The Sihayo gold belt, which hosts the Sihayo and Sambung gold resources, is a 15 km long NW-SW trending corridor of Permian calcareous volcano-sedimentary rocks and associated intrusions. These rocks are highly prospective for sediment-hosted gold, epithermal gold-silver veins, and porphyry-related gold and copper mineralisation. The Sihayo gold belt is located on fault strands from the western margin of the dextral transtensional jog in the TSFZ. The bulk of the gold resources at Sihayo and Sambung is hosted by a NW-SW striking, moderately NE-dipping package of Permian shallow marine fossiliferous limestones. The gold is generally submicron size and, unless weathered (oxidised), it is locked in disseminated fine-grained arsenian pyrite mineralisation in multiple stratabound replacement-style jasperoid lenses and discordant bodies within the karstified, hydrobrecciated and tectonised host rocks. The resources are classified as sediment-hosted gold (SHG) deposits.

The mineralised Permian limestones and volcaniclastic rocks are disconformably overlain by Tertiary siliciclastic sandstones and carbonaceous mudstones. Uplift and erosion have removed most of the caprock at Sambung, but about 70% of Sihayo is covered by Tertiary caprock, which is up to 150 m thick or more on the eastern side of the resource. Diorite intrudes the Permian rock package in dykes, sills and laccolith, and some of these intrusions extend across the disconformity into the Tertiary caprocks.

Mining method
- Conventional open pit mining using 40 t class shovels and 40 t class articulated dump trucks.
- Drill and blast will be required in transition and primary material only. Oxide ore is assumed to be 50% free dig. Oxide waste is assumed to be 30% free dig. 4m benches will be mined in 2m flitches to increase selectivity.
- The mine’s development is planned in several stages to enable lower stripping requirements at the start of the mine life and backfilling of mined-out pits.
- A network of pioneering roads will be built to access the two deposits and the necessary mining infrastructure; allowance in the mining costs and the number of mining equipment has been made to account for this task.

Pit design
- Optimum pit volume determined using GEOVIA Whittle TM computer software based on the mining models LG_SIH_3.dm for Sihayo and LG_SAM.dm for Sambung.
- The revenue factor 1 shells were selected for the Sihayo and Sambung deposits in order to maximize the mine life.
- Inferred Mineral Resources were considered as waste for pit optimization and economic evaluations.
- Pit staging limits between revenue factor 0.34 and revenue factor 1 were targeted to minimize stripping ratio and enable backfilling of mined-out pits with waste material.
- Pit designs developed in Datamine computer software using the pit optimization shells as a guide and based on the Measured and Indicated Mineral Resources only.
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