Biogenic dolomite, calcite and native sulphur, formed by the action of sulphate-reducing bacteria on evaporites, including anhydrite, overlying mid-Miocene hydrocarbon-bearing strata. The hydrocarbons might have been the reducing agents in view of the occurrence of petroleum at depth.
The sulfur occurs in an uplifted horst block consisting of evaporite-carbonate rocks overlying the middle Miocene oil- and gas-bearing strata. The evaporite deposits are interpreted to be a composite sequence that includes deposits of shallow lagoonal (subaqueous) and supratidal (sabkha) environments.
The sulphur occurs as fine disseminations in Miocene anhydrite and in more coarsely crystalline form in fissures and cavities in anhydritic dolomite and in interstices between rosettes of eucrystalline aragonite. The aragonite layers overlie anhydrite and thus occupy an anomalous position in the normal evaporite sequence.
Ref.: Schnellmann, G.A. (1959) Formation of sulfur by reduction of anhydrite at Ras Gemsa, Egypt. Economic Geology: 54(5)(August, 1959): 889-894.
Youssef, E.L. & Sayed, A.A. (1988) Journal of the Japan Association of Mineralogists, Petrologists and Economic Geologists, 83, 296-307.
Youssef, E.L. & Sayed, A. A. (1989) Geology and genesis of sulfur deposits at Ras Gemsa area, Red Sea coast, Egypt. Geology: 17(9)(September 1989): 797.
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Map Reference: 27°40'0"N , 33°34'59"E
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