High Sulphidation, Vuggy Silica – Textural Atlas

The atlas has been updated with images from the Onto Deposit in Indonesia courtesy of David Burrows. The Onto deposit currently has an indicated resource of 0.76 billion tonnes (Gt) at 0.93% Cu, 0.56 g/t Au, 5 g/t Ag, and 350 ppm As (7 Mt contained Cu, 13 Moz Au) and an inferred resource of 0.96 Gt at 0.87% Cu, 0.44 g/t Au, 3 g/t Ag and 350 ppm As (8.3 Mt contained Cu, 14 Moz Au). In addition to these resources, an exploration target of 0.6 to 1.7 Gt at 0.4 to 0.7% Cu and 0.2 to 0.3 g/t Au has been delineated in a sur- rounding envelope based on drilling at approximately 200 × 200- to 400 × 400-m centers. Also recent samples are included from the Khvav Project in Cambodia.

Residual vuggy silica clasts in a fine-grained siliceous matrix from the Cliffs Prospect, Khvav, Cambodia.
Onto, Indonesia: Drill hole VHD034 at 845m which was the end of the drill hole in discovery hole VHD034. Last 2-m interval grades 0.6% Cu and 2 g/t Au. Vuggy residual quartz alteration with well-preserved A-B veinlet stockwork in the early porphyry. Not pyrite filling vug space in top left, with covellite filling vugs closer to the pencil. CREDIT: David Burrows

Vuggy silica textures are formed by the dissolution of phenocrysts and entire clasts by hot and strongly acidic fluids that are generated during the cooling and crystallization of near surface intrusive bodies. Vuggy silica is often mineralized but is also a strong indicator of a very active hydrothermal system and epithermal Cu-Au-Ag and porphyry Cu-Au deposits at depth.

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