Abstract

The solubility of SnO 2 in chloride + or - fluoride-bearing fluids in equilibrium with a number of crystalline, silicate acid buffers, has been measured at 2.0 kbars, as a function of temperature (700 degrees -800 degrees C), oxygen fugacity (QFM to QFM + 1.5 log units), and fluid chemistry. Silicate buffers included sanidine-sillimanite-quartz, analbite-sillimanite-quartz, anorthite-sillimanite-quartz, talc-quartz, and (ortho)enstatite-quartz. Hundreds to tens of thousands of parts per million of tin can be dissolved in dilute, chloride-bearing acid solutions. Fluoride was found to have no significant influence on the solubility of SnO 2 at 700 degrees C. In alkali chloride-bearing, acid solutions, across the entire range of oxygen fugacities examined, tin transport is effected by a complex series of stannous chloride-bearing species. These include simple chloride, mixed ligand (hydroxy chloride), and alkali-bearing chloride and hydroxy chloride stannous complexes (SnOHCl, SnCl 2 , KSnOHCl 2 , KSnCl 3 , K 2 SnCl 4 , K 3 SnCl 5 , K 4 SnCl 6 , and NaSnOHCl 2 , NaSnCl 3 , etc). Apparent equilibrium constants for the predicted aqueous tin species have been calculated and species distribution plots derived for different solution compositions. The solubility of SnO 2 is favored by increasing fluid acidity (m (sub HCl, aq ) ), elevated aqueous alkali/acid and K/Na ratios, and reducing conditions, but appears to be only weakly enhanced by temperature increases in the 500 degrees to 750 degrees C range.

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