Structural Analysis and Exhalite Studies in the Peelwood - Cordillera Area, NSW

Abstract

Field mapping in the Peelwood-Cordillera area reveals the complex spatial relationships exhibited by widely variable lithofacies, which reflect cyclical periods of deposition associated with an unstable, submarine volcanic environment. Rapid lateral and vertical facies changes, and the lack of useful marker horizons preclude the definition of major structural features, although it is probable that the area responded to deformation in a similar fashion to adjoining areas. Widely developed kink folding is interpreted as the result of a later phase of deformation, and is developed on all scal.es. The waning stages of active volcanic cycles are marked locally by the formation of sub-economic deposits of stratabound, pyritic base metal mineralization. Massive sulphides are general.ly enclosed by, and partial.ly laterally equivalent to, high silica cherty rocks believed also to be the result of volcanic exhalations. Geochemical analyses of the cherts show low and irregular abundances of all elements except silica, and the correlations they displayed indicate that most elements were probably supplied to these rocks from a detrital fraction. Petrographic evidence suggests at least partial derivation by silicification of pre-existing volcanic or volcaniclastic rocks, and the occurrence of radiolarian remains further supports a composite origin for these rocks, involving volcanic and elastic components in addition to chemical preci pitation.