Large-volume platinum ore deposits in zonal mafic-ultramafic complexes of the Ural-Alaskan type and the outlook for their development

The results of mineralogical-technological studies of PGM mineralization in zonal mafic-ultramafic complexes of the Ural-Alaskan type are given. All studied massifs in the Urals and Kamchatka are characterized by similar evolution of mineral assemblages. The chromite (platinum-chromitite-dunite) and dunite (platinum-pegmatoid dunite) geological-economic types of small platinum deposits and occurrences are separate enriched sites (ore shoots) of large-volume platinum ore deposits. These are rather thick and extended zones of recrystallized dunites with attributes of high-temperature structural deformations and intense fluid reworking. Low Pt grade in ore (<0.5 gpt) is determined by fine and very fine (grain size class — 80 μm) euhedral PGM crystals distributed rather uniformly in ore mass. The high and occasionally anomalous Pt contents (up to 1 kgpt and higher) are related to large xenomorphic segregations of PGM, which concentrate largely in the marginal parts of separate chromite segregations. The significant part of productive Pt-bearing mineralization is hosted in olivine matrix of igneous rocks, so that recovery of platinum cannot be associated only with separation of chromite ore. The direct gravity concentration of platinum ore without preliminary separation of chromite concentrate is recommended as the main technique of platinum recovery. The technological scheme provides for two-stage comminution of ore with between-cycle separation of coarse the PGM fraction into the concentrate as a commodity product. The results obtained allow us to regard the aforementioned mineralization as a new geological and economic type of lode platinum deposits, whose potential is comparable with active platinum reserves in the complex Cu-Ni ores of the Noril’sk district.     

Rutile Enriched in Chalcophile Elements (Sb,Sn, Te), and Ti-rich Varieties of Tripuhyute and Cassiterite from Sublimates of Active Fumaroles at the Tolbachik Volcano,Kamchatka, Russia

Geology of Ore Deposits - Abstract—The paper contains data on rutile, tripuhyite, and unusual Ti-rich cassiterite found in sublimates of active fumaroles at the Tolbachik volcano, Kamchatka,...     

Features of the Ore Forming Process on the Dvoinoye Epithermal Au–Ag Deposit (Western Chukotka)

The results of thermobaric geochemical study of ores of the Dvoinoye epithermal Au–Ag deposit are considered. Study of the fluid inclusions has shown that the ores were formed from low-salinity hydrothermal solutions with Na, Ka, and Mg chlorides and CO₂, HS^–, CH₄ trace fluxes at the time when the temperature dropped from 370 to 130°C. The results are compared with data obtained from the closely located Kupol and Sentyabr’skoye deposits.     

New Data on the Geochemistry of Mississippi-Type Ores at the Sardana Deposit (Northeastern Russia)

New data obtained using a modern analytical technique on the geochemistry and conditions of the formation of Mississippi-type ores at the Sardana deposit are presented. Comparative analysis related to other deposits of the same type was carried out. The geochemical data point to a considerable role of metamorphism of the enclosing carbonate–terrigenous masses in ore formation at the deposit.     

Global Metallogenic Zonality of the Pacific Ore Belt

This article discusses problems of global metallogenic zonality of the Pacific Ore Belt (POB), which is understood as the complex of volcanogenic–plutonogenic units related to the evolution of the lithosphere of marginal seas; this lithosphere combines both continental and oceanic metallogenic features and also possesses a characteristic specificity of ore accumulation. It is shown that the ideas by S.S. Smirnov about the POB zonality have not considerably changed with time and, moreover, have been supported by the new global tectonic concepts. Nevertheless, the nature of metallogenic homogeneity of the external (Ag–Cu) and internal (Sn–W) zones of the POB seems to be more complicated and ambiguous. The metallogenic role of the Ag/Au ratio in ores of POB deposits is shown.     

Peculiarities of ore formation at the N’yavlenga Au-Ag epithermal deposit,Northeast Russia

Thermobarogeochemical studies have revealed the relatively high-temperature ore-bearing fluid of the N’yavlenga deposit. The dependence between the homogenization temperatures of the fluid inclusions and salinity of the fluid and the bimodal distribution of salinity values indicates mixing of two different fluids in the ore-bearing system. These facts are related to the thermal metamorphism of ores from the N’yavlenga deposit and indicate the complex relations of the early Au-Ag epithermal and late Au-Cu-Mo porphyry mineral complexes in orebodies of the deposit.     

Source inclination and the resolution provided in 3D Doppler tomography

The resolution provided in 3D Doppler tomography is analyzed. The basis for correcting 3D tomographic structures taking into account the influence of the inclination of the structure on the geometry of the summarized transfer function (STF) used in the reconstruction is presented. The same resolution can be achieved along the axis of rotation and in the orbital plane of a system for an inclination of 54°44′. The positions of the centers of structural features in a tomogram should be preserved when correcting for differences in elongation along the main axes due to the difference in resolution along these axes. Examples of simulations used to estimate possibilities for 3D reconstruction in the central sector of inclination angles, and also for values of these angles near the periphery, are presented. A comparison with results obtained using the radioastronomical approach (RA) and the filtered back-projectionmethod testifies that the latter leads to appreciably larger distortions during a 3D reconstruction. The effectiveness of considering two inclinations, as can be realized for precessing systems, is indicated; this can also be useful in other practical applications.     

The origin of low-frequency maxima in the spectra of seismic noise

The evidence attesting to the possibility of the largest spectral maximum in seismic noise with a peak frequency of 0.14–0.22 Hz to form as a result of low-frequency dissipation of elastic wave energy in rocks is presented. According to this mechanism, elastic wave energy in rock, which can be considered as a two-component medium (solid matrix + pore water), is dissipated in the form of low-frequency pulses whose energy is the lower the smaller the coefficient of porosity. It is assumed that weak seismic events continuously occur in the frequency range above 6 Hz, and their dissipated energy is a source of the low-frequency noise.