Genesis of High-Grade Hematite Orebodies of the Hamersley Province, Western Australia--a Reply

Sir: We are very thankful for the constructive comments provided by Kneeshaw and Kepert. Unfortunately, the competitive ownership structure of the iron ore mining industry in the Hamersley province limits our personal knowledge of the Mount Whaleback deposit to occasional mine visits and to the available literature, published and unpublished. We do, however, have access to the data on the smaller Giles Mini and Lido deposits, 50 and 10 km west of Mount Whaleback, respectively, and to extensive exploration mapping in the Ophthalmia Ranges to the north. Direct proof for rotation of the orebody, as it is preserved at Paraburdoo in the approximately 50° dip of the overlying Proterozoic hematite conglomerates of the Mount McGrath Formation, is not preserved at Mount Whaleback. However, we believe that there is sufficient information available in the literature to think that a rotational model for a large part of the deposit is perfectly plausible. First, and above all, as stated in Taylor et al. (2001), F2 folds are more upright with axial planes dipping about 50° S in the southern and western part of the deposit, away from the Whaleback fault (e.g., as shown on Section No 315120E (fig. 4) in Powell et al., 1999). Interestingly, the ore-controlling faults are also more upright in this part of the deposit, which suggests an intimate link between the dip of these fault planes and dip of the axial planes of F2 folds. Secondly, …