Gold deposits hosted in Ordovician sedimentary rocks of the Rinconada range (Jujuy- Argentina): implications for exploration.

Abstract

In this presentation, we aim to synthesize the information obtained in a sector of the Puna Argentina and to establish some exploration guides for gold deposits hosted in Ordovician sedimentary rocks of the Rinconada Range (Jujuy province- Argentina). This area constitutes a key place for the occurrence of slate belt gold type deposits. The studies carried out in four sectors allow to establish preliminary constraints regarding genetic controls on the mineralization. These controls are: the stratigraphic arrangement of the sequence, the folding style, and the geochemistry of wall rock alteration. Interbedded sequences with approximately equal proportion of sandstone and mudstone are the most favorable, due to differences in rheologic behavior during folding. Mineralization is structurally controlled and occurs typically along large anticline hinges. Most of the gold occurs in bedding-parallel veins (19 g/t Au) but host rocks without quartz vein also have signs of mineralization (0,6 g/t Au). Geochemical data indicate that the hydrothermal systems were rich in Au-As (Sb) together with subordinate quantities of base metals (Pb, Zn, Cu, and (Mo)). The As/Sb ratio constitutes a good guide to establish optimal levels of mineralization, although the dispersion and fixation mechanisms, as well as the availability of elements in the sedimentary environment may condition this relationship. The relationship between sedimentary environment, deformation style of the sequence and the structural level involved, is the key for the localization of manifestations of economic interest. Mineral occurrences in the Rinconada range have affinities with turbidite-hosted gold deposits in the Victoria mining district of Australia and similar slate belt settings elsewhere.