Discovery of the Kencana Au-Ag ore deposit, Indonesia

Discovery of the Gosowong, Toguraci and Kencana ore deposits on Halmahera Island in Indonesia owes much to serendipity, good science and necessity. The deposits are examples of high grade, low-sulphidation epithermal Au-Ag mineralisation and were discovered between 1992 and 2003.

Gosowong and Toguraci were identified with surface sampling even though outcrop was mostly absent and were mined by open pit. The much larger and deeper Kencana deposit had no identifiable surface expression and is being mined underground. The Gosowong, Toguraci and Kencana deposits contained in situ mineral resources which totalled >6.0 M oz Au, with an average grade of >20 g/t Au.

Gosowong was discovered serendipitously while exploring for epithermal Au and porphyry Au-Cu mineralisation in Miocene-age andesitic volcanic rocks. Discovery is generally attributed to sampling a very short stream which closely parallels the strike of the Gosowong vein. Discovery of the Toguraci cluster of ore shoots, in several adjacent epithermal veins during a necessity-driven search for additional ore to sustain the Gosowong mining operation, followed from re-sampling a narrow quartz vein.

The Kencana deposit is about three times the size of the combined Gosowong and Toguraci deposits and was discovered by applying good science, but was assisted by serendipity.

Speaker: Dan Wood, AO

Dan Wood retired as an exploration geologist in 2008 after 24 years with BHP and 18 years with Newcrest Mining where he was Executive General Manager Exploration. Newcrest was judged by Metals Economics Group of Canada to have been the World’s most successful gold explorer, 1992-2005.

He has received several international exploration awards and is the 2017 Thayer Lindsley Visiting Lecturer for the Society of Economic Geologists. In 2015, he was appointed an Officer of the Order of Australia (AO) by the Australian Government for his service to the mining industry.