Summary:
Tenke-Fungurume is classified as a strata-bound copper cobalt deposit. Multistage mineralization took place with at least four separate dolomitization and four silicification events associated with several sulphide stages, with differing mineral assemblages. During syngenetic to early diagenetic stages of basin extension, highly oxidized and saline residual marine bittern brines migrated through the RAT basal red-bed sequence. The brines also possibly circulated into the basement, mobilizing copper as chloride complexes. With increased subsidence, lithostatic load from the 7,000 m of overlying Katanga Supergroup drove copper-cobalt- rich brines laterally and vertically toward basin edges. Copper and cobalt sulphides were precipitated where the brines encountered reductants, including organic-rich, stromatolitic, sour gas, or pyrite-rich beds. Sulfur sources appear to be from evaporitic anhydrite in proximal and deeper parts of hypogene ores. Diagenetic pyrite may have contributed additional sulfur in the reduced, stratigraphically higher parts of the Mines Series. The bulk of the copper sulphides appear to have formed during diagenetic stages. At peak orogeny, local remobilization of early stage sulphides took place, resulting in mineralogically distinct late-stage sulphide veins that cut clean earlier mineralization assemblages. Supergene oxidation in the Miocene to Pliocene led to the development of high-grade oxide copper-cobalt mineralization.
The Tenke-Fungurume deposits lie in the largest tectonic window of Roan Group rocks in the Central African Copperbelt. This central Roan window is surrounded by Nguba and Kundelungu lithotectonic assemblages. The Mines Series forms a series of scattered tectonic blocks referred to as ‘écailles’. These are fault bounded on all sides and tend to form tight, upright or recumbent anticlines or monocliines. The écailles can range from several 10’s to over 500 m in length and extend downdip from 20 to 200 m.
The Luflian Arc is an intensely folded zone composed of three distinct but related structural units. The outer unit, within which the Tenke Fungurume group of deposits is located, is the most northerly, consisting of tightly folded and thrust blocks of Roan age rocks which have been tectonically transported from south to north, and now rest upon a younger Kundelungu foreland.
The Tenke Fungurume concession encloses thrust slices of various dimensions and orientations. The northern portion is relatively undisturbed with a gentle northerly dip, while the southern portion is occupied by the Dipeta syncline. At its eastern extremity the syncline is closed by a series of thrust blocks which form the Fungurume section of the deposits. At the western end, the northern limb of the syncline is terminated by a major dislocation which offsets the Tenke deposits to the northeast.
Within the east west trending Dipeta syncline both the northern and southern limbs can be traced in more or less continuous ridges of Lower Roan rocks, with more resistant RSC forming the crestal spines. These ridges run approximately parallel for a distance of 14 km, apparently undisturbed. Drilling and geophysical surveys indicate that the syncline is a gently box-folded recumbent isoclinal fold with steep to overturned inside flanks and a relatively flat bottom.
As is the case with the Kolwezi Nappe, it is possible that the mineralized mega-fragments represent transported blocks of large dimension riding as nappes, or related structures, on series of decollement planes. The overall transport direction has been interpreted as being from south to north.
Both to the north and south, the Dipeta syncline is flanked by numerous écailles of Lower Roan rocks. They attain a maximum development south of the syncline where they form, in general, randomly oriented blocks. By contrast the thrust blocks to the north of the northern flank of the syncline are smaller and fewer in number, generally aligned sub-parallel to the strike of the Dipeta syncline, and are seen to rest upon the lower member of the Dipeta formation (RGS) of Upper Roan age.
The copper-cobalt mineralization at Tenke-Fungurume is mainly associated with two dolomitic shale horizons (RSF and SDB respectively), each ranging in thickness from 5 to 15 m, separated by some 20 m of cellular silicified dolomite (RSC). Primary copper and cobalt mineralogy is predominately chalcocite (Cu2S), digenite (Cu9S5) bornite (Cu5FeS4), and carrollite (CuCo2S4). Oxidation has resulted in widespread alteration producing malachite (Cu2CO3(OH)2), pseudomalachite (Cu5(PO4)2(OH)4), chrysocolla (hydrated copper silicate) and heterogenite (Co3+O(OH)).
Dolomite and quartz are the main gangue minerals present. Dolomite or dolomitic rocks make up the bulk of the host strata. Weathering of the host rocks is normally depth related, intensity decreasing with increasing depth, producing hydrated iron oxides and silica at the expense of dolomite, which is leached and removed. As a result, gangue acid consumption (GAC) is lower in the oxide zone.