Physicochemical Mechanisms of Cassiterite and Wolframite Precipitation in the Granite-Related Hydrothermal System: Thermodynamic Modeling

摘要

Recent studies based on data from tin and tungsten deposits are aimed, on the one hand, at searching for reasons of formation of large and superlarge deposits and, on the other hand, at refining the physicochemical conditions of formation of the studied deposits using new methods and approaches, which significantly expand or even modify available concepts. The analysis of presently available data shows that the main processes responsible for the formation of Sn—W mineralization at the granite-related deposits are as follows: (a) cooling, (b) mixing of fluids of different composition and genesis, and (c) heter-ogenization (boiling) of fluids [1—6 and others]. Under natural conditions, the formation-of tin—tungsten ores was presumably controlled by one of these three processes that lead to the required chemical change in fluid composition or by their combined effect that intensifies the metal accumulation in ores [7]. It is obvious that the possible role of each of these factors and physicochemical mechanism of precipitation of Sn—W mineralization in a definite hydrothermal system can be deciphered only by thermodynamic modeling. This determined the aim and character of our study. The work is based on the results of studying the large vein-greisen Iul'tin Sn—W deposit (Chukotka, Russia), thus reducing our considerations to one highly productive hydrothermal system.