Name: Kencana mine.
Location: The Kencana mine is located in Indonesia’s Gosowong gold province, which covers an area of around 30 000 ha. Gosowong is situated on Halmahera Island, in the North Maluku province.
Brief Description: Kencana is currently one of the highest grade, underground gold mines in the world. The life-of-mine has been extended to 2015.
Brief History: Underground development of the Kencana mine began in February 2005, with the first underground ore mined in March 2006.
Products: Gold and silver.
Mining Method: Underground.
Reserves: Total proven and probable reserves as at June 30, 2011, were 5.2-million tons, with a grading of 13 g/t gold and 16 g/t silver.
Resources: Total measured, indicated and inferred resources as at June 30, 2011, were 4.8-million tons, with a grading of 16 g/t gold and 22 g/t silver.
Geology: Economic mineralisation is hosted within the Gosowong formation, which is dominated by basalts, dacites, volcaniclastic rocks and intermediate intrusions. Volcanic rocks overlie the Gosowong formation. In the late Pliocene, the Gosowong and volcanic sequences were locally intruded by andesite porphyry and quartz diorite.
Two styles of mineralisation have been recognised within the Gosowong district, namely low-grade uneconomic copper/gold porphyry mineralisation and high-grade gold/silver epithermal veining. A number of epithermal deposits have been recognised, including Gosowong, Toguraci, Gosowong North, Dongak, Tobobo, Langsat and Kencana.
Major Infrastructure and Equipment: Kencana K1 is the first underground mine at the Gosowong site. Owing to underground conditions at Kencana and variability of the orebody, an underhand cut-and-fill mining method using paste fill was chosen. Mining is carried out using twin boom jumbos, loaders and articulated dump trucks. Mined-out areas are backfilled with cemented paste fill.
The existing Gosowong processing plant is used to process the Kencana ore. The processing plant comprises a primary jaw crusher followed by semiautogenous and ball mills ahead of a cyanide leach circuit. Gold and silver are recovered from the pregnant solution using the Merrill-Crowe (zinc precipitation) process before smelting to produce doré bars.
Prospects: Over five-million ounces of gold has been discovered in the Gosowong epithermal field. Future exploration is focused on discovering extensions to the existing Kencana deposit, testing known fertile structures around the Toguraci area that was previously mined as an openpit and regional exploration in the 30 000 ha contract of work.
In addition, improvement programmes are under way to increase throughput of the Gosowong process plant in the short term through the removal of key bottlenecks.
Controlling Company: Newcrest Mining (82.5%) and PT Aneka Tambang (17.5%).
Contact Person: Head of investor relations Steve Warner.
Newcrest Mining, tel: +61 3 9522 5316,
fax: +61 3 9522 5502, email: firstname.lastname@example.org, and