Ore-forming Conditions and Genesis of the Tamdroust Copper Mineralization: Evidence from Structure, Mineralogy, and Stable Isotopes

The Tamdroust copper deposit, located in the Bou Azzer–El Graara inlier (central Anti-Atlas, Morocco), is hosted in Lower Cambrian carbonate–siliciclastic formations. Copper mineralization is structurally controlled by an N110°–N150° fault system and occurs mainly within greenish siltstones and dolostones deposited in a shallow marine platform setting influenced by terrigenous deposits. Two mineralization styles are recognized: disseminated sulfides in host rocks and vein–veinlet stockworks along fracture corridors. Three paragenetic ore stages are distinguished: (1) early disseminated and veinlet-type bornite–chalcopyrite–pyrite associated with quartz–calcite; (2) hydrothermal enrichment along fault zones marked by the replacement of bornite by chalcocite, together with digenite and covellite; and (3) supergene weathering producing native copper and secondary carbonates (malachite, azurite, tenorite). Sulfur isotope data (δ³⁴S ≈ +10.2‰) indicate a dominant contribution from thermochemical reduction of evaporitic sulfates. Carbon and oxygen isotopes in calcite (δ¹³C = –3.6 to –2.6‰ VPDB; δ¹⁸O = –15.8 to –15.2‰ VPDB) suggest hydrothermal fluids at moderate temperatures (~150–160°C) derived from mixed meteoric–basinal brines. The spatial distribution of mineralization reflects redox-controlled precipitation at the interface between oxidized hematite-rich red beds and reducing green siltstones and carbonates. These results support a model of epigenetic, stratabound copper mineralization formed during Hercynian tectonic reactivation of Cambrian carbonate–evaporite sequences. The Tamdroust deposit shares strong similarities with Jbel N’Zourk and Jbel Laassal, providing a predictive analog for regional exploration targeting redox interfaces and structurally focused brine pathways.