Aeromagnetics?an effective geological mapping aid for the willyama complex?

Abstract

Geological and aeromagnetic trends in the Willyama Complex are generally parallel, but there is an almost complete lack of correlation in detail between magnetic rock units and mapped rock units. In particular, anomalies do not consistently correlate with amphibolites or with linear zones of retrograde metamorphism. Ground follow-up in four selected areas has shown that major anomalies in these areas delineate outcropping stratigraphic magnetite bearing horizons within pelitic and psammitic metasediments, gneisses and leucocratic rocks, except to the northeast of the Mount Vulcan antiform. Here, a roughly circular anomaly which is grossly discordant with outcrop geology delineates a magnetic body at a depth of about 250 m and with a diameter of about 4 km. The continuous stratigraphic magnetite bearing horizons generally include minor discontinuous lenses of chemically precipitated magnetite rich rocks such as quartz-magnetite, banded iron formation and sillimanite-magnetite. The magnetic horizons occur close to Broken Hill type lode horizon in two of the areas investigated, and close to stratiform copper mineralization in the other two areas. Because of their continuity they are of great assistance in delineating complex structures within these prospective stratigraphic intervals. It is concluded that detailed magnetic maps of the Willyama Complex contain a considerable amount of significant geological information, and if carefully integrated with other available geological data, are a cost-effective means of resolving structural and stratigraphic problems in many areas.