Genesis of the Zhaokalong Fe-Cu Polymetallic Deposit at Yushu, China: Evidence from Ore Geochemistry and Fluid Inclusions

The ore types of the Zhaokalong Fe-Cu deposit are divided into two categories: sulfide-type and oxide-type. The sulfide-type ore include siderite ore, galena-sphalerite ore and chalcopyrite ore, whereas the oxide-type ore include magnetite ore and hematite ore. The ore textures and structures indicate that the Zhaokalong deposit is of the sedimentary-exhalative mineralization type. Geochemical analyses show that the two ore types have a high As, Sb, Mn, Co and Ni content. The REE patterns reveal an enrichment of the LREE compared to the HREE. Isotopic analysis of siderite ore reveal that the 13CPDB ranges from 2.01 to 3.34 (parts per thousand) whereas the 18OSMOW ranges from 6.96 to 18.95 (parts per thousand). The fluid inclusion microthermometry results indicate that homogenization temperatures of fluid inclusions in quartz range from 131 to 181 degrees C, with salinity values of 1.06 to 8.04 wt% NaCl eq. The mineralizing fluid therefore belongs to the low temperature low salinity system, with a mineralizing solution of a CO2-Ca2+(Na+, K+)-SO42 (F, Cl)-H2O system. The geochemical results and fluid inclusion data provide additional evidence that the Zhaokalong deposit is a sedex-type deposit that experienced two stages of mineralization. The sulfide mineralization probably occurred first, during the sedimentary exhalative process, as exhibited by the abundance of marine materials associated with the sulfide ores, indicating a higher temperature and relatively deoxidized oceanic depositional environment. After the main exhalative stage, hydrothermal activity was superimposed to the sulfide mineralization. The later stage oxide mineralization occurred in a low temperature and relatively oxidized environment, in which magmatic fluid circulation was dominant.