Some limitations on the possible composition of the ore-forming fluid

Trace Elements Investigations 633
This report concerns work done partly on behalf of the Division of Raw Materials of the U.S. Atomic Energy Commission



The activity rations of various important anions (S, CO3, SO4, OH, F, and Cl) in hydrothermal solutions at the time of deposition are evaluated using a simple thermodynamic technique. The rations are interpreted in the light of the mineralogy of ore deposits and limites are placed on the variability of each ratio in hydrothermal solutions. All of the calculations are made for 25°C and cautious extrapolation to higher temperatures seems justified; however, additional data for elevated temperatures and pressures are needed before more than approximate values may be assigned to these ratios in the ore-forming fluid.

The calculated partial pressure of CO2 in the ore fluid is generally less than one atmosphere, which suggests that a dense CO2 phase cannot be considered an importatn ore fluid for most deposits. The partial pressure of H2S is usually less than 10-4 atmospheres which makes it extremely difficult to defend the heory that metals (other than the easily complexible mercury, arsenic, antimony, and perhaps fols and silver) are transported in quantity as complex sulfide and hydrosulfides. The sulfate to sulfide ration is such that the oxidation potential at the time of deposition is defined by the following equation: Eh (in volts) = 0.22 ± 0.04 - 0.059 pH.

Publication type Report
Publication Subtype USGS Numbered Series
Title Some limitations on the possible composition of the ore-forming fluid
Series title Trace Elements Investigations
Series number 633
DOI 10.3133/tei633
Year Published 1956
Language English
Publisher U.S. Geological Survey
Description 41 p.
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