Contributions to the regional geology of the Broken Hill area from geophysical data

The Lower Proterozoic Willyama metamorphic complex and overlying Adelaidean sediments in the Caloola, Kantappa, and Torrowangee Synclinorial Zones form an area of Precambrian outcrop with notable topographic relief. Surrounding areas are the Mundi Mundi Plains to the west, the Menindee Trough to the southeast, and the Bancannia Trough to the east. Other topographic highs are formed by Precambrian and Palaeozoic rocks in the Bynguano Range to the east of the Bancannia Trough, and by Ordovician sediments in the Scopes Range which lies between the Bancannia Trough and the Menindee Trough. The WiIIyama Complex is fringed to the southeast and east by an area within which a considerable proportion of the Earths crust has anomalously high magnetic susceptibility. However, the remainder of the WiIIyama Complex is distinguished from surrounding areas by having a considerable proportion of its crustal section composed of material with anomamously low magnetic susceptibility. The Willyama Complex and overlying Adelaidean sediments form a block which is bounded by major structures, including north-trending structures to the east and to the northwest. The Redan Fault forms the major boundary of Precambrian outcrop to the southeast of Broken HiII, but shallow basement persists about another 30 km to the southeast, to the edge of the Menindee Trough. Northeast to north-northeast trends within the Willyama Complex continue beneath the southern part of the Torrowangee sediments and terminate against the north-northwest trending Euriowie Inlier - an interpreted horst structure. A north-northwest structural trend is inferred in the basement to the Caloola Synclinorial Zone. North-trending features are apparent in the Kantappa Synclinorial Zone and in the basement to the east and west of the Precambrian block. There are four persistent magnetic marker horizons within the Adelaidean sediments of the Caloola Synclinorial Zone. Magnetic horizons within other areas of Adelaidean sediments are less well developed. Pre-Adelaidean basement beneath the Caloola Synclinorial Zone is inferred to be at a depth of about 3500 m; beneath the Kantappa Synclinorial Zone it is at a depth of a few hundred metres. The magnetic basement beneath the Mundi Mundi Plain is divided by an east-west structure at 31Â°39S, to the south of which the basement is at a depth of about 150 m, and to the north of which the basement depth increases from 500 m to 7000 m in the north. The area of deep basement is inferred to be overlain by a thick sequence of Adelaidean sediments. An inferred intrusive body about 40 km east of Broken Hill may have been localised by the intersection of a number of major structures in this area. Magnetic basement in this area occurs at depths in the order of 150 m. This and other areas of shallow basement beneath the Mundi Mundi plain and to the southeast of the Redan Fault may have considerable base-metal exploration potential. The Bancannia Trough is usually fault-bounded on both sides. On the western side a south-southeast extension of the Nundooka Creek Fault forms the boundary of the main trough while further to the southwest a north-south structure forms the boundary of a shallower extension of the Trough. Palaeozoic sediments within the Trough reach a maximum depth of about 8000 m, and are underlain by extensive areas of andesite which are inferred to have originated from three igneous centres beneath the Trough. The Menindee Trough has a magnetic basement at a maximum depth of about 7000 m. Airborne spectrometer data delineate the major surface geological and drainage features. The outcrop area of WiIIyama Complex is well defined by above average radiation levels. The largest anomalies have been recorded within the Euriowie Inlier and over areas of reported uranium occurrences in the west of the Precambrian block.

Tags: Earth Sciences, GA Publication, Journal, NSW, Published_External
Organization: Geoscience Australia Data