Physicochemical Parameters of the Formation of Hydrothermal Deposits: A Fluid Inclusion Study. I. Tin and Tungsten Deposits

摘要

The author's database, which presently includes data from more than 18500 publications on fluid and melt inclusions in minerals and is continuing to be appended, was used to generalize results on physico-chemical parameters of the formation of hydrothermal deposits and occurrences of tin and tungsten. The database includes data on 320 tin and tin-tungsten deposits and occurrences and 253 tungsten and tungsten-tin deposits around the world. For most typical minerals of these deposits (quartz, cassiterite, tungsten, scheelite, topaz, beryl, tourmaline, fluorite, and calcite), histograms of homogenization temperatures of fluid inclusions were plotted. Most of 463 determinations made for cassiterite are in the range of 300-500°C with maximum at 300-400°C, while those for wolframite and scheelite (453 determinations) fall in the range of 200-400°C with maximum at 200-300°C. Representative material on pressures of hydrothermal fluids included 330 determinations for tin and 430 determinations for tungsten objects. It was found that prem-ineral, ore, and postmineral stages spanned a wide pressure range from 70-110 bar to 6000-6400 bar. High pressures of the premineral stages at these deposits are caused by their genetic relation with felsic magmatism. Around 50% of pressure determinations lie in the range of 500-1500 bar. The wide variations in total salinity and temperatures (from 0.1 to 80 wt % NaCl equiv and 20-800°C) were obtained for mineral-forming fluids at the tin (1800 determinations) and tungsten (2070 determinations) objects. Most of all determinations define a salinity less than 10 wt % NaCl equiv. (-60%) and temperature range of 200-400°C (-70%). The average composition of volatile components of fluids determined by different methods is reported. Data on gas composition of the fluids determined by Raman spectroscopy are examined. Based on 180 determinations, the fluids from tin objects have the following composition (in mol %): 41.2 CO2, 39.5 CH4, 19.15 N2, and 0.15 H2S. The volatile components of tungsten deposits (190 determinations) are represented by 56.1 CO2, 30.7 CH4, 13.2 N2, and 0.01 H2S. Thus, the inclusions of tungsten deposits are characterized by higher CO2 content and lower (but sufficiently high) contents of CH4 and N2. The concentrations of tin and tungsten in magmatic melts and mineral-forming fluids were estimated from analysis of individual inclusions. The geometric mean Sn contents are 87 ppm (+610 ppm/-76 ppm) in the melts (569 determinations) and 132 ppm (+ 630 ppm/-109 ppm) in the fluids (253 determinations). The geometric mean W values are 6.8 ppm (+ 81/-6.2 ppm) in the magmatic melts (430 determinations) and 30 ppm (+ 144 ppm/-25 ppm) in the mineral-forming fluids (391 determinations).