Fluid inclusions, H-O-S-Pb isotopes, and Rb-Sr geochronology of the Augaro gold deposit, West Eritrea, NE Africa: Implications for ore genesis

Abstract

Northeast Africa is an emerging world-class gold province due to the numerous lode gold deposits with Au resources of over 43 Moz discovered in the Nubian Shield. The Augaro gold deposit, located in the Adobha-Augaro Cu-Au belt of west Eritrea, is composed of several auriferous quartz veins. The orientations of the auriferous quartz veins in this deposit are strictly controlled by NE-trending shear zones and nearly E-trending fractures. The most common metallic mineral is pyrite, and gold has been identified as native gold, electrum, and calaverite. Fluid inclusion study, H-O-S-Pb isotope analysis, and Rb-Sr dating were carried out in the Augaro gold deposit. A petrographic investigation revealed that fluid inclusions of type W (Liquid-rich aqueous), type C (CO2-rich), and type S (halite-bearing) are prevalent in auriferous quartz veins. The H2O, NaCl, and CO2 are the main components of the metallogenic fluids, which are medium-low temperatures (150–360 °C) and medium to low salinities (<34 wt% NaCl eqv.). The physicochemical features of fluid inclusions indicate that magmatic fluids experienced phase separation earlier in their evolution and mixed with meteoric water subsequently. Rb-Sr dating of fluid inclusions in auriferous quartz suggests that the Augaro gold deposit formed during the post-orogenic stage (543 ± 14 Ma) of East African orogeny in the Late Neoproterozoic, which is a new metallogenic epoch for the lode gold deposits in Nubian Shield. Geological and Geochemical features refer to the Augaro gold deposit being an intrusion-related gold deposit (IRGD).