Hydrothermal alterations associated with Gold-sulphide occurrences in the eglab massif, southwestern algeria

Abstract

The Eglab massif, located in southwestern Algeria, represents the easternmost part of the Reguibat Shield within the West African Craton. This study focuses on the characterization of hydrothermal alteration assemblages associated with sulphide-gold mineralization in the Yetti-Eglab Junction Zone (Y-EJZ), with particular emphasis on the Akilet Deilel gold occurrence. Through macroscopic and microscopic petrographic analysis of ten samples, the investigation revealed three main lithological facies were identified: conglomerate (metagreywacke), quartz veins, and metasomatite. Two generations of hydrothermal veinlets (V1: carbonate-rich; V2: finer opaque-grained, cross-cutting) and three quartz generations (Q1: coarse xenomorphic; Q2: automorphic; Q3: microcrystalline chalcedony) and seven distinct hydrothermal alteration types: sericitization, chloritization, carbonatization, silicification, epidotization, sodic alteration, and supergene oxidation which indicate a complex, multi-stage hydrothermal history. The alteration assemblages are characteristic of orogenic gold systems, structurally controlled by the Yetti-Eglab Shear Zone (Y-ESZ). Gold occurs as native gold in microfractures within brecciated arsenopyrite and galena, and as inclusions in chalcopyrite and galena, indicating late- stage precipitation. Strong supergene alteration produced iron and copper hydroxides associated with supergene gold enrichment, explaining high surface grades (up to 311 g/t Au) compared to depth (~1.5 g/t Au)(ORM,2002) Fluid inclusion data suggest low-temperature hydrothermal fluids (160–280°C) of probable meteoric origin circulating through deep crustal faults, with possible magmatic contribution. The mineralization is interpreted as a late tardi-Eburnean event post-dating 2.065 Ga. These findings contribute to the understanding of Paleoproterozoic metallogenesis and provide exploration guidelines for the Eglab massif.