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 low-energy conditions and are thought likely to be of volcanogenic origin. The mine sequence has undergone low-grade regional Greenschist facies metamorphism, which is seen by the development of chlorite in some of the host rocks, more notably the felsic volcanic rocks.

The true thickness of the mine sequence is not well understood. One interpretation is that the mine sequence has a true thickness of about 200 m; however, the footwall contact is not well defined and it is difficult to distinguish between the mine sequences in the field due to the fine-grained nature of the host rocks. A second interpretation is that within the shear zone, repetition of these units by shearing creates a structural thickening of the sequence.

The hangingwall rocks at Selinsing are a distinctive sequence of predominantly competent, well-bedded, dark-coloured limestones. Towards the base of the limestones is a narrow unit of black, well-bedded carbonaceous shales, which may be calcareous in places. The contact of these hangingwall units with the mine sequence below is thought to be a tectonic or faulted contact due to the unconformable nature of the bedding on either side of the contact. The contact itself is characterised by large water-filled clay-lined cavities. The footwall contact of the mine sequence is poorly understood as the base of the mine sequence has not been extensively explored. However, the footwall rocks consist of the same type of grey-black limestone as found in the hangingwall and it is thought that the footwall rocks are the same as the hangingwall, repeated due to faulting. This would mean that the less competent mine sequence rocks were more deformed by shearing due to rheological contrasts between the limestones and the argillites and arenites. The hangingwall limestones have locally-developed folding resulting from easterly compression.

The gold mineralisation at Selinsing is hosted within a shear zone that strikes at 350° and dips 60° to 70° to the east, with the higher grade mineralised shoots within the main mineralised shear plunging to the southeast. The main shear zone is hosted within a sequence of felsic tuff and very fine clastic argillite with calcareous material and limestone in the hangingwall. High grade mineralisation is often associated with quartz stockworks and quartz-carbonate veins within highly deformed sedimentary rocks. Pressure and temperature studies on fluid inclusions in quartz from veins suggest that the mineralisation formed at a temperature in the order of 200°C to 350°C and at a depth of between 2 km and 5 km (Makoundi, 2011).

The gold at Selinsing is generally in the form of fine grained gold particles (<20 µm) commonly associated with pyrite and arsenopyrite and rarely with chalcopyrite. Visible (mm-scale) gold, although not common, occurs in quartz veins within the shear zone. The higher grade quartz veins can be over a metre in true thickness and have been traced up to 300 m along strike and 200 m down dip. Lower grade gold mineralisation occurs as finely disseminated gold within intensely deformed envelopes around the quartz veins within the shear zone. Disseminated pyritisation also occurs within the deformed country rock within the shear zone, with the presence of euhedral arsenopyrite as a good indicator of elevated gold grades.

The Buffalo Reef deposit occurs approximately 1 km to the east of the Raub-Bentong suture. The area is dominated by argillite and limestone of Permian age to the east, with conglomerates and sandstones of Devonian age to the west. Low grade regional metamorphism up to Greenschist facies (locally up to Amphibolite facies) occurs throughout the area (Naidu, 2005). The sediments have subsequently been intruded by granitic bodies of approximately Jurassic age. These intrusive bodies occur to the east of Buffalo Reef and generally form elevation highs.

The dominant structural feature present is a 200 m wide, north-south striking shear zone, with an apparent sinistral sense of displacement, which parallels the tectonic Raub-Bentong suture to the west. The shear zone is composed of graphitic shale with minor interbedded fine-grained sandstone and tuffaceous rock (Naidu, 2005). Bedding within the sediments typically dips 65° to 75° to the east and strikes towards a bearing of 330° to 360° (Flindell et al., 2003).

Gold mineralisation at Buffalo Reef is structurally controlled and associated with Permian sediments within a 200 m wide shear zone that parallels the north-south trending Raub-Bentong suture. Mineralisation occurs over a total strike length of approximately 2.6 km. Rocks within the Buffalo Reef shear zone have typically undergone silica-sericite-pyrite alteration to varying degrees (Flindell et al., 2003).

The gold occurs within moderately to steeply east-dipping veins and fracture zones, which range in thickness from 1 m up to 15 m in thickness (average thickness is approximately 10 m in the main mineralised veins), although local flexures in the veins can host mineralisation up to 25 m in thickness. Veins, which are boudinaged in some areas, are generally composed of massive quartz with 1% to 5% (by volume) sulphide minerals, namely pyrite and arsenopyrite, along with varying amounts of stibnite. The stibnite generally occurs in association with elevated gold grades; however, the presence of gold does not necessarily indicate high stibnite levels (i.e. the stibnite tends to be associated with gold, rather than the gold being associated with stibnite).

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:
• Drill and blast activities;
• Load and haul activities;
• Rehabilitation activities.

The current assessment of the contractor facilities is unchanged, and the hard stand provides for the repair and maintenance of the contractor’s fleet consisting of:
- 18 haul trucks ranging from 20 t to 80 t capacity;
- 9 excavators ranging in bucket capacity from 1.5 m 3 to 3.2 m3;
- Various ancillary equipment such as water bowsers, compactors, dozers, graders and light personnel carriers.

The Selinsing and Buffalo Reef deposits are surface outcropping deposits with near surface oxide material suitable for gravity and CIL processing. As such, open pit mining has been carried out for some nine years mining economic oxide material generally above 0.5 g/t Au but considerable material below this grade has also been mined and stockpiled.

The Selinsing deposit is largely sub-vertical dipping and is hosted by a 20–100 m thick shear zone that dips 55° to 75° towards mine grid east (082° true grid).

Mining at Selinsing is more advanced than at Buffalo Reef and has occurred initially as one pit, then as depth increased, twin open pit mining developed in Pit 4 and Pit 5. In both Selinsing open pit areas, oxide mining is largely complete, leaving mainly transition and fresh material to mine.

Mining at Buffalo Reef has occurred since 2012, again mining oxide gravity and CIL treatable material following a pit limit. There are two main areas of Buffalo Reef comprising of:
* Buffalo Reef South (BRS C2, C3 and C4) includes material in several tenements:
- Block 7 (tenement yet to be titled but now acquired by Monument);
- Damar Buffalo Reef South (tenement MC1/111).
- Damar Buffalo Reef Central (tenement ML12/2012).
* Buffalo Reef North (BRN).

Mining of BRS currently consists of several pit areas:
- BRS C2 – Buffalo Reef southern area;
- BRS C3 and 4 – Buffalo Reef central area.
Mining to date has generally been via small pits influenced by surface topography, with the largest pit developed to date being BRC2.

Unlike the Selinsing area, Buffalo Reef is considered tabular and at BRS ore occurs in a main tabular mineralised zone which is typically 10–20 m thick, along with numerous minor sub-parallel mineralised structures. At BRN, the mineralisation is less continuous and narrower when compared to BRS.

There is significant exploration potential at the Selinsing Gold Mine Project with the sulphide orebodies open at all directions allowing for potential in both open pit and underground mining. Currently, there is no plan for any underground operations. In order to progress the operation through to sulphide ore production the Selinsing Gold Sulphide Processing Project (SGSP) has been initiated.

The existing comminution circuit comprises primary, secondary and tertiary crushing, with two stages of ball milling operating in closed circuit with current throughput of approximately 3,000 t/d.

Orway Mineral Consultants (OMC) report describes the specifications of the existing crushing equipment.

Orway Mineral Consultants (OMC) carried out a mill assessment to estimate the maximum grinding power available. The pinion power is the estimated power draw at the mill shell. This value is approximately 7.5% lower than the motor power input due to drive train losses. Based on the OMC (Feb 2018) ball mill power model, the maximum pinion power available from the two ball mills is 1,830 kW (i.e. 1,330 kW from primary mill and 500 kW from secondary mill).

Based on the mill feed size F80 of 8.0 mm, a milling rate in the range of 88–118 tonnes per hour (t/hr) can be expected when processing these materials while still maintaining the target grind P80 of 75 µm.

The existing 3,000 t/d oxide plant consists of three-stage crushing, a 5,000-t surge capacity crushed ore stockpile (COS) stockpile reclaimed to primary and secondary ball mills in series followed by gravity separation and a CIL circuit. Tails are discharged to the TSF and surplus process water detoxified and discharged to a series of polishing ponds.

The Selinsing operation has now limited supply of gold-bearing material that can be processed by the current oxide plant. Currently, the plant processes oxide ore, tailings and leachable sulphide ore.

Progressing to a stage of sulphide ore process capability in a timely manner is now of the utmost
concern. In order to progress the operation through to sulphide ore production the Selinsing Gold Sulphide Processing Project (SGSP) has been initiated.

The current unit operations at the Selinsing processing plant comprise the following circuits:
-Crushing;
-Grinding and classification;
-Gra ........