Control of sulfide droplet accumulation on mineralization distribution in the Jinchuan Ni-Cu sulfide deposit: insights from numerical simulation of magma cooling

• A two-phase flow model reveals that 40–80 vol% of olivine accumulated after the end of magma emplacement in the Jinchuan intrusion. • The original geometry of the intrusion was shaped by magma flow at the velocities of 10 -2 ∼ 10 -4 m/s along inclined lithological boundaries • Cooling simulations show distinct solidification times and sulfide droplet penetration distances between No.1 and No.2 orebodies. • Sulfide melt crystallization modeling links magma cooling to chalcophile element heterogeneity and ore zoning. The abundant net-textured ores in the Jinchuan Ni-Cu sulfide deposit have been attributed to the coalescence of early-dispersed sulfide droplets within olivine cumulus. However, the dynamic mechanisms responsible for sulfide distribution remain unclear. To address this gap, this study quantitatively investigates the genetic links between ore formation and magma-cooling processes, aiming to clarify the controls of magma cooling on mineralization distribution in magmatic systems. Using a two-phase mixing flow model, we first simulate olivine accumulation during magma emplacement, revealing that 40–80% of olivine had already accumulated in the shallow reservoir after the end of magma emplacement. Thermal and dynamic calibration further indicates that the Jinchuan intrusion was shaped by magma flow at velocities of 10 −2 to 10 −4 m/s along inclined lithological boundaries. A coupled heat transfer and Brinkman equation model was then employed to simulate the magma cooling and crystallization in olivine cumulus. Results reveal that initial volume fractions of olivine minimally impacted magma cooling, with the complete solidification times of 3.0 kyr and 1.25 kyr for the No. 1 and No. 2 orebodies, respectively. Different magma cooling conditions resulted in the static cumulative penetration distance (SCPD) of sulfide droplets being two to three times higher in the No. 1 orebody than in the No. 2 orebody, consistent with the ratio of mineralized vertical extent. However, this ratio is significantly smaller than the vertical thickness ratio of these two net-textured ores, suggesting that the different magma flow dynamic conditions (e.g., flow velocity, duration, and even volume fraction of carried sulfide melts) during sulfide-rich magma emplacement have caused different degrees of localized sulfide accumulation between them. Furthermore, the higher SCPD in the No. 1 orebody facilitated continuous downward addition of microdroplets, promoting abundant formation of net-textured ores. Finally, modeling of sulfide melt fractional crystallization highlights that magma cooling is a key factor controlling chalcophile element heterogeneity. The Cu-rich ores in the western extension of the No. 1 orebody are interpreted as products of late-stage magma replenishment, with their locations indicating the magma conduit entrance zones.