Nanggulan Formation and Its Problem as a Basement in Kulonprogo Basin, YOGYAKARTA

DOI: 10.17014/ijog.4.2.71-80Nanggulan Formation consists of the oldest clastic rock sequence exposed in Kulonprogo area, Yogyakarta. This paper discusses the position of Nanggulan Formation as a basement. The method used in this research is surface and subsurface investigations based on gravity surveys. The rock assemblage is exposed and distributed partly in the east flank of Kulonprogo Mountains with weak undulated morphology. The rock sequence is composed of sand to clay grain sizes such as sandstone, quartz sandstone, calcareous sandstone, claystone, fossiliferous claystone, calcareous claystone, siltstone, and coal seam intercalations. The total thickness of the sequence is less than 200 m. Based on the fossil and palynology investigations, previous investigators concluded the age of the rock was Eocene to Middle Miocene. The geological structures developed in the rocks are the lithological stratification, fractures, folding, and faulting. The subsurface interpretation based on gravity data revealed the rock was located under the andesite breccias with 2.44 g/cc density. The density of the rock sequence was 2.63 g/cc. The gravity interpretation shows a strong indication that Nanggulan Formation underlies the andesitic breccias presumably associated with Old Andesite Formation exposed in Kulonprogo Mountains. The limited distribution, the thickness, and the closed environmental deposition of Nanggulan Formation found in the present investigation raised problems on the position of the formation as the basement of Old Andesite Formation occurring in the Kulonprogo Mountain

Identifikasi Batuan Gunung Api Purba Di Pegunungan Selatan YOGYAKARTA Bagian Barat Berdasarkan Pengukuran Geolistrik

Daerah penelitian berada di perbatasan antara Dataran Yogyakarta dengan Pegunungan Selatan Yogyakarta bagian barat. Secara morfologi dan litologi yang tersingkap, indikasi gunung api purba yang dibuktikan dengan keterdapatan batuan gunung api seperti lava, breksi, dan tuf. Tujuan dari penelitian ini adalah identifikasi adanya batuan gunung api purba di bawah permuaan sepanjang Berbah-Imogiri berdasarkan data geolistrik. Metode yang digunakan adalah melakukan pengukuran geolistrik di empat lokasi secara mapping dengan konfigurasi dipole-dipole. Panjang bentangan untuk setiap lintasan 500 meter. Hasil pengukuran geolistrik menunjukkan pada lintasan 1 di Sumber Kulon-Kalitirto, Kecamatan Berbah,diinterpretasi adanya batuan gunung api berupa lava basal dan tuf. Lintasan 2 di Pilang-Srimulyo, Kecamatan Piyungan, diinterpretasi berupa breksi skoria. Lintasan 3 di Ngeblak-Bawuran, Kecamatan Pleret, diinterpretasi adanya tuf dan lava. Lintasan 4 di Guyangan-Wonolelo, Kecamatan Pleret diinterpretasi berupa tuf dan lava. Batuan gunung api secara umum terbaca mempunyai nilai tahanan jenis yang tinggi, yaitu >300 Ωm. Adanya kandungan air atau mineralisasi cenderung menurunkan nilai tahan jenis batuan gunung api tersebut. The study area is located between western part of Yogyakarta plains and Southern Mountains. The morphology and lithology along the Berbah-Imogiri show the existence of an ancient volcano. This is proven by outcrop of volcanic rock like lava, breccia and tuff. The aim of this study is to identify the existence of ancient volcanic rocks along Berbah-Imogiri based on geoelectrical data. The method used to perform measurements at four locations geoelectrical mapping with dipole-dipole configuration a long stretch of track for every 500 meters. Geoelectrical measurement results showed on track 1 in Source Kulon-Kalitirto, District Berbah, interpretedas volcanic rocks such as basalt lava and tuff. Tracks 2 in Pilang-Srimulyo, District Piyungan, iterpreted as volcanic rocks of scoria breccia. Tracks 3 in Ngeblak-Bawuran, District Pleret, interpreted as lava and tuff. And track 4 on Guyangan-Wonolelo, District Pleret interpreted as form of tuff and lava. Volcanic rocks are generally having a high resistivity value > 300 Ωm. The content of water or mineralization tends to reduce the resistivity value of resistant volcanic rock

Some Key Features and Possible Origin of the Metamorphic Rock-Hosted Gold Mineralization in Buru Island, Indonesia

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\u27 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

MODELO ESTRUTURAL DE GOVERNANÇA DA INFORMAÇÃO PARA BANCOS

The banking industry is recognized as one of the highest information technology (IT) investments in Brazil and worldwide, by having well-defined business processes, and its dynamism in adopting new technologies and processes. In this context, with data from a survey conducted with IT executives of banks operating in Brazil, a structural regression model of information governance (IG) was tested. The main objective is to validate a GI model for banks. The results showed that, in the perception of the IT executives surveyed, the information governance factors - Policies, Systems (IS / IT) and Structure - have direct and indirect effects on value

East Asia in World Trade: The Decoupling Fallacy, Crisis and Policy Challenges

This paper examines the export experience of China and other East Asian economies in the aftermaths of the global financial crisis against the backdrop of pre-crisis trade patterns. The analysis is motivated by the decoupling' thesis, which was a popular theme in the Asian policy circles in the lead-up to the onset of the recent financial crisis, and aims to probe three key issues: Was the East Asian trade integration story that underpinned the decoupling thesis simply a statistical artifact or the massive export contraction caused by an overreaction of traders to the global economic crisis and/or by the drying up of trade credit, which overpowered the cushion provided by intra-regional trade? What are the new policy challenges faced by the East Asian economies? Is there room for an integrated policy response that marks a clear departure from the pre-crisis policy stance favoring export-oriented growth? The findings caution against a possible policy backlash against openness to foreign trade arising from the new-found enthusiasm for rebalancing growth, and make a strong case for a long-term commitment to non-discriminatory multilateral and unilateral trade liberalization

Eksplorasi Geokimia untuk Menentukan Daerah Prospek Mineralisasi Emas Tipe Urat Epitermal: Studi Kasus di Daerah Tompaso, Kabupaten Minahasa Selatan, Sulawesi Utara

Sulawesi Utara termasuk daerah Tompaso, Kabupaten Minahasa Selatan merupakan jalur magmatik yang potensial menghasilkan endapan bijih hidrotermal. Penelitian ini bertujuan menentukan daerah prospek mineralisasi emas khususnya tipe urat epitermal berdasarkan eksplorasi geokimia meliputi geokimia batuan dan sedimen sungai, khususnya metode BLEG (Bulk Leach Extractable Gold). Metode penelitian meliputi pemetaan geologi, alterasi dan jalur urat, percontoan (bijih/batuan dan sedimen sungai), dan analisis geokimia. Sampel bijih dianalisis dengan metode FA/AAS untuk emas dan metode AAS untuk unsur lain, sedangkan analisis sampel sedimen sungai dilakukan dengan metode cyanide leach dan AAS. Hasil penelitian menunjukkan batuan induk mineralisasi berupa lava andesit dan intrusi diorit. Batuan ini mengalami alterasi silica-clay, argilik, dan propilitik. Perpaduan antara pemetaan geologi, zona alterasi, dan jalur urat dengan eksplorasigeokimia batuan dapat menentukan daerah prospek mineralisasi yaitu Prospek Asam dan Polangkok. Pada Prospek Asam, sampel bijih memiliki kandungan emas sampai 0,03 ppm dengan anomali emas pada sampel BLEG menunjukkan nilai threshold 13,52 ppb Au. Pada Prospek Polangkok ditemukan 2 jalur urat (P1 dan P2) berarah baratlaut-tenggara dengan lebar sampai 5 m. Urat P1 memiliki kadar Au mencapai 0,31 ppm dan pada urat P2 mencapai 0,16 ppm Au. Mineralisasi pada Prospek Polangkok didukung oleh anomali Ag pada sampel BLEG dengan nilai threshold 67,18 ppb. Kedua daerah prospek tersebut direkomendasikan untuk eksplorasi lanjut (follow-up exploration)

Potensi Bahaya Gunung Api terhadap Calon Tapak PLTN, Studi Kasus: Gunung Api Semadum, Kalimantan Barat

Aspek kegunungapian merupakan salah satu aspek penting dalam survei pemilihan calon tapak Pembangkit Listrik Tenaga Nuklir (PLTN). Survei bahaya gunung api dilaksanakan pada radius 150 km dari calon tapak PLTN, meliputi survei produk gunung api tua hingga gunung api aktif. Salah satu gunung api muda di daerah Kalimantan Barat adalah Gunung Api Semadum yang terletak di Desa Pisak, Kecamatan Tujuhbelas, Bengkayang berumur Pliosen-Plistosen dengan jarak 115 km dari calon tapak PLTN di Pantai Gosong, Kecamatan Sungai Raya, Bengkayang, Kalimantan Barat. Tujuan penelitian ini adalah untuk mengetahui karakteristik dan potensi bahaya gunung api Semadum terhadap rencana Calon Tapak PLTN. Metodologi yang digunakan adalah interpretasi citra DEM-SRTM untuk mengetahui pola topografi, dilanjutkan dengan kegiatan lapangan pemetaan geologi, pengambilan contoh batuan produk gunung api Semadum dan analisis Petrografi serta geokimia menggunakan X-Ray Fluorescence (XRF). Gunung Semadum tersusun oleh lava andesit-basalt berstruktur vesikuler-skoria, lava andesit berstruktur masif, batuan piroklastika berupa breksi piroklastik dengan fragmen andesit (bom dan blok), breksi lapili/tuf, dan Kubah lava. Kompleks ini secara geokimia tersusun atas trakhiandesite dan dasit yang memiliki afinitas calc-alkaline. Berdasarkan sifat magma dan sebaran produknya, gunung api Semadum tidak memiliki potensi bahaya gunung api terhadap Calon Tapak PLTN