ANALISIS KOMPREHENSIF KARAKTERISTIK GEOLOGI DAN GEOKIMIA MINERALISASI PORFIRI CU-AU DI PRIGI, JAWA TIMUR

This research focuses on understanding porphyry Cu-Au deposits in the Oligocene-Miocene Sunda-Banda magmatic arc, specifically in Prigi Village, Watulimo District, Trenggalek Regency, East Java. The region, located on an ancient volcanic circular structure within this metallogenically significant arc, holds potential for porphyry Cu-Au deposits. The study uses surface geological mapping, laboratory analyses (petrography, mineragraphy, AAS), and report preparation. Alteration in the area is classified into five zones based on mineral associations: propylitic (chlorite-epidote±carbonate), potassic (magnetite-biotite-sericite±chlorite), SCC (sericite-clay-chlorite-magnetite), phyllic (sericite-illite±pyrite-quartz), and argillic (illite-smectite±quartz). Ore minerals include sulfides like chalcopyrite, bornite, covellite, chalcocite, magnetite, pyrite, and gold, and oxides such as malachite, hematite, goethite, and jarosite. AAS analysis shows copper content of 0.09% and 0.02%, and gold content of 0.9 ppm and 0.04 ppm in samples LP 93 A and 94, respectively. The study area also features porphyry stockwork veins, classified as type A (granular quartz±pyrite-chalcopyrite), type M (quartz-magnetite±chalcopyrite), type B (comb quartz-centerline chalcopyrite-bornite-pyrite), type C (chalcopyrite±quartz), and type D (pyrite-quartz). The porphyry deposits experienced three stages of alteration and mineralization: early mineralization with diorite intrusion and prograde alteration, intermineral phase with porphyritic andesite intrusion, and a late retrograde alteration phase linked to the final intrusion.