The Veladero High-Sulfidation Epithermal Gold Deposit, El Indio-Pascua Belt, Argentina: Geochronology of Alunite and Jarosite

Abstract

The world-class Veladero high-sulfidation epithermal gold deposit is located near the northern end of the El Indio-Pascua metallogenic belt in Argentina. New 40Ar-39Ar alunite and jarosite ages were obtained at four mineralized centers in the Veladero district: the Amable and Filo Federico orebodies that compose the Veladero deposit, and the Argenta and Fabiana satellite centers. These ages indicate that magmatic-hydrothermal alteration and related gold mineralization were episodic, and activity in the Veladero district occurred over a period of approximately 3 m.y. The earliest magmatic-hydrothermal alteration in the Veladero district is recorded by alunite from Argenta that formed at 13.12 ± 0.18 Ma. At the Fabiana prospect, alunite is dated at 10.09 ± 0.08 Ma. At the Veladero deposit, the alteration and mineralization at the Filo Federico and Amable orebodies formed at different times despite their close proximity. Previously available data indicate that alunite at Amable formed at 11.93 ± 0.09 Ma, whereas Filo Federico alunite samples are younger and yield 40Ar-39Ar ages of 11.05 ± 0.12 and 10.34 ± 0.11 Ma. The oldest postmineralization jarosite alteration at Amable is dated at 11.8 ± 0.3 Ma and the youngest is dated at 8.58 ± 0.17 Ma. The age constraints suggest that the spatially overlapping Amable and Filo Federico orebodies formed approximately 1 m.y. apart, at about 11.9 Ma at Amable and after 11.1 Ma at Filo Federico. The results demonstrate that the Veladero district is host to the oldest centers of significantly mineralized magmatic-hydrothermal alteration within the El Indio-Pascua metallogenic belt. Magmatic-hydrothermal alteration and gold mineralization at the Veladero deposit broadly overlapped with isolated centers of middle to late Miocene volcanic activity in the region, dated at 12.7 ± 0.9 to 11.0 ± 0.2 Ma. In contrast to Veladero, the other high-sulfidation deposits in the belt are significantly younger with reported 40Ar-39Ar alunite alteration ages of other major deposits in the belt ranging from 9.4 (the Lama deposit at Pascua Lama) to 6.2 Ma (the El Indio deposit). These deposits formed during volcanic quiescence caused by shallowing of the Nazca plate below South America during the late Miocene, whereas Veladero formed prior to the cessation of volcanism. Fertile magmas of roughly 13 to 10 Ma were previously thought to be restricted to the Maricunga metallogenic belt approximately 200 km north of Veladero, but the present study demonstrates that mineralization in this age range occurred as far south as Veladero. These results are significant for regional exploration, in particular in the area between the Maricunga and El Indio-Pascua metallogenic belts.