The Santa Cruz Central Caldera Field: a new frontier in the exploration for gold and silver in concealed Jurassic calderas of the Chon Aike volcanites of southern Patagonia, Argentina ?

CHERNICOFF, C.J.; SALANI, F.M.

Salta

Simposio; 15th Quadrennial Symposium of the International Association on the Genesis of Ore Deposits (IAGOD); 2018

International Association on the Genesis of Ore Deposits (IAGOD)

The Patagonian region of Argentina hosts an extensive volcanic field of mainly acidic character referred to as the Chon Aike Volcanic Province (Kay et al., 1989; Pankhurst et al., 1998; Sruoga et al., 2010). Its genesis is related to the extensional context that preceded, and eventually caused, the breakup of the Gondwana supercontinent. The effusion of the acidic volcanites and pyroclastics is thought to be related to the combination of calderas and large fractures.In the Deseado Massif, southern Patagonia, this volcanism contains gold and silver epithermal deposits, on account of which it has been defined as an Au-Ag metallogenic province (Schalamuk et al., 1999). Among the main caldera structures identified by other authors in the Deseado Massif (e.g.Férnandez et al. 1996; Guido, 2004; Echavarría et al. 2005; Sruoga et al. 2008 y 2010; Ruiz et al. 2011) are the La Josefina, the Cerro 1º de Abril, the El Dorado-Monserrat and the Cerro Torta Calderas, all of them in the extra-Andean zone, as well as the La Peligrosa Caldera located in the Andean region.The present authors have identified a caldera field ?Santa Cruz Central Caldera Field (Salani and Chernicoff, 2018a, 2018b)? on the basis of the geological interpretation of the aeromagnetic survey of the Deseado Massif (SEGEMAR, 1998). Although this caldera field is covered by Neogene and Quaternary deposits, it is clearly bound to be related to the surrounding volcanites and pyroclastics of the Chon Aike Formation, particularly the nearby outcrops exposed at the río Seco (ca. 48°42´S/68°15´W).The Santa Cruz Central Caldera Field is formed by four calderas ?and a number ofassociated lava domes? which extend in a roughly latitudinal corridor for at least 150 km (Fig. 1). Three of these calderas are larger than 20 km wide, the whole caldera field being controlled by NNE-SSO and ENE-OSO regional structural lineaments (herein detected as magnetic features) well known elsewhere in the exposed portion of the Deseado Massif, where they have been assigned to a transtensional context (e.g. Sruoga et al., 2008, and references therein).Numbered 1 to 4 from west to east, the calderas comprising the Santa Cruz Central Caldera Field are: 1) The smallest caldera, centered at 49ºS/69ºW, with a maximum diameter of 14 km. In the immediate proximity of this caldera there is a 4 km-wide lava dome centered at 48º53?S/67º30´W located at the intersection of two fractures. 2) A 23 km wide caldera, centered at 48º53?S/ 68º29?W, hosting 1-2 km wide eruptive bodies inside it. 3) The largest caldera (3a), centered at 48º52?S/68º02?W, has a maximum diameter of 30 km, with aligned, 1 to 3.5 km-wide, domes following the circular pattern of the ring fractures. Internally, there also occurs a concentric nested structure of 14 km in diameter (3b), with 600 m-wide igneous bodies in its interior. 4) A 25 km wide caldera, centered at 48º47?S/68º46?W, hosting a 5 km-wide igneous body in its interior plus two lava domes ranging in size 1-2 km in the southern caldera rim.Given the known occurrence of gold and silver mineralization associated with calderas and large fractures elsewhere in the Deseado Massif, our identification of the Santa Cruz Central Caldera Field may well open a new frontier in the exploration for Au-Ag mineralization in this region.