Presentation Information
[R7-02]Fluid inclusion studies on auriferous quartz veins from Kwaka, Niger state, North central Nigeria
*Abdulrahman Ahmadu1, Madhusoodhan Satish Kumar1 (1. Niigata University)
Keywords:
Gold,Quartz veins
Fluid inclusions are effective tools that provide indispensableinformation about the geological processes involved in gold deposition. Occurrences of gold-bearing quartz veins have been reported in several regions of Niger State, Nigeria. In this study, I conducted a detailed fluid inclusion analysis of gold quartz veins in Kwaka, Niger State to provide insights into the unresolved fluid origin. The Nigerian basement, located within the Pan-African mobile belt, is divided into two: The West Nigerian Subshield(WNS), which comprises Archean to Paleoproterozoic rocks, including gneisses and metasedimentary rocks (Schist Belts) ofgreenschist to amphibolite-facies grade, extends NE-SW, consistsof schists, phyllites, and some granitoids. The East Nigerian Subshield is composed of Paleoproterozoic rocks of granulite-facies grade. Neoproterozoic granitoids (Older Granites) formed during the Pan-African (600 ± 150 Ma) orogeny appear in both subshields. Previous studies indicate gold occurrence in Schist Belts of WNS, usually within quartz veins in shear zones subordinate to the major regional transcurrent fault system. In this study, three different fluid inclusion types are identified based on petrographic features and microthermometry, categorized as Type I (aqueous-salts), Type II (aqueous-carbonic), and Type III (carbonic) fluids. Type I contains H2O± NaCl± KCl inclusions, with low to moderate salinities and total homogenization temperatures between 100°C and 320°C. Type II exhibits H2O-CO2 inclusions, with TmCO2 values clustering around the CO2 triple point, ThCO2 between 14°C and 30°C, withtotal homogenization temperatures around 160°C and 350°C. Type III contains CO2±H2O, showing TmCO2 between -58°C and -57°C, ThCO2 within the critical point of CO2, and densities around 0.5 to 0.6 g/cm³. Melting temperatures from microthermometry indicate varied fluid compositions of H2O-NaCl-KCl, CO2, and CO2+H2O. Density values correspond to a pressure of approximately 0.5 to 1 Kbar at an estimated depth of ~2 km. Sulfidation, fluid mixing, and phase separation are likely the main mechanisms for precipitation, with CO2 a dominant volatile phase. Gold precipitation may have been facilitated by mixing aqueous saline fluids of varying salinities, interpreted as carriers of gold as complexes.