Geology and Characteristics of Hydrothermal Ore Mineralization at Ngerjo Area, Pacitan Regency, East Java, Indonesia

• Main Authors: , Vilachit, Dethvanhxay, , Dr. Arifudin Idrus
• Format: Theses and Dissertations NonPeerReviewed
• Published: [Yogyakarta] : Universitas Gadjah Mada 2014
• Subjects: ETD
• Online Access: https://repository.ugm.ac.id/133725/; http://etd.ugm.ac.id/index.php?mod=penelitian_detail&sub=PenelitianDetail&act=view&typ=html&buku_id=74516
• Institution: Universitas Gadjah Mada

The Ngerjo area is the location of study area, situated in Pacitan Regency, East Java, Indonesia. The purposes of this research are to understand the geological condition and factors controlling the formation of deposit, to map the hydrothermal alteration, and characterize the ore mineralization, provide guidelines for further exploration in Ngerjo area. There were seventy samples taken from the field investigation, which Petrography, Ore microscopy, X-ray diffraction, and Geochemical analysis (XRF and AAS) are applied for this research. The rock types that define the geology include volcanic rock and sedimentary rocks. The geological map was drawn base on interpretation of petrography and bulk-rock geochemistry (XRF) combination with field investigation. There are two types of hydrothermal alteration such as propylitic and argillic alteration zones which are supported by petrography, whole- rock geochemistry, x-ray diffraction analysis and field observation. The mineralization of the research area is mainly controlled by geological structures and the trend direction of the quartz veins is mainly North-East to South-West direction. The quartz+base metal veins are commonly characterized by the presence of pyrite, galena, sphalerite, chalcopyrite, and covellite. Chemical compositions of veins based on geochemical AAS results show high grade a potential base-metal ores (Pb, Zn, Cu) and quite low precious metals (Au, Ag), copper (Cu) potential range from 625 to 54520 ppm, lead (Pb) potential range from 154 to 99000 ppm, Zinc (Zn) potential range from 674 to 128500 ppm, silver (Ag) potential 9.5 to 395 ppm and gold potential range from 12 to 3850 ppb. The protolith of the base metal mineralization is porphyritic host by andesite lava, which quartz veins showing open-space filling partly indicated by coarse-grained quartz within comb, dog-teeth, cockade, crustiform banded and massive texture. Based on these characteristics, the veins are probably categorized as lowsulphidation epithermal system.