RI-04 Interpretation of Lake Washington Magnetic Anomaly, Meeker County, Minnesota

A magnetic anomaly centered at Lake Washington, in southeastern Meeker County, has been outlined by a ground magnetometer survey. The anomaly is arcuate in outline, about 8.5 miles long and a maximum of 5 miles wide, and has a maximum amplitude greater than 3,000 gammas. A gravity traverse was made across the anomaly to aid in interpretation. Combined magnetic and gravity data are interpreted to indicate that the source is a basin-shaped body having a substantially greater density than the adjacent rocks that lies at a shallow depth. The lithology of the source is not known because of a lack of subsurface data, but is inferred to be either Precambrian iron-formation or mafic igneous rock. The anomaly warrants further investigation