Alterasi dan Mineralisasi di Daerah Pertambangan Rakyat Cihonje, Kecamatan Gumelar, Kabupaten Banyumas, Jawa Tengah
Chusni Ansori dan Eko Puswanto
Balai Informasi dan Konservasi Kebumian Karangsambung, LIPI, Kebumen
E-mail: chus001@lipi.go.id
Sari
Daerah Cihonje secara administratif berada di Kecamatan Gumelar, Kabupaten Banyumas, Jawa Tengah, merupakan salah satu dari beberapa daerah prospek penambangan emas di rangkaian Pegunungan Serayu Selatan Bagian Barat.
Tujuan penelitian ini adalah untuk mengetahui jenis alterasi dan mineralisasi yang berkembang pada batuan breksi vulkanik anggota Formasi Halang bagian bawah di daerah Cihonje, melalui pengamatan lapangan dan analisa laboratorium, yaitu analisa petrografi, XRD (X-ray Diffraction), dan AAS (Atomic Absorption Spectrometry).
Berdasarkan analisis XRD dijumpai mineral kuarsa, gipsum, orthoklas, nakrit, pirit ke arah atas berkembang muskovit, kalsit, halosit, dan dolomit. Komposisi kimia di dalam batuan relatif rendah (Au<0.05 ppm, Ag : 0.03 ppm, Cu : 0.017, Pb : <0.025, Zn : 0.01 ppm). Tipe alterasi yang berkembang berupa silisifikasi dan argilik. Berdasarkan karakteristik mineralisasi di daerah penelitian dikategorikan sebagai sistem epitermal sulfidasi rendah.
Kata kunci: Cihonje-Gumelar, penelitian, alterasi dan mineralisasi.
Abstract
Cihonje area administratively was situated in Gumelar, Banyumas District, Central Java, is one of several gold mining prospect in the west part of the Southern Serayu area Mountains Range. The objectives of this research in order to understand alteration and mineralization which developed in volcanic breccias member of the lower part of Halang Formation at Cihonje area, through field observation and laboratory analyses are petrography analysis, XRD (X-ray Diffraction), and AAS (Atomic Absorption Spectrometry).
According to XRD analysis was found quartz, gypsum, orthoclase, nacrite, pyrite, muscovite, calcite, halloysite, and dolomite. Chemical compositions of the rocks are low (Au : <0.05 ppm, Ag: 0.03 ppm, Cu : 0.017, Pb : <0.025, Zn : 0.01 ppm). The alteration type consists of silisification and argillic. According to characteristics of mineralization in the research area is categorized into epithermal low sulfidation system.
Keywords: Cihonje-Gumelar, research, alteration and mineralization.
