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All Journal IJOG : Indonesian Journal on Geoscience Jurnal technoscientia Jurnal RISET Geologi dan Pertambangan Eksplorium : Buletin Pusat Pengembangan Bahan Galian Nuklir Journal of Geoscience, Engineering, Environment, and Technology Jurnal Geologi dan Sumberdaya Mineral Buletin Sumber Daya Geologi Jurnal GEOSAPTA International Journal of Community Service Learning Jurnal Abdi: Media Pengabdian Kepada Masyarakat Prosiding Seminar Teknologi Kebumian dan Kelautan (SEMITAN JURNAL TEKNOLOGI TECHNOSCIENTIA Indonesian Journal on Geoscience Indonesian Journal on Geoscience Journal of Applied Geology Ophiolite : Jurnal Geologi Terapan Jurnal Geologi dan Sumberdaya Mineral

Arifudin Idrus

Universitas Gadjah Mada

Author-ID : 285193

Humanities Chemical Engineering, Chemistry & Bioengineering Chemistry Civil Engineering, Building, Construction & Architecture Computer Science & IT Earth & Planetary Sciences Economics, Econometrics & Finance Education Energy Engineering Environmental Science Industrial & Manufacturing Engineering Languange, Linguistic, Communication & Media Law, Crime, Criminology & Criminal Justice Materials Science & Nanotechnology Mechanical Engineering Physics Social Sciences Other

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

DOI: 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 ‘orogenic gold type’. The orogenic gold deposit could be a new target of gold exploration in Indonesia in the future.

Geology and Characteristics of Pb-Zn-Cu-Ag Skarn Deposit at Ruwai, Lamandau Regency, Central Kalimantan Arifudin Idrus; L. D. Setijadji; F. Thamba
Indonesian Journal on Geoscience Vol 6, No 4 (2011)
Publisher : Geological Agency

DOI: 10.17014/ijog.v6i4.126This study is dealing with geology and characteristics of mineralogy, geochemistry, and physicochemical conditions of hydrothermal fluid responsible for the formation of skarn Pb-Zn-Cu-Ag deposit at Ruwai, Lamandau Regency, Central Kalimantan. The formation of Ruwai skarn is genetically associated with calcareous rocks consisting of limestone and siltstone (derived from marl?) controlled by NNE-SSW-trending strike slip faults. It is localized along N 70° E-trending thrust fault, which also acts as the contact zone between sedimentary and volcanic rocks in the area. The Ruwai skarn is mineralogically characterized by prograde alteration comprising garnet (andradite) and clino-pyroxene (wollastonite), and retrograde alteration composed of epidote, chlorite, calcite, and sericite. Ore mineralization is typified by sphalerite, galena, and chalcopyrite, formed at early retrograde stage. Galena is typically enriched in silver up to 0.45 wt % and bismuth of about 1 wt %. No Ag-sulphides are identified within the ore body. Geochemically, SiO is enriched and CaO is depleted in limestone, consistent with silicic alteration (quartz and calc-silicate) and decarbonatization of the wallrock. The measured resources of the deposit are 2,297,185 tonnes at average grades of 14.98 % Zn, 6.44% Pb, 2.49 % Cu, and 370.87 g/t Ag. Ruwai skarn orebody was originated at moderate temperatures of 250 - 266 °C and low salinity of 0.3 - 0.5 wt.% NaCl eq. The late retrograde stage was formed at low temperature of 190 - 220 °C and low salinity of ~0.35 wt.% NaCl eq., which was influenced by meteoric water incursion at the late stage of the Ruwai Pb-Zn-Cu-Ag skarn formation.

Thermal and Infrared Studies of Garnierite from the Soroako Nickeliferous Laterite Deposit, Sulawesi, Indonesia Sufriadin Sufriadin; Arifudin Idrus; S. Pramumijoyo; I. W. Warmada; I. Nur; A. Imai; A. M. Imran; Kaharuddin Kaharuddin
Indonesian Journal on Geoscience Vol 7, No 2 (2012)
Publisher : Geological Agency

DOI: 10.17014/ijog.v7i2.137Mineralogical characterization of some garnierite samples from Soroako have been conducted using X-ray diffraction, thermal analysis, and infrared spectroscopy methods. XRD patterns reveal the samples mainly containing the mixture of kerolite (talc-like phase) and serpentine with minor smectite, sepiolite, and silica. Thermal analyses of garnierite samples indicated by DTA curves are in good agreement with patterns that have been reported in literature. Three endothermic peaks normally occur in the ranges between 58º C and <800º C illustrating three steps of weight losses: adsorbed, bound, and hydroxyl/crystal water. One additional weight loss in low temperature region of sepiolite is corresponding to the lost of zeolitic water. Infrared spectra appeared in 3800 - 3200 cm-1 region generally exhibit broad absorption bands, indicating low crystallinities of studied samples and can be assigned to the presence of hydroxyl group bonded to octahedral coordination mainly Mg atom. The bands observed at 1660 cm-1, 1639 cm-1, 1637 cm-1, and 1633 cm-1 in all samples indicate water molecules. FTIR spectra displaying the strong bands at 1045 cm-1, 1038 cm-1, and 1036 cm-1 could be related to the presence of Si-O-Si bonds linking to tetrahedral coordination. The strong absorption bands appeared at 511 cm-1, 505 cm-1, 499 cm-1, and 496 cm-1 in respective samples are attributed to divalent cation bonds (e.g. Mg, Ni-O). Both TG/DTA and FTIR seem to be the powerful tool in diagnosing the crystal chemistry of garnierite which is mainly composed of phyllosilicate minerals.

Characteristics and Origin of Sedimentary-Related Manganese Layers in Timor Island, Indonesia Arifudin Idrus; E. M. Ati; A. Harijoko; F. M. Meyer
Indonesian Journal on Geoscience Vol 8, No 4 (2013)
Publisher : Geological Agency

DOI: 10.17014/ijog.v8i4.169Sedimentary-related manganese layers have been discovered in South Central Timor Regency, Timor Island, Indonesia, which is tectonically active and being uplifted due to north-trending tectonic collision between Timor Island arc and Australian continental crust. The manganese layers of 2 to 10 cm-wide interbed with deep sea sedimentary rocks including reddish - reddish brown claystone, radiolarian chert, slate, marl as well as white and pinkish calcilutite of Nakfunu Formations. Stratigraphically, the rock formations are underlain by Bobonaro Formation. Two types of manganese ores found comprise manganese layers and manganese nodule. The manganese layers strongly deformed, lenticular, and segmented, are composed of manganite [MnO(OH)], groutite [MnO(OH)], pyrolusite (MnO2), lithioporite (Al,Li) MnO2(OH)2, and hollandite [Ba (Mn4+, Mn2+)8O16] associated with gangue minerals including calcite, quartz, limonite [FeO(OH)], hematite (Fe2O3), and barite (BaSO4). Whilst the nodule type is only composed of manganite and less limonite. Geochemically, the manganese layers have grade of 63 - 72 wt.% MnO, whereas the nodule one has grade of 63 - 69 wt.% MnO. Generally, iron in Mn ore is very low ranging from 0.2 to 1.54 wt.% Fe2O3, averaged 0.76 wt.%. Hence, Fe/Mn ratio which is very low (0.003 - 0.069), typically indicates a sedimentary origin, which is also supported by petrologic and petrographic data showing layering structure of manganite and lithioporite crystal/grain. Trace element geochemistry indicates that manganese ore was precipitated in a reduction condition. Rare earth element (REE) analysis of manganese ore shows an enrichment of cerium (Ce) suggesting that the ore is basically originated in a marine environment. The manganese nodule is interpreted to be formed by chemical concretion process of unsoluble metals (i.e. mangan, iron) in seawater (hydrogenous) and precipitated on deep sea bottom. On the other hand, the manganese layer is a detrital diagenetic deposit formed by Mn remobilization in seawater column, precipitated and sedimented on the deep sea bottom. Manganese layers have probably been influenced by ‘hydrothermal process’ of mud-volcano activities, proven by the presence of quartz and barite veinlets cutting the Mn layers, manganite recrystallization to be pyrolusite along veinlets cutting manganite and lithioporite layers, and the presence of pyrite and sulphur associated with Mn layers. Field data also exhibit that the significant manganese layers are mostly found around mud volcanoes. The closely spatial and genetic relationships between manganese layers and mud-volcanoes might also be an important guide for the exploration of Mn deposit in the region.

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

DOI: 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, discontinous, 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 ‘mineralized zone’ 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 ºC and a typical low salinity (0.36 to 0.54 wt.% NaCl eq). Based on those key features, gold mineralization 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.

Petrography and Mineral Chemistry of Magmatic and Hydrothermal Biotite in Porphyry Copper-Gold Deposits: A Tool for Understanding Mineralizing Fluid Compositional Changes During Alteration Processes Arifudin Idrus
Indonesian Journal on Geoscience Vol 5, No 1 (2018)
Publisher : Geological Agency

DOI: 10.17014/ijog.5.1.47-64This study aims to understand the petrography and chemistry of both magmatic and hydrothermal biotites in porphyry copper-gold deposits, and to evaluate the fluid compositional changes during alteration processes. A total of 206 biotite grains from selected rock samples taken from the Batu Hijau porphyry Cu-Au deposit was analyzed. Detailed petrography and biotite chemistry analysis were performed on thin sections and polished thin sections, respectively, representing various rocks and alteration types. A JEOL JXA-8900R electron microprobe analyzer (EMPA) was used for the chemistry analysis. The biotite is texturally divided into magmatic and hydrothermal types. Ti, Fe, and F contents can be used to distinguish the two biotite types chemically. Some oxide and halogen contents of biotite from various rocks and alteration types demonstrate a systematic variation in chemical composition. Biotite halogen chemistry shows a systematic increase in log (XCl/XOH) and decrease in log (XF/XOH) values from biotite (potassic) through chlorite-sericite (intermediate argillic) to actinolite (inner propylitic) zones. The y-intercepts on the log (XCl/XOH) vs. XMg and log (XF/XOH) vs. XFe plotted for biotite from potassic and intermediate argillic zones are similar or slightly different. In contrast, the y-intercepts on the log (XCl/XOH) vs. XMg and log (XF/XOH) vs. XFe plotted for biotite from inner propylitic zone display different values in comparison to the two alteration zones. Halogen (F,Cl) fugacity ratios in biotite show a similar pattern: in the potassic and intermediate argillic zones they show little variation, whereas in the inner propylitic zone they are distinctly different. These features suggest the hydrothermal fluid composition remained fairly constant in the inner part of the deposit during the potassic and intermediate argillic alteration events, but changed significantly towards the outer part affected by inner propylitic alteration. High halogen content, particularly Cl, in hydrothermal biotite may portray that copper and gold were transported in mineralizing fluids in the form of chloride complexes CuCl2- and AuCl2-, respectively.

Geochemical Characteristics of Limestone of Wonosari-Punung Formation, Gunungkidul Regency, Yogyakarta, Indonesia Didik Dwi Atmoko; Anastasia Dewi Titisari; Arifudin Idrus
Indonesian Journal on Geoscience Vol 5, No 2 (2018)
Publisher : Geological Agency

DOI: 10.17014/ijog.5.2.179-197A geochemical study was carried out to determine the geochemical characteristics of limestone in Wonosari-Punung Formation, and to suggest its depositional conditions and the source of rare earth elements. The study was conducted at Ponjong Area, Gunungkidul Regency, Daerah Istimewa Yogyakarta, Indonesia. White limestone which contains more abundant calcite is characterized by the highest CaO concentration. Red limestone which is associated with impure minerals such as siderite, rodochrosite, hematite, and titanite is typified by depleted CaO but higher SiO2, Fe2O3, MnO, and TiO2 concentrations. Grey limestone characterized by depleted CaO and higher MnO contents is considered to be influenced by the presence of impure minerals of manganite (Mn2O3.H2O) and/or pyrolusite (MnO2). Depletion of Sr concentration in the coloured limestone indicates that the diagenetic process increases from the white limestone to the coloured limestone. The process possibly occurred post-deposition of the limestones. The limestones show positive Mn* values (2.46 - 2.95) and authigenic U values (0.89 - 3.38) that suggest an oxidative environment. The Ce/Ce* values (0.57 - 0.80), Eu/Eu* values (1.04 - 1.88), high Y/Ho ratio, and low LaN/YbN ratio are indications that the rare earth elements in the limestones were derived from terrigenous materials. The positive Eu anomaly and enrichment of Cr and Mn of the limestones are indications of hydrothermal fluid activity taking place in the studied area. Based on the geochemical characteristics of the Punung-Wonosari limestones, the depositional environment and the source of rare earth elements of the limestones were therefore influenced by a combination of hydrothermal fluid activity with small amount of terrigenous material input and post depositional diagenetic process.

Komatiitic Lamprophyre in West Sulawesi: First Evidence for >1350°C and 3.5 - 3.8 GPa Mantle Melts Shaban Godang; Fadlin Fadlin; Bambang Priadi; Arifudin Idrus; I Gde Sukadana
Indonesian Journal on Geoscience Vol 8, No 1 (2021)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.8.1.39-58

DOI: 10.17014/ijog.8.1.39-58The presence of lamprophyric lavas of Late Cenozoic in Talaya Volcanic Formation at the boundary between the subregencies of Mamuju and Tabulahan (Western Sulawesi) associated with the mantle enrichment rocks of the Adang Volcanics is the subject of this study. Petrologically, lamprophyre is composed of orthopyroxene (enstatite), clinopyroxene (augite), biotite, leucite, amphibole, magnetite, and autometasomatism of chlorite in grain minerals and groundmass. The lamprophyre is classified into monchiquite shoshonitic lamprophyre, and it has a komatiitic composition with the ratio of MgO/Al2O3 > 0.7906 (in wt %). The komatiitic monchiquite lamprophyre is characterized by high MgO (10.02 - 12.67 %), relatively low alumina (Al2O3= 10.98 - 11.70 %), SiO2= 46.43 - 47.8 %, TiO2 (0.84 - 1.00 %), FeOt (7.75 - 7.88 %), and relatively high content of alkaline (Na2O: 2.20 - 2.59 %; K2O: 1.58 - 2.45 %; Total alkali: 4.00 - 4.89 %, and CaO (9.29 - 10.71 %). The geochemical trace element plots using various diagrams suggests the geotectonic setting of the lamprophyric rock was formed in suprasubduction alkaline continental-arc, and the proposed source of magmatism comes from the suprasubduction activities from the east. The protolith of magma was originated from partial melting of depleted MORB mantle (DMM), composed of pyroxene-peridotite (garnet-lherzolite). The partial melting conditions are suggested to occur at high pressure (3.5 - 3.8 GPa) and the depth of ~120 km with melting temperature of >1350°C, and the magma is dominantly controlled by olivine fractional crystallization.

Geochemistry Study of Cross-castic Magma Alkalinity Evolution Shaban Godang; Bambang Priadi; Fadlin Fadlin; Theo Van Leeuwen; Arifudin Idrus
Indonesian Journal on Geoscience Vol 8, No 2 (2021)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.8.2.177-196

DOI:10.17014/ijog.8.2.177-196The discrimination of magmatic alkalinity is a classic study that has never stopped for the past ninety years. Various methodologies have been developed since Shand’s classification using the method of alumina saturation to approach silica saturation and the methodology without involving alumina and silica such as K2O vs. Na2O and others, while the aim is to find out the evolution of alkalinity during the magmatic differentiation. The classical magmatic alkalinity evolution has been known as a castic magma alkalinity evolution, where the initial magma in the form of magma-X(a) will evolve along the stages of differentiation and remain a derivative of the initial magma {magmaX(a)}. The same philosophy is also explained in the ternary AFM diagram. Is the magmatic differentiation, followed by fractional crystallization, always an evolution of alkalinity based on caste? This question often raises current debates. This study takes the example of cogenetic volcanic and albitites. The application of the cogenetic volcanic using the selected diagram, which is ‘Three in one an overlaid diagram’. The output of the diagram presents the differentiation of magma which based on the evolution of Mg-series and Fe-series in a discontinuous branch of Bowen 1922 that can take place the castic and cross-castic, e.g. (a) from Mg-series to Mg-series {castic}, (b) from Mg-series to Feseries {cross-castic}, (c) from high-Mg tholeiitic basalt to calc-alkaline series {cross-castic}, (d) from Fe-series to Fe-series {castic}. While the evolution of magmatic alkalinity based on the continuous branch and refer to Trapezoid model generally occurring a cross-castic, e.g. (A) from sodic calc-alkaline to sodic alkaline-calcic, (B) from sodic calc-alkaline to shoshonitic alkaline-calcic, (C) from sodic calc-alkaline to potassic calc-alkaline, (D) from potassic calc-alkaline to shoshonitic alkaline-calcic, (E) sodic alkaline-calcic to sodic alkaline/peralkaline, (F) shoshonitic alkaline-calcic to potassic/ultrapotassic alkaline-calcic (cross-castic in subalkaline), (G) shoshonitic/potassic alkalinecalcic to shoshonitic/potassic alkaline/peralkaline. In this study, Fossa delle Felci volcanics (Italy) shows the evolution of magma from Mg-series to Mg-series, but the evolution of alkalinity of magma reveals the cross-caste (from sodic calc-alkaline to shoshonitic alkaline-calcic). Salak volcanics (Western Jawa) shows the evolution of magma from the Mg-series to Fe-series (cross-castic), and also the cross-castic in the evolution of alkalinity from sodic calc-alkaline to alkaline-calcic. Gothara albitites (India) clearly reveal the sodic-rich alkaline, which the magma generates from the evolution of sodic alkaline-calcic to sodic alkaline without the presence of potassic.

Eksplorasi Geokimia untuk Menentukan Daerah Prospek Mineralisasi Emas Tipe Urat Epitermal: Studi Kasus di Daerah Tompaso, Kabupaten Minahasa Selatan, Sulawesi Utara Arifudin Idrus; Fadlin Fadlin; Hill Gendoet Hartono
EKSPLORIUM Vol 42, No 1 (2021): Mei 2021
Publisher : Pusat Teknologi Bahan Galian Nuklir - BATAN

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17146/eksplorium.2021.42.1.6230

ABSTRAK Sulawesi Utara termasuk daerah Tompaso, Kabupaten Minahasa Selatan merupakan jalur magmatik yang potensial menghasilkan endapan bijih hidrotermal. Penelitian ini bertujuan menentukan daerah prospek mineralisasi emas khususnya tipe urat epitermal berdasarkan eksplorasi geokimia meliputi geokimia batuan dan sedimen sungai, khususnya metode BLEG (Bulk Leach Extractable Gold). Metode penelitian meliputi pemetaan geologi, alterasi dan jalur urat, percontoan (bijih/batuan dan sedimen sungai), dan analisis geokimia. Sampel bijih dianalisis dengan metode FA/AAS untuk emas dan metode AAS untuk unsur lain, sedangkan analisis sampel sedimen sungai dilakukan dengan metode cyanide leach dan AAS. Hasil penelitian menunjukkan batuan induk mineralisasi berupa lava andesit dan intrusi diorit. Batuan ini mengalami alterasi silica-clay, argilik, dan propilitik. Perpaduan antara pemetaan geologi, zona alterasi, dan jalur urat dengan eksplorasigeokimia batuan dapat menentukan daerah prospek mineralisasi yaitu Prospek Asam dan Polangkok. Pada Prospek Asam, sampel bijih memiliki kandungan emas sampai 0,03 ppm dengan anomali emas pada sampel BLEG menunjukkan nilai threshold 13,52 ppb Au. Pada Prospek Polangkok ditemukan 2 jalur urat (P1 dan P2) berarah baratlaut-tenggara dengan lebar sampai 5 m. Urat P1 memiliki kadar Au mencapai 0,31 ppm dan pada urat P2 mencapai 0,16 ppm Au. Mineralisasi pada Prospek Polangkok didukung oleh anomali Ag pada sampel BLEG dengan nilai threshold 67,18 ppb. Kedua daerah prospek tersebut direkomendasikan untuk eksplorasi lanjut (follow-up exploration). ABSTRACT North Sulawesi, including the Tompaso region, South Minahasa district, is a part of the magmatic belts hosting potential hydrothermal ore deposits. This study is aimed to determine the prospect area for epithermal vein-type gold mineralization, based on geochemical exploration including rock and BLEG (Bulk Leach Extractable Gold) stream sediment geochemistry. Mapping of geology, alteration and vein direction, sampling (ore/rock and stream sediment), and geochemical analysis were performed. Gold in rock samples was analyzed by FA/AAS, and other elements were detected by AAS, while BLEG samples were analyzed using the cyanide leach and AAS methods. The study area is occupied by andesitic lava and diorite, which are suffered by silica-clay, argillic and propylitic alteration. An integration of geological mapping, alteration zones and vein direction with lithogeochemical survey enables to determine the prospect areas, which consist of Asam and Polangkok prospects. At the Asam prospect, the ore sample contains gold up to 0.03 ppm, where the gold anomaly in BLEG samples show a threshold of 13.52 ppb Au. At the Polangkok prospect, two NW-SE trending veins (P1 and P2 Veins) were discovered with a width of up to 5 m. Vein P1 and P2 contains of up to 0.31 and 0.16 ppm Au, respectively. Mineralization at the Polangkok prospect coincides with Ag anomaly of BLEG samples with a threshold of 67.18 ppb. The two prospect areas are recommended for follow-up exploration.

Co-Authors A. Harijoko A. Harijoko A. Imai A. Imai A. M. Imran Abdul, Abdul Agung Harijoko Ahmad Ahmad Aji Syailendra Ubaidillah Aji Syailendra Ubaidillah Anastasia Dewi Titisari Araki, Naoto Asrafil Asrafil Ati, E. M. Atmoko, Didik Dwi Atmoko, Didik Dwi Bambang Priadi Dana, Cendi D. P. Danny, Rama Didik Dwi Atmoko Didik Dwi Atmoko Djoko Wintolo, Djoko Donatus Hendra Amijaya E. M. Ati E. M. Ati Edy Nursanto Ernowo Ernowo Ernowo Ernowo Ernowo Harjanto Ernowo Harjanto, Ernowo Ernowo, Ernowo F. M. Meyer F. M. Meyer F. Thamba F. Thamba Fadlin Fadlin Fadlin Fadlin Fadlin Fadlin Fadlin Fadlin Fadlin Idrus Fadlin Idrus Fadlin, Fadlin Fadlin, Fadlin Ferian Anggara Franklin Franklin Franklin Franklin Franklin, Franklin Franz Michael Meyer Franz Michael Meyer Franz Michael Meyer, Franz Michael Godang, Shaban Godang, Shaban Hakim, Fahmi Handayani, Esti Harijoko, A. Harjoko, Agung Hasria Hasria Hasria Hasria, Hasria Herfien Samalehu Herfien Samalehu Hill Gendoet Hartono Himawan Tri Bayu Murti Petrus I Gde Sukadana I Wayan Warmada I. Nur I. Nur I. Nur Idrus, Fadlin Imai, A. Imai, Akira Indra Sanjaya Irzal Nur, Irzal Isyqi Isyqi Iwan Setiawan Iwan Setiawan Johan Arif, Johan Kaharuddin Kaharuddin Kaharuddin, Kaharuddin Kant, Win Khant, Win Koichiro Watanabe, Koichiro Kolb, Jochen L. D. Setijadji L. D. Setijadji Lai, Chun-Kit Leeuwen, Theo Van Lia Novelia Agung Lia Novelia Agung, Lia Novelia Lucas Donny Setijadji Mansur, Suaib Meak, Ignas A. Meyer, F. M. Meyer, Franz M Mochammad Aziz Mochammad Aziz, Mochammad Moetamar Moetamar Moetamar Moetamar Moetamar, Moetamar Mohamad Anis Mohamad Anis, Mohamad Mudinillah, Adam Myaing, Yu Yu Nugroho Imam Setiawan Nur, I. Nur, I. Okki Verdiansyah Pramumijoyo, Pranayoga Pramumijoyo, S. Pratomo, Septyo Uji Priadi, Bambang Prihatmoko, Sukmandaru Putranto, Sapto Putranto, Sapto Rahmah, Yuyun Prihatining Rahmayuddin, Rahmayuddin Rika Ernawati Rohaya Langkoke S. Pramumijoyo S. Pramumijoyo Sapto Putranto Setiawan, Iwan Setiawan, Iwan Setijadji, L. D. Setijadji, Lucas D Shaban Godang Shaban Godang Sindern, Sven Siti Rahmawati H. Budiawan Subagyo Pramumijoyo, Subagyo Subagyo Subagyo Subagyo Subagyo Sufriadin, Sufriadin Sukadana, I Gde Sukamandaru Prihatmoko Sukamandaru Prihatmoko, Sukamandaru Sukmandaru Prihatmoko Sukmandaru Prihatmoko Sutarto Sutarto Sutarto Sutarto Sven Sindern Syafruddin Maula Syafruddin Maula Tamba, Fenny Thamba, F. Theo Van Leeuwen Thwee Aye, May Titisari, Anastasia Dewi Tun, Myo Min Wahyu Widodo Wahyu Widodo Waterman Sulistyana Bargawa Yonezu, Kotaro Yu Yu Myaing Yurniadi, Feddy

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