ABSTRAK Pegunungan Kulon Progo merupakan produk magmatisme Busur Sunda-Banda tersusun atas formasi andesit tua. Daerah Sumbersari merupakan bagian dari gunung api Gajah, batuan gunung api tertua Kulon Progo. Indikasi mineralisasi tipe porfiri ditemukan di daerah ini sehingga menarik untuk diteliti lebih lanjut. Penelitian ini bertujuan untuk mengetahui potensi keterdapatan mineral logam berharga (Cu-Au). Metode penelitian yang digunakan adalah pemetaan geologi, analisis petrografi dan mikroskopi bijih, serta analisis geokimia menggunakan XRF dan ICP-MS. Geologi daerah penelitian terletak pada fasies sentral-proksimal Khuluk Gajah, terususun atas intrusi mikrodiorit, mikrodiorit kuarsa, andesit, andesit basaltik-diorit, dan batugamping. Alterasi hidrotermal berkembang pada batuan beku diorit, mikrodiorit, dan sebagian pada andesit. Alterasi hidrotermal dibagi menjadi beberapa kelompok, yaitu ilit-serisit±biotit sekunder, epidot-aktinolit-kalsit±ilit, epidot-kalsit±ilit, dan ilit-serisit±kuarsa. Beberapa fase mineralisasi berkembang, antara lain fase epidot-aktinolit yang diikuti mineralisasi magnetit-kalkopirit, fase biotit-magnetit-kalkopirit-bornit, dan fase akhir serisit-mineral lempung-pirit menggantikan keseluruhan sistem. Analisis geokimia pada batuan teralterasi menunjukan indikasi mineralisasi Cu-Au dengan kadar 491–1447 ppm (0,14%) Cu dan 0,02–0,3 ppm Au dengan rasio elemen Cu:Au adalah 1,01. Karakter geokimia menunjukkan adanya korelasi kuat Cu terhadap Au.ABSTRACT Kulon Progo Mountain is Sunda-Banda Arc magmatism product composed of an old andesite formation. Sumbersari Area is part of the Gajah volcanic, which is the oldest rock of Kulon Progo volcanics. Indication of porphyry type mineralisation has been found in the area which makes the area interested for further research. The research methodologies are geological mapping, petrography and ore microscopy, and geochemical analysis using XRF and ICP-MS. Geology of the area located in central-proximal facies of Khuluk Gajah, consist of microdiorite, quartz-microdiorite, andesite, basaltic-dioritic andesite intrusions, and limestone. Hydrotermal alteration is developing into certain groups like illite-sericite ± secondary biotite, epidote-actinolite-calcite ± illite, epidot-calcite ± illite, and illite-sericite ± quartz. Some mineralisation phases are developed like epidote-actinolite followed by magnetite-chalcopyrite mineralisation, biotite-magnetite-chalcopyrite-bornite phase and the late phase of sericite-clay-pyrite replacing the entire system. Geochemical analysis on altered rocks show Cu-Au mineralisation indication ranging from 491-1,447 ppm (0.14%) and 0.02-0.3 ppm respectively, with Cu:Au ratio is 1.01. Geochemical characteristic shows strong correlation of Cu to Au.
The study area, i.e Humpa Leu East is a porphyry prospect located in Hu'u district, Sumbawa Island, Indonesia. This study is aimed to understand the characteristics of veins, the distribution of veins and mineralogy, microthermometric conditions of ore fluids, distribution of elements, and their implications for exploration and deposit model. The Hu'u district is a paleo-volcano member of the Miocene to Plio-pleistocene volcanic rocks. Hydrothermal alteration evolved to get out from the tonalitic body, consists of potassic, propyllitic and overprinted by phyllic and advanced argillic. The mineralization is dominated by chalcopyrite, associated with quartz±anhydrite veins, and hydrothermal breccia. Hydrothermal fluids temperature measured at the value of 109.9 °C - 525.3 °C and > 550 ° C with an averaging range of Th is 296.5 -329.7 °C, and salinity of 10.9 wt% NaCl eq. Quartz veins occur as a package or series of porphyry type veins designated as EDM-M1-A1, A2-A3-Apsb-anh, A3-A2, M2-Apsb-A2-A3, M1-B-C, C-D-anhydrite, and epithermal veins. Hydrothermal fluids possibly have mixed by high-temperature hyper-saline fluids to medium temperature low saline fluids. The Humpa Leu East can be identified as a 'push-up porphyry system' that still remains more extensive system underneath or in the side area. These results can be used for understanding the texture of veins as a vectoring to ore, metal distribution in veins and rocks. Early type veins such as type A have more intensive metal content and are followed by type B, C and weaken until the latest stage.
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