^Geological Characteristics, Hydrothermal Alteration, and Mineralization of Porphyry Deposits in Sidomulyo Area, Trenggalek Regency, East Java^
Oan Marcello Lukas Watania(a) , Raden Aditya Manggala Yudha(a), Danis Agoes Wiloso(a)

(a) Indonesia AKPRIND University, Jl. Kalisahak No. 28 Kota Yogyakarta 55222
E-mail: marcellowatania[at]gmail.com, adityamanggala.geo[at]gmail.com

Abstract

East Java, as a part of the Eastern Sunda Magmatic Arc on Java Island, is a location that has the potential for metal endowment. In fact, it has been proven that mineralization in East Java has economical ore deposits that consist of porphyry and epithermal systems from Selogiri, Pacitan, Trenggalek and extending to Tumpangpitu. This paper is aimed at investigating and discussing the characteristics of geology, hydrothermal alteration, and mineralogy as well as their relationship with parageneses at Sidomulyo area, Trenggalek regency, East Java. The research methodology includes field data recording, rock sampling and several analyses i.e petrography, ore microscopy, and clay analysis (X-Ray Diffraction). The lithological units comprise andesitic tuff, tonalite, coarse diorite, and fine-grained diorite.The hydrothermal alteration classified into 8 zones based on mineral assemblages: (1) actinolite - orthoclase - magnetite, (2) secondary biotite - k-feldspar, (3) epidote - chlorite - actinolite, (4) sericite - shreddy chlorite - muscovite - illite, (5) sericite - illite - quartz - pyrite, (6) phyrophyllite - diaspore - quartz - alunite, (7) kaolinite - illite - quartz, and (8) chlorite - epidote. Mineralization style is deposited into disseminated sulfides and stockwork veins associated with pyrite, magnetite, chalcopyrite, bornite, covellite, and chalcocite. The characteristic of hydrothermal alteration implicates prograde and retrograde by multiple intrusion stages. The prograde alteration produces sodic calcic and potassic alteration that characterized by presence of rich actinolite and secondary biotite associated with epidote, K-feldspar, and albite at intrusion bodies. The post structural cuts the previous hydrothermal alteration inflict decreasing temperature formed sericite and clay alteration as retrograde alteration around intrusion bodies. Mineralization styles are deposition on dissemination in rocks and vein stockwork at magnetite and quartz veins deposi

Keywords: Dioritic Complex, Copper Mineralization, Eastern Sunda Magmatic Arc

Topic: Mineral and Energy Regulation and Economics