Gajah tidur prospect is the deepest explored part of the grasberg igneous complex (gic) located at the elevation between 1,600 – 3,000m, almost 2.5 km below the pre-mining surface. the grasberg porphyry cu-au deposit is hosted by three main monzonitic to dioritic intrusive units, emplaced approximately 3 ma which consists of the dalam, the main grasberg intrusion (mgi) and the kali. deep drilling have been carried out and sited at 3,026 m elevation of kucing liar exploration drift and drill down to approximately to 2,050m elevation at holes kl98-10-21 and kl98-10-22. the objective is to explore the vertical extension of deep grasberg porphyry cu-au deposit. kl98-10-21 drilled through the center of the grasberg intrusive complex while kl98-10-22 has drilled outward into the carbonate and sedimentary wall rock and both drilled up to 1,700m in length. the drill section provides important new data on the evolution of the grasberg igneous complex (gic). the results of study of this drill section are integrated with previous works to characterize especially on advance argillic –high sulfidation type of silica-sericite-pyrite-covelite-enargite and alunite-pyrophyllite-andalusite-halloysite alteration and mineralization assemblages which observed in both intrusions and the wall rock. based on the drill core logging, petrography and geochemical analysis of selected samples of the two drill holes mentioned earlier, the bottom of the grasberg cu-au porphyry ore body seems to decreased and terminated at about 2,750m elevation probably due to overprinted by intense silica-sericite alteration locally approaching 95-100% by volume and observed phyllic and advanced argillic of high sulfidation alteration in the top 165m of the underlying kucing liar porphyry.the advanced argillic alteration is hypogene and composed of pyrophyllite, kaolinite-dickite, with sporadic zunyite, diaspore, alunite and svanbergite, and late sulfur, gypsum and anhydrite. intense silica, phyllic, advanced argillic and acid-sulfate alterations which are occur beneath the higher level porphyry copper zone is anomalous compared to other porphyry systems. some high temperature clay minerals above indicate that the magmatic hydrothermal fluid is more play significant role than the meteoric fluid.