PETROLOGY AND MINERALISATION OF CIPATUJAH AND KARANGNUNGGAL AREA, TASIKMALAYA REGENCY

• Main Author: Habibie Mardhatillah, Nur
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/78492
• Institution: Institut Teknologi Bandung

The subdistrict of Cipatujah and Karangnunggal are located in the southern region of Tasikmalaya Regency. Physiographically, The research area is part of the development of a Backarc basin of The Bogor Basin. It has geological conditions that consist of the Jampang Formation, which comprises volcanic rocks from the late Oligocene to the early Miocene, the Kalipucang Formation and the Pamutuan Formation, which consist of sedimentary rocks from the middle Miocene, and the Bentang Formation, which consists of sedimentary rocks from the late Miocene. The Jampang Formation is a volcanic rock that was partly deposited in a marine environment. This formation was formed in the subduction zone of a volcanic arc from the back-arc basin of the Proto Bogor Basin, allowing for alteration and mineralization processes to occur in a marine environment. This is supported by the discovery by JICA in 1996, which reported the presence of alteration and mineralization products such as gypsum, barite, and sericite in the Jampang volcanic rocks in the southern Tasikmalaya area, leading to further research. The research conducted is the result of surface mapping with sample analysis including petrographic analysis, mineralogical analysis, and X-ray diffraction (XRD). The field mapping results reveal that the Jampang Formation consists of lava units, tuff units, and volcanic breccia units. The Kalipucang Formation consists of limestone sandstone, the Pamutuan Formation consists of sandy limestone, and the Bentang Formation consists of tuff sandstone and limestone sandstone units. Alteration and mineralization products in the Cipatujah and Karangnunggal areas are found in the lava, tuff, and volcanic breccia lithologies of the Jampang Formation. The results of the field mapping are then grouped based on rock associations, alterations, and mineralizations, followed by petrographic analysis, mineralogical analysis, and X-ray diffraction (XRD). From the analysis and mapping results, two areas with significant alteration and mineralization characteristics were found, namely the Jodang Area and the Cikapinis Area. The Jodang Area's alteration is divided into silicification zone and sub-propylitic zone, consisting of the alteration assemblages of Quartz + Illite ± Chlorite ± Kaolinite ± Zeolite ± Sericite. The mineralization in the Jodang Area includes Azurite, Malachite, Pyrite, Chalcopyrite, Gypsum, Anhydrite, Barite, and Jasper. This low-degree alteration and mineralization zone is interpreted as part of an epithermal ore model of the submarine volcanic massive sulfide system in a distal facies. The presence of alteration and mineralization in the Jodang Area is disseminated and fills fractures in the tuff and volcanic breccia lithologies of the Jampang Formation. On the other hand, the alteration in the Cikapinis Area is divided into silicification zone and phyllic zone, with the alteration assemblages of Quartz + Pyrophyllite ± Sericite ± Cristobalite. The mineralization found in the Cikapinis Area includes pyrite, chalcopyrite, sphalerite, and marcasite. The alteration and mineralization zone in this area constitute a set of high-degree alteration mineral associations that are estimated to be part of the hydrothermal system of the volcanic massive sulfide in the medial facies. The presence of alteration and mineralization in the Cikapinis Area is disseminated and also fills fractures in the tuff and volcanic breccia lithologies of the Jampang Formation. Generally, the mineralization in the research area is found in the sub-propylitic and phyllic zone, controlled by structures and lithology. The petrogenesis and paragenesis of the research area can be simplified into four stages: (1) Formation of the Bogor Basin and volcanic activation in the late Oligocene, (2) Formation of the Jampang Formation and massive sulfide ore in the early Miocene, (3) Deposition of sediments in the Pamutuan Formation and Kalipucang Formation, as well as the intrusion of granodiorite in the middle Miocene, (4) Deposition of sediments in the Bentang Formation in the late Miocene.