Petrology of the Jurassic Shah-Kuh granite (eastern Iran), with reference to tin mineralization
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Keywords:
Porphyritic
Fractional crystallization (geology)
Cassiterite
Igneous differentiation
Ilmenite
Tourmaline
Felsic
The lepidolite-subtype pegmatite at Lhenice is a member of the
South-Bohemian pegmatite field (Novak & Cempirek, 2010); the
nearest rare-element pegmatites include Lhenice II, Nova Ves
and Chvalovice I and II. All pegmatites are characterized by
high Li and P contents and similar mineral composition
(elbaite, schorl, biotite, K-feldspar, lepidolite). The Lhenice
pegmatite is moderate-sized and highly fractionated, with
abundant lepidolite, elbaite, amblygonite and cassiterite.
Tourmaline samples were analysed using EMPA and LA-ICP-MS.
Primary, metasomatic and recrystallized tourmaline generations
were characterized.
Pegmatite
Tourmaline
Cassiterite
EMPA
Columbite
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The Xuebaoding W-Sn-Be deposit located in the Songpan-Ganze Orogenic Belt (Sichuan Province, China) is a hydrothermal deposit with less developed pegmatite stage. The deposit is famous for the coarse-grained crystals of beryl, scheelite, cassiterite, apatite, fluorite, muscovite, and others. The orebody is spatially associated with the Pankou and Pukouling granites hosted in Triassic marbles and schists. The highly fractionated granites are peraluminous, Li-Rb-Cs-rich, and related to W-Sn-Be mineralization. The mineralization can chiefly be classified based on the wallrock and mineral assemblages as muscovite and beryl in granite (Zone I), then beryl, cassiterite and muscovite at the transition from granite to triassic strata (Zone II), and the main mineralized veins composed of an assemblage of beryl, cassiterite, scheelite, fluorite, and apatite hosted in metasedimentary rock units of marble and schist (Zone III). Due to the stability of tourmaline over a wide range of temperature and pressure conditions, its compositional variability can reflect the evolution of the ore-forming fluids. Tourmaline is an important gangue mineral in the Xuebaoding deposit and occurs in the late-magmatic to early-hydrothermal stage, and can thus be used as a proxy for the fluid evolution. Three types of tourmalines can be distinguished: tourmaline disseminations within the granite (type I), tourmaline clusters at the margin of the granite (type II), and tourmalines occurring in the mineralized veins (type III). Based on their chemical composition, both type I and II tourmalines belong to the alkali group and to the dravite-schorl solid solution. Type III tourmaline which is higher in X-site vacancy corresponds to foitite and schorl. It is proposed that the weakly zoned type I tourmalines result from an immiscible boron-rich aqueous fluid in the latest stage of granite crystallization, that the type II tourmalines showing skeletal texture directly formed from the undercooled melts, and that type III tourmalines occurring in the mineralized veins formed directly from the magmatic hydrothermal fluids. Both type I and type II tourmalines show similar compositional variations reflecting the highly fractionated Pankou and Pukouling granites. The higher Ca, Mg, and Fe contents of type III tourmaline are buffered by the composition of the metasedimentary host rocks. The decreasing Na content (<0.8 atoms per formula unit (apfu)) and increasing Fe3+/Fe2+ ratios of all tourmaline samples suggest that they precipitated from oxidized, low-salinity fluids. The decreasing trend of Al content from type I (5.60–6.36 apfu) and type II (6.01–6.43 apfu) to type III (5.58–5.87 apfu) tourmalines, and associated decrease in Na, may be caused by the crystallization of albite and muscovite. The combined petrographic, mineralogical, and chemical characteristics of the three types of tourmalines thus reflect the late-magmatic to early-hydrothermal evolution of the ore-forming fluids, and could be used as a geochemical fingerprint for prospecting W-Sn-Be mineralization in the Xuebaoding district.
Tourmaline
Cassiterite
Pegmatite
Muscovite
Scheelite
Fluorite
Topaz
Greisen
Arsenopyrite
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The research focused on the composition of tourmaline from tin ore deposits and ore occurrences within the Verkhneurmiysky ore cluster in the Amur region. The aim of the study is to determine the indicative signs of tourmaline from cassiterite-quartz and cassiterite-silicate formations. This research is based on the materials of a long-term study of the mineralogy of the Far East deposits, conducted at the Mining University under the scientific supervision of Professor Yu.B.Marin. The relevance of the study involves predicting of tin and associated mineralization. For the first time, SIMS and Mössbauer spectroscopy were used to study tourmaline from this region. We identified the typomorphic characteristics of the tourmaline composition, which are proposed to be used as indicators of tin-ore deposits. Typomorphic characteristics of tourmaline from cassiterite-quartz formation: schorl (Mg/(Mg + Fe) = 0.06) with a high content of Al and K; Fe3+/(Fe3+ + Fe2+) = 0.03; ZFe3+ = 1 %; impurities: Nb, LREE (La, Ce, Pr), Be, Bi, F, Li, and Mn; LREE content > 9 ppm; positive Gd anomaly. Typomorphic characteristics of tourmaline from cassiterite-silicate formation: schorl-dravite (Mg/(Mg + Fe) = 0.22) with a high Ca content; Fe3+ / (Fe3+ + Fe2+) = 0.17; ZFe3+ = 9 %; impurities: Zr, Y, Cr, V, Sn, In, Pb, W, Mo, Ti, HREE, Eu, Sr, Sb, and Sc; the content of Y is > 2 ppm, of HREE is > 3 ppm, Eu is > 0.1 ppm. The formation conditions of the cassiterite-silicate ore mineralization were more oxidizing than those of the cassiterite-quartz one. Tourmaline, formed under oxidizing conditions, contains such impurities as Sn, In, Nb, Bi, Sc, and LREE. The content of Sn isomorphic impurity in tourmaline reaches 8000 ppm.
Cassiterite
Tourmaline
Greisen
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Tourmaline
Cassiterite
Wolframite
Greisen
Andalusite
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Abstract Southwest of the Middle Proterozoic Åland rapakivi batholith (1575 Ma) there occur dolerites closely associated with quartz-feldspar porphyries. The dolerites and the quartz-feldspar porphyries were formed during a bimodal igneous event characterizing the initial stages of the rapakivi intrusion. A coarse-porphyritic porphyry carries abundant mafic and hybrid enclaves interpreted as resulting from simultaneous intrusion and mixing of basaltic (dolerite) and granitic (porphyry) melts. The fine-grained mafic enclaves are a Fe-enriched differentiation product of the doleritic melts that intruded the country rock. Mixing tests indicate that the hybrid enclaves are a result of magma mixing between melts now represented by the mafic enclaves and the coarse-porphyritic porphyries. Discrepancies resulting from mixing tests at three localities within the porphyry are explained by variations in the degree of homogenization that are due to the incorporation into the hybrids of early phenocrysts formed from the two end member melts. The coarse-porphyritic porphyry also has petrographical features such as tiny mafic enclaves, labradorite xenocrysts and quartz ocelli, which indicate that the composition of the porphyry itself had been to some extent influenced by mixing. It is suggested that the incorporation of the tiny mafic enclaves and labradorite xenocrysts into the porphyry occurred during the very earliest stage of the bimodal intrusion event, when the mafic melt interacted with a porphyry melt newly formed by anatexis. New surges of mafic melt chilling against acid melt generated the fine-grained mafic enclaves. The hybrid magma, now represented by the hybrid enclaves, was formed by mixing of the contrasting magmas.
Porphyritic
Igneous differentiation
Phenocryst
Magma chamber
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Cassiterite
Tourmaline
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Determing the age and precise bulk composition of pegmatites is challenging due to 1) the metamictization of zircon grains and 2) their coarse grain size and heterogeneity. Cassiterite and tourmaline are common in pegmatites and in the case of the former can be used to date pegmatites and while the latter can be used to monitor petrogenesis. This study presents in situ cassiterite U-Pb dating and tourmaline geochemical and B isotopic data from the Nanyangshan Li-Be-Nb-Ta-Rb-Cs-Sn mineralized pegmatite in the North Qinling terrane of China to investigate their age and petrogenesis. The Nanyangshan pegmatite host abundant spodumene, lepidotite, beryl, cassiterite, columbite and tourmaline and can be roughly divided into black tourmaline (Tur B)-cassiterite and pink tourmaline (Tur P)-spodumene bearing phases. Most of the cassiterite are homogenous in appearance although some (<10 %) have core-rim structures. The cassiterite crystals mainly yielded U-Pb ages of ∼ 410 Ma, although the the rims yielded ages of ∼ 370 Ma. Both Tur B and Tur P are rich in Li and are elbaites, with Tur B closer to shorl and Tur P to elbaite. Clear correlations exist between some trace elements (Li and Sn) with major elements (Na/(Na + X□) in the tourmalines, indicating the potential crystal chemical effects on their incorporation. The boron isotopes of the tourmalines vary from −19.36 ‰ to −15.91‰ and decrease from Tur B to Tur P. This implies the boron in the Nanyangshan pegmatite was mainly derived from partial melting of metasedimentary souce rocks with the variation likely caused by fractionation. Tur P is closely associated with spodumene and has higher concentratios of Li, Be, Nb, Ta whereas the Tur B is closely associated with cassiterite and has higher concentrations of Sn, suggesting that tourmaline chemistry could be a reliable geological record of the environment and useful exploration tool.
Tourmaline
Cassiterite
Pegmatite
Columbite
Geochronology
Petrogenesis
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Cassiterite
Tourmaline
Greisen
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The composition of tourmaline in the San Rafael Sn–Cu lode, in southeastern Peru, provides an important record of the early evolution of the hydrothermal system that produced the world’s richest tin deposit. Many forms, colors and compositions of tourmaline, ranging from dravite to schorl, are present in the deposit, but the late tourmaline that accompanied deposition of early cassiterite has an unusual dark green color, and exhibits a strong trend of enrichment in iron. Appearance of this tourmaline in the paragenesis coincided with a marked change in the vein style, reflecting an opening of the vein system, and a dramatic change in the mineralogy of vein and alteration assemblages, evident from the precipitation of other iron-rich minerals (Fe-rich chlorite and cassiterite). This abrupt change in the plumbing of the hydrothermal system was associated with the introduction of dilute, relatively oxidizing, externally derived waters of meteoric origin that mixed with hot magmatic brines carrying high concentrations of dissolved tin and iron. The resulting sudden cooling, dilution, and oxidation of the ore fluids created the conditions required for massive precipitation of cassiterite and formation of a very large, high-grade ore deposit.
Cassiterite
Tourmaline
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