Pioneering data on detection, identification and quantification of key carbonate minerals using spectral tomography

Abstract

In this study, we present, for the first time, the spectral computed tomography (sp-CT) signatures of key carbonate rock-forming minerals namely, calcite, magnesian calcite, dolomite, and magnesite. Although the raw spectra of these phases may not be readily distinguishable, we demonstrate that they appear in clusters on a multi-energy histogram derived from laboratory sp-CT. These clusters show a strong correlation with the MgCO₃ mol.% of the carbonate phases. In addition to discriminating among these carbonate phases, we demonstrate the capability of time-resolved sp-CT to monitor mineral replacement reactions in carbonates. As an example, we analyze a series of time-lapse sp-CT images of a carbonate sample undergoing hydrothermal dolomitization in the laboratory. The results reveal a progressive transformation of pure calcite into an Mg-rich carbonate, with the sp-CT data indicating a final composition of approximately 32 mol.% MgCO₃. This estimate, while lower than the 46–50 mol.% MgCO₃ determined through complementary chemical analysis, provides a valuable first-order approximation. This contribution introduces a novel methodology for visualizing, monitoring, and quantifying such chemical reactions in multi-phase carbonate systems, in 2D, 3D and even 4D, offering advantages over destructive techniques such as 3D FIB-tomography. Our findings pave the way to further exploration of carbonate diagenesis and open up new perspectives for the application of spectral tomography in Earth sciences.