The Silangan Project tenements consist of two main ore deposits: Boyongan and Bayugo.
Boyongan ore deposit is wholly owned by Silangan Mindanao Mining Co., Inc. (SMMCI).
Bayugo ore deposit: Bayugo-Silangan deposit is wholly owned by SMMCI, Bayugo-Kalayaan deposit is a joint venture with Manila Mining Corporation, its subsidiary Kalayaan Copper Gold Resources, Inc. (KCGRI), and Philex Mining which currently holds a 5% interest with an option to increase its stake up to 60%.
Philex Mining Corp. (PMC) owns 100% stake in SMMCI.
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Summary:
The Silangan Project, consists of the following deposits: Sta. Barbara I (formarly Boyongan) and Sta. Barbara II (formerly Bayugo).
Boyongan porphyry copper-gold deposit is part of the belt of gold-rich copper deposits in the Surigao Mining District of north-east Mindanao Island, Philippines. The district lies within a welldefined, transtensional segment of a Pliocene-Quaternary volcano-plutonic arc related to subduction of the oceanic Philippine Sea Plate at the Philippine Trench.
Boyongan Orebody Geology
The blind porphyry deposits carry high-grade copper and gold values and are hosted by a complex of composite diorite porphyry stocks and diatreme breccias. The composite diorite porphyry stocks and diatreme breccias were emplaced into volcanic and sedimentary rocks of the Bacuag Formation (Upper Oligocene – Lower Miocene age basalts, volcanic breccias and limestones) and the Motherlode Turbidite Formation (Upper Miocene age, silty mudstones). Intense quartz stockwork veining developed within the stocks and the adjacent breccia wallrocks.
The Boyongan and Bayugo deposits are centered on two related early-mineralization cylindrical composite diorite porphyry stocks and are typical of island-arc style deposits. Emplacement appears to have taken place in conjunction with the earliest phase of mineralizing fluids. Since their late Pliocene emplacement (2.3–2.1 Ma; sensitive high resolution ion microprobe uranium- lead-zircon dating) at depths of 1.2 – 2 km, these deposits were exhumed, deeply weathered and buried (Braxton et al, 2009).
At both deposits, hypogene copper and gold are concentrated in two distinct eastern and western zones flanking discrete, high-aspect ratio ('pencil-shaped') stocks. Intense quartz stockwork veining has developed within the stocks and the adjacent breccia wallrocks.
The porphyry hosts underwent pervasive potassium-silicate alteration and have been affected by a weakly developed illite-chlorite-smectite alteration event and by localized zones of illite-pyrite and vuggy quartz related to phyllic and advanced argillic overprints, respectively.
In the Boyongan Deposit, the deep supergene profile contains malachite, azurite, chysocolla and cuprite as the principal copper phases, and importantly, copper in silicates such as kaolinite, dickite, biotite and phlogopite. Chalcopyrite and bornite are the dominant hypogene sulfides and pyrite is minimal. The Boyongan Deposit is hosted by potassic altered diorite porphyry. Copper and gold mineralization occurs as quartz veins disseminated within porphyritic intrusions. The sulfide zone is dominated by chalcopyrite and weak bornite, whilst the main gold species are pure gold, electrum, gold and silver tellurides locked in pyrite, bornite and on rare occasions within chalcopyrite.
Boyongan Intrusives
The Boyongan Deposit is centered on a complex of composite diorite stocks and diatreme breccias emplaced into volcanic and sedimentary rocks. The intrusions share a common phenocryst assemblage containing plagioclase and hornblende locally with minor (fewer than two percent volume) biotite and/or clinopyroxene. They lack igneous quartz. The diorite complex at the Boyongan Deposit contains at least seven discrete diorite phases, distinguished on the basis of texture and timing relationships to veining, alteration and brecciation. Mineralizing and brecciation events serve to subdivide diorite emplacement into temporally distinct episodes. Initial magmatism formed an early diorite complex consisting of at least three intrusive phases: bird’s-eye diorite porphyry, medium-grained diorite porphyry, and fine grained diorite. These intrusive events pre-dated copper-gold mineralization.
A large, pre-mineralization silt-sand-matrix breccia complex partially fragmented the early diorite complex and surrounding wallrock. A series of ECD then intruded the silt-sand-matrix breccia complex. These intrusions bear a spatial relationship to elevated copper-gold grades and quartzvein stockworks. Quartz-magnetite-cemented breccias formed in spatial and temporal relation to the ECD-series intrusions.
A series of moderately-altered inter-mineralization and late-mineralization diorite porphyry stocks and dykes cut the ECD porphyry stocks. At the Boyongan Deposit, these are the intermineralization diorite porphyry stock and the late-mineralization diorite porphyry dykes.
A second significant phase of brecciation, (intermineralization hydrothermally cemented breccia), developed in association with the ECD porphyries, following the formation of the diatreme breccia complex. During the emplacement of ECD-series intrusions, volumetrically significant quartzmagnetite-cemented breccias formed in the Boyongan Deposit’s eastern high-grade zone.
Mineralization location and general description
Initially, the Boyongan Deposit formed by hypogene mineralization processes, displaying mineralization characteristics and vein paragenesis consistent with the porphyry vein classification of Braxton (2007), Corbett and Leach (1997) and Sillitoe (2000).
The main geological features and controls on the mineralization are the early coarse-grained diorite porphyries, which form the focus for the copper and gold mineralization. Drill core logging enabled the definition of three principal intrusive phases emplaced in the early diorite complex. The ECD porphyries are the intrusive phases associated with intense quartz-vein stockworks and elevated copper-gold grades. Drillhole data indicates that these bodies are roughly cylindrical at depth and broaden towards the upper 250 m to 300 m. At Boyongan, the diatreme breccia complex and the ECD series are the main host to mineralization. A series of moderately-altered inter-mineralization and late-mineralization diorite porphyry stocks and dykes cut the progenitor porphyry stocks. The mineralization associated with the porphyry stocks terminate at the Quaternary paleosurface.
The deposits show typical porphyry style mineralization with characteristic magmatic hydrothermal alteration patterns. A pervasive potassic alteration zone is clearly defined in the progenitor intrusive rocks and associated with the mineralizing phase. Illite-smectite-pyrite alteration, usually associated with argillic alteration, overprints the potassic zone in various degrees. Skarn alteration is observed along the contacts between carbonate-rich units and intrusive rocks. Propylitic alteration is well developed along the periphery of the diorite stocks and dissipates outwards.