Siting of gold and characteristics of gold-bearing massive sulfides from the interior of the felsic-hosted PACMANUS massive sulfide deposit, eastern Manus basin (PNG)

Precious- and base metal-rich massive sulfides from the interior of the active Roman Ruins site (

Pacmanus

) locally contain abundant native gold in two distinct mineralogical associations:(I) with chalcopyrite-sphalerite dominated mineral assemblages and (II) with sphalerite-barite-amorphous silica-rich mineral assemblages. The silver content is variable and is lower for Cu-Zn-hosted gold (avg. 3.6 wt.% Ag; range from 1.2 to 8.7 wt.% Ag) and higher for Zn-Ba-hosted gold (avg. 11.3 % Ag; range from 8.0 to 16.4 wt.% Ag). The latter is in marked contrast to previously published results for surface samples from

Pacmanus

that showed only high gold fineness values. The FeS-content of sphalerite associated with native gold is low in the Cu-Zn-rich core section (0.1 to 6.0 mole % FeS; avg. 0.6 mole % FeS), but higher in Zn-Ba-rich mineral assemblages (0.1 to 18.7 mole % FeS; avg. 6.5 mole % FeS) indicating a larger variability in the sulfur activity than previously documented. The combination of the siting of gold at Roman Ruins and the variability of the gold fineness and the Fe-content of associated sphalerite is distinct from most other seafloor hydrothermal systems and indicates that refining of primary gold is not responsible for the enrichment of gold in Zn-rich sulfide assemblages at Roman Ruins.