Reconstructing volatile exsolution in a porphyry ore-forming magma chamber: Perspectives from apatite inclusions

Abstract

Porphyry-type deposits in the shallow crust (3-5 km) are formed from metal-rich fluids exsolved from underlying magma chambers (5-15 km). However, a direct volatile record of the fluid exsolution in the magma chamber is commonly lacking.Here, we analyse the compositions of apatite inclusions (in biotite and plagioclase phenocrysts, and fully-/partly-included in zircon microphenocrysts) and the apatite in groundmass from the largest Cretaceous Luoboling porphyry Cu-Mo deposit in South China. In combination with thermodynamic models, we reconstructed the volatile This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

Using zircon and apatite chemistry to fingerprint porphyry Cu – Mo ± Au mineralization in the Delamerian Orogen, South Australia

“…The S (0.02-0.56 wt% SO 3 ) and Cl (0.01-0.58 wt% Cl) in apatite from the Delamerian porphyry systems are significantly lower than those from porphyry deposits in subducted magmatic arcs (normally 0.12-0.60 wt% SO 3 and 0.2-3.0 wt% Cl). Recent studies have shown that zircon-hosted apatite inclusions prior to volatile exsolution commonly contain relatively high magmatic Cl and SO 3 contents essential to potential porphyry Cu-Mo ± Au mineralization Huang et al 2024). All the apatite crystals analyzed in this study were separated and hand-picked from intrusive rocks and they probably occur as microphenocrysts in groundmass or as inclusions hosted by plagioclase and biotite.…”

“…Cl and SO 3 contents than those hosted by zircon, due to fluid exsolution or re-equilibrium with post-exsolution melt (e.g., Sun et al 2023;Huang et al 2024). This is one of the likely reasons that apatites from the Delamerian porphyry prospects have significantly lower S and Cl signatures than those from typical porphyry Cu deposits in magmatic arcs.…”