MAGMA FERTILITY ANALYSIS IN THE CANDRIAN PORPHYRY DEPOSIT, BANYUWANGI, EAST JAVA, INDONESIA

• Main Author: Syarief, Omar
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/87119
• Institution: Institut Teknologi Bandung

This study aims to identify the elemental composition that serves as an indicator of magma fertility within the context of mineral exploration, to understand the conceptual relationship between magma fertility characteristics and the presence of economically viable porphyry mineralization systems, and to develop a conceptual model that guides the identification of geochemical and tectonic factors influencing the formation of mineral deposits. Specifically, this research explores magma fertility and its implications for the formation of economically viable mineral deposits within the porphyry hydrothermal system at the Candrian Prospect in Banyuwangi, East Java. Located within the Sunda-Banda magmatic arc, this area is known for its rich copper and gold resources, particularly in the form of porphyry deposits. The main focus of the research is to identify key geochemical elements to assess magma fertility and to evaluate the mineralization potential of the region. The geochemical approach adopted in this study is based on the analysis of immobile elements, which provide information about composition and magmatic processes. Several magma fertility indicators, such as the V/Sc, Sr/Y, and Nb/Ta ratios, are used as key parameters in assessing mineral fractionation. Element content data were obtained using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis applied to rock samples collected from the Candrian prospect location. After data collection, validation was carried out through statistical analysis to ensure the accuracy and precision of the results, by checking natural correlations between elements such as Hf/Zr and Nb/Ta, and utilizing alteration indices for further selection and classification. In addition to magma composition analysis, regional tectonics are considered a significant factor in influencing magma evolution in this area. The subduction of the Indo-Australian plate beneath the Eurasian plate along the Sunda-Banda arc creates tectonic conditions favorable for porphyry deposit formation. The dynamic subduction geometry facilitates dehydration of the subducting plate and the introduction of volatile materials into the mantle, which enriches the magma with mineralizing elements such as Cu and Au. Additionally, calc-alkaline magma with high oxygen and water content shows a greater tendency to form economically viable mineral deposits, underscoring the relevance of this study area for further exploration. The study also identifies the role of opaque mineral fractionation, such as magnetite and ilmenite, in magma evolution. Magnetite crystallization in highly oxidized magma reduces vanadium (V) content relative to scandium (Sc), affecting the V/Sc ratio and serving as a magma fertility indicator. A higher ratio suggests early crystallization of hornblende, which generally supports fertile porphyry copper mineralization. Geochemical mapping in the prospect area also reveals high-pressure fractionation, indicated by high Sr and low Y content, suggesting garnet and hornblende fractionation that enhances mineralization potential. Hydrothermal alteration identified in the research area includes alteration types such as potassic, phyllic, skarn, as well as broader distributed argillic and propylitic alterations. The presence of minerals such as K-feldspar and biotite in the potassic alteration zone indicates high temperature and pressure conditions that support the formation of Cu-Au porphyry mineralization systems. These alteration zones serve as valuable indicators in early exploration activities for identifying areas with high economic mineralization potential, particularly in the Candrian region. In conclusion, this research emphasizes the importance of immobile element-based geochemical analysis for assessing magma fertility and the relevance of tectonic factors in determining mineralization potential in porphyry deposits. The study successfully develops a conceptual model linking magma fertility with mineralization potential, providing a more targeted exploration framework. The use of geochemical parameters such as the V/Sc, Sr/Y, and Nb/Ta ratios as indicators of magma fertility holds the potential to increase exploration efficiency, reduce costs, and minimize the risk of failure in mineral exploration activities. Overall, this research contributes to the development of a more efficient mineral exploration method that can be applied not only in the Tujuh Bukit District but also in other areas with similar tectonic and hydrothermal conditions. The conceptual model developed is expected to serve as a valuable reference for further research and exploration of porphyry deposits and other hydrothermal systems with economic mineralization potential.