Analytical Hierarchy Process (AHP) is a Multi Criterion Decision Making (MCDM) Technique. It can handle any complex, multicriterion, and multiperson problems. In AHP, the problems are decomposed into a hierarchically structure and are given the weights according to its importance. Thus, the strength with which one alternative dominates another with respect to a given criterion can be identified. The output is a priority ranking indicating the overall preference for each decision alternative. This paper describes the application of AHP to select a geothermal prospect in Sulawesi Island to be developed in the near future. The alternatives consist of three geothermal prospects. i.e., Suwawa, Pulu, and Marana. Three major criteria are used and applied into those three prospects: Geoscience, Infrastructure, and Social-culture aspects. Under each of these major criteria, there are several subcriteria. Geoscience criterion which consists of Resources, Geothermal System, and Geological Risk Subcriteria is given the highest weight with the assumption that if resources are large and can be developed commercially, then there is no reason not to be exploited; the technology and other infrastructure aspects are no longer an obstacle. The result shows that Suwawa Prospect is the best option to be developed in the near future. The second option or rank is Marana Prospect, and the third is Pulu Prospect. This result is in agreement with the future plan of the development of Sulawesi Island. If the regulation and plan of development were suddenly changed, the goal of this AHP might not be appropriate anymore, and the second or third option might replace the first rank. The benefits of using AHP are (1) the facts and reasons behind the decision are well documented, (2) able to handle quantitative and qualitative inputs, (3) able to accommodate environmental, social and other influences, and (4) able to handle subjective judgments of individuals. Lessons learned from AHP application for geothermal prospect selection could be extended into multi criterion decision making at a group level.
Keywords: AHP, MCDM, geothermal prospect, geological risk
Gajahmungkur 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.
Keywords: Gajahmungkur paleovolcano, statistical interrelation, volcanic facies, Old Andesite
In order to gain insights into the detailed physical disintegration characteristics of various types of mudrock, a series of static slaking exposure and immersion tests were carefully carried out in this study. The intent of this paper is to exhaustively describe and discuss the results of the tests, including slaking mechanism, mode and rate/intensity. In general, it can be obviously identified that there are significant different susceptibilities of each mudrock tested to slake-disintegration. These differences can not only be identified from the results of slaking exposure test but also from slaking immersion test. It seems that there is also an agreement in both testing results, which show that the most resistant mudrock to slaking was Ikeshima shales, and was comparatively, followed by Ombilin siltstones, Tanjung Enim mudstones-claystones, and Subang claystones as the worst slaking characteristic. The detailed differences in fundamental characteristics of physical disintegration characteristics will further widely be discussed in this paper.
Keywords: disintegration, mudrock, exposure, immersion, slaking test
Rinjani is the second highest volcano in Indonesia with an elevation of 3726 m above sea level. The steep and highest cone of Rinjani consists mainly of loose pyroclastic ejecta and contains a crater with a few solfataras. The West of this cone is Segara Anak caldera. The western side of the caldera is occupied by a 230 m deep lake, covering an area of 11 km² and its volume was (before the 2009 eruption) estimated 1.02 km3. This is probably the largest hot volcanic lake in the world.The lake water is neutral (pH: 7-8) and its chemistry dominated by chlorides and sulfates with a relatively high TDS (Total Dissolved Solids: 2640 mg/l). This unusual TDS as well as the lake surface temperatures (20 - 22°C) well above ambient temperatures(14 - 15°C) for this altitude, reflect a strong input of hydrothermal fluids. Numerous hot springs are located along the shore at the foot of Barujari volcanic cone. Bathymetric profiles show also several areas with columns of gas bubbles escaping from the lake floor indicating a significant discharge of CO gas into the
lake. The mass and energy balance model of Rinjani Crater Lake produce total heat lost value on the average of 1700 MW. Most of the heating periods of the lake occurred when the heat released by the surface of the lake to the atmosphere was lower than the heat supplied from the hydrothermal system. Peaks of heat losses correspond to period of strong winds. Crater lake monitoring can provide a basic information about deep magmatic activity and surface processes that occur in the volcano. The monitoring also contributes to predict the next eruption in order to improve mitigation of volcanic eruption. Precursory signals of the May 2009 eruption can be seen from significant changes in the temperature and chemistry of some of the hot springs, the increase of Fe concentrations in spring #54, chemical plume of low pH and dissolved oxygen, acidification of Segara Anak Lake, and increasing of lake surface temperatures. The new lava flow from May - August 2009 eruption covers an area of 650,000 m2. The shoreline was significantly modified by the entry of lava into Segara Anak Lake. The area of the lake is reduced by 460,000 m2.
Keywords: geochemical, thermodinamic modeling, Segara Anak, Rinjani
The 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.
Keywords: alteration, vein texture, gold mineralization, Bunikasih
The 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.
Keywords: coal, features, paleo-depositional, Bukit Asam coalfield, South Sumatra