Alteration and ore distribution in the Proterozoic Mines Series, Tenke-Fungurume Cu–Co district, Democratic Republic of Congo

Abstract

Two sediment-hosted stratiform Cu-Co deposits in the Tenke-Fungurume district of the Central African Copperbelt were examined to evaluate the alteration history of the ore-hosting Mines Series and its implications for ore distribution and processing. Core logging and petrography, focused on lithology and timing relationships, outlined a complex alteration sequence whose earliest features include formation of anhydrite nodules and laths, followed by precipitation of dolomite. Later alteration episodes include at least two silica introductions, accompanied by or alternating with two dolomite introductions into the existing gangue assemblages. One introduction of Cu-Co sulfides accompanied the last episode of dolomite alteration, overprinting an earlier generation of ore whose gangue association was unidentifiable. Sulfides and some carbonates were subsequently modified by supergene oxidation, transport, and reprecipitation to 100-200 m depth. Presentday ore distribution resulted from these successive processes. Ore is concentrated in two shale-dominated units on either side of a cavernous silicified dolomite, which is interpreted as the main conduit for the mineralizing fluids. Sulfide ores precipitated at the redox or sulfidation contacts between this dolomite and the shales. Later, supergene fluids dissolved and moved some of the metals, redepositing them as oxides and carbonates. Solubility differences between Cu and Co in supergene conditions caused them to precipitate separately. Thus, modern ore distribution at TenkeFungurume results both from original hypogene lithologyand contact-related precipitation and from supergene oxidation, transport, and Cu-Co decoupling. The supergene fluid flow also redistributed gangue minerals such as dolomite, which has an economically important influence on the processing costs of supergene ores.

Cobalt

“…Large deposits in this region from which byproduct cobalt is currently or has been produced include Kamoto, KOV, and Tenke Fungurume, all in Congo (Kinshasa) (El Desouky and others, 2010;Fay and Barton, 2012), and Nkana in Zambia (Brems and others, 2009). …”

Factors controlling the precipitation of copper and cobalt minerals in sediment-hosted ore deposits: Advances and restrictions

“…Flow boundaries are open at the side opposite the inflow and at the bottom, to allow a vertical migration of fluid from layer 2 at the top downward in layer 1. In this model the main lateral flow of the mineralising fluid is in the RSC, conforming to the fluid migration recently proposed by Fay and Barton (2012) for the hydrothermal diagenetic mineralisation phase. The total time modelled varies between 30,000 and 40,000 years, requiring more than 20,000 simulation steps.…”

“…Although such a model explains the mineral zoning observed our model is preferred since it also explains the observed paragenesis of the minerals. High-grade mineralisation in the Lower and Upper ore bodies at the contact with the RSC, with a sharp cut-off at the contact, has been described for the stratiform ore bodies at Tenge-Fungurume (Fay and Barton, 2012;Schuh, 2006). However, mineralisation in both ore bodies occurs in a thicker sequence, especially in the laminated rocks of the Lower orebody.…”

Geology of the Enterprise Hydrothermal Nickel Deposit, North-Western Province, Zambia

“…In these deposits, early magnesian carbonate (principally magnesite, at least at Kolwezi) crystal growth occurred in carbonate lithologies, while Mg-chlorite formed in more argillaceous rocks (Oosterbosch, 1951;Bartholomé et al, 1972;Hoy, 1989;El Desouky et al, 2009. Alternating periods of magnesian alteration (dolomitization) and silicification were followed by precipitation of sulfides with quartz (Fay and Barton, 2012) or quartz and dolomite (El Desouky et al, 2009). It is possible that the metasomatic/mineralization event at the Enterprise nickel deposit is analogous to the late mineralization event observed Fig.…”