Anita Yuliyanti
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BATUAN PEMBAWA EMAS PADA MINERALISASI SULFIDA BERDASARKAN DATA PETROGRAFI DAN KIMIA DAERAH CIHONJE, GUMELAR, BANYUMAS, JAWA TENGAH Indarto, Sri; Sudarsono, Sudarsono; Setiawan, Iwan; Permana, Haryadi; Al Kausar, Andrie; Yuliyanti, Anita; Dewi Yuniati, Mutia
JURNAL RISET GEOLOGI DAN PERTAMBANGAN Vol 24, No 2 (2014)
Publisher : Indonesian Institute of Sciences

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Abstract

The bearing rocks and hosted rocks of base metals and gold in Indonesia generally occurs in Tertiary age of volcanic rocks. However, base metals and gold mineralizations in Cihonje area, Gumelar, Banyumas that have potential as hosted rocks of base metals and gold are in Tertiary sedimentary rock. Therefore, the rocks need to be investigated by field research for sampling and then laboratory petrographic and chemical analysis for some selected rock samples. The results obtained are calcareous sandstones, silicified and argillitized breccias and mineralized as members of the Rambatan Formation; sandstones as a member of Halang Formation that has weak propylitization and slightly mineralized; andesite basaltic of Kumbang Formation and veins of metal - quartz- adularia - calcite. Alteration and hydrothermal mineralization is caused by the intrusion of basaltic andesite Kumbang Formation that has shape of sill or dyke. From SiO2 vs K2O contents and FeO */MgO versus SiO2, some volcanic rocks samples of Kumbang Formations indicate the composition of basalt and basaltic andesite that are partially in tholeitic series, but generally are calc - alkaline. Members of Rambatan Formations and Lower Halang Formations interpreted as hosted rocks, Kumbang Formations are hosted rock and metal bearing rocks, while veins of metal-quartz-adularia-calcite are the metal bearing rocks. The sulphide minerals consist of pyrite, chalcopyrite, sphalerite, galenas. Gold mineralization and base metal occurred in epithermal–mesothermal and low sulphidation zones.ABSTRAKBatuan pembawa logam dasar dan emas di Indonesia umumnya terdapat pada batuan volkanik berumur Tersier, namun berbeda dengan batuan yang berpotensi sebagai pembawa logam dasar dan emas yang terdapat di daerah Cihonje, Gumelar, Banyumas yang terdapat pada batuan sedimen Tersier. Kondisi ini mendorong untuk dilakukan penelitian dengan tujuan untuk mengetahui kenapa keberadaanya pada sedimen Tersier. Untuk mencapai tujuan tersebut dilakukan penelitian lapangan, pengambilan conto batuan terpilih untuk dilakukan dianalisis petrografi dan kimia batuan. Hasilnya menujukkan bahwa didapatkan batupasir gampingan, breksi tersilisifikasi dan terargilitisasi serta termineralisasi sebagai anggota Formasi Rambatan, batupasir anggota Formasi Halang terpropilitisasi lemah serta sedikit termineralisasi, andesit basaltik Formasi Kumbang dan urat-urat kalsit-adularia-kuarsa-logam. Alterasi dan mineralisasi hidrotermal yang terjadi disebabkan oleh intrusi andesit basaltik Formasi Kumbang berbentuk sill atau dyke. Pada batuan volkanik Formasi Kumbang kandungan SiO2 vs K2O dan FeO*/MgO vs SiO2 menunjukkan komposisi basalt dan andesit basaltik yang sebagian termasuk seri toleitik dan umumnya kapur – alkali. Batuan anggota Formasi Rambatan dan Formasi Halang bawah diinterpretasikan sebagai jebakan (perangkap), batuan Formasi Kumbang sebagai jebakan dan pembawa logam, urat kalsit-adularia-kuarsa-logam adalah pembawa logam. Mineral – mineral sulfida terdiri dari pirit, khalkopirit, sfalerit, galena. Mineralisasi emas dan logam dasar dapat terjadi pada zona epitermal – mesotermal bersulfida rendah.
MINERALOGI BENTONIT TASIKMALAYA SEBAGAI MEDIA PENYERAP CO2 MELALUI KARBONASI HIDROTERMAL Yuliyanti, Anita; Mursito, Anggoro Tri; Widodo, Widodo; Muharam, Syamsul Rizal
JURNAL RISET GEOLOGI DAN PERTAMBANGAN Vol 28, No 1 (2018)
Publisher : Indonesian Institute of Sciences

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Abstract

Kristalinitas mineral kalsit yang terpresipitasi pada proses karbonasi hidrotermal dianalisis menggunakan metode XRD (X-ray diffraction) semi-kuantitatif dengan bantuan piranti lunak komersial PeakFit® serta SEM (scanning electrone microscope) untuk memperoleh ukuran kristalit dan bentuk morfologinya. Bentonit Tasikmalaya mengandung mineral-mineral potassium, kalsium, magnesium silikat berupa montmorilonit, klinoptilolit, dan anortit serta  mampu menyerap CO2 dan menyimpannya dalam bentuk mineral kalsit. Hasil analisis menunjukkan bahwa ukuran kristalit kalsit yang terbentuk mempunyai korelasi dengan prosentase gas CO2 yang terserap. Penyerapan CO2 tertinggi tercapai pada bentonit CaBK dan NaBK dengan penambahan Ca(OH)2 pada suhu rendah masing-masing sebesar 9,9% dari massa percontoh. Adapun kristalinitas mineral kalsit terbesar tercapai pada bentonit CaBK yang menghasilkan kristalit kalsit berukuran 463,36Ǻ. Hasil penelitian menunjukkan bahwa bentonit Tasikmalaya mampu menyerap CO2 dan menyimpannya dalam bentuk kalsit. Calcite precipitated during hydrothermal carbonation process was analyzed using semi-quantitative XRD (X-ray diffraction) method, supported with commercial software PeakFit®, and SEM (scanning electrone microscope) method to study its crystallite size and morphology. Tasikmalaya bentonite consist of potassium, calcium, magnesium silicate minerals as montmorillonite, clinoptilolite, and anorthite. The result indicates that crystallite sizes correlate with absorbed CO2 percentage. The highest CO2 absorption was obtained from CaBK and NaBK bentonite with addition of 9.9% Ca(OH)2 for each sample at low temperature. Largest calcite crystallinity obtained from CaBK bentonite that resulted 463.36Ǻ crystallites size. The result indicates that Tasikmalaya bentonite has an ability to absorb and store CO2 as calcite.   
ZONA PERMEABEL DI KAWAH GUNUNG PAPANDAYAN BERDASARKAN GAS RADON DAN THORON Nurohman, Heri; Bakti, Hendra; Indarto, Sri; Permana, Haryadi; Yuliyanti, Anita; Kausar, Andrie Al; Gaffar, Eddy Z.
JURNAL RISET GEOLOGI DAN PERTAMBANGAN Vol 26, No 2 (2016)
Publisher : Indonesian Institute of Sciences

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Abstract

One of the methods used in geothermal exploration is to take advantage of the presence of radon in nature. In this study, we measured radon and thoron in Papandayan Volcano area, which was assumed to have a high geothermal potential. Measurements were carried out in around the crater of the volcano by using Rad7 on soil and water. The duration of measurement in each point is 15 minutes at a depth of 75 cm with a sniff mode. The result indicated that the concentration of radon gas is relatively high. The high concentration might be interpreted as the permeable zone, which associated with the zone of faults or fractures. The results also showed relatively high concentrations of radon gas around the east and the west of the crater. This concentration reflects the presence of permeable zones that may be associated with the southwest trending fault - northeast and also the presence of the caldera boundary. The continuity of permeable zone below the surface was interpreted based on the thoron- radon ratio (220Rn / 222Rn). A high ratio (indicating the source of radon shallow) found in the northern ridge of the Papandayan crater.Salah satu metode yang digunakan dalam kegiatan eksplorasi panasbumi adalah dengan memanfaatkan keberadaan gas radon alam. Dalam penelitian dilakukan pengukuran gas radon dan thoron di lokasi Gunung Papandayan karena daerah ini diduga memiliki potensi panas bumi yang tinggi. Kegiatan pengukuran dilakukan di sekitar kawah Gunung Papandayan dengan menggunakan alat Rad7 pada media tanah dan air. Lama pengukuran pertitik adalah 15 menit pada kedalaman 75 cm dengan mode sniff. Hasil pengukuran menunjukkan konsentrasi gas radon yang relatif tinggi, yang dapat diinterpretasikan sebagai keberadaan zona permeabel, berkaitan dengan adanya zona rekahan atau patahan. Hasil pengukuran menunjukkan konsentrasi gas radon yang relatif tinggi di sekitar tebing kawah timur dan barat. Konsentrasi tersebut mencerminkan keberadaan zona permeabel, yang mungkin berasosiasi dengan patahan berarah baratdaya – timurlaut, dan juga keberadaan batas kaldera. Kemenerusan zona permeabel sampai ke bawah permukaan dianalisa berdasarkan rasio thoron/radon (220Rn/222Rn). Rasio tinggi ditemukan (menunjukkan sumber radon dangkal)  dipunggungan utara kawah Papandayan.
Characteristics and genesis of montmorilonitic claystone from Bandung area, Wonosegoro, Boyolali, Central Java, Indonesia Yuliyanti, Anita; Warmada, I Wayan; Titisari, Anastasia Dewi
Journal of Applied Geology Vol 3, No 1
Publisher : Geological Engineering Department Universitas Gadjah Mada

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Abstract

The Bandung bentonite deposit is located in Wonosegoro District, Boyolali Regence, Central Java. Characteristics of bentonite in this area are very important due to increase demand on bentonite in the industry. Several methods are used to characterize the bentonite in this area, such as PLM (polarizing light microscope), X-Ray Diffraction and Scanning Electron Microscope combined with EDX measurements. The montmorilonitic claystone belongs to Kerek Formation from Banyuurip Member. This deposit consists of mainly montmorilonitic claystone interbedded with tuffaceous sandstone. Petrographical analysis shows that montmorilonitic claystone consists of mostly clay minerals with small amount of calcite, volcanic glass, feldspar, quartz, and opaque minerals. The clay minerals are likely as alteration product of volcanic glass. The oriented XRD analyses show that the clay samples consist of Ca-montmorilonite, illite, and kaolinite. Physico-chemical analyses of montmorilonitic claystone display that the initial CEC (cation exchange capacity) is 20 mgrek.Na2O/200gr (54 mg.Na2O/100gr) and low swelling ability for about 2 times of its initial volume. Based on its mineralogical association, textures, and stratigraphic position, the montmorilonite is formed from devitivication of volcanic glass in a diagenetic environment with over 2 km thicks of overburden. Keywords: Bentonite, montmorillonitic claystone, devitrivication, diagenesis, montmorillonite