PROCESSES CONTROLLING MAGMA FERTILITY AT BUENAVISTA DEL COBRE PORPHYRY COPPER DEPOSIT (CANANEA, MEXICO): A NEW PETROGENETIC MODEL BASED ON ZIRCON U-Pb DATING AND APATITE GEOCHEMISTRY

The transition to green energy technologies over the next decades will drive a significant demand for copper, as it is essential for renewable energy systems, electric vehicles, and grid upgrades. Indeed, copper's efficiency in conducting electricity makes it critical to powering the global shift toward cleaner, electrified infrastructure, while supply constraints could further heighten its importance. Porphyry copper deposits are the world’s primary source of copper (~75%), making them a key target for increasing copper resources to meet growing global demand. The Buenavista del Cobre deposit, located in the Cananea Mining District, Sonora, Mexico, is a world-class porphyry Cu-Mo deposit. It produces around 1.7% of the world’s copper and accounts for 60% of Mexico's copper production.

Zircon U-Pb dating of ore-related porphyritic bodies reveals that magmatic activity at Buenavista del Cobre lasted at least 4 million years, from 59.7 ± 0.5/1.1 Ma to 56.1 ± 0.2/0.9 Ma. The deposit consists of several porphyry intrusions, classified as "ore-rich" and "ore-poor" based on their metal content, allowing the study of processes that influence magma fertility. Combining our new geochronological data with apatite geochemistry from the different porphyries suggests that magma oxidation states were similar across the deposit, but variations in rare earth element (REE) signatures and Sr compositions point to fractional crystallization as a key factor influencing porphyry fertility. In addition, ore-rich intrusions show higher Cl content in apatite (>0.4 wt%) compared to ore-poor intrusions (<0.2 wt%), highlighting the role of initial magma Cl content in the mineralization process. Based on this, we propose a new petrogenetic model showing that fractional crystallization of hydrous minerals (e.g., hornblende) at upper crustal levels led to low H₂O content in the residual magma, forming ore-poor porphyries. Conversely, fractionation of anhydrous minerals (e.g., plagioclase) increased H₂O content, resulting in ore-rich porphyries.

These findings provide new insights into the petrogenetic processes controlling porphyry copper fertility and emphasize the importance of apatite geochemistry as a tool for exploration in brownfield and greenfield areas.