Preliminary evaluation of an X-ray diffraction-based hydrothermal alteration index for ammonium nitrate/fuel oil-equivalent powder factor calibration in open-pit porphyry copper blasting records

This article proposes and preliminarily evaluates an Experimental Hydrothermal Alteration Index (IAH_E) to support ammonium nitrate/fuel oil-equivalent powder factor estimation in open-pit porphyry copper blasting records. The index is the ratio of X-ray diffraction-derived Brittleness and Elasticity mineralogical components and is interpreted as an indirect alteration indicator rather than a direct geomechanical measurement. The primary quadratic calibration used all 21 records and yielded R ²  = 0.416, but leave-one-out cross-validation showed poor predictive stability ( Q ²  = −5.77). A secondary 16-record subset, obtained after residual-informed separation, yielded R ²  = 0.727 in-sample but Q ²  = −21.49 and is therefore reported only as a data-dependent exploratory analysis, not as independent validation. Monte Carlo propagation showed high IAH_E uncertainty when either component approached trace abundance, while the quartz sensitivity analysis did not establish predictive superiority for either formulation. Exploratory factor analysis provided partial support for the Brittleness-Elasticity structure. IAH_E may complement powder-factor analysis, but larger sample-matched datasets, direct geomechanical anchors, and external domain-specific validation are required.