Mapping critical mineral resources using airborne geophysics, 3D joint inversion and geology differentiation: A case study of a buried niobium deposit in the Elk Creek carbonatite, Nebraska, USA

Abstract

ABSTRACTCritical minerals are an integral part of the energy transition because of their important and, sometimes irreplaceable, uses in solar panels, wind turbines, electrical vehicles, etc. Mapping critical mineral resources is, therefore, essential to achieving the net‐zero emission goal by 2050. We present a case study on using airborne geophysical data, borehole and physical property measurements to characterize the Elk Creek Carbonatite complex located in the southeast of Nebraska, USA. It hosts the largest known niobium deposit in the United States and contains a high level of rare earth element mineralization. Our goal is to develop a better understanding of the three‐dimensional structures and composition of the Elk Creek Carbonatite complex as well as its critical mineral resource potential. We performed three‐dimensional joint inversion of the airborne gravity gradiometry and magnetic data to produce structurally similar density and susceptibility models. We carried out geology differentiation, a process of classifying recovered physical property values into distinct units, and obtained a three‐dimensional quasi‐geology model for the Elk Creek Carbonatite complex. We identified 12 geologic units, each of which is characterized by a distinct range of physical property values. Our quasi‐geology model, especially Units 9 and 11, shows a remarkable consistency with the borehole assay measurements. Unit 9 is spatially coincident with the known niobium ore zone. Unit 11 represents a significant volume of highly dense and magnetic materials below the deepest boreholes. These materials are likely associated with unexplored niobium mineralization. Our study demonstrates the added value of three‐dimensional geophysical joint inversions and geology differentiation in the context of critical mineral exploration under a thick sedimentary overburden.