MINERALOGICAL AND FLUID INCLUSIONS EVIDENCE FOR THE GENESIS OF UMM ADDEBBAA-UMM KABU BERYL BELT, SOUTH EASTERN DESERT, EGYPT | ||||
| Nuclear Sciences Scientific Journal | ||||
| Article 1, Volume 5, Issue 1, 2016, Page 1-14 PDF (1.69 MB) | ||||
| Document Type: Original Article | ||||
| DOI: 10.21608/nssj.2016.30821 | ||||
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| Author | ||||
| SAYED A. M. OMAR | ||||
| Nuclear Materials Authority,Cairo, Egypt | ||||
| Abstract | ||||
| Beryl mineralization in quartz veins and pegmatites, are common deposits of tectonic–hydrothermal and/or igneous origin. The beryl-specialized granites association at Umm Addebaa–Umm Kabu belt is manifested in the field by the development of a system of beryl-bearing pegmatitic pods and quartz veins. The emplacement of these syn-tectonic pegmatitic leucogranites from which K- and Be-rich fluid phases were derived, are confined to the shear zones, as well as a broad zone of alkali metasomatism. Microthermometic studies of primary fluid inclusions within beryl growth zones are consistent with beryl precipitation from H2O-CO2 ± CH4 bearing saline brines. The estimated fluid composition is approximately 0.88 mol% H2O, 0.017 mol% CO2 ± 0.001 mol% CH4 and 0.10 mol% NaCl (2- 11 wt.% NaCl eq.). Fluid inclusion results are consistent with that mineralization in pegmatites and quartz veins that are formed by two genetic stages. The first stage is characterized by temperature of formation in the range of 216.4 – 378.3 °C, with corresponding pressures along fluid inclusion isochore paths ranging from 1.04 to 2.25 bar. The second stage is of aqueous fluid represented with low temperature (177-255°C) and pressure # 1 bar, but high saline (16-22 wt.% NaCl eq.) which might explain mixing of the early carbonaceous fluid with late meteoric water accompanied with pressure release. Thus, it can be inferred that the Be-bearing solutions were moderately saline, but CO2 (and possible CH4)-rich fluid implies that Be was most probably complexed by carbonate (+CH4) - chloride base. The different paragenetic types of emerald and beryl associated with granitoid rocks indicates that the chemistry of the Be-bearing fluids (rather than that of the bulk rock), and syn-tectonic intrusions of leucogranites and pegmatites (Be deriving sources) along major ductile shear zones are the important factors controlling the crystallization of beryl. | ||||
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