Deformation, Alteration and Geochemical Footprint of a Gold-Bearing Shear Zone in Metagranitoid and Metasediment, East Cameroon Goldfield

Abstract

The Gankoumbol-Djouzami-Beka (GDB) area investigated in this study is part of the Central Cameroon Shear Zone (CCSZ) which is a network of anastomosing NE-SW-trending brittle-ductile mega shear. Primary gold mineralization in the area is restricted to secondary structures in the hydrothermally altered metagranitoids and metasediments pointing to a link between deformation, fluid flow and attendant mineral alteration synchronous with gold precipitation. Here, we document the spectrum of fault rocks that adorn the shear zone at the GDB area, ranging from ultramylonite/mylonite at the center of the shear zone that grades outwards through protomylonite to cataclasite at the margins. Shear sense indicators point to sinistral shear with a dominant prolate-type strain ellipsoid. The metagranitoid is subalkaline, with fault rocks characterized by alterations such as K-feldspar alteration, silicification, sericitization and sulphidation which affects the geochemistry of this altered assemblage. The least altered metagranitoid and fault rocks samples show LREE enrichment, depletion in HREE and a negative Eu anomaly depicting plagioclase fractionation over the various alteration categories. On the multielement variation plots, positive Rb, K, Sm, Pb, and Th anomalies and negative Nb, Sr, Ba, Ti and Zr anomalies are observed, resulting from hydrothermal alteration for the fault rocks. Gold (up to 1.8 g/t) mineralization is associated with sericitization, silicification and sulphidation. Hydrothermal alteration in fault rocks results to enrichment Mn, Cu, S, Au, Te, Fe, Bi, Ba, Mo, Mg, and depletion in Nb, Sn, As, Sb and Ga. Au-S-Cu-Mn-Te-Fe-Mo-Bi metal association constitutes a pathfinder element class reflecting gold mineralization contemporaneous with sulphidation.