Ore microscopy & Fe isotope of the Xinqiao deposit and their constraints on the ore genesis

Systematical field work and ore microscopy studies have been carried out in the Xinqiao deposit. The fact that the skarn-associated magnetite is cut by the colloidal pyrite in the stratiform ore body provides a new constraint on the ore genesis of the stratiform sulfide ore body in Xinqiao deposit. The Fe isotope compositions of siderite minerals from the siderite ore bodies in Xinqiao and Fenghuagnshan skarn Fe-Cu ore bodies were analyzed and compared. Fe isotope compositions of the siderite from Xinqiao deposit are different from those from sedimentary and hydrothermal vein-type deposits, but similar to those from the Fenghuanghsan skarn Fe-Cu deposit. Moreover, the fact that the heavy Fe isotope enrichment in magnetite related to siderite and colloidal pyrite indicates that the siderite and colloidal pyrite cannot be altered to be magnetite. Fe isotope compositions in sulfide ores, quartz-monzodiorite stock and limestone wall-rock in Xinqiao strata bound sulfide and skarn ore were examined. The δ57Fe values of endoskarn and the earliest formed magnetite are lower than those of the quartz-monzodiorite, while δ57Fe values of limestone wall-rock are higher than those of the igneous stock. Moreover, such features as spatial and temporal zoning, evolution of Fe isotope are consistent with fluid exsolutionary and evolutionary theory, also accordant with basic theory of Fe isotopic fractionation, which suggests that two types of ores be resulted from the same hydrothermal fluid system and Fe element came from the same magmatic source. The Fe isotope characteristics, together with ore minerals paragenesis relationship, demonstrate that the Xinqiao Cu-S-Fe-Au deposit is a typical hydrothermal skarn deposit, rather than the multi-stage syngenetic-hydrothermal compound deposit