Mineralization Of Luohe-Xiaobaozhuang Iron Deposit In The Lu-Zong Volcanic Basin, Anhui Province

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 which was found in 70s. Xiaobaozhuang deposit was found in recent year, which is located beneath the Luohe deposit. Although Luohe and Xiaobaozhuang deposits are located in different depth, they belong to the same metallogenic system. so this article called it Luohe-Xiaobaozhuang deposit. the mineral assemblage and alteration type of deposit is similar to NingWu porphyrite iron deposit. But two layer orebody mineralization characteristics and alteration type is different to typical porphyry iron deposit model. The thesis based on the former work of Luohe deposit, we carried out detailed study on the geology characteristic of deposit through carefully field work, mineralography and EPMA analysis. Studied the alteration periods, alteration zoning and ore deposit genesis in detail. Based on the preliminary established the Luohe-Xiaobaozhuang deposit metallogenic model. Through the research work, mainly obtained the following results:The main alteration mineral assemblage includes anhydrite-diopside, 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 and chlorite-epidote-carbonate stage is the main stage for ore forming. Anhydrite-pyrite-carbonate-quartz stage can further divide into anhydrite-pyrite sub-stage and quartz-sericite sub-stage.An of Plagioclase of deposit range in 1.40～43.02, therein, albite and oligoclase are the production of alteration, fresh andesine An range in 31.15～43.06. Or end range in 91.12～97.88, all of them are orthoclase. Di end member range in 49.62-88.7, Hd end member range in 10.8～46.3, Jo end member range in 0.5～6.5, belong to typical Di-Hd solid solution series (Di49～89Hd11～46.Fo0.5～7). Garnet mainly dominate by andradite (53～89) Followed by grossular (3～36), belong to andradite and grossular solid solution series (Ad61～91Gr3～34Prp+Sps2～8)Luohe-Xiaobaozhuang ore body occurring as lens in the Zhuanqiao formation, Although structure of wall rock in deep is porphyritic, gradient transition to upper volcanic rocks, they are different volcanic facies.2000 meters exploration in mining area did not found intrusive rocks which relation to mineralization, Because of Zhuanqiao group volcanic rocks cannot provide metallogenic ore-forming materials, this thesis consider the Xiaobaozhuang deposit mineralization material source and ore-forming fluid is from dioritic magma in the deep.Limestone-gypsum rocks was found in the deep as the basement strata of mining area, through analyze the Triassic sedimentary gypsum, the δ34S of white sucrosic anhydrite in deep range in +30.61～+32.17%o, with an average of +31.3%o, formed from gypsum reforming. the δ34S of pyrite range in+ 10.08～+10.19%o, the higher δ34S value of pyrite illustrate the ore-forming hydrothermal sulfur derived from magma sulfur contamination by formation of sulfur.Metallogenic substances of Luohe-Xiaobaozhuang deposit may be derived from Concealed porphyry intrusive body or hypabyssal instrusive, Triassic salt and anhydrite layer provides the mineralizer, and provides the hydrothermal migration channels. Ore-forming hydrothermal filling and metasomatism formed vein orebody, block and disseminated ore body. Luohe-Xiaobaozhuang deposit is a special type of porphyry iron deposit in volcanic rock.