Bulk Density of Stratified Iron Ores and Its Relationship to Grade and Porosity

Bulk density and grade were determined on a variety of ore samples from the Mount Tom Price iron ore mine and the interrelationship between these properties and porosity deduced.Variable porosity is responsible for the wide scatter of data points and low accuracy of prediction in the grade of a single sample from grade/bulk density relationships.However, with a sufficient number of such data points, as from a nuclear geophysical borehole logging operation, the mean ore grade in an exploration-type drill hole (~63 per cent Fe) could be determined by regressionanal~sis with 95 per cent confidence intervals of approximately ± 1 per cent Fe. From the same logging operation, utilizing core data for calibration of the probe, the -mean fractional porosity for the drill hole (0·19 ± 0·016 at 95 per cent confidence interval) was deduced. This is less accurate than the corresponding result obtained on core material in the laboratory (0·20 ± 0·005).The range of porosity was from 0·08 for dense, high grade sectIOns of the ore, to 0·28 for friable ore of high grade or goethitic ore of lower grade. Shale band porosity ranged from 0·15 to anomalously high values of 0·48 believed to be caused by leaching of iron minerals from the shale. Porosity values for the iron ore component of the deposit are comparable to those found for the Cockatoo Island (W.A.) mine, and for sections of the Krivoy Rog (Ukraine) iron ore deposit of the Soviet Union.