features of an epithermal low-sulfidation gold system. The quartz-lode and quartz-carbonate mineralization
is characterized by open-space textures, typically with sharp-walled veins and multi-stage brecciation of the
late Neoproterozoic (~560 Ma) rhyolitic and granophyric host rocks. Silicic alteration by cryptocrystalline
quartz is abundant; potassic alteration is expressed by muscovite and K-feldspar blastesis, commonly with
dispersed hematite laths. Sulfide content is low. Relict pyrite and chalcopyrite occur in comb and cockade
quartz. Gold occurs disseminated in the volcanic and subvolcanic wall rocks and as late vein infill.
The coexistence of vapor-rich and liquid-rich fluid inclusions in quartz, quartz textures, and the presence of
adularia and calcite in the vein mineralogy suggest boiling concomitant with gold deposition in a structural
setting favoring high fluid flow. Fluid inclusions in quartz define a temperature range of 350–380 °C and low
salinity (~1.5–7 wt.% NaC1 equiv.) for the ore system. Pressure is estimated at 200–250 bars, indicating a
maximum paleo-depth of 2500 m (hydrostatic). It appears likely that the Wadi Abu Khushayba system
represents the near-surface epithermal expression of a larger unexposed mesothermal system. Such
mesothermal systems are typical elsewhere in the Arabian–Nubian Shield, but are not exposed in
southwestern Jordan where the present-day erosional level is close to the unconformity of the transgressive
Early Cambrian platform sedimentation |
