BULAGIDUN PROSPECT - A COPPER, GOLD AND TOURMALINE BEARING PORPHYRY AND BRECCIA SYSTEM IN NORTHERN SULAWESI, INDONESIA

The Bulagidun Cu-Au prospect, in a remote area of north Sulawesi, was identified during follow-up of stream sediment and panned concentrate geochemical anomalies. Soil geochemistry and drilling outlined areas of disseminated and fracture controlled Cu-Au mineralization. Soil sampling shows a close association of Cu and Au anomalies with three mineralized breccia zones. Numerous weak metal anomalies also correlate with peripheral quartz-sulfide veining. The three separate bodies contain a geological resource of more than 14.4 Mt at 0.68 ppm Au and 0.61 wt.% Cu. A series of intrusions into regionally-widespread andesitic volcanic rocks (ca. 9.4 Ma) vary in composition with time, from early diorite to quartz diorite to late tonalite and post-mineral andesitic dykes. Early actinolite alteration is overprinted by hydrothermal biotite+magnetite. Coarse biotite + magnetite+/-quartz+/-K-feldspar+/-pyrite+/-chalcopyrite open space filling occur within hydrothermal breccia, and postdates the pervasive biotite + magnetite alteration. This later alteration, and retrograde chlorite, co-exist with up to ten percent chalcopyrite and pyrite. A propylitic (chlorite +/- epidote +/- carbonate) zone surrounds the actinolite and biotite zones, and is accompanied by weak vein-controlled Au-Pb-Zn and local As mineralization. A fracture- and permeability-controlled overprinting of sericite + clay + chlorite +/- quartz +/- carbonate alteration ( 8.75 Ma) partially destroys earlier silicates. Disseminated blebs of radiating tourmaline are widespread in the breccia bodies, and only partially co-eval with visible sulfide mineralization. Bulagidun is characteristic of island-arc porphyry Cu-Au mineralization. However, the abundant tourmaline is unusual in the southwest Pacific; this characteristic is similar to tourmaline-bearing breccia pipes in Chile, Arizona and elsewhere that only rarely contain economic-scale disseminated Cu ores.