Quantitative geophysical interpretation of gravity gradient and magnetic data over a buried carbonatite: The Elk Creek deposit, Nebraska, USA

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

“…Its susceptibilities span a wide range, as shown in Figure 2b. The apatite dolomite carbonatite, dolomite carbonatite breccia, barite dolomite carbonatite, dolomite carbonatite, apatite dolomite carbonatite breccia and syenite share similar physical property values, as shown in Figure 2, and were grouped together as undifferentiated carbonatites and syenite in previous work (e.g., Drenth, 2014;Kass et al, 2015). The mafic rocks are, on average, less dense and more magnetic than the undifferentiated carbonatite and syenite.…”

“…To minimize the effect of these biased mean values, we choose to focus on the median values when it comes to understanding the physical property values of different lithologies. According to the previous studies by Drenth (2014) and Kass et al (2015), the lithologies at ECCC can be roughly classified into four categories: (1) the gneissic country rock, (2) undifferentiated carbonatite and syenite, (3) mafic rock and (4) magnetite dolomite carbonatite. The country rock over the ECCC is composed of a heterogeneous mix of Precambrian igneous and metamorphic rocks, including gneiss, granites, diorites, gabbros and schists (Xu, 1996).…”

“…Kass et al. (2015) performed two separate three‐dimensional (3D) gravity gradient and magnetic amplitude inversions to construct 3D density contrast and susceptibility models. Based on the clustering features in a crossplot, they classified the inverted physical property values into four units corresponding to the four lithological assemblages reported in Drenth (2014), that is, the gneissic country rock, undifferentiated carbonatite and syenite, mafic rocks and magnetite dolomite carbonatite.…”

“…Despite the encouraging results, no 3D classification model was developed or shown in Kass et al. (2015). The discussion of each unit and comparisons with assay measurements were also lacking.…”

“…Based on the clustering features in a crossplot, they classified the inverted physical property values into four units corresponding to the four lithological assemblages reported in Drenth (2014), that is, the gneissic country rock, undifferentiated carbonatite and syenite, mafic rocks and magnetite dolomite carbonatite. Despite the encouraging results, no 3D classification model was developed or shown in Kass et al (2015). The discussion of each unit and comparisons with assay measurements were also lacking.…”