Hydrothermal Tourmaline from the Girvas Paleovolcano (Onega basin, Karelian Craton): Morphology and Chemical Composition
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Tourmaline
Ilmenite
Synopsis Qualitative analysis of three mineral samples from northern Mozambique was accomplished by X-ray diffraction (XRD), microscopy, scintillation, and magnetic determination. Chemical characterization was accomplished using ICP-OES and pressed powder XRF after dissolution using microwave-assisted digestion and flux fusion. The samples consisted of a mixture of minerals with tantalite as the major component, with minor amounts of microlite, quartz, mica, accessory garnet, and tourmaline. Incomplete dissolution was obtained using microwave digestion, with maximum recoveries of 90.25 ± 0.06% and 88.90 ± 0.04% for Nb 2O5 and Ta2O5 respectively. Complete dissolution using Li 2B4O7 resulted in recoveries of 98.5 ± 0.2% Nb2O5 and 100.4 ± 0.3% Ta2O5.
Tourmaline
Characterization
Powder Diffraction
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Placer deposit
Economic geology
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Many years ago (1971) a paper appeared in the American Mineralogist titled “A Pseudomorphic Quartz-Tourmaline Relationship from Northern Nigeria.” I remember it well because I was troubled by the e...
Tourmaline
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Solution channels in quartz, microcline, and plagioclase of a granite were produced by exposure of the rock to an artificial hydrothermal system. Electron microprobe analyses, beam-scanning photographs, and element profiles show that the mineral grains are homogeneous and unaltered within a few micrometers of the channels. The channels, which are 3 to 7 ..mu.. in diameter, appear to have formed by removal of material in solution. In the sample material, no new minerals produced by alteration or deposition were detected by microprobe analysis. The apparent absence of such alteration products (e.g., clays) may be due to (1) sample preparation which removed fine-grained alteration products during polishing; or (2) concentrations of such minerals in such small amounts that they are below the limits of detectability with the microprobe. The granite is seen to be preferentially attacked by the hydrothermal solution along grain boundaries and cracks. Similar solution effects are observed in amphibolites exposed to the artificial hydrothermal system. Plagioclase crystals in the amphibolite are partially dissolved so that delicate porous boxwork structures remain.
Microcline
Microprobe
Silicate minerals
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Abstract Several high‐sulfidation epithermal gold orebodies in the Mankayan Mineral District were formed in an environment that has been already affected by earlier porphyry‐type mineralization. This study reports the geologic and geochemical characteristics of the Carmen and Florence epithermal orebodies, which are located in the south of the Lepanto main enargite–gold orebody. The gold‐bearing epithermal quartz veins in the Carmen and Florence areas are of two types: (i) the enargite‐rich veins and (ii) the quartz–pyrite–gold (QPG) veins. The two types of veins are mainly hosted by the Cretaceous Lepanto Metavolcanics basement rocks, with minor veins cutting the Pleistocene Imbanguila Dacite Pyroclastics. The mineral assemblages and homogenization temperatures of fluid inclusions indicate that the Carmen and Florence orebodies were deposited by fluids varying from high to very high sulfidation state. The enargite and QPG epithermal veins of Carmen and Florence cut porphyry‐type quartz veinlet stockworks and veins that host polyphase hypersaline fluid inclusions that did not homogenize at or below 400°C. These high‐temperature quartz exhibits distinctly different mineral chemistry from the quartz of the QPG and enargite‐rich epithermal veins. In particular, the Ti content of quartz of the porphyry‐type veinlet stockwork is elevated (>100 ppm), whereas the Ti concentration of the epithermal vein quartz crystals are below detection limits. The Fe concentration of quartz is high in epithermal vein quartz (>300 ppm), whereas nearly undetected in the porphyry‐type stockwork veinlet quartz. Multiple generations of quartz with different mineral chemistry, fluid inclusions morphology, temperature, salinity and bulk gas compositions, and stable isotopic ratios indicate the variable hydrothermal conditions throughout the mineralization history of the Mankayan District. The temperature, pH, sulfidation state, oxidation state, and fluid composition vary among the orebodies in Carmen and Florence areas. Furthermore, the characteristics of earlier alteration affected the apparent characteristics of subsequent mineralization.
Stockwork
Quartz monzonite
Argillic alteration
Sericite
Chalcedony
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Bosiite, ideally NaFe3+3Al4Mg2+2Si6O18(BO3)3(OH)3O is a rare
member of the tourmaline supergroup, recently found in Darasun
gold deposit, Transbaikal, Russia as a hydrothermal mineral in
gold-bearing quartz vein with sulphides. New occurrence of
bosiite was discovered on the contact of the elbaite-subtype
pegmatite with host migmatite at Řecice, Czech Republic; We
provide a brief description of its mineral assemblages and
composition. Bosiite is probably result of late hydrothermal
alkaline fluid alteration of primary biotite. Hydrothermal
fluids brought B2O3, mobilized Na (albite) and oxidized Fe to
Fe3+, and removed K, and part of Mg. Occurrence of bosiite is
probable in other elbaite pegmatites as well, as their late
fluids are frequently alkaline with high a(B2O3).
Pegmatite
Tourmaline
Nepheline
Muscovite
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Tourmaline
Rutile
Alkali feldspar
Ilmenite
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Ilmenite
Rutile
Mineral resource classification
Tourmaline
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