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

摘要

Sir: Muntean et al. (2007) are thanked for their long-anticipated discussion of our reinterpretation of the Pueblo Viejo high-sulfidation epithermal gold-silver deposit as a product of Late Cretaceous-early Tertiary rather than Early Cretaceous magmatism. The reinterpretation is based on evidence that the gold-silver mineralization post- rather than predated deposition of the thick, regionally extensive Hatillo Limestone (Sillitoe et al., 2006). Their discussion tries to diminish the significance of our new, district-wide observations, reiterates the limited evidence from the Pueblo Viejo mine, and presents a previously unpublished U-Pb zircon age (regrettably, without the supporting analytical data) and its interpretation. Here, we welcome the opportunity to restate the key district-scale features that led us to conclude that the gold-silver mineralization-along with formation of the adjoining 10-km-long Loma la Cuaba advanced argillic lithocap-took place beneath the Hatillo Limestone, before commenting on Muntean et al.'s (2007) main mine area observations and conclusions. Muntean et al. (2007) infer that the silicification and associated iron-oxide replacement described from the base of the Hatillo Limestone is a local feature and possibly even a replacement of an older limestone bed in the underlying Los Ranchos Formation rather than of the Hatillo Limestone itself. Although we present in some detail the drill intercept from Piedra Iman as a type example of the replacement phenomenon, we nowhere imply that the silicification is merely a localized feature. In fact, quartz-iron oxide replacement along the base of the Hatillo Limestone is district-wide and exposed intermittently for at least 3 km along the basal contact of the Limestone with the underlying Los Ranchos Formation as well as occurring as erosional remnants on the dip slope exposed after Hatillo Limestone removal (see Sillitoe et al., 2006; fig. 2). Although outcrop is generally poor, especially near the Pueblo Viejo mine, small exposures and contiguous float trains are more numerous and widespread farther west and reveal unambiguous partial replacement of limestone by massive fine-grained silicification plus associated magnetite and derivative hematite. Breccia texture, like that shown in our figure 3a, and limestone cut by veins and pods of massive silicification, as illustrated by our figure 3b, are commonplace. There is no possibility that the limestone replaced is any other than the Hatillo. Nevertheless, as clearly stated, the silicification does extend from the limestone into the uppermost parts of the underlying Los Ranchos Formation, thereby making distinction of former limestone and volcanic rocks difficult.