Conversations with the Earth

Tuesday, September 10, 2013

Mineralization Study of Ringin Putih Vein, Southern Mountain Part of East Java, Indonesia

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Ringin Putih district is located in the Southern Mountain Part of East Java. This area shows the epithermal system indication which is a part of the Early Cretaceous tectonic evolution of the Sunda-Banda arc. The lithologies of the Ringin Putih area are dominated by an andesitic-basaltic lava, tuff, clay, and pyroclastic rocks. The mineralization indications are characterized by the copper mineralization and the presence of ubiquitous sulphide minerals. Petrography, mineralogy, X-Ray Diffraction (XRD) analysis was conducted in order to obtain the basic data for the mineralization and alteration properties. The indication of quartz-feldspar-actinolite (?)-epidote-chlorite, often with magnetite facies, indicates that the sample represent propylitic alteration, that is caused by the iron and the sulfur-bearing hydrothermal fluids; whilst the pyrophyllite-quartz-sericite-illite is correspond with the illite-kaolinite group minerals, and represent the phyllic alteration. Pyrophyllite-rutile are tend to be formed in the acidic environments and the oxidized fluids; while the smectite-illite-chlorite-epidote-biotite were formed in the near-neutral pH and reduced fluids. The transition from the acidic-oxidized fluids into the near neutral-reduced fluid gives the preliminary indication of fluids from the great depth and fluids from the near surface water.

The magmatic arc system in Indonesia is the result of a complex history of tectonic events including the plate subduction and the arc magmatism. The Sunda-Banda volcanic island arc is the longest arc in Indonesia, extending from Aceh to East Damar (Carlile and Mitchell, 1994). Based on Van Bemmelen (1949) physiography, the area study is located in the Southern Mountain Part of East Java, with normal fault as a dominant structure, that potentially control the circulation of magmatic fluid and mineralization.

The Southern Mountain belt of East Java and the Southern part of Cianjur as a part of the Southern part of mountain belt of Java are thought to have potentially metallic mineral deposits, as well as the products of subduction. In general, these areas are underlain by the various volcanic-sedimentary rocks that are of Tertiary to Quaternary in age and some igneous rocks that are locally attributed to the formation of hydrothermal alteration and mineralization (Widodo et. al., 2002; Widodo, 2003).

Widodo et. Al. (2002) conducted semi-detailed investigations during the cooperative exploration of DIM-JICA in Blitar, East Java and Cianjur, West Java. Widodo (2003) also invent the ore mineral in Malang District, Lumajang District: Tempursari (Lumajang District), Seweden (Blitar District) and Suren Lor (Trenggalek District).

Sulistijo (2010) carried out detail field sampling for the ore minerals in Blitar and Tulungagung District, including Gunung Gede and Ringin Putih, Blitar. The study of geological and hydrothermal alteration in Sumberboto and vicinity were conducted by Permana (2011).
Hakim and Sulistijo (2012) studied the combination of satellite imagery, geological prospecting, geochemical study and mineralogy analysis to analyze the copper prospect in Seweden, Blitar.
This study aimed to elucidate the ore-forming minerals by optical mineralogy and mineragraphy analysis, and obtain basic data for the mineralization characteristics in Ringin Putih district.

Sumatra and Java is a system of Sunda Banda arc, as a results of the convergence betwen Indo-Australian arc and Eurasian arc in Cenozoic. Sunda Banda arc lies from Northern Sumatra (Aceh), Java, Nusa Tenggara, until Banda Island. (Katili, 1975; Hamilton, 1979; Carlille and Mitchel, 1994).
Regional stratigraphy in the area of research is dominated by the product of volcanic activity, intrusive rock, and limestone. Pacitan, Ponorogo, Wonogiri, and Blitar, located in the Old Volcanic Metallogenic, formed in Mandalika Formation, and sediment rock from Arjosari Formation (Samodra, 1992).
Mandalika Formation is the oldest formation (Oligo-Miocene) that appears in the location of study. The most prospective host for mineralization lies on the Mandalika Formation (Oligo-Miocene). Mandalika Formation consists of andesite-lava-basalt, porphyry latite, rhyolite and dacite. Andesite lava is dominated by pyroxene, andesite, hornblende, and trachyte andesite that can be altered into propylitic, further more can be altered into kaolinite.

Campurdarat Formation formed in Early Miocene, consists of crystalline limestone and claystone intercalation (Siregar and Praptisih, 2008). Four carbonate facies have been recognized within this formation. Packstone facies comprising three subfacies i.e. nodular packstone subfacies, algal foraminifera packstone subfacies and milliolid packstone subfacies developed in back-reef, lagoon and tidal channel environments. Float stone facies were deposited in back-reef and reef-zone environments. Rudstone facies interpreted to be deposited on the reef-flat. Boundstone facies which forms the reef-core can be devided in two subfacies i.e. bafflestone subfacies and framestone subfacies. These boundstone facies were deposited in reef-crest – reef-front environments. The Campurdarat carbonate rocks are interpreted to represent a barrier-reef of Early Miocene age with the back-reef part towards the South and the reef front part towards the North (Siregar and Praptisih, 2008).

Intrusive rock (Oligocene-Miocene) that is consisted of dacite, diorite, and tonalite intruded the Mandalika Formation and the Campurdarat Formation. Dacite crystal form in fine-coarse grained, color in white-grey consists of porphyritic with bipiramidal phenocryst quartz, feldspar, hornblende, and ore mineral (Permana, 2011 in Samodra, 1992).

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