Mineralization Of Polymetallic Sulfides On South Mid-Atlantic Ridge (SMAR) At 15°S

This article selects the South Mid-Atlantic Ridge(SMAR) 15 ° S hydrothermal area as the research object.Samping the basement rocks and polymetallic sulfide for detailed petrographic, chalcography, mineral chemistry, geochemistry research to discuss the source of polymetallic sulfide ore-forming materials,the hydrothermal characteristics and the metallogenic process.The study area is a hydrothermal sulfide deposit located in SMAR 15 ° S which is belong to slow slowspreading ridge.Determining the rock samples for normal type mid-ocean ridge tholeiite(N- MORB) and enrichment of mid-ocean ridge tholeiite(E- MORB) by the bulk elements, trace elements and rare earth elements analysis.So make a speculation that the study area had experienced two periods of magmatic activity.There are lots of melt inclusions in plagioclase of the basalt.Daughter metal minerals occur in the melt and walls of the melt inclusions. By the scanning electron microscopy(SEM), energy spectrum and Raman spectrum analysis, the daughter metal minerals are chalcopyrite, pyrite and magnetite. These minerals may be derived from magmatic liquation and degassing progress, and can be involved into the hydrothermal fluid and ore-forming. But the magma does not provide the ore-forming elements for sphalerite.So the sphalerite may be completely from the reaction between hydrothermal fluid and basement rocks. Therefore, there are two sources of hydrothermal ore-forming materials: magma source and water- rock reaction.By the analysis of mineral composition and mineral chemistry to the metal sulfide, the hydrothermal fluid had experienced three phases of evolution.The first phase of pyrite + sphalerite.The high temperature fluid mixed with sea water and then the temperature dropped due to the formation of the chimney wall.After the cold sea water mixed decreases ending, the temperature to stabilize. Mineral is given priority to with colloidal pyrite, pitting pyrite, contains some it morphologically sphalerite. The temperature of the fluid ranges in 236.31 ? ~ 379.88 ?, with average of 309?,which belongs to moderate temperature phase.The second phase ofsphalerite +pyrite+ chalcopyrite.The hydrothermal fluid temperature rise in this phase and then the temperature steady.The main mineral is metasomatism structure sphalerite.After the temperature is steady,the euhedral pyrite, sphalerite and hypidiomorphic chalcopyrite formed. The temperature of the fluid ranges in294.06 ~ 555.76 ?, with average of 429.46 ?,which belongs to moderate –high temperature phase.The third phase of chalcopyrite.In this phase due to the deep magma chamber naturally cooling, the temperature droped.Finally, as the new heating magma intrusion,the temperature is on the rise again.The main mineral is chalcopyrite, early stadge with replacement structure and later appearing euhedral-granular texture. The temperature is over 500 ?,which belongs to high temperature phase.Compared with the previous SMAR15° S sulfide samples, in terms of mineral chemical composition, the pyrite and chalcopyrite are with no inheritance, and the sphalerite is with strong inheritance.