SEDIMENT HOSTED VEIN MINERALIZATION AS A GUIDE TO THE METALLOGENIC AND TECTONIC EVOLUTION OF NW ARGENTINA

Numerous examples of Sediment Hosted Vein (SHV) type mineralization in Early Paleozoic sedimentary rocks of the Santa Victoria basin in the Puna region of NW Argentina provide new evidence for geodynamic interpretation of this area. SHV deposits consist of gold in quartz-carbonate veins hosted by Neoproterozoic to Early Paleozoic passive margin sedimentary rocks that have undergone fold-thrust deformation. SHV deposits are some of the largest gold deposits in the world. All SHV deposits occur with a common set of characteristics that unite them as a class. These characteristics are consistent with those observed in the Puna region and therefore, by analogy, allow us to offer new geodynamic interpretations. A simplified reinterpretation of the development of early Paleozoic continental margin of northwest Argentina is as follows. • The Rio de la Plata craton began rifting in Neoproterozoic. Some volcanics at this time may be rift related. • Continental-derived passive margin sediment was deposited on extended and sagging crust and now forms the Cambrian Puncoviscana Fm. • Deformation of Puncoviscana rocks began as the craton moved westward into its passive-margin sequence causing west-vergent folding, uplift and migration to the west of active sedimentation to form the Santa Victoria Sequence. Continued westward movement of the craton caused Ocloyic fold and thrust deformation of the passive margin sequence. Docking of other terranes around this time can not be ruled out, but terrane collision is not necessary to explain Ocloyic deformation.

Structural interpretation of Santa Victoria rocks reveals a series of NW trending, semi-regular, spaced fault zones that cut both the Paleozoic and recent tectonic belts. These fundamental structural breaks are interpreted to represent early basin/sub-basin transfer zones which subsequently have been reactivated to serve as favourable fluid conduits. We postulate that this pre-existing structural framework was critical for the subsequent metallogenic and geologic history of the region including emplacement of SHV gold mineralization as well as the alignment of major Miocene volcanic complexes. Similar major NW trending structural corridors align giant Cu-porphyry deposits within the Chilean Cu belt immediately to the west.