In the Silangan region, intrusions of andesite porphyry and dioritic plutons are widespread. Dating by ANU-PRISE (ANU-Prise is an externally funded group within the Research School of Earth Sciences at the Australian National University) for Anglo returned mid to late-Pliocene ages for most altered or mineralised intrusions (Anglo 2008a). The majority of intrusions from the Pacific Cordillera exhibit andesitic to trachyandesitic compositions, but also include a relatively minor component of basaltic andesites, dacites and monzonites of calc-alkaline and high-K calc-alkaline affinity.

Porphyry intrusions commonly occur as plugs, dykes and sills of hornblende andesite porphyry, generally within a 20 km wide belt, which includes the majority of the known epithermal gold and copper-gold porphyry deposits and prospects. The igneous activity is closely related to splays off the Philippine Fault, probably because the fault exploited hotter rocks along the axial zone of the magmatic arc (Anglo 2008a).

Intrusive clusters occur along major structural lineaments and at the intersection of lineaments. The Maniayao Highlands immediately north of Lake Mainit forms the largest igneous complex in the Surigao District and is situated in an area of maximum extension within a pull-apart basin. Other clusters of intrusive rocks in the area tend to comprise of five to ten individual intrusions occurring as individual conical hills. There are several such clusters in the Suri ........

Silangan will employ an underground mining method called Sub-level Caving. Load-HaulDump (LHD) units will be utilized to extract the ore from the production drifts after which ore will be trucked from underground to the processing plant at the surface.

Mine production rate is determined by the rate of development and commissioning of production drifts and sublevels. In each production drifts, the critical path to sustained production rate is the precision in drilling and blasting production drill holes and equal drawing from the production drifts to promote desired caving. The mine will operate at an annual production rate of 4 Million metric tons.

Production will start after a 2.5-year development and construction period. A rapid ramp up to 4 Million tons wil happen on the first two years, after which the production rate will be maintained for most of the 21-year mine life until it wanes.

Mine Design
Industry standard panel dimensions are used at the Boyongan deposits i.e. extraction drive spacing of 15 m, level spacing of 25 m, ore drive width of 5 m. Standoff distances for work areas to caving zones are typically influenced by:
- yielding and stress relaxation due to caving;
- blast vibration.

PSM recommends that all capital development is located at least 20 m outside of a zone defined by a 45° subsidence zone.

For added conservatism, however the following parameters were applied based on industry stan ........

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Initially copper and gold will be recovered thru a series of copper leaching and gold leaching process which produces copper cathode and gold-silver dore respectively. At year 3 of operations, copper flotation will be added to the process and will produce copper concentrate containing copper and gold as the sulfides parts of the orebody are started to be mined. The mill tailings will be stored in the TSF.

The crushing, grinding, copper flotation, copper leaching, gold leaching and tailings impoundment processes of the metallurgical plant will be designed to match the 4 Million metric tons per year output of the sub-level cave mine.

Silangan’s ore is a mix of copper oxide and sulfide minerals. This complex mineralogy dictated the employment of an intricate metallurgical flowsheet, which results to three saleable products. The Run-of-Mine (ROM) ore will average to 0.63 percent copper and 1.20 grams per metric ton gold. After processing, ROM will be converted to the ........