Vol 56, No 1 (2018)

This paper reports the first results of a study of 11 isotope systems (³He/⁴He, ⁴⁰Ar/³⁶Ar, ³⁴S/³²S, ⁶⁵Cu/⁶³Cu, ⁶²Ni/⁶⁰Ni, ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, ^206–208Pb/²⁰⁴Pb, Hf–Nd, U–Pb, and Re–Os) in the rocks and ores of the Cu–Ni–PGE deposits of the Norilsk ore district. Almost all the results were obtained at the Center of Isotopic Research of the Karpinskii All-Russia Research Institute of Geology. The use of a number of independent genetic isotopic signatures and comprehensive isotopic knowledge provided a methodic basis for the interpretation of approximately 5000 isotopic analyses of various elements. The presence of materials from two sources, crust and mantle, was detected in the composition of the rocks and ores. The contribution of the crustal source is especially significant in the paleofluids (gas–liquid microinclusions) of the ore-forming medium. Crustal solutions were probably a transport medium during ore formation. Air argon is dominant in the ores, which indicates a connection between the paleofluids and the atmosphere. This suggests intense groundwater circulation during the crystallization of ore minerals. The age of the rocks and ores of the Norilsk deposits was determined. The stage of orebody formation is restricted to a narrow age interval of 250 ± 10 Ma. An isotopic criterion was proposed for the ore-bearing potential of mafic intrusions in the Norilsk–Taimyr region. It includes several interrelated isotopic ratios of various elements: He, Ar, S, and others.

The paper presents results of testing currently used models proposed to describe Cr-spinel–melt equilibrium: models of the MELTS family by M.S. Ghiorso with colleagues, the SPINMELT program by A.A. Ariskin and G.S. Nikolaev, and the “MELT–CHROMITE spinel calculator” by А.А. Pustovetov and R.L. Roeder. The new calibration of the SPINMELT model presented in this publication enables calculating a sixcomponent (Mg, Fe²⁺, Cr, Al, Fe³⁺, and Ti) composition of Cr-spinel and the \(T - {f_{{o_2}}}\) parameters of its stability on the liquidus of basaltic melts under pressures up to 15 kbar. The model is based on results of 392 runs from 43 experimental studies, including systems of normal alkalinity at \({f_{{o_2}}}\) ≤ QFM + 2. The experimental dataset (which was extended compared to that used for the previous calibration) allowed us not only to estimate the pressure effect, but also apply the model to aluminous and hydrous systems. Tests of the SPINMELT-2.0 model show that the errors of the calculated temperature of the spinel–melt equilibrium increase with pressure from 16°C at 1 atm to 50°C at 15 kbar. Experimental spinel compositions are reproduced by the model accurate to < 3 at % Al and Cr, and no worse 1 at % for the other cations.

The minimal set of conditions is found under which a primitive genetic code can be formed in the chemical world in which polypeptides and polynucleotides can be produced. Molecular modeling demonstrates that multiple cycles of synthesis and thermal destruction of biopolymers result in spontaneous complication of their structure. This evolutionary progressive complication of polypeptides and polynucleotides coding them results in certain specific functions of the polypeptides, which are similar to properties of enzymes. Computer simulations confirm the internal logical consistency of the simplified scenario suggested for the origin of a genetic code as a process of transferring information on the structure of biomolecules to the historical future, in spite of the continuous thermal decomposition of these structures.

The standard enthalpy of formation of stannite (Cu₂FeSnS₄) was calculated from the calorimetric measurements of the reactions of its formation from simple synthetic sulfides: Cu₂S + FeS₂ + SnS → Cu₂FeSnS₄ and ₂CuS + FeS + SnS → Cu₂FeSnS₄. Using published data for the binary sulfides, the standard enthalpy of formation of stannite from the elements was determined as ΔfH°_298.15(Cu₂FeSnS₄) =–(417.28 ± 2.28) kJ mol^–1.