Results of the reinterpretation of materials of IV geotraverse of NHS (PK 295- 400) in the central part of the Holovanivsk suture zone

This work provides the reinterpretation results of the research outcomes with the DSS method on geotraverse IV on section PK 295-400 in order to clarify a seismic section in the Holovanivsk area of high gravity. A number of points of diffraction and seismic sites have been identified in Earth’s crust (at a depth of 2-60 km), which gives an opportunity to considerably specify the data on the deep structure of the studied area. The position in a section of the Talnivska fault zone is clarified due to the identification of additional points of diffraction and a large number of short reflective elements at a depth of 2-8 km. In the central part of the section (PK 338-355), horizontal and inclined elements (at the depths of 2-9 km and 24-44 km) and a series of short steeply inclined reflective elements (at depths of 8-26 km) form the area of the medium which at the depth of 2-44 km differs in its characteristics from the host rocks. This allowed tracing the listriс shear zone that stretches continuously from a depth of 8 km on PK 355 to 44 km on PK 304. All this, as well as available seismotomographic data, allows us to suppose that the Talnivska fault zone is traced up to depths of 100-600 km as a boundary between blocks with different Vp velocities and degrees and gaps in the Golitsyn—Geiko layer. The listriс shear zone is connected to the main part of the Talnivska fault zone near the surface. According to the given re-interpretation of GSS data on geotraverse IV, the supply channel of the intrusive body of hyperbasites is rather narrow at depths of 60-33 km, and starting only from depth of 30 km and almost to the surface the body expands up to 15 km in width. Focusing on the area of increased Vp velocities at a depth of 2-33 km, one can assume that the main intrusive body that consists of hyperbasites and basite-Dunites, peridotites, pyroxenites, gabbro, and amphibolites, the density of which exceeds the density of rocks by 0.1-0.22 g/cm3, is located at these depths along the axis of the central part of the Holovanivsk suture zone.

New Geochemical and Mineralogical Data on Rocks and Ores of the NE Flank of the Oktyabr’skoe Deposit (Norilsk Area) and a View on Their Origin

The Oktyabr’skoe deposit in the Norilsk ore district is the largest platinum-copper-nickel deposit in the world. It contains a huge main orebody (2.4 km3) of massive sulfide ores and some smaller sulfide bodies. Almost all publications on this deposit are devoted to the main orebody. However, to solve the problems of the deposit genesis, it is necessary to take into account the geological structure of the entire area and the composition of all orebodies. For the first time we present data on the inner structure, geochemical and mineralogical characteristics of the intrusive body, and related the disseminated and massive sulfide ores (orebody number C-5) in the northeastern flank of the deposit. The intrusion studied in the core of the borehole RG-2 consists of several horizons including the following rock varieties (from bottom to top): olivine gabbro-dolerites, taxitic gabbro-dolerites, picritic gabbro-dolerites, troctolites, olivine-free gabbro-dolerites, ferrogabbro, and leucogabbro. The intrusion shows a strong differentiated inner structure where high-Mg rocks (up to 25 wt.% MgO troctolites and picritic gabbro-dolerites) in the bottom are associated with low-Mg rocks (6–7 wt.%, gabbro-dolerites, leucogabbro, ferrogabbro) without intermediate differentiated members (8–12 wt.% MgO olivine gabbro-dolerites). Rocks are characterized by low TiO2 content (≤1 wt.%). Taxitic gabbro-dolerites, picritic gabbro-dolerites, and troctolites contain disseminated sulfide chalcopyrite-pyrrhotite mineralization (32 m thick). Cu and Ni concentrations reach up 0.74 and 0.77 wt.%, respectively. Massive ores (27 m) occur in the bottom part of the intrusion. The ores consist of pentlandite, chalcopyrite and pyrrhotite, the latter mineral dominates. Their chemical composition is stable: Cu/Ni ~1, Pd/Pt varies from 5 to 6. The C-5 orebody is similar to the C-3 orebody in terms of mineral and chemical compositions, and differ from the nearby the C-4 orebody which is characterized by a Cu/Ni ratio changing from 5 to 8. On the basis of geochemical and mineralogical data, it is assumed that orebodies C-3 and C-5 are associated with one intrusion, while the orebody number C-4 is related to another intrusive body. Thus, the deposit has a more complex structure and includes several more intrusions than is usually considered.

Review of geothermochronological and thermobarometric techniques for the construction of cooling and exhumation curves or paths for intrusive igneous rocks

The present study reviews radiometric and thermobarometric techniques used to construct cooling curves or paths to characterize intrusive bodies and to calculate cooling and exhumation rates. To construct these curves or paths, the temperature, time and depth variables must be estimated in intrusive bodies by applying various analytical techniques, including thermobarometry and U-Pb zircon, Ar-Ar hornblende and muscovite, fission track and (U-Th)/He zircon and apatite dating, in combination with a geological framework of reference for each intrusive body. The authors recommend to determine the crystallization age by zircon U-Pb dating, to quantify the emplacement depth using thermobarometry methods according to the composition of the intrusive body, to calculate the initial cooling ages with hornblende and muscovite Ar-Ar methods, as well as to calculate the cooling/exhumation ages in the upper crust using low-temperature thermochronology methods. These cooling curves or paths in intrusive bodies are highly relevant when studying compressive or extensional areas because they partly represent the thermal history of the era, thereby providing data on the magmatic and tectonic evolution of the region. Thus, these studies are highly important for designing geodynamic models and for their possible application in developing the tectonic model of the country.

Effects of igneous intrusions on source rock in the early diagenetic stage: A case study on Beipiao Formation in Jinyang Basin, Northeast China

Mesozoic intrusive bodies play an important role in the temperature history and hydrocarbon maturation of the Jinyang Basin in northeastern China. The Beipiao Formation, which is the main source rock in Jinyang Basin, was intruded by numerous igneous bodies and dykes in many areas. The effects of igneous intrusive bodies on thermal evolution and hydrocarbon generation and migration in the Beipiao Formation were investigated. A series of samples from the outcrop near the intrusive body were analyzed for vitrinite reflectance (R0%) and other organic geochemical parameters to evaluate the lateral extension of the thermal aureole. The R0 values of the samples increase from a background value of ∼0.9% at a distance above 200 m from the intrusive body to more than 2.0% at the vicinity of the contact zone. The width of the altered zone is equal to the thickness of the intrusive body outcropped in the field. Organic geochemical proxies also indicate the intrusive body plays a positive and beneficial role in the formation of regional oil and gas resources. Due to the influence of the anomalous heat from the intrusive body, the hydrocarbon conversion rate of the source rocks of the Beipiao Formation was significantly improved. The accumulation properties and the storage capacity of the shales also greatly improved due to the intrusive body as indicated by the free hydrocarbon migration in the shales. This new understanding not only provides a reliable scientific basis for the accurate assessment of oil and gas genesis and resources in the Jinyang Basin but also provides guidance and reference for oil and gas exploration in the similar type of basin.

Geochronology and geochemistry of late Silurian-early Devonian mafic-ultramafic complexes in the eastern section of Qilian block, NW China: Implications for late early Paleozoic tectonic evolution of the Qilian orogeny belt

<p>Field relationships, mineralogy, petrology, geochemistry, geochronology, and Nd-Hf-O isotopes of the mafic-ultramafic rocks from the east part of the Qilian block are studied in the present work. The Aganzhen intrusive body only exposed in the Zhigoumen, Shiguanzi, Xianggoumen outcrops and includes Hornblende peridotite, wehrlite, olivine-bearing pyroxenite, hornblende-bearing pyroxenite, websterite, clinopyroxenite, hornblendite, olivine-bearing gabbro. The gabbroic rocks are also layered or massive cumulates with rock types varying continuously from noritic gabbro through hornblende gabbro to dioritic norite. Contact metamorphic zones are well developed between the Aganzhen intrusive body and the country rock. Major element contents of Aganzhen ultramafic-mafic rocks show subalkalic series and are characterized by low SiO<sub>2</sub> contents (38.09-54.96 %), low TiO<sub>2</sub> contents (0.09-0.72 %), low P<sub>2</sub>O<sub>5</sub> contents (0.00-0.36 %) and alkali contents (Na<sub>2</sub>O+K<sub>2</sub>O 0.01-5.35 %), but high MgO contents (9.68-33.06 %), Ni contents (116-1505 ppm), Cr contents (713-2808 ppm). Similar LREE-rich pattern ((Ce/Yb)<sub>N</sub> =0.95-3.80 except two Samples) and tiny Eu anomaly (Eu/Eu* =0.6-1.2) indicate the Aganzhen ultramafic-mafic rocks have the same magma source. Trace elements are enriched in LILE (Rb, Th, U, K), relatively depleted in HFSE (Nb and Ta), and the La/Yb, Ce/Yb, Th/Yb, Nb/La, La/Sm values suggest the limited crustal contamination during the rise of the magma. The ε<sub>Nd</sub> (430 Ma) values are −6.9–+2.5 and T<sub>DM</sub> values are 3.6–1.4 Ga. The SHRIMP ages are 433±2 Ma for the Zhigoumen websterite(101-2101A), 434±3 Ma for Shiguanzi hornblendite(101-2104A) and 412±3 Ma for the Xianggoumen serpentinite(101-2107A). In situ zircon O-Hf isotope, the δ<sup>18</sup>O compositions of vary from +9.03 to +9.50 (except three points +11.33, +12.38, +12.44) and ε<sub>Hf</sub>(t) value is +0.29 to +4.13 for the Zhigoumen pyroxenite(101-2101A), the δ<sup>18</sup>O compositions of vary from +6.39 to +7.12 and ε<sub>Hf</sub>(t) value is +7.76 to +13.26 for Shiguanzi gabbro(101-2104A), and the δ<sup>18</sup>O compositions of vary from +4.68 to +5.31 and ε<sub>Hf</sub>(t) value of +0.28 to +2.79 for the Xianggoumen serpentinite(101-2107A). According to the above datum, we suggest that middle Paleozoic magmatisms last ~20 m.y. (434-412 Ma) on the northern margin of the Qilian Block was related to the Early Paleozoic continental collision between the Qilian and Alax blocks, and to subsequent subduction and thermal underplating.</p>

Platinum and platinoids in the Bolotisty gold-placer deposit (Khabarovsky Krai, Russia)

The article shows the results of studies the platinum mineralization (within the framework of studying the complexity of deposits) in the waste of heavy concentrate in the southeastern flank of the Bolotisty gold-placer deposit, which the located in the Khabarovsky Krai (Russia). The deposit is localized in the “erosion window” among the covers of Miocene basalts and Eocene andesites, where Cretaceous sedimentary, tuffaceous-sedimentary rocks of the basement of the volcano structure, broken through by an Eocene intrusive body of intermediate and basic composition, come to the surface. An abbreviated mineralogical analysis for monofraction of precious metals was carried out for a concentrate fraction weighing 1.813 kg with a grain size of -3.0 + 0.1 mm. Gold and platinum were found - 1.38 mg and 1.08 mg. Platinum has an iron impurity up to 3-5 % Fe and Cu, Ir, Rh impurities are variable. There are plate-like inclusions of native osmium with an admixture of ruthenium in 43 % of the studied platinum grains. There are single inclusions of ehrlichmanite. A large amount of high-temperature dipyramidal quartz, along with magnetite, chromite, tourmaline and other minerals is a characteristic feature of the concentrate and platinum grains of this area.