TIPE ENDAPAN MINERAL PADA BATUAN METAMORF KUBAH BAYAH, BANTEN

Abstrak

Penelitian ini dilakukan di daerah Kubah Bayah, Kecamatan Cihara, Kabupaten Lebak, Provinsi Banten, dengan tujuan untuk mengidentifikasi karakteristik, jenis, asosiasi mineral ubahan, mineral logam, dan tipe endapan mineral pada batuan induk berupa batuan metamorf. Petrografi dan mineragrafi adalah metode yang digunakan dalam penelitian ini. Berdasarkan hasil petrografi, didapatkan 6 jenis batuan metamorf, yaitu sekis klorit, sekis biotit klorit, sekis muskvoit klorit, sekis biotit muskovit klorit, sekis garnet biotit muskovit klorit, dan sekis aktinolit klorit sebagai batuan induk. Berdasarkan hasil identifikasi mineral ubahan dan asosiasinya, alterasi daerah penelitian dibagi ke dalam 2 zona mineral alterasi, yaitu zona epidot – klorit ± kuarsa yang termasuk ke dalam tipe alterasi propilitik dan zona serisit ± pirit yang termasuk ke dalam tipe alterasi filik. Selanjutnya, hasil mineragrafi, menunjukkan bahwa terdapat 2 asosiasi mineralisasi logam bijih, yaitu pos-metamorfik dan sin-metamorfik. Mineral penyusun asosiasi mineralisasi pos-metamorfik terdiri atas pirit, kalkopirit, sfalerit, bornit, kovelit, dan hematit, sedangkan mineral penyusun asosiasi mineralisasi sin-metamorfik terdiri atas pirit. Selain itu, juga teridentifikasi mineral logam berharga berupa emas pada asosiasi mineral pos-metamorfik. Berdasarkan karakteristik di atas, maka tipe endapan yang terbentuk di  daerah penelitian adalah didominasi oleh tipe endapan hidrotermal yaitu endapan epitermal sulfidasi menengah. Namun, sebagian kecil juga hadir, diduga sebagai endapan orogenik yang dicirikan oleh urat-urat paralel foliasi yang diisi oleh kuarsa sekunder, klorit sekunder, mineral lempung sekunder, dan mineral opak dan mineralisasi berupa mineral pirit yang terbentuk mengikuti foliasi pada mineral klorit.

Kata kunci: Kubah Bayah, Zona alterasi – mineralisasi, batuan metamorf, epitermal sulfidasi menengah

This research was conducted in the Bayah Dome area, Cihara District, Lebak Regency, Banten Province, with the aim of identifying the characteristics, types, associations of alteration minerals, metallic minerals, and types of metallic mineral deposits in metamorphic – hosted rocks. Petrography and mineragraphy are the methods used in this study. Based on the petrographic results, 6 types of metamorphic rocks were obtained, namely chlorite schist, chlorite biotite schist, chlorite muscovite schist, chlorite muscovite biotite schist, chlorite muscovite biotite garnet schist, and chlorite actinolite schist as the host rock. Based on the identification of alteration minerals and their associations, the alteration of the study area is divided into 2 zones of alteration minerals, namely the epidote - chlorite ± quartz alteration mineral zone which belongs to the propylitic alteration type and the sericite ± pyrite alteration mineral zone which belongs to the phyllic alteration type. Furthermore, mineragraphic results show that there are 2 ore metal mineralization associations, namely post-metamorphic and syn-metamorphic. The constituent minerals of the post-metamorphic mineralization association consist of pyrite, chalcopyrite, sphalerite, bornite, covellite and hematite, while the constituent minerals of the syn-metamorphic mineralization association consist of pyrite. In addition, valuable metal minerals in the form of gold were also identified in the post-metamorphic mineral association. Based on the above characteristics, the type of deposits formed in the study area is dominated by medium sulfidation epithermal deposits. However, a small part is also present, presumably as orogenic deposits characterized by foliation parallel veins filled with secondary quartz, secondary chlorite, secondary clay minerals, and opaque minerals and mineralization in the form of pyrite minerals formed following foliation on chlorite minerals.

Keywords: Bayah Dome, Alteration-mineralization type, Metamorphic-hosted rock, Intermediate sulfide ephitermal