To characterize the hydrothermal processes of East Pacific rise at 9°-10°N, sulfide mineral compositions, textural, and geochemical features of chimney ores were studied using ore microscope,scanning electron microscope, X-ray diffraction analysis, and electron microprobe techniques. Results show that there are three mineral assemblages for the hydrothermal chimney ores, namely：（i） anhydrite ＋ marcasite ＋ pyrite, （ii） pyrite ＋ sphalerite ＋ chalcopyrite, and （iii） chalcopyrite ＋ bornite ＋ digenite ＋ covellite. Mineral assemblages, zonational features, and geochemical characteristics of the ore minerals indicate that ore fluid temperature changed from low to high then to low with a maximum temperature up to 400 ℃. The chimney is a typical black smoker. The initial structure of the chimney was formed by the precipitation of anhydrites, and later the sulfides began to precipitate in the inner wall.
