The Siana gold (silver-lead-zinc) mineralisation is characterised as a high sulphidation regime of epithermal affiliation, hosted predominantly within tectonised volcano clastics altered carbonate and basaltic lithological assemblages.

The mineralization at Siana occurs over broad widths (up to 80m in the central carbonate zone) but the deposit envelope is orientated approximately northsouth.

The mineralisation at Siana is controlled by lithology, structure and breccias and changes in wall rock alteration and ore mineralogy with depth.

In cross section, the central carbonate breccia varies between 20m to 80m in width below the current open pit floor (the main ore zone). Adjacent and west, the volcaniclastic sediments are often bleached and carbonate altered, and host some economic gold mineralisation. Distal chlorite altered sediments are barren. The basalt hosted mineralisation to the east occurs in numerous discrete soft, bleached, pyritic alteration zones, often 10m or more in width, over a lateral distance of approximately 140 metres. Hard fresh basalt between the lodes is barren. Mineralisation progressively narrows to the north and south in both the carbonate and basalt hosts, but is known to persist to approximately 400m below surface, but narrowing. The mineralisation is generally is sub vertical to steeply dipping to the east at approximately -70 degrees. The main mineralised zone strikes N-S to NNW-SSE and also trends to the NE in the northern section of the resource. The Siana resource has a strike length of approximately 500 metres with mineralisation down to approximately 500 metres below surface.

The operation is mined using conventional open pit mining methods using top hammer drill rigs, CAT 40 tonne articulated dump trucks and CAT 374 (~80 t) hydraulic excavators. Mining bench heights are 5 m with mining generally conducted on 2 x 2.5 m flitches. The mining rate is a nominal 8,000 bcm/d.

Mining and processing activities at Siana were suspended in April 2017 pending an improvement in operating conditions in the Philippines. [2019, AR, p.15]

Before the suspension, the deposit was mined by open pit methods, with a plan to transition to underground mining following completion of the open pit. Underground mine development has commenced, with 445m of development completed, three portals and establishment of several critical surface infrastructures to the mine.

The dominant mineralisation for the Siana Mineralisation is gold and silver with the gold to silver ratios from less than 1:1 to silver being greater than 7:1. Material mined from Siana open pit is process on site at the Siana CIL Gold processing plant. Design capacity is 1.1 Mtpa. Processing recoveries for gold vary between 75 to 85% for gold and nominally 40 to 45% for silver. Product produced is a gold/silver dore as bullion.

The plant comprises single stage crushing, SAG milling, gravity concentration and high intensity cyanidation, leaching and adsorption (CIL), followed by carbon elution and electrowinning to produce combined gold and silver doré. The tailings from the cyanide leach area are treated in a detoxification circuit to minimize cyanide concentration prior to discharge to the tailings storage facility. The plant design also includes various reagent mixing facilities as well as water, air and electrical services. The plant uses well-tested technology.