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Geology and Deposit Model of Primary Tin Mineralization in Bangka Island, Indonesia: Case Study on Pemali Tin Mine

MANINJI, LAMECK, Dr. Lucas Donny Setijadji ; Dr. Ir. I. Wayan Warmada

2015 | Tesis | S2 Teknik Geologi

Mineralisasi timah primer di Pemali Tambang Timah kurang jelas diketahui atau dipahami sebaik baiknya. Kebutuhan untuk memahami mineralisasi telah diharuskan oleh basis berkurang sumber daya endapan timah sekunder di Pulau Bangka. Untuk menyelidiki soal tersebut, tujuan penelitian ini adalah untuk memperbarui peta geologi daerah penelitian dari salah satu yang diproduksi pada tahun 1990; menentukan komposisi kimia batuan mineral dan sampel tanah menggunakan metode geokimia; mengidentifikasi bijih dan mineral alterasi terkait dari sampel yang dikumpulkan menggunakan mikroskop dan XRD; dan, menentukan sifat model deposit timah primer di daerah penelitian. Pengamatan geologi dan pengambilan sampel dilaksanakan selama penelitian lapangan. Analysis laboratorium terkandung petrografi (8 sayatan tipis); ICP-MS (7 sampel); bulk, AD dan EG dipisahkan XRD liat analisis (14 sampel masing-masing); dan mikroskop mineral bijih (17 bagian dipoles). Setidaknya dua singkapan granit yang diamati: granit Klabat yang relatif tua; dan, granit Aplit yang relative muda menengah dan berbutir dua-mika. Hasil penelitian menunjukkan bahwa mineralisasi timah primer di daerah penelitian terkontrol struktural NW-SE sesar normal yang relatif tua. Mineralisasi timah primer, bersama-sama dengan pengendapan logam dasar, juga terbatas pada emplacement granit Aplit yang berbutir dua mika, dengan konsentrasi bijih tertinggi di zona greisen di atasnya. Granit Klabat memiliki mineralisasi Sn yang sangat rendah. Eksolusi mineral bijih telah diamati dari sampel batuan yang berasal dari sepanjang sekitar sesar sinistral NE -SW yang kelihatannya bersifat pos mineralisasi. Kasiterit dikaitkan dengan mineral seperti sfalerit, arsenopirit, stanit, kalkopirit, bornit, monasit dan wolframite. Sementara konsentrasi logam dasar meningkat dengan kedalaman mulai dari zona greisen ke bawah; As, Pb, Sn dan W diamati tertinggi di zona greisen daripada granit Aplit di bawahnya. Antara alterasi hypogene yaitu greisenization, silisifikasi dan filik; hampir semua yang overprint oleh alterasi supergen argilik (intermediate), yaitu pelapukan laterit dalam dan oksidasi. Model candangan timah primer di Pemali menyerupai kombinasi deposit timah Uni Soviet dan pengendapan mineral lapisan Cornish sederhana meskipun beberapa perbedaan mengakibatkan keperluan perbaikan dari hasil kombinasi keduanya. Dalam hal ini, model konseptual mineralisasi timah utama telah dibangun berdasarkan hasil penelitian ini. Keterbatasan pembangunan sebuah model ideal termasuk tidak dapat diaksesnya data perboran selama periode penelitian dan kurangnya informasi yang jelas mengenai jumlah dan kepastian fase mineralisasi timah di daerah penelitian. Kedua fakta tersebut dapat menyebabkan penyederhanaan model endapan.

Primary tin mineralization at Pemali Tin Mine is neither clearly known nor clearly understood. The need to understand the mineralization has been necessitated by the dwindling resource base of secondary placer tin deposits in Bangka Island. To probe into the problem, the objectives of the study were to update the geological map of the study area from the one produced in 1990; determine the chemical composition of mineralized rocks and soil samples using geochemical methods; identify ore and associated alteration minerals from collected samples using microscopy and XRD; and, determine the nature of the model of the primary tin deposit in the study area. Geological observations and sampling were contacted during fieldwork. Laboratory work entailed petrography (8 thin sections); ICP-MS (7 samples); bulk, air dried and EG separated clay XRD analysis (14 samples each); and ore mineral microscopy (17 polished sections). At least two granitic outcrops were observed: the older Klabat granite and the younger medium grained two-mica Aplite granite. Results indicate that tin mineralization in the study area is structurally controlled by the relatively older NW - SE trending normal fault. Primary tin mineralization, together with base metals deposition, is also restricted to the emplacement of the medium grained two-mica Aplite granite, with the highest ore concentration in the greisen zone above it. The Klabat granite has very low Sn mineralization. Ore mineral exsolutions were observed along the vicinity of the post mineralization NE - SW trending sinistral fault. Cassiterite is associated with minerals such as sphalerite, arsenopyrite, stannite, chalcopyrite, bornite, monazite and wolframite. While base metal concentration increased with depth; As, Pb, Sn and W were observed to be highest in the greisen rather than the Aplite granite. Types of hypogene alteration are greisenization, silicification and phyllic alteration; almost all of which were overprinted by supergene (intermediate) argillic alteration, deep lateritic weathering and oxidation. The Pemali Tin Deposit Model resembles that of a combination of the U.S.S.R. tin deposit and the simplified general order of deposition of the Cornish lode minerals although some differences resulted in ammendments of the resultant. In this case, a conceptual model of primary tin mineralization has been constructed based on findings of this research. Limitations to the construction of an ideal model included inaccessibility of drillhole data during the period of research and lack of clear information regarding the exact number of tin mineralization phases in the study area; both of which may lead to oversimplification of a deposit model.

Kata Kunci : Geologi, Model Endapan, Mineralisasi Timah Primer, Pemali Tambang Timah ; Geology, Deposit Model, Primary Tin Mineralization, Pemali Tin Mine

  1. S2-2015-354194-bibliography.pdf  
  2. S2-2015-354194-title.pdf