Fluid Evolution in the Patricia Zn-Pb-Ag vein deposit (Paguanta, NE Chile): fluid inclusion assemblages and laser ablation ICP-MS evidence

Abstract

The Patricia Zn-Pb-Ag ore deposit represents the first known example of economic mineralization in the northern part of the Andean late Eocene – Oligocene metallogenic belt in Chile. The hydrothermal evolution has been deduced based on detailed mineralogy, fluid inclusion petrography, microthermometry and laser ablation ICP-MS analysis. We present microthermometric data for fluid inclusion assemblages (FIAs) in co-genetic ore and gangue minerals through the different mineralization stages. In the pre-ore stage, early quartzhosted FIAs indicate high salinity values (22 to 6 wt.% NaCl) with homogenization temperatures from 270 to 205ºC. During the base metal and silver stage, a drop in temperature from 250 to 140 ºC and salinity less than 10 wt.% NaCl is related to the main ore precipitation. Primary FIAs in the post-ore stage indicate temperature up to 245ºC and low salinity (4 to 3 wt.% NaCl). The LAICP- MS analyses of fluid inclusions show that the metal content in the base metal stage is significantly higher than in the pre-ore and post-ore stages. This study documents the existence of different fluid pulses characterized by cooling and low salinity conditions favourable for the main ore deposition during the base metal and silver stage. The ore mineralogy and the associated hydrothermal alteration define the Patricia ore as an intermediate-sulfidation epithermal deposit with low-sulfidation events.