Characteristics of chlorite from the Baguamiao gold deposit in Shaanxi Province and its geological implication

In order to discuss petrogenic and ore-forming significances of chlorite of the Baguamiao gold deposit in Shaanxi province, the chlorite minerals from wall rocks, lamprophyre and ores of different stages were chemically analyzed by means of electron-microprobe.Four types of the chlorite in the deposit were identified, namely chlorite derived from altered biotite in wall rocks(typeⅠ), chlorite in(with)quartz-sulfide veins(type Ⅱ), wormlike chlorite included in quartz(type Ⅲ)and chlorite in altered albite in lamprophyre(type Ⅳ).The former three types of chlorites are mainly Fe-rich prochlorite and minor pycnochlorite, indicating that they could be formed in a partial reducing environment.The phenomenon that Mg ions were mainly substituted with Fe ions in its lattice suggests that the formation of those chlorites is closely associated with the argillaceous wall rocks under several metamorphisms, and affected by mafic hydrothermal fluid.According to the chlorite geothermometer, these chlorites were formed in low-moderate temperature ranging from 198℃ to 255℃.It is believed that the hydrothermal fluid was gradually evolved from faintly acid to nearly neutral and finally to faintly acid with the continuous decrease of temperature in the mineralization process.Favorable formation environment of gold is close to neutral conditions.