Structural and geochemical processes controlling the formation of Egyptian Alabaster at Wadi Mawathil area, Eastern Desert, Egypt

Abstract

Wadi Mawathil area is characterized by the existence of carbonates, represented by “Egyptian Alabaster” (calcite alabaster) and “Bucchino” (recrystallized limestone). One of the most important geological heritage in Egypt is the Egyptian Alabaster quarries. The “Egyptian Alabaster” is considered the main economic resource in the study area and the recrystallized limestone occasionally can be quarried. Field study revealed that the study area is covered by Middle Eocene rocks represented by the “Sannur Formation” surrounded by quaternary sediments; it exhibits karst features. Detailed field and structure studies on the study area show the existence of NW–SE and NE–SW structural trends. The NW–SE fault trends are mainly striking from N25° to 55° W and dip toward NE, SW, and SSW. These fault intersections form channels for groundwater that dissolves limestone. Petrographically, these limestones show three microfacies types, namely foraminiferal biomicrite, sandy biosparite, and alabaster facies. Foraminiferal biomicrite and sandy biosparite microfacies reflect quite an open marine and shallow subtidal depositional environment, while the alabaster facies was precipitated from hydrothermal groundwaters within open fractures, cavities, or karst system. The X–ray fluorescence analysis of alabaster shows an increase in the content of some trace elements such as I, Cr, Th, W, Ag, U, Ni, Zn, Pb, and Ga, and they also show high concentrations of some REE such as Sc, Ce, and La. The major oxides show CaO with an average of 55.47% indicating calcite as a major mineral component in these karstified rocks. The geological, structural, and geochemical studies carried out on the rocks in the study area, indicated that the alabaster rocks were formed in two stages: the first one is the dissolving of limestone by thermal waters in the existence of heavy meteoric water during the rainy periods of the Pleistocene age. The second stage is the re-precipitation of the limestone in the form of “alabaster” and/or “recrystallized limestone” by calcium carbonate saturated meteoric water that percolated through the fractures and fissures of the Eocene limestone.