Mineralogy of the Zhangjiawa skarn iron deposit in Shandong Province and its implications for metallogenic environment

Abstract: The Zhangjiawa skarn iron deposit with high-grade iron is located in Laiwu of Shandong Province within southeastern North China Craton. The Laiwu hydrothermal metasomatic iron deposit is located at the unconformity between Carboniferous Benxi Formation and Ordovician Majiagou Formation and near the contact zone between Majiagou Formation and Late Yanshanian diorite, with the mineral reserves reaching a large-size deposit. Recent researches show that mineral compositions are somewhat different with the distance from the contact zone. The inner zone consists of calcium skarn minerals such as garnet, pyroxene, amphibole and episode, while the outer zone is composed of magnesium skarn minerals such as phlogopite and serpentine. The zoning structures of garnets and pyroxene in the Zhangjiawa iron deposit indicate that the ore-forming environment of the deposit changed gradually with the evolution of mineralization. The environment was somewhat reducing and acid at the beginning and, with the growth of silicate minerals and magnetite, became oxidative and alkaline. Finally, polymetallic sulfides crystallized and the environment became acid and reducing.