Geology, Alteration and Mineralisation at Kluwih area, Lorok Area, Pacitan Regency, East Java, Indonesia

Provinces and Case Studies

Mr Vernando Pratama Harefa

Masyarakat Geologi Ekonomi Indonesia

The research area is located in the Kluwih and surrounding areas, Lorok District, Pacitan Regency, East Java. The lithotectonic study area entered the Sunda-Banda magmatic arc in Oligo-Miocene age. The purpose of this study was to determine the geological conditions, alteration and mineralization of the study area.

The research method used through literature studies, surface geological mapping and geomagnetic geophysical data, laboratory analysis in the form of petrographic and mineragraphy analysis and the preparation stage of the report.

Based on the results of the mapping, the stratigraphy of the study area consisted of Dacite intrusion, lava intersections and volcanic breccias, tuff breccias and diatrema breccias. The developing geological structure consists of a downward strike slip fault and right normal that forms a dilational veins environment. The type of alteration that develops consists of the advanced argillic zone(alunit-vuggy silica massive), propylitic (chlorite-smectite-carbonate-epidot), argillic zone (kaoline-illite-smectite) and silicification zone. The veins that develop in the form of quartz veins are relatively north-south and southeast-northwest with a thickness of 10-200 cm. The texture of the veins in the study area is massive, banded, comb and crustiform. Megascopic and mineragraphic observations showed basic metal mineral content associated with quartz veins, namely chalcopyrite, pyrite, sphalerite, tennantite, tetrahydrite, galena, hematite, gold and silver. Based on vein characteristics and key sulphide species, the study area was included in the intermediate sulfidation epithermal deposits.

Keywords: Kluwih, alteration, mineralization, base metal, intermediate epithermal sulfidation

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