The role of vapor in the transportation of tin in hydrothermal systems: Experimental and case study of the Dachang deposit, China

In order to understand metal transportation by vapor, which was found by detecting volcanic gases, authors performed vapor–liquid separation experiments at sub-critical states. The experiments indicate that the metal transportation by vapor of hydrothermal systems is derived from the liquid and vapor separation occurred in the transitions from a supercritical state to liquid–vapor immiscibility field at a sub-critical state of metal bearing hydrothermal fluids of NaCl–H2O.The data of the fluid inclusions in minerals suggest that major ores were deposited in the temperature range from 300 to 500°C in hydrothermal systems. The study on fluid inclusions in minerals of hydrothermal deposits provides evidence that the principal ore minerals of the deposits precipitated in the period from a supercritical state to a sub-critical state of the NaCl–H2O. A case study of fluid inclusions in minerals of the Dachang tin deposit, China indicates the evolution of ore-forming fluids occurred in the L–V immiscibility field of NaCl–H2O.The experiments of liquid and vapor two-phase immiscibility field of a tin bearing fluid show that Sn was redistributed in vapor phase and liquid phase, when the tin bearing supercritical fluid (NaHCO3–HCl–H2O) separates into liquid and vapor phases for a decreasing in temperature or pressure. The experiments prove that tin could be transported by vapor phase in hydrothermal systems.