Regional Geology

by :
Anggoro Tri Mursito
Research Centre for Geotechnology
Indonesian Institute of Sciences (LIPI)
Jl. Sangkuriang, Komplek LIPI Gedung 70, Bandung 40135
anggoro@geotek.lipi.go.id

abstract
An artificial soil mixed made out of electrical-coal power plant wastes (fly ash) and material from the coal mine sites (clay and gravel G5) has been created for the reclamation of open pit mine site. Physico-chemical properties were measured over time to examine them in a chronosequence of 22 plots (each 400m2) with systematically changing mixtures (1,2 and 3 components of varying proportions were established and planted. In the field plots, available nutrient content was initially high but established only for some of plots. Due to ecological function measurement, physical parameter, which is hydraulic conductivity, is one of several physic properties will have to be monitored and analysed.
According to the development value of the year of 2003 (spring) shows that increasing of water permeability classes (class 6) is leaning to the direction of fly ash and tegel (clay) composition. Class 5 are only in the trial plot number 5 and 9. Only in one trial plot which is drop in class 4 (trial plot 16), but it is still classified into “good” class (according to “Arbeitskreis Standortskartierung, 1996”). The trial plot number 1 has also classified into class 6, because the substrate composition in this trial is only 100% of gravel. It has to be the highest class, but it is not always the highest value of water permeability. All the trial plots are classified into high to very-very high. Compared results between initial (spring, 2000) and recent measurement (spring, 2003) is shown that extremely increased in the trial plot 3 and 13. In the year of 2003, in trial plot number 3 and 13 are suddently flare up to 4 classes (from class 2 to 6). As also analysed by Computed Tomography images of one component substrate (100 % of tegel) shows that cracked structures clearly appear as a results of decreasing precipitation in the last winter and also highly increasing of temperature as well. High percentage of cracked means that water can easily flows. Most of the trial plots are increasing of classes due to the season differences. The others (trial plot number 1, 5, 6 and 9) remain in the same class.

Same grade doesn’t means that same value of water permeabilty as well, but e.g. trial plot 1 has same class compared to the result in 2000 and that means very very high.

From : The 33rd Annual Convention & Exhibition 2004 Indonesian Association of Geologist

Asnawir Nasution1), Akira Takada2), Rosgandika Mulyana1)
1)Directorate of Volcanology and Geological Hazard Mitigation, Indonesia
2)Geological Survey of Japan

ABSTRACT
The eruptive history of Rinjani voclano during the last 10 ky before the caldera formation was studied. The eruption rate of Rinjani volcano was kept constant (0.6 km3/ky) during a stratocone building stage between 12-6 ka. It decreases becoming 0.15 km3/ky for the last period of 5.2 ky before the caldera forming eruption (6-8 ka). During the low activity stage, three eruptions occured; Propok Pumice and Lembar Lava Flow (DRE: 0.1 km3 and 0.4 km3, respectively), Rinjani Ash and Rinjani Pumice (DRE: 0.3 km3). The magma path shifted 5 km toward the eastern flank to grow Rinjani volcano. The volcanic activity migrated more 5 km eastward for low activity stage, erupting Propok Pumice and Lembar Lava Flow. The activity migrated back to Rinjani summit yielded ash and pumice. Syn¬caldera stage started with plinian pumice (DRE: 3 km3) and a huge pyroclastic flow (DRE: >7 km3), and, finally, Segara Anak caldera of 6 km x7 km was formed at the center of Central Lombok Volcanic Complex. 14C datings indicates that the climax of caldera forming eruption was the periode of AD 1210-1 300 years B.P., which is the third youngest caldera in Indonesia.
Keywords: caldera, pyroclastic flow, Plinian eruption, eruptiion rate, Rinjani volcano, Lombok island

From : The 33rd Annual Convention & Exhibition 2004 Indonesian Association of Geologist

Asran Ilyas, Adi Ton ggiroh, Agustinus T*
Geological Engineering, Hasanuddin University, Makassar, South Sulawesi, INDONESIA
asranjlyas@yahoo.com, adi_unhas@yahoo.com

ABSTRACT
On mining process in the ore zone of laterite nickel deposit in Sorowako area then needed the prediction of the deposit in lateral continuity in underground. This prediction is very important in order to create the section of lateral continuity of laterite nickel deposit in underground between the nearest of two drill points in order to get the mining process effectively and efficiently. One of the prediction technique that could be develope is by using the minerals content series from top to bottom from the outcome of the logging data’s between the nearest of two drill points by using geological and statistical approach. From the outcome of the prediction, it is get that this prediction technique is good enough and could be applied and developed for the mining process needed and developing of science and technology in the future.
Keywords : prediction, minerals content series, geological and statistical approach.

From : The 33rd Annual Convention & Exhibition 2004 Indonesian Association of Geologist

Awang H. Satyana 1), Edward Erwanto 1), C. Prasetyadi 2)
1) Exploration Division, Badan Pelaksana Migas, Jakarta
2) Geology Department, University of Pembangunan Nasional Veteran, Yogyakarta

Abstract
A major wrench zone, left-lateral slip in nature, strongly deformed a series of Late Oligocene to Pleistocene rocks in the northern coastal line of East Java and its eastern islands and offshore areas. The fault zone trends west – east forming a deformed zone of 15 to 40 km wide and 675 km long from Rembang area in the west through Madura Island and Kangean Islands to Sakala offshore area in the east. The deformed zone is called the Rembang-Madura-Kangean-Sakala (RMKS) Fault Zone.
Based on the regional setting of East- and Southeast Sundaland, it is known that the RMKS Fault Zone occurred at the hinge belt or shelf edge to slope area of a geologic transition from the stable Eastern Sunda Shelf to the north (the Northern Platform) to the deep-water area to the south. There is a contrast of sedimentary facies to the north and south of the RMKS Fault Zone. Tectonically, the stable Eastern Sunda Shelf is considered to overlie the expected micro-continent called the Paternoster¬Kangean. Therefore, the RMKS Fault Zone is located at the southern margin of the micro-continent. Basement lithology and configuration to the north and south of the RMKS Fault Zone are different.
A number of mechanisms are considered to origin the RMKS Fault Zone. These include : the westward stress driven by the collision of the Buton-Tukang Besi and Banggai-Sula to the east of Sulawesi, westward stress due to the collision of Australia with Timor and anti-clockwise bending of the Banda Arc, and northward stress due to the subduction of the Indian oceanic crust beneath Java. The initiation of the RMKS Fault Zone was in the upper Early Miocene in Sakala area and younger westward until the Middle Miocene in Rembang area.
Along the RMKS Fault Zone, flower structures are definitely identified on seismic sections, showing basement-involved, deeply-rooted vertical master faults with upward diverging splays/strands that have mostly reverse separations. In map view, these splays are mapped as fold and fault belts trending west-east and west northwest-east southeast. Extensional component of the wrench zone subsided the Paleogene rifted blocks such as the Central Deep and formed a number of normal faults. Tectonic inversion related with both pure and simple shear deformations is observed along the fault zone. Shale diapirism commonly occurs to the south of the fault zone and its occurrence is related to wrench tectonism in thick shale sequences deposited rapidly to the south of the RMKS Fault Zone.

From : The 33rd Annual Convention & Exhibition 2004 Indonesian Association of Geologist

Bambang Nugroho Widi* ), Sudarsono**)
*) Direktorat Inventarisasi Sumber Daya Mineral, Bandung
**)Puslitabang Geo-Teknologi LIPI, Bandung

Abstract
Tungsten mineralization occurrences in the Suguntu area, Latupa form an unique mineralization to study, particularly in the Indonesia Archipelago geological setting. It is usually occurred commonly in the continental or cratonic environment granitic rock. The presence of gold and a number of other sulfide- oxide minerals such as arsenopyrite, chalcopyrite and mangan as mineral association make the mineralization become more interesting and important in this region. Mineralization in this area is indicated by the presence of tungsten mineral (wolframite) bearing quartz vein intruding the granitic and metasediment host rocks. The vein trend is generally of about N 170 ° E to 190° with dip of about 70° to 90° with thickness from few centimeters to nearly 20 centimeters. Altered rocks type present in this area involve argil itization, propyl itization, seritization (phyll ic). Silicification found locally, particularly near to the vein. Based on the physical appearrence on the specimens, minerals association recognized are cahalcopyrite, pyrite, magnetite, hematiti and mangan. It seem mineralization formed in the mesothermal environment, at depth lower than epithermal zone (more than 500 meters below the paleosurface) with temperature formation > 300°. However, in order to ensure this suggestion, study on geochemistry, ore microscopy, fluid inclusion, petrography, pima, etc, are hughly needed to obtain an imagination clearly in connection to know the relationship between tungsten (wolfram) and gold mineralization.

From : The 33rd Annual Convention & Exhibition 2004 Indonesian Association of Geologist

Bambang Tjahjono Setiabudi
Directorate of Mineral Resources Inventory
E-mail: BTSetiabudi@hotmail.com

ABSTRACT
Mineral Resource Assessment is a field of research and application of quantitative appraisal methods to evaluate potential mineral resources. Principally it describes mineral deposits, measures their grade and tonnage, estimate the occurrence of the undiscovered deposits and estimates mineral resources in the permissive tracts. The main objectives are to outline the principal areas in Indonesia that have potential for selected undiscovered mineral resources and to estimate the probable amounts of those mineral resources to a depth of 1 km below the earth’s surface. The assessment is carried out using the USGS 3-Part Quantitative Mineral Resource Assessment Method. The 3-part method consists of firstly, delineating tracts for commodities and porphyry Cu deposit types based on the geology of the ore deposits, secondly, estimating the amount of resources contained in the undiscovered deposits using appropriate ore characteristics and metal contents based on grade and tonnage models and thirdly, estimating number of undiscovered deposits of each type for each delineated area. Overview of porphyry copper resources in Indonesia as the results of mineral assessment includes standardized database for known mineral deposits and occurrences, digital regional-scale maps of tracts permissive for current known deposits as well as undiscovered mineral resources, and estimates of undiscovered mineral resources within permissive tracts for copper (copper-gold).

From : The 33rd Annual Convention & Exhibition 2004 Indonesian Association of Geologist

By :
Binarko Santoso and Bukin Daulay
R and D Centre for Mineral and Coal Technology
Jalan Jenderal Sudirman 623 Bandung 40211
Ph. 022-6030483, fax. 022-6003373, email binarkos@tekmira.esdm.go.id

ABSTRACT
Study on organic petrology was carried out on both East and South Kalimantan Palaeogene and Neogene coals. West and Central Kalimantan coals are ignored in the study, because their geological conditions are not favourable and the seams are usually thin and generally rich in argillaceous or arenaceous mineral matter.
Similarities and differences in type and rank characteristics in the coals reflect their geological setting. Rank and type variation of the coals were assessed by petrographic examination of 40 samples. The coals are dominated by vitrinite, common exinite and rare inertinite and mineral matter. The type differences reflect climatic influence and differences in peat conditions.
Rank of the coals depends largely on the geological age and the level of temperature under confining pressure (burial depth). Increased depth of burial and increased temperature and pressure over a period of time, consequently result in higher rank. Reflectance measurements on the coals indicate that there is a substantial difference in rank between Palaeogene and Neogene coals. The Palaeogene coals are sub-bituminous to high volatile bituminous rank (Rvmax of 0.53- 0.67%), whereas Neogene coals are brown to sub-bituminous rank (Rvmax of 0.30-0.57%), according to the Australian classification.

From : The 33rd Annual Convention & Exhibition 2004 Indonesian Association of Geologist

Bob W.H. Adibrata(1), Y. Hirosiadi(2), E. Septama(3), A. Rachmanto(4)
1bobwikan@pertamina.com, 2yosihiro@pertamina. com, Geology Section, Technology Support Division,
Pertamina Upstream, Kwarnas Bld 15th Fl, Jl. Medan Merdeka Timur No. 6, Jakarta 10110 INDONESIA
3erlangga@pertamina-sumbagteng.com, Exploitation Section, Pertamina DOH Sumbagteng, Bajubang, Jambi
36611, INDONESIA
4ambar@pertamina-dohsbs. com, Recent address: Exploitation Section, Pertamina DOH Sumbagsel, Prabumulih,
Sumatera Selatan, INDONESIA

Abstract
Focus of this study is re-activity of a non-economic field into production by combining old vintage 2D seismic data with current 3D seismic data, supporting with archival, conventional log data and limited sidewall core and thin section analysis. The reservoir consists of bioclastic wackestone overlying by coral bindstone in the Upper Miocene Equivalent of Baturaja Formation, at Ketaling Barat field, Jambi, Indonesia. The objective of this study is to evaluate and test a multiple attribute analysis whereby carbonate facies can be determined and to characterize the distribution of potential carbonate reservoir.

From : The 33rd Annual Convention & Exhibition 2004 Indonesian Association of Geologist

Engkon K.Kertapati
Geological Research and Development Centre

Abstract
The low-seismicity Central Kalimantan has never experienced any earthquake damage. Thus, earthquake-resistant design has not been specifically required in the building codes. However, it has been
realized that urban and mine areas located rather distantly from earthquake sources may also be affected by tremors. The key is basically determined by how well seismic hazards derived from seismic potency can be estimated. In this paper, the potential ground motion in terms of the peak ground accelerations ( PGAs) due to long – distance East Kalimantan and West Sulawesi earthquakes ( far field earthquake ) is investigate, following a probabilistic seismic hazard assessment approach. Earthquakes that have occurred in radius of 500 km ( far field ) in the last 50 year are used. Based on the PGAs of more than 50 % East Kalimantan and West Sulawesi earthquakes recorded in Central Kalimantan, the attenuation relationship of Fukushima and Tanaka ( 1992 ) is found to correlate well with the high-rate attenuation characteristic of the region. The predicted design basis PGA for Tailings Dam , i.e. PGA with 10 % probability of being exceeded in a 50-year exposure time, on rock out-crops site is 0.041 g ( g = gravity value ), or 0.103 g on soft soil. And 0.105 g with 10 % probability of being exceeded in a 1000 year exposure time on rock out-crops or 0.261 g for soft soil. However, the increasing number of felt tremors in recent years demonstrates such as: Muarateweh Earthquake, which occurred on July 05, 1996, that although no significant damage was report, the earthquake was strongly felt.
Keywords: ground acceleration, ground-motion, attenuation function, earthquake- resistant design

From : The 33rd Annual Convention & Exhibition 2004 Indonesian Association of Geologist

Eko Soebowo, Herryal Z. Anwar, Dwikorita Karnawati
Pusat Penelitian Geoteknologi – LIPI

Abstract
Kebumen Region and others Southern Part of Central Java have a long history on landslide hazard occurrences. Landslides in this area are influenced by the litological condition, morphology, structure, hidrology, rainfall and others factor. Therefore, landslides potential area information is primarily important to design the effective mitigation system. Engineering geological study which has been done in this area indicate that landslides distribution concentrate mainly at Ayah-Karangbolong-Alihan-Rowokele area, at litological unit of weathered volcanic breccia with structures zone at this area, and at contact zone between this rocks and sedimentary rock. Whereas at Tugu, Panusupan, Sambeng, North Karangsambung at litology marly clay and tuffaceous sandstone and phyllite. The landslide tipical is generally debris flow, slump and creeping. The result of this study are useful to design the mitigation strategy of landslide hazard and also may be used for land conservation requirement, particularly to develop a Master Plan of this area.

From : The 33rd Annual Convention & Exhibition 2004 Indonesian Association of Geologist