Moetamar Moetamar
Center for Geological Resources, Geological Agency, Bandung

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Some Key Features and Possible Origin of the Metamorphic Rock-Hosted Gold Mineralization in Buru Island, Indonesia Idrus, Arifudin; Prihatmoko, Sukmandaru; Hartono, Hill. Gendoet; Idrus, Fadlin; Ernowo, Ernowo; Franklin, Franklin; Moetamar, Moetamar; Setiawan, Iwan
Indonesian Journal on Geoscience Vol 1, No 1 (2014)
Publisher : Geological Agency

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Abstract

DOI: 10.17014/ijog.v1i1.172This paper discusses characteristics of some key features of the primary Buru gold deposit as a tool for a better understanding of the deposit genesis. Currently, about 105,000 artisanal and small-scale gold miners (ASGM) are operating in two main localities, i.e. Gogorea and Gunung Botak by digging pits/shafts following gold-bearing quartz vein orientation. The gold extraction uses mercury (amalgamation) and cyanide processing. The field study identifies two types/generations of quartz veins namely (1) Early quartz veins which are segmented, sigmoidal, dis­continous, and parallel to the foliation of host rock. The quartz vein is lack of sulfides, weak mineralized, crystalline, relatively clear, and maybe poor in gold, and (2) Quartz veins occurred within a ‘mineralized zone’ of about 100 m in width and ~1,000 m in length. The gold mineralization is strongly overprinted by an argillic alteration zone. The mineralization-alteration zone is probably parallel to the mica schist foliation and strongly controlled by N-S or NE-SW-trending structures. The gold-bearing quartz veins are characterized by banded texture particularly colloform following host rock foliation and sulphide banding, brecciated, and rare bladed-like texture. The alteration types consist of propylitic (chlorite, calcite, sericite), argillic, and carbonation represented by graphite banding and carbon flakes. The ore mineralization is characterized by pyrite, native gold, pyrrhotite, and arsenopyrite. Cinnabar, stibnite, chalcopyrite, galena, and sphalerite are rare or maybe absent. In general, sulphide minerals are rare (<3%). Fifteen rock samples were collected in Wamsaid area for geochemical assaying for Au, Ag, As, Sb, Hg, Cu, Pb, and Zn. Eleven of fifteen samples yielded more than 1.00 g/t Au, in which six of them are in excess of 3.00 g/t Au. It can be noted that all high-grade samples are originally or containing limonitic materials, that suggest the role of supergene enrichment. Interestingly, most of the high-grade samples contain also high grade As (up to 991ppm), Sb (up to 885 ppm), and Hg (up to 75 ppm). Fluid inclusions in both quartz vein types consist of four phases including L-rich, V-rich, L-V-rich, and L1-L2-V (CO2)-rich phases. Mineralizing hydrothermal fluid is typified by CO2-rich fluid, moderate temperature of 300 - 400 ºC and a typical low salinity (0.36 to 0.54 wt.% NaCl eq). Based on those key features, gold mineraliza­tion in Buru Island meets the characteristics of LS epithermal or orogenic gold deposit types; however, it tends to be fitter with orogenic gold deposit rather than another type.  
Geologi Dan Mineralisasi Daerah Satoko Kabupaten Polewali Mandar, Sulawesi Barat Ernowo, Ernowo; Widhi, Bambang Nugroho; Moetamar, Moetamar
Buletin Sumber Daya Geologi Vol 7, No 1 (2012): Buletin Sumber Daya Geologi
Publisher : Buletin Sumber Daya Geologi

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Abstract

Batuan pembawa mineralisasi daerah Satoko berupa syenodiorit yang telah mengalami ubahan argilik dengan komposisi didominasi monmorilonit dan haloisit dengan sedikit nontronit. Luas daerah mineralisasi sekitar 0.49 km, dalam bentuk urat-urat kuarsa yang teramati pada beberapa sumur uji. Urat kuarsa berwarna putih susu dengan struktur banded, vuggy dan dog teeth terisi pirit sangat halus, oksida besi, hematit dan limonit. Ketebalan urat kuarsa bervariasi antara 2 – 4 cm dan membentuk zona urat mencapai lebar 40 cm. Analisis kimia dari conto urat kuarsa menunjukkan nilai tertinggi kandungan unsur logam 6.326 ppm Au, 40 ppm Cu, 5.526 ppm Pb, 379 ppm Zn, 5 ppmAg, 4.65% Fe, 35 ppmAs, 8 ppm Mo dan 7 ppm Sb. Korelasi yang erat ditunjukkan oleh kemunculan Cu, Pb dan Zn dengan nilai koefisien diatas 0,8, sedangkan Au menunjukkan korelasi negatif dengan unsur-unsur lain. Analisis inklusi fluida mengindikasikan mineralisasi terjadi pada kisaran temperatur antara 220°-300°C dan kedalaman 291,53 – 863,16 m Kisaran temperatur tersebut merupakan lingkungan tipe mineralisasi epitermal.
Karakteristik Cebakan Bauksit Laterit Di Daerah Sepiluk - Senaning, Kabupaten Sintang, Kalimantan Barat Toreno, Eko Yoan; Moetamar, Moetamar
Buletin Sumber Daya Geologi Vol 7, No 2 (2012): Buletin Sumber Daya Geologi
Publisher : Buletin Sumber Daya Geologi

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Abstract

Keberadaan bauksit laterit di daerah Sepiluk-Senaning, Kabupaten Sintang, Kalimantan Barat terbentuk pada kemiringan lereng 10° s.d. 14°. Batuan asal yang terdapat di daerah ini adalah batuan gunungapi pra-Tersier dengan jenis fonolit kaya akan kandungan unsur aluminium dengan mineral gibsit, felspar dan cliachit yang mudah larut kemudian mengalami proses laterisasi. Penyelidikan bauksit didaerah ini dilakukan dengan channel sampling pada sumur uji dengan ketebalan rata-rata bauksit laterit sebesar 2,6 m dan pengambilan conto sebanyak 39.Hasil korelasi antara penampang sumur uji, memperlihatkan penyebaran bauksit lateritmenipis ke arah tenggara-baratlaut. Berdasarkan hasil analisis kimia terhadap conto laterit diperoleh kadar rata-rata 52,64 % Al O ; 3,60% SiO ; 9,83 % Fe O dan 1,34 % TiO dengan faktor konkresi 0,58 %.
Some Key Features and Possible Origin of the Metamorphic Rock-Hosted Gold Mineralization in Buru Island, Indonesia Idrus, Arifudin; Prihatmoko, Sukmandaru; Hartono, Hill. Gendoet; Idrus, Fadlin; Ernowo, Ernowo; Franklin, Franklin; Moetamar, Moetamar; Setiawan, Iwan
Indonesian Journal on Geoscience Vol 1, No 1 (2014)
Publisher : Geological Agency

Show Abstract | Original Source | Check in Google Scholar | Full PDF (998.411 KB)

Abstract

DOI: 10.17014/ijog.v1i1.172This paper discusses characteristics of some key features of the primary Buru gold deposit as a tool for a better understanding of the deposit genesis. Currently, about 105,000 artisanal and small-scale gold miners (ASGM) are operating in two main localities, i.e. Gogorea and Gunung Botak by digging pits/shafts following gold-bearing quartz vein orientation. The gold extraction uses mercury (amalgamation) and cyanide processing. The field study identifies two types/generations of quartz veins namely (1) Early quartz veins which are segmented, sigmoidal, dis­continous, and parallel to the foliation of host rock. The quartz vein is lack of sulfides, weak mineralized, crystalline, relatively clear, and maybe poor in gold, and (2) Quartz veins occurred within a ‘mineralized zone’ of about 100 m in width and ~1,000 m in length. The gold mineralization is strongly overprinted by an argillic alteration zone. The mineralization-alteration zone is probably parallel to the mica schist foliation and strongly controlled by N-S or NE-SW-trending structures. The gold-bearing quartz veins are characterized by banded texture particularly colloform following host rock foliation and sulphide banding, brecciated, and rare bladed-like texture. The alteration types consist of propylitic (chlorite, calcite, sericite), argillic, and carbonation represented by graphite banding and carbon flakes. The ore mineralization is characterized by pyrite, native gold, pyrrhotite, and arsenopyrite. Cinnabar, stibnite, chalcopyrite, galena, and sphalerite are rare or maybe absent. In general, sulphide minerals are rare (<3%). Fifteen rock samples were collected in Wamsaid area for geochemical assaying for Au, Ag, As, Sb, Hg, Cu, Pb, and Zn. Eleven of fifteen samples yielded more than 1.00 g/t Au, in which six of them are in excess of 3.00 g/t Au. It can be noted that all high-grade samples are originally or containing limonitic materials, that suggest the role of supergene enrichment. Interestingly, most of the high-grade samples contain also high grade As (up to 991ppm), Sb (up to 885 ppm), and Hg (up to 75 ppm). Fluid inclusions in both quartz vein types consist of four phases including L-rich, V-rich, L-V-rich, and L1-L2-V (CO2)-rich phases. Mineralizing hydrothermal fluid is typified by CO2-rich fluid, moderate temperature of 300 - 400 ºC and a typical low salinity (0.36 to 0.54 wt.% NaCl eq). Based on those key features, gold mineraliza­tion in Buru Island meets the characteristics of LS epithermal or orogenic gold deposit types; however, it tends to be fitter with orogenic gold deposit rather than another type.