Exploration for phosphorite in Australia-A case history

The discoveries of phosphorite in the lower Middle Cambrian sediments of the Georgina Basin resulted from systematic Australia-wide exploration programs by several companies. The exploration involved the application of concepts relating basin stratigraphy, lithologie associations, tectonics and phosphate occurrences to paleogeo-graphy, in particular paleolatitude, and areas of supposed oceanic upwelling. Lithologie and gamma-ray logs, magnetic, gravity and seismic survey data were derived from work done by oil companies and the Bureau of Mineral Resources. In terms of technique, these data and their interpretations were integrated with the results of examination, chemical testing and selected analyses of cores and cuttings, together with university rock and palaeontological collections. This was followed by the field examination of favorable suites of sediments and/or established phosphogenic sections, the gamma-ray logging of abandoned water bores, and, finally, rotary drilling. The discoveries constitute reserves of several billion tons. The first discovery was at Duchess, and this resulted from the recognition of a phosphorite interval at depth in a stratigraphie oil well, followed by prospecting of the nearest outcrop of equivalent rock. The D Tree and Lily Creek deposits were found almost simultaneously, while the other deposits were found the following year. The shallow deposit of Wonarah, which occurs in the center of the Basin, was found by subsurface stratigraphie analysis of drillers' logs of old water bores together with the gamma-ray logging of uncapped holes : success came with the second exploratory hole.