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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 âmineralized 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

Metamorphic Rock-Hosted Orogenic Gold Deposit Type as a Source of Langkowala Placer Gold, Bombana, Southeast Sulawesi Idrus, Arifudin; Nur, I.; Warmada, I. W.; Fadlin, Fadlin
Indonesian Journal on Geoscience Vol 6, No 1 (2011)
Publisher : Geological Agency

DOI:Â 10.17014/ijog.v6i1.114In 2008, placer gold was discovered in Langkowala area (Bombana Regency), Southeast Sulawesi, Indonesia, and more than 60,000 traditional gold miners in the early 2009 have been operating by digging vertical pits and panning active stream sediments. The grade of placer gold ranges from 50 to 140 g/t. Local geological framework indicates that the placer gold is not related to volcanic rock-related hydrothermal gold deposit, e.g. epithermal, skarn or porphyry. This paper describes a preliminary study on possible primary deposit type as a source of the Langkowala (Bombana) secondary placer gold. A field study indicates that the Langkowala (Bombana) placer/paleoplacer gold is possibly related to gold-bearing quartz veins/veinlets hosted by metamorphic rocks particularly mica schist and metasediments in the area. These quartz veins/veinlets are currently recognized in metamorphic rocks at Wumbubangka Mountains, a northern flank of Rumbia Mountain Range. Sheared, segmented quartz veins/veinlets are of 2 cm to 2 m in width and contain gold in a grade varying between 2 and 61 g/t. At least, there are two generations of the quartz veins. The first generation of quartz vein is parallel to foliation of mica schist and metasediments with general orientation of N 300oE/60o; the second quartz vein generation crosscut the first quartz vein and the foliation of the wallrock. The first quartz veins are mostly sheared/deformed, brecciated, and occasionally sigmoidal, whereas the second quartz veins are relatively massive. The similar quartz veins/veinlets types are also probably present in Mendoke Mountain Range, in the northern side of Langkowala area. This primary gold deposit is called as âorogenic gold typeâ. The orogenic gold deposit could be a new target of gold exploration in Indonesia in the future.

KARAKTERISTIK ENDAPAN EMAS OROGENIK SEBAGAI SUMBER EMAS PLACER DI DAERAH WUMBUBANGKA, BOMBANA, SULAWESI TENGGARA -, Fadlin; AsyÃ¢Â€Â™ari, Muhammad Amril
POROS TEKNIK Vol 4, No 1 (2012)
Publisher : Politeknik Negeri Banjarmasin

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Penemuan endapan emas placer di Sungai Tahi Ite, Bombana (Harian Kompas, 18 Sep-tember 2008) cukup unik, karena di Indonesia tidak umum cebakan emas ditemukan pa-da batuan metamorf. Endapan ini diduga merupakan endapan emas orogenik karena daerah tersebut dikontrol oleh struktur yang sangat kuat dengan batuan samping berupa metamorf. Tujuan dari penelitian ini untuk memahami zona-zona ubahan, serta lebih lan-jut mengenai mineralisasi dan karakteristik endapan emas orogenik tersebut. Penelitian ini menggunakan metode pemetaan permukaan dan penggabungan hasil analisa petro-grafi, mineragrafi, XRD, AAS (fire assay) serta inklusi fluida. Terdapat 4 (empat) tipe alte-rasi di lokasi penelitian yaitu (1) silisifikasi, (2) argilik (clayÂ± silica), (3) klorit-karbonat dan (4) karbonisasi. Dari hasil AAS (fire assay) nilai emas tertinggi diperlihatkan pada sampel WB-02-C1 :2,52 ppm, WB-02-C2 : 1,06 ppm, WB-03: 0,94 ppm dan WB-04 : 1,31 ppm. Terdapat 3 generasi urat yang ada di lokasi penelitian di mana generasi pertama adalah urat yang sejajar foliasi, urat tipe ini terbentuk pada temperatur yaitu 221,9 oC. dengan nilai salinitas yaitu 7,17 wt,%NaCl ekuivalen. Sedangkan urat generasi kedua adalah urat kuarsa yang memotong foliasi, memiliki kandungan mineral sulfida yang cukup dominan serta memiliki kadar emas yang cukup potensi dibandingkan dengan urat generasi perta-ma, urat ini terbentuk pada temperatur 188,4 oC dengan salinitas antara 3,87 wt,%NaCl ekuivalen. Urat generasi ke tiga yaitu urat kalsit-kuarsa, merupakan fase akhir dari en-dapan emas orogenik yang ada di lokasi penelitian, terbentuk pada temperatur 138,2 oC. dan salinitas 1,91 wt.%NaCl ekuivalen. Urat kuarsa tersebut memiliki karakterisistik yang khas secara fisik yaitu masif, kadang kadang tersegmentasi dan sigmoidal. Endapan emas orogenik pada daerah penelitian ini berada pada zona transisi antara epizonal â mesozonal pada kedalaman kurang lebih 5-6 kilometer pada fasies green schist.

Geochemical Signatures of Potassic to Sodic Adang Volcanics, Western Sulawesi: Implications for Their Tectonic Setting and Origin Shaban, Godang; Fadlin, Fadlin; Priadi, Bambang
Indonesian Journal on Geoscience Vol 3, No 3 (2016)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.3.3.195-214

DOI:10.17014/ijog.3.3.195-214The Adang Volcanics represent a series of (ultra) potassic to sodic lavas and tuffaceous rocks of predominantly trachytic composition, which forms the part of a sequence of Late Cenozoic high-K volcanic and associated intrusive rocks occurring extensively throughout Western Sulawesi. The tectonic setting and origin of these high-K rocks have been the subject of considerable debates. The Adang Volcanics have mafic to mafitic-intermediate characteristics (SiO2: 46 - 56 wt%) and a wide range of high alkaline contents (K2O: 0.80 - 9.08 %; Na2O: 0.90 - 7.21 %) with the Total Alkali of 6.67 - 12.60 %. Al2O3 values are relatively low (10.63 - 13.21 %) and TiO2 values relatively high (1.27 - 1.91 %). Zr and REE concentrations are also relatively high (Zr: 1154 - 2340 ppm; Total REE (TREY = TRE): 899.20 - 1256.50 ppm; TRExOy: 1079.76 - 1507.97 ppm), with an average Zr/TRE ratio of ~ 1.39. The major rock forming minerals are leucite/pseudoleucite, diopside/aegirine, and high temperature phlogopite. Geochemical plots (major oxides and trace elements) using various diagrams suggest the Adang Volcanics formed in a postsubduction, within-plate continental extension/initial rift tectonic setting. It is further suggested magma was generated by minor (< 0.1 %) partial melting of depleted MORB mantle material (garnet-lherzolite) with the silicate melt having undergone strong metasomatism. Melt enrichment is reflected in the alkaline nature of the rocks and geochemical signatures such as Nb/Zr > 0.0627 and (Hf/Sm)PM > 1.23. A comparison with the Vulsini ultrapotassic volcanics from the Roman Province in Italy shows both similarities (spidergram pattern indicating affinity with Group III ultrapotassics volcanics) and differences (nature of mantle metasomatism).

THE METAMORPHIC ROCK-HOSTED GOLD MINERALIZATION AT BOMBANA, SOUTHEAST SULAWESI: A NEW EXPLORATION TARGET IN INDONESIA Idrus, Arifudin; Fadlin, Fadlin; Prihatmoko, Sukmandaru; Warmada, I Wayan; Nur, Irzal; Meyer, Franz Michael
Jurnal Geologi dan Sumberdaya Mineral Vol 22, No 1 (2012): Jurnal Sumber Daya Geologi
Publisher : Pusat Survei Geologi

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Placer gold has been discovered in Bombana, SE-Sulawesi, Indonesia. The placer gold is not associated with volcanic rock-related gold deposits. This paper discusses the primary gold mineralization as the source of the placer gold. The placer gold is possibly derived from gold-bearing quartz veins hosted by Pompangeo Metamorphic Complex (PMC). Pyrite, chalcopyrite, cinnabar, stibnite and tripuhyite are present. Sheared, segmented vein varies in thickness from 2 cm to 2 m. The veins contain erratic gold in various grades from below detection limit (0.005 g/t) to 134 g/t. At least three generations of veins are identified. The first is parallel to the foliations, the second crosscuts the first generation of veins/foliations, and the third is of laminated deformed quartz+calcite veins at the late stage. The first veins are mostly massive to crystalline, occasionally brecciated and sigmoidal, whereas the second veins are narrower than the first and relatively brecciated. Gold grades in the second and third veins are relatively higher than that in first veins. Fluid inclusion study of quartz veins indicates abundant H2O-NaCl and a small amount of H2O-NaCl-CO2 inclusions. Temperature of homogenization (Th) and salinity of the first vein vary from 184.7 to 245.3 ºC and 5.26 to 9.08 wt.% NaCl eq., respectively. The second generation vein was originated at Th of 132.1-283.4 ºC and salinity of 3.55-5.86 wt.%NaCl eq., whereas the third generation vein formed at lowest Th varying from 114 to 176ºC and less saline fluid at salinity range between 0.35 and 4.03 wt.% NaCl eq. Gold is mainly identified in the form of 'free gold' among silicate minerals. Mineralogically, gold is closely related to cinnabar, stibnite, tripuhyite and possibly minor arsenopyrite. Metamorphogenic gold deposits would be the new target of gold exploration in Indonesia.Keyword: Gold mineralization, orogenic-type, Bombana, Southeast Sulawesi, Indonesia

Magmatisme Tholeitik pada Active Continental Margin (ACM) di Serayu Bagian Utara dan Selatan – Banyumas, Jawa Tengah Fadlin, Fadlin; Godang, Shaban; Nur Hamzah, Wildan
Jurnal Geologi dan Sumberdaya Mineral Vol 19, No 1 (2018): Jurnal Geologi dan Sumberdaya Mineral
Publisher : Pusat Survei Geologi

Abstract - The significant amount of basaltic lava with geological age from Eocene to Miocene is found in Serayu Physiographic, Central Java. The basaltic lava has become a very interesting to observe due to its geological phenomenon and characteristics of the basaltic lava found in various tectonic positions. The objective of this research is to obtain the geological data in the form of petrological data and geochemical data from Ponjen (northern Serayu) and Kalisoka (southern Serayu) that spreading in the physiographic. The survey aimed to deduce the petrogenesis of basalt lava in the research area. The research method is using petrographic analysis and geochemical analysis by X-Ray Fluorescence (XRF), and Inductive Couple Plasma Mass Emission Spectrometry (ICP-MS). The data processing results of basalt lava by using geochemical major oxides for both zones indicating the tholeiitic origin magma and the type of plagioclase in form of labradorite. The magmatism of Ponjen-Kalisoka was formed from the tectonic setting of Active Continental Margin (ACM) with significant anomaly characteristic of Ta (Tantalum; Ta = 0,70 - 1,98 ppm) compares with basalt Gede volcanic (West Java; Ta = 0, 26 - 0.40 ppm) which is calc-alkaline which are both formed from ACM. The tholeiitic basalt of Ponjen-Kalisoka is proposed has contaminated with mantle magma which is possibly in form of intracontinental rifting resulted in Ponjen-Kalisoka's trace element becoming more into the transitional tholeiitic/calc-alkaline. The magmatism of Ponjen-Kalisoka's volcanic is a transitional magmatism (back arc volcanism) from southern volcanism (tholeiitic series) toward a calc-alkaline at northern part volcanism, such as the potassic calc-alkaline of Ungaran volcanic.Keyword: Serayu physiographic, Active Continental Margin (ACM), tholeiitic / transitional tholeiitic / calc-alkaline, magma contamination

Evolusi Plagioklas Dan Karakteristik Geokimia Lava Basalt Gunungapi Purba Menganti, Kebumen, Jawa Tengah Fadlin, Fadlin; Aulia R, Astika; Hamzah, Wildan Nur
Dinamika Rekayasa Vol 15, No 2 (2019): Jurnal Ilmiah Dinamika Rekayasa - Agustus 2019
Publisher : Jenderal Soedirman University

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.20884/1.dr.2019.15.2.259

Keberadaan jalur subduksi memiliki karakteristik magmatisme dan vulkanisme yang berbeda.Â Karakteristik ini akan tercermin pada morfologi gunungapi, karakteristik letusan, asosiasi batuan terutamaÂ karakteristik mineralogi dan geokimia batuan beku tersebut, sehingga penelitian detil berkaitan dengan karakteristikÂ mineralogi dan geokimia batuan beku sangat dibutuhkan untuk memahami genesa magmatisme dan vulkanisme diÂ daerah tersebut. Lokasi penelitian berada di Pantai Menganti, Kecamatan Ayah, Kabupaten Kebumen, Jawa Tengah.Â Metode penelitian yang digunakan yaitu analisis petrografi untuk mengetahui komposisi mineral penyusun lavaÂ basalt, lebih jauh lagi untuk mengidentifikasi evolusi mineral plagioklas dan analisis geokimia ICP-MS (InductivelyÂ Coupled Plasma Mass Spectrometry) untuk mengetahui kandungan unsur jejak (trace element) dan unsur tanahÂ jarang (Rare Earth Element/REE). Evolusi plagioklas penyusun lava basalt Pantai Menganti berupa penurunanÂ komposisi nilai An (Anorthite), labradorit (An52-59) menjadi andesine-labradorit (An43-50) karena dikontrol olehÂ diferensiasi magma normal berupa fraksinasi kristal, dalam hal ini tidak menunjukkan adanya magma mixing.Â Berdasarkan kajian geokimia didapatkan hasil berupa afinitas magma pembentukan lava basalt di daerah penelitianÂ berada pada tholeitik hingga transisi dengan tatanan tektonik berupa Active Continental Margin (ACM).

KARAKTERISTIK ENDAPAN EMAS OROGENIK SEBAGAI SUMBER EMAS PLACER DI DAERAH WUMBUBANGKA, BOMBANA, SULAWESI TENGGARA -, Fadlin
POROS TEKNIK Vol. 4 No. 1 (2012)
Publisher : P3M Politeknik Negeri Banjarmasin

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Studi Alterasi, Mineralisasi Dan Inklusi Fluida Prospek Hidrotermal (Pb-Zn-CuÂ±Au-Ag) Kubah Kulonprogo Bagian Selatan, Jawa Tengah Fadlin, Fadlin; Hajar Sulystiawan, Isnu; Adi Prasetyo, Luthfi
Jurnal Geologi dan Sumberdaya Mineral Vol 20, No 4 (2019): Jurnal Geologi dan Sumberdaya Mineral
Publisher : Pusat Survei Geologi

Ore potential especially base metals, gold and silver in the Kulonprogo Mountains have been a discussion of Indonesian geologists for a long time, until now its prospects as economic value has not been found, which made it a challenge to conduct an intensive and detailed study. This study is conducted to understand the mineralization-alteration characteristics and the deposit fluid of the study area. The method used in this study is a surface geological mapping, laboratory analysis such as mineragraphy, X-ray diffraction, ore geochemistry (Atomic Absorption Spectrometry-fire assay) and fluid inclusion. Alteration zone of the study area is divided into prophylitic, advanced argilic, argilic and silicification. Vein texture that develop in the study area is a massive quartz, stock work, and vuggy quartz which has NE-SW orientation, while the sulphide mineral abundance which found are enargite, pyrite, chalcopyrite, sphalerite, malachite, and molybdenite, occur in quartz veins or disseminated in gangue rock. Ore geochemistry AAS-fire assay of five vein samples show Au and the highest Ag content shown in sample 3 (Au:3.8. g/t, Ag:10 g/t). Fluid inclusion analysis results show homogenization temperature value (Th) which is 293,4-322,4o C, melting temperature (Tm) is -5,22o C until -6,3o C with average salinity value 10,58-12,89 wt,%NaCl equivalent. Hydrothermal fluid evolution of the study area is at the mixing with cooler phase and less saline fluids. Fluid is estimated from magmatic water that slowly mixed with meteoric water which is shown by the cooling temperature and salinity value. Based on alteration, mineralization, vein texture, ore geochemistry and fluid inclusion data results, therefore the deposit type at the study area is an intermediate epithermal sulphidation (IS).Keyword: alteration-mineralization, intermediate epithermal sulphidation, fluid inclusion, Kulonprogo Dome.

Geochemical Signatures of Potassic to Sodic Adang Volcanics, Western Sulawesi: Implications for Their Tectonic Setting and Origin Shaban, Godang; Fadlin, Fadlin; Priadi, Bambang
Indonesian Journal on Geoscience Vol 3, No 3 (2016)
Publisher : Geological Agency

DOI:10.17014/ijog.3.3.195-214The Adang Volcanics represent a series of (ultra) potassic to sodic lavas and tuffaceous rocks of predominantly trachytic composition, which forms the part of a sequence of Late Cenozoic high-K volcanic and associated intrusive rocks occurring extensively throughout Western Sulawesi. The tectonic setting and origin of these high-K rocks have been the subject of considerable debates. The Adang Volcanics have mafic to mafitic-intermediate characteristics (SiO2: 46 - 56 wt%) and a wide range of high alkaline contents (K2O: 0.80 - 9.08 %; Na2O: 0.90 - 7.21 %) with the Total Alkali of 6.67 - 12.60 %. Al2O3 values are relatively low (10.63 - 13.21 %) and TiO2 values relatively high (1.27 - 1.91 %). Zr and REE concentrations are also relatively high (Zr: 1154 - 2340 ppm; Total REE (TREY = TRE): 899.20 - 1256.50 ppm; TRExOy: 1079.76 - 1507.97 ppm), with an average Zr/TRE ratio of ~ 1.39. The major rock forming minerals are leucite/pseudoleucite, diopside/aegirine, and high temperature phlogopite. Geochemical plots (major oxides and trace elements) using various diagrams suggest the Adang Volcanics formed in a postsubduction, within-plate continental extension/initial rift tectonic setting. It is further suggested magma was generated by minor (< 0.1 %) partial melting of depleted MORB mantle material (garnet-lherzolite) with the silicate melt having undergone strong metasomatism. Melt enrichment is reflected in the alkaline nature of the rocks and geochemical signatures such as Nb/Zr > 0.0627 and (Hf/Sm)PM > 1.23. A comparison with the Vulsini ultrapotassic volcanics from the Roman Province in Italy shows both similarities (spidergram pattern indicating affinity with Group III ultrapotassics volcanics) and differences (nature of mantle metasomatism).

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