Airborne gravity gradient expression of a buried niobium and rare earth element deposit: Elk Creek carbonatite, Nebraska

Abstract

The Elk Creek carbonatite, a buried intrusion in southeast Nebraska, hosts the largest known niobium deposit in the U.S. and a rare earth element deposit. Airborne gravity gradient (AGG) data are interpreted to study the signature of the complex, using such tools as terrain corrections, matched filtering, lineament mapping, and forward modeling. The carbonatite produces a vertical gravity gradient high, explained by high densities compared to country rocks. An unusually dense carbonatite unit, magnetite beforsite, hosts niobium ore and sources a smaller central gravity gradient high. AGG data indicate the presence of dense rocks below existing boreholes, thought to be a large volume of magnetite beforsite.