The Kombat mineralised zones are carbonate-hosted base metal sulphide deposits associated with hypogene filled karst cavities and only occur along parallel “roll structures”, which are thrust-related folds. One “roll” parallel to the main Kombat Mine “roll” is present at surface at Kombat Station approximately 1,500 m to the north. The mineralised karst is thought to be caused by the upward migration of corrosive, evaporitederived brines through the Huttenberg carbonates. These brines were expelled from the basin during compression, migrated up the thrusts into folds and encountered oxidized meteoric groundwater and formed corrosive suphuric and carbonic acids. These acids were blocked by the impermeable and reducing Mulden shales resulting in the precipitation of base metal sulphides.

The orebodies are epigenetic, hydrothermal, and metasomatic replacement and fracture-fill Cu-Pb-(Ag) type deposits. Common to all types of mineralisation is the small quantity of associated hydrothermal gangue minerals such as calcite, quartz, dolomite, and seldom barite. The degree of oxidation of massive sulphides is independent of the depth, it is controlled by the proximity of the ores to the water-bearing faults and steeply foliated sandstone aquifers.

Massive and Semi-massive Sulphides are elongated, foliated zones of mineralised dolostone related to centres of tectonic and sedimentary brecciation in dolostone stratigraphy. The replacement ore is best developed in breccia matrices, lenses of feldspathic sandstone, in pervasively calcitised dolostone and particularly in oölitic, pelletal/detrital units closest to the slate contact.

At least four breccia types can be distinguished. These are firstly the syn-depositional sedimentary breccia with angular dolostone clasts in a micritic and often calcitic matrix and secondly the stylo-breccia with an anastomising or quadrangular meshwork of net-vein fractures. The fault breccia (associated with post-ore fractures) and the solution collapse breccia (associated with karsting and localised by a north-east trending fault) have little volumetric extent and no control on hypogene mineralisation (Innes and Chaplin, 1986). A foliation is frequently superimposed where breccia grades into transposition breccia in which clasts are attenuaded and boudinaged. High grade mineralisation extends away from the centres of brecciation along zone of recrystalised dolostone. All gradations of mineralisation from finely disseminated sulphides to completely replaced rock exist in the sandstone and in the dolostone. Five types of massive and semimassive sulphides are recognised: 1) bornite and chalcopyrite (+/-galena, sphalerite and tennantite); 2) galena; 3) pyrite and galena; 4) chalcopyrite +/- pyrite in a carbonaceous host; and 5) a supergene assemblage consisting of chalcocite, digenite and malachite (+/- covellite, cuprite, native copper and native silver) (Innes and Chaplin, 1986).

A reticulate or anastomosing mesh of mineralised calcitic micro-fractures is developed adjacent to shears, faults and broad zones of pervasive calcitization below massive sulphides. It is therefore regarded as the “root zones” of the massive ore (Dean, 1995). With increasing deformation it grades into sutured stylolites. The stylo-cumulates contain magnetite, bornite, galena and chalcopyrite. In oxidised zones chalcocite, malachite, copper and hematite are found. It is common for mineralisation of this type to merge into alteration breccias and massive replacement Cu-Pb ores (Innes and Chaplin, 1986).

Galena-rich Alteration Breccias are confined to Kombat East orebodies where steep breccia bodies of pipe-like configuration exist. An unaltered core of close-packed angular dolostone blocks is surrounded by a bleached, calcitised fringe induced by hydraulic fracturing which permitted increased fluid flow along the fracture system. The mineral assemblage comprises galena, pyrite and subordinate chalcopyrite.

t is an alteration facies of the feldspathic sandstone affected by penetrative deformation and therefore formed early in the mineralizing process. Fine-grained, euhedral pyrite is disseminated in a generally strongly foliated sericite-quartz matrix. Ore minerals are seldom present.

Iron-manganese Oxide/silicate Association
This compositionally and texturally layered Fe- and Mn-assemblage is always associated with feldspathic sandstone and discrete steeply orientated zones of tectonic deformation. It forms an integral part of the orebodies of Asis West, Kombat Central and Kombat East. Larger bodies, with an estimated undeformed size of 50 m in length by 10 m thick comprise hematite and magnetite in juxtaposition to layered Mn-oxides and -silicates within a zone of transposition. There is no intralayer admixture of magnetite and Mn ores. All MnFe orebodies contain interfoliated sandstone sliver and lenticles. The main banded ore minerals are magnetite, hausmannite, hematite, barite, calcite, tephroite, alleghanyite, pyrochroite, and small amounts of pinkish jasperoidel rock. Sulphides such as pyrite, chalcopyrite, and galena are present in small amounts. Mn-ores are fine grained and polymineralic aggregates with a well-defined internal mineral banding (band width: 1 to 6 mm) of magnetite alternate with the assemblage leucophoenicite-tephroite-Cu and kutnahorite-barite-barysilite. They occur only in zones of tectonic transposition. In Fe-rich ores, granular magnetite is interlayered with schistose specular hematite and sandstone (Dean, 1995). The layered Fe-Mn bodies are confined to the Kombat Mine and predate the sulphide formation. Fe-rich metasomatism of the dolostone could be expected to produce large amounts of Ca- and Mg amphiboles, epidote, diopside-hedenbergite, and andradite but only an amphibole(-mica) association with small amounts of epidote has been formed in the dolostone. Shortly before the deposition of the Kombat Formation, the emplacement of Fe- and Mn-carbonates/-hydrous oxides on the carbonate platform margin together with the feldspathic sandstone could have taken place during a rifting phase (Dean, 1995). The analogy between the layered Fe-Mn bodies of Kombat and volcanic exhalative class of Fe-Mn ore is described by Innes and Chaplin (1986).

Epithermal Association
This association commonly comprises transgressive vuggy veins containing euhedral calcite, quartz, and chalcopyrite. It postdates the main period of mineralisation. In addition, a number of narrow veins containing galena, sparry rhodochrosite, helvite, and barite cross-cut the lenses of Fe-Mn oxides/silicates and adjacent bodies of massive galena-chalcopyrite (Innes and Chaplin, 1986).

The Kombat mining operations comprise conventional open pits and underground cut and fill mining operations. The Kombat East and Kombat Central open pits reach a depth of 95 m. Kombat East stripping ratio is 8.01 with 0.46 Mt of ore at a copper grade of 1.26%. Kombat Central has a higher stripping ratio at 8.74 with 0.53 Mt of ore at a copper grade of 1.49%. Gross Otavi has a stripping ratio of 10.18 with 0.53 Mt of ore at a copper grade of 1.16% and a lead grade of 3.39%. Asis Far West requires 6,865 m of development and contains 0.85 Mt of ore at a copper grade of 3.67% and Asis West requires 11,153 m of development and contains 1.74 Mt of ore at a copper grade of 4.08%.

The first area mined is the combined East and Central Pits which deliver a total of 54 kt of concentrate with 22% copper content for export. The combined pits have a life of four years delivering an average copper head grade of 1.38% mining at an average of 21 ktpm.

During the third year of operation of the East and Central open pit operations, the underground mines are in a position to start treating ore at an average 60 ktpm with an average head copper grade of 3.72%. The underground mines will deliver a total of 284 kt of concentrate with approximately 30% copper content for export. The combined underground mines have a life of five years when mining at an average rate of 60 ktpm.

The final area to be mined is Gross Otavi that targets high grade lead of 3.39% Pb. The pit will start operation concurrently with the underground operations and has a life of five years. The pit will deliver a total of 30 kt of concentrate with 45% Pb content, which will be further treated to also deliver a secondary product of 22 kt of 18% copper concentrate.

The combined open pits and underground mines have a life of eight years mining 4,071 kt at an average mined grade of 2.84% Cu.

The existing Kombat plant has a capacity of 30 ktpm and consists of a three-stage crushing, rod and ball milling, flotation, concentrate thickening and filtering plant which is capable of producing separate copper and lead concentrates. Historic production efficiencies were used to estimate plant recoveries. The plant will produce a copper concentrate when treating material from Kombat, Asis and Asis Far West areas at recoveries of between 87% and 93%. Lead and copper concentrates will be produced when treating Gross Otavi material at recoveries of 80% and 70% respectively.

The owner-operated plant will be refurbished before it is recommissioned to treat open pit material from the Kombat area at a throughput of 30 ktpm. The plant will then be expanded to 60 ktpm in year 4 before underground production commences in year 5 at Asis Far West.