The mid- and long-wave infrared hyperspectral characteristics of the carbonate minerals of the Hirvilavanmaa orogenic gold deposit, Central Lapland Greenstone Belt, Finland

Orogenic gold deposits form an economically important deposit type that are characterized by quartz-carbonate veins in the proximal parts of the deposits. Although these veins are visible to the human eye, detecting chemical and mineralogical differences in the carbonate minerals traditionally requires time-consuming laboratory work. Information about the mineralogical and chemical differences in the carbonate minerals can be particularly useful because some orogenic gold deposits have ferroan alteration halos larger than the deposit itself, and such information can be used for mineral exploration. Chemical variations within the carbonate minerals are well known to be detectable in the visible-near infrared and short-wave infrared wavelength regions (VNIR-SWIR; 400–2500 nm). However, there are not many studies that have assessed such variations in the mid-wave infrared (MWIR) and long-wave infrared (LWIR) wavelength regions between 2500 nm and 12,000 nm. To overcome this knowledge gap, we studied five spectral bands associated with carbonate minerals in the MWIR and LWIR wavelength regions to establish the ability to use them for mineral exploration. To this end, we used hyperspectral drill core data from the Hirvilavanmaa orogenic gold deposit in northern Finland. The results, validated using Mineral Liberation Analyser (MLA) and electron probe microanalysis (EPMA) data, suggest that mineralogical changes, associated with ore-forming processes, can be detected in all studied bands, providing a mineral exploration tool to complement the traditionally used hyperspectral sensing and laboratory analytical methods.