STUDY OF HIGH SULFIDATION-EPITHERMAL DEPOSIT IN THE VOLCANIC ENVIRONMENT : A CASE STUDY IN BANJARHARJO AREA, AYAH DISTRICT, KEBUMEN REGENCY, CENTRAL JAVA

Arizal Nur Ikhsani; Falah Purnama Aji; Mochammad Aziz

Arizal Nur Ikhsani Geological Engineering, Universitas Jenderal Soedirman, Purbalingga, Indonesia
Falah Purnama Aji Geological Engineering, Universitas Jenderal Soedirman, Purbalingga, Indonesia
Mochammad Aziz Geological Engineering, Universitas Jenderal Soedirman, Purbalingga, Indonesia

Abstract

Indications of hydrothermal deposits have been found in Ayah District, Kebumen Regency, Central Java. In this area, there are products from the ancient volcanic activity of Menganti which has an age from Oligocene to Miocene. The existence of volcanic activity makes hydrothermal deposits can develop and have the potential to produce metal minerals. This study aims to identify the characteristics of alteration and mineralization that are developing in the research area. The methods used in the research are in the form of surface geological mapping and rock sampling for laboratory analysis in the form of Petrography, Mineragraphy, SEM (Scanning Electron Microscopy), Atomic Absorbtion Spectophotometry (AAS) and XRD (X-Ray Diffraction). The stratigraphic conditions of the research area from old to young consist of Dacitic Tuff Breccia, Andesite Lava, and Andesite Intrusion. The developing alterations are in the form of propylitic (Chl+Smc), argilic(Kao+Ill-Smc), advanced argillic(Kao+Alunite-Diaspor-Dickite-Barite), and silicification (Si-Qtz). The presence of ore minerals such as enargite, chalcocite and covellite is an indicator that high sulphidation alteration type mineralisation is developing in this area. The alteration and mineralization of the research area are controlled by the geological and lithological structure of the rock, where there are horizontal faults in the southeast-northwest direction and horizontal faults in the southwest-northeast direction. Andesite intrusion arises through the activation of the fault so that it can alter the rock it passes through. Based on AAS analysis there are also levels of economically valuable minerals, especially gold (Au) of 203.122 ppm and copper (Cu) of 2,500.05. Based on the alteration and mineralization characteristics from the results of laboratory analysis, the epithermal deposits in the study area have a high sulfidation type.