The structural environment of the Bendigo gold field [Victoria

Abstract

The Bendigo, Vic., goldfield has produced over 16,000,000 ounces of gold, chiefly between 1851 and 1915. It is one of a number of gold-mining districts in southeastern Australia in a region underlain by a thick series of Ordovician slates and sandstones that is closely folded and intruded by Devonian (?) granitic rocks. At Bendigo gold-bearing quartz reefs occur close to the axes of several anticlines, especially on domes.The folds, faults, and quartz reefs are discussed and the conclusion reached that all three were developed during a long period of compressive stresses that affected Bendigo and a large surrounding region. The slates and sandstones yielded at first by folding but later by reverse faulting as well, especially in the axial portions of the folds. The connecting system of faults along each anticline provided an independent channelway and locus of deposition for ore solutions. Evidence is presented that compression and faulting continued during deposition of the reefs. It is believed that the reefs grew mainly by accretion. Tensional rifts roughly parallel to the axial planes of the anticlines and later than the quartz deposits are occupied by lamprophyre dikes that have been considered Tertiary but may belong to the Devonian (?) period of folding, intrusion, and mineralization.