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 o f disseminated and fracture controlled Cu-Au mineralization. Soil samp ling shows a close association of Cu and Au anomalies with three miner alized breccia zones. Numerous weak metal anomalies also correlate wit h 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 vol canic rocks (ca. 9.4 Ma) vary in composition with time, from early dio rite to quartz diorite to late tonalite and post-mineral andesitic dyk es. Early actinolite alteration is overprinted by hydrothermal biotite +magnetite. Coarse biotite + tite+/-quartz+/-K-feldspar+/-pyrite+/-cha lcopyrite open space filling occur within hydrothermal breccia, and po stdates the pervasive biotite + magnetite alteration. This later alter ation, and retrograde chlorite, co-exist with up to ten percent chalco pyrite and pyrite. A propylitic (chlorite +/- epidote +/- carbonate) z one 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 + chlorit e +/- quartz +/- carbonate alteration ( 8.75 Ma) partially destroys ea rlier silicates. Disseminated blebs of radiating tourmaline are widesp read in the breccia bodies, and only partially co-eval with visible su lfide mineralization. Bulagidun is characteristic of island-arc porphy ry Cu-Au mineralization. However, the abundant tourmaline is unusual i n 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.