Zircon and apatite constraints on the multi–stage magmatic–hydrothermal evolution of the Baishizhang molybdenum Deposit, Nanling Range

The Baishizhang (BSZ) deposit is a typical Late Jurassic Mo-only deposit in the Nanling Range. The host rocks in the mining area record multiple stages of magmatic intrusion and hydrothermal alteration, indicating that the region experienced multiple magmatic-hydrothermal events. Here, zircon and apatite from BSZ granitoids were analyzed to determine their geochemical and isotopic compositions, providing insights into the nature of the magmatic-hydrothermal fluid and the temporal framework of magmatic-hydrothermal events. Zircon and apatite U-Pb dating constrains multiple stages, including early magmatic intrusion at ca. 438–416 Ma, and later hydrothermal events recorded by apatite (ca. 243–170 Ma) and zircon (ca. 127 Ma). The early magmatic stage is characterized by low oxygen fugacity ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>Δ</mml:mi> </mml:math> FMQ ≤ +0.2), indicating limited capacity for Mo transport. Magmatic zircons show variable <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>ε</mml:mi> </mml:math> Hf(t) values from –5.50 to –0.84, consistent with heterogeneous crustal sources or magma mixing. Hydrothermal apatites display high F and low Cl contents, along with variable ( 87 Sr/ 86 Sr) i ratios (0.72579–0.76503), suggesting formation in an open, F-rich hydrothermal system. Their Nd isotopic compositions (–11.8 to –4.7) indicate a contribution from mantle-derived components. Apatite Mn–in–apatite oxybarometry indicates that hydrothermal fluids at ca. 235–170 Ma were relatively oxidized, whereas fluids at ca. 243 Ma were relatively reduced. Hydrothermal zircons are enriched in trace elements, with high Y/Ho (&gt; 28) and low Zr/Hf (&lt; 28) ratios, and exhibit pronounced REE tetrad effects, indicating evolution in a F-rich and relatively reduced hydrothermal environment. Their low <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>ε</mml:mi> </mml:math> Hf(t) values (–10.42 to –4.70) suggest a dominant crustal contribution. This study demonstrates that the BSZ deposit can be defined as a long-lived, multi-stage evolving system, with the main mineralization pulse concentrated in the Late Jurassic, representing a composite deep-sourced magmatic-hydrothermal system. This research highlights the use of zircon and apatite as powerful tools in revealing the nature of the hydrothermal fluids and the temporal framework of the multiple magmatic-hydrothermal events.