This Cambrian marble deposit, which has been quarried by BHP since August 1942 to supply metallurgical fluxes to its Whyalla Steelworks, has recently been surveyed, mapped at 1:1200 scale and sampled through its entire extent to determine stone grades and reserves, to identify areas of interest for future mine planning,and to place an estimate on the life of the current quarry. In the currently active Quarry Area, indicated reserves were calculated for open-hearth grade stone, for blast furnace grade stone and for marginal grade stone. Potential stone reserves were also calculated for the newly mapped Western Area (~50-54 million tons). These March 1956 reserves estimates were based on geological information available from sampling of surface outcrops and of 37 previous, old or recently completed diamond drillholes. During the period October 1956-October 1957 BHP completed its further programme of evaluation drilling (11 vertical diamond holes) to place qualitative limits on the Western Area limestone occurrence. High grade stone was delineated which is of significantly better quality than that being quarried presently, with best grades of 2.65% SiO2 and 0.8% MgO being obtained. The indicated reserves are now 7.7 million tons, within larger reserves of slightly lower grade, which figures could increase with additional diamond drilling. However, at this stage there is no indication from the deposit of the presence of limestone assaying less than 1% SiO2 or 0.75% MgO, and therefore it is suggested that the search for limestone of this grade should be extended outside of the Rapid Bay area.