– 1 – PETROLOGY AND GEOCHEMISTRY OF INTRUSIVE ROCKS FROM SELOGIRI AREA, CENTRAL JAVA, INDONESIA

Selogiri is one of the gold prospects in Indonesia. The deposit model is espected to be a porphyry copper-gold deposits, which overprinted by low sulfidation epithermal gold quartz deposits. Geochemically, the calc-alkaline rocks from Selogiri range from primitive to relatively fractionated compositions, as reflected by SiO2, MgO contents and variable concentrations of the mantle-compatible elements (67–272 ppm V, 4–81 ppm Ni). These data are consistent with K2O contents, low average K2O/Na2O ratios (0.4), with some anomalous K2O/Na2O ratios (up to 50) and Ba/Zr ratios (up to 8.5), which indicate moderate potassic alteration. The concentration of copper and gold in the bulk-rock is low, Cu < 0.1% and Au < 0.1 ppm, respectively). Most economic porphyry Cu systems are characterized by multiple intrusions and repeated episodes of mineralizing hydrothermal activity, the Selogiri deposit formed during a single or up to two times intrusion periods. Therefore, the short period of hydrothermal activities in Selogiri did not reach an economic ore deposit