Structural control on the localisation and deep oxidation of the Skorpion supergene zinc deposit, Namibia

Abstract

The localisation and the metallogenesis of both hypogene sulphide and supergene non-sulphide mineralisation at the Skorpion Mine in southernmost Namibia have been — at least partly — structurally controlled. The hypogene Late Proterozoic hybrid VHMS/SHMS Zn-(Cu-Pb-Ba) ores of this district have formed in an environment, regionally controlled by the intersection of a 1^st-order basin margin fault with a major transform/transfer fault. Bi-modal volcanism, anomalously high heat flow and hydrothermal activity have been the other regionally significant controls for the hypogene ore formation.

The supergene ores have formed from meteoric oxidation of base metal sulphides, channelled by factures of a late-stage brittle fault system. This anastomosing, steeply dipping fault array with a dextral oblique-slip reverse sense of movement has apparently formed in a (local?) transpressional crustal regime. The fault system opened abundant dilatational joints and fractures, providing improved permeability and an enlarged reactive rock surface of the host rocks. Meteoric waters have been able to percolate and convect along the fault system and to oxidise the hypogene ores to more than 700 m depth.

The fault system has been reactivated in neotectonic and even Recent times, as documented by faults truncating and off-setting the overburden. Other fault systems on land and offshore southwestern Africa show similar NNW-SSE strikes and might document the genetic connection of these (generally extensional) fault systems with the Skorpion Fault.