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All rights reserved Dry processing of minerals is an attractive choice in a mining environment where process water is in short supply. Sensor-based sorting has the potential to perform dry separation of ore from gangue at an early stage of the processing, 1 also helping to reduce energy consumption due to downstream crushing. In order to develop a sensorbased sorting process, selection of a suitable sensor is of critical importance. In practice, a near infrared (NIR) sensor can detect characteristic absorbance features on the mineral surface due to the presence of hydroxyl-, carbonate-and water-bearing minerals, while certain minerals absorb NIR across ranges of wavelengths. A NIR spectrum is some combination of the true spectra of its constituents 2 which may reveal information about the functional groups present. Given small-scale heterogeneity, i.e. assorted minerals side-by-side inside an area of measurement, the total mineral composition may not be discernible from a spectrum. To understand the extent of this confounding on the application of NIR, it is instructive to compare NIR spectra of pure minerals associated with mining applications. Potential applications could entail the classification of economically important hydrothermallyformed minerals. These are formed near the Earth's surface by alteration of primary ores by low temperature oxidising meteoric waters. 3 Compared to primary ores, the grade of valuable heavy metals in hydrothermal deposits is relatively low. However, with increasing demand for commodities such as iron, copper etc., development of these deposits is becoming viable. 4 This paper analyses the NIR spectra of individual minerals present in a supergene copper deposit in Chile. This analysis provides a basis for developing a sorting process for copper-bearing secondary minerals. BackgroundIn the NIR wavelength range, from 780 nm to 2525 nm, electronic processes, such as crystal-field effects, charge transfer, Dry processing of minerals is increasingly attractive in a mining environment where water is a scarce commodity. Sensor-based sorting has the potential to perform dry separation of ore from gangue at an early stage of the processing, also helping to reduce energy consumption due to downstream crushing. In order to develop a sensor-based sorting process, selection of a suitable sensor is of critical importance. In practice, a near infrared sensor can measure characteristic features of carbonate, hydroxyl and water groups contained in minerals and rocks. This paper examines the process of establishing the suitability of a near infrared sensor for distinguishing hydrothermally-formed minerals. It is concluded that characteristic absorption features in near infrared spectra offer a more robust route to separating out minerals than the level of absorption.

Assessment of radiological risk was carried out on twenty soil samples collected from agricultural, mining and mine processing areas in Anka, Zamfara State, North Western Nigeria. The measurement of activity concentration of 226 Ra, 232 Th and 40 K was performed using the gamma-ray spectrometer equipped with a high purity germanium detector. The values of the activity concentration of 226 Ra ranged from 24.69±4.26 to 82.20±15.62 Bqkg -1 , with a mean of 47.06±14.01 Bqkg -1 ; 232 Th ranged from 22.52±3.44 to 159.47±16.81 Bqkg -1 , with a mean of 75.97±9.11; while 40 K ranged from 27.20±8.03 to 542.64±156.93 Bqkg -1 , with a mean of 216.02±62.37 Bqkg -1 . The concentration of the Radium equivalent in the study area ranged from 60.41 to 307.30 Bqkg -1 , with mean value of 172.33 Bqkg -1 . The absorbed dose rate in air was calculated and the values ranged between 26.80 and 135.02 nGyh -1 , with a mean of 76.64 nGyh -1 . The external hazard index was computed and the values ranged from 0.163 to 0.830, with a mean of 0.465. This value is within the safe limit of 1. The annual effective dose rate was calculated from the activity concentration with the minimum value of 32.87 µSvy -1 , while the maximum was 165.58 µSvy -1 , with a mean of 93.99 µSvy -1, which is higher than the world average of 80 µSvy -1 but less than the recommended annual effective dose safe limit of 1 mSvy -1 . Therefore, the soil does not constitute radiological threat to the local population in the environment.

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