Multiphase Melt Inclusions in the Jinchuan Complex, China: Implications for Petrogenic and Metallogenic Physico-Chemical Conditions

Abstract

Three types of melt inclusions were identified in pyroxenes, olivine, and chromite from the Jinchuan intrusion–sulfide inclusions (I), crystallized polyphase inclusions (II), and fluid inclusions (III). Sulfide inclusions in chromite are spherical and occur parallel to chromite growth planes. Polyphase inclusions are found in olivine and consist of olivine, orthopyroxene, chrome-spinel, amphibole, and sulfide daughter minerals. Primary fluid inclusions are usually found in olivine and pyroxene with spherical to tubular shapes. Laser Raman analyses were used to identify daughter minerals and fluid phases in the inclusions. The result shows that fluids consist mainly of CO2, with minor amounts of SO2, H2S, and CH4. This indicates that the parental magma of the Jinchuan intrusion contains abundant volatiles. Microthermometry shows that Type-II inclusions in dunite and sulfide-rich lherzolite have higher trapping temperatures (1000° to 1050°C), whereas trapping temperatures in sulfide-poor lherzolite are lower (900° to 950°C). The result of low-temperature microthermomentry indicates that the CO2 homogenization temperatures of +10° to +15°C correspond to depths of 12.9 to 15 km (deep-level magma chamber) and the homogenization temperatures of +26° to +29°C correspond to depths of 6.9 to 9.3 km (upper magma chamber). The immiscible sulfide in the inclusions demonstrates that segregation of the sulfide melt occurs at an early stage during magmatic differentiation.