Gold Mineralization at the Forecast Hydrothermal Field in Southern Mariana Trough

Abstract

Gold-rich (up to 72.6 ppm) massive sulfide and hydrothermally altered host rock were collected by remotely operated vehicle, HAEMIRE, from the Forecast hydrothermal field in Southern Mariana Trough. Gold-rich massive sulfide is featured by Zn-rich (up to 51.1 wt.%) ore, mainly composed of sphalerite, pyrite, chalcopyrite and galena with tennantite and electrum as minor minerals. The altered host rock can be subdivided into sulfide-rich part and altered silicate part. The sulfide-rich part is mainly composed of sphalerite and pyrite with minor chalcopyrite while XRD examination shows that montmorillonite ± anorthite are predominant in the altered silicate part. The FeS contents in sphalerite represent a decreasing trend as mineralization advanced (6.5