Overview
The “Barisan Porphyry Belt” is a series of Copper-Gold Porphyry prospects on north-western tip of the island of Sumatra, part of the Republic of Indonesia. Barisan Gold Corporation (TSXV:BG) has an 80% stake in the project area with 2 local Indonesian companies owning the remaining 20%. Barisan Gold is a spin-off of the East Asia Minerals Corp (TSXV:EAS) which has 3 somewhat more advanced Indonesian projects. Barisan itself has two other of active project areas in the region: The Abong epithermal gold prospect, and the Takengon gold and copper porphyry prospect. All of these are very early stage projects and are in the exploration phase of development.
Regional Geology
Part of the Pacific Ring of Fire, Sumatra is located on the border of the active subduction of the Australian plate beneath the Eurasian plate. (See our article on Plate Boundaries and Mineral Deposits.) This makes Sumatra very tectonically active and
is responsible for historical and ongoing episodes of volcanism on the island. The island itself, while part of the volcanic arc, is also composed of the accreted remains of several ancient tectonic plates making for a complex and interesting geology.
Copper-porphyry deposits are known to be concentrated along the Pacific Ring of Fire, and those of south-east Asia are known to be associated with gold.
Project Geology
The project area consists of volcanic-derived sedimentary rocks, limestone and diorite porhyry – potentially the ore rock. Porphyry is a term used to describe a rock that consists of larger crystals within a matrix of smaller crystals. In this case, the porphyritic rock is a diorite. In this region diorite porphyries are associated with subduction zone volcanism and copper-gold mineralization. The diorite porphyries on this property hydrothermally altered, with argillic (clay rich) and phyllic (quartz and mica-rich) zones. Based on work completed thus far, mineralization is moderate at around 0.4 g/t gold and 0.2% copper.
Discussion
Of the six prospects identified by Barisan, at least four have been drilled.
There are typical zoning patterns of hydrothermal alteration commonly associated with porphyry copper deposits which can be identified by the mineral assemblages in the rocks. Copper porphyry deposits are typically low grade, but very large. The task set before Barisan is not only to identify economic grades, but vast quantities at economic grades.
Barisan’s 2013/2014 drill program yielded some decent results, such as 212 meters at 0.8% copper and 0.6 g/t gold, but these don’t seem to have been enough to keep the project going. Barisan does not seem to exist anymore, and there is no record of exploration on the site since 2014.
Further Reading
East Asia Minerals (Corporate Site)
USGS Preliminary Model of Porphyry Copper Deposits (Research)
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