Geochemistry and origin of the ore-forming fluids in hydrothermal-magmatic systems in tectonically active zones

Abstract

Data on fluid inclusions and stable isotope compositions (O, H, C, and S) in minerals have been summarized for large-and middle-scale mesothermal gold deposits (Nezhdaninsk, Berezovsk, Kochkar', Svetlinsk, Darasun, and Maisk), cassiterite-silicate-sulfide deposits of Sikhote Alin (Solnechnoe, Arsen'evsk, and Vysokogorsk), vein silver-base metal deposits in the Southern Verkhoyansk region (Prognoz and Kupol'noe), and epithermal copper-bismuth-silver-base metal deposits of the Karamazar district in Tajikistan (Kanimansur, Tary Ekan, and Zambarak). It is shown that ores precipitated from fluids with salinity varying from brines (up to 60 wt % NaCl equiv) to dilute fluids (1-3 wt % NaCl equiv). As a rule, fluids of different compositions entered the hydrothermal-magmatic system. A fluid mixture of ç 2 é-ëé 2 -NaCl ± CH 4 ± N 2 predominated in the orogenic (mesothermal) gold-bearing hydrothermal systems, with deposition of the final-stage gold-bearing sulfosalts from aqueous-salt fluid. Brines played a significant role in the formation of cassiterite-silicate-sulfide and vein silver-base metal deposits. The brines often coexisted with a low-density vapor-rich fluid at the ore deposition site. The obtained data suggest a predominant magmatic component in the hydrothermal-magmatic systems, with a significant contribution of meteoric waters.

Isotope and geochemical evidence for the influence of ore-bearing solutions on basic dykes of the Dal’negorskii ore region

“…We should emphasize that these are the first evidence for participation of meteoric fluid in the formation of the skarn deposit, the origin of which is always related to magmatic processes. This conclusion is consistent with establishment of the sig nificant role of a meteoric component in mixed ore forming fluid systems for other ore deposits of this region, for example, tin ones [6,7].…”

“…The revealed meteogenic nature of ore bearing solutions, which are active at the stage of the forma tion of rich mineralization, distinguishes the Dal'negorskoe skarn borosilicate deposit from most orogenic deposits in this region, for which mixing of fluids of different natures is often established, includ ing participation of meteoric waters; however, the magmatogene component in the ore forming fluid is usually clearly registered [6,7].…”

“…At the stage of the datolite ore formation, the ore bearing fluid was exclusively meteogenic as well (δ 18 О from -2.5 to -5.5‰), and the performed estimation of the chemical composition of ore bearing fluid dem onstrated that it was characterized by high concentra tions of K and Ba, a low K/Na ratio, and other specific features [1,5]. The high temperature interaction of pre ore subalkaline and alkaline basalts with such fluid resulted in an increase in the K and Ba concentrations, change of K/Na ratio in rocks, and violation of the KAr isotope system, which was reflected in their age dat ings [1].The revealed meteogenic nature of ore bearing solutions, which are active at the stage of the forma tion of rich mineralization, distinguishes the Dal'negorskoe skarn borosilicate deposit from most orogenic deposits in this region, for which mixing of fluids of different natures is often established, includ ing participation of meteoric waters; however, the magmatogene component in the ore forming fluid is usually clearly registered [6,7].We studied the oxygen isotope parameters of basic rocks from pre ore and postore dykes located not only within the borosilicate deposit, but on the flanges of the ore region as well in order to establish the scales of abundance of waters of meteoric origin during the for mation of the Dal'negorskii ore region and, if possible, estimate the age limits of hydrothermal system activity. Similarly to altered pre ore rocks occurring directly in the skarn borosilicate ore zone [1], the data obtained for rocks of the whole studied area were compared with the concentration of minor elements and K-Ar age datings.…”

Au-bearing gabbro-tonalite-granodiorite-granite plutons of the urals: Age, geochemistry, and magmatic and ore evolution

“…E mail: gerfer@online.ural.ru exhausted by these topics. Taking into account recent isotopic and geochemical data, the origin and compo sition of ore forming fluid and its role at different stages of the evolution of the ore-magmatic system are of great interest (Bortnikov, 2006). These questions are outside the scope of our paper.…”

Sources of high-pressure fluids involved in the formation of hydrothermal deposits

“…Hence, most of trace, espe cially, ore components, were supposedly delivered from these sources. The conception of different sources of ore forming systems underlies the modern theory of hydrothermal ore formation (Bortnikov, 2006;etc.). A high fluid pressure does not contradict this theory and even complements it, expanding our knowledge of physicochemical parameters of ore forming processes.…”