Estimation of heavy and opaque mineral contents of beach and offshore placers using rock magnetic techniques

Exploration for placer deposits involves heavy and opaque mineral data that are conventionally obtained using toxic and expensive chemicals and time-consuming and tedious microscopic counting of a large number of grains. In this investigation, we have used rock magnetic properties to obtain estimates of heavy and opaque mineral contents of placers from the SW coast of India. Magnetic susceptibility and other magnetic properties show strong correlations with heavy and opaque (r > 0.87 andr > 0.94; significant at the 1% level) mineral contents. As one or more types of magnetic minerals are invariably present in placers, magnetic properties may be used as a proxy for heavy and opaque mineral contents. This simple, rapid, inexpensive, and nondestructive method may be adopted by those involved in placer exploration to rapidly scan a large number of samples and delineate economically important pockets for more detailed investigations. This method saves considerable time and tedium. Using magnetic properties, rather than radioactivity, as a proxy for heavy and opaque mineral contents is more advantageous because one or more magnetic minerals are always present, but a radioactive mineral may not always be present in placers. An important limitation is that the ratio of magnetic to heavy/opaque mineral contents should not vary widely.