TY - JOUR

T1 - Vapor transport-induced Cu isotope fractionation

T2 - insights from open-system fluid cooling experiments

AU - Lazarov, Marina

AU - Qi, Dongmei

N1 - Publisher Copyright: © 2025 Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

PY - 2026/1/5

Y1 - 2026/1/5

N2 - Vapor transport is a critical mechanism for metal sequestration, enrichment, and isotope fractionation in geological systems. However, the isotopic fractionation of metals, such as copper (Cu), during open-system vapor transport has not been experimentally calibrated. To address this, we simulated vapor condensation in an open system and investigated the Cu isotope composition variation during rapid cooling and depressurization. Vapor-like fluids were produced from reactions between copper, copper chloride (CuCl) solids and H2O, HCl solutions at 800°C and 200 MPa. Experiments were performed in argon cold seal pressure vessels (Ar-CSPVs). The cooling process induced phase separation and resulted in up to 50% fluid loss, mimicking vapor escape from a magmatic system. A reference experiment with no fluid loss exhibited negligible isotopic fractionation, with final fluid compositions matching that of the starting materials. In contrast, significant fluid loss led to the enrichment of 65Cu in the residual fluids. Fractionations up to 2.12 ± 0.04‰ were observed between the final fluid and initial solid, most apparent for the chloride system. This systematic isotopic shift conforms to a kinetic Rayleigh fractionation model, implying that vapor removal as the main cause for Cu isotope fractionation. The expelled vapor preferentially concentrates the lighter isotope of 63Cu, while vapor condensation during cooling and depressurization enriches the residual fluid in 65Cu. These findings demonstrated that vapor escape during incipient phase transition can induce significant Cu isotope fractionation in open systems. Consequently, the use of Cu isotopes has direct implications for tracing fluid evolution pathways, identifying metal sources, and understanding metal enrichment processes in porphyry, epithermal, and other volcanic-hydrothermal systems.

AB - Vapor transport is a critical mechanism for metal sequestration, enrichment, and isotope fractionation in geological systems. However, the isotopic fractionation of metals, such as copper (Cu), during open-system vapor transport has not been experimentally calibrated. To address this, we simulated vapor condensation in an open system and investigated the Cu isotope composition variation during rapid cooling and depressurization. Vapor-like fluids were produced from reactions between copper, copper chloride (CuCl) solids and H2O, HCl solutions at 800°C and 200 MPa. Experiments were performed in argon cold seal pressure vessels (Ar-CSPVs). The cooling process induced phase separation and resulted in up to 50% fluid loss, mimicking vapor escape from a magmatic system. A reference experiment with no fluid loss exhibited negligible isotopic fractionation, with final fluid compositions matching that of the starting materials. In contrast, significant fluid loss led to the enrichment of 65Cu in the residual fluids. Fractionations up to 2.12 ± 0.04‰ were observed between the final fluid and initial solid, most apparent for the chloride system. This systematic isotopic shift conforms to a kinetic Rayleigh fractionation model, implying that vapor removal as the main cause for Cu isotope fractionation. The expelled vapor preferentially concentrates the lighter isotope of 63Cu, while vapor condensation during cooling and depressurization enriches the residual fluid in 65Cu. These findings demonstrated that vapor escape during incipient phase transition can induce significant Cu isotope fractionation in open systems. Consequently, the use of Cu isotopes has direct implications for tracing fluid evolution pathways, identifying metal sources, and understanding metal enrichment processes in porphyry, epithermal, and other volcanic-hydrothermal systems.

KW - Cooling

KW - Cu isotope fractionation

KW - Kinetic

KW - Open system

KW - Rayleigh fractionation

KW - Vapor-to-liquid transformation

UR - http://www.scopus.com/inward/record.url?scp=105030205331&partnerID=8YFLogxK

U2 - 10.1016/j.chemgeo.2025.123155

DO - 10.1016/j.chemgeo.2025.123155

M3 - Article

VL - 699

JO - Chemical Geology

JF - Chemical Geology

SN - 0009-2541

M1 - 123155

ER -