The Elder Creek deposit: the upper plate expression of an auriferous Carlin-type hydrothermal system?

The largest Carlin Au-deposits of northern Nevada are largely restricted to
Lower Paleozoic, carbonate dominated sedimentary rock sequences forming a “lower
plate” to the overlyingmainly siliciclastic Roberts Mountain allochthon (RMA).Gold
mineralization occurs close to the Roberts Mountain thrust, which separates the two
rock packages. The siliciclastic “upper plate” rocks above the thrust are poor hosts for
Carlin gold mineralization; a consequence of limited reactivity with Carlin ore fluids
(inhibiting gold precipitation) and relatively lowpermeability.Nevertheless, ore fluids
responsible for mineralization in the lower plate must have drained through upper
plate lithologies along structural conduits. Previous studies suggest that ore fluids
were moderately acidic (pH = 4.3–4.4), lowtemperature (180–240°C), and lowsalinity
(2–3 wt.% dissolved NaCl equivalent).