PDAC Thayer Lindsley Award Recipients: The Onto Discovery Team
Through the integration of Inco, Vale inherited a long presence in Indonesia since the late 1960s and was one of the few companies to persist with exploration in Indonesia after 1997. In late 2007 Vale initiated an exploration program for porphyry copper deposits in eastern Indonesia, with a focus on advanced argillic alteration lithocaps. Although common in Indonesia, lithocaps were relatively poorly explored, and when exploration is successful there is the potential to preserve the intact, high grade, upper portions of porphyry copper-gold systems. Vale acquired an option over the Hu’u Contract of Work where regional exploration in the 1980s and 1990s had identified an extensive lithocap (5 km x 9 km). The team were immediately rewarded in 2011 when the first exploration drill hole intersected 414 m @ 0.45% copper and 0.26 g/t gold from 138 m within a diorite porphyry stock. Although too small for Vale, the porphyry mineralization provided encouragement to persist in the lithocap environment with deep drilling. The Onto deposit was discovered in July 2013 with the intersection of 287m containing 0.97% copper and 1.13 g/t gold from 548 m to the end of hole at 835 m. The most recent resource estimate completed in December 2021 reported 2.1Bt @ 0.86% copper and 0.48 g/t gold (PT Sumbawa Mining, 2022). The project is currently at the feasibility study stage.
