The mineralogy and geochemistry of the copper, lead, and zinc sulphides of the Otavi mountainland

Abstract

Abstract taken from "Opsommings', Bloemfontein, 1980, pp. 156-157:

Although a variety of trace elements are present in all the sulphides, their concentrations are too low to influence the economic potential of any of the deposits. The regional distribution of these elements indicates that the metamorphosed rocks of the Swakop Group, which lie to the immediate south of the Otavi Mountainland, had a definite influence on the deposition pattern of trace elements in the sulphides. The colour of the sphalerite investigated is mainly related to the manganese content of this sulphide. In contrast to sphalerite deposits elsewhere, only a slight correlation exists between the iron content and the colour of the sphalerite

The sulphide deposits of the Otavi Mountainland exhibit features which are characteristic of Mississippi Valley-type deposits, which could indicate that their mode of deposition was similar to that of the latter. The marbles and schists of the Swakop Group are considered to be the provenance area of the lead, zinc and a portion of the copper mineralisation. The expulsion of metal ions and salts from the sediments during diagenesis of the abovementioned group initiated the formation of mineralised brines. Migration of the brines commenced during metamorphism of the Swakop Group, from the high-grade Damaran metamorphic rocks in the south to the less affected Damaran dolomitic rocks of the Otavi Mountainland in the north. The algal beds in the lithostratigraphic units of the Mountainland indicate that conditions were ideal for bacterial action to take place. This bacterial action resulted in the formation of hydrogen sulphide which remained trapped in the dolomitic rocks. Subsequent faulting of these dolomitic rocks at the time when the Swakop Group deposits were structurally deformed, released the trapped hydrogen sulphide. The migrating mineralised brines and hydrogen sulphide reacted to form lead-zinc sulphide deposits in the fault and breccia zones

The major copper deposits are found in the Hüttenberg Formation in association with the pseudo-aplite. The injection of the pseudo-aplite at the time when the brines permeated the rocks of the Mountainland would account for the intimate association which exists between copper, lead and zinc mineralisation in the Otavi Mountainland. The intimate relationship which exists between the sulphides and the fault zones implies that the mineralisation in the Otavi Mountainland is late syntectonic to early post-tectonic with regard to the deformation of the Damara Supergroup which is dated at approximately 550 Ma