Fracture growth and damage zone evolution in fault-vein systems determined through scaling relations in alteration halo-bearing hydrothermal veins

Abstract

Understanding how fluids flow to form halo-bearing veins is essential to assess the fundamental processes involved in fracture propagation and the formation of hydrothermal ore deposits. Haloes may mimic damage zones during fracture propagation, contributing to the identification of scaling relations between halo width and fracture displacement. In this work, we examine geometry, kinematics and mineral composition of well-exposed halo-bearing fault-vein network field samples. We studied a total of 18 veins from Iron-Oxide Copper Gold (IOCG) deposits in the Chilean Atacama Desert and from the Chinese Cathaysia tectonic block. Vein length and width and halo width were measured directly at the outcrop and later under optical microscope. We established a scaling relation, over five orders of magnitude, between halo width (HW) and vein width (VW) of the form ${\log }_{10}HW=1.07*{\log }_{10}VW+1.04$ which suggests that the majority of analyzed haloes were formed as a result of crack tip process zone damage. Such ratios and scaling relationships, apart from elucidating the physical mechanisms driving halo/damage zone formation, have potential implications for a more reliable estimation of the nature and size of ore grade variations away from high-grade mineralized veins to the relatively lower-grade surrounding wall rock volumes.