The Mineralized Characteristics Of Polymetallic Sulfides On Mid-Atlantic Ridge(MAR) At 26°S

The hydrothermal field in Mid-Atlantic Ridge at 26°S is the major object of research. Through the study of the collected basalt samples and polymetallic sulfides to discuss their mineralogy, geochemistry characteristics, petrographic features of polymetallic sulfide, chimney reconstruction, mineralization process and sources of mineralization material. We mainly carried out two aspects of research:(1) Discuss the ore-controlling factors, mineralization conditions and mineralization process of sulfide mineralization in the typical hydrothermal field at slow-spreading ridge and reveal the mineralization process of hydrothermal sulfide deposit.(2) Through investigate rock geochemistry, ore-deposit geochemistry, other analysis methods(e.g. electronic probe, laser Raman analysis, etc), and the metallogenetic elements’ relation between basalt and hydrothermal sulfide present the sources of mineralization materia.The 26°S hydrothermal field located in a depression between two volcanic top on the along-axis topographic high near the center of the 26°S segment and surrounded by massive pillow-shaped basalt which is fresh and is not be altered.The slow-spreading ridge has massive magma supply and shallow magma chambers. It is the main heat source of hydrothermal activities in the area. The rock samples which were collected from 26°S segment, as depleted mantle melting, is Normal Mid Oceanic Ridge Basalt(N-MORB). During magma evolution, the composition of the magma is changing. Polymetallic sulfides of hydrothermal field is composed of chalcopyrite, pyrite and sphalerite. Ecto entad,the content of Fe, S, As increase and content of Zn, Ni decrease, only the pyrite at 15°S segment shows Zn content increase while the form is more euhedral. The mineralogical of sulfide shows that the 26°S segment lacks of sulfate minerals. So there is only sulfide mineralization period in the mineralization process. Based on mineral intergrowth association and structural characteristics, it can be divided into 4 mineralization stages: Fe-rich mineralization stage, Fe-Zn mineralization stage, Fe-Cu mineralization stage, Cu-rich mineralization stage. During ore-forming process, a chimney-like structure comes into being. To be specific, from outside to the center, it consists of colloid form pyrite(dominating) â†' colloid form pyrite + sphalerite + subhedral-euhedral chalcopyrite â†' coarse grain euhedral crystalline-granular chalcopyrite + speckle and framboidal-pyrite â†' xenomorphic crystalline-granular chalcopyrite. Through petrographic analysis of basement, contract of Cu content and Zn content in the basement of different hydrothermal field, study of melt inclusion and polymetallic microcrystalline sulfide scattered in the glass, as well as contrast of basement and sulfide, it is discovered that the metallic elements during the mineralization might not be extracted from the interaction of hydrothermal fluid and basalt, but be originated from a kind of mineralization fluid directly separated from postmagmatic hydrothermal.