GEOCHEMICAL CHARACTERISTIC OF SOIL AND GEOCHEMICAL PROFILE OF DRILLCORE IN THE ELANG CU-AU PORPHYRY DEPOSIT, SUMBAWA, NUSA TENGGARA BARAT, INDONESIA

• Main Author: Bastian, Arief
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/86721
• Institution: Institut Teknologi Bandung

The demand for copper and gold has increased significantly, but finding new exposed porphyry deposits has become more challenging. Elang porphyry Cu-Au deposit is one of few world class deposits, discovered in the last 30 years, located in Sumbawa Island, Indonesia. This study aims to understand the characteristics and geochemical patterns of the surface and vertical profiles of the Elang porphyry deposit. The data used in this study consists of geochemistry analysis from soil and drill core samples, with a focus on the analysis of five key elements: copper (Cu), gold (Au), molybdenum (Mo), lead (Pb), and zinc (Zn). The Cu-Au mineralization at Elang occurs within tonalite intrusions and along the contact zones with volcanic andesitic rocks. The Elang porphyry deposit is characterized by a complex hydrothermal alteration zone, starting with biotite ± magnetite alteration, surrounded by chlorite + epidote, and transitioning to sericite and clay mineral zones due to the cooling of magmatic fluids and interaction with meteoric water. This process creates fractures that enhance the alteration of feldspar into clay minerals. The Cu mineralization is associated with tonalite delta and charlie intrusions, with primary copper sulphide minerals such as chalcopyrite, bornite, and covellite occurring either as disseminated or as fillings within fractures with quartz, along with oxide minerals like magnetite and hematite, and some replacement minerals, such as sphalerite and galena. The geological and mineralization variations result in a distinct geochemical expression of the porphyry deposit. In the center of the Elang porphyry mineralization, geochemical soil anomalies of Cu and Mo show high anomalies, while Zn and Pb show low anomalies. A wide zone of high Au anomalies is associated with the presence of an epithermal system to the south and east of the Elang porphyry deposit, particularly at the Ladam and Sebu prospects. Geochemical data from core samples reveal a vertical zonation pattern of CulAu ratios, starting with Cu>Au in the upper zone, Cu=Au in the middle, and Cu<Au in the lower zone, with a repetition of Cu>Au at depth, accompanied by high Mo anomalies. The presence of this repeated anomaly suggests the existence of a deeper porphyry intrusion, which has been confirmed by the discovery of a new porphyry intrusion to the south of Elang. Understanding the geology and geochemical characteristics of the Elang deposit provides valuable insights for exploration strategies aimed at discovering similar deposits elsewhere