Precise calculations of Nickel content in pyropes

The nickel content in pyropes interested researchers due to the possibility to create an algorithm for calculating the temperature boundaries of its joint crystallization with diamonds. Griffin proposed such a calculation algorithm, which was named the diamond-bearing corridor with his name [1]. Determination of nickel content in pyropes on microanalysts is difficult for several reasons. The first reason is the limit of detection of nickel in pyropes, which is very high for the determination of this element on electron microscopes (at least 15 ppm). And then, such an analysis is possible at a quantitative level with a probe beam current of 300nA and an analysis time of 3 minutes. The study of the correlation ratios of nickel with other elements in pyropes allowed us to determine two elements that have a significant correlation with the nickel content in pyropes - these are titanium and manganese and their content in pyropes is acceptable for quantitative determination. On the ion microanalyzer, more than two hundred analyses were performed for pyropes from the kimberlite pipes Botuobinskaya and Nyurbinskaya, the remaining determinations were made from kimberlites tr. Jubilee and tr. Victory with the use of a new technique for the determination of nickel in pyropes in the microanalyzer JXA-8230. In total, 443 definitions of nickel in pyropes were performed at the quantitative level. Such definitions made it possible to calculate the functional dependence of nickel contents on titanium and manganese contents. The STATISTICS program is used for such calculations (Fig. 1).

Fig. 1. Map of level lines (nickel manganese titanium for 443 definitions) with the calculation of functional dependence

The calculation of nickel contents in pyropes makes it possible to fully use the Griffin geothermometer to determine the number of pyrope grains from the diamond-bearing corridor area.

• Griffin W.L., Ryan C.G. Trace elements in indicator minerals: Area selection and target evaluation in diamond exploration. J. Geochem. Explor., 1995. Vol. 53., pp, 311-357