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All Journal Bulletin of Scientific Contribution : Geology IJOG : Indonesian Journal on Geoscience
Mega F. Rosana, Mega F.
Padjadjaran University
Civil Engineering, Building, Construction & Architecture Earth & Planetary Sciences Energy Environmental Science

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Magma Chamber Model of Batur Caldera, Bali, Indonesia: Compositional Variation of Two Facies, Large-Volume Dacitic Ignimbrites Sutawidjaja, Igan S.; Rosana, Mega F.; Watanabe, K.
Indonesian Journal on Geoscience Vol 2, No 2 (2015)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (2369.989 KB) | DOI: 10.17014/ijog.2.2.111-124

Abstract

DOI:10.17014/ijog.2.2.111-124Batur is one of the finest known calderas on Earth, and is the source of at least two major ignimbrite eruptions with a combined volume of some 84 km3 and 19 km3. These ignimbrites have a similar compositions, raising the question of whether they are geneticaly related. The Batur Ignimbrite-1 (BI-1) is crystal poor, containing rhyodacitic (68 - 70wt % SiO2), white to grey pumices and partly welded and unwelded. The overlying Batur Ignimbrite-2 (BI-2) is a homogeneous grey to black dacitic pumices (64 - 66 wt % SiO2), unwelded and densely welded (40 - 60% vesicularity), crystal and lithic rich. Phase equilibria indicate that the Batur magma equilibrated at temperatures of 1100 - 1300oC with melt water contents of 3 - 6 wt%. The post-eruptive Batur magma was cooler (<1100oC) and it is melt more water rich (> 6 wt % H2O). A pressure of 20 kbar is infered from mineral barometry for the Batur magma chamber. Magmatic chamber model is one in which crystals and melt separate from a convecting Batur magma by density differences, resulting in a stratified magma chamber with a homogeneous central zone, a crystal-rich accumulation zone near the walls or base, and a buoyant, melt-rich zone near the top. This is consistent with the estimated magma temperatures and densities: the pre-eruptive BI-1 magma was hoter (1300oC) and more volatile rich (6 wt % H2O) with density 2.25 g/cm3 than the BI-2 magma (1200oC; 4 wt % H2O) in density was higher (2.50 g/cm3). Batur melt characteristics and intensive parameters are consistent with a volatile oversaturation-driven eruption. However, the higher H2O content, high viscosity and low crystal content of the BI-1 magma imply an external eruption trigger.
POTENSI GEOWISATA DI KAWASAN TELUK CILETUH, SUKABUMI, JAWA BARAT Hardiyono, Adi; Syafri, Ildrem; Rosana, Mega F.; Yuningsih, Euis Y.; -, Herry; Andriany, Suci Sarah
Bulletin of Scientific Contribution Vol 13, No 2 (2015): Bulletin of Scientific Contribution
Publisher : Fakultas Teknik Geologi Universitas Padjadjaran

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (853.992 KB) | DOI: 10.24198/bsc.v13i2.8396

Abstract

Ciletuh be local Geopark since August 2014, and now towards preparing to become a National Geopark. This geopark is proposed by the government of Sukabumi in 2014. Remains of the geology in this geopark is the emergence of ophiolite complex as a result of fossil tectonic subduction between the Eurasian plate and the Indo-Australian Plate at the age cretasius. Geomorphology tectonic activity form the shape known as the Ciletuh amphitheater, and also the unique shapes result of water erosion that formed the rocks that looks into unique shapes like dragon-stone, frogs-rock, buffalo-stone. etc. There is also the conservation of green turtles and other wild animals such as sea eagles, panthers also conservation Raflesia flowers, Cantigi and mangrove forests to support geopark Ciletuh. Geopark Ciletuh can be divided into four complexes, namely Geoarea Tamanjaya, Geoarea Ciwaru-Mount Rhinos, Geoarea Citisuk-Cikepuh and Geoarea Citirem Ujunggenteng.Some programs geotrek made to visit geoarea either road, or by sea with a boat, also made supporting facilities such as hotels, homestays, local guides and signs.
PETROLOGI BATUAN OFIOLIT DAERAH SODONGPARAT, KAWASAN CILETUH, SUKABUMI Rosana, Mega F.; Yuningsih, Euis T.; Saragih, Kessar D.; Ikhram, Rinaldi; Ardiansyah, Nugraha
Bulletin of Scientific Contribution Vol 13, No 3 (2015): Bulletin of Scientific Contribution
Publisher : Fakultas Teknik Geologi Universitas Padjadjaran

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (1152.757 KB) | DOI: 10.24198/bsc.v13i3.8409

Abstract

Ophiolite outcrops offers a unique opportunity to learn directly oceanic lithosphere, as ophiolite represents one of the few outcrops of rock that body can not be reached. Ophiolite is interpreted in the context of plate tectonics, as part of the oceanic lithosphere thrust into the continent during the first phase of orogenesa. Many geologists believe that the definition of ophiolite according to Penrose Field Conference in 1972, which is a typical sequence of rocks composed of, starting from the bottom: the complex ultramafic, gabbro complex, complex sheeted mafic dikes, complex mafic-volcanic and sedimentary pelagos. Ophiolite sequence may be incomplete, torn or termetamorfisme. Group ophiolite in area Ciletuh is an assemblage of mafic rocks (basalt, gabbro and ultramafic (peridotite, serpentinite), which is closely associated with the sedimentary-volcanic and metamorphic rocks. Generally ofiolitnya a sequence ophiolite very incomplete, and the mechanism of the transferor-tempatannya (emplacement ) can be equated with ophiolite "Cordilleran", which is rather a ophiolite (ocean floor, which did not contain fragments of the continent) above the subduction complex.
QUARTZ VEIN INFILL STRUCTURE MODE IN KENCANA DEPOSIT, GOSOWONG GOLDFIELD, INDONESIA Electricia, K.S.; Rosana, Mega F.; Yuningsih, Euis Tintin; Syafri, Ildrem; Viqnoriva, S.N.
Bulletin of Scientific Contribution Vol 15, No 1 (2017): Bulletin of Scientific Contribution
Publisher : Fakultas Teknik Geologi Universitas Padjadjaran

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (751.317 KB)

Abstract

ABSTRACTGosowong province has economic mineralisation which is classified as low sulphidation epithermal veining system containing high-grade of gold and silver. It is characterizes by various veins hosted in Holocene Quaternary volcanic rocks, mineralisation generally occurs in host rock andesite. The Kencana epithermal vein system in Gosowong Au-Ag district hosted by two main sub-parallel North-West trending major fault structures, named Kencana One (K1) and Kencana Two (K2) with strike lenght extend up to 600m. Both structures joined by link structures, appears to be Kencana Link (K-Link) as the thickest link structure. The Kencana One (K1) is the first underground mine in Gosowong district. The nature of underground conditions at Kencana has a high variability of gold grades. Thus due to extremely high grades ore in Kencana, it is need to be precise and thoroughly handling to obtain best results. Primary mineralisation occurs in multistage veins, breccias and stockwork veins as infill structures. This study confirming that there is a strong correlation between quartz vein infill structure mode versus gold grade which classified into (1) 1.01-3.0g/t Au, dominated with wall-rock breccia and stockwork, (2) 3.01-6.0g/t Au, dominated with wall-rock breccia follows by stockwork, (3) 6.01-20.0g/t Au, dominated with wall-rock breccia follows by quartz lode and stockwork, (4) 20.01-80.0g/t Au, dominated by wall-rock breccia follows by vein breccia and quartz lode, (5) >80g/t Au, dominated by wall-rock breccia. In terms of production quartz vein infill mode together and quartz vein texture with gold grade has been used as the main reference for geologist to make a direction in the process of ore drive determination in underground mining operations. Keywords: Kencana, low sulphidation epithermal, quartz vein infill modeSARIGosowong memiliki mineralisasi ekonomis yang merupakan epitermal sulfida rendah yang mengandung emas dan perak dengan kadar tinggi. Cebakan dicirikan dengan kehadiran urat yang bervariasi dengan batuan vulkanik kuarter sebagai batuan induk berumur Holosen, mineralisasi umumnya terjadi di dalam batuan induk andesit. Kencana berada di dalam area Cebakan Au-Ag Gosowong. Kencana terdiri dari dua struktur besar yang berdampingan, dinamakan Kencana Satu (K1) dan Kencana Dua (K2) dengan arah jurus sepanjang 600m. Keduanya dihubungkan dengan struktur yang dinamakan Kencana Link (K-Link) yang merupakan struktur bukaan yang paling tebal. K1 adalah tambang bawah tanah pertama di Gosowong. Kondisi bawah tanah di Kencana menunjukkan variasi tubuh bijih emas yang mengandung kadar emas yang bervariasi. Dengan adanya kadar emas yang tinggi, maka penangannya harus tepat dan seksama untuk mendapatkan hasil terbaik. Secara umum mineralisasi terjadi secara bertahap dalam urat kuarsa, breksiasi, dan urat stockwork. Penelitian ini menegaskan bahwa terdapat korelasi yang kuat antara tipe struktur urat kuarsa dengan kadar emas yang diklasifikasikan menjadi (1) 1.01-3.0 g/t Au, didominasi oleh breksiasi batuan dinding dan stockwork, (2) 3.01-6.0 g/t Au, didominasi oleh breksiasi batuan dinding diikuti oleh stockwork, (3) 6.01-20.0 g/t Au, didominasi oleh breksiasi batuan dinding diikuti oleh quartz lode dan stockwork (4) 20.01-80.0 g/t Au, didominasi oleh breksiasi batuan dinding diikuti oleh breksiasi urat kuarsa dan quartz lode (5) > 80g/t Au, didominasi oleh breksiasi batuan dinding. Di dalam proses produksi, tipe struktur urat kuarsa dan  tekstur urat kuarsa bersama dengan kadar emas menjadi petunjuk untuk geolog dalam menentukan arah penambangan emas di dalam tambang bawah tanah.Kata kunci: epitermal sulfida rendah, Kencana, tipe struktur urat kuarsa
Co-Authors Adi Hardiyono, Adi Electricia, K.S. Euis T. Yuningsih, Euis T. Euis Tintin Yuningsih Euis Y. Yuningsih, Euis Y. Herry -, Herry Igan S. Sutawidjaja Ildrem Syafri K. Watanabe, K. Kessar D. Saragih, Kessar D. Nugraha Ardiansyah, Nugraha Rinaldi Ikhram Suci Sarah Andriany, Suci Sarah Viqnoriva, S.N.