Mineralogy, geochemistry and origin of the phosphorites at Um El-Huwtat mine, Quseir, Central Eastern Desert, Egypt

Abstract

AbstractX-Ray diffraction results for the study mine are mainly represented by two phases (phosphatic and non-phosphatic). First phase is represented by apatite (fluorapatite) which is the dominant. The second phase includes carbonate minerals; calcite, dolomite, evaporated mineral (gypsum), sulphide mineral (pyrite), in addition to quartz as a silicate mineral. These results are confirmed by the petrographic study. The detailed microscopic examinations indicate that the phosphorites at the study mine is essentially composed of phosphatic lithoclasts (mainly collophane), phosphatic bioclasts (bone fragments, spines and teeth of vertebrates such as shark fish as well as coprolites), opaques, and quartz embedded in a microcrystalline phosphatic matrix (contains some of dahllite) associated with a microcrystalline quartz according to their decreasing order of abundance. The paragenetic sequence of the studied phosphorites is as follows: fluorapatite, collophane then followed by dahllite. The redox-sensitive trace elements, its ratios, authigenic uranium as well as Fe/Ti can be signifying the redox conditions. Also, they revealed that the study rocks are deposited under the oxic to anoxic environment coupled with hydrothermal solution. The trace and rare earth elements are generally associated with phosphatic rocks. Thus, the phosphatic rocks of Um El-Huwtat mine, Quseir can be considered as sources of trace and rare earth elements. Also, pyrite can be considered as another possible source for REEs. The studied phosphatic rocks characterized by light REE (LREE = 69 ppm) enrichment than heavy REE (HREE = 25 ppm). All the recoded values of the heavy metals for the study mine are higher than those in Tunisia (400.3 ppm), Morocco (571.75 ppm) and Jordan (187 ppm). The post-depositional conditions are responsible for the enrichment of U and Th and/or intensive chemical weathering in Quseir area. Enrichment Factor (EF) indicated that the enrichment or deletion of the elements may be a function of that association and the origins of the various phosphate fractions. The studied phosphatic rocks are suitable for industrialized fertilizers according to the world guides.