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 ........

Selection of mining method for Boyongan deposit is limited to underground methods because of the current regulatory environment. Porphyry deposits can most economically be mined using caving techniques. For Boyongan, a sub-level cave mining operation was designed, which has a number of advantages over block cave mining.

Sub-level cave mining method to mine the Boyongan orebody was selected on account of the following.
1. Further scrutiny identified higher-grade portions of the Boyongan orebody are located at higher elevations such that a top-down mining approach is expected to provide better economic results.
2. Faster development rate as the initial production level is developed at the upper portions of the orebody versus developing the production level at the bottom of the orebody in a Block cave mine.
3. Streamlined the metallurgical process as the initial ore mined at the first two years of operations are purely oxide ore which will require copper and gold leaching process only. The copper flotation plant that process sulfide ore will only be required in the third year of operation.

Sub-level cave mining, in principle, is a method that is suitable for moderately fractured ore bodies, which when drilled and blasted will collapse by its own weight thereby creating fragments of rocks that are subsequently extracted. The process consists of driving a series of evenly spaced openings called production drifts in a direction dictated by ........

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