Precipitation of sulfide minerals from Cu(I)-, Pb- and Zn-containing seawater heated with pyrite at 300 degrees C

In order to examine the chemical processes of massive sulfide deposition ex perimentally, synthetic seawater containing CuCl, PbCl2 and/or ZnCl2 was he ated with pyrite at 300 degrees C and a saturated water-vapor pressure for 120-168 hours. Under the experimental condition, chalcopyrite precipitated with magnetite rapidly as fine grains of less than 0.1 to 5 mu m in size. G alena of 10 to 50 mu m precipitated more slowly than chalcopyrite, and spha lerite of less than 5 to 20 Crm precipitated much more slowly. Thermodynami c calculation indicated that the experimental solution containing CuCl was supersaturated with respect to CuFeS2. The experimental results suggest that mixing of seawater with hydrothermal fluids under the sea floor causes rapid precipitation of Cu-Fe sulfides lea ding to generation of Zn-rich hydrothermal solution. The outer walls of bla ck smoker chimneys at the mid-oceanic ridges may have been formed from such Zn-rich solution. The present study also supports the idea that chalcopyri te disease in Kuroko ores might be produced by coprecipitation of chalcopyr ite with sphalerite during the initial stage of Kuroko mineralization.