Shear zones, gold mineralization and structural history in the leonora district, eastern goldfields province, Western Australia

The regional pattern of deformation in the Leonora district is the result of three main episodes of deformation, each of which produced distinctive structures and regional features. The earliest episode was nappe-like, and produced gently dipping mylonite, orthogneiss and schist in discrete zones of deformation. These zones are easterly striking in areas not affected by later deformation events, but movement directions are not consistent throughout the region, being south-directed in the west and north-directed in the east. The second episode resulted in a widespread north to northwest-striking crenulation of the early schistosity and long wavelength, open, upright regional folds. These folds affected the early orthogneiss. Regional northwest-striking strike-slip faults, dominated by the sinistral Mt George shear zone, with an attendant cleavage and sub-horizontal stretching lineation, are the product of a third episode of deformation. In the east a southeasterly striking, widely spaced crenulation is evidence of a fourth episode, whereas in the west, east-northeast-striking faults cross-cut all earlier structures. Mineral deposits are invariably associated with deformational structures in the Leonora district. The larger deposits (e.g. Sons of Gwalia) lie within early shear zones up to 0.5 km wide, which can be traced through a number of prospects to the north. Later large shear zones are largely unmineralized, although small fourth generation faults are the site of small prospects. A model of main mineralization during early deformation with remobilization of ore into later structures is consistent with the regional structural evolution of the district.