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Some Key Features and Possible Origin of the Metamorphic Rock-Hosted Gold Mineralization in Buru Island, Indonesia Idrus, Arifudin; Prihatmoko, Sukmandaru; Hartono, Hill. Gendoet; Idrus, Fadlin; Ernowo, Ernowo; Franklin, Franklin; Moetamar, Moetamar; Setiawan, Iwan
Indonesian Journal on Geoscience Vol 1, No 1 (2014)
Publisher : Geological Agency

DOI:Â 10.17014/ijog.v1i1.172This paper discusses characteristics of some key features of the primary Buru gold deposit as a tool for a better understanding of the deposit genesis. Currently, about 105,000 artisanal and small-scale gold miners (ASGM) are operating in two main localities, i.e. Gogorea and Gunung Botak by digging pits/shafts following gold-bearing quartz vein orientation. The gold extraction uses mercury (amalgamation) and cyanide processing. The field study identifies two types/generations of quartz veins namely (1) Early quartz veins which are segmented, sigmoidal, disÂcontinous, and parallel to the foliation of host rock. The quartz vein is lack of sulfides, weak mineralized, crystalline, relatively clear, and maybe poor in gold, and (2) Quartz veins occurred within a â€˜mineralized zoneâ€™ of about 100 m in width and ~1,000 m in length. The gold mineralization is strongly overprinted by an argillic alteration zone. The mineralization-alteration zone is probably parallel to the mica schist foliation and strongly controlled by N-S or NE-SW-trending structures. The gold-bearing quartz veins are characterized by banded texture particularly colloform following host rock foliation and sulphide banding, brecciated, and rare bladed-like texture. The alteration types consist of propylitic (chlorite, calcite, sericite), argillic, and carbonation represented by graphite banding and carbon flakes. The ore mineralization is characterized by pyrite, native gold, pyrrhotite, and arsenopyrite. Cinnabar, stibnite, chalcopyrite, galena, and sphalerite are rare or maybe absent. In general, sulphide minerals are rare (<3%). Fifteen rock samples were collected in Wamsaid area for geochemical assaying for Au, Ag, As, Sb, Hg, Cu, Pb, and Zn. Eleven of fifteen samples yielded more than 1.00 g/t Au, in which six of them are in excess of 3.00 g/t Au. It can be noted that all high-grade samples are originally or containing limonitic materials, that suggest the role of supergene enrichment. Interestingly, most of the high-grade samples contain also high grade As (up to 991ppm), Sb (up to 885 ppm), and Hg (up to 75 ppm). Fluid inclusions in both quartz vein types consist of four phases including L-rich, V-rich, L-V-rich, and L1-L2-V (CO2)-rich phases. Mineralizing hydrothermal fluid is typified by CO2-rich fluid, moderate temperature of 300 - 400 ÂºC and a typical low salinity (0.36 to 0.54 wt.% NaCl eq). Based on those key features, gold mineralizaÂtion in Buru Island meets the characteristics of LS epithermal or orogenic gold deposit types; however, it tends to be fitter with orogenic gold deposit rather than another type. Â

Nanggulan Formation and Its Problem As a Basement in Kulonprogo Basin, Yogyakarta Hartono, Hill Gendoet; Sudradjat, Adjat
Indonesian Journal on Geoscience Vol 4, No 2 (2017)
Publisher : Geological Agency

DOI:Â 10.17014/ijog.4.2.71-80Nanggulan Formation consists of the oldest clastic rock sequence exposed in Kulonprogo area, Yogyakarta. This paper discusses the position of Nanggulan Formation as a basement. The method used in this research is surface and subsurface investigations based on gravity surveys. The rock assemblage is exposed and distributed partly in the east flank of Kulonprogo Mountains with weak undulated morphology. The rock sequence is composed of sand to clay grain sizes such as sandstone, quartz sandstone, calcareous sandstone, claystone, fossiliferous claystone, calcareous claystone, siltstone, and coal seam intercalations. The total thickness of the sequence is less than 200 m. Based on the fossil and palynology investigations, previous investigators concluded the age of the rock was Eocene to Middle Miocene. The geological structures developed in the rocks are the lithological stratification, fractures, folding, and faulting. The subsurface interpretation based on gravity data revealed the rock was located under the andesite breccias with 2.44 g/cc density. The density of the rock sequence was 2.63 g/cc. The gravity interpretation shows a strong indication that Nanggulan Formation underlies the andesitic breccias presumably associated with Old Andesite Formation exposed in Kulonprogo Mountains. The limited distribution, the thickness, and the closed environmental deposition of Nanggulan Formation found in the present investigation raised problems on the position of the formation as the basement of Old Andesite Formation occurring in the Kulonprogo Mountain.

Asal-usul Pembentukan Gunung Batur di daerah Wediombo, Gunungkidul, Yogyakarta Hartono, Gendoet; Bronto, Sutikno
Indonesian Journal on Geoscience Vol 2, No 3 (2007)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.2.3.143-158

http://dx.doi.org/10.17014/ijog.vol2no3.20073Physiographically, the Gunung Sewu Subzone is predominantly composed of limestone of the Wonosari Formation, but in Wediombo area volcanic rocks of the Wuni Formation is exposed. The Wediombo volcanic rocks contain lava flows and volcanic breccias associated with Batur intrusive rock, in which all the rocks have andesitic composition. The problem is whether the Wedi- ombo volcanic rocks originated from far distance area which then was intruded by local magma after its deposition, or it is an association of the Wediombo volcanic and the Batur intrusive rocks which both are the remnants of a paleovolcano in the area. To identify the central facies of the paleovolcano, the geological principle that â€œthe present is the key the pastâ€ is used as a geological approach.Wediombo area forms a high landscape showing an elevation of about 280 m above sea level with dips of the outer slopes 20 - 40%. The drainage pattern developing in the area fol- lows the existing circular structure to form subradial - radial patterns. The high landscape shows a circular structure with a diameter of less than 2 km and it opens to the Indian Ocean. Besides the Mount Batur intrusive rock, there are some other dikes which have been already hidrothermally altered, with some mineralization in the circular structure. Meanwhile, the outer slopes are composed of alternating lava flows and fragmental volcanic rocks of 22 - 25o in dip forming a concentric pattern. Petrologically, the Batur intrusive rock is light to dark grey in color, hypocrystalline porphyritic texture, with phenocryst ranges from 1.2 - 2.2 mm in size, subhedral-euhedral crystals, fine vesicular structures. The rock comprises plagioclase, pyroxene, hornblende and opaque minerals. Geochemically, the rock indicates an island arc tholeitic magma (SiO = 60.38 â€“ 64.53 wt%, K O = 0.63 â€“ 0.85 wt%). Those data indicate that the circular structure was the central facies and the outer slope was the proximal facies of the Wediombo paleovolcano in Gunungkidul Yogyakarta. Â

Gumuk gunung api purba bawah laut di Tawangsari - Jomboran, Sukoharjo - Wonogiri, Jawa Tengah Hartono, Gendoet; Sudrajat, Adjat; Syafri, Ildrem
Indonesian Journal on Geoscience Vol 3, No 1 (2008)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.3.1.37-48

http://dx.doi.org/10.17014/ijog.vol3no1.20084This paper discusses the study on the basalt volcanic rocks and the volcano morphology indicating the existence of an ancient submarine volcano in Tawangsari-Jomboran sub-regency, Sukoharjo- Wonogiri, Central Java. In general, this basalt volcanic rocks were identified as andesite breccia which might be grouped into the Mandalika Formation of Oligosen-Miosen age (Surono et al., 1992). The origin of the Mandalika Formation in relation to the classic sedimentation process and the submarine volcanism is still needed to be evaluated. The present study was based on the detailed descriptions of the rocks both in the field and in the laboratory. The autoclastic basalt outcrops consisting of breccias show the characteristics of the igneous rock fragment component embedded in the groundmass with the same composition, namely igneous rock, dark grey to black in colour; porphyritic texture, rough surface, brecciated; pillow structures, massive, fine vesicularities, amygdaloidal filled with calcite, and radial fractures; calk-alkaline andesite composition ( SiO = 54.71% , K O = 1.15% ). This rock body attains the Â dimension of 2 - 5 m length, and 40 cm - 1 m in diameter with the direction of the deposition varies following the direction of the eruption source. Brecciated structures on the surface was controlled by the high cooling rate and the low flow, while the interior of the rock is massive because it was not in a direct contact to the cooler mass outside. Autoclastic basalt breccias and or the pillow basalt lava was interpreted to be formed by the undulating low gradient of morphology with the average angle of <10o. On the other hand, the low basaltic magma viscosity produced the effusive eruption related to the formation of the low angle morphology. The distance between the hills generally composed of pillow basalt is between 500 m - 1 km. The typical pillow structure of the igneous rock as described above is interpreted to be the product of the lava flow related to the effusive eruption Â from a submarine volcano located under or close to the seawater surface.Â Â

Analisis stratigrafi awal kegiatan Gunung Api Gajahdangak di daerah Bulu, Sukoharjo; Implikasinya terhadap stratigrafi batuan gunung api di Pegunungan Selatan, Jawa Tengah Hartono, Hill Gendoet; Bronto, Sutikno
Indonesian Journal on Geoscience Vol 4, No 3 (2009)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.4.3.157-165

http://dx.doi.org/10.17014/ijog.vol4no3.20091Generally, Tertiary volcanisms in the Southern Mountains, Central Jawa were started with the formation of pillow lavas having basalt to basaltic andesite in composition. This initial stage volcanism developed into a Â construction period of composite volcanoes that consist of alternating basaltic to andesitic lava flows, breccias, and tuffs. The construction period could be followed by a destructive phase, producing pumice-rich pyroclastic breccias, lapillistones, and tuffs of high silica andesite to dacite, or even rhyolite in composition. A stratigraphic measuring section at Bulu area, Sukoharjo Regency, presents an alternat- ing fine-grained andesitic volcaniclastic material and some limestones, with the total thickness is 143.33 m. The thickness of bedded volcaniclastic material tends to be thickening upward from 35 m until 90 m. The grain size of the volcaniclastic material also tends to be coarsening upward from clay size through silt and fine sand to coarse sand and granules. Paleontological analysis on fossils contained in the lime- stone gives an age of Early Miocene (N7 - N9). The volcaniclastic rocks is conformably overlain by the Mandalika Formation, comprising alternating andesitic breccias, lavas, and tuffs. These data imply that the fine-grained volcaniclastic material is an initial product of the construction period of Gajahdangak Volcano in the area, that formed the Mandalika Formation. This Formation is overlain by the Semilir Formation, composed of pumice-rich pyroclastic breccias and tuffs with dacitic composition. This as- sociated volcanic rock reflects a product of a caldera explosion or a destructive phase. Based on the characteristics of lithology of volcanic products from the initial stage, to a construction and destruction period, and compiled age data, the Southern Mountains represent formal volcanic rock units that are able to be divided into many formations. Â

Some Key Features and Possible Origin of the Metamorphic Rock-Hosted Gold Mineralization in Buru Island, Indonesia Idrus, Arifudin; Prihatmoko, Sukmandaru; Hartono, Hill. Gendoet; Idrus, Fadlin; Ernowo, Ernowo; Franklin, Franklin; Moetamar, Moetamar; Setiawan, Iwan
Indonesian Journal on Geoscience Vol 1, No 1 (2014)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.1.1.9-19

DOI:Â 10.17014/ijog.v1i1.172This paper discusses characteristics of some key features of the primary Buru gold deposit as a tool for a better understanding of the deposit genesis. Currently, about 105,000 artisanal and small-scale gold miners (ASGM) are operating in two main localities, i.e. Gogorea and Gunung Botak by digging pits/shafts following gold-bearing quartz vein orientation. The gold extraction uses mercury (amalgamation) and cyanide processing. The field study identifies two types/generations of quartz veins namely (1) Early quartz veins which are segmented, sigmoidal, disÂcontinous, and parallel to the foliation of host rock. The quartz vein is lack of sulfides, weak mineralized, crystalline, relatively clear, and maybe poor in gold, and (2) Quartz veins occurred within a â€˜mineralized zoneâ€™ of about 100 m in width and ~1,000 m in length. The gold mineralization is strongly overprinted by an argillic alteration zone. The mineralization-alteration zone is probably parallel to the mica schist foliation and strongly controlled by N-S or NE-SW-trending structures. The gold-bearing quartz veins are characterized by banded texture particularly colloform following host rock foliation and sulphide banding, brecciated, and rare bladed-like texture. The alteration types consist of propylitic (chlorite, calcite, sericite), argillic, and carbonation represented by graphite banding and carbon flakes. The ore mineralization is characterized by pyrite, native gold, pyrrhotite, and arsenopyrite. Cinnabar, stibnite, chalcopyrite, galena, and sphalerite are rare or maybe absent. In general, sulphide minerals are rare (<3%). Fifteen rock samples were collected in Wamsaid area for geochemical assaying for Au, Ag, As, Sb, Hg, Cu, Pb, and Zn. Eleven of fifteen samples yielded more than 1.00 g/t Au, in which six of them are in excess of 3.00 g/t Au. It can be noted that all high-grade samples are originally or containing limonitic materials, that suggest the role of supergene enrichment. Interestingly, most of the high-grade samples contain also high grade As (up to 991ppm), Sb (up to 885 ppm), and Hg (up to 75 ppm). Fluid inclusions in both quartz vein types consist of four phases including L-rich, V-rich, L-V-rich, and L1-L2-V (CO2)-rich phases. Mineralizing hydrothermal fluid is typified by CO2-rich fluid, moderate temperature of 300 - 400 ÂºC and a typical low salinity (0.36 to 0.54 wt.% NaCl eq). Based on those key features, gold mineralizaÂtion in Buru Island meets the characteristics of LS epithermal or orogenic gold deposit types; however, it tends to be fitter with orogenic gold deposit rather than another type. Â

Nanggulan Formation and Its Problem As a Basement in Kulonprogo Basin, Yogyakarta Hartono, Hill Gendoet; Sudradjat, Adjat
Indonesian Journal on Geoscience Vol 4, No 2 (2017)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.4.2.71-80

DOI:Â 10.17014/ijog.4.2.71-80Nanggulan Formation consists of the oldest clastic rock sequence exposed in Kulonprogo area, Yogyakarta. This paper discusses the position of Nanggulan Formation as a basement. The method used in this research is surface and subsurface investigations based on gravity surveys. The rock assemblage is exposed and distributed partly in the east flank of Kulonprogo Mountains with weak undulated morphology. The rock sequence is composed of sand to clay grain sizes such as sandstone, quartz sandstone, calcareous sandstone, claystone, fossiliferous claystone, calcareous claystone, siltstone, and coal seam intercalations. The total thickness of the sequence is less than 200 m. Based on the fossil and palynology investigations, previous investigators concluded the age of the rock was Eocene to Middle Miocene. The geological structures developed in the rocks are the lithological stratification, fractures, folding, and faulting. The subsurface interpretation based on gravity data revealed the rock was located under the andesite breccias with 2.44 g/cc density. The density of the rock sequence was 2.63 g/cc. The gravity interpretation shows a strong indication that Nanggulan Formation underlies the andesitic breccias presumably associated with Old Andesite Formation exposed in Kulonprogo Mountains. The limited distribution, the thickness, and the closed environmental deposition of Nanggulan Formation found in the present investigation raised problems on the position of the formation as the basement of Old Andesite Formation occurring in the Kulonprogo Mountain.

PENYEBARAN AKUIFER DI FORMASI NANGGULAN PADA SISI TIMUR DOME KULON PROGO BERDASARKAN DATA SOUNDING RESISTIVITY Winarti, Winarti; Hartono, Hill Gendoet
Prosiding Seminar Nasional Sains dan Teknologi Terapan Inovasi Teknologi Infrastruktur Berwawasan Lingkungan
Publisher : Institut Teknologi Adhi Tama Surabaya

Show Abstract | Download Original | Original Source | Check in Google Scholar

Pegunungan Kulon Progo merupakan bagian dari Pegunungan Serayu Selatan bagian timur. Pegunungan ini mempunyai mempunyai bentuk dome (dome like) berarah utara-selatan. Sampai saat ini, diyakini bahwa Formasi Nanggulan merupakan formasi tertua sekaligus menyadi dasar dari Dome Kulon Progo, yang berumur Eosen. Litologi penyusun dari Formasi Nanggulan berupa batupasir dengan sisipan lignit, sisipan napal pasiran, batulempung dengan konkresi limonit, sisipan napal-batugamping dan batupasir tufan. Secara umum pada daerah-daerah yang tersusun oleh Formasi Nanggulan khsususnya di sisi timur dari Dome Kulon Progo mengalami kesulitan untuk mendapatkan air tanah. Tujuan dari penelitian adalah mengaplikasikan metode resistivitas untuk mengetahui variasi litologi yang ada di Formasi Naggulan, sehingga dapat diketahui pola penyebaranÂ akuifer. Metode yang dipergunakan adalah melakukan pengukuran geolistrik secara sounding di 6 lokasi yang berbeda, dengan target kedalaman 125 meter. Secara umum dari hasil pengukuran sounding resistiviti menunjukkan adanya variasi litologi berupa batupasir tufan kering, batupasir tufan basah, batulempung tufan basah dan batulempung basah. Batupasir tufan basah dimungkinkan sebagai lapisan akuifer mempunyai nilai tahanan jenis antara 32-80 Ohm.m. Pola penyebaran batupasir tufan basah di selatan dijumpai tidak menerus berada pada kedalaman dangkal (5-12 meter) dan kedalaman dalam (40-80 meter). Sedangkan pada bagian utara penyebaran lapisan batupasir tufan basahÂ dijumpai hanya setempat berada pada kedalaman 40 meter.

Identification and Stratiraphic Position of Mollusk Type Locality at West Progo Stage Hita Pandita; Gendoet Hartono
Journal of Geoscience, Engineering, Environment, and Technology Vol. 4 No. 2 (2019): JGEET Vol 04 No 02 : June (2019)
Publisher : UIR PRESS

The location of the discovery of mollusk fossils on the island of Java is spread in various places. One location is in the Kulon Progo region known as West Progo beds. However, due to the lack of studies of mollusk fossils in the Kulon Progo region, this resulted in a lack of understanding of the location of the discovery. This study was intended to re-record the location of fossil molluscs discovery in the Kulon Progo region, with the aim of contributing to the stratigraphic arrangement in Kulon Progo. Research methods include literature studies, field investigations and laboratory analysis. The literature study includes libraries of the Dutch colonial era regarding the location of the discovery of mollusk fossils. Field studies in the form of stratigraphic measurements and sampling. Laboratory investigations include petrographic observations and identification of micro and macro fossils. The results of the investigation successfully re-identified the Kembang Sokkoh and Spolong locations which are two types of locations on the West Progo beds. Based on the lithological characteristics of the two locations included in the Jonggrangan Formation, with the Lower Miocene age based on an analysis of the fossil content of the molluscs.

Potensi Bahaya Gunung Api Terhadap Calon Tapak PLTN, Studi Kasus: Gunung Api Semadum, Kalimantan Barat Fuad Nur Hussein; I Gde Sukadana; Rachman Fauzi; Hill Gendoet Hartono; Sunarko Sunarko; Tyto Baskara Adimedha; Alfian Maulana Anwar
Jurnal Pengembangan Energi Nuklir Vol 22, No 2 (2020): Desember 2020
Publisher : Pusat Kajian Sistem Energi Nuklir, Badan Tenaga Nuklir Nasional

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17146/jpen.2020.22.2.6124

Aspek kegunungapian merupakan salah satu aspek penting dalam survei pemilihan calon tapak Pembangkit Listrik Tenaga Nuklir (PLTN). Survei bahaya gunung api dilaksanakan pada radius 150 km dari calon tapak PLTN, meliputi survei produk gunung api tua hingga gunung api aktif. Salah satu gunung api muda di daerah Kalimantan Barat adalah Gunung Api Semadum yang terletak di Desa Pisak, Kecamatan Tujuhbelas, Bengkayang berumur Pliosen-Plistosen dengan jarak 115 km dari calon tapak PLTN di Pantai Gosong, Kecamatan Sungai Raya, Bengkayang, Kalimantan Barat. Tujuan penelitian ini adalah untuk mengetahui karakteristik dan potensi bahaya gunung api Semadum terhadap rencana Calon Tapak PLTN. Metodologi yang digunakan adalah interpretasi citra DEM-SRTM untuk mengetahui pola topografi, dilanjutkan dengan kegiatan lapangan pemetaan geologi, pengambilan contoh batuan produk gunung api Semadum dan analisis Petrografi serta geokimia menggunakan X-Ray Fluorescence (XRF). Gunung Semadum tersusun oleh lava andesit-basalt berstruktur vesikuler-skoria, lava andesit berstruktur masif, batuan piroklastika berupa breksi piroklastik dengan fragmen andesit (bom dan blok), breksi lapili/tuf, dan kubah lava. Kompleks ini secara geokimia tersusun atas trakhiandesite dan dasit yang memiliki afinitas calc-alkaline. Berdasarkan sifat magma dan sebaran produknya, gunung api Semadum tidak memiliki potensi bahaya gunung api terhadap Calon Tapak PLTN.

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