Geological setting, mineralogy, and isotopic characterization of the Jbel N’Zourk copper deposit, central Anti-Atlas, Morocco

Abstract

The Jbel N’Zourk copper deposit in the central Anti-Atlas preserves textural and mineralogical features reflecting a complex formation history. High-grade copper mineralization is predominantly confined to the carbonate, siltstone, and evaporite layers within the lower members of the Early Cambrian Adoudou Formation. The mineralization is spatially associated with a prominent NNW-SSE-trending fault, which likely played a crucial role in the localization and concentration of copper mineralization across the region.

The mineralization is manifested by massive, disseminated, and stockwork occurrences of Cu-sulfides such as bornite, chalcopyrite, and digenite. Stable isotope analyses of the ore-associated calcite yield δ¹³C values ranging from −9 to + 2.9 ‰ and δ¹⁸O values from + 19.5 to + 22 ‰. These isotopic signatures suggest a mixed origin of carbon, likely encompasing organic matter dehydroxylation and marine carbonate dissolution. Oxygen isotope signatures indicate significant diagenetic processes affected mineralization, while sulfur isotope data of bornite (δ³⁴S: 13.3–21.6 ‰) suggest marine sulfate as the primary sulfur source. The δ³⁴S data, along with the evaporitic and carbonate sequences in the marine Adoudounian Formation, demonstrate that thermochemical sulfate reduction (TSR) was the dominant process, converting sulfate into sulfide and facilitating Cu deposition.

The evolution of ore fluids progressed through deep-seated hydrothermal fluid migration, sulfate interaction driving TSR-driven sulfide precipitation, and subsequent fluid remobilization. This dynamic system, influenced by episodic fluid pulses, resulted in stockwork and open-space filling textures within karstic cavities at shallow crustal levels. These features support a model of Cu-rich hydrothermal mineralization, where faults and folded structures, formed or reactivated during the Variscan tectonic events, were the main controls on ore deposition at Jbel N’Zourk.