Geological and Isotopic Constraints on the Copper Ore Formation in Ta Phoi area, Lao Cai Province, Northwestern Vietnam: Implications for Metallogenic Processes

The Ta Phoi copper deposit, located in the northeastern Phan Si Pan zone, Northwestern Vietnam, is a significant site of Neoproterozoic Cu mineralization. Its distinct geological characteristics justify its investigations, especially in comparison to nearby IOCG Sin Quyen deposit. This study is aimed at clarifying the genesis, ore-forming conditions, and fluid evolution of the Ta Phoi deposit through an integrated approach combining geological, petrographic, geochemical, and isotopic data analysis. The research specifically employs U-Pb dating of sphene, sulfur isotope analysis, and fluid inclusion microthermometry to identify the age, origin, and physicochemical environment of the mineralization. Sphene U-Pb dating yielded concordant ages of 810.7 ± 4.6 Ma and 819.5 ± 2.0 Ma, indicating a Neoproterozoic mineralization event temporally linked to regional granodiorite and diorite intrusions. Sulfur isotope values (δ³⁴S = +2.2 to +3.1‰) suggest a magmatic origin for ore-forming fluids. Fluid inclusion data detected fluid temperatures ranging from 163.1°C to 410°C, fluid salinities of 2.1–16.25 wt% NaCl equiv., and formation pressures of 44–100 MPa at depths of 3.4–6.5 km. These results confirmed that the Ta Phoi deposit formed from medium- to high-temperature, magmatogene hydrothermal fluids in a subduction-related continental arc setting; it may represent a porphyry-related skarn or endoskarn system that developed in response to magmatic fluid migration along lithological contacts and faults. These findings provide new insights into the metallogenic framework of the Ta Phoi deposit and highlight its potential for further Cu exploration in Northwestern Vietnam.