Diagnetic pyrite framboids in the phosphate deposits of Abu-Tartur area, Western Desert, Egypt

Abstract

The pyrite framboids enclosed in the phosphate deposits of Abu-Tartur area, Western Desert, Egypt, occur as discrete individuals and as clustered aggregates. They are intimately associated with the organic matter contained in the phosphates. The morphology and other characteristics of these framboids are presented.

A biogenic mode of formation is suggested for such framboids. Bacterial action on soft organic rich sediments resulted in formation of local concentration of hydrogen sulfide. By the increase in activity of the latter in presence of Fe²⁺ and organic matter, a hydrophobic sulfide gel might have formed. It is considered possible that precipitation of the sulfide around bacteria in the gel would promote formation of globular pyrite rather than other forms, and clustering of the globules may be a result of precipitation of the sulfide around bacterial growths. However, the possibility of forming the framboids as an internal consequence of pyrite crystallization by increasing forces of surface tension is not completely excluded.