Geochemistry of El Dorado-Monserrat epithermal prospect, Santa Cruz, Argentina.

Abstract

This paper is devoted to the geochemistry of lodes and host rocks from the El Dorado-Monserrat epithermal Au-Ag deposits. The distribution haloes of the studied metals show great variations as demonstrated by the coss-cut sections through the host rocks. An increase of contents was found in close relationship with the presence of narrow veinlets carrying ore minerals. The highest Au-Ag contents were found in the Monserrat area where quartz as well as barite veins were analyzed. The results allow to establish that the former ones are Au-enriched while the barite lodes have higher Ag grades. Most of the elements show a log normal distribution with long queues towards the highest values. Many samples with different quartz textures have also been studied, those with replacement and massive textures have higher Au-Ag contents that those with banded textures. The latter is possible due to the lower formation temperatures of the banded quartz. The geochemical and textural differences found between both areas suggest that they represent different exposition levels. Monserrat, where there are coarse-grained quartz textures and carbonate replacements intergrown with pyrite and adularia, is the deepest one, and it coincides with the precipitation level of the noble elements; El Dorado represents superficial levels, with massive chalcedony and recrystallization textures, with higher contents of Hg and lack of Au-Ag.