All-Russia Research Institute of Geology and Mineral Resources of the World Ocean, Russian Federation

Primary sulfides from cores of holes 957M, 957C, and 957H drilled during the ODP Leg 158 on the active hydrothermal TAG mound (Mid-Atlantic Ridge, 26 degrees 08'N) were examined for the concentration of several elements. Based on 262 microprobe analyses, it has been established that the sulfides are characterized by an extremely heterogeneous distribution of noble metals (Au, Ag, Pt, and Pd) and several associated elements (Hg, Co, and Se). Noble metals are arranged in the following order in terms of decreasing abundance, i.e., concentration level above the detection limit (the number of analyses containing the specific element is given in parentheses): Au (65), Ag (46), Pt (21), and Pd (traces). The associated trace elements make up the following series: Co (202), Hg (132), and Se (49). Main carriers of the "invisible" portion of noble metals are represented by pyrite (Au, Hg), marcasite and pyrite (Ag, Co), sphalerite and chalcopyrite (Pt, Pd), and chalcopyrite (Se). The noble metal distribution in sulfides reveals a lateral zonality: the maximal concentration and abundance of Au in chalcopyrite (or Pt and Ag in chalcopyrite and pyrite) increase from the periphery (Hole 957H) to the center (holes 957C and 957M) of the hydrothermal mound, while the Au distribution in pyrite displays a reversed pattern. The Co distribution increases with depth. This work discusses the vertical zonality in the distribution of elements mentioned above and their response to the evolution of ore genesis.