Pit-wall face mapping of carbonate mixtures using LWIR remote sensing

Carbonates are the focus of this study because of their common use in the local mineral industry. The Swiss cement industry consumes approximately 4 Mtpa of raw limestone material to produce cement. The chemical (mineralogical) requirements of carbonates in a limestone quarry are specifically determined by the content of MgO weight percent (≤ 2.8 wt% MgO) used as input for the production of cement. Primary source of that MgO impurity is dolomite, which is occurring in the stratigraphical units of the Portlandian (Twannbach Formation late Jurassic 140ma) and in the Purbeckian (Goldberg Formation, early Cretaceous >145ma). Carbonate lithology mapping has already been undertaken using hyperspectral imaging within the NIR-SWIR wavelength region (Kurz et al 2012), as based on laboratory work from Hunt et al (1971), Gaffey (1986,1987) and Zaini et al (1995). This current study aims to map the calcite dolomite mixtures using HyperCam LWIR hyperspectral imagery on a pit wall. In a first pass the identification of these different mineral species is targeted and will be tested against mineralogy determined by x-ray diffraction (XRD) from field samples. The other goal is to quantitatively determine the content of MgO interpreted by in the imagery and tested using x-ray fluorescence (XRF) analysis of pit wall samples. A feasibility study measured artificial dolomite and calcite mixtures with a Bruker FTIR Vertex 70-VTX and showed the potential of the LWIR to quantify CaO or MgO weight percentages compared to XRF. Such analysis is possible due to the fundamental internal vibrational modes within LWIR wavelengths related to bending and stretching movements of C-O bonds. In this study the position of the symmetric bend.