Model Mineralisasi Pembentukan Opal Banten

DOI: 10.17014/ijog.v5i3.100Opal is a beautiful precious gemstone that is equal or more valuable than diamond. In Indonesia, precious opal is found at the Lebak Regency, Province of Banten. Banten\u27s opal widely has been recognized due to its beautiful opalescence. This paper is a review of the last research; preliminary study of Banten\u27s opal, characteristics of opal-CT and determining of opal type from geochemical data, added by new data to compile concept and to make mineralization model. In order to fulfill these targets, field geology research and analysis of mineralog/gemology, petrography, X-RD, and major and trace element geochemistry have been done. The Banten\u27s opal is opal-CT showing opalescence (play of colour), weathering, and leaching silica from volcanic glass by dark grey claystone hosted. Mineralization model is divided into three periods; at Early Pliocene volcanic clastic sediments rich in volcanic glass occured as fluvial sediments. Afterwards, at Late Pliocene - Pleistocene folding, weathering and leaching of silica took place. Intensive jointing, faulting, and folding quickened weathering and leaching processes to formed opal at limb of anticline through Holocene. The prospecting area of Banten\u27s opal is in tuff unit with intercalation of conglomerate or pumiceous breccia, at limb of anticline. The host rock of opal is dark grey claystone which underlies polimict conglomerate/pebbly sandstone sequence with cross stratification, imbricated, and erossional stucture; more than 8 m deep

MENGOPTIMALKAN PEROLEHAN MINERAL MAGNETIK PADA PROSES SEPARASI MAGNETIK PASIR BESI PANTAI SELATAN KABUPATEN KEBUMEN, JAWA TENGAH

Potensi pasir besi Pantai Selatan Kebumen cukup tinggi. Material ini terdiri atas mineral magnetik dan bukan magnetik; yang pertama berupa magnetit lepas dan magnetit ikat yang berasosiasi dengan olivin, piroksin dan horblende, sedangkan yang kedua berupa kuarsa, K-feldspar, plagioklas, zirkon, rutil dan karbonat/fosil. Pemisahan optimum antara mineral magnetik dengan bukan magnetik dengan kadar Fe total maksimal memerlukan penelitian lapangan dan laboratorium. Penelitian lapangan dilakukan untuk pengambilan percontoh pada dua lokasi terpisah di bagian timur dan barat pantai Kebumen. Analisis laboratorium meliputi pengujian separasi magnetik pada fraksi kasar (-20 +35 mesh), sedang (-35+60 mesh) dan halus (-60+120 mesh) dengan intensitas magnetik 200 , 1000 dan 3000 Gauss. Mineral magnetik hasil separasi dianalisis kandungan Fe total, SiO2 dan TiO2 menggunakan metode AAS. Berdasarkan hasil analisis, mineral magnetik lebih banyak terdapat di bagian timur dengan prosentase sejumlah 66,46 % berat dan kadar Fe total 56,57 % yang didapat dari hasil separasi magnetik partikel berukuran -60+120 mesh dengan intensitas 200 G. Pemisahan mineral magnetik untuk percontoh berasal dari bagian barat menggunakan partikel berukuran -120+200 mesh dan intensitas magnetik 200 G. Hasilnya menunjukkan persentase mineral magnetik sebanyak 34,39 % berat dengan kadar Fe total 60,72 %. Kadar Fe total mineral magnetik berlawanan dengan SiO2 sedangkan TiO2 mengikuti pola Fe total

ANALISIS CADANGAN, KUALITAS DAN DAMPAK PENAMBANGAN LEMPUNG SEBAGAI BAHAN BAKU GENTENG SOKA DAN BATA, DI KABUPATEN KEBUMEN

Penelitian ini bertujuan untuk mengkaji tingkat kebutuhan, pemanfaatan, sebaran, kualitas, cadangan lempung dan dampak lingkungan disekitar sentra industri genteng di Kecamatan Sruweng dan Pejagoan Kabupaten Kebumen, yang mencakup kegiatan lapangan dan laboratorium. Penelitian lapangan meliputi penelitian sebaran bahan galian, aktivitas penambangan serta dampak lingkungan yang terjadi. Penelitian laboratorium mencakup analisis XRD menggunakan alat RINT2000 wide angle geniometer dan kimia mineral menggunakan metode AAS (Atomic Absorbtion Spectrometer). Lempung tersebar pada 13 lokasi seluas 1.320,870 Ha, dengan jumlah cadangan 19.544.143,00 m3. Berdasarkan analisis XRD, lempung mengandung kaolinit, monmorilonit, illit serta mineral induk. Kualitas lempung yang berasal dari Kebakalan setara dengan lempung dari Kedawung, lempung Kebagoran mempunyai kualitas lebih rendah dibandingkan lempung Kedawung, sementara itu lempung Plumbon kurang baik. Analisis kimia menunjukkan bahwa lempung dari Kebakalan dan Plumbon mengandung Fe2O3 sebesar 18,48 – 20,15 %. Indeks plastisitas berkisar antara 19,23 – 28,12% , susut kering sekitar 6%, susut bakar 9.5% sehingga memenuhi syarat untuk genteng keramik. Tingkat produksi genteng diperkirakan 174.424.333 bh/th, produksi batu bata 60.300.000 bh/th, maka diperlukan lempung 369.528,88 m3/th. Cadangan lempung yang ada diperkirakan dapat memenuhi kebutuhan selama 52,9 tahun. Nilai ekonomi cadangan lempung Rp 1,95 triliun, nilai potensial kerugian lahan akibat tidak panen Rp 84,78 milyar, nilai sewa sawah pada petani seharga Rp 63 juta/Ha, sehingga menguntungkan. Dampak lingkungan yang terjadi mencakup; hilangnya tanah penutup dan kesuburan tanah, perubahan topografi yang tidak sesuai karakter lahan serta rusaknya infra struktur. Untuk mengurangi perlu melokalisir area penambangan di sekitar Kebakalan-Logandu, melakukan reklamasi paska tambang dengan mengembalikan tanah pucuk, pemanfaatan lahan bekas tambang menjadi tempat perikanan/pemancingan, pembuatan zonasi kawasan tambang serta PERDA Pertambangan

POTENSI BAHAN TAMBANG, PENATAAN WILAYAH USAHA PERTAMBANGAN (WUP) DAN WILAYAH PERTAMBANGAN RAKYAT (WPR) DI KEBUMEN

Potensi kelompok mineral logam Kebumen terdiri atas pasir besi, mangan, dan emas; sedangkan kelompok batubaranya berupa serpih bitumen; kelompok bukan logam meliputi kaolin, Ca-bentonit, fosfat guano, tras, felspar, asbes dan talk. Kelompok batuan meliputi batugamping, tanah liat, andesit, diabas, gabro, basal, marmer, pasir-batu (sirtu) dan tanah merah. WUP mineral logam tersebar pada tiga lokasi yaitu kawasan Pantai Selatan (11.640 ha), tinggian Karangbolong (5.680 ha) dan Kebumen Utara (5.709 ha). WUP bukan logam tersebar pada dua lokasi, yaitu tinggian Karangbolong (1.875 ha) dan Kebumen Utara (7.488 ha). WUP batuan tersebar di kawasan tinggian Karangbolong (5.680 ha), Rowokele (5.587 ha), Karanganyar (7.598 ha) dan Kutowinangun Utara (14.980 ha). WPR dengan komoditas pasir sungai tersebar di S. Pedegolan, S. Kedungbener, S. Luk Ulo, S. Karanganyar, S. Kemit, S. Sampang dan Muara S. Cincingguling, serta WPR batubara pada tinggian Karangbolong

Geomorphosite Assessment at North Karangsambung -Karangbolong Geopark Kebumen, as Tools of Geotourism Development

Geopark is a sustainable regional development concept that combines geological, biological, and cultural diversity through conservation and education activities to improve the community's welfare. Kebumen Regency has a National Geopark Karangsambung-Karangbolong (GNKK) covering 543,599 Km2 with 41 geosites, ten cultures, and eight biosite since 2018. The northern part of the area is a geological heritage that is widely used for field geological education. The study aims to identify and assess geosites and geomorphosite in the north area, describing the region's geomorphological processes and geological evolution. Field research was conducted to get an overview of geological diversity, geomorphology, and geosite and determine the selected geomorphosite. Geomorphosite assessment is done quantitatively using the Kubalikova method by assessing five main parameters that include; Intrinsic and scientific value, the value of education, economic value, conservation value, and added value. The scientific and intrinsic value of Pentulu Indah (PI) = 4, while Wagirsambeng = 3. Educational value of PI = 4, while Wagirsambeng = 2. Economic value is still not satisfactory, but P.I. = 2, while Wagirsambeng = 1.5. Conservation value of P.I. = 3.5, while Wagirsambeng = 2.5. Added value PI = 2.75 while Wagirsambeng = 1.5. Based on those, geomorphosite Pentulu Indah is 16,26 point or a good value (87.83 %) while Wagirsambeng is 10.5 point or fairly level (56.75 %)

Petrologi dan Geokimia Batuan Dasit Komplek Mélange Luk Ulo

Kompleks Mélange Luk Ulo (KMLU) disusun berbagai macam bongkah batuan yang tercampur secara tektonik dalam masa dasar lempung hitam, salah satu bongkah batuannya adalah dasit. Penelitian ini bertujuan untuk mengetahui karakteristik petrologi dan geokimia batuan dasit KMLU untuk mengetahui lingkungan tektonik dan sejarah pembentukannya. Metode yang digunakan antara lain adalah analisis petrografi, analisis unsur utama menggunakan fusion inductively coupled plasma, analisis unsur jejak dan unsur tanah jarang menggunakan inductively coupled plasma mass spectrometry, serta analisis umur absolut menggunakan metode K-Ar. Dasit KMLU memiliki tesktur porfiritik, disusun fenokris kuarsa, plagioklas, dan feldspar alkali tertanam dalam masa dasar mikrokristalin kuarsa dan mikrokristalin biotit. Kandungan unsur SiO2 yang tinggi (66,56-71,64%) dan K2O yang rendah (0,41-1,27%) menunjukkan batuan memiliki afinitas magma toleit. Unsur low ionic potential pada Dasit KMLU mengalami pengkayaan relatif terhadap MORB sebanyak 2-8 kali sedangkan unsur-unsur high ionic potential lebih rendah dibandingkan MORB, mengindikasikan batuan terbentuk pada tatanan tektonik busur kepulauan. Pengkayaan unsur tanah jarang ringan sebesar 3 - 9 kali dibandingkan kondrit yang disertai pola pengurangan (depletion) berangsur-angsur dari unsur La hingga Eu juga mengindikasikan tatanan tektonik busur kepulauan. Pengukuran umur absolut menunjukkan kisaran 65-48 juta tahun lalu, menunjukkan bahwa Dasit KMLU terbentuk dari magmatisme busur kepulauan pada masa Kapur akhir–Eosen Awal.The Luk Ulo Mélange Complex (KMLU) is an assemblage of various blocks of rock that are mixed tectonically and blanked by scaly clay matrix, in which one of blocks is dacite. This research aims to determine petrological and geochemical characteristics of dacite in order to define its tectonic environments and formation history. The methods used in this research were petrography analysis, geochemical analysis including major elements using fusion inductively coupled plasma (fus ICP), trace and rare earth elements using inductively coupled plasma mass spectrometry (ICP-MS) and K-Ar dating method.  The dacite has a porphyritic texture composed of quartz, plagioclase, and alkali fledspar phenocrysts in microcrystaline biotite and quartz matrix. The high SiO2 content (66.56 - 71.64%) and low K2O content (0.41 - 1.27%) indicating tholeiitic magma affinity source. The low ionic potential elements such as Sr, K, Rb, Ba dan Th in this rock have been enriched 2 - 8 times compared to MORB, whereas the high ionic potential elements of Ta, Nb, Ce, P, Zr, Hf, Sm, Ti, Y dan Yb are lower compared MORB suggest an island arc character. Enrichment of light rare earth elements  (La, Ce, Pr, Nd, Pm, Sm and Eu) is 3 - 9 times compared to chondrit accompanied by gradual depletion pattern of La to Eu elements also indicating an island arc environment.  K-Ar dating analysis shows a range of 65 - 48 Mya or during the Late Cretaceous – Early Eocene. It is concluded that the dacite of the Luk Ulo Complex was formed in an island arc tectonic setting during the Late Cretaceous – Early Eocene

The Influence of Molasses Concentration on the Physical and Mechanical Properties of Evaporation Boat Waste-Based Crucibles

Crucibles are essential tools used in many industries, and their production can be resource-intensive and costly. This study aims to determine the potential of evaporation boat waste produced by the plastic metallization industry with molasses as a binder in crucible production. This study explores the effects of various concentrations of molasses on the mechanical and physical properties of crucibles made from evaporation boat waste. The evaporation boat waste used in this study was crushed and filtered with a 100-mesh sieve. Molasses were added during the mixing process with concentrations of 0 wt.%, 5 wt.%, 10 wt.%, 15 wt.%, and 20 wt.%. The mixing process was done for 120 minutes, followed by compaction with a pressure of 25 MPa. The green body formed is dried at 100?C for 300 minutes. In this study, firing was done at 1150?C temperature with 240 minutes of holding time. The specimens in this study were characterized using XRD, SEM, density, hardness, and 3-point bending tests. The results showed that the resulting crucible only had BN and TiB2 crystalline phases. Using molasses as a binder showed that crucible specimens did not form a new crystalline phase. Increasing the molasses content from 0 wt.% to 5 wt.% led to an increase in the physical and mechanical properties of the crucible specimens. However, the mechanical and physical properties of the crucible specimens decreased with the use of molasses that exceeded 5 wt.%. The best mechanical and physical properties of crucible specimens were produced using 5 wt.% molasses. This composition has a weight percentage of BN and TiB2 of 68.9% and 31.1%, with density, hardness, and flexural strength of 2.36 g/cm3, 64 HRA, and 31.5 MPa

Model Mineralisasi Pembentukan Opal Banten

DOI: 10.17014/ijog.v5i3.100Opal is a beautiful precious gemstone that is equal or more valuable than diamond. In Indonesia, precious opal is found at the Lebak Regency, Province of Banten. Banten’s opal widely has been recognized due to its beautiful opalescence. This paper is a review of the last research; preliminary study of Banten’s opal, characteristics of opal-CT and determining of opal type from geochemical data, added by new data to compile concept and to make mineralization model. In order to fulfill these targets, field geology research and analysis of mineralog/gemology, petrography, X-RD, and major and trace element geochemistry have been done. The Banten’s opal is opal-CT showing opalescence (play of colour), weathering, and leaching silica from volcanic glass by dark grey claystone hosted. Mineralization model is divided into three periods; at Early Pliocene volcanic clastic sediments rich in volcanic glass occured as fluvial sediments. Afterwards, at Late Pliocene - Pleistocene folding, weathering and leaching of silica took place. Intensive jointing, faulting, and folding quickened weathering and leaching processes to formed opal at limb of anticline through Holocene. The prospecting area of Banten’s opal is in tuff unit with intercalation of conglomerate or pumiceous breccia, at limb of anticline. The host rock of opal is dark grey claystone which underlies polimict conglomerate/pebbly sandstone sequence with cross stratification, imbricated, and erossional stucture; more than 8 m deep.</p

Sistem Lapisan Sosial dan Sistem Keagamaan Megalitik-hindu Kuno di Lima Wilayah Kecamatan di Kabupaten Kebumen

Keberadaan sejumlah sebaran artefak Megalitik dan Hindu kuno di lima kecamatan di Kabupeten Kebumen masih minim pengkajian khususnya dari perspektif sosiologis. Keberadaannya lebih didominasi oleh sejumlah narasi yang bersifat mitologis tinimbang historis dan sosiologis.. Metode penelitian yang digunakan dalam penelitian ini adalah kualitatif dengan pendekatan eksplorasi dan deskriptif. Penelitian ini dianalisis menggunakan teori Fungsional Struktural. Hasil riset menujukkan bahwa wilayah Kebumen kuno merupakan tempat tinggal beberapa lapisan masyarakat lebih tua yang hidup di era Megalitik yang ditandai dengan keberadaan sejumlah punden berundak dan struktur batu andesit. Lapisan masyarakat berikutnya adalah masyarakat era Hindu kuno pemuja Siwa yang ditandai dengan keberadaan sejumlah Lingga dan Yoni serta Ganesha. Sekalipun minus data dokumenter mengenai keberadaan masyarakat yang meninggalkan warisan Megalitik dan Hindu kuno, namun melalui analisis fakta sosial material keberadaan artefak dan analisis simbol-simbol keagamaan, didapatkan sejumlah kesimpulan awal yang menjadi landasan bagi penelitian sosiologis berikutnya. Berdasarkan data yang ada dapat disimpulkan bahwa berbagai lapisan sosial keagamaan kuno telah berkontribusi membentuk kehidupan sosial budaya masyarakat Kebumen masa kini