The vein system in the Arinem area is a gold-silver-base metal deposit of Late Miocene (8.8-9.4 Ma) age located in the southwestern part of Java Island, Indonesia. The mineralization in the area is represented by the Arinem vein with a total length of about 5900 m, with a vertical extent up to 575 m, with other associated veins such as Bantarhuni and Halimun. The Arinem vein is hosted by andesitic tuff, breccia, and lava of the OligoceneMiddle Miocene Jampang Formation (23-11.6 Ma) and overlain unconformably by Pliocene-Pleistocene volcanic rocks composed of andesitic-basaltic tuff, tuff breccia and lavas. The inferred reserve is approximately 2 million tons at 5.7 g t -1 gold and 41.5 g t -1 silver at a cut-off of 4 g t -1 Au, which equates to approximately 12.5t of Au and 91.4t of Ag. The ore mineral assemblage of the Arinem vein consists of sphalerite, galena, chalcopyrite, pyrite, marcasite, and arsenopyrite with small amounts of pyrrhotite, argentite, electrum, bornite, hessite, tetradymite, altaite, petzite, stutzite, hematite, enargite, tennantite, chalcocite, and covellite. These ore minerals occur in quartz with colloform, crustiform, comb, vuggy, massive, brecciated, bladed and calcedonic textures and sulfide veins. A pervasive quartz-illite-pyrite alteration zone encloses the quartz and sulfide veins and is associated with veinlets of quartz-calcite-pyrite. This alteration zone is enveloped by smectite-illite-kaolinitequartz-pyrite alteration, which grades into a chlorite-smectite-kaolinite-calcite-pyrite zone. Early stage mineralization (stage I) of vuggy-massive-banded crystalline quartz-sulfide was followed by middle stage (stage II) of banded-brecciated-massive sulfide-quartz and then by last stage (stage III) of massive-crystalline barren quartz. The temperature of the mineralization, estimated from fluid inclusion microthermometry in quartz ranges from 157 to 325°C, whereas the temperatures indicated by fluid inclusions from sphalerite and calcite range from 153 to 218 and 140 to 217°C, respectively. The mineralizing fluid is dilute, with a salinity <4.3 wt% NaCl equiv. The ore-mineral assemblage and paragenesis of the Arinem vein is characteristically of a low sulfidation epithermal system with indication of high sulfidation overprinted at stage II. Boiling is probably the main control for the gold solubility and precipitation of gold occurred during cooling in stage I mineralization.

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 (D d) and Ratio of bifurcation (R b). The value of D d respectively from 1.45 to 4.05, R b from 2 to 10. While the morphotectonic analysis uses basin shape index (Bs), valley floor width-valley height ratio (V f), and asymmetry factor (AF). The value of Bs from 1.27 to 6.25, V f 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 WE 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.

The researched area is situated at Mount Rendingan and its surrounding area, Lampung Province, the southern part of Sumatra Island. It has a big potential of geothermal resource in line with a unique graben like bowl landform and geothermal surface manifestations. This research was carried out using remote sensing and field observation methods. The remote sensing method used topography and Shuttle Radar Topography Mission-Digital Elevation Model (SRTM-DEM) maps to analyze morphotectonic attributes, and the result was validated by morphotectonic data analysis from field observation. The purpose of this research is to evaluate the relation between morphotectonic and the appearances of geothermal surface manifestations. The interpretation of SRTM-DEM and topographic maps are supported by morphotectonic analyses,which indicate that the geothermal surface manifestations in this area are controlled by tectonic activity. It has various levels of lift which are shown by the values of valley height weight ratio (V f) from 0.16 to 3.31 and the values of mountain front sinuosity (S mf) from 1.05 to 2.09. The morphotectonic characteristics can describe the geological structure activity levels which are reflected in the landform and its rock. The volcanic areas consist of igneous rocks which have small primary permeabilities. However, the development of geological structure can cause fractures in the rock that step in as a medium for passing geothermal fluid from depth to surface. They are found on the fault intersection zone system trending NE-SW and NW-SE, NNE-SSW and NNW-SSE, and WE system directions that indicate the fault system is correlated with the appearances of geothermal manifestations.

ABSTRAK Makalah 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.