The gravity method has played an increasingly important role in the search for new reserves of Fe ores since the development of highly portable gravimeters capable of a high degree of precision. This method has been used in the search for and study of direct shipping ores, but it has proven to be especially useful in the study of large tonnage, wide, near surface "taconite type" ore bodies that have been the primary concern of the Fe ore industry during the past decade. The gravity method was first applied to Fe ore exploration as a tool for detecting nonmagnetic ores, but advantages of this method over other exploration methods have also made it useful under certain geological conditions in the study of magnetic ores and regional structures favorable for the occurrence of Fe ore. However, the gravity method is restricted by several limitations that must be realized and understood if the application of the method is to be successful. In addition, the full utilization of the method is dependent on a complete understanding of the density relationships of ores and their contrast with the country rocks. This is made particularly difficult by the wide range of densities of Fe ores that can lead to the association of both positive and negative gravity anomalies with Fe ore bodies. The end result is that the amount and quality of information interpreted from the results of gravity surveying is a direct function of the auxiliary geological information available either through geological or other geophysical studies.

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