Yessenia Fernandez, BSc
Y. Fernandez1, F. Rivera2
1School of Geological Engineering, Faculty of Geological, Mining and Metallurgical Engineering, Universidad Nacional Mayor de San Marcos, Lima, Lima, Perú
2Antofagasta Minerals, Perú
Vectoring toward mineralized centers in porphyry Cu systems remains a key challenge during exploration, particularly in deposits characterized by complex intrusive architectures and multiple magmatic–hydrothermal pulses. In such settings, conventional lithological and structural criteria may be insufficient to discriminate fertile intrusions. Mineral geochemistry provides an effective alternative by recording the physicochemical conditions of magma–fluid interaction. Among alteration minerals, biotite is especially suitable due to its stability during carolinaearly magmatic and hydrothermal stages and its capacity to incorporate elements sensitive to these processes.
This study evaluates the geochemistry of hydrothermal biotite as an exploration vectoring tool in the Zafranal Cu porphyry deposit, located in the Western Cordillera of southern Peru. The deposit is hosted by metamorphic and volcano-sedimentary rocks intruded by multiple dioritic to quartz dioritic bodies, resulting in a complex intrusive framework and a well-developed hydrothermal zonation dominated by potassic alteration at the core. Biotite samples were collected from different intrusive units with variable mineralization affinity and degrees of hydrothermal alteration.
Major and trace element compositions of biotite were determined by electron microprobe analysis. The dataset was evaluated using the XMg parameter [Mg/(Mg+Fe)] as a primary discriminator, in combination with bivariate diagrams involving elements sensitive to magmatic–hydrothermal processes (e.g., F, Ti, Mn, Cl) and integrative geochemical indices. This approach aimed to identify systematic compositional trends and to define coherent biotite populations related to distinct geological environments.
The results reveal non-random, systematic compositional variations in biotite. XMg effectively organizes the dataset and allows the recognition of at least two main biotite populations. One population is characterized by lower XMg values and relatively higher Ti and Mn contents, reflecting a more magmatic signature. A second population displays higher XMg values, enrichment in F, and depletion in Ti and Mn, consistent with increased hydrothermal influence. These populations correlate with different intrusive phases and alteration styles, particularly potassic alteration associated with hypogene Cu mineralization.
The observed geochemical patterns demonstrate that biotite consistently records magmatic–hydrothermal processes controlling porphyry system evolution. At Zafranal, biotite geochemistry proves to be an effective tool for discriminating intrusive units with different mineralization potential and for supporting exploration vectoring at the deposit scale. The methodology and results highlight the broader applicability of biotite geochemistry as a vectoring tool in comparable porphyry Cu systems.