Amer and three co-authors reported in early 2021 that the A-type younger granite pluton and associated fluorite of Gabal El-Erediya, Eastern Desert, Egypt, have been investigated geologically and geochemically. Granites are genetically high-K-calc-alkaline syeno-granites that show a high LREE/HREE ratio
with noticeable negative Eu anomaly.
Additionally, the visible tetrad pattern and negative Eu anomaly of the investigated granites point to fractional crystallization and fluid-melt interactions during the last stage of magmatic differentiation. They were probably generated within an extensional environment and were crystallized at temperature ~ 740°C and pressure ~ 1.9 kbars. Two types of U-rich fluorite mineralization were recorded including colorless and violet types. The hydrothermal fluids forming fluorites were related to late-stage differentiation of the felsic magma with a crystallization temperature ranging from 118 to 336°C.
The authors concluded that the above discussion postulates that:
- The ErdSG are considered as high-fluorine silicic rocks (HFSR), where the fluorine performed an important role in enriching U in late-stage hydrothermal-magmatic fluids.
- Fluorite is an important indicator for U mineralization.
- The fluorine is the main factor for the enriching of uranium in the late-stage hydrothermal-magmatic fluids. Eight representative granite samples have been collected in El-Erediya area in order to determine the origin, geochemical behavior, petrochemical characteristics, mineralization, and their tectonic settings. Eleven fluorite samples were analyzed (electron microprobe analyses) to clarify the environment of formation and its relation to U mineralization.
The results of the analyzed samples can be concluding as follows:
1. Syeno-granites are strongly evolved and fractionated granites with high-fluorine content.
2. They are mineralized granites, slightly peraluminous, derive from highly K-calc-alkaline magma with potassic affinity and emplaced as post-orogenic granitoids.
3. They are highly differentiated granite, considered as A2- type granites, which are derivatives of basaltic/ amphibolitic sources underplating in the lower crust.
4. They are considered as uraniferous granite and favorable for U mineralization.
5. The fluorite is formed and concurrent with the uranium mineralization, showing that the source of the uranium is the hosted granite, which is transported as U-fluoride complex. The solubility of the U in the hydrothermal solutions is mainly controlled by the fluoride complex formation.
6. The fluorine is the main factor for the remobilization and enrichment of U in the hydrothermal solutions. The U-rich granite subjected to tectonic and hydrothermal processes causing alterations of rock-forming minerals. These processes are mostly responsible for U concentration and its redistribution, which form U-rich fluorite mineralization along cavities and fractures in granite hosted rocks.
7. Fluorite varies from colorless to dark violet in color. They recorded high U content.
8. The average Th/U ratio in colorless and violet fluorite type (Avg. 0.46 and 0.52, respectively) and syenogranite (Avg. 1.13) is less than 3 and appears that rock units suffering post-magmatic process result in mobilization of uranium relative to thorium, which is suitable for leaching.
9. The minimal temperature of fluorites origin can be estimated from the homogenization temperatures of primary fluid inclusions in fluorites (118 and 336°C); also, they have high REE contents related to a hydrothermal-magmatic system.
Finally, they concluded that the syenogranite considered as HFSR, which included two types of fluorites according to their U and REE contents. The colorless fluorite is poor in U and REE, relative to the violet type, which is rich in U, and REE. The F-enriched granite can be considered as fertile and possess the same chemical characteristic parameter of fertile granite.
Read on: https://www.i2mconsultants.com/downloads/corp/Amer2021_Article_GeochemicalInsightIntoGraniteH.pdf
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