A resource estimate has been calculated for the Boyongan copper-gold deposit on the island of Mindanao in the southern Philippines. The deposit is part of the 250-sq.-km North project, owned equally by
An inferred resource of 99 million tonnes grading 0.65% copper and 1.02 grams gold per tonne was estimated in the oxide category, whereas the sulphide category consists of 120 million tonnes grading 0.39% copper and 0.51 gram gold.
A three-dimensional computer block model was used to calculate the resource, which was based on 72 holes (38,421 metres) drilled to a 100-metre-by-100-metre spacing.
A cutoff grade of 0.4% copper-equivalent was used for the sulphide material; the cutoff for the oxide material was 0.6%. The estimate was based on gold and copper prices of US$388 per oz. and US$1.14 per lb. Recoveries were estimated at 75% for oxide copper, 85% for sulphide copper, and 65% for gold.
The deposit is associated with two diorite porphyries buried beneath 50-300 metres of volcaniclastic rocks. Gold mineralization is concentrated closer to the intrusions, especially in areas of quartz stockwork adjacent to the intrusives. There is a shallow, oxide, copper-gold zone that is primarily composed of cuprite, azurite, malachite, chrysocolla, neotocite, chalcocite and native copper. This is followed by a transitional oxide-sulphide zone and, at greater depth, a sulphide zone containing pyrite, chalcopyrite, bornite and rare molybdenite.
Philex Gold and Anglo American Exploration (Philippines) operate the project under jointly owned Silangan Mindanao Mining. The resource calculation was verified by consulting firm AMEC Americas.
Exploration continues in other areas of the North project. The Bayugo zone, 1,200 metres northwest of Boyongan, was drilled in 2003. Highlights from two holes were recently reported: one intercept graded 0.43% copper and 1.08 grams gold over 58 metres, while the other cut 39 metres of 1.28% copper and 0.83 gram gold.
The estimate was classified according to CIM Standards on Mineral Resources and Reserves.
The North project is in northeastern Mindanao, 20 km north of Surigao City in the province of Surigao del Norte.
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