An appraisal of limestone reserves at Elsey Prospect, NT.

Abstract

This is a comprehensive report documenting the reserves of limestone at a prospect known as Elsey Limestone. Both mottled grey-brown crystalline limestone outcrop and more friable porous chalky white limestone are present. Previous workers suggested the former are Tindall Limestone and the latter was Tertiary. The two have quite different chemical compositions that would influence their potential uses for manufacture of cement and/or quicklime. The deposits are held under EL 3333. In addition, several mineral claims have been applied for. Exploration and evaluation of the deposit was conducted by Eupene Enterprises. The area was gridded on 100 m centres. Following a single hole drilled by the current leaseholder Blake Investments, Eupene supervised an additional 23 short NQ core holes on the grid. Depths varied from 3 m to 9.45 m. The core was photographed and geologically logged. Assay of selective composite of diamond-saw cut core was undertaken by the Department of Mines and Energy. SG determinations and calculations were undertaken on 15 core specimens of both porous and nonporous types. Hard rock reserves were arbitrarily divided into first and second grade based on potential end use. First grade had over 95% CaCO3, less than 1% MgCO3 and less than 3% SiO2. Second grade was over 90% CaCO3, less than 1% MgCO3 and less than 5% SiO2. The reserve was estimated by blocking using drillhole centres and a cavity factor to offset the SG. Some 821,000 tonnes of first grade limestone grading 96.5% CaCO3, 0.5% MgCO3, 1.8% SiO2 and 0.2% Fe2O3 can be regarded as proven. Second grade proven reserves are 631,000 t averaging 93.7% CaCO3, 0.7% MgCO3, 3.6% SiO2 and 0.4% Fe2O3. When this is combined with the first grade, the total hard rock reserve is 1,451,000 t grading 95.3% CaCO3, 0.6% MgCO3, 2.6% SiO2 and 0.3% Fe2O3. Eupene was confident that these reserves could be increased by further drilling. Mining by pit would be to a maximum of 10 m. The second type of limestone present, the chalky limestone is associated with red soils. It has been tested by previously by auger drilling. Its quality is sufficient as direct shipping limestone. An additional 24 auger holes were drilled on 100 m centres. Drilling was in two campaigns and may have had slightly different recoveries and had different treatment prior to assay. Nearly 260,000 cubic metres or about 492,000 t of chalky limestone grading greater than 90% CaCO3 and averaging 93% CaCO3, 4.4% SiO2 is present. Eupene was of the opinion that, even at this grade, this could be doubled with further work. Lowering the cutoff grade to say 85% would also increase reserves within the area of existing drilling. It was suggested that blending the two limestone types should be further investigated. The report contains photographs and tabulated assay data.