Index of Active Tectonic Assessment: Quantitative-based Geomorphometric and Morphotectonic Analysis at Way Belu Drainage Basin, Lampung Province, Indonesia

The occurrence of subduction zones caused by the collision between the Eurasian-Western Indonesia Plate due to an increase tectonic, volcanic and magmatic activities along Sumatra Island. This study covers the area of Way Belu Drainage Basin, located near Bandar Lampung City, Lampung Province, southern part of Sumatra, Indonesia. The area composes of a complex geological structure as the result of tectonic activities. In this study, geomorphic indices assessment such as morphometric and morphotectonic quantitative analysis are undertaken to identify the Index of Active Tectonics (IAT). The morphometric analysis uses Drainage density (Dd) and Ratio of bifurcation (Rb). The value of Dd respectively from 1.45 to 4.05, Rb from  2 to 10. While the morphotectonic analysis uses basin shape index (Bs), valley floor width-valley height ratio (Vf), and asymmetry factor (AF). The value of Bs from 1.27 to 6.25, Vf   from 0.16 to 3.30, and AF from 22.73 to 83.77 in ranges which is derived average IAT value is 2.20. It may considered that at the Way Belu Drainage Basin has moderate to high tectonic activity. From the joint measurement results on the fracture zone express that the main pattern of faults has trend NWW-SSE, NE-SW, NNE-SSW, NW-SE, and W-E directions. Furthermore, based on the combination of the quantitative geomorphology indices assessment which is supported by remote sensing and field assessment shows that those features closely related to the Semangko Fault System with the NNW-SSE fault trend parallel to its fault

Epithermal Gold-Silver Deposits in Western Java, Indonesia: Gold-Silver Selenide-Telluride Mineralization

DOI: 10.17014/ijog.v1i2.180The gold-silver ores of western Java reflect a major metallogenic event during the Miocene-Pliocene and Pliocene ages. Mineralogically, the deposits can be divided into two types i.e. Se- and Te-type deposits with some different characteristic features. The objective of the present research is to summarize the mineralogical and geochemical characteristics of Se- and Te-type epithermal mineralization in western Java. Ore and alteration mineral assemblage, fluid inclusions, and radiogenic isotope studies were undertaken in some deposits in western Java combined with literature studies from previous authors. Ore mineralogy of some deposits from western Java such as Pongkor, Cibaliung, Cikidang, Cisungsang, Cirotan, Arinem, and Cineam shows slightly different characteristics as those are divided into Se- and Te-types deposits. The ore mineralogy of the westernmost of west Java region such as Pongkor, Cibaliung, Cikidang, Cisungsang, and Cirotan is characterized by the dominance of silver-arsenic-antimony sulfosalt with silver selenides and rarely tellurides over the argentite, while to the eastern part of West Java such as Arinem and Cineam deposits are dominated by silver-gold tellurides. The average formation temperatures measured from fluid inclusions of quartz associated with ore are in the range of 170 – 220°C with average salinity of less than 1 wt% NaClequiv for Se-type and 190 – 270°C with average salinity of ~2 wt% NaClequiv for Te-type.</div

HIDROGEOKIMIA AIRTANAH PADA DAERAH PANTAI: STUDI KASUS DATARAN RENDAH KATAK, DESA SUMBER AGUNG, KABUPATEN BANYUWANGI

This paper describes the groundwater quality assessment conducted in Katak lowland area, in Banyuwangi District, East Java. The quality of water salinity had been identified during field observation. In order to identify the origin of saline groundwater, a hydrogeochemical study has been carried out by analysing of 12 groundwater wells, 3 surface water and sea water. Hydrogeochemical analysis identified major ion elements on Piper′s diagram to know the facies and dominant ion content in ground water study area. The interpretation of plots for different major ions suggests that saline water in Katak are typically salt water intrusion and flushing salt residue in marine sediment/limestone. This hydrochemical research area provides new insights into the geochemical relationships between freshwater and seawater at different depths in coastal and alluvial sediments. Saltwater intrusion occurs due to cone of depression caused by concentrated exploitation of groundwater in the south/coastal area, and flushing mainly by groundwater flow through marine sediment/limestone in the northern area. Groundwater zonation is characterized by hydrochemical type from natrium chloride type in the southern area to calciumsulphate  type in the northern  area. Controlled by hydrodynamic of groundwater with salt water and flushing of geochemical by ground water, respectively. AbstrakMakalah ini menjelaskan hasil dari penilaian kualitas airtanah yang dilakukan di daerah dataran rendah Katak, di Kabupaten Banyuwangi, Jawa Timur. Kualitas airtanah yang asin telah teridentifikasi saat observasi lapangan. Dalam rangka mengidentifikasi asal air asin di daerah Katak, studi hidrogeokimia dilakukan terhadap sampel airtanah dari 12 airtanah sumur/bor, 3 air permukaan dan air laut. Analisis hidrokimia dilakukan dengan pengeplotan unsurunsur ion utama pada diagram Piper untuk mengetahui fasies dan kandungan ion dominan pada airtanah di daerah penelitian. Interpretasi plot untuk ion utama menunjukkan bahwa salinitas di daerah Katak diakibatkan oleh intrusi air laut dan pembilasan garam-garam pada sedimen marine/batugamping. Penelitian hidrokimia di daerah dataran rendah Katak memberikan wawasan baru mengenai hubungan antara air tawar dan air laut pada kedalaman yang berbeda di dalam sedimen pantai dan aluvial. Intrusi air asin terjadi karena kerucut depresi yang disebabkan oleh eksploitasi air tanah terkonsentrasi di bagian selatan yang merupakan daerah pesisir dan pembilasan karena aliran air tanah melalui sedimen marine/batugamping di Utara. Zonasi jenis airtanah diketahui dari karakteristik hidrokimianya, mulai dari jenis natrium klorida di Selatan sampai kalium sulfat di Utara. Hal tersebut masing-masing dikontrol oleh hidrodinamika airtanah dengan air asin dan pelarutan kimia batuan oleh airtanah