Interpretation of new airborne magnetic and radiometric data covering much of the eastern Inverell and western Grafton 1:250 000 map sheet areas (the Inverell survey area) has demonstrated the value of high-resolution airborne geophysics. These new data were collected as part of the Exploration NSW initiative over a geologically diverse part of the New England region.

Preliminary interpretation of the data has resulted in a greatly enhanced understanding of the structure; lithological distribution; origin of felsic volcanic rocks; and controls on mineralisation of the region.

The Inverell survey area in the New England Orogen hosts known mineralisation — including granite-related cassiterite, tungsten, molybdenum, gold, silexite (quartz–topaz greisen) and silver-rich lead, zinc and copper; seafl oor manganese oxide–rhodonite and copper–lead–zinc; and alluvial deposits of tin, sapphires and diamonds. Interpretation of the geophysical data has improved understanding of relationships between structurally controlled granite-related mineralisation and various fault and fracture sets, and between the occurrence of sapphires and Tertiary volcanic rocks.

Airborne magnetic data have indicated the presence of large, circular magnetic bodies with characteristics resembling calderas. These bodies represent the source of much of the felsic Wandsworth Volcanic Group in the area and may have potential for epithermal mineralisation. The aeromagnetic data have also proved useful for identifying concealed granite plutons, dykes and plugs and major crustal fractures.

Radiometric data provide a valuable tool distinguishing major Tertiary eruptive suites in the region, including areally extensive younger volcanic rocks in the west, and an older corundum-associated suite in the east. The radiometric data are also useful for interpreting the surface geology, for identifying previously unrecognised geological units and relationships, and for distinguishing some pluton phases.

Contents of Issue No. 121 of Quarterly Notes include:

• Introduction
• Regional geology
• Radiometric and magnetic interpretation
• Enhanced prospectivity