SATELLITE-ALTITUDE GEOPOTENTIAL FIELDS AND CRUSTAL MINERALIZATION

Magnetic measurements made by satellites in low Earth orbit (POGO, Magsat, Ørsted and CHAMP) record the long-wavelength (> 400 km) field anomalies that are predicted to be the result of contrasts in magnetization occurring in the deeper regions of the crust and uppermost mantle. In Europe satellite data have revealed significant signals over the regions of Kiruna, Sweden (>9 nT) and Kursk, Russia (>15 nT). These areas are also the location of the largest known iron-ore deposits in Europe. In addition, high amplitude anomalies in Africa are also associated with significant iron deposits. Not only is there a direct relationship between magnetic anomalies and metalliferous areas, but also linear patterns of magnetic anomalies can delineate deep-seated crustal discontinuities that are indications of significant fracture zones that often localize the emplacement of mineral deposits. Examples of these linear features are, indicated by long-wavelength anomalies, occur in western United States, Rondonia in western Brazil and elsewhere. Examples of these studies were presented in a special volume of Global Tectonics and Metallogeny (2003). In addition, gravity data, now available from the CHAMP satellite, give us the opportunity to correlate these magnetic anomalies (produced by contrasts in magnetization) with gravity anomalies (produced by density variations). Detailed correlations were made in two different regions of Europe, South and Central Finland (south of the Outokumpu mining district), and the Pannonian Basin (overlying the subducted Dinaridic ocean crust) (Taylor et al., 2003). In both regions there was a positive correlation between the magnetic and gravity anomaly fields. While these satellite altitude geopotential anomalies provide us with a new and broad scale approach to studying the heterogeneity of the Earth’s crust, they are also a new data set, and detailed investigations are in the beginning stages.