New Approach of Structural Setting of Gold Deposits in Birimian Volcanic Belt in West African Craton: The Example of the Sabodala Gold Deposit, SE Senegal

摘要

The Sabodala gold deposit in the Mako volcanic Belt (SE-Senegal, West African Craton) occurs in mafic and ultramafic rocks overlain by clastic sedimentary rocks and felsic volcanic-volcaniclastic sequences. It is a structurally controlled mesothermal vein gold deposit developed in deformed rocks units near the Falombo pluton. The Sabodala Goldfield comprises several faults systems striking N-S to NE-SW. New structural evolution consisting of both thrusting and transcurrent events has been defined for the Sabodala Goldfield. The majority of the gold at Sabodala occurs on the western flank of a large, doubling plunging dome (the Sabodala Antiform) and is also associated with sinistral wrenching that overprints early structures within the Sabodala Mine. The gold bearing veins are hosted by flat lying and NW-trending shear zones. The NW-trending faults acted as transfers syn-gold mineralization, although only discrete segments of these faults were active during the main stage of gold mineralization. Late exhumation resulted in extension along fault zones was responsible for the juxtaposition of medium and low grade metamorphic rocks. The granitic suite of the Falombo pluton is linked to exhumation. Final dextral transpression postdating exhumation produced shearing and folding. Gold lodes developed during brittle deformation are associated with high fluid pressures in a northwest-southeast shortening regime. These are termed mainly the Sabodala deposit, and secondary the Niakafiri and Masato deposits.