Abstract

New and revised thermochemical data are used in the construction of fugacity diagrams for various elements found in hydrothermal ore deposits at temperatures of 100 degrees C, 250 degrees C, 400 degrees C, and 600 degrees C. The fields considered cover the following ranges of fugacities: CO 2 , 10 (super -2) -10 2 ; O 2 , 10 (super -60) -10 (super -40) at 100 degrees C to 10 (super -24) -10 (super -10) at 600 degrees C; S 2 , 10 (super -24) -10 (super -8) at 100 degrees C to 10 (super -14) -10 (super +2) at 60 degrees C. For each temperature, separate sets of diagrams show, respectively, the stability fields of appropriate minerals and the fugacities of expectable gas phases. Applying these diagrams to the evolution of hydrothermal fluids on cooling suggests a combination of chemical equilibria within the fluids and pH- controlling wall-rock reactions determine mineralogy.

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