The Silangan copper-gold project is located in Surigao del Norte province, Philippines. Silangan Mindanao Mining (SMMCI), a wholly-owned subsidiary of Philex Mining Corporation (PMC), owns and operates the mine.
The mining concession consists of three deposits namely Boyongan, Bayugo, and Kalayaan. PMC owns Kalayaan deposit in a joint venture with Manila Mining Corporation and also holds an option to further increase its stake up to 60% in the project.
The project currently focuses on developing the Boyongan deposit, which lies in the MPSA-149 tenement. The deposit is expected to be mined from 2022.
Feasibility study for the Boyongan deposit was published in July 2019 for a production capacity of 4Mtpa, with an estimated investment of £606.1m ($745m). The mine life is estimated to be 21 years.
Silangan copper-gold project reserves
As of July 2019 estimates, the Boyongan deposit of Silangan has an estimated reserve of 81.44 metric tons (Mt) grading 0.626% Copper (Cu) and 1.20 grams per tonne of gold (Au). The recoverable metal volumes are estimated to be 917.7Mlbs of coper and 2.99Moz of gold.
Mining and ore processing at the Boyongan deposit
Philex Mining proposes to employ sub-level caving mining method for the Boyongan underground deposit. Ore will be extracted from the production drifts using load-haul-dump (LHD) units and trucked to the processing plant at the surface.
The plant is capable of processing four million tons per annum (Mtpa) of ore, at an average of 12,000 tons per day. The ore will undergo crushing, grinding, classification, atmospheric leach, and counter current decantation circuits.
The pregnant leach solution (PLS) will pass through clarification and cooling unit, raffinate neutralisation and thickening, followed by solvent extraction (SX) and copper electro-winning (EW) to produce copper cathode.
The plant will also feature gold leaching, adsorption and desorption circuits, carbon regeneration units, and electro-winning circuit to produce a gold dore.
For the first three years of production, a series of copper/gold leaching processes will be conducted to produce copper cathode and gold-silver dore respectively.
Copper flotation unit, flotation reagents handling, concentrate thickening and filtration, and concentrate handling units will be commissioned during the third year of operation to recover copper and gold from the mixed sulphide ore.
SRK Consulting was engaged to make an independent evaluation of the project, while Ausenco conducted value-engineering studies on the Silangan copper-gold project.
Jacobs Philippines prepared the environmental studies of the project, while Mining Plus designed the sub-level cave mine including the development and production infrastructure.
Oliveros compiled the mineral resource estimate of the Boyongan deposit, while Knight Piesold designed the tailings storage facility of the project.
From Surigao City, the project can be accessed through the Philippine-Japan ‘Friendship’ Highway (Asian Highway) to the municipality of Tubod and continued by a network of unsealed private roads.
Power required for the underground mine will be sourced from the Anislagan substation through a 2.3km-long, 69kV transmission line. It will be transmitted to the high-voltage switchyard located at the northern end of the processing plant.
Nasipit Port will be used for the import of commodities for both operational and execution phases, while Surigao Port will be used for the export of the produced copper cathode.
Silangan copper-gold project location, geology, and mineralisation
The Silangan mining project is situated at the north-eastern region of Mindanao Island, approximately 750km from Manila. The main ports leading to the island are located 30km north of the project area in Surigao City.
The Boyongan prospect lies within a volcanic centre that rises from the Mainit Graben. The region occupies the orogenic belt that extends more than 400km of the northern most portion of the Eastern Mindanao Ridge or Mindanao, Pacific Cordillera.
The project is located within a 40,000km horseshoe-shaped basin in the Circum-Pacific belt, which hosts a series of oceanic trenches, volcanic arcs and belts, and/or plate movements.
The Boyongan deposit contains high-grade copper and gold hosted in composite diorite porphyry stocks and diatreme breccias, emplaced into volcanic and sedimentary rocks of late Pliocene age.