Tembang encompasses an extensive low-sulphidation epithermal system comprising northwest and northeast trending, gold-silver bearing quartz sulphide veins hosted in Miocene intrusive volcanic and volcaniclastic rocks. Tembang is believed to be focused within a zone of dilation created by faulting associated with the Trans Sumatra Fault Zone that parallels the Sumatran volcanic arc.

Individual vein lodes have strike lengths of between 200 and 500m, however mineralised trends are observed to be greater than 1km. Vein widths are typically less than 2m, however at Berenai vein lodes or complexes are greater than 5m and locally up to 10m. Gold-silver mineralisation is found associated with quartz chalcedony veins, vein breccias and vein stockworks with a low sulphide content. The veins display typical epithermal characteristics including crustiform-colloform banding, silica pseudomorphs after bladed calcite, adularia, amethyst and bands of fine grained dark sulphides.

The depth extent of the economic mineralisation outlined to date appears to be approximately 300 metres, however several high grade vein lodes have not been closed off at depth. As such, the potential for resource growth is considered to be high in that most known deposits remain open at depth, along with a pipeline of prospective near mine exploration targets.

The current Tembang life-of-mine plan is based on the five open pit mines at Berenai, Asmar, Tembang, Buluh-Siamang and Bujang, with the Belinau underground mine developed via decline from the former Belinau open pit.

The underground mine plan for Belinau provides access to the vein lenses via decline from surface. The decline has been developed from inside the existing Belinau open pit, well above the pit bottom to deal with high intensity rainfall events, which are common in the region. The total length of the decline will be approximately 1,360 metres with a 1-in-7 gradient taking the mine to a depth of around 235 metres. Mining is by long-hole stoping with backfill, retreating from the vein limits back to the access crosscut. The mining method is a combination of top down conventional stoping along to the west and to the east and a slight variation to the typical Avoca or bench stoping method, with a 3m bench cut into the ore drive floor on each planned cemented aggregate fill (CAF) level. The mining method reflects the vertical nature of the wall rock and competent host rock either side of the vein. It is expected that approximately 40% of ore production will be from development and 60% from long-hole stoping. Development and operations at Belinau are currently on an ‘owner-operator’ basis.

- subscription is required.