Isotopic and geochemical study of the conditions of tin ore formation of Solnechnoye deposit(Far East of Russia).

Abstract

Physical chemical characteristics of the Solnechnoye tin deposit hydrothermal system have been stud ied. Ores of cassiterite-tourmaline type was formed in a vertically dipping fracture zone, extended up to 8 km in a metamorphosed mass of sandstone-shale rocks. This rock mass transfers in its root part to a granitoid massif (quartz diorites-monzonites).The evolution in composition of the mineral-forming solution was studied by gas-chromatographic analysis of gaseous phase of fluid inclusions. The analysis of aqueous extracts from fluid inclusions (AAS, potentiometry, ICP and ionic chromatography) was also performed. It was found that as the process proceeded from the preore quartz-tourmaline stage to productive quartz-cassiterite, the values of axco-' a(s11), C02/CH4, HCO3/Cl and pH increased. The value of foe corresponded to the F-Q-M buffer on thie preore stage and increased up to that of the Ni-NiO buffer during the formation of the main part of cassiterite ores.Study of organic compounds showed that a greater degree of oxidation in comparison to the preore stage is typical for the quartz-cassiterite and the main sulfide stages. It means that organic compounds participated in redox reactions which took place in the solutions during the precipitation of these mineral assemblages.The 8180 values of fluids calculated from the 8180 values obtained for the minerals show a distinct trend of decrease toward later stages. The 8D values for the waters from the inclusions are close to those found for contemporary meteoric waters (-120%o). A transport model of non-isothermal isotope exchange between water and arbitrary number of minerals along the fluid flow paths was used for the interpretation of these isotope data as well as of the data on the isotope composition of the wall-rocks. Descending flow of meteoric waters was found to interact with sandstone-shale rocks and with granitoids before entering into the discharge zone. Thus while studying reasons of ore formation in a given hydrothermal system it is necessary to answer subsequently several questions: a) what are the main changes in the physical chemical prop erties of fluid in the process of the ore formation; b) which of the factors plays the decisive role in the deposition of ore material; c) with which re actions these changes are coupled; and d) which properties of the hydrothermal system are respon sible for the changes of physical chemical condi tions in the solutions. Large economic tin deposit Solnechnoye was chosen for the main object of our study. This de posit is a typical representative of tourmaline type of cassiterite-silicate formation according to the classification (Lugov et al., 1976). Some ques tions of geological structure, chemical and miner alogical compositions of this deposit have been discussed by several authors (Gonevchuk et al., 1984). Many papers (Bannikova et al., 1984(Bannikova et al., , 1989Kokorina, 1982;Sushchevskaya et al., 1978Sushchevskaya et al., , 1984 are dedicated to the problems of physical chemi cal conditions of its for...

Magmatic Nature of Mineralizing Fluids in the Solnechnoye Sn Deposit (Russia) Deduced from Isotopic (H, O) Compositions of Tourmaline

“…The change of mineral assemblages of these stages shows that early sodium chloride fluids gave way to dilute, alkaline bicarbonate–chloride–fluoride fluids. This was interpreted by Bannikova et al ., (1994) as a possible result of the mixing of exogenic waters of meteoric origin into the ore‐forming system. The fluid inclusion studies of Radkevich et al .…”

“…The higher range of δ 18 O compositions of fluids in tourmalines from the Glavnaya and Pridorozhnaya ore zones, compared to those from the Avral and Levosilin barren zones, is likely to be due to interaction of magmatic fluid with wallrocks (cf. Bannikova et al ., 1994). This process probably resulted in favorable physico‐chemical conditions that induced precipitation of cassiterite from the mineralizing fluids.…”

“…The fluid inclusion studies of Radkevich et al . (1967), Bannikova et al . (1994), and Bortnikov et al .…”

“…The quartz‐tourmaline metasomatite horizon overlies the granitoid and underlies quartz‐sericite metasomatic rocks and sericitized terrigenous sedimentary rocks. The mineralization of the deposit has been classified in four main stages (Radkevich et al ., 1967; Bannikova et al ., 1994). Stage 1 is a pre‐ore quartz‐tourmaline assemblage with accessory sericite, chlorite and topaz.…”

“…Physico‐chemical data describing transport and deposition of Sn in hydrothermal environments allow deduction of processes associated with the precipitation of cassiterite (SnO 2 ), such as fluid mixing, fluid heterogenization (boiling or immiscibility) and fluid interaction with wallrocks (Eugster, 1985; Heinrich, 1990; Sushchevskaya & Ryzhenko, 2002; Bortnikov et al ., 2005; Sushchevskaya et al ., 2006). Systematic studies of materials from large Sn and Sn–W deposits, such as Panasqueira in Portugal (Noronha et al ., 1999), Huanuni in Bolivia (Müller et al ., 2001), Brandberg West in Namibia (Macey & Harris, 2006), Svetloye, Khinganskoye, and Solnechnoye in Far East Russia (Bannikova et al ., 1994; Sushchevskaya et al ., 2000; Spasennykh et al ., 2002) helped to conclude that these deposits formed from magmatic fluids, which were mixed with meteoric waters, and interacted with the country rocks before the precipitation of ore minerals. Geochemical studies of Sn deposits in Russia (Ryzhenko et al ., 1998; Sushchevskaya & Ryzhenko, 2002) led to the conclusion that Sn deposits also formed by fluid‐rock interactions in hydrothermal systems where the mineralizing fluid was mainly magmatic and partly meteoric in origin.…”