引用本文：张嵩松,杨晓勇,李伟,王克友,韩长生,阳运楼.2022.繁昌地区矽卡岩型铁矿成矿流体与成矿年代学研究[J].地质学报,96(4):1297-1320. Zhang Songsong,Yang Xiaoyong,Li Wei,Wang Keyou,Han Changsheng,Yang Yunlou.2022.Study of ore- forming fluid and ore- forming age of skarn- type iron ore in the Fanchang area[J].Acta Geologica Sinica,96(4):1297-1320.
Abstract:The Fanchang area is located in the Middle- Lower Yangtze metallogenic belt, where the skarn type iron ore and zinc ore are the main metallogenic types. These deposits are relatively small in scale and different from the neighboring Ningwu basin.It is therefore important to obtain insights into the Mesozoic diagenesis and mineralization in the Middle- Lower Yangtze metallogenic belt. In this study, ore- forming fluid and ore- forming age of the Xiaoyangchong skarn- type zinc- iron deposit and the Songyuan skarn- type pyrite deposit have been investigated. The source of ore- forming fluid of the skarn type deposit in the Fanchang area has been discussed, then the comparison with the porphyrite- type iron ore in the Ningwu basin has been illustrated. First of all, results of fluid inclusion experiments show that the transparent minerals, such as quartz and calcite in the two deposits, comprise mainly gas- liquid two- phase inclusions. In the quartz- sulfide stage, the homogenization temperature of fluid inclusions varies from 150~380℃, and the salinity is 3. 6%~22. 0%NaCleq, density from 0. 70~1. 00 g/cm3 leading to the mineralization depth of 0. 50~2. 00 km, reflecting the characteristics of epithermal mineralization. Secondly, results of electron probe analysis show that andradite is dominant while grossularite is secondary in both the deposits. Combining with the variation trend of trace elements in the garnet composition belt, it indicates that the garnet has formed in an oxidizing and alkaline environment. Thirdly, based on the comprehensive analysis and discussion of H, O, S isotopes, as well as the multi- genetic types of magnetite, it is concluded that not only the mixing of magmatic water and surface water, but also deep brine would also have been involved in the mineralization process during the evolution process from skarn stage to quartz- sulfide stage. Finally, compared with porphyrite type iron ore in the Ningwu basin, the formation temperature range of magnetite in skarn in the Fanchang area is narrower and lower. Additionally, the Re- Os age of pyrites in the main mineralization stage of the Xiaoyangchong zinc- iron deposit is 125. 7 Ma, obtained by general Os correction, later than that of porphyrite type iron ore in the Ningwu area.