Tectonic and structural aspects at the Otjihase Mine, Matchless belt, Namibia

Abstract

Abstract provided by author:

Ore zone lithologies include stringery-, massive- and semi-massive sulphides, mineralised magnetite-quartzites and disseminated sulphide mineralisation within quartz-biotite-chlorite schists. Chalcopyrite is the main economic mineral and mainly occurs as matrix to pyrite and in coarse-grained pods. Lithological and metal zoning within the Main Shoot is distinct and is an indication that the macroscopic shape of the orebody is largely unaffected by later ductile deformation

North-south trending normal faults of the Windhoek Graben have disrupted the continuity of the ore shoots. In section, the faults appear to have a listric shape. The major faults have pronounced scissor movements and as a result the dips of the blocks within fault zones are affected

Intense ductile deformation has affected the ore bodies, with isoclinal refolding, boudinaging, duplexes of more competent bands and smearing of the schists. Squeezing and remobilisation of the sulphides into the schistosity and low pressure pods has taken place. Successive folding and thrusting during the D2 deformational event resulted in the dominant structural style. Fold axes of drag folds plot onto a great circle in stereographic projection, indicating the formation of sheath folds. The axial planar cleavages of competent layers is steeper than the S (0, 1) foliation and suggests a structural right way-up. The presence of chloritic alteration above the ore shoots, is suggestive of footwall alteration indicating that the sequence was overturned during the D1 deformational event