Fluid evolution and ore genesis of the Amensif Zn Cu (Pb-Ag-Au) distal skarn deposit (western High Atlas, Morocco): Constraints from fluid inclusions, crush-leach analysis, REY geochemistry, and Pb isotopes

This study investigates the genesis of hydrothermal mineralization at the Amensif Znsingle bondCu (Pb-Ag-Au) ore deposit, hosted within Cambrian carbonates. Three stages of mineralization are identified, beginning with a pre-ore phase characterized by early pyrite precipitation from high-temperature (395–426°C), highly saline (53.0–59.3wt% NaCl + CaCl$_2$) magmatic-hydrothermal fluids under reducing conditions, consistent with a negative Eu anomaly in the Rare Earth Elements and Yttrium (REY) data. Stage I is marked by homogenization temperatures (340–395 °C) and moderate salinities (23.3–24.4wt% NaCl + CaCl$_2$), indicating mixing of magmatic and cooler meteoric fluids. Stage II involves cooler (225–260°C), less saline (17.6–20.4wt% NaCl + CaCl$_2$) fluids, indicating dilution with meteoric waters. Principal Component Analysis (PCA) of crush-leach data indicates the involvement of both brine and vapor phases in metal transport and mineralization.

Lead isotopic and REY data point to a common metal source derived from both mantle and crustal reservoirs, with isotopic uniformity indicating thorough Pb mixing. This aligns with a conceptual metallogenic model in which deep-seated ENE-WSW faults enable magma ascent during post-collision collapse, whereas reactivated NE-SW and NW-SE faults provide pathways for metal-rich magmatic-hydrothermal fluids exsolved from a Permian granitic magma. ... mehrFluid mixing and fluid-rock interaction processes facilitated ore deposition in the Cambrian carbonates. These findings provide new insights into the structural and geochemical factors controlling ore genesis at the Amensif deposit and similar magmatic-hydrothermal skarn systems associated with the Hercynian/Variscan orogeny.