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PUEBLO VIEJO HIGH-SULFIDATION EPITHERMAL GOLD-SILVER DEPOSIT, DOMINICAN REPUBLIC: A NEW MODEL OF FORMATION BENEATH BARREN LIMESTONE COVER A DISCUSSION

2007; Volume: 102; Issue: 4 Linguagem: Inglês

10.2113/gsecongeo.102.4.755

1554-0774

John V. Muntean, Greg Hall, S. E. Kesler, A. Mueller, Dennis O’Brien, Norman Russell,

Paleontology and Stratigraphy of Fossils

Sillitoe et al. (2006) suggest that the Pueblo Viejo Au-Ag deposit is younger than its Early Cretaceous Los Ranchos Formation host rocks. This interpretation contrasts with our earlier observations that the mineralization is coeval with the Los Ranchos Formation. Although a younger age would allow Pueblo Viejo to be conveniently grouped with many other high-sulfidation deposits in a subaerial calc-alkaline setting, evidence for it conflicts with geologic observations in and around the deposit. The new interpretation of the age of mineralization depends largely on the contention that the Hatillo Limestone, which overlies the Los Ranchos Formation, was replaced along its basal contact by silica and magnetite that are coeval with Pueblo Viejo mineralization. In their figure 2 (p. 1429), Sillitoe et al. show two “silicified and iron-oxide–bearing zones along the poorly exposed base of the Hatillo Limestone outliers.” One of these zones is along the southern edge of the Pueblo Viejo mine where mine workings and exploration drill holes immediately south of the contact provide good exposures. In this area the contact, which is tectonized locally, ranges from a basal conglomerate with silicified cobbles to calcareous sandstone-siltstone-mudstone with abundant marine fossils. Silicified cobbles require that silicification preceded deposition of the Hatillo Limestone. Similarly, carbonaceous sediments containing silicified boulders and cobbles and underlying fragmental rocks with clasts exhibiting different alteration assemblages are widespread in the mine area (Russell and Kesler, 1991, fig. 3). Sillitoe et al. (2006) do cite one outcrop containing veinlets of iron oxide (limonite) with marginal silicification (Russell and Kesler, 1991, p. 210–211) as evidence of “…silicification and iron oxides in the basal few meters of the Hatillo Limestone.” They acknowledge, however, that we interpreted these features as (paleo)supergene, which they clearly are. Furthermore, they are …