Defect-impurity composition of diamonds from the Carnic deposits from North-east of Siberian plate

Yakovlev V.G., Pavlushin A.D.

Diamond and Precious Metal Geology Institute SB RAS, Yakutsk, Russia

451059@Mail.Ru

At present, the problem of the nature of native sources of alluvial diamonds, common in the north-eastern part of the Yakut diamond-bearing province, is still actual. On the territory of nijnelensk district a new industrial type of diamond source presented with volcano-sedimentary rocks of Upper Triassic Carnic stage – tuffites, recently has been discovered [1].

The aim of this study is to determine the characteristic structural and impurity defects in diamond crystals selected from the tuffites of the Lensky region by the method of IR-spectroscopy (A collection of diamonds has been provided by "Nizhne-Lenskoye" public corporation). Diamonds are geo-referenced to the stretched outputs of diamond deposits of Carnia located on the right and left banks of the Lena River, in a region of Bulkur anticline.

The studies were conducted on the infrared Fourier spectrometer "FT-801" in the shooting mode - absorption in the frequency range 450 - 3900 cm^-1. The characteristics of the IR-spectra of diamond crystals of I, III and V of mineralogical varieties according to Yu.L. Orlov have been obtained.

All systems of absorption bands have general peaks at wavelengths 1100, 1215, 1282 cm^-1 corresponding to defect A, have same peaks at wavelengths 1010, 1100, 1175, 1332 cm^-1 corresponding to defect B₁ and a general single peak at 1375 cm^-1which is responsible for defect C. Enumerated defects are related with nitrogen in various coordination positions in a diamond structure. Most of spectra include one peak at 3107cm^-1 and 1405cm^-1, in few cases, they accompanying with satellite at 3235cm^-1. Their presence is interlinked with fluctuations of C-H groups in the structure. In most cases, spectra peaks at wavelengths 1525 and 1550cm^-1 are also fixed. They haven’t visible associations with absorption bands related with A, B₁ - defects.

At single instances, peaks at 1451cm^-1 and 2785cm^-1 in the frequency range of spectra are detected.

On the basis of individual characteristics of the spectra two groups of diamonds have been revealed.

For the first group of diamonds, besides absorption bands corresponding to A, B₁ defects, presence of couple of peaks at wavelengths 1525 and 1550 cm^-1 are typical. According (V.G Vince, A.P. Eliseev) these two peaks are fixing B₂ – defect. In some cases, a insignificant offset to 1-1,5 cm^-1 from mean value in the sides of higher or low-frequency range of a spectrum may occur. This set of defects characterizes I and V mineralogical varieties of researched diamonds.

The second group of diamonds yields spectrum lines at frequencies 1100, 1215, 1282 cm^-1 and corresponds to defect A, lines at 1010, 1100, 1175, 1332 cm^-1 corresponding to defect B_1. Other peaks characterizing defects-impurities in this group of diamonds were not found. The defect’s set of this group determine I, III and V diamond varieties.

Thus, each diamond group is characterized with specific set of defects in the structure and individual morphologic characteristics. It gives some reason to identify two genetically insulated groups of diamonds with individual history of growth and the subsequent existence.

References:

1. Pavlushin A.D., Grakhanov S.A., Smelov A.P. Paragenetic association of minerals on the surface of diamond crystals from deposits of the Carnic layer of the North-east Siberian Platform // National geology , p.3-12, 2010, No,5

2. Vince V.G., Eliseev A.P., Sarin V.A. The physical basis of modern methods of refinig natural and cut diamonds // Precious metals. Precious stones, p. 127-148, 2009, No, 3