Gold mineralisations in the Canan area, Lepaguare District, east-central Honduras: Fluid inclusions and geochemical constraints on gold deposition

Gold mineralisations in the Canan area (Honduras) occur within altered metamorphic rocks crossed by quartz veins which filled the fractures where the hydrothermal fluids carrying gold flowed. Quartz crystals of the veins contain abundant fluid inclusions which have been divided into four main types on the basis of the petrographic features and microthermometric data. The association of L-rich and V-rich inclusions with the same major components supports boiling at the time of entrapment. The trapped hydrothermal fluid consists of an aqueous solution (0.9–4.8 wt.% NaCl equivalent) plus a CO2–CH4-bearing bubble. Some fluid inclusions contain graphite of hydrothermal origin.Microthermometric and spectroscopic data on fluid inclusions indicate that hydrothermal fluids carrying goldwere at T=300 °C, P=500–1400 bar, log fO2 ~−37.6±2.5 andwith a pH value of 2.9 ± 0.4. Large amounts of sulphides (mainly pyrite) are associated with gold. We infer that Au was transported as Au–S complex, in particular as Au(HS)°. The activity of sulphur in the hydrothermal fluids was at least 10−2. The precipitation of gold can be related to several processes that reduced the stability of AuHS°: 1) boiling and vapour loss following the pressure drop caused both by fracture opening and fluid uprise, 2) sulphidation as a result of the presence of Fe2+ (and other metal cations) from the mineralogical alteration (mainly of biotite and chlorite) in the wall-rocks and 3) hydrothermal alteration of feldspars and micas into kaolinite and diaspore with increase in pH of the hydrothermal fluids. The mineralogical, petrological, geochemical features and the geological setting are broadly consistent with those of orogenic-type gold deposits.