Summary:
Barberton Mines comprises Fairview Mine, Sheba Mine, New Consort Mine and the BTRP.
The mineralisation at Barberton Mines is classified as Achaean epigenetic hydrothermal lode gold deposits within a granite greenstone terrain. The distribution and localisation of these orebodies in the BGB can be largely attributed to the combined influence of thermal metamorphism and structural deformation.
Mineralisation is typically continuous in the short- to medium-range on strike with long-range geological and grade continuity being experienced down-dip. Gold occurs in either vein-hosted ore lode deposits or as free milling gold associated with fine grade sulphides, mainly pyrite and arsenopyrite.
The Barberton deposits are thus mineralised shears with gold occluded in sulphide minerals. The sulphides often occur as massive assemblages in the shear structure. Lower-grade ore, in the wall rock, forms as a result of the alteration process during fluid flow and is associated with disseminated sulphide minerals. A late stage of gold mineralisation occurred in brittle fractures with the formation of quartz veins. These quartz veins often contain free gold in visible clusters.
Fairview Mine
The Fairview Mine orebody is an epigenetic hydrothermal lode gold deposit. Three distinct types of mineralisation occur at the mine:
• Refractory sulphidic ore, which constitutes the bulk of the mined ore, is hosted in the greywacke and shale sequence of the Fig Tree Group. The mineralisation is found in close association with an anastomosing shear system that often parallels the stratigraphy and lithological contacts. Auriferous pyrite and arsenopyrite mineralisation are confined to ribbon-like shoots within the shear system and as disseminations in the wall rock.
• A coarse clastic unit of the Fig Tree Group hosts a series of hanging wall bodies. This coarse clastic unit consists of thick-bedded to massive greywacke, grading into arenite with interbedded granule stone layers. Two quartz-porphyry dykes and two dolerite dykes intrude the host rock sediments. Blue-black quartz veins, quartz-carbonate veins and stockworks are recognised in the hanging wall area.
Refractory gold-quartz-carbonate-sulphide ore occurs as disseminated to massive pyrite and arsenopyrite mineralisation.
• Quartz veins, containing free-milling gold, occur in the Moodies Group in the footwall of the Sheba Fault. Gold mineralisation generally occurs within the vein, but may penetrate the adjacent host rock. Only minor pyrite and arsenopyrite are associated with this ore type.
The deepest intersection on a Fairview orebody is at a depth of 1,660m below the adit elevation, approximately 100m below the current mining platforms.
Sheba Mine
The Sheba orebody is an epigenetic hydrothermal lode gold deposit. Three distinct types of mineralisation occur at the mine:
• Refractory sulphidic ore (MRC section), which constitutes the bulk of the mined ore, is hosted in the greywacke and shale sequence of the Fig Tree Group. The mineralisation is found in close association with a shear system in the immediate hanging wall of greenschist anticlines of the Zwartkoppie Formation. Auriferous pyrite and arsenopyrite mineralisation occurs as massive replacement veins within the shear system and as disseminations in the wall rock.
• The ZK section is characterised by the occurrence of visible gold and disseminated pyrite in the greenschist as the prominent mineralisation, in association with shear and fracture-hosted smoky and white quartz veins.
• The mineralisation of the Royal Sheba orebody is encapsulated in a shear envelope of the Sheba Fault, ranging in width from 5m to 25m. The gold mineralisation occurs predominantly in sulphide minerals and as native gold.
The deepest orebody intersection on Sheba Mine is 1,200m below shaft collar elevation. The orebody is open at depth.
Consort
The Consort orebody is an epigenetic hydrothermal lode gold deposit. Gold mineralisation at the Consort section is associated with the contact between the underlying schist of the Onverwacht Group and the overlying metapelite of the Fig Tree Group. This contact is marked by the presence of the Consort ‘bar’, a highly siliceous banded chert layer. The Consort Bar is thought to be a silicified mylonite occupying the contact. A series of north-dipping tabular pegmatites, termed the Muiden Reef pegmatites, displace the south-dipping Consort contact and the mineralised shoots. Some scheelite mineralisation has been recorded, which is associated with the pegmatites.
The deepest intersection of the Consort orebody is 1,450m below adit elevation. The orebody is open at depth.
Barberton Tailings Retreatment Plant (BTRP)
The material is confined to the deposition sites of historical tailings and extends approximately 1m beneath the historical footprint into the residual soil profile. The ore consists of oxidised tailings containing pyrite and arsenopyrite-associated gold, which was not recovered in the initial treatment process.
The BTRP operation re-treats previously processed gold ore in the form of slime or tailings material. The slime emanated mostly from historical mining and processing activities of the same orebodies that are currently being mined underground from the existing Barberton Mines operations. Deposition material of historically treated metallurgical tailings from Fairview, Consort and Sheba Mines.
Sheba Fault
The Sheba Fault project straddles the contact between the arenites of the Moodies Group to the north (Eureka Syncline) and the Fig Tree Group’s greywacke and shale to the south (Ulundi Syncline), like the stratigraphic occurrence of Sheba Mine. The contact is marked by the presence of the regionally identifiable Sheba Fault. The two synclines (Eureka and Ulundi) were refolded due to the immense force present during deformation, resulting in back-to-back isoclinal folds that dip steeply to the south.
The mineralisation of the Sheba Fault orebodies is encapsulated in a shear envelope of the Sheba Fault, ranging in width from 5m to 25m. The gold mineralisation occurs predominantly in finely disseminated sulphide minerals (mainly pyrite) and native gold.