Buletin Sumber Daya Geologi

DELINEATION OF RESISTIVITY VALUE IN GEOTHERMAL TAMBANG SAWAH USING MAGNETOTELLURIC METHOD

Andre Rahmat Al Ansory — 2023-11-29

The subsurface structure of the geothermal field in Desa Tambang Sawah has been mapped. This research aims to delineate the resistivity values in the area of Tambang Sawah Village, Lebong Regency, Bengkulu Province based on magnetotelluric measurements which can later identify low, medium, and high resistivity values to interpret geothermal in the research area. The magnetotelluric (MT) method with electrical and magnetic sensors is used to collect data in the field. There are two electrical sensors in horizontal direction (Ex, Ey) and three magnetic sensors in horizontal direction. (Hx, Hy) and vertical (Hz). The results obtained from this study are that resistivity values of 20-50 ohm.m are considered as reservoirs, while resistivity of 0.26-0.8 ohm.m is considered as caprock, and resistivity greater than 300 ohm.m is considered as hot rock.

SUMBER DAYA DAN KARAKTERISTIK ENDAPAN PASIR BESI DI CIHERAS, KABUPATEN TASIKMALAYA

Teuku Ishlah — 2024-01-04

Iron is a metal commodity that is widely used in human civilization, and is now used as a raw material for making steel and a mixture of raw materials for cement. Therefore, research activities on iron sand deposits are still needed, especially in ex-mining areas that are interesting for re-examination, because increase of metal price, so decrease the cut off grade for iron sand concentrate mining and the possibility of the presence of other high value minerals.

The research location is located in Ciheras Village, Cipatujah District, including Block Ciheras-1, Block Ciheras-2, and Block Cikalong, Cikadu Village, Cikalong District, Tasikmalaya Regency, West Java Province. The aim of this research is to determine the availability, quality and estimation of inferred resources for iron sand deposits.

The research used geological mapping methods, and sampling using a hand auger at a distance of 400 meters between drilling points in the direction of the base line and 40 meters in the direction of the cross line. A total of 71 points were drilled to a depth of between 2.0 meters to 4.0 meters and samples of iron sand were taken for laboratory analysis including specific gravity (BJ), magnetic percentage (MD), sieve/grain fraction analysis, grain mineralogy analysis, XRF , AAS, and colorimetry.

The calculation results for the iron sand resources of the Ciheras-1 Block are 257,138 tonnes, the Ciheras-2 Block is 512,199 tonnes, and the Cikalong Block is 491,970 tonnes, bringing the total to 1,261,308 tonnes. Average percentage of magnetism in the Ciheras-1 Block; 24.02%, Ciheras-2 Block; 14.7%, and Cikalong Block; 8.01%. These iron sand deposits come from rocks and ash from volcanic eruptions which are transported by river water to estuaries and deposited on beaches. High economic value elements in the form of Titanium and Vanadium in beach sand deposits in the research area whose levels and occurrence are comparable to the element Fe.

DERAJAT LATERITISASI DAN PENGAYAAN UNSUR FE-NI-CO PADA BATUAN HARSBURGIT DI PULAU SEBUKU, KALIMANTAN SELATAN

Fasya Zahra Fauziyyah Ramdani — 2024-01-04

The tropical climate in Indonesia causes a high level of chemical weathering or lateritization of ultramafic rocks which results in the enrichment of economic elements such as Fe, Ni and Co. These elements accumulate in the limonite and saprolite zones. This research was conducted on Sebuku Island which composed of ultramafic rocks, especially harzburgite. This study aims to determine the effect of the degree of lateritization in the limonite, saprolite and bedrock zones on the enrichment of economic elements. A number of 95 samples collected from 9 drill holes and analyzed using XRF to determine the main elements and economic elements. The degree of lateritization is calculated from the SiO₂ content divided by the total accumulation of SiO₂, Al₂O₃ and Fe₂O₃ resulting the S/SAF index which describes the intensity of the chemical reaction. The lowest value of the S/SAF index indicates a higher degree of lateritization. Each limonite, saprolite and bedrock zone has S/SAF index values ranging from 0.16 to 58 (strong lateritization), 0.27 to 0.85 (medium lateritization-kaolinization) and 0.77 to 1.24 (mother rock). The zone with a strong degree of lateritization contains Fe levels between 36% to 51%, Ni 0.80% to 1.38% and Co 0.07% to 1.17%. The bedrock contains 4.86% to 7.99% Fe, 0.20% to 1.76% Ni and 0.005% to 0.015% Co. The degree of lateritization in the limonite zone is higher than the saprolite and bedrock zones. This is caused by the decomposition of silica minerals to form the iron and aluminum oxide-hydroxide bearing minerals. The degree of lateritization has a positive correlation with the enrichment of Fe and Co. However, the distribution of high Ni not correlated with the index of lateritization.

KARAKTERISTIK ENDAPAN BIJIH BESI LATERIT PADA BLOK BARAT DAN BLOK TIMUR PT SILO, KABUPATEN KOTABARU, KALIMANTAN SELATAN BERDASARKAN ANALISIS GEOKIMIA DAN MINERALOGI

Ayumi Hana Putri Ramadhani — 2024-01-08

This research was conducted to identify the characteristics of laterite deposits in the western and eastern blocks of Sebuku Island, Kotabaru Regency, South Kalimantan using field observation methods, and laboratory analysis including titration, XRF, XRD and petrography analysis. The characteristics of the western block laterite deposits are 10 meters until 15 meters deep. The red limonite zone has Fe content of 51.25% with a mineral composition of hematite, magnetite, goethite, ilmenite, spinel. The yellow limonite zone has Fe content of 50.1% with a mineral composition of goethite, hematite, gibsite, ilmenite. The saprolite zone has Fe content of 16.2%, the mineral composition is hematite, chrysotile, goethite, garnet, diopside. The characteristics of the eastern block laterite deposits are that they have a depth of 6 meters until 7.5 meters. The red limonite zone has Fe content of 47.38% with a mineral composition of hematite, goethite, ilmenite, spinel. The yellow limonite zone has Fe content of 38.70% with a mineral composition of goethite, hematite, chromite, gibbsite, spinel. The saprolite zone has Fe content of 15.08%, the mineral composition is hematite, goethite, diopside, fayalite. The bedrock of the research area is in the form of periodotite, namely dunite and harzburgite which have been serpentinized. The mineral composition of the bedrock is olivine, pyroxene, opaque minerals and several secondary minerals, namely serpentine and talc. The west block bedrock has Fe content of around 7.73 % until 8.03% while the east block bedrock has Fe content of around 6.59 % until 7.49%.

REKOMENDASI AREA LOKASI TAPAK SUMUR EKSPLORASI PANAS BUMI MENGGUNAKAN PEMODELAN SISTEM INFORMASI GEOGRAFIS DI DAERAH PROSPEK CISOLOK-CISUKARAME, SUKABUMI, JAWA BARAT

Husin Setia Nugraha — 2024-01-08

The use of Geographic Information System (GIS) modelling in developing geothermal resources has been widely carried out, from the initial survey and exploration to exploitation or production stages. This GIS modelling aims to delineate specific locations that are considered to have geothermal resources or are suitable for geothermal field production facilities. This study aims to obtain a map of the recommended wellpad area for the optimal geothermal exploration well drilling location by considering technical and non-technical parameters. This research was conducted in the Cisolok-Cisukarame geothermal prospect area in Sukabumi Regency, West Java Province. The map is produced by integrating eight parameters that will affect the amount of drilling costs: prospect area, slope, reservoir crest depth area, geological structure, water source, access road, settlement area, surface manifestation area, and cultural heritage area. In the early stages, buffer areas and classifications were made for these parameters with a specific range of values based on several considerations. Furthermore, spatial data integration is carried out using vector overlaying boolean operations. The result is a map of the wellpad recommendation area for geothermal exploration wells in the Cisolok-Cisukarame area, with an area of approximately 6.31 km² (19.62% of the P₉₀ prospect area). Using a 120-meter fishnet produces eight large cluster areas and five small cluster areas, which are suitable for wellpad of standard hole. Meanwhile, the 50-meter fishnet produces the same number of clusters and five other smaller clusters. The results of this study can be used as recommendations for areas to be used as well as footprint locations and planning for further field survey activities such as geotechnical and infrastructure surveys.