Chapter 20: The Pueblo Viejo Au-Ag-Cu-(Zn) Deposit, Dominican Republic

The world-class Pueblo Viejo Au deposit in the central Dominican Republic is one of the largest high-sulfidation epithermal Au deposits globally, with past production plus resources and reserves of 41.7 million ounces (Moz) in the Moore and Monte Negro deposits. Mineralization occurs within a 2- × 2-km Early Cretaceous volcano-sedimentary basin filled with felsic volcanic and volcaniclastic rocks, interlayered carbonaceous sedimentary units, and underlying andesitic flows and tuffs. The volcanic stratigraphy was developed during a period of tholeiitic magmatism that transitioned to calc-alkaline magmatism at the time of emplacement of the late- to postmineral Monte Negro dike (~109 Ma). Additional geologic controls to mineralization include high-angle, NE- and NW-faulting, phreatomagmatic breccias, and possible volcanic domes. Mineralization is present across the stratigraphic sequence, with mineralization at Moore dominantly hosted within quartz-bearing volcaniclastic rocks and overlying carbonaceous sedimentary units, whereas that at Monte Negro is in the andesitic sequence as well as overlying epiclastic and sedimentary units. Alteration at the shallowest level is dominated by quartz-pyrophyllite, whereas alunite alteration defines the deep roots to the ore-forming environment. Mineralization comprises early disseminated-type and late veins filled with pyrite ± sphalerite. Hypogene ore is refractory in nature, with Au in solid solution or as mineral inclusions within arsenian pyrite. Re-Os ages of 113.4 ± 2.6 Ma for auriferous pyrite along with new geologic observations appear to confirm an Early Cretaceous age for mineralization, although Re-Os enargite ages suggest the possibility of a second mineralization event in the Eocene.