STUDY OF FLUID INCLUSIONS THROUGH MICRO-THERMOMETRIC ANALYSIS OF QUARTZ-TOURMALINE MINERALIZED VEINS FROM AN OROGENIC AU-DEPOSIT

The Clearwater Au deposit is located within the Eastmain River greenstone belt from the La Grande volcano-plutonic sub-province (2752-2696 Ma). The Au-mineralization is mainly controlled by the development of a set of extension and shear quartz-tourmaline veins, as well as impregnation of the host volcanoclastic and mafic host rocks. The area is complex and experienced at least 2 stages of deformation. The tectono-metamorphic history of the investigated area is quiet complex and experienced at least two episodes of deformation within amphibole and Upper greenschist (epidote – actinolite – chlorite assemblage) facies conditions.

In this research, we aim to characterize the composition of mineralizing fluid as well as the P-T conditions of Au-mineralization. To do so, we performed a detailed fluid inclusion study based on petrology and micro-thermometry approaches coupled with detailed micro-Raman analysis.

The ore (Au) stage is associated with the trapping of primary fluid inclusions within quartz veins. These primary fluid inclusions are CO2-rich and high-salinity (NaCl) aqueous fluid inclusions. In addition to CO2, Raman analysis shows evidences of other gas phases such as CH4 and H2S in minor quantities.

Whereas the temperature of homogenization (Th) indicates that the temperature of vein formation is at least 240˚C, we are currently working on refining the P-T conditions estimations through a thermodynamic approach pressure corrections.

Such fluid composition is typical for Au-orogenic deposits worldwide and are assumed to be formed during the immiscibility of hydrothermal fluids.