Abstract
<jats:p>Purpose. The study aims to establish the fundamental regularities of microcrack evolution in banded iron formations (BIF) of the PR1 sx2 f horizon at the Novokryvorizke deposit during successive stages of dry crushing and wet ball milling. The research provides a quantitative assessment of defect structure transformation throughout a complete technological disintegration cycle, focusing on the multiscale nature of crack development in heterogeneous magnetite–quartz systems under conditions consistent with industrial processing. Methodology. The investigation was conducted using quantitative mineralogical and petrographic analysis of thin and polished sections prepared from the initial ore samples and from products of three successive crushing stages and three grinding stages. Measurements were performed using a Polam R-312 polarizing microscope at fixed magnifications to ensure statistical reliability. For each processing stage, the mean, median, and modal crack lengths were determined. The intensity of defect formation was evaluated through the linear crack density coefficient and the numerical crack density coefficient. Statistical evaluation focused on relative percentage changes compared to the natural state, enabling the identification of nonlinear trends in the defect network evolution. Results. The results demonstrate that during disintegration, the mean microcrack length decreases by 93–96 % relative to initial values, while the numerical crack density coefficient increases by up to +3854 %, indicating a dramatic transition of the rock into a highly defective state. Crushing stages act as an initiation phase, triggering a large-scale inversion of the defect field characterized by simultaneous growth in total crack length and crack number. In contrast, wet ball milling shifts the system into a «supercritical defectivity» regime dominated by massive generation of short-scale microcracks. The crack network evolution exhibits a cascade mechanism and hierarchical self-organization, where longer ancestral cracks are realized as macro-fractures, while a new population of ultra-short defects forms within the resulting fragments. Scientific novelty. For the first time, quantitative regularities of multiscale microcrack transformation in iron quartzites of the specified stratigraphic horizon have been established for a full industrial disintegration cycle. The phenomenon of «defect field inversion» in a heterogeneous magnetite–quartz medium has been substantiated, being driven by the contrast in elastic properties between quartz and magnetite and by stress concentration at phase boundaries. Specific defectogenesis regimes—initiation and supercritical defectivity—have been identified. Practical significance. The findings allow considering microcrack density as a controllable structural parameter for optimizing comminution processes at mining and processing plants. The revealed patterns serve as a scientific basis for developing energy-efficient crushing and grinding regimes aimed at controlled defect formation, enhanced mineral liberation, and improved selectivity of iron quartzite beneficiation.</jats:p>