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IJOG : Indonesian Journal on Geoscience

IJOG
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Published by Geological Agency of Indonesia

ISSN : 23559314 EISSN : 23559306 DOI : -

Core Subject : Science,

Earth & Planetary Sciences

The spirit to improve the journal to be more credible is increasing, and in 2012 it invited earth scientists in East and Southeast Asia as well as some western countries to join the journal for the editor positions in the Indonesia Journal of Geology. This is also to realize our present goal to internationalize the journal, The Indonesian Journal on Geoscience, which is open for papers of geology, geophysics, geochemistry, geodetics, geography, and soil science. This new born journal is expected to be published three times a year. As an international publication, of course it must all be written in an international language, in this case English. This adds difficulties to the effort to obtain good papers in English to publish although the credit points that an author will get are much higher.

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Articles 796 Documents

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Alteration and Vein Textures Associated with Gold Mineralization at the Bunikasih Area, Pangalengan, West Java Andri S. Subandrio; N. I. Basuki
Indonesian Journal on Geoscience Vol 5, No 4 (2010)
Publisher : Geological Agency

DOI: 10.17014/ijog.v5i4.108The Bunikasih vein system in the Pangalengan district of West Java is a low-sulfidation, adularia sericite epithermal gold deposit. It is hosted by Late Miocene andesitic volcanic and volcanoclastic rocks occurring in the south western margin of Malabar Volcano complex. Gold ore and alteration minerals related to deposition of gold in Bunikasih deposits superimposed on Late Tertiary-Quaternary andesitic formation that were altered and mineralized by some hydrothermal events. The veins consist almost entirely of quartz, with small amounts of adularia, bladed calcite, pyrite, and gold. Gold ore shoots are vertically restricted and are more continuous horizontally. The veins display complex and multi episodic filling with texture characteristics of open space precipitation such us colloform, lattice bladed, crustiform banding, vugs, breccia, and cockade and comb texture. The presence of bladed calcite and silica pseudomorph after bladed calcite suggests that the hydrothermal fluids boiled. In the Cibaliung section of the area, anomalous gold is related to veins trending northeast - southwest, milky quartz with dark grey to black manganese staining is found intermittently for a length of about 800m. The mineralized andesite ore bodies exhibit broad alteration patterns adjacent to mineralization, passing from fresh rock into anargillic, chlorite zone, and then sericite-silica close to mineralization. An argillic assemblage composed of kaolinite with fine-grained pyrite bulb is present in the upper portions and surrounding of the quartz vein system. The veins range from centimeter to meter in size. Of 24 vein samples collected, gold averages up to 0.3 grams per tone ("g/t"), to a high of 24.6 g/t. The Bunikasih epithermal gold deposit was mined by people for more than 10 years, mainly for the gold ore.

The Evolution of Gajahmungkur Paleovolcano, Wonogiri, Central Java, as A Reference to Revize the Terminology of “Old Andesite Formation” Ildrem Syafri; A. Sudradjat; Nana Sulaksana; G. Hartono
Indonesian Journal on Geoscience Vol 5, No 4 (2010)
Publisher : Geological Agency

DOI: 10.17014/ijog.v5i4.109Gajahmungkur is a Tertiary paleovolcano located in Wonogiri Regency, Central Java. The volcanic product of this volcano are widely distributed and composed of important elements of the stratigraphic sequence in the Southern Mountain area. The volcanic products so far have been simply classified as “Old Andesite Formation” which apparently is not in line with the stratigraphic code and the Indonesian Stratigraphic Code. The description of paleovolcano therefore might contribute to the revision of the “Old Andesite Formation”. The evolution of Gajahmungkur paleovolcano commenced with the formation of a submarine volcano, and then at the second phase a composite volcano emerged above sea level forming a volcano island. The third phase was the self destruction resulting in a formation of a caldera. Pumiceous components dominated the products. At the fourth phase, the activities began to decline producing more basaltic rocks. The statistical analysis of the interrelation between various physical properties of the clastic rocks leads to the identification of volcanic facies and the location of the paleovolcano vent.

Macroscopic, Microscopic, and Paleo-depositional Features of selected Coals in Arahan, Banjarsari, Subanjeriji, and South Banko Regions, South Sumatra Nana Suwarna; Y. Kusumahbrata
Indonesian Journal on Geoscience Vol 5, No 4 (2010)
Publisher : Geological Agency

DOI: 10.17014/ijog.v5i4.110The Arahan, Banjarsari, Subanjeriji, and Banko Regions, parts of the Bukit Asam coalfield, is situated in the Lematang Depression of South Palembang Sub-basin, South Sumatera Basin. Twenty two fresh outcrop and subcrop samples of Seam B, A, Benuang, Enim, and Jelawatan of the Mio-Pliocene Muaraenim coals have been analyzed macroscopically and microscopically, to assess the characteristics and depositional environment of the coal present. On the basis of lithotype analysis, accompanied by organic-petrological and SEM analyses, the coal seams of the Muaraenim Formation show variations in the predominance of some macerals, indicating successions of environmental changes. Petrographically, the dominant maceral group is vitrinite, present in high to very high values (69.4 – 97.4 %); whilst the minor one is inertinite showing a low to moderate amount (0.4 – 22.0 %), followed by low to moderate value of exinite (0.4 – 18.2 %). Vitrinite reflectance values are present in a low to moderate level, varying from 0.34 to 0.55 %, with one sample showing value of 0.59 %. Mineral matter dominated by clay minerals, with minor pyrite and carbonate, displays a low degree (0.4 – 5.4 %), with one sample of 12.0 %. Organic facies study tends to indicate that the coals were deposited in a wet forest swamp to limnic zone, within lower delta plain to transgressive area. This condition has supported the depositional setting interpreted from sedimentary facies associations that shows a shallow-water continental margin sequence, varying from a fluvial to deltaic environment. The organic facies concept is thus applicable in basin studies context and has potential to become an additional tool for interpretation of depositional environment.

Focal Mechanism and Parameter of Volcano-Tectonic Earthquake Source, in Mount Guntur, West Java Sri Hidayati; Y. Suparman; A. Loeqman
Indonesian Journal on Geoscience Vol 6, No 1 (2011)
Publisher : Geological Agency

DOI: 10.17014/ijog.v6i1.111Guntur Volcano in West Java is one of the most active volcanoes in Indonesia. The last eruption took place in 1847 and the volcanic activity has been dormant since then, however its seismicity is active. During the period of July to October 2009, the hypocenter distribution of VT earthquakes is mostly located at western flank of the volcano, beneath Guntur - Gandapura craters at the depth of less than 5 km. The depth pattern shows deeper to the northwest. The VT earthquakes deeper than 5 km were not found in this period. The focal mechanism of VT earthquakes are oblique normal fault, strike-slip fault and oblique reverse fault types. The mechanism of those earthquakes is not uniquely determined probably due to complicated structures at Guntur volcano complex area, which is aligned in NW-SE direction. T-axis of the oblique normal fault is trending in northwest - southeast direction similar to the structures found in the summit area of Gunung Guntur Volcano. Similarly, one of the strike-slip fault nodal line and P-axis of oblique reverse fault are also trending in northwest - southeast. Ploting of the earthquake source parameters (seismic moment, corner frequency, and stress drop) made to hypocenter distance shows no significant difference on those parameters between earthquakes at close and far distances to Kabuyutan station. It is probably due to the hypocenters are not concentrated in one zone. Meanwhile, the relationship between seismic moment (Mo) and seismic source radius (r) shows that for earthquakes with moment of smaller than 1018 dyne cm, the radius of the hypocenter is constant which is namely 60 m.

Turbidite Facies of the Halang Formation in Ajibarang Area, Central Java Praptisih Praptisih; Kamtono Kamtono
Indonesian Journal on Geoscience Vol 6, No 1 (2011)
Publisher : Geological Agency

DOI: 10.17014/ijog.v6i1.112An understanding of deepwater turbidite sediments is very important mainly dealing with the determination of a reservoir geometry. The problem arising in the turbidite sediment geometry is very complex and varied, and its existence depends on how, when, and type of its environment. In Central Java, the broad turbidite sediment distribution of the Halang Formation is needed to be observed its facies association. This paper will discuss the turbidite facies of Halang Formation in the Ajibarang area. The method used to analyze the turbidite facies is by measuring stratigraphic sections and observing the lithofacies characteristics to reconstruct its depositional environment. The Halang Formation outcrop in the Ajibarang area is dominantly composed of alternating sandstone and claystone or marl. Based on the observation, the turbidite facies of Halang Formation, in the Ajibarang area, was deposited on a submarine fan system at the middle fan of suprafan lobes. Compiling with the previous studies, the source of the Halang Formation is indicated to be derived from the south southwest.

Sediment Distribution related to Gold and Silver Placer Deposits in Offshore of Sambas Besar Estuary, Sambas Regency, West Kalimantan Ediar Usman; I. W. Lugra
Indonesian Journal on Geoscience Vol 6, No 1 (2011)
Publisher : Geological Agency

DOI: 10.17014/ijog.v6i1.113Result of grain size analysis of the sea floor sediments from the study area indicates four sediment types, those are silt, sandy silt, silty sand, and sand. The silt unit has the widest distribution that is around 127.2 km2, sandy silt 12.65 km2, sand 1.176 km2, and silty sand 0.44 km2. Result of gold and silver content analysis from some selected samples indicates that the highest gold and silver amount are at PMK-08 location in northern part of the study area with gold content of 0.21 ppm and silver 13.36 ppm; both are silt sediment types. The highest gold and silver content occur within medium - coarse sediments containing subrounded grains of quartz and pyrite, at northern part of the study area. The presence of silver and gold is suggested to be controlled by a north-south longshore current pattern. The source of sediments from Sambas Besar River follows the longshore current, e.g. in northern estuary from south to north, and at southern estuary from north to south direction.

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.

Nannoplankton Assemblage Succession Throughout Cretaceous/ Tertiary Boundary in the “P” Well Section, Santos Basin, Brazil Panuju Panuju
Indonesian Journal on Geoscience Vol 6, No 1 (2011)
Publisher : Geological Agency

DOI: 10.17014/ijog.v6i1.115The massive change in calcareous nannoplankton assemblages throughout Cretaceous/Tertiary (K/T) boundary (65.5 M.a.) has been illustrated by several authors. The diverse and abundant assemblage disappears suddenly above the Cretaceous/Tertiary boundary. This event is related to the most dramatic environmental changes in the Earth's history due to the catastrophic events, those are meteorite impact (Chicxulub) and supervolcano eruption (Deccan) occurring at the end of Cretaceous. The succeeding age was a time of rapid evolution of nannoplankton during Paleocene. A quantitative method analysis of nannoplankton throughout Maastrichtian to Paleocene of “P” well section, Santos Basin, Brazil, indicated that the nannoplankton assemblages abruptly decrease in diversity and abundance and mostly change in species composition. The various complex shapes of species at Maastrichtian also underwent changing to simple plain shapes and small at Paleocene. The sedimentary section ranges from the top of zone CC23 (Coccolith Cretaceous 23) to NP9 (Nannoplankton Paleogen 9). It is bounded by the Last Occurrence (LO) of Tranolithus pachelosus at the base and Fasciculithus tympaniformis at the top. The biostratigraphic discontinuity characterized by the absence of zone CC26 to NP4 is an indicator for the presence of an unconformity at K/T boundary within analyzed section. The Cretaceous nannoplankton assemblages are dominated by Genera Watznaueria, Micula, Arkhangelskiella, Cribrosphaerella, Eiffellithus, Predicosphaera, and Retecapsa, whilst the Paleocene assemblages are dominated by Genera Toweius, Ericsonia, and Coccolithus. Survivor Cretaceous species recovered into Tertiary sediments consist of Braarudosphaera bigelowii, Biscutum melaniae, Neocrepidolithus neocrassus, Placozygus sigmoides, Cyclagelosaphaera reinhardtii, Markalius inversus, and Scapolithus fossilis.

The Characteristics of Lahar in Merapi Volcano, Central Java as the Indicator of the Explosivity during Holocene Adjat Sudradjat; Ildrem Syafri; E. T. Paripurno
Indonesian Journal on Geoscience Vol 6, No 2 (2011)
Publisher : Geological Agency

DOI: 10.17014/ijog.v6i2.116Merapi Volcano in Central Java has been the most active volcano during Holocene time. As a strato volcano, Merapi exhibits alternating volcanic activities of effusive and explosive characters and self destruction. The explosivity index has evolved during the last ten thousand years. The effusive activities were characterized by the occurrence of lava flows, the development of lava dome, and the production of the “nuee ardente d’avalanche” called Merapi type. The explosive stage is frequently accompanied by the occurence of pyroclastic flows. The present investigation is attempted to reveal the relationship between the characteristics of lahar and the evolution of the activity of Merapi Volcano. The quantitative analysis was focused on the size and shape of the lahar components particularly that of pumice as the main indicators in 73 measured stratigraphic columns of lahar deposits. In addition, the main chemical element rim structures of hornblende identified in lahar components indicate the different lahar units. There are five lahar units and five groups of Merapi activities which can be distinguished. It can be concluded that the characteristics of lahar reflect the evolution of the activities in the past. The risk analyses of Merapi Volcano therefore can be enlarged to cover the possible hazard based on the lahar characteristics.

Fossilization Type of Elephas hysudrindicus from Blora on the Basis of Petrographic and Scanning Electron Microscopic Analyses Danny Z. Herman
Indonesian Journal on Geoscience Vol 6, No 2 (2011)
Publisher : Geological Agency

DOI: 10.17014/ijog.v6i2.117Either fossils of the hominid or vertebrate have long been known from terraces along the Solo River in Central and East Java. Most terraces consist of andesitic sand to andesitic tuffaceous sand with either gravelpebble or conglomerate and some of them contain vertebrate fossils. It is in this place, an ancient elephant fossil named Elephas hysudrindicus was discovered in 2009. This fossil was discovered at an abandoned sand quarry of Sunggun area, Medalem Village, Kradenan Subregency, Blora Regency which and can be mentioned as a great event for the Geological Museum. It was said as a phenomenal discovery, because the fossil was found within the terrace with condition of nearly complete skeleton of an individual elephant. Some bone fragments of Elephas hysudrindicus fossil is treated as rock specimens because a number of minerals fill in either pore spaces or cavities or cracks within bones, and such infilling minerals can be observed in cut sections of the bones. Main goals of the study are to determine the distribution and type of minerals within the bones, interpret environment of deposition, and identify fossilization type. The methodology used in this study consists of petrographic and Scanning Electron Microscopic (SEM) analyses. Based on the petrographical observation, some bone specimens of Elephas hysudrindicus fossil are characterized by fibrous and porous feature with cracks occuring locally. Whilst, examination with SEM shows that the bone specimens are apparently composed of collophane or massive cryptocrystalline variety of apatite as the principal component of fossil bone, having physical characteristic of spheroidal structure and cavities of 100 to 1500 micron (μ) in diameter. Most cavities and pore spaces are predominantly filled in by either authigenic crystals of rhombohedral calcite and lesser pseudohexagonal kaolinite with either slightly minerals of manganese oxide or iron oxide or ilmenite, including oxidized kaolinite and calcium iron silicate. Impregnation during diagenesis may be the most appropriate expression for fossilization process of the Elephas hysudrindicus. It is indicated by the existing authigenic minerals within the bones cavities, pore spaces, and cracks which are possibly due to precipitation of mineralized fluids originated from groundwater within the terrace.

Page 38 of 80 | Total Record : 796

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Contact Name
Ivan Ferdian

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Journal Mail Official
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Location
Kota bandung,

Jawa barat

INDONESIA