The Buffalo Reef and Selinsing gold deposits are thought to be mesothermal lode gold deposits, with auriferous quartz-pyrite-arsenopyrite±stibnite veining, with associated hydrothermal alteration. The two deposits are structurally controlled and thought to be part of the same structural trend, with the Buffalo Reef deposit occurring along strike and to the north of the Selinsing deposit.

The Selinsing gold deposit is hosted by a 20 m to 100 m thick shear zone that dips 55° to 75° towards mine grid east (082° true grid). This zone or “envelope” of sheared rocks has been variably mineralised and intruded by gold-bearing quartz veins and stockworks. The quartz veins are likely to have been emplaced along fault surfaces, which are thought to be reverse thrusts caused by compression from the east. Strike-slip movement is not thought to be significant; however, a north-westerly trending structure, which post-dates the gold mineralisation, has been identified and may have a strike-slip component. The host rocks for the Selinsing shear zone consist of a series of finely interbedded argillites and very fine-grained arenites, along with sequences of quartz-rich, variably silicified sediments of likely tuffaceous origin, which are referred to as “felsic tuff” and a few thin beds of quartzite conglomerate. These host rocks are collectively known as “the mine sequence series”.

The mine sequence sediments are deep marine epiclastic sediments, originally laid down in l ........

The Selinsing operation consists of:
• Selinsing Gold Mine;
• Buffalo Reef Project;
• Exploration leases and blocks.

Historical mining of visible gold at Selinsing by crude means probably occurred for centuries prior to 1888, when British companies began production on a larger scale utilising machinery for primary processing treatment, with intermittent mining continuing at Selinsing up until June 2007 when Monument acquired the Selinsing Project. Mining was restarted in July 2009.

Open pit mining commenced at Buffalo Reef in 2012 and uses the same mining contractor as for the Selinsing Pit. To date the majority of mining and ore treatment history has been associated with oxide material but at the Selinsing and Buffalo Reef deposits an extensive gold sulphide ore deposit remains in fresh and transitional material yet to be mined and treated.

The mining method is conventional open pit drill and blast, load and haul on a 2.5 m mining flitch with a 10 m high blasting bench, reflective of semi-selective mining. The maximum excavator bucket size of 2.3 m3 is matched to this selectivity.

Open pit mining at both Selinsing and Buffalo Reef has historically been carried out by a local contractor Minetech Construction Sdn Bhd (Minetech). who has been involved in the operation since Monument acquired the operation.

The contract is current, and Minetech is responsible for the mining of ore and waste including: