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All Journal Jurnal Geologi dan Sumberdaya Mineral (Journal of Geology and Mineral Resources)
Hamdan Z.Abidin, Hamdan
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Education Energy Engineering Environmental Science

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Pb-Zn-Ag DEPOSITS AT TANJUNG BALIT, LIMAPULUH KOTA REGENCY, WEST SUMATERA Z.Abidin, Hamdan
Jurnal Geologi dan Sumberdaya Mineral Vol 18, No 4 (2008): Jurnal Sumber Daya Geologi
Publisher : Pusat Survei Geologi

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Abstract

A Pb-Zn-Ag deposit located at Tanjung Balit, Limapuluh Kota Regency, West Sumatra, is hosted within the meta sedimentary rocks of the Tapanuli Group. The lithology consists of interbedded shale, meta sandstone, slate and phyllite (Kuantan Formation). The deposit is in the form of veins, veinlets and disseminated. The thickness of veins ranges from few centimeters up to 5 meters.  In places, some ore bodies are conformable with the host rocks. The main ores are lead, sphalerite, chalcopyrite, pyrite and silver with minor marcasite, magnetite, chalcosite and gold. Hydrothermal mineral assemblages consist of silica, illite, monmorillonite, pyrophyllite, muscovite, siderite, diaspore, dickite, magnesite, chlorite, carbonate, rhodochrosite, analcime, alunite, smectite, ankerite, calcite, dolomite, sericite and zeolite. Fluid inclusion measurements of secondary inclusions within quartz veins indicate that the homogenization temperature (Th) ranges from 185 - 350ºC. The presence of alunite, higher content of base metals as well as higher temperature range of the secondary fluids suggests that the deposit may characterize a high suphidation epithermal type. Keywords : Tanjung Balit, Tapanuli Group, fluid inclusion,  high sulphidation epithermal
Petrology of Lava from The Maninjau Lake, West Sumatera H.Harahap, Bhakti; Z.Abidin, Hamdan
Jurnal Geologi dan Sumberdaya Mineral Vol 16, No 6 (2006): Jurnal Sumber Daya Geologi
Publisher : Pusat Survei Geologi

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Abstract

Andesitic lavas and rhyolitic tuffs are the main products of the Maninjau Lake during Pleistocene. The lava is distributed up to radius of 20 km, whiles the tuff 100 km that suggests a high explosive volcanic. The lava is exposed beautifully along the road from Bukit Tinggi to Lubuk Basung mapped as Qamj on the 1:250 000 geologic map of Padang Quadrangle. The lava is having sheeting joint in some parts, dark gray, highly porphyritic in texture with phenocrysts of plagioclase, clino- pyroxene, ortho-pyroxene and opaques. Quartz phenocryst occurs in rhyolite lavas that are rarely found in the area. Xenoliths of diorite are occurred in some andesite. The lavas have narrow range in silica composition ranging from 54-60 wt % and rarely up to 69 wt%. K2O versus SiO2 relationship shows that analyzed samples belong to calc-alkaline series which are mainly of high-K. While the trace element of the rocks is summarized on the spider diagram, here their patterns strongly resemble the typical of arc lavas with enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high field strength elements (HFSE) and heavy REE (HREE). More over, these patterns show an Nb resembling the arc type magma commonly resulted from subduction, whether in island arc or active continental margin. The geochemical characteristic of the lava from Maninjau Lake is a lower concentration of Ba, Sr and La than other active continental margin like the Andes volcanic rocks. Like many other subducted related rocks, the andesite characterize a very evolved magma, where they have low MgO concentrations (3 wt%) with Mg# 30-53. According to the plate tectonic model, Sumatera is on the continental side to subduction process since Eocene until the present. The presence of subducted magma character in Maninjau Lake area was argued to have been accounted during the eastward subduction of the India-Australia Oceanic Crust. It seems also that Sumatra Fault Zone is a very important agent to conduit magma onto the surface in the Barisan Ranges including the lava resulted from Maninjau Lake. Keywords :  petrology, andesitic lava, rhyolitic tuff, Maninjau, Pleistocene
Co-Authors Bhakti H.Harahap, Bhakti