Journal of Applied Geology, vol. 5(2), 2020, pp. 73–83 DOI: http://dx.doi.org/10.22146/jag.55235 Hydrothermal Alteration of High Sulfidation Epithermal Deposits in Secang Area, Tulungagung, East Java, Indonesia Septyo Uji Pratomo, Anastasia Dewi Titisari * , and Arifudin Idrus Department of Geological Engineering, Faculty of Engineering, Universitas Gadjah Mada, Yogyakarta, Indonesia ABSTRACT. This research aims to determine geological condition and alteration in ep- ithermal high sulfidation mineralization as an initial guide for further exploration stages. Detailed geological mapping with a scale of 1:12,500 was conducted to identify geolog- ical aspects and distribution of alteration zones. Selected rocks samples were prepared for laboratory analysis, which are petrography, XRD (X-Ray Diffraction), and FA-AAS (Fire Assay-Atomic Absorption Spectrometry) analyses. The geological condition of the research area consists of six rock units from the oldest to youngest: andesite lava, andesitic breccia, microgranodiorite intrusion, polymict breccia, limestone, and alluvial deposit. Ge- ological structures found are left strike-slip fault with right strike-slip fault as accompany. The result of XRD analysis shows the presence of minerals, which are: smectite, kaolin- ite, illite, diaspore, alunite, and pyrophyllite. The alteration zones of the research area are propylitic, argillic, advance argillic, and silicification zones. The further exploration stage is recommended to focus on the southwest and northeast of the research area. Keywords: Tulungagung · Epithermal · High-sulfidation · Alteration · Vuggy quartz. 1 I NTRODUCTION PT. ANTAM Tbk., which is one of an Indone- sian mining company that was in collaboration with Newcrest Mining Ltd. in the series of East Java Regional Mapping Program 2017, have been carried out regional exploration activities covering seven districts in East Java Province including Pacitan, Trenggalek, Tulungagung, Blitar, Malang, Lumajang, and Jember. The re- gional exploration indicated a prospect area of Tulungagung shows partially oxidized vuggy silica with 0.13 ppm Au and 25 ppm Cu, which is a feature of high sulfidation epithermal de- posits. The mapping program was also found that rocks samples with the highest Au 8.3 ppm and Cu 460 ppm (ANTAM, 2017-unpubl. data). Several previous researchers have investigated regional geological conditions that include re- search sites such as Samodera et al. (1992) * Corresponding author: A.D. TITISARI, Depart- ment of Geological Engineering, Universitas Gadjah Mada. Jl. Grafika 2 Yogyakarta, Indonesia. E-mail: adewititisari@ugm.ac.id divided geological formations into Tulunga- gung quadrangle geological map. Widodo et al. (2002) and Widodo (2003) explained the po- tential of ore minerals in the southern moun- tains belt of East Java. Besides, Widodo and Simanjuntak (2002) mentioned the Kalidawir- Tanggunggunung-Campurdarat area as one of the prospect areas in the Tulungagung area, which is characterized by an argillized tuff with limonitic veinlets of 1,476 ppb Au content. However, the Secang area, which is located in Campurdarat Subdistrict, Tulungagung Re- gency of East Java, Indonesia (Figure 1) and one of the prospect area in the regency, has not been carried out detailed geological investiga- tion including delineation the distribution of alteration zones, determination and identifica- tion of sulfide minerals that supported by pet- rography, X-ray diffraction (XRD), and ore geo- chemistry using the fire assay AAS (FA-AAS) method. By recognizing the alteration zone will support in recommending further exploration target areas. 2502-2822/© 2020 The Authors. Open Access and published under the CC-BY license.