Geological characteristics of Xiaobaozhuang iron deposit in the Lu-Zong volcanic basin, the Middle-Lower Yangtze River Valley Metallogenic Belt

Luohe iron deposit is located in the northwest of Lu-Zong volcanic basin，which is the largest iron deposit in the Middle-Lower Yangtze River Valley Metallogenic Belt. Xiaobaozhuang deposit was found in 2013, which is located 800 ～ 1000m deep beneath the Luohe deposit. The discovery of Xiaobaozhuang deposit is one of the most significant prospecting progresses in the Middle-Lower Yangtze River Valley Metallogenic Belt. Based on the former work, we carried out detailed study on the geology characteristic of deposit through carefully field work, mineralography and EPMA analysis. Although Luohe and Xiaobaozhuang deposits are located in different depth, they belong to the same metallogenic system. Xiaobaozhuang ore body occurring as lens in the Zhuanqiao Formation，located 800 ～ 1000m below the Luohe orebody, ore structure are dominated by disseminate. The main ore minerals are magnetite and pyrite. The main gangue minerals are anhydrite，diopside and carbonate. The typical mineral assemblage is magnetite-anhydrite-diopside. The main ore structures include massive and disseminated structure. The main ore textures include euhedral-subhedral granular texture, anhedral granular texture and metasomatic pseudomor-phic texture. The main alteration mineral assemblage includes anhydritediopside， chlorite-epidote，pyrite-anhydrite and carbonate. The mineralization process of the deposit can be divided into four stages such as alkali feldspar stage，anhydrite-diopside-magnetite stage，chlorite-epidote-carbonate stage and anhydrite-pyrite-carbonate-quartz stage. Therein, anhydrite-diopside-magnetite stage is the main stage for ore forming. Based on the geological characteristics of the Xiaobaozhuang iron deposit and compared to Ningwu iron deposits, the article considers the Xiaobaozhuang deposit mineralization material source and ore-forming fluid is from dioritic magma in the deep，mineralization and alteration ares developed in the volcanic formation far from intrusive rock. It is obviously different from Ningwu iron deposits，similar to some apatite-magnetite deposits in Andean metallogenic belt in Chile. It is a special type of porphyry iron deposit in the Middle-Lower Yangtze River Valley Metallogenic Belt.