Magmatic initial and saturated water thresholds determine copper endowments: Insights from apatite F-Cl-OH compositions

Sun, Yingcai; Zhou, Qiushi; Wang, Rui; Humphreys, Madeleine C.S.

Abstract

Magmatic volatiles (H2O, F, Cl), especially water, are critical in the formation of porphyry copper deposit, for its significance as a carrier for metals. However, accurately quantifying the water contents of deep ore-forming magma remain a challenge. Here, we used apatite and forward modelling methods to reconstruct magmatic water evolution histories, with special concern on the control of initial magmatic H2O contents and water saturation threshold to porphyry mineralization. Samples investigated include granitoid rocks and apatite from highly copper-mineralized and barren localities. Generally, our research suggested that both ore-related and ore-barren magma systems are hydrous, the modeled magmatic water contents vary significantly among systems whether mineralized or not, and the major difference lies in the threshold of water saturation (6.0 wt% for barren, and up to 10.0 wt% for highly mineralized). Combined with whole rock geochemistry data (high K2O and Sr/Y contents) and modeling result (high modeled water thresholds), we think the ore-related magmas are stored at deeper depth with higher water solubility. In conclusion, we propose that the level of magmatic water saturation plays a crucial role in the formation of porphyry copper systems. Fertile magma has higher water solubility to which deeper storage depth is a critical contributing factor, and can get significantly water enriched upon saturation.

Citation

Sun, Y., Zhou, Q., Wang, R., & Humphreys, M. C. (2025). Magmatic initial and saturated water thresholds determine copper endowments: Insights from apatite F-Cl-OH compositions. Geoscience Frontiers, 16(1), Article 101962. https://doi.org/10.1016/j.gsf.2024.101962

• Journal Article Type: Article
• Acceptance Date: Nov 9, 2024
• Online Publication Date: Nov 20, 2024
• Publication Date: 2025-01
• Deposit Date: Nov 22, 2024
• Publicly Available Date: Nov 22, 2024
• Journal: Geoscience Frontiers
• Print ISSN: 1674-9871
• Electronic ISSN: 2588-9192
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 16
• Issue: 1
• Article Number: 101962
• DOI: https://doi.org/10.1016/j.gsf.2024.101962
• Public URL: https://durham-repository.worktribe.com/output/3099476