Genesis of the Jinchanggouliang gold deposit, Chifeng, China: Constraints from fluid inclusions and isotopic geochemistry

摘要

The Jinchanggouliang gold deposit which located south of the Hingan-Mongolian Orogenic Belt is a large gold deposit in the Chifeng-Chaoyang region. Field evidence and petrographic observations indicate that the mineralization processes can be divided into three stages: including milky or grey quartz (stage I), quartz-pyrite (stage II), quartz-polymetallic sulfides (stage III). Five types of FIs have been identified in the Jinchanggouliang deposit: (1) solid-bearing inclusions (type 1), liquid-rich inclusions (type 2); vapor-rich inclusions (type 3); pure vapor inclusions (type 4) and CO2-H2O inclusions (type 5). The first stage contains mainly type 2, but also minor type 3 and 4 FIs; the FIs display homogenization temperatures of 317-384 degrees C and salinities of 4.0-12.5 wt% Nan eq. The stage II contains all types of FIs (mainly type 2, less abundant type 3 and 5, rarely type 1 and 4) which show homogenization temperatures of 288-382 degrees C and salinities of 1.6-41.4 wt% NaCl eq. The types of FIs in stage III are the same as stage II; These FIs yield the lowest homogenization temperatures of 245-363 degrees C and salinities of 1.1-36.8 wt% NaCl eq. The ore-forming fluids are characterized by moderate-high temperature and great fluctuating salinity magmatic hydrothermal fluids. The type 2 and 3 FIs commonly coexist with simultaneously trapped type 5 FIs, and the type 2 and 3 FIs have similar homogenization temperatures but contrasting homogenization modes (to the liquid and vapor, respectively) in the main mineralization stages which suggests fluid boiling occurred in these two stages. Combined with the previous H-O isotopic data it can be concluded that the ore-forming fluids are of granitic magmatic origin. The S-Pb isotopes indicate that the ore materials were mainly derived from deep magma. Petrographic observations and microthermometric analysis indicating that fluid boiling was the main mineral precipitation mechanism, and fluid boiling mainly occurred in the temperature range from 290 degrees C to 370 degrees C. In general, from the view of fluid inclusions and isotopes geochemistry, the Jinchanggouliang gold deposit is most probably a magmatic hydrothermal deposit.