In gold ore deposits of gold could be associated with chalcopyrite. The problem is that so far it is not clear why certain minerals are accompanied by gold. To answer these questions requires study different types of point defects in their structure, identification of positions impurity.

Was investigated area of chalcopyrite "Panimba" deposits (Krasnoyarsk region, Russia). The chemical composition of the studied chalcopyrite was determined by X-ray spectral (XRS) on «Camebax-Misro" in the laboratory of microprobe analysis (EPMA) in Novosibirsk- city.

Table 1. Selected results EPMA and calculations of the density of the impurity (ρ) and the vacant positions (n) in the structure of chalcopyrite.

Chalcopyrite is almost always a non-stoichiometric [3-4]. Given the presence of the impurity atoms in the structure of chalcopyrite should clarify the formula: (Fe)_α (Z)_ϱ(Cu)_ϰ(S₂)_β, where Z may represent impurity atom, e.g., Co, Ni, Au and Zn. Table 1 shows the values ​​ ϱ_Cu, ϱ_Co, ϱ_Au и ϱ_Zn, calculated on the basis of determining the weight percentage content of impurity atoms in the chalcopyrite. The ratio S / (Fe + Cu) in this case is the ratio of 2β/(α+ϰ), because each anionic vacant position corresponds to two sulfur atoms, consequently, the density vacant positions (n) is defined by the equation: n = β-(α+ϰ)/2. The calculated value of the ratio S / (Fe + Cu) were compared with the results of microprobe analysis and point defect density, defined as n = 1 - (Fe + Cu) / S.

Note that a negative value corresponds to the density of anion vacancies, and a positive value - the density of cation vacancies.

If α, ϰ and β are equal to unity (stoichiometric composition CuFeS₂), then, as the calculation of iron in the sample shall be 30.43 wt. %, copper - 34.63 wt. % , sulfur - 34.94 wt. %. Only in this case the structure of chalcopyrite no cationic or anionic vacancies.

Analysis of Table 1 allows to make a conclusion that the total density of the impurity atoms is practically independent of the ratio S / (Fe + Cu) in the samples. This is only possible if the impurity atoms occupy octahedral voids in the packed layers of sulfur atoms.

In the diamond structure, each atom is surrounded tetrahedrally by four neighbors. These atoms form two interpenetrating face-centered cubic (fcc) sublattices, each of which is occupied by atoms of a derivative component in the structure of sphalerite. Note, however, that when a cubic close packing of atoms busy all the octahedral and tetrahedral voids is corresponds to the existence in the structure of the four interpenetrating fcc sublattices [1-2].

The unit cell of chalcopyrite has a tetragonal crystal system and corresponds to the structure of the superstructure of sphalerite, as formed by two cell types sphalerite, put on each other along the axis of the "c". In such a structure should be free octahedral sites, and they occupy the impurity atoms. These positions do not depend on the density of the vacant positions in the parent matrix.

Note that samples with the same density vacant positions, the density of impurity atoms may vary both in magnitude and type of impurity. The analysis of the results shows that the presence of impurity in the structure of chalcopyrite possibly in the absence vacant positions.

Note that the samples in which the density vacant positions in the structure exceeds the value 1,45·10^-2 within "Panimba" deposits is not detected.

2. Hall S. R., Stweart J. M. The crystal structure refinement of chalcopyrite, CuFeS2. // Acta Crystallographica. – 1973. – V. B29. – P. 579-585.

3. Kase K. Tin-bearing chalcopyrite from the Izumo vein, Toyoha mine, Hokkaido, Japan. // The Canadian Mineralogist. –1987. – V. 25. – P. 9-13.

4. Larocque A. C. L., Hodgson C. J., Cabri L. J., Jackman J. A. Ion-microprobe analysis of pyrite, chalcopyrite and pyrrhotite from the Mobrun VMS deposit in northwestern Quebec: evidence for metamorphic remobilization of gold. // The Canadian Mineralogist. - 1995. - V. 33. - P. 373-388.