Short-wave infrared spectroscopy for vectoring mineralization in intermediate-sulfidation epithermal deposits: A case of study on La Primavera Au–Ag vein system, Neuquén basin, Argentina

Abstract

The La Primavera vein system is an intermediate sulfidation deposit part of the Andacollo mining district (184,600 tn @ 47,100 oz AuEq). The mineralized structures are hosted in Upper Triassic to Lower Jurassic bimodal volcanic and epiclastic rocks. These rocks underwent very low-grade metamorphism due to crustal thinning and elevated thermal gradients associated with the evolution of the rift Neuquén Basin, and are overprinted by hydrothermal alteration related to the epithermal veins. Short-wavelength infrared (SWIR) spectroscopy has been used to identify specific spectral reflectance alteration minerals features. This study integrates spectral, petrographic, and geochemical analyses of alteration minerals and whole rock, associated with La Primavera epithermal vein system, to evaluate the controls on the hydrothermal alteration and the potential of spectral techniques in mineral exploration. The results demonstrate that host rock composition plays a primary role in the development of alteration assemblages. Variations in the spectral absorption features of phyllosilicates, particularly illite and chlorite, reflect compositional differences that can be linked to relative changes in temperature and fluid acidity. The W|2200| absorption feature of illite varies systematically along sampled transects, indicating both lithological control and proximity to mineralized structures. Also, the Illite Spectral Maturity (ISM) values are higher near the veins and decrease with distance, providing a reliable vector toward mineralization. Similarly, chlorite compositional variation serves as an effective indicator of proximity to mineralized structures. Intermediate Fe-Mg chlorites occur near the veins, while Mg-rich varieties dominate distal zones. In addition, this combination of techniques has been a useful tool for distinguishing mineral phases specific to regional metamorphism from those related to hydrothermalism. In this way, spectral analysis has been proven to be a powerful tool in the initial steps of low to intermediate epithermal deposits exploration.