Tourmaline as a Recorder of Ore-Forming Processes in the Xuebaoding W-Sn-Be Deposit, Sichuan Province, China: Evidence from the Chemical Composition of Tourmaline
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Abstract:
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.Keywords:
Tourmaline
Cassiterite
Pegmatite
Muscovite
Scheelite
Fluorite
Topaz
Greisen
Arsenopyrite
Topaz is commonly supposed to have been formed by the action of fluorine-bearing vapours on felspar, but evidence has recently been advanced with the object of showing that some important veins intrusive in the porphyritic granite of Gunong Bakau, a mountain 4,426 feet high, situated in the centre of the Main Granite Range of the Malay Peninsula, were formed of a rock in which “the topaz and cassiterite are not alteration products of previously formed minerals”. The author of this theory gives the rock the descriptive name of ‘quartz-topaz’, and adds as his reasons for not calling it ‘greisen’ the fact that in places it contains very little mica and that, unlike the majority of greisens, it is not an alteration product.
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Abstract Gunung Paku near Klian Intan, Perak, is a primary tin deposit in Malaysia mined since 200 years ago, contributing 3–5% of tin ore concentrates previously, and recently over 70% of the Malaysian tin. Gunung Paku is located within the western Tin belt of Peninsular Malaysia associated with biotite granite (184–230 Ma) of the Main Range Granitoid which extends up to the southern part of Peninsular and Central Thailand. The primary tin mineralization style at the Gunung Paku is mainly associated with widespread occurrence of sheet‐like quartz veining systems parallel to the strike of the host rocks and confined within a narrow N–S trending fault zone. The mineralization formed within a thick sequence of metasedimentry rock that belongs to the Baling Formation of Palaeozoic age. The host rock of weakly metamorphosed argillite generally experienced strong tropical weathering that resulted in a thick sequence of light grey to light brown oxidized profile. The mineralized veins range from simple quartz‐cassiterite, quartz‐tourmaline‐cassiterite to complex quartz‐cassiterite‐polymetallic sulfide veins. Wall rock alterations at Gunung Paku are mainly characterized by the hypogene type alteration consisting of silicification, tourmalinization, chloritization, sericitization and kaolinization normally adjacent to mineralized quartz veins and brecciated‐fault gouge zones. Pyrite, arsenopyrite, cassiterite, rutile, chalcopyrite, trippkeite (CuAsO4), scorodite, covellite and other secondary iron‐oxyhydroxide are the common metallic minerals that accompanied the tin mineralization. Other minor occurrences include trace amounts of complex lead‐bismuth‐antimony‐molybdenum bearing minerals.
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Arsenopyrite
Greisen
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Topaz was previously considered as a typical hydrothermal mineral, and topaz greisen a typically altered rock. However, the geological and geochemical evidence in recent years has made it clear that the layer-like topaz greisen at the top of Ta- and Nb-bearing albite
Topaz
Greisen
Cassiterite
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This paper is concerned, primarily, with the nature and genesis of the multi mineralic veins at Tekka, Perak, Peninsular Malaysia. The rock types in the area include marble, schist and granite. The granite emplacement and resulting tensional fractures, that trend approximately E-Wand dip northwards, provided passage ways for ascending mineralising agents, and the veins and adjacent country rocks became the sites of deposition of an impressive number of mineral species. The genesis of these mineralised bodies was complex and involved at least three phases of mineralisation that were separated by periods of renewed fracturing. From a mineralogical and temporal point of view the veins can be classified into three main types:- (a) An early quartz-tourmaline type with or without cassiterite, wolframite, arsenopyrite and minor amounts of other sulphide-bearing species. (b) A second (later) type consisting of quartz with or without cassiterite, wolframite, arsenopyrite and minor amounts of other sulphide-bearing minerals. (c) A third, and still later, type consisting of quartz, stannite, other sulphides and sulpho-salts, with or without cassiterite and arsenopyrite. The common non-metallic gangue minerals present are quartz, tourmaline, topaz, sericite, muscovite and fluorite, and, in addition, a number of supergene secondary products which includes varlamoffite. Wall-rock alteration adjacent to the veins includes silicification, tourmalinisation, greisenisation and kaolinisation. The deposit is best classified as xenothermal because of the telescoping of high-temperature mineral species such as cassiterite, columbite/tantalite and wolframite which are closely associated with ones believed to be low-temperature minerals, such as galena and stibnite.
Cassiterite
Arsenopyrite
Wolframite
Topaz
Greisen
Tourmaline
Sericite
Pegmatite
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Topaz, so common an accessory in tin lodes in all parts of the world, has hitherto been looked upon as comparatively rare in Cornwall. When massive, or even in the form of small, well-developed crystals, it is a mineral easily overlooked, or apt cursorily to be mistakcn for quartz. The presence of topaz as a microscopic accessory in granite, greisen, and rarely elvans, from most of the Cornish masses, has been determined by Dr. J. S. Flett in the course of the work of the Geological Survey; while the late Mr. J. H. Collins was responsible for the record of other interesting localities. In the present notes I have collected all the available information respecting its mode of occurrence and localities ; and have added several new ones, at some of which the mineral occurs in considerable mass, thus affording evidence that topaz is in Cornwall, as in the case of other countries, a comparatively common associate of cassiterite and wolframite, both in granite and sedimentary rocks.
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Greisen
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Wolframite
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A study has been made of the Sn-W and sulphide vein mineralization at Cerro Avión and Valdehornillos, south end of the Villar del Ciervo granite (Salamanca, Spain). In this paper we summarize the mineralogical and chemical characteristics of the ore minerals, the processes of hydrotermal alteration, the mineral paragenesis, and the sulphur isotopic ratios of several sulphides. A first mineralization stage resulted in greisenization of the granite and deposition of cassiterite and wolframite, as well as some arsenopyrite disseminated within the greisenized granite. The main mineralization stage formed mostly arsenopyrite, with lesser amounts of other sulphides and bismuth. Scheelite resulted from the transformation of wolframite. Supergenic stage forming scorodite, covellite and iron oxides. Temperatures of formation, as derived from the arsenopyrite and chlorite geothermometers, range from 500 to 450 °C for the first stage, and between 315-250 °C for the main stage. Sulphur isotopes indicate an igneous derivation for the sulphur.
Cassiterite
Arsenopyrite
Wolframite
Greisen
Scheelite
Ore genesis
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Topaz
Cassiterite
Phenocryst
EMPA
Sericite
Greisen
Fluorite
Muscovite
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Topaz was previously considered as a typical hydrothermal mineral, and topaz greisen a typically altered rock. However, the geological and geochemical evidence in recent years has made it clear that the layer-like topaz greisen at the top of Ta- and Nb-bearing albite granite has magmatic characteristics.
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Greisen
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