Emilia Saltos, MSc
E. Saltos1, S. Barker1, M. Hohl1
1Mineral Deposit Research Unit, Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, British Columbia, Canada
Carbonate replacement deposits (CRDs) are globally significant sources for Ag-Pb-Zn (Cu) and form from low-temperature hydrothermal fluids interacting with carbonate rocks. The fluid-rock interaction typically leaves a narrow footprint of visible alteration, which poses a challenge during exploration. Ore body geometry is either stratigraphically controlled, as the mineralizing fluids follow more permeable horizons, or fault-controlled, forming near-vertical ore zones. Calcite veins are abundant in CRDs and form as an expression of hydrothermal fluid movement. Elevated amounts of certain elements, like Mn or Fe, can cause fluorescence in calcite under shortwave ultraviolet light (SWUV). A bright red UV response is associated with high Mn concentrations and commonly increases with proximity to mineralization.
The Guigui exploration project is situated in the southern part of the world-class Santa Eulalia CRD district. Most CRD-style mineralization is primarily hosted within a 1200 m package of prospective Cretaceous limestones. The limestone sequence is overlaid by pre-mineralization Tertiary rhyolites and tuffs, with carbonate veins crosscutting both units.
This study integrates the distribution and intensity of the visually logged UV response with the portable X-ray fluorescence (pXRF) geochemistry data from drill core to assess potential mineralization vectors. PXRF analyses were obtained from carbonate veins crosscutting volcanics and limestone, as well as their adjacent wall rock. A multivariate analysis is applied to effectively discriminate between lithologies and identify hydrothermal footprints, including subtle potassic centres and Mn halos. Furthermore, a key objective is to determine whether the UV fluorescence and geochemical trends of carbonate veins cropping out in the pre-mineral volcanic cap, as well as in the limestones, can be used to characterize cryptic alteration halos. This relationship can be utilized as an on-site tool for exploring CRD systems that extend into upper volcanics.