Genetic Mineralogy Study Of Metallic Sulfide Minerals From Lanjiahuoshan Ore Block Of Panzhihua Fe-Ti-V Oxide Deposits

Panzhihua Fe-Ti-V oxide deposits are super large mineral deposits which have huge reserves and are located in Emeishan large igneous province. The in-depth study of their metallogenic process will not only help to promote the deep exploration work, but also help to further understand the plume metallogenic process.Based on the geological survey, the Lanjiahuoshan Ore Block of Panzhihua Fe-Ti-V oxide deposits was selected as the research object. Through the integrated use of in-situ microanalysis methods, the species, occurrence, chemical composition and paragenesis relationship of metallic sulfides were studied systematically.The observation results indicated that the metallic sulfide minerals were mainly pyrrhotite, followed by pyrite and chalcopyrite. The pyrrhotite had four kinds of occurrences, namely granular, droplet, leaf-shaped and stockwork. The pyrite had granular and hem-like two kinds of occurrences. The chalcopyrite was often paragenesis with pyrrhotite and surrounded by silicate minerals.According to their chemical compositions, the pyrrhotite was divided into three types, namely troilite, hexagonal pyrrhotite and monoclinic pyrrhotite. The amount of the troilite was little. And the troilite was often preserved from the later transformation by the surrounding metallic oxide minerals formed at high temperatures. The hexagonal pyrrhotite was more common and was mainly interstitial granular. The monoclinic pyrrhotite was mainly leaf-shaped and stockwork. The composition of pyrite and chalcopyrite is more stable, and has less isomorphism replacement.The paragenesis metallic oxide minerals included titanium magnetite, magnetite, ilmenite and magnesiospinel. The exsolution of the solid solution was widespread. For example, titanium magnetite had the exsolution of both ilmenite and magnesiospinel. The paragenesis gangue minerals included pyroxene, plagioclase, olivine and so on. The pyroxene often had schiller texture.Among the metallic sulfide minerals, metallic oxide minerals and gangue minerals, there was reaction rim texture. The exsolution, schiller texture and reaction rim texture indicated that in the plume metallogenic process, the magma rapidly rose up when the differentiation was not sufficient, and the differentiation occurred again during the cooling crystallization.Combined with the results of previous work, the geochemical behavior of the ore-forming elements and the mineral formation condition during the metallogenic processes were analyzed and discussed. The forming process of the metallic sulfide minerals was divided into three stages. In the first stage, it is the early fractional crystallization of magma. Small amount of metallic sulfides liquated from the magma as small droplets, and were surrounded by silicate mineral. This stage formed "pyrrhotite+chalcopyrite" paragenetic association of minerals. In the second stage, it is the late fractional crystallization of magma. In this process, a large number of metallic sulfides formed and most of them were pyrrhotite. In the third stage, most of the metallic sulfide minerals were the products of post-magmatic hydrothermal. They were stockwork and formed "pyrrhotite+chalcopyrite" paragenetic association of minerals.In conclusion, the feature of type, occurrence, composition and paragenetic association of the metallic sulfide minerals, can indicate the changes of physical-chemical conditions in the magmatic process, which can be used as identification in the resource prospecting and exploration.