Vol 57, No 4 (2019)

Mössbauer spectra of pyrite (FeS₂) are measured within a temperature range of 90–295 K. The isomer shift is described by the Debye model with a Mössbauer temperature θ_M = 551.4 K. These results are used to calculate the kinetic energy of thermal vibrations of the iron sublattice of pyrite and the iron β-factor for pyrite: 10³\({\text{ln}}{{\beta }_{{^{{{\text{57}}}}{\text{Fe}}{{{\text{/}}}^{{{\text{54}}}}}{\text{Fe}}}}}\) = (1.2665 ± 0.0391)x – (0.4584 ± 0.0283) × 10^–2x² + (0.2581 ± 0.0239) × 10^–4x³; x = 10⁶/T ² (K^–2). The calculated iron β-factor in pyrite is in good agreement with results of ab initio calculations, ⁵⁷Fe nuclear inelastic X-ray resonant scattering in synchrotron experiments, and direct isotope exchange experiments between pyrite and Fe²⁺ dissolved in water. The heat capacity of pyrite is measured within a temperature range of 79–300 K and is described using the Thirring expansion. Based on this expansion, the kinetic energy of thermal vibrations of the total crystalline lattice of pyrite is calculated. The kinetic energy of the thermal vibrations of the sulfur sublattice in pyrite is found by subtracting the kinetic energy of the iron sublattice from the total kinetic energy of pyrite crystalline lattice. The temperature dependence of ³⁴S/³²S β-factor for pyrite, which was calculated from the kinetic energy of the sulfur sublattice, is 10³\({\text{ln}}{{\beta }_{{^{{{\text{34}}}}{\text{Fe}}{{{\text{/}}}^{{{\text{32}}}}}{\text{Fe}}}}}\) = (1.7532 ± 0.0623) x – (1.0470 ± 0.0752) × 10^–2x² + (1.0424 ± 0.1126) × 10^–4x³; x = 10⁶/T² (K^–2). This value of the ³⁴S/³²S β-factor is in good agreement with the ab initio calculations and with results of isotope-exchange experiments in the pyrite–sphalerite–galena system.

The paper presents first experimental data on gold solubility in CO–CO₂ and C–O–S fluids with a low H₂O concentration under reduced conditions, a pressure of 200 MPa, and a temperature of 950°C. Gold solubility in C–O–S fluid is approximately 27 ppm. The estimate of gold solubility in CO–CO₂ fluid with 10–15 mol % CO is less accurate, and the solubility is no lower than 2–3 ppm but may reach 200–300 ppm. The high gold solubility in reduced CO₂ fluid determined in the course of this research, and our earlier estimates of high platinum solubility (Simakin et al., 2016), may explain the deposition of mineralization of these noble metals in the Guli intrusion, polar Siberia, as a result of fluid extraction of these metals and their redeposition at a temperature slightly below the solidus. The reduction of the largely oxidized CO₂ fluid, which was determined using mineralogical sensors, was likely related to the subsolidus oxidation of olivine.

Magmatic rock plays a key role in controlling tectonics. By determining the chronology, petrogenesis and tectonic significance of newly discovered granite porphyry and granite units, this study documents the Bangong-Nujiang Neo-Tethys ocean evolution and the tectonic environment of the Zanzongcuo zone. Based on laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb dating of zircons, the ages of the granite porphyry and the granite are 113.74 ± 0.68 and 79.58 ± 0.83 Ma, respectively. Thus, these intrusive rocks formed at different times in the Cretaceous. The two studied intrusive bodies are I-type granitoids with peraluminous characteristics. The granite porphyry and the granite belong to the medium- to high-K calc-alkaline and low-K calc-alkaline series, respectively. These rocks are enriched in large ion lithophile elements (LILEs, e.g., Rb, U, and Th) and light rare earth elements (LREEs) but depleted in high field strength elements (HFSEs, e.g., Nb, Ta, and Ti). The granite porphyry and the granite have δEu values of 0.69–0.82 and 0.6–0.73, respectively, and have moderately negative Eu anomalies. The granite porphyry formed in a subduction-related structural environment and represents an arc-type granite. The granite formed in a collisional tectonic environment and represents a granite that formed in a within plate setting. The geochronologic and tectonic characteristics of these two intrusive rocks indicate that the Zanzongcuo zone experienced a series of tectonic events in the Cretaceous, including oceanic crust subduction in the late Early Cretaceous, continent-continent collision, and intraplate compression in the late Late Cretaceous. Furthermore, the Bangong-Nujiang Neo-Tethys ocean closed in the late Early Cretaceous.

The Kaixinling coal is located in the eastern part of the North Qiangtang Basin, which were the important coal resources in Tibetan Plateau. A total of thirty coal samples were collected from the Kaixinling area to determine the concentrations, distribution patterns, occurrences and origins of platinum group elements (PGEs) in the Permian coal. The total contents of PGEs are low ranging from 0.56 to 1.89 ng/g with a weighed mean value of 1.21 ng/g. The contents in Os exhibit considerably positive anomaly compare to the Upper Continental Crust and the ordinary Chinese coal. The individual PGEs in coal samples from the Kaixinling area exhibit various modes of occurrence. Pd and Pt are mainly concentrated in clay minerals and P-bearing minerals. Ir is probably present in clay minerals and partly controlled by other Fe-bearing and P-bearing minerals. Os is associated with organic matter and partly related to calcite. Three possible origins of PGEs were identified in coal seams in the Kaixinling area. Pd, Pt and Ir are mainly terrigenous inputs. Rh and Ru are derived from mixed sources (seawater and terrigenous supply), while Os is mainly derived from seawater.