MAYKHEL HAGANA GINTING, EFRAIM (2021) MODEL GENETIK ENDAPAN GREISEN BERDASARKAN INTEGRASI RESPONS GEOFISIKA DAN STUDI GEOLOGI DI DAERAH PEMALI, BANGKA, KEPULAUAN BANGKA BELITUNG GENETIC MODEL OF GREISEN DEPOSITS BASED ON GEOPHYSICAL RESPONSE INTEGRATION AND GEOLOGICAL STUDIES IN PEMALI REGION, BANGKA, BANGKA BELITUNG ISLANDS. Other thesis, Universitas Pembangunan Nasional "Veteran" Yogyakarta.
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INTISARI MODEL GENETIK ENDAPAN GREISEN BERDASARKAN INTEGRASI RESPONS GEOFISIKA DAN STUDI GEOLOGI DI DAERAH PEMALI, BANGKA, KEPULAUAN BANGKA BELITUNG 1Efraim Maykhel Hagana Ginting 1Teknik Geofisika Universitas Pembangunan Nasional “Veteran” Yogyakarta *Email : efraimmayhel@gmail.com Letak geografis yang dilalui oleh Sabuk Timah Asia Tenggara adalah latar belakang Indonesia berada pada peringkat pertama produsen timah dunia. Pemali adalah bagian dari Kepulauan Timah Bangka Belitung yang setiap tahunnya dapat menghasilkan hingga 270 ton timah dari aktivitas tambang terbuka. Endapan timah primer yang sulit dipelajari karena intensya pelapukan tropis selama Neosen dan Kuarter menjadi tantangan bagi geofisika dalam melanjutkan eksplorasi bawah permukaan. Survei geofisika terdiri dari gravitasi, magnetik, resistivitas, time-domain induced polarization, dan handheld susceptibilitymeter. Secara regional, granit pembawa timah diketahui teremplasemen pada shear zone yang direpresentasikan oleh zona gravitasi dan magnetisme tereduksi (-2.7 hingga -0.9 mGal dan 20 – 30 nT). Zona ini juga berkorelasi dengan kontak aureola luas akibat terobosan pluton granit post-orogenik (2.67 g/cc dan 1.95 x 10-3 cgs) yang kemudian menuju permukaan diikuti dengan pelapukan, alterasi serisitisasi, dan alterasi argilik pada metabatulempung (densitas mencapai 1.7 g/cc). Disana terdapat kontak aureola sempit (kupola tergreisenisasi) yang dicirikan oleh anomali magnetik tunggal bersifat konsentris dimana terdiri dari dike, baked contact, dan batuan samping. Dike granit bertekstur sedang direpresentasikan oleh induksi magnetik paling tinggi (28 – 34.5 nT), amplitudo FVD gravitasi yang menuju positif (-0.003 hingga -0.0004 mGal/m) di sepanjang profil nilai gravitasi rendah, tubuh resistivitas (800 – 1600 ohm.m) berbentuk vertikal, dan chargeabilitas paling rendah (0 – 10 msec). Sekis mika direpresentasikan oleh remanensi magnetik yang tinggi (16.5 – 34 nT), tubuh resistivitas (1600 hingga >3200 ohm.m) berbentuk lateral, dan chargeabilitas (10 – 50 msec). Metabatulempung teralterasi/terlapukan direpresentasikan oleh nilai terendah dari magnetik, gravitasi, dan resistivitas (11 – 27 nT, -0.007 hingga -0.003 mGal/m, dan 25 – 800 ohm.m) serta chargeabilitas menengah (10 – 30 msec). Korelasi antara magnetisme dan sumber mineralisasi timah primer yang berbanding lurus dibuktikan oleh nilai magnetik paling tinggi (33 – 45 nT) pada granit bertekstur sedang yang mengandung turmalin Fe, nilai magnetik dan suseptibilitas menengah (28 – 34.5 nT dan 56 x 10-3 cgs) pada granit bertekstur sedang terfoliasi, serta nilai magnetik dan suseptibilitas paling rendah (29 – 30 nT dan 18 x 10-3 cgs) pada granit bertekstur sedang yang mengandung turmalin Mg. Model 2D magnetik juga mengonfirmasi nilai suseptibilitas granit bertekstur sedang yang mengandung turmalin Fe lebih besar (0.0007 cgs) daripada granit bertekstur sedang terfoliasi (0.00065 cgs). Solusi Euler data magnetik (N = 0.5), lineamen gradien horisontal gravitasi, anomali resistivitas paling rendah (0 – 400 ohm.m) dan chargeabilitas paling tinggi (50 – 70 msec) mengonfirmasi sesar berarah NW-SE yang mengontrol ruang untuk emplasemen host rock dan cebakan mineralisasi Sn paling baik (761.33 - 1718.67 ppm) yang berasosiasi dengan logam sulfida. Model genetik endapan timah primer akhirnya tergambarkan sebagai dike granit bertekstur sedang teralterasi greisen dengan lebar ± 100 m pada elevasi mulai dari -70 m yang semakin dalam berkorelasi dengan granit bertekstur kasar teralterasi albitisasi. Semakin ke luar sistem, dijumpai sekis mika/hornfels yang teralterasi silisifikasi dan metabatulempung yang teralterasi argilik dan terlapukan. Adapun vein system direfleksikan oleh granit bertekstur sedang terisi vein dan kumpulan alterasi greisenisasi. Kata Kunci: Geofisika, Granit, Greisen, Model, Timah ABSTRACT GENETIC MODEL OF GREISEN DEPOSITS BASED ON GEOPHYSICAL RESPONSE INTEGRATION AND GEOLOGICAL STUDIES IN PEMALI REGION, BANGKA, BANGKA BELITUNG ISLANDS 1Efraim Maykhel Hagana Ginting 1Teknik Geofisika Universitas Pembangunan Nasional “Veteran” Yogyakarta *Email : efraimmayhel@gmail.com Geographical location where Southeast Asian Tin Belt pass through is the main reason that Indonesia ranked first in the world tin producer. Pemali is part of Bangka Belitung Tin Island that anually produced 270 tons of tin from open pit activities. Primary tin deposits which difficulty studied due to intense tropical weathering during Neogene and Quatenary is a challange to subsurface geophysical exploration. The survey consists of gravity, magnetic, resistivity, time-domain induced polarization, and handheld susceptibilitymeter. On regional scale, tin-bearing granite is known to be emplaced in a shear zone represented by reduced zone of gravity and magnetism (-2.7 to -0.9 mGal and 20-30 nT). This zone is also correlated with extensive aureola contact due to post-orogenic granite pluton intrusive (2.67 g / cc and 1.95 x 10-3 cgs) which followed by weathering, sericitization alteration, and argillic alteration in metaclaystone towards the surface (density up to 1.7 g / cc). There is a narrow aureola contact (greisenized cupola) which is characterized by a single concentric magnetic anomaly consists of dyke, baked contact, and wall rock. Dyke of medium textured granite is represented by the highest magnetic induction (28 - 34.5 nT), positive gravitational FVD amplitude (-0.003 to -0.0004 mGal/ m) along the low gravity value profile, vertical resistive body (800 - 1600 ohm.m), and the lowest chargeability (0 - 10 msec). The mica schist is represented by high magnetic remanence (16.5 - 34 nT), lateral resistive body (1600 to> 3200 ohm.m), and high enough chargeability (10 - 50 msec). Altered/weathered metaclaystone is represented by the lowest values of magnetic, gravity, and resistivity (11 - 27 nT, -0.007 to -0.003 mGal/m, and 25 - 800 ohm.m) and medium chargeability (10 - 30 msec). The correlation between magnetism and primary tin mineralization sources which is directly proportional is evidenced by the highest magnetic value (33 - 45 nT) in medium textured granite containing Fe tourmaline, medium value of magnetic and susceptibility (28 - 34.5 nT and 56 x 10- 3 cgs) in foliated medium textured granite, and the lowest valueof magnetic and susceptibility (29 - 30 nT and 18 x 10-3 cgs) in medium textured granite containing Mg tourmaline. The 2D magnetic model also confirms that susceptibility value of medium textured granite which contains tourmaline Fe is greater (0.0007 cgs) than foliated medium textured granite (0.00065 cgs). Euler's solution of magnetic data (N = 0.5), horizontal gravitational gradient lineament, low resistivity anomaly (0 - 400 ohm.m) and highest chargeability (50 – 70 msec) confirm the NW-SE trending fault that controls the extensional domain for host rock emplacement and as a favourable trap of Sn mineralized (761.33 - 1718.67 ppm) in association with metal sulfides. The genetic model of primary tin deposition is finally described as a medium-textured granite altered greisen with a width of ± 100 m at elevations ranging from -70 m which is correlated with albitized coarse textured granite at depth. Heading outside the system, we can find a mica schists/hornfels altered silicified and metaclaystone altered argillic and weathered. The vein system is reflected by medium textured granite filled with veins and greisenization alterations. Keywords: Geophysics, Granite, Greisen, Model, Tin
| Item Type: | Thesis (Other) |
|---|---|
| Subjects: | Q Science > QC Physics |
| Divisions: | Faculty of Engineering, Science and Mathematics > School of Civil Engineering and the Environment |
| Depositing User: | Muji Isambina |
| Date Deposited: | 15 Feb 2021 04:37 |
| Last Modified: | 15 Feb 2021 04:37 |
| URI: | http://eprints.upnyk.ac.id/id/eprint/24646 |
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