Domainal fabrics of hematite in schistose, shear zone-hosted high-grade Fe ores: The product of the interplay between deformation and mineralization

摘要: Abstract Schistose high-grade hematite orebodies (>64 wt % Fe) in the Iron Quadrangle, Minas Gerais, were formed shear zones by hydrothermal alteration of Paleoproterozoic Caue BIF during Transamazonian orogenesis. The ore is comprised platy (specularite) grains that define foliation and overprint a relict banded martite-hematite fabric resembling, at first sight, mylonite. EBSD analyses m-scale schistose orebody from Pau Branco mine show specularite grew as elongated plates with (00.1) plane parallel to foliation. population measured grain aspect ratio (GAR) homogenous different scales, longest axes crystals align stretching lineation (L//X) building continuous domains, or anastomose around stretched iron oxide aggregates rootless fold hinges. pole figure shows usually maximum centered on Z often girdle perpendicular L. The {10.4} has configuration symmetric cleft corresponding {11.0} {10.0} figures present well developed girdles an X. Microstructures associated crystal-plastic behavior dynamic recrystallization are missing probably results precipitation strain-controlled oriented anisotropic syntaxial growth favorably intervention fluids Fe enrichment. zone provided pathways for percolation mineralizing under temperatures varied 140 350 °C higher, ductile ductile–brittle conditions. orthorhombic CPO (crystallographic preferred orientation) nevertheless contrast asymmetry simple observed torsion experiments Siemes et al., 2010 , 2011 due volume loss possibly flattening component deformation zone.