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Abstract: Experimental Study of Pyrite Oxidation at pH 5-9.5; Implications for Formation of Roll-Type Uranium Deposits

Martin B. Goldhaber, Richard L. Reynolds

Previous studies of pyrite oxidation have emphasized highly acidic pH conditions owing to the importance of the acid mine-drainage problem. However, pyrite oxidation attending the formation of sedimentary roll-type uranium deposits does not occur in this very low pH range, as evidenced, for example, by the presence of limonite pseudomorphs after pyrite/marcasite. Accordingly, a study of pyrite oxidation has been carried out emphasizing the pH range 5 to 9.5. These experiments were conducted at a constant pH and oxygen partial pressure. The rate of addition of base necessary to maintain a constant pH was monitored. Samples were withdrawn periodically and analyzed for total sulfur in solution, in thiosulfate, and in sulfite. Our data show that the rate of oxidation markedly increases as pH increases, particularly above pH 7. Thiosulfate was found to be an important product during short-term (less than 24 hour) experiments. Sulfite was detected, but at lower concentration than the thiosulfate. The results of this study are compatible with a nonbiogenic mechanism of roll-front development proposed previously by Granger and Warren.

AAPG Search and Discovery Article #90969©1977 AAPG-SEPM Rocky Mountain Sections Meeting, Denver, Colorado