Tracing the genesis of skarn‐type iron deposit in central North China Craton: Insights from mineral zoning textures in ore‐forming intrusion

Abstract

The Handan–Xingtai region in the southern Taihang Mountains in central North China Craton hosts several skarn‐type iron deposits. Here we investigate an ore‐forming intrusion associated with a typical iron skarn deposit to explore the magmatic evolution from mineral zoning textures, and to constrain the ore genesis. We report results of X‐ray mapping of the composition of amphibole and plagioclase. The amphibole thermobarometers suggest: (a) magma chamber at a depth of 17 km; (b) two types of magma with different physical and chemical properties, one representing the main magma chamber with high water content, and the other characterized by more mafic composition and higher oxygen fugacity. The final emplacement depth of magma is estimated as ca. 1.5 km. The oxygen fugacity shows an obvious increase from the primary magma chamber to its emplacement depth. The zoning texture of plagioclase and amphibole suggest that the mafic magma was injected into felsic magma chamber many times, leading to magma mixing. We construct a petrogenetic and metallogenic model which envisages the following processes: (a) during 135–120 Ma, mantle‐derived magma and crust‐derived magma underwent mixing and homogenization at the crust–mantle boundary; (b) the hybrid magma rose to the middle crust and formed a magma chamber; (c) multiple injection of mafic magma into the felsic magma chamber resulted in oscillatory zoning; (d) the magma with high water content and higher modal content of plagioclase and amphibole formed through multiple magmatic injection‐mixing‐crystallization processes; and (f) the high water content and higher oxygen fugacity enabled the hybrid magma to rise to the shallow crust, where it released iron‐rich melt and fluids, which reacted with the surrounding limestones to generate the skarn‐ type iron deposit.