Integrative Analysis of the Geothermal Structure in Kepahiang: Insights from Magnetotelluric, Gravity, and Remote Sensing Techniques

This research was conducted to determine the structure and depth of the reservoir using remote sensing as an initial survey to assess the geological alignment direction, employing ALOS PALSAR radar imagery. Subsequently, further surveys were conducted using the magnetotelluric and gravity methods to analyze the structure and depth of the geothermal reservoir. The magnetotelluric data were processed using Phoenix software, where the data was transformed from the time domain to the frequency domain using Fourier transformation, and processed to obtain apparent resistivity and phase. The MT data was integrated with gravity data, and the gravity data underwent standard correction procedures to obtain the Complete Bouguer Anomaly (CBA) map. Two-dimensional (2D) inversion using the NLCG algorithm and 2D forward modeling of the gravity data were performed. The dominant alignment pattern obtained was northwest-southeast, with an orientation of 320° NW or 140° SE. Based on the results of geological alignment, a profile is produced that is perpendicular to the straightness. The results from the 2D inversion and gravity forward modeling indicated that the geothermal reservoir is likely located beneath the caprock at an estimated depth of approximately 1800 m, with resistivity values ranging from 32 to 256 Ohm-m and a density value is 2.6 gr/cc.This research was conducted to determine the structure and depth of the reservoir using remote sensing as an initial survey to assess the geological alignment direction, employing ALOS PALSAR radar imagery. Subsequently, further surveys were conducted using the magnetotelluric and gravity methods to analyze the structure and depth of the geothermal reservoir. The magnetotelluric data were processed using Phoenix software, where the data was transformed from the time domain to the frequency domain using Fourier transformation, and processed to obtain apparent resistivity and phase. The MT data was integrated with gravity data, and the gravity data underwent standard correction procedures to obtain the Complete Bouguer Anomaly (CBA) map. Two-dimensional (2D) inversion using the NLCG algorithm and 2D forward modeling of the gravity data were performed. The dominant alignment pattern obtained was northwest-southeast, with an orientation of 320° NW or 140° SE. Based on the results of geological alignment, a profile is produced that is perpendicular to the straightness. The results from the 2D inversion and gravity forward modeling indicated that the geothermal reservoir is likely located beneath the caprock at an estimated depth of approximately 1800 m, with resistivity values ranging from 32 to 256 Ohm-m and a density value of 2.6 gr/cc

Identification of gold mineralization zones of low sulfidation epithermal systems using geoelectrical and magnetic methods in Ciparay area, Cibaliung

Abstrak. Cibaliung merupakan daerah pertambangan mineral yang berada di Provinsi Banten. Hal ini, dibuktikan dengan adanya lubang tambang emas di daerah Cikoneng dan Cibitung. Penelitian tentang geofisika penting dilakukan guna menemukan cadangan emas baru di daerah Ciparay yang terletak di Sebelah Tenggara Cikoneng dan Cibitung. Metode geofisika yang digunakan di antaranya magnetik, resistivitas, dan induced polarization (IP). Metode magnetik digunakan sebagai survei pendahuluan untuk menggambarkan keberadaan struktur geologi pengontrol mineralisasi emas. Melalui peta reduce to pole dapat diketahui adanya tanda-tanda keberadaan struktur geologi yang ditunjukkan oleh anomali negatif (-220 hingga -135 nT) di Bagian Barat Daya daerah penelitian. Hasil teknik edge detectors menunjukkan adanya pola struktur dengan arah Northwest (NW) dan North-Northeast (NNE) yang dominan berada di Bagian Barat Daya sebelah Utara daerah penelitian. Metode resistivitas dan IP digunakan sebagai survei detail untuk menentukan keberadaan mineral yang terkandung dalam batuan. Hasilnya menunjukkan bahwa zona potensi mineralisasi ditunjukkan oleh anomali tinggi (resistivitas 50 ohm.m dan chargeability 40 msec). Resistivitas tinggi diduga sebagai respons batuan induk andesitic sedangkan, nilai chargeability tinggi merupakan respons dari hadirnya mineral-mineral bijih seperti emas dan perak. Zona potensi mineralisasi berada pada posisi patok 350-800 dengan arah persebaran mengikuti arah struktur geologi pengontrolnya yaitu NW dan NNE. Abstract. Cibaliung is a mineral mining area located in Banten Province. The area including gold mining in Cikoneng and Cibitung areas. Geophysical research is important to find new gold reserves at the Ciparay area, located in the Southeast of Cikoneng and Cibitung. Geophysical methods used include magnetic, resistivity, and IP. The magnetic method was applied as a preliminary survey to delineate the presence of the geological structure controlling the gold mineralization. Based on the RTP map, signs of the presence of geological structures are shown by anomalies -220 to -135 nT in the Southwestern part of the study area. The results of edge detector techniques show the existence of structural patterns in the direction of NW and NNE which are dominant in the Southwestern North of the study area. The resistivity and IP methods are employed for detailed investigation in order to obtain to determine the presence of minerals contained in rocks. The results show that the mineralized zones are indicated by high resistivity ( 50 ohm.m) and high chargeability ( 40 msec). High resistivity response is caused by andesitic source rock whereas, high chargeability response is related to the presence of ore minerals such as gold and silver. The mineralization prospect zone is indicated at the position of 350-800 and its direction corresponds to the direction of its geological structure namely NW and NNE.Keywords: New gold reserves, Negative magnetic anomalies, High resistivity, High chargeability.

Penentuan Anomali Gayaberat Regional dan Residual Menggunakan Filter Gaussian Daerah Mamuju Sulawesi Barat

Gravity method is a geophysical method that has been frequently used in prospecting mineral resources. The parameter of searched object is based on variations of gravity acceleration measurements on the surface due to variations in sub-surface geological changes. Research area is located in Mamuju Area of West Sulawesi Province where tectonically a complex geological region, which is at a meeting of three large plates, the Pacific plate, the Indo-Australian plate and the Eurasian plate and the smaller Philippine plate. In addition, Mamuju is an area with a high radioactivity dose rate that has potency to radioactive minerals resources. The purpose of the research is to obtain gravity anomalies by using qualitative separation and interpretation of regional and residual gravity anomalies. Complete Bouguer Anomaly (CBA) value of the research area obtained from the measurements was 46.0 – 115.7 mGal. Based on the CBA map, the separation process of regional gravity anomalies and residual using Gaussian filtering technique conducted. This filtering technique works based on spectral analysis of gravity amplitude changes in spatial where the result is a cutoff wave number of 1.1736 x 10-3/meter and a wavelength of 5373.45 m. The regional and residual gravity anomalies range from 51.8 to 102 mGal and -10.4 to 14.8 mGal respectively. The depth of influence of each anomaly is calculated based on their spectral wavelengths, resulting 970.97 m and 100.21 m for regional and residual anomalies respectively. There are five zones based on the residual anomaly map, which are zones A, B, C, D and E. The heaviest positive gravity anomaly is found in zone A and B, which is predicted to be influenced by Adang lava with relative north – south distribution

Penentuan Anomali Gayaberat Regional dan Residual Menggunakan Filter Gaussian Daerah Mamuju Sulawesi Barat

AbstrakMetode gayaberat merupakan metode geofisika yang sudah sering digunakan dalam prospeksi sumberdaya mineral. Parameter objek pencarian berdasarkan variasi pengukuran percepatan gayaberat di permukaan yang diakibatkan oleh variasi perubahan geologi bawah permukaan. Lokasi penelitian di daerah Mamuju Provinsi Sulawesi Barat yang secara tektonik merupakan wilayah geologi kompleks berada pada pertemuan tiga lempeng besar yaitu Pasifik, Indo-Australia, dan Eurasia serta Lempeng Filipina yang berukuran lebih kecil. Selain itu Mamuju merupakan wilayah dengan laju dosis radioaktivitas tinggi sehingga berpotensi memiliki sumberdaya mineral radioaktif. Tujuan dari penelitian adalah mendapatkan anomali gayaberat dengan cara melakukan pemisahan dan interpretasi secara kualitatif anomali gayaberat regional dan residual. Nilai Anomali Bouguer Lengkap (ABL) daerah penelitian yang didapat dari hasil pengukuran adalah 46,0 – 115,7 mgal. Berdasarkan peta ABL tersebut proses pemisahan anomali gayaberat regional dan residual dilakukan dengan menggunakan teknik Gaussian Filtering. Teknik filtering ini bekerja berdasarkan analisis spektrum perubahan amplitudo gayaberat secara spasial yang hasilnya berupa bilangan gelombang dengan cutoff sebesar 1,1736 x 10-3/ m dan panjang gelombang sebesar 5373,45 m. Anomali gayaberat regional dan residual berturut-turut memiliki rentang nilai 51,8 sampai 102 mGal dan -10,4 sampai 14,8 mGal. Kedalaman wilayah spektrum masing-masing anomali tersebut dapat dihitung berdasarkan panjang gelombangnya yaitu anomali regional sebesar 970,97 m dan anomali residual sebesar 100,21 m. Terdapat lima zona berdasarkan peta anomali residualnya yaitu zona A, B, C, D, dan E. Anomali gayaberat positif paling besar terdapat pada zona A dan B yang diperkirakan dipengaruhi oleh keberadaan lava Adang dengan arah penyebaran relatif utara – selatan. AbstractGravity method is a geophysical method that has been frequently used in prospecting mineral resources. The parameter of searched object is based on variations of gravity acceleration measurements on the surface due to variations in sub-surface geological changes. Research area is located in Mamuju Area of West Sulawesi Province where tectonically a complex geological region, which is at a meeting of three large plates, the Pacific plate, the Indo-Australian plate and the Eurasian plate and the smaller Philippine plate. In addition, Mamuju is an area with a high radioactivity dose rate that has potency to radioactive minerals resources. The purpose of the research is to obtain gravity anomalies by using qualitative separation and interpretation of regional and residual gravity anomalies. Complete Bouguer Anomaly (CBA) value of the research area obtained from the measurements was 46.0 – 115.7 mGal. Based on the CBA map, the separation process of regional gravity anomalies and residual using Gaussian filtering technique conducted. This filtering technique works based on spectral analysis of gravity amplitude changes in spatial where the result is a cutoff wave number of 1.1736 x 10-3/meter and a wavelength of 5373.45 m. The regional and residual gravity anomalies range from 51.8 to 102 mGal and -10.4 to 14.8 mGal respectively. The depth of influence of each anomaly is calculated based on their spectral wavelengths, resulting 970.97 m and 100.21 m for regional and residual anomalies respectively. There are five zones based on the residual anomaly map, which are zones A, B, C, D and E. The heaviest positive gravity anomaly is found in zone A and B, which is predicted to be influenced by Adang lava with relative north – south distribution

Application of Time Domain Induced Polarization (TDIP) Methods to Metallic Minerals Prospect on Kasihan Region, Pacitan Regency, East Java, Indonesia

Metallic mineral exploration activities primarily base metals often have problems because the resources of metallic minerals located below surface are associated with the surrounding rock. Application of Induced Polarization method was carried out in the area of mineral prospects at Kasihan Village, Pacitan District, East Java. The Induced Polarization (IP) data were taken by Syscal Junior 458, using Dipole-dipole and Wenner configuration for mapping and Schlumberger configuration for sounding. Magnetic data were obtained by Geotron Magnetometer. Estimation of pyrite mineral deposit was done using modeling of Res2Dinv and RockWork15. Combination of resistivity and chargeability is conducted to identify the boundaries of mineralization zones. The high resistivity value is correlated with the content of silicate minerals in the mineralized zone, whereas the higher chargeability means high degree of metallic mineral deposits (pyrite). The assesment of two different mineralized zones in metal content is known by combining chargeability and resistivity with magnetic anomaly

Impact of lower plate structure on upper plate deformation at the NW Sumatran convergent margin from seafloor morphology

We present results from multibeam bathymetric data acquired during 2005 and 2006, in the region of maximum slip of the 26 Dec. 2004 earthquake (Mw 9.2). These data provide high-resolution images of seafloor morphology of the entire NW Sumatra forearc from the Sunda trench to the submarine volcanic arc just north of Sumatra. A slope gradient analysis of the combined dataset accurately highlights those portions of the seafloor shaped by active tectonic, depositional and/or erosional processes. The greatest slope gradients are located in the frontal 30 km of the forearc, at the toe of the accretionary wedge. This suggests that long-term deformation rates are highest here and that probably only minor amounts of slip are accommodated by other thrust faults further landward. Obvious N–S oriented lineaments observed on the incoming oceanic plate are aligned sub-parallel to the fracture zones associated with the Wharton fossil spreading center. Active strike-slip motion is suggested by recent deformation with up to 20–30 m of vertical offset. The intersection of these N–S elongated bathymetric scarps with the accretionary wedge partly controls the geometry of thrust anticlines and the location of erosional features (e.g. slide scars, canyons) at the wedge toe. Our interpretation suggests that these N–S lineaments have a significant impact on the oceanic plate, the toe of the wedge and further landward in the wedge. Finally, the bathymetric data indicate that folding at the front of the accretionary wedge occurs primarily along landward-vergent (seaward-dipping) thrusts, an unusual style in accretionary wedges worldwide. The N–S elongated lineaments locally act as boundaries between zones with predominant seaward versus landward vergence.<br/

Spatial distribution of hotspot material added to the lithosphere under La Réunion, from wide-angle seismic data

Wide-angle seismic lines recorded by ocean bottom and land seismometers provide a pseudo three dimensional investigation of the crust and upper mantle structure around the volcanically active hotspot island of La Réunion. The submarine part of the edifice has fairly low seismic velocities, without evidence for intrusives. An upper unit with a velocity-depth gradient is interpreted as made of material erupted subaerially then transported and compacted downslope. Between this unit and the top of the oceanic plate, imaged by normal incidence seismic reflection, a more homogeneous unit indicated by shadow zones on several wide-angle sections may correspond to lavas of a different nature, extruded underwater in the earlier phase of volcanism. Coincident wide angle and normal incidence reflections document that the oceanic plate is not generally downwarping toward the island but doming instead toward its southeastern part, with limited evidence for some intracrustal intrusion. Deeper in the lithosphere, the presence of a layer of intermediate velocity between the crust and the mantle is firmly established. It is interpreted as resulting from the advection of hotspot magmatic products. Possibly partially molten, and of a composition for which the crust is a density barrier. The extensive wide-angle coverage constrains the extent of this body. It does not show the elongated shape expected from plate drift above a steady hotspot supply. Alternative propositions can hence be considered, for example, that La Réunion is caused by a solitary wave of hotspot material or by a young hotspot. The size of the underplate, 140 km wide and up to 3 km thick, corresponds to less than half the volume of the edifice on top of the plate. (Résumé d'auteur