Short notes: Production of pixel maps of airborne magnetic data for Australia, with examples for the Roper River 1:1 000 000 sheet

Abstract

The Bureau of Mineral Resources (BMR) has begun producing and releasing a series of standard 1 : 1 000 000 sheet pixel maps of gridded airborne magnetic data for various parts of Australia. The new series is based on a standard mesh size of 0.25 min. The first of these maps are being produced for those areas where digital data exists; other areas will follow as analogue data are converted to digital form. Maps produced on high resolution pixel plotters are superior to contour maps and are the only practical means of displaying gridded data over large areas. Over small areas, machine contouring may be viable because of the ease with which a hard copy with desired projection and scale can be produced. Grids of magnetic data are warped to accommodate projection, annotated, and displayed on a pixel plotting device, which can accommodate up to 4000 ´ 4000 pixels on a photographic negative in black and white or colour. The negative is then enlarged linearly by photographic means to produce a hard copy with the required scale. Examples are shown here of magnetic pixel maps of the Roper River 1 : 1 000 000 sheet. They include total intensity in black and white, colour, and two gradient presentations. These maps reveal new information in the form of magnetic dykes, volcanic extrusions, and deep-seated, possibly granitic, bodies.