Magnetic properties of drill core and surface samples from the Calico Hills area, Nye County, Nevada

The interpretation of the aeromagnetic survey of the Calico Hills area of the Nevada Test Site, Nye County, Nevada, required the determination of magnetic properties of rocks exposed in the region. Eighty-two samples representing a variety of units found at the surface show that most rocks in the Calico Hills, other than parts of the Eleana Formation, are relatively nonmagnetic. The magnetic vector of the Eleana Formation at the surface was found to point northward and downward. Remanence directions were scattered, but a remanence azimuth of 16? east of north was assigned on the basis of present-day declination. Measurements of 123 samples of the Eleana Formation from the exploratory drill hole UE25a-3 indicate that some facies are strongly magnetic. The average total magnetization of the argillite samples is 3.89 A/m (0.00389 emu). These samples have an average natural remanent inclination of 76?. Results of demagnetization demonstrated that this relatively high inclination is due, at least in part, to a soft vertical component of remanent magnetization. The magnitude of the component could not be determined. Further tests showed that the tendency to pick up a soft component of magnetism may be a function of rock type. Inhomogeneity of the Eleana argillite was probably the cause of some differences in remanence values between large and small samples from the same depth.