Abstract

The importance of NIR spectroscopy has been successfully demonstrated in the present study of smithsonite minerals. The fundamental observations in the NIR spectra, in addition to the anions of OH⁻ and CO₃^2–, are Fe and Cu in terms of cation content. These ions exhibit broad absorption bands ranging from 13,000 cm⁻¹ to 7000 cm⁻¹ (770 nm to 1430 nm). One broad diagnostic absorption feature centred at 9000 cm⁻¹ (1110 nm) is the result of ferrous ion spin allowed transition, (⁵T_2g → ⁵E_g). The splitting of this band (> 1200 cm⁻¹) is a common feature in all the spectra of the studied samples. The light green coloured sample from Namibia show two Cu(II) bands in NIR at 8050 cm⁻¹ and 10,310 cm⁻¹ (1240 nm and 970 nm) assigned to ²B_1g → ²A_1g and ²B_1g → ²B_2g transitions. The effects of structural cations substitution (Ca²⁺, Fe²⁺, Cu²⁺, Cd²⁺ and Zn²⁺) on band shifts in the electronic spectral region of 11,000 cm⁻¹ to 7500 cm⁻¹ (910 nm to 1330 nm) and vibrational modes of OH⁻ and CO₃^2– anions in the 7300 cm⁻¹ to 4000 cm⁻¹ (1370 nm to 2500 nm) region were used to distinguish between the smithsonites.

© 2008 IM Publications LLP

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