Jurnal Geologi dan Sumberdaya Mineral

Subsurface Modeling of High Sulfidation Epithermal Deposit Systems Based on Geomagnetic Data in the Tulungagung Area, East Java

2025-05-08T00:21:14+00:00

The presence of metallic minerals in vuggy silica in Tulungagung, East Java, is characteristic of the high sulfidation epithermal (HSE) deposit system. This research quantitatively analyzes the distribution and geometry of metal mineral deposits in the research area using geomagnetic methods. The research analyzes the alteration and mineralization zones of the HSE deposits and builds a subsurface model. The geomagnetic method aims to determine subsurface conditions based on the magnetic properties of rocks. This research was conducted as many as 417 points with a distance between points of 50 - 700 meters, randomly from a lot area of 95 km2. The results of the reduce-to-pole (RTP) map analysis show that the alteration and mineralization zones of the HSE are seen in low magnetic anomaly values due to dominant alteration and the presence of complex faults, so that destructive magnetite occurs. The results of wave spectrum analysis obtained an estimated regional depth of ± 539 meters, which was used for subsurface modeling. The model shows the environment and geometry of the HSE deposits. The presence of alteration and mineralization in the study area is at low susceptibility values < 2 x 10-3 SI, controlled by faults and permeable lithologies. Dacite intrusions with high susceptibility values > 15 x 10-3 SI are interpreted as host rocks carrying mineralization in the study area.

The uplift rate of Sulawesi East Arm and the activity of Batui Fault using a tectonic geomorphology approach in the Luwuk Area, Sulawesi

2024-11-26T02:34:31+00:00

Sulawesi is a tectonically active area with convergent triple-junction amidst Eurasian, Indo-Australian and Pacific Plate. The study area is located in the suture zone of sedimentary Banggai-Sula Microcontinent and East Sulawesi Ophiolite. This research is aimed to determine fault activity and rate of tectonic uplift of Luwuk mountainous area. Field geological mapping had been done to determine lithology and geological structure along with morphometric analysis to measure definitive result of tectonic activities. Geological structure features which encountered in this area are Batui Thrust, Pasini Thrust, Lobu Balongan Fault Zone, and Lambangan Anticline. The sedimentary rocks have average N315oE dip direction with angle of 41o. Based on tectonic geomorphology and morphometric analyses are resulting the most active tectonic areas passed by the Batui and Pasini Thrust which have NE-SW direction and Lobu Balolang Fault Zone relative to others. The Batui Thrust is considered as active fault intersected the East Sulawesi Ophiolite and Banggai-Sula Microcontinent which segmented with wrench faults. Number of thrust faults parallel to the Batui Thrust generate Batui Thrust Belt which propagate from the ultramafic rocks to the sedimentary rocks within the suture zone. As a result, the presence of active fault is uplifting the East Arm of Sulawesi with 0.408 ± 0.008 mm and 0.213 ± 0.046 mm uplift rate per year by the presence of high altitude Celebes Molasses. These rates are getting higher to the west.

Keywords: Batui Thrust, East Sulawesi Ophiolite, Luwuk, morphometry, tectonic geomorphology, uplift rate

Analisis Spasial-Temporal Kerugian Perumahan Akibat Likuifaksi (Studi Kasus Gempa Palu Tahun 2018 di Balaroa, Petobo, dan Jono Oge)

2025-02-02T03:58:50+00:00

Gempa Palu tahun 2018 menyebabkan kerusakan parah pada wilayah metropolitan yang padat penduduk, karena ukurannya yang merusak dan tingginya kerentanan lokasi ini terhadap gangguan seismik. Fenomena ini telah banyak diteliti, dan para peneliti secara umum sepakat bahwa solusi perumahan yang tangguh dan integrasi teknologi geospasial mutakhir ke dalam pekerjaan manajemen bencana sangat penting. Tujuan Penelitian ini adalah memperkirakan jumlah penduduk terken dampak likuifaksi dengan data Google Earth. Metode yang digunakan adalah OBIA (Object Base Interpretation Analysis) yaitu mendeteksi bangunan rumah yang ada sebelum hilang akibat likuifaksi, kemudian menghitung jumlah penduduk dari jumlah bangunan yang hilang. Hasil temuan penelitian ini mengungkapkan kerugian perumahan yang signifikan di ketiga wilayah karena likuifaksi. Ketiga wilayah itu adalah Balaroa, Petobo dan Jono Oge. Petobo adalah wilayah yang mengalami perpindahan penduduk yang sangat mencolok. Hasil penelitian dapat memberikan uraian terperinci secara spasial tentang dampak likuifaksi pada area permukiman agar selanjutnya lingkungan perkotaan dapat beradaptasi terhadap peristiwa seismik. Hasil penelitian ini juga menujukkan bahwa perlu adanya integrasi langkah-langkah perencanaan perkotaan yang komprehensif. Sebagai kesimpulan, penelitian ini menggarisbawahi pentingnya strategi jangka pendek dan jangka panjang dalam manajemen bencana dan perencanaan perkotaan, yang menganjurkan pendekatan kolaboratif untuk membangun lanskap perkotaan yang tangguh, terutama di daerah yang rawan gempa bumi. Arah penelitian di masa mendatang disarankan, fokus pada penilaian kualitatif dan pengembangan kebijakan untuk meningkatkan infrastruktur yang tahan gempa.

Kata kunci: Data Google Earth, dampak likuifaksi, analisis spasial, kehilangan rumah, perpindahan penduduk

Reconstruction of Geological History Based on Stratigraphic Analysis in the Gombong Region, North Serayu Basin

2024-12-10T06:53:58+00:00

In the North Serayu Basin, there are deepsea sedimentary material and volcanic material are deposited in the terrestrial environment. The varied depositional environments require a detailed geological understanding. Because research has yet to be carried out regarding the reconstruction of the geological history in the Gombong area, this research was carried out to study and understand the chronology of deposition and the condition of its geological structure. Research methods include field observation, stratigraphic analysis, and surface geological structure analysis. From old to young, the stratigraphy of the research area is the Shale Interbedded Unit with Rambatan Sandstone, the Halang Tuff Unit, the Dacite Intrusion Unit, and the Slamet Basalt Lava Unit. The reconstruction of the geological history of the research area began in the Middle Miocene - Late Miocene with the deposition of the Shale Interbedded Unit with Rambatan Sandstone in the lower Bathyal-Abysal bathymetric environment (500-2000 m) and the Halang Tuff Unit was deposited in the Late Miocene-Pliocene-finger conformity. Then, during the Late Miocene, the deposition of the Dacite Intrusion Unit occurred, which had an unconformable relationship (nonconformity) with interbedded shale units with Rambatan Sandstone below. Then, in the Late Miocene - Pliocene, due to the compressional regime phase of the Java Island subduction, a geological structure was formed with the principal stress (σ1) trending relatively northwest- southeast, which resulted in the Sarawak right-slip fault, the Mendelem thrust fault and the Gunungtiga normal fault. Furthermore, during the Pleistocene, volcanic activity continued, producing the Slamet Basalt Lava Unit, which had an incongruent relationship (nonconformity) with the Dacite Intrusion Unit below it.

Keywords: Geological History, Stratigraphy, North Serayu Basin.

Analisis Stabilitas Lereng Menggunakan Metode RMR dan SMR di Daerah Malanu, Distrik Sorong Utara, Kota Sorong, Provinsi Papua Barat Daya

2025-03-20T06:11:01+00:00

Kondisi lereng pada kawasan tambang batuan di Daerah Malanu, Distrik Sorong Utara, Kota Sorong sangat menarik, karena terdapat rekahan-rekahan yang kemungkinan menyebabkan lereng berada dalam kondisi tidak stabil dan berpotensi menimbulkan bencana. Tujuan dari penelitian ini adalah untuk menganalisis kualitas massa batuan, tingkat kestabilan lereng, dan upaya perkuatan lereng, sehingga dapat memberikan informasi kepada instansi terkait dan masyarakat mengenai kondisi lereng tersebut. Metode yang digunakan adalah scanline sampling, analisis RMR, analisis SMR, dan analisis kinematik. Dari hasil analisis, didapatkan bahwa lereng 1 memiliki nilai RMR 65 (baik), tipe runtuhan guling, dan nilai SMR 65 (stabil), lereng 2 memiliki nilai RMR 67 (baik), tipe runtuhan baji, dan nilai SMR 59,5 (stabil sebagian), lereng 3 memiliki nilai RMR 63 (baik), tipe runtuhan bidang, dan nilai SMR 57 (stabil sebagian), lereng 4 memiliki nilai RMR 63 (baik), tipe runtuhan bidang, dan nilai SMR 13 (sangat tidak stabil), serta lereng 5 memiliki nilai RMR 60 (sedang), tipe runtuhan guling, dan nilai SMR 60 (stabil). Rekomendasi perkuatan yang disarankan oleh Romana (1985) adalah perkuatan (IIb) untuk lereng 1, perkuatan (IIIa) untuk lereng 1,2, dan 5, serta perkuatan (Va) untuk lereng 4.

Kata kunci: Massa Batuan, Kestabilan lereng, Scanline, RMR, SMR

A Pollen Record Of Alluvium Unit And Vegetation Landscape From Bangka Island, Indonesia

2025-04-22T04:21:36+00:00

This study presents a pollen record of the purported Holocene Alluvium in Bangka Island, Indonesia. This alluvial unit’s age and stratigraphic position have been disputed, and this pollen study is expected to provide crucial evidence on the matter. The pollen content is also likely to reveal the vegetation landscape and environment of the samples, further enhancing our understanding of the area. Three samples were taken from outcrops at three different points of the alluvial deposit, and the samples were rich in pollen and spores. We identified 54 pollen and 12 spore taxa. The pollen assemblages suggest that the samples were deposited in an open forest environment of the evolving disturbed heath forest ecosystem. Several cultivated plant pollens indicate that the samples were deposited in modern times.

Keywords: Holocene, alluvium, stratigraphy, pollen, Bangka, vegetation landscape

Keywords: Holocene, alluvium, stratigraphy, pollen, Bangka, vegetation landscape