rock was found in the Krkonoše and Jizera Mountains in the western Sudetes. In Poland, this metasomatic rock occurs at the contact between leucogranite and mica schist (associated with hydrothermal kaolinization) in a narrow zone between the settlements of Rebiszow and Gierałtówek. On Czech territory, similar topaz quartzolite (greisen rock), consisting of up to 65 % quartz and 32 % topaz, was found near the settlements of Růžek and Vítkov near Chrastava in association with orthogneiss. The high content of topaz in this rock offers the possibility of using it as an abrasive in high-speed abrasive water jet technology for cutting and surface treatment of hard metallic and nonmetallic materials. In the crushed form, after being concentrated in a treatment plant, topaz could be a natural abrasive with a wide range of applications. However, the results of technological testing of the physical and mineralogical characteristics of the topaz concentrate indicate its unfavorable properties caused by the high fissility of topaz. This leads to losses of topaz during its technological adjustment to the required grain size or during recycling. It has been shown that abrasive concentrates with topaz content above 90 % are promising, especially for special applications of abrasive water jet technology. Mastering the technology for processing of the source raw material, i.e. topaz quartzolite, into a topaz-rich concentrate, and subsequent applied research on the use of topaz abrasives in industry are crucial. [ABSTRACT FROM AUTHOR]

The Sn-W ore deposits in the Krupka surroundings are associated with greisens, which occur in the upper parts of Late Variscan granitoid intrusions. Fluid inclusions were studied in samples of quartz, cassiterite, apatite, fluorite, and topaz in greisenized granites, greisens, and hydrothermal veins with Sn-W mineralization. The greisenization process took place at temperatures 370–490 °C and pressures 155–371 bars, and associated fluids had predominantly low salinity and a low gas (CO2, N2 and CH4) content. The post-greisenization stage was connected with the formation of (i) low-salinity (0–8 wt. % NaCl eq.) fluid inclusions with homogenization temperatures 35 wt. % NaCl eq.) fluid inclusions with homogenization temperatures 140–370 °C, often containing trapped crystals of quartz, topaz, and sulfides, or daughter crystals of salts and carbonates, which were identified by microthermometric measurements, electron microprobe analysis, and Raman spectroscopy. Analyses of fluid inclusion leachates have shown that Na and Ca chlorides predominate in fluids. According to hydrogen stable isotopes, the source of greisenizing and post-greisenizing fluids was not only magmatogenic but also meteoric water or fluids derived from sedimentary rocks.

This paper is a scientific overview of studies of accessory cassiterite from rare metal granites, pegmatites, and accompanying greisens in 1990–2021. The earlier and newest data on the morphology, physical and chemical features of accessory cassiterite, and its economic facility are summarized. The consolidated database includes 1759 cassiterite compositions from more than 100 publications. We have confirmed previous and identified new indicator features of cassiterite from rare metal granites, pegmatites, and greisens: concentrations of isomorphous components (Ta, Nb, Fe, Ti, Mn, W, Sc, In, Zr, Hf, U), informative ratios (Nb/Ta, Zr/Hf, Fe/Mn), and main substitution schemes ("tapiolite" and "hydrothermal"). The average trace element content in cassiterite from granites, pegmatites, and greisens is 6.68, 4.87, and 1.18 wt %, respectively. Based on the published data, the solubility limit of tapiolite (Fe,Mn)(Ta,Nb)2O6 in the structure of cassiterite is calculated. These limit is 0.1–11, 0.7–12.8, and 0.1–3.3% in granites, pegmatites, and greisens, respectively. The tapiolite endmember proportion in cassiterite ranges from 0.1 to 12.8%. It is noted that tantalum-bearing cassiterite is predominantly observed in Li–F plumasite granites and LCT lepidolite pegmatites with the high phosphorus concentration over the range of 0.12–2.50 wt % P2O5. The Ta2O5 content in accessory cassiterite reaches 17.9–18.4 wt % and promises additional economic prospects for rare metal pegmatites and granites. Cassiterite can be used as an alternative source of tantalum, indium, niobium, and scandium. Typical occurrences of accessory cassiterite have been identified in granites of the Beauvoir massif (France), in pegmatites of the Peerless (USA) and Varuträsk (Sweden) deposits, and in greisens of the Kester and Polyarnoe deposits (Yakutia). Accessory cassiterite is an advanced mineral geochronometer for rare metal granites and pegmatites, since it is not susceptible to radiation damage and disruption of the U–Pb isotope system. [ABSTRACT FROM AUTHOR]

Trace elements in quartz reflect the physio-chemical conditions of growth of the mineral and are also capable of tracing the evolution history of the associated ore-forming fluid, and are therefore a potential discrimination signature for different styles of ore genesis. In this study, we compile data on quartz trace elements from 25 porphyry, pegmatitic, greisen, skarn, epithermal, Carlin and Mississippi Valley type (MVT) deposits. Trace elements that relate to the Si4+ substitution types and precipitation conditions of quartz, such as Li, Al, Na, P, K, Ti, Fe and Ge, have been chosen to plot different geochemical diagrams. The quartz Ti vs. Al/Ti, Al vs. Al/Ti and Ti–10Ge–Al/50 diagrams reveal the evolution of the hydrothermal fluids in different types of ore deposits. The results confirm that Ti4+ incorporation into quartz is generally related to temperature variation, whereas Al3+ incorporation is more likely controlled by pH fluctuation. The trace element compositions of quartz from porphyry, greisen, pegmatitic, skarn, epithermal, Carlin and MVT deposits are distributed along a C-shape curve in the Ti–10Ge–Al/50 diagram, which is consistent with temperature decrease. In addition, there are different independent partitions in the Ti–P–Na geochemical source discrimination diagrams, which potentially discriminate the quartz from porphyry, pegmatitic, greisen, skarn, epithermal and Carlin type of deposits. This study shows that quartz trace elements can be used as a useful proxy for tracing the evolution of the hydrothermal fluids in different types of ore deposits and are also a useful auxiliary tool to discriminate different modes of ore genesis. [ABSTRACT FROM AUTHOR]

The Koklan W–Mo deposit in Transuralia is confined to the eponymous Middle Permian leucogranitic pluton, which intrudes a sequence of the Lower Paleozoic crystalline schists with lenses of ultramafic rocks, marbles, and skarns. The economic stockwork W–Mo mineralization spans both outer and inner contacts of the pluton and is related to greisenization. The economic subdivision of ores is based on host rocks. The ores of granite and schist types (88.7% in total) are dominant in contrast to strongly subordinate ultramafic and skarn types. Molybdenum is mostly contained in molybdenite and, rarely, in scheelite. Tungsten is mainly related to scheelite; wolframite is extremely rare. The Mo and W contents of ores and rocks show no correlation. The major ore minerals are pyrite, molybdenite, and scheelite; subordinate minerals include chalcopyrite, pyrrhotite, and magnetite, and rare minerals are arsenopyrite, gersdorffite, nickeline, pentlandite, tetrahedrite, bornite, galena, native bismuth, bismuthinite, Bi sulfosalts, and uraninite. [ABSTRACT FROM AUTHOR]

The discovery of placer tin in southern Stewart Island caused New Zealand's only known tin-rush. The source of at least some of the placer tin is greisenised granodiorite and metasedimentary rocks on the crest of the Tin Range. There are three mineralised lithologies: a sericite-quartz greisen, a quartz-topaz greisen, and a gahnite-schist greisen. However, very little cassiterite (SnO2) is observed and instead wolframite ((Fe,Mn)WO4) and gahnite (ZnAl2O4) are common. U-Pb dating of host early Paleozoic Pegasus Group metasediments indicate the area experienced metamorphism at ∼117 Ma (monazite), with granodiorite emplacement at 107.9 ± 2.2 Ma (zircon). U-Pb isotope and trace element analysis of xenotime in the mineralised zone reveals three distinct growth phases: one at 107.5 ± 1.8 Ma that overlaps with granodiorite emplacement, and then 94.2 ± 0.9 Ma and 91.6 ± 0.6 Ma. Although it is not clear precisely which growth phase correlates with mineralisation, it must have been a mid-Cretaceous event and we correlate it with the ∼108 Ma Tin Range Granodiorite. The window of mineralisation, ∼ 108-92 Ma, means that this event was likely associated with the initiation of thinning of the Zealandia lithosphere as a precursor to separation from Australia and Antarctica. [ABSTRACT FROM AUTHOR]

The Abu Dabbab albite granite (ADAG), in the central Eastern Desert of Egypt, hosts the most significant rare metal ore deposit in the northern part of the Neoproterozoic Arabian‐Nubian Shield. Here, we report detailed field, petrographic, mineralogical and geochemical investigation of the ADAG, an isolated stock‐like granitic body with sharp intrusive contacts against metamorphic country rocks, probably emplaced at about 600 Ma. The fine‐grained porphyritic upper unit is a preserved remnant of the shallowly‐emplaced apex of the magma chamber, whereas the medium‐grained lower unit crystallized at deeper levels under subvolcanic conditions. The peraluminous leucocratic ADAG shares common geochemical characteristics with post‐collisional intraplate A‐type magmas. In addition to the conspicuous enrichment in Na2O, the ADAG is remarkable for its anomalous concentrations of Ta, Nb, Li, Hf, Ga, Sn, Zn and heavy rare‐earth elements. Nb‐Ta minerals in the ADAG are mixed with Fe‐Mn oxides, forming black patches that increase in abundance toward of the base of the intrusion. Columbite‐tantalite, cassiterite and wolframite are the most important ore minerals. Pronounced negative Eu anomalies (Eu/Eu∗ = 0.10–0.24) reflect extreme magmatic fractionation and perhaps the effects of late fluid‐rock interaction. The ADAG was most likely generated by partial melting of the juvenile middle crust of the ANS as the geotherm was elevated by erosional uplift following lithospheric delamination and it was emplaced at the intersection of lineations of structural weakness. Although formation of the ADAG and its primary enrichment in rare metals are essentially due to magmatic processes, late‐stage metasomatism caused limited redistribution of rare metals. Fluid‐driven subsolidus modification was limited to the apex of the magma chamber and drove development of greisen, amazonite, and quartz veins along fracture systems. [ABSTRACT FROM AUTHOR]

The Kougarok prospect is situated in a Sn-W (+Ta, Nb, Li, Be) metallogenic belt formed in a post-collisional to within-plate tectonic environment. Crystal fractionation of granitic magma, combined with its mixing/mingling with mantle-derived mafic magma, is proposed as the major process causing the formation of the complex B-rich to Li-F-type granitic suite and associated Sn-rare metal (Ta, Nb, Li) mineralization. An intrusion of alkalic (potassic lamprophyric) mafic magma into a crystallizing biotite-tourmaline granite magma reservoir may have supplied a geochemically distinct assemblage of volatiles (F) and associated metals (Li, Ta, Nb) into the boron- and Sn-rich granitic system. An alternative model considers differentiation-driven unmixing of mafic and granitic silicate melts sequestering different volatile and mineralizing species that could also trigger magma-fluid and fluid-fluid unmixing, with separation of gaseous fluid coexisting with immiscible granitic and mafic magmas in the form of magmatic melt-fluid-crystal "suspension." Biotite-tourmaline granite was accompanied by early quartz-tourmaline-cassiterite greisen at > 430–380 °C followed by quartz-tourmaline-chlorite-cassiterite stockwork at < 350 °C. The immiscibility of F- and B-rich fluids was followed by preferred ascent of F-rich fluids upward in the granitic magma reservoir, with its strong enrichment in F, Li, Ta, and Nb and subsequent crystallization of zinnwaldite granite at a shallower level, with separation of homogenous high-salinity magmatic fluid at ~ 600 °C. Crystallization and fluid exsolution continued at lower temperatures, followed by formation of topaz-quartz stockscheider at 550–500 °C. Ta-Nb mineralization in the uppermost part of the zinnwaldite granite appears to be associated with final episodes of magmatic crystallization, particularly W-Nb-rutile and columbite-tantalite with a higher Nb content. Some Ta-Nb minerals, such as columbite-tantalite with a higher Ta content, appear to be also stable during the post-magmatic stage, in quartz-tourmaline+topaz greisen and higher-temperature quartz-albite-Li mica alteration that replace zinnwaldite granite at ~ 500 to 400 °C. Nearly contemporaneous, lower-temperature quartz-albite-Li mica alteration and quartz-muscovite, quartz-topaz, and quartz-fluorite greisens formed from boiling fluids at 390–350 °C and caused removal of Ta-Nb minerals. Instead, fluid cooling and neutralization of boiling fluids affected Sn solubility and promoted massive cassiterite deposition in the late greisens. The latest phyllic quartz-sericite-carbonate alteration assemblage, comprising arsenopyrite, pyrrhotite, chalcopyrite and other sulfides, native Bi, and Bi tellurides, formed from boiling fluids at < 310 °C. [ABSTRACT FROM AUTHOR]

The Badzhal tin magmatic-fluid system of the eponymous volcanoplutonic zone in the Middle Amur Region has been studied to reveal special characteristics of the transition from granite crystallization to rare-metal deposition. Therefore, the authors have conducted an in-depth study of melt, fluid-melt, and fluid inclusions and oxygen isotope composition of minerals from granitic rocks of the Verkhneurmiisky pluton within the Badzhal volcanoplutonic zone and minerals of the Pravourmiisky and Blizhnee Sn-W deposits. Greisen alteration and hydrothermal veins at the Pravourmiisky and Blizhnee deposits resulted from a single magmatic-fluid system related to the Verkhneurmiisky granite pluton, which is one of domes of the Badzhal batholith. The transition has been traced from magmatic crystallization of granite to hydrothermal ore formation and evolution of magmatic fluid from its separation to Sn and W deposition. Mixed fluid-melt inclusions directly support tin-bearing fluid separation during melt crystallization. The glass compositions indicate that granite and porphyry granite crystallized from felsic metaluminous to peraluminous melts with an ASI index and alkali content ranging from 0.95 to 1.33 and from 6.02 to 9.02 wt %, respectively. The Cl and F concentrations in glasses are 0.03–0.14 and 0.14–0.44 wt %, respectively, and are higher than those in the bulk rock compositions, 0.02 and 0.05–0.13 wt %, respectively. These differences indicate that Cl and F could have been removed from a granitic melt during its crystallization and degassing. The H2O concentration estimated based on the electron deficiency of summed microprobe analyses is 8–11 wt %. This was estimated taking into account the possible effect of "sodium loss" (Nielsen and Sigurdson, 1981) when analyzing hydrated glasses. Taking into account the high uncertainty of such estimation (Devine et al., 1995), this value is extremely uncertain and the studied melts should be considered as containing 9.5–10.0 wt % H2O. The melt inclusion study shows that some of the magmatic rocks of the Badzhal ore-magmatic system formed at approximately 650°C. The melt from which these rocks crystallized was felsic, moderate in fluorine, and meta- and peraluminous. Low-temperature crystallization is probably caused by high water pressure and elevated fluorine content. These inclusions most likely characterize the final stage of the pluton, at which crystals, residual melt, and magmatic fluid phase coexist. Fluid responsible for the formation of greisens at the Pravourmiisky deposit has features very close to those of supercritical fluid trapped by magmatic minerals. Its salinity, ranging from ∼9 to 12 wt % NaCl equiv., and maximal temperature of 550°C (taking into account pressure correction for ∼1 kbar) are close to those of magmatic fluid. This makes it possible to relate the origin of the fluid to cooling of the pluton. Greisen and quartz-cassiterite-topaz veins of the Pravourmiisky deposit formed from magmatic fluid at a decreased temperature from 550–450 to 480–380°C. The fluid responsible for the formation of quartz-cassiterite veins at the Blizhnee deposit also separated from magma as indicated by the oxygen isotope composition ( δ 18 O H 2 O ~ 8.5 ‰ ), which evolved in a shallower environment under much lower pressure. This resulted in fluid with a salinity of ∼13 wt % NaCl equiv. at 420–340°C being separated into a low-density low-saline vapor and brine with a salinity of 33.5–37.4 wt % NaCl equiv. The oxygen isotope composition of the mineralizing fluid was governed by equilibrium with granite within a wide temperature range (from ∼700°C to the onset of greisen crystallization). The agreement between the measured data and those calculated based on the suggested model indicates that a significant volume of external fluid having different isotopic features and not in equilibrium with the Verkhneurmiisky granite did not enter the magmatic-fluid system. The revealed differences in the physicochemical formation conditions of the two studied deposits are not critical and support their formation within a single magmatic-fluid system. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Among rock-forming minerals, mica best expresses vertical zoning of granite plutons. • Primary micas are trioctahedral micas of the annite–zinnwaldite–lepidolite series. • Biotite displays distinctly higher contents of Sn, Nb, Ta and W than zinnwaldite. • During greisenization, primary magmatic zinnwaldite was fully re-equilibrated. • Late local muscovitization was accompanied by a new input of Sn to the mica. Abstract The Li-Sn-W deposit Cínovec/Zinnwald in the eastern Erzgebirge (Czech Republic and Germany) represents one of the worldwide best known examples of complex rare-metal plutons with pervasive greisenization. Mica from altogether 38 samples representing all granite and greisen varieties from the present surface to the depth of 1596 m was analysed using electron microprobe (EMPA) and laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) for major (including F, Rb) and trace (Li, Sc, Ga, Ge, Nb, In, Sn, Cs, Ta, Tl, W) elements, respectively. All primary micas at Cínovec are trioctahedral Li-Fe micas close to the annite–zinnwaldite–trilithionite series. Biotite from granites in the deeper part of the pluton (depth of 735–1596 m) contains 33.9–39.6 wt% SiO 2 , 19.6–23.8 wt% FeO, 0.5–0.7 wt% Rb 2 O, 0.9–1.8 wt% Li 2 O, 3.4–4.8 wt% F, 381–937 ppm Nb, 34–134 ppm Ta, 20–46 ppm W, and 93–617 ppm Sn. Zinnwaldite from granites in the upper part of the pluton (depth of 0–735 m) contains 41.2–48.5 wt% SiO 2 , 8.9–15.2 wt% FeO, 0.9–1.9 wt% MnO, 2.0–4.4 wt% Li 2 O, 0.8–1.9 wt% Rb 2 O, 7.0–8.6 wt% F, 43–464 ppm Nb, 101–213 ppm Sn, 6–80 ppm Ta, and 28–52 ppm W. Zinnwaldite from bodies of pervasive greisen and quartz-zinnwaldite veins is, compared to zinnwaldite from granites, relatively slightly enriched in Si, Mn and Ga, and depleted in Fe, F, Rb, Sn, W and Nb; Li and Ta contents are similar. Contents of Li, Rb and F, and the Fe/Mn and Nb/Ta values in mica closely positively correlate with those in the bulk rock, illustrating an upwards fractionation of parental melt. In contrast, the contents of high-field-strength elements in mica do not correspond to their contents in the bulk rock (melt): they were controlled by the order of crystallization of mica vs. accessory oxide minerals. Therefore, biotite generally contains distinctly higher Sn, Nb, Ta, and W than zinnwaldite. Dioctahedral micas of the muscovite–phengite series were found only as a late product of alteration of primary trioctahedral mica. Replacement of greisen-stage zinnwaldite by muscovite is chemically expressed in a strong depletion in Fe, F, and Li, and an enrichment in Sn. The share of trioctahedral mica in the bulk-rock budget of Sn decreases from 40–70% in biotite granite to less than 5% in greisen; in the case of Nb and Ta from 20–50% to less than 10%. The share of mica in the budget of W, mostly in the range of 2–15%, is stable through the whole pluton. [ABSTRACT FROM AUTHOR]

Massive greisens are commonly associated with Sn-W mineralization and constitute low-grade high-tonnage deposits. The formation of this type of deposit results from an intense pervasive metasomatic alteration involving a major fluid and mass transfer through a nominally impermeable parental granite. A decrease in the volume of the solid phases associated with the mineral replacement reactions may be a potential process for creating pathways to enhance fluid flow. Here, we explore the effects of the replacement reactions related to greisenization on the granite's mineralogy and petrophysical properties (density, porosity, and permeability), as well as their potential implications for fluid flow in the case of the world-class Panasqueira W-Sn-(Cu) deposit, Portugal. Mineralogical and microtextural analyses of greisenized facies show that the total replacement of feldspars by muscovite is associated with a volume decrease of the solid phases that induces a significant porosity generation in greisen (~8.5%). Greisenization experiments coupled with permeability measurements show that the replacement of feldspars by muscovite permits new pathways at the crystal scale that significantly enhance the transient permeability. Moreover, permeability measurements performed on representative samples with different degrees of greisenization show that permeability increases progressively with the level of alteration from 10-20 m2 in least granite to 10-17 m2 in greisen. The correlation between the permeability and porosity evolutions demonstrates that the porous texture developed during replacement reactions creates new pathways that enhance significantly the permeability in greisen systems. The occurrences of mineral-bearing metals such as cassiterite in the newly formed porosity of greisen provide evidence that greisenization can be a decisive process for enhancing fluid flow and promoting transport of metals in Sn-W deposits. Finally, we present a model involving a positive feedback between greisenization and permeability, in which mineralizing fluids are able to generate their own pathways in initially impermeable granite via replacement reactions, which in turn promote further hydrothermal alteration and mass transport. [ABSTRACT FROM AUTHOR]

The Hämmerlein polymetallic deposit is hosted in skarn, schists, and gneisses that reached their metamorphic peak at ~ 340 Ma during the Variscan orogeny. The deposit is spatially closely associated with one of the most voluminous granites of the Erzgebirge, the Eibenstock granite which intruded the metamorphic units at ~ 320 Ma, and locally also developed greisen mineralization. Cassiterite is the main ore mineral in the Hämmerlein skarn and in greisen mineralizations associated with the Eibenstock granite. The age of skarn formation is bracketed by multi-mineral Rb-Sr isochron ages of the gneisses (~ 340 Ma) and the end of ductile deformation (> 330 Ma). The dated calc-silicate minerals of the skarn have elevated Sn contents, which implies that some Sn was present in the system during regional metamorphism, i.e., well before the emplacement of the Eibenstock granite. Tin in the > 330 Ma old skarn silicates possibly was mobilized from the metamorphic wall rocks. Retrogression of the skarn mineral assemblage may have released some Sn that formed cassiterite in an assemblage with chlorite and fluorite. The Sr isotope signatures of fluorite indicate that this late assemblage is not related to cooling of the metamorphic rocks, but to the emplacement of the Eibenstock granite, which introduced additional Sn into the skarn. Thus, mineralization in the Hämmerlein deposit includes Sn that was introduced during two different events from different sources. [ABSTRACT FROM AUTHOR]

The Echassières district in central France contains complex rare-element ore deposits, whose formation is related to exotic igneous events and several hydrothermal episodes that are not entirely understood to date. Tungsten mineralization consists of three generations of wolframite, characterized by distinct Fe/Mn ratios (8.4; 3.5 and 0.3, for wolframite a, b and c, respectively), formed during three separate hydrothermal episodes related to the Variscan orogeny. Wolframite a occurs in quartz veins of the La Bosse stockwork where it crystallized before the Barrovian metamorphism that affected these veins and the host rock. After metamorphism, before intrusion of the Beauvoir and Colettes granites, wolframite b crystallized in the stockwork during massive topazification. High concentrations of wolframite c occur in the proximal quartz veins in the Mazet area, while only scant amounts are found in the La Bosse stockwork. In both settings, wolframite c precipitated from the fluid responsible for greisen alteration that massively affected the Beauvoir granite. In the La Bosse stockwork, greisen alteration is characterized by hydrothermal topaz that is texturally and chemically distinct from that precipitated during topazification. Supergene alteration responsible for kaolinization of Beauvoir and Colettes granites caused remobilization of a non-negligible amount of tungsten (W) during replacement of wolframite by W-rich goethite in all units of the Echassières district. This model for multiple W mineralizing events is novel and can prove essential in distinguishing potential economic deposits worldwide.

The world-class W-Sn Panasqueira deposit consists of an extensive, subhorizontal vein swarm, peripheral to a late-orogenic greisen cupola. The vein swarm consists of hundreds of co-planar quartz veins that are overlapping and connected laterally over large distances. Various segmentation structures, a local zigzag geometry, and the occurrence of straight propagation paths indicate that they exploited a regional joint system. A detailed orientation analysis of the systematic joints reveals a geometrical relationship with the subvertical F fold generation, reflecting late-Variscan transpression. The joints are consistently orthogonal to the steeply plunging S-S intersection lineation, both on the regional and the outcrop scale, and are thus defined as cross-fold or ac-joints. The joint system developed during the waning stages of the Variscan orogeny, when already uplifted to an upper-crustal level. Veining reactivated these cross-fold joints under the conditions of hydraulic overpressures and low differential stress. The consistent subperpendicular orientation of the veins relative to the non-cylindrical F hinge lines, also when having an inclined attitude, demonstrates that veining did not occur during far-field horizontal compression. Vein orientation is determined by local stress states variable on a meter-scale but with the minimum principal stress consistently subparallel to fold hinge lines. The conspicuous subhorizontal attitude of the Panasqueira vein swarm is thus dictated by the geometry of late-orogenic folds, which developed synchronous with oroclinal buckling of the Ibero-Armorican arc. [ABSTRACT FROM AUTHOR]

A new finding of Zn-spinel (gahnite) in biotite metasomatic rock of the Verkhneurmiysky copper-tungsten-tin ore cluster is described in this paper, including the chemical composition of gahnite, its paragenesis, and place in the regional evolution history of hydrothermal processes. Gahnite is commonly localized in biotite-microcline metasomatic rocks at the lower subore stage of the greisen metasomatic column in proximity to the exocontact of the rare-metal granite massif. Gahnite from rare-metal ore occurrences belongs to the hercynite-gahnite-franklinite isomorphic series and contains significant isomorphic admixtures of iron (24.3%) and manganese (0.65%). Based on our results and earlier published data, it is suggested that gahnite can be a mineral-indicator of rare-metal metasomatism. [ABSTRACT FROM AUTHOR]

The origin and nature of extreme energy cosmic rays (EECRs), which have energies above the $5\cdot10^{19}~\mbox{eV}$ -the Greisen-Zatsepin-Kuzmin (GZK) energy limit, is one of the most interesting and complicated problems in modern cosmic-ray physics. Existing ground-based detectors have helped to obtain remarkable results in studying cosmic rays before and after the GZK limit, but have also produced some contradictions in our understanding of cosmic ray mass composition. Moreover, each of these detectors covers only a part of the celestial sphere, which poses problems for studying the arrival directions of EECRs and identifying their sources. As a new generation of EECR space detectors, TUS (Tracking Ultraviolet Set-up), KLYPVE and JEM-EUSO, are intended to study the most energetic cosmic-ray particles, providing larger, uniform exposures of the entire celestial sphere. The TUS detector, launched on board the Lomonosov satellite on April 28, 2016 from Vostochny Cosmodrome in Russia, is the first of these. It employs a single-mirror optical system and a photomultiplier tube matrix as a photo-detector and will test the fluorescent method of measuring EECRs from space. Utilizing the Earth's atmosphere as a huge calorimeter, it is expected to detect EECRs with energies above $10^{20}~\mbox{eV}$ . It will also be able to register slower atmospheric transient events: atmospheric fluorescence in electrical discharges of various types including precipitating electrons escaping the magnetosphere and from the radiation of meteors passing through the atmosphere. We describe the design of the TUS detector and present results of different ground-based tests and simulations. [ABSTRACT FROM AUTHOR]

In the Tamanrasset area of the Pan-African Tuareg Shield, some of the late Pan-African intrusions collectively known as the Taourirt granites are associated with tin and tungsten prospects of both the quartz-vein and greisen types, with a variety of greisen styles. The mineralized intrusions are albite-topaz-protolithionite granites and microgranites. In the present work, we combine new observations and mica analyses with a reinterpretation of existing wall-rock geochemical data in order to assess the possible role of both magmatic-hydrothermal and external fluids in the greisenizing process at Tamanrasset. Greisens at Tamanrasset appear to result from two process: the first is acid leaching forming quartz-topaz and quartz-rich greisens, followed by an episyenitization which is characterized by quartz dissolution and replacements by Li-rich micas, leading to mica-rich greisens (that could better be named "pseudo-greisens"). Distinct trends recorded by the mica compositions in the granitic rocks and the greisens allow to disentangle the involvement of magmatic-hydrothermal fluids, on the one hand, and of mainly metamorphic external fluids, on the other hand, in the greisenizing process. The latter fluids were CO 2 -rich, and could have contributed to the source of the acidity. • Mica crystal chemistry as a proxy for the growth medium (melt, fluid). • First formed quartz-topaz greisen overprinted by muscovitisation (pseudo-greisen). • Magmatic-hydrothermal and metamorphic fluids both involved in greisenization. • Source of tin (as cassiterite) in the magmatic-hydrothermal fluids. [ABSTRACT FROM AUTHOR]

Czech small city with a relatively young name ‒ Košťany ‒ was called entirely differently in the past. There were converging artificial streams that contained tin ore. Not far from these watercourses several Celtic artifacts were found and a world-renowned Celtic treasure was placed into a nearly water spring. Therefore, the search for the origin of the name of the village focused on a possible Celtic origin. The original name of the village was Costen or Kosten. And in the Cornish language (originally surviving Celtic language on the peninsula Cornwall) there exists a word costean ‒ it is read kosten. [ABSTRACT FROM AUTHOR]

Evolved greisenized granites with rare metal mineralization in the eastern part of Erzgebirge provide a unique record of magmatic-hydrothermal transition. We provide new field and petrological observations from an old mining district Knottel (Krupka, Czech Republic), as basis for subsequent microanalytical study. Biotite or two-mica quartz-feldspar gneisses were intruded by a hidden steep granite stock Knottel - its deeper part consists of medium-grained topaz-zinnwaldite alkali-feldspar granite, which evolved upwards into a fine-grained variety with local unidirectional solidification textures. The granites were cross-cut by gray-black greisenized zones, with variable proportions of quartz, mica and topaz. Large body of K-feldspar pegmatite with lenses of coarse-grained milky biotite-quartz pegmatite is located in the upper part of the stock. The pegmatite contains veinlets of dark gray fine-grained zinwaldite-quartz greisens and light gray mica-poor quartz greisens. The uppermost part of the Knottel stock is composed of a coarse-grained quartz rock (quartzite) with accessory molybdenite, fluorite, topaz, mica and clay minerals. The contacts between coarse- and fine-grained quartz-rich rocks or greisens are generally sharp. The coarse-grained quartz stock was intersected by quartz veins with molybdenite mineralization that extend to its exocontact and produced greisenization (zwitterization) of the surrounding gneisses. Younger dykes of granitic aplites have cross-cut the gneisses, K-feldspar pegmatite as well as molybdenite-bearing quartz veins. Spatial zoning of the granite-pegmatite-quartz system is compatible with disequilibrium differentiation promoted by variations in volatile constituents. Crystallization of the volatile-rich melt probably commenced from the intrusion wall with a formation of K-feldspar pegmatite. A boundary melt layer, ahead of the solidification front and enriched in components complementary to feldspar and volatiles, have likely been responsible for solidification of coarse-grained quartz rocks and release of solute-rich aqueous fluids. The sequence of coarse-grained quartz rocks, fine-grained quartz rocks and greisens, and cross-cutting quartz veins may be interpreted as a record of protracted supersaturation in silica-rich media spanning the magmatic-hydrothermal transition. [ABSTRACT FROM AUTHOR]

To investigate the potential of tourmaline as a geochemical monitor, a comprehensive dataset on major, minor and trace element concentrations as well as Fe 3+ /ΣFe ratios of tourmaline is presented. The dataset includes samples from five plutonic complexes related to diverse magmatic to hydrothermal stages of the Cornubian Batholith (SW England). Tourmaline composition found in barren and cassiterite-bearing samples include all three primary tourmaline groups and tourmaline species with the general endmembers schorl, dravite, elbaite, uvite, feruvite, foitite and Mg-foitite. Based on textures and compositions, it is possible to distinguish not only between late-magmatic and hydrothermal tourmaline, but also between several formation stages. Hence, tourmaline monitors late-magmatic processes and the partitioning of elements during exsolution of an aqueous phase. For example, in hydrothermal tourmaline Sn is strongly enriched, while Ti, Cr, V and Sc are depleted compared to late-magmatic tourmaline of the same sample. Several tourmaline generations that precipitated from magmatic fluids can be distinguished with differing major and minor elements and REE patterns depending on the composition of the melt from which they were expelled from. Strongly zoned tourmaline allows for unraveling the hydrothermal history of a distinct location including ore precipitation. The precipitation of SnO 2 in the study area was probably caused by mixing between acidic, reduced, Sn-bearing magmatic fluids and oxidized meteoric fluids, which is in agreement with London and Manning (1995) and Williamson et al. (2000) . Hence, the ability of tourmaline composition to monitor changes in Sn concentration and redox conditions in hydrothermal fluids has potential as an exploration tool. [ABSTRACT FROM AUTHOR]

Veins and pervasive wall-rock alteration composed of coarse muscovite±quartz±pyrite are documented for the first time in a porphyritic granite at Luhr Hill in the Yerington District, Nevada. Coarse muscovite at Luhr Hill occurs at paleodepths of ~6-7 km in the roots of a porphyry copper system and crops out on the scale of tens to hundreds of meters, surrounded by rock that is unaltered or variably altered to sodic-calcic assemblages. Coarse muscovite veins exhibit a consistent orientation, subvertical and N-S striking, which structurally restores to subhorizontal at the time of formation. Along strike, coarse muscovite veins swell from distal, millimeter-thick muscovite-only veinlets to proximal, centimeter-thick quartz-sulfide-bearing muscovite veins. Crosscutting relationships between coarse muscovite veins, pegmatite dikes, and sodic-calcic veins indicate that muscovite veins are late-stage magmatic-hydrothermal features predating final solidification of the Luhr Hill porphyritic granite. Fluid inclusions in the muscovite-quartz veins are high-density aqueous inclusions of ~3-9 wt% NaCl eq. and <1 mol% CO that homogenize between ~150 and 200 °C, similar to fluid inclusions from greisen veins in Sn-W-Mo vein systems. Our results indicate that muscovite-forming fluids at Luhr Hill were mildly acidic, of low to moderate salinity and sulfur content and low CO content, and that muscovite in deep veins and alteration differs in texture, composition, and process of formation from sericite at shallower levels of the hydrothermal system. Although the definition of greisen is controversial, we suggest that coarse muscovite alteration is more similar to alteration in greisen-type Sn-W-Mo districts worldwide than to sericitic alteration at higher levels of porphyry copper systems. The fluids that form coarse muscovite veins and alteration in the roots of porphyry copper systems are distinct from fluids that formed copper ore or widespread, shallower, acidic alteration. We propose that this style of veins and alteration at Luhr Hill represents degassing of moderate volumes of overpressured hydrothermal fluid during late crystallization of deep levels of the Yerington batholith. [ABSTRACT FROM AUTHOR]

Occurrence of so-called "vein greisens" is one of characteristic features of the Variscan peraluminous granites in the western part of the Krušné hory/Erzgebirge area (Nejdek-Eibenstock Pluton, Horní Blatná body). The "veins" actually represent steeply dipping zones consisting of tens to hundreds of individual roughly parallel cm- to dm-thick stringers of metasomatic greisen reaching total thickness to several meters, and lengths of hundreds of meters. They mostly consist of quartz and Li-bearing mica with some topaz and cassiterite. Greisens of this type were mined at Přebuz, Rolava and Horní Blatná since the 15th century until 1945. The aim of this study is to distinguish magmatic and hydrothermal quartz in greisen, i.e. to differentiate relics of the original magmatic quartz from quartz originated hydrothermally during greisenization. We studied a series of samples from the historic mine Streitpingen situated in the Horní Blatná granite body near the village of Potůčky. The parent rock of greisens is medium-grained alkali-feldspar granite composed of 40 vol.% quartz, 29 vol.% albite, 20 vol.% perthitic K-feldspar and 9 vol.% Li-enriched biotite with small amount of topaz, apatite, rutile, monazite and zircon (Tables 1, 2). The zone of greisenization is up to 5 m thick and enriched with quartz (87 vol.%) and topaz (9 vol.%). The content of mica decreased to 3 vol.% and both feldspars disappear. Greisen is penetrated by monomineralic up to 10 cm thick quartz veins (> 97 vol.% quartz) with abundant tiny cavities. Veins are composed of clear long columnar crystals (5 mm diam., up to 5 cm long) which are coated with a thin layer (~ 1 mm) of milky white quartz. For comparison, we analyzed also quartz from quartz-tourmaline fillings of miarolitic cavities (5-10 cm diam.) in granite, traditionally called as "tourmaline suns", which are widespread in the central and northern parts of the Nejdek-Eibenstock Pluton (Schust et al. 1970). Internal structure of analyzed quartz grains visualized by cathodoluminescence (CL) is shown in Figs 1 and 2. Trace elements in quartz were analyzed using laser-ablation ICP-MS (for detail of the method used see Breiter et al. 2013). Average contents of the analyzed element in selected quartz crystals are shown in Table 3, all the individual analyses of selected elements are shown in Fig. 4. Contents of Al, Ti, and Li across selected crystals are given in Fig. 5; position of these profiles is shown in Figs 2b, c and 3. Aluminum, Li, and Ti are the most abundant trace elements in quartz. The content of Al in phenocysts of magmatic quartz and quartz from tourmaline suns corresponds roughly to 400 ppm (range 300-500 ppm), whereas only 115-270 ppm were found in the greisen quartz. The Al-contents in hydrothermal quartz strongly fluctuate: the clear domains contain 50-340 ppm Al, while 500-2400 ppm were detected in cloudy crystal cores, and 1100-4800 ppm Al in the milky white crystal rims. Content of Ti in magmatic quartz fluctuates between 40 to 100 ppm with extreme values up to 200 ppm near the margins of some crystals. Quartz from tourmaline suns contains 10-40 ppm Ti, while quartz from the greisen approximately 20 ppm Ti, and the hydrothermal quartz from veins generally contains < ppm Ti. The contents of Li in magmatic quartz and quartz from tourmaline suns range between 30-50 ppm. Contents of Li in quartz from greisen and clear domains of hydrothermal quartz are rather smaller, approximately 10-30 ppm. The highest Li-values in the range of 70-170 ppm were found in the milky hydrothermal quartz. The contents of Li and Al reveal positive correlation. Our preliminary research has shown that quartz originated during metasomatic greisenization differs from the primary magmatic quartz by lower intensity of cathodoluminescence and significantly lower concentrations of trace elements Al, Ti, and Li. [ABSTRACT FROM AUTHOR]

The paper considers for the first time the morphology, composition, and conditions of formation of the greisens of the Solnechnoe deposit (Komsomol'sk ore district), a typical cassiterite-silicate assemblage. The greisens are localized in the root parts of the deposit and represent a system of veins and veinlets formed in the contraction fractures of the metasomatically altered roof of the monzogranite intrusion (age of 94-92 Ma). The cassiterite-chlorite-carbonate-muscovite-quartz composition of the greisens with admixture of topaz, fluorite, and apatite reflects the composition of the monzogranites. The greisens are close in age (85.3 Ma on muscovite) to the granitic aplites (80-85 Ma on the whole-rock and biotite) of the final phase of the intrusive magmatism. The fluid regime of their formation differs from that of the economic ores in higher temperature, pressure, and salinity. One distinguishing feature of the greisens is elevated contents of LREE, U, and Th, which are incorporated in the REE fluorcarbonates, thorite, and uranothorite crystallizing together with cassiterite. [ABSTRACT FROM AUTHOR]

The Sn-W (Li, Nb, Ta)-deposit Cínovec/Zinnwald is situated at both sides of the Czech-German border in the eastern part of the Krušné hory/Erzgebirge Mts. The deposit is genetically linked to intrusion of late Variscan highly fractionated granite, the latest evolutionary stage of a volcano-plutonic system of the Teplice caldera. The ore-bearing albite-zinnwaldite granite forms a cupola-like mostly hidden body with an elliptical N-S elongated outcrop (1.4 x 0.3 km). Its upper part to the depth of 750 m is formed by albite-zinnwaldite granites, while the deeper part with biotite granites. In the uppermost part of the pluton (the "canopy") to the depth of ~300 m, the granite is altered, crosscut with flat quartz-zinnwaldite veins and partly greisenized (Fig. 1). Historical mining of quartz-zinnwaldite veins with cassiterite and wojframite between 1378 and 1990 provided about 8-10 millions of metric tons of Sn + W ore. Increase in the prices of the high-tech metals and especially Li recently sparked a new wave of interest in the both parts of the Cínovec ore deposit: in Germany (Nessler - Seifert 2015), and in the Czech Republic (GEOMET company, this article). The company GEOMET started in 2014 a new borehole campaign in order to authenticate results of the old exploration and to summarize Li-resources in the southern part of the Cínovec deposit. The borehole CIS-2 was chosen for detailed petrological and mineralogical study (Tab. 1). A Stockscheider (marginal pegmatite) forms several dm to 2.5 m thick layer at the contact between granite cupola and surrounding rhyolite. The upper part of the cupola to the depth of 200-250 m under the contact is formed by fine-grained albite- zinnwaldite granite composed of 46% quartz, 38% albite, 4% relict of K-feldspar, 5% zinnwaldite, 5% sericite (alteration product of Kfs), and 0.2% fluorite. This granite crystallized in situ from volatile-enriched melt. Mica free-granite (typically composed of 33% quartz, 38% albite, 28% Kfs and max. 1% mica) with intercalations of feldspatite forms ~200 m thick zone beneath the albite-zinnwaldite granite. Fluids enriched in fluorine and metals released during crystallization of these feldspar-rich rocks migrated upward forming irregular bodies of quartz-zinnwaldite greisen dispersed within the albite-zinnwaldite granite. Li-bearing tri-octahedral mica from granites and greisens should be termed as zinnwaldite. In addition to about 3.5 w t. % Li2O, it contains also ca 1 w t.% Rb2O (Tab. 2). Along the borehole CIS 2 upwards, the contents of Si, Li, and Rb systematically increase and the contents of divalent elements decrease (Fig. 3). Among the oxide ore minerals (Fig. 2), cassiterite (Tab. 3, Fig. 4a), columbite (Tab. 4, Fig. 4b) and scheelite (Tab. 5) are common, while minerals of the microlite/pyrochlore group (Tab. 6) are rare. In terms of the debate on future exploitation of the deposits, the most significant mineralogical findings are as follows: (i) the main carrier of tungsten is scheelite, (ii) the main parts of Nb and Ta presented in the greisen form very fine-grained columbite, only minor parts are hosted in cassiterite. [ABSTRACT FROM AUTHOR]

The Artjärvi and Sääskjärvi granite stocks at the western margin of the Wiborg rapakivi batholith are multiphase rapakivi granite intrusions in which the most evolved phase is topaz-bearing granite. The Artjärvi stock is composed of porphyritic and even-grained biotite granite and even-grained topaz granite, and the Sääskjärvi stock comprises even-grained biotite granite and porphyritic topaz granite. The granites are metaluminous to peraluminous A-type granites, showing within-plate (WPG) geochemical characteristics. The topaz granites from the Artjärvi and Sääskjärvi stocks are petrographically and geochemically similar to other topaz-bearing rapakivi granites in Finland. The anomalous geochemistry of the topaz granite is essentially magmatic; postmagmatic reactions have only slightly modified its composition. Greisen veins, some of which are mineralized, are widely found associated with the Artjärvi and Sääskjärvi stocks. The most characteristic feature of the Artjärvi granite stock is a stockscheider at the roof contact of the topaz granite. The stockscheider is composed of schlieren layering and pegmatite layers parallel to the contact. The most probable mechanism for the formation of the schlieren layering is velocity-gradient sorting parallel to the flow, which led to accumulation of mafic minerals along the upper contact of the topaz granite. Cooling and contraction of the topaz granite formed fractures parallel to the roof contact and the residual pegmatite magmas were injected along the fractures forming pegmatite layers. Textures like graphic intergrowths, aplitic groundmass and fan-shaped alkali feldspar crystals associated with the Artjärvi porphyritic biotite granite and pegmatite indicate crystallization from undercooled magma. Miarolitic cavities found in the porphyritic biotite granite and topaz granite indicate at least local volatile saturation.