Composition and origin of the dolostones of Um Bogma Formation, Lower Carboniferous, West Central Sinai, Egypt

Abstract

Dolostones of Um Bogma Formation, Lower Carboniferous, have been possibly originated due to two different fluids. The main fluid source is related to meteoric water. The second fluid originated from deeper hydrothermal sources ascended through faults. The diagenetic features of Um Bogma Formation show many processes with conspicuous effects, including dolomitization, neomorphism, mechanical and chemical compaction, as well as it characteristics with stylolites, sutured and concave–convex contacts between grains. Based on mineralogical composition and petrography, the diagenetic environments are distinguished into shallow marine, near surface meteoric and burial environments. Dolostones in the studied area are possibly subjected to chemical and biochemical weathering. Um Bogma dolostones are nearly stoichiometric and ordered. Mineralogical and geochemical studies indicated that dolomite crystals were deposited in mixing zone of marine and meteoric water. In addition, it is formed in the near-surface oxidizing environment. The Sr distribution coefficient and Y content of the studied dolostones indicated that they are formed in temperature >110 and <150 °C. The CF (Contamination factor) and Igeo (Geo-accumulation index) have doubtlessly indicated that the Um Bogma dolomite rocks are polluted especially for Fe, Rb, Co, Cu, W, S, Ba, Zn, Zr and As. The studied dolomites of Area 45 and Um Bogma Mine sections are characterized by enrichment of Co and Cu, which indicated their deposition in marine environment. The studied dolomite of Um Bogma Mine is characterized by the enrichment of Zn, W, Ba, Mn, Ti and As which derived from hydrothermal solution. Consequently, the dolostones of the Um Bogma Formation are similar to those in Cayman Formation, Indies.