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Fluid inclusion studies can contribute in the understanding of physicochemical conditions controlling the molybdenite mineralization, and to suggest the fluid evolution model of these mineralizations. Both quartz veins and their hosted granite in Gattar area are choice in the study. The present data was processed using FLUIDS, package of computer programs for fluid inclusion studies (program 1: BULK version 01/03, (development by Ronald J. Bakke 2003)
Taking all available information into consideration, the following model of fluid evolution is suggested. There are two stages of mineralization fluids. The oldest recorded fluid is represented by remnants which are only preserved in granite samples as a result of strong acidic hydrothermal fluids where oxidation of molybdenite to ferro-molybdenite (Fe2(Mo4)3.H2O) in granite is significance. These fluids are of rich water of pure NaCl system, low saline (1.73 to 11.70 wt% NaCl eq.) and with Th values around 200°C. The tectonic history of the region and oxidation patterns confirms the fluid inclusion data that oxidation may have begun at high pressure 19.7 K.bar and reach to about 5.7 K.bar.
However the pH can remain above the stability field of Mo when alkaline hydrothermal solution are affected the granites and alternatively it will be free to migrate and supergene enrichment of Mo in the form of molybdenite, will apply where there are only minor amounts of pyrite and increasing in H2S fugacity then precipitate along the week fractured quartz vein surfaces. The detailed fluid inclusions study in the molybdenite bearing-quartz veins is in harmony with the previous modeling where it indicates that the last fluids are homogenized at lower temperature (rang from 126.7 to 170°C) due to cooling with addition of some divalent salts (MgCl2 ± CaCl2) as a result of wall-rock interaction. These fluids are generated under lower pressure (from 4 to 5 K. bar) and characterized with high salinity (14.72 to 23.3 wt% NaCl eq.). It can be concluded that subsequent cooling and change in the pH are considered the two factors that have triggered molybdenite precipitation.
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