Amer and two co-authors reported in mid-June 2023 on the petrogenesis of A-type granites and associated fluorite in the Qattar area, Northeastern Desert, Egypt. These granitoids show a geochemical signature typical for an A-type granite, characterized by a slightly peraluminous, highly SiO2, alkalis (Na2O+K2O), U, Rb, Zr, contents, and belong to a group of Ferroan granites with low MgO, CaO, and MnO contents and high FeOtot/ FeOtot+MgO ratios.
These rocks emplaced during a late-collisional stage at a temperature of~755.3°C and pressures from 2.33 to 2.95 kbars under oxidizing conditions (log fO2 -14.85 to -14.91). Moreover, a high 10,000×Ga/Al ratio, negative Eu anomaly, and the tetrad pattern of Qattar alkali–feldspar granites backed up their formation by fractional crystallization and fluid-melt interactions during the late stage of magmatic differentiation.
Fluorite mineralization is recorded as four fluorite types (sky blue-, light-yellow-, colorless-, and yellow-type) formed by hydrothermal processes. These fluorites show a wide range of rare-earth element variations (ΣREE from 76.05 to 166.15) and negative Eu anomaly, which indicates crystallization temperatures above 200°C. Moreover, Gd / Yb ratios are < 1 in sky blue and light-yellow fluorite and >1 in colorless and yellow fluorites, reflecting various conditions of REE leaching.
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