THE GENESIS OF THE TIGRININE-TAABEST MVT PB-ZN ORE DEPOSIT IN CENTAL HIGH ATLAS: CONSTRAINTS FROM FLUID INCLUSION AND C-O-S-PB ISOTOPES STUDIES

The Mississippi valley type Pb-Zn ore deposit of the Tigrinine-Taabest Pb-Zn ore district, located in the Moroccan Central High Atlas, is hosted in hydrothermally dolomitized Liassic carbonates. The mineralogical paragenetic sequence is simple: Quartz-dolomite-pyrite-copper-galena-sphalerite. Fluid inclusions carried out on sphalerite reveal that ore is precipitated from a NaCl-KCl-CaCl₂-MgCl₂ basin-derived warm (123 ^oC) and saline (34 wt% eq. NaCl) brine.

The δ³⁴S values range from 6.6 to 9.4‰ and from 12.7 to 13.0‰ for galena and sphalerite respectively with an average δ³⁴S_fluid of 13‰. Sulfur derived most likely from Triassic sulfates through thermochemical-sulfate reduction. Galena samples have a homogeneous Pb composition with ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios ranging from ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios ranging from 18.229 to 18.236, 15.643 to 15.655, and 38.448 to 38.527 respectively. This Pb composition plots in the upper crust and the orogene and suggest well-mixed source rocks of metals.

During the African-European continental collision (Alpine orogeny), the metal-bearing fluids were remobilized and migrated through major E-W to NE-SW- trending faults. Mixing of the hot, ore-bearing fluids with a cooler fluid are likely the main cause of ore precipitation as indicated by C-O isotopes and fluid inclusions data.