Problems of analytical determination of precious metals in black shale rocks of the South of Russia

Abstract

Abstract: Relevance. In recent years, many publications have drawn attention to the prospects for the detection of noble-metal mineralization in the black shale strata of the North Caucasus. The results of single determinations of Au, Pt and Pd performed by atomic absorption spectroscopy (AAS) or mass spectrometry in inductively coupled plasma (MS ICP) are presented as justification. At the same time, the possibilities of the methods used and the results obtained were not analyzed by the authors. This article attempts to fill this gap. Aim. To evaluate the capabilities of analytical methods of AAC and MS ICP for determining the contents of Au, Pt and Pd in black shale strata. Methods. The results of determination of Au, Pt and Pd contents in the black shale strata of the North Caucasus, given in the published works, are used. Their analysis is carried out in terms of the adequacy of the applied methods to the tasks and conclusions. The main emphasis is placed on assessing the reliability of various modifications of the AAC and MS ISP to correctly determine the contents of Au, Pt and Pd. Results. Since the AAC and MS ICP methods cannot provide detection of natural Au, Pt and Pd contents directly from the geological sample material, there is a need for preliminary concentration of these elements. On the other hand, the complexity of the composition of geological samples is the cause of numerous influences from matrix components on the analytical signals of the elements being determined, which also requires the use of various techniques to get rid of such influence. Each of the applied additional analytical procedures can create its own errors and lead to a relative change in the contents of Au, Pt and Pd. It is shown that it is possible to obtain an incorrect result at the instrumental stage of analysis by AAC and MS ICP methods. The AAC result may be influenced by the superposition of spectral lines of matrix elements on the analytical lines of the Au, Pt and Pd defined. In the case of MS ICP, distortion of the result may occur with spectral polyatomic overlays (mass interference). It is concluded that both characterized instrumental methods are indeed the best for determining Au, Pt and Pd in geological objects. However, when publishing the results, it is necessary to describe in detail and metrologically evaluate the applied modifications of these methods, the analytical lines and isotope ratios used, as well as all sample preparation procedures and their characteristics.