Volcanic Dome Emplacement and Au-Ag-Zn Mineralization at the Moore Deposit, Pueblo Viejo District, Dominican Republic

Atotal of 5.3 million ounces of gold and 24.4 million ounces of
silver has been recovered from five open pits in the Pueblo Viejo
district since mining commenced in 1975. Although oxide ore has
been largely mined out, an underlying sulfide resource contains an
additional 35 million ounces of gold, 203 million ounces of silver, 3
million tonnes of zinc, and 0.4 million tonnes of copper. Much of
this resource (14 million ounces) is located in the Moore deposit, the
largest of the sulfide gold ore deposits in the Pueblo Viejo district.
Gold, silver and zinc mineralization throughout the Pueblo
Viejo district is spatially and temporally related to previously unrecognized
Early Cretaceous volcanic domes that vary from basaltic
andesite to dacite in composition. In the Moore deposit, gold mineralization
surrounds a dacite porphyry volcanic dome and vent breccia.
The dome’s intrusive origin is indicated by tilting of flat-lying
epiclastic carbonaceous sedimentary rocks adjacent to the dome
margin, by the presence of crosscutting contacts between the dacite
porphyry and surrounding sedimentary rocks, and, most importantly,
by the presence of a baked contact metamorphic aureole adjacent to
the dome margin. Steeply dipping reverse faults formed along the
dome margin as the dacite porphyry shouldered its way through surrounding
sedimentary rocks.
A genetic link between dome emplacement and gold mineralization
is indicated by their spatial association and by evidence for
coeval dome emplacement and hydrothermal alteration. Gold was
likely derived by hydrothermal leaching of the accumulating volcanic
pile and/or by condensation of volcanic gas.