Abstract

Gold mineralization along the Deborah anticline, Bendigo, Australia, occurs in quartz veins that are categorized into two main groups: those associated with folds and those associated with faults. The relative chronology of the structural development and quartz vein emplacement is characterized by the initial development of the fold and the subsequent formation of bedding- and cleavage-parallel veins. Saddle reefs may have developed at this stage; reverse faults and their associated veins formed after folds had locked up. Major gold-hosting structures include saddle reefs, reverse faults, and composite fold-fault structures where reverse faults have disrupted saddle reefs. Some reverse faults are interpreted to have propagated along preexisting structures, such as bedding-parallel veins. Although gold is hosted in fold-related structures, the majority is found in veins associated with later faults. Folds and fold-related veins strongly controlled the location of these later formed reverse faults and their associated veins. A fault-based fracture system was superimposed on preexisting dilational sites, such as bedding-parallel veins and saddle reefs, and it is possible that this allowed for the introduction of a larger volume of fluids during faulting than was possible during folding.

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