Geology, formation conditions, and ore content of the Turgoyak granite massif and carbonaceous deposits of its western framing (South Ural)

The article describes the geological structure of the Turgoyak granitoid massif (γϬС1–2ts), Urenga (RF2ur) and Uytash (RF3uš) suites. In the Late Vendian time the rocks first experienced regional metamorphism under the conditions of the cummingtonite-amphibolite facies at a temperature of 550–595 °C and a pressure of 250400 МПа, and then in local areas — diaftoresis (T=520530 °C and P=130170 МПа). During the formation of the Turgoyak massif (T=770810 °C and P=210250 МПа), the rocks of the Urengin and Uytash suites were subjected to contact metamorphism. This metamorphic processes made the black shale gold to remove from the black shale zone of the amphibole-hornfels facies and caused its redeposition within the albite-epidote-hornfly zone.

Relationship between magmatic, metamorphic and hydrothermal processes within the Baikal-Muya terrane (Eastern Siberia): constraints from a high-precision geochronological study of the Kedrovsky granitoid massif

High-precision dating of granitoids is significant for identification the ages of the main stages of crust formation in various blocks of the continental crust. In this work, we dating the Kedrovskiy diorite-granodiorite massif localized within the South Muya block of the Baikal-Muya accretion terrane (BMT) (Eastern Siberia) among the Neoproterozoic gabbroids of the Kedrovskiy complex and metasedimentary rocks of the Kedrovskaya Formation. The results of U-Pb (ID TIMS) and 39Ar-40Ar geochronological studies of the Kedrovskiy massif are discussed. The formation of the massif (781 3 Ma) occurred at an early stage formation of the Proterozoic continental crust of BMT during accretion of Baikalids with the Siberian craton. A later thermal event (626 11 Ma) of the Ediacaran stage evolution BMT is reflected in the formation of of biotite-quartz-feldspar veins that cut through the granitoids of the Kedrovka massif. The obtained geochronological data show that the gold mineralization of the Kedrovskiy deposit (273 4 Ma) was not generated by the Kedrovskiy massif granitoids.

ZIRCON IN HIGH‐MG DIORITE OF THE CHELYABINSK MASSIF (SOUTH URALS): MORPHOLOGY, GEOCHEMICAL SIGNATURE, AND PETROGENESIS IMPLICATIONS

The article is focused on the morphology, trace element composition, U‐Pb and Lu‐Hf systems in zircon in high‐Mg diorite of the Chelyabinsk granitoid massif. Our analytical studies of the U‐Pb and Lu‐Hf isotope systems and the trace element composition were performed using mass spectrometry (MS) with inductively coupled plasma (ICP) and laser ablation (LA) of samples. It is established that the zircon formed at the last stages of crystallization of the basic melt under subsolidus conditions at low (600–700 °C) temperatures, which distinguishes it from the zircon of most other high‐Mg rocks of the intermediate composition. The internal structure of the zircon and the concentration of trace elements are locally altered under the influence of a fluid, which led to a partial disruption of the U‐Pb and Lu‐Hf isotopic systems. For the least altered areas in the zircon crystals, the age of crystallization of the parent high‐Mg melt is 362±2 Ma, which coincides with the age estimated from the geological data. Considering the isotope composition of Hf in the zircon and the trace element concentrations, there are grounds to relate the formation of high‐Mg diorite in the Chelyabinsk granitoid massif with a mixed mantle‐crustal source.

Petrographical petrochemical characteristics of Xa Yu granitoid massif, Binh Thuan province

Xa Yu granitoid is isometric shape, with the exposure of 7.5 km2 area. The petrographical component consists of medium – coarse to small grained biotite granite. The vein rocks are incusive of aplite, pegmatoid,…The main mineral components are plagioclase, potassium felspate, quartz, biotite, and little horblende. The common accessory mineral components are zircon, orthite and apatite. Chemical components of rocks are: SiO2: 65.96 –76.50, Na2O: 1.85 –3.30, K2O: 3.60 – 5.27, K2O+Na2O: 5.45 –7.18; K2O/Na2O: 1.23 – 1,95. The content of Ba, Sr is low but Rb is higher, variability Rb/Sr: 0.552 –10.526; Ba/Sr: 0.379 – 1.816, Ba/Rb: 0.055 – 3.092; K/Rb: 235.3 – 246.9, Type I-S-granite.