Published: Kurguzova A., Klyukin Yu.Arsenic-Borum-Thorium fluids of greisens from Severnyu granitic massif // ECROFI XXII Abstract Book. 2013. Antalya, Turkey. — pp.65-68
“Zwitter” can be translated from Germany as “hybrid” or “hermaphrodite”. This term is known from Georg Agricola times, it were using for describing atypical tin-bearing rock with mixed composition. During medieval times at Alternberg (Sachsen) “zwitters” were altered granites with abundant grains of quartz, muscovite, lepidolite, tourmaline, topaz and cassiterite.
Lithium mica from siderophillite(KFe2AlAl2Si2O10(OH)2)—polylithionite (KLi2AlSi4O10F2), row is typomorphic mineral of zwitters. This mica usually substitutes magmatic biotite from granites. Zwitters are enriched by Fe, Mn, Ti and some lithophile (Cs, Li, P, F) and chalkophil (S, As, Zn, Pb, Sn, Bi) chemical elements. Na, K, Mo, Sr are carrying out. Accessory minerals are consequence of such geochemical character of metasomatic solutions, zwitters have combination of rare-metal (monazite, wolfrmite, wolframoxiolite, tungsten-niobium rutile, columbite) and sulfide (lelligite, pyrite, bismuthine, As-thorite rousveltite) accessory mineralization. There are detected mix of Th-As-Bi mineral phases besides decribed accessory minerals. These “mineral phases” usually associate with typical zwitters mineral, like lithium mica, Th-monazite, yttrium fluorine, hafnium zircon, tungsten-niobium rutile). According to 45 iom microprobe analyses (JSM-6460LV, Mining University, Saint-Petersburg) Th-As-Bi phases have invariable composition and they usually characterized by relation Th>>As>Bi. Variations of element content are (at. %): Th 0,20-0,23; As 0,05-0,10; Bi 0,02-0,07.
We studied fluid inclusions in quartz from zwitters by microthermometry (thermocamera Linkam THMS 600 Mining University, Saint-Petersburg) and ion microprobe (JSM-6390LV, Yekaterinburg) for identification conditions of metasomatic rocks formation.
Fluid inclusions in quartz have diverse phase composition. Sometimes inclusions have trapped minerals, this fact indicates their primary genesis. Secondary fluid inclusions are located in cracks, in chains crossing one ore more quartz grains. Surely, zwitters have magmatic quartz from granites and new metasomatic quartz. Macroscopically “granitic” quartz is dark-colored, grains are 2-5 mm size. As a rule, this magmatic quartz have two-phases inclusions with low salinity (3 mass. % NaCl) and with methane in gas phase. Methane was diagnosed by absebse phase transition during cooling up to 196 and gas-hydrate formation at interval from -80 to -40. Metasomatic quartz is colorless or milky. This quartz overgrows on dark-colored magmatic quartz. Fluid inclusions in metsomatic quartz are actually high-salinity, contains halite and others salts. Gas phase is mainly methane in all types of fluid inclusions in zwitters. Fluid inclusions in zwitters have mixed salts composition, there are NaCl, KCl, CaCl2 (eutectic temperatures are 42-440). Obviously, other compounds (salts and acids) presence in fluid inclusions. These compounds are detected under microscope (fig. ), but they are undiagnosed by microthermometry. Moreover, some hard phase dissolving during heating from +50 +700 are presented in fluid inclusions in quartz from zwitters.
Opened fluid inclusions in quartz and mica were analyzed by ion microprobe. Ion microprobe data confirmed presence in fluid inclusions NaCl, KCl, CaCl2, FeCl2 and there were found Cu and Mg cations, which obviously aren’t chlorine complexes.
Besides Th-As-Bi phases with variable composition were founded. Intergrowth of such mineral phases with typical zwitters accessory minerals were mentioned above. However, coposition of Th-As-Bi phases in fluid inclusions differ from their composition in mineral intergrowths. In fliud inclusions concentrations of Th, As and Bi are same (at. %): Th 0,05-0,09; As 0,01-0,02; Bi 0,01-0,11. The most probably, in fluid inclusions these chemical element presents as acids (висмутовой, мышьяковистой (HAsO2 или мышьяковой H3AsO4) and hydrates. Thus, Th-As—Bi specialization of zwitter solutions reflected not only in new Th-As-Bi mineral phases, but in fluid inclusions also. Now we don’t know surely forms of transportation and precipitation of this elements. But we surely know that Th, As and Bi are closely associated in zwitters and these element are typomorphic for zwitters at Severny massif.
References
1) Alekseev V.I. et. Al. (2012) Conference Problems of mineralogy, petrology and metallogeny. Scientific reading memory P.N. Chirvinsky 8, 197-203
2) Ruiz-Conde A et al (2013) Current Microscopy Contributions to Advances in Science and Technology 2, 1137-1145
Acknowledgment
Yu. Marin, V. Alexeev (National University of Mineral Resources)S. Glavatskich (Institute of Geology and Geochemistry)
S. Glavatskich (Institute of Geology and Geochemistry)
S. Uhlig (Bergakademie Freiberg, Freiberg, Germany)
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