Characterizing a buried niobium deposit using airborne geophysics, joint inversion, and geology differentiation
Abstract
Demand for critical minerals is projected to increase dramatically in the next few decades due to their indispensable usage in rapidly growing clean energy technologies. Ensuring a steady supply of critical minerals is, therefore, essential to meet the global target of net zero emissions. Airborne geophysics holds great promise for identifying prospective areas of critical mineral resources because of its ability to survey large areas within days. We focused on the Elk Creek Carbonatite Complex (ECCC) located in southeastern Nebraska, USA which hosts the largest known niobium deposit in the United States. Exploratory drilling has helped classify the shallow lithological units and identified known niobium deposits. However, the deeper part of the ECCC remains largely unknown because the deepest boreholes extend only about 1000 m in depth. Our goal is to develop a better understanding of the composition of the ECCC and to determine if there are undiscovered critical mineral resources. Using airborne gravity gradient and magnetic data, we performed 3D joint inversion to construct structurally coupled density contrast and susceptibility models. We then carried out geology differentiation, an emerging method in geophysics which focuses on the identification of geologic units in the subsurface. It classifies the recovered physical property values into distinct units based on information from boreholes, physical property measurements, previous studies, and grouping patterns of the inverted values in a cross-plot. This results in a 3D quasi-geology model showing the spatial distribution of the various geologic units. We identified 11 units, one of which corresponds to the known niobium deposit. The most significant discovery from our work is a large volume of dense and strongly magnetized materials below the deepest boreholes. This volume is directly underneath the known niobium deposit, and is likely to be associated with undiscovered niobium mineralization. Our study shows that airborne geophysics, when combined with joint inversion and geology differentiation, is an effective way of exploring critical mineral resources at deeper depths, even in regions of sparse geological information. We believe that the methods developed in our work can be readily extended to other areas.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMNS24A..05L