One of the principles of prospecting is to confine detailed exploration to relatively small areas considered most favorable for the occurrence of ore. Ore is often found in and around the boundaries of igneous intrusives and a method is given for localizing ore-search around intrusives ranging in size from small stocks to batholiths. The method is based on the occurrence of broad areas of higher-than-normal radioactivity in the igneous rock in the vicinity of ore structures. Nine intrusives were examined and high radioactive anomalies occurred in the neighborhood of associated ore bodies, whereas no such concentration was found in two intrusives barren of ore.The distinctive association of radioactivity with ore is believed to be independent of whether the so-called igneous body was formed from a cooling magma or from heated and recrystallized sediments; or whether the ore solutions were genetically related to the present erosion surface or were derived from unknown sources at some greater depth.

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