南岭中段板角沅石英脉型锡矿床成矿流体演化及成矿机制OA

The Banjiaoyuan tin deposit is located in the central section of the Nanling metallogenic belt and is a quartz vein-type tin deposit with large-scale potential.Its mineralization process can be divided into three stages:greisen stage(Ⅰ),cassiterite-quartz stage(Ⅱ),and barren quartz stage(Ⅲ),with stage Ⅱ being the main mineralization stage.Petrographic observations,microthermometric measurements,and laser Raman analyses were conducted on fluid inclusions in quartz from each mineralization stage.The results show that the homogenization temperatures of fluid inclusions in stage Ⅰ quartz range from 210 to 333℃(average 255℃),with salinities of 3.39-7.86 wt.%NaCleqv.;in stage Ⅱ quartz,homogenization temperatures range from 190 to 288℃(average 225℃),with salinities of 2.23-6.87 wt.%NaCleqv.;and in stage Ⅲ quartz,homogenization temperatures range from 140 to 230℃(average 174℃),with salinities of 0.35-5.40 wt.%NaCleqv.From early to late stages,both the temperature and salinity of the ore-forming fluids gradually decrease,indicating that the mineralizing fluids belonged to a medium-temperature,low-salinity NaCl-H2O±CH4±CO2±N2 system.LA-ICP-MS in situ analysis reveals that cassiterite is enriched in high-temperature incompatible elements such as In,Nb,Ta,and W.The Nb/Ta ratio ranges from 2.1 to 58.1(average 5.64),and the Zr/Hf ratio ranges from 8.8 to 23.5(average 16.8).Significant variations in the contents of Mn,Th,Ta,and other elements within cassiterite growth zones reflect periodic fluctuations in physicochemical conditions during its crystallization.Combined with fluid evolution patterns,it is proposed that the pulsating injection of ore-forming fluids released through multi-stage differentiation of a deep-seated magma chamber,along with fluid mixing and cooling,collectively led to cassiterite precipitation.