scholarly journals U-Th-He Geochronology of Pyrite from Alteration of the Au-Fe-Skarn Novogodnee-Monto Deposit (Polar Urals, Russia)—The Next Step in the Development of a New Approach for Direct Dating of Ore-Forming Processes

Geosciences ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 408
Author(s):  
Olga Yakubovich ◽  
Ilya Vikentyev ◽  
Ekaterina Ivanova ◽  
Mary Podolskaya ◽  
Ivan Sobolev ◽  
...  
Keyword(s):  
Mass Fraction ◽  
Magmatic Activity ◽  
Skarn Deposit ◽  
Ore Formation ◽  
New Approach ◽  
Polar Urals ◽  
Alteration Halo ◽  
Ore Bodies ◽  
He Isotopes ◽  
Single Grain

We report on the application of the U-Th-He method for the direct dating of pyrite from the alteration halo of the Novogodnee-Monto Au-Fe-skarn deposit, Polar Urals. The deposit is genetically related to the formation of volcanogenic complexes of the Ural Paleozoic belt. A modification of the original methodology for measuring U, Th and He isotopes in a single grain allowed us to determine a U-Th-He age of 382 ± 8 Ma (2σ) based on six pyrite samples from the altered rocks of the deposit (U mass fraction ~0.2 mg/kg; Th/U ~ 3.5; 4He specific volume ~ 10−5 cm3·STP·g−1). This age is consistent with estimates of the age of ore formation and coeval with the end of the period of island arc magmatic activity. Our results indicate that U-Th-He dating for pyrite samples of ~1 mg in weight from the hydrothermal-metasomatic halo of ore bodies is possible, providing a crucial next step in the development of U-Th-He pyrite geochronology.

scholarly journals Zonality of ore-forming chrome spinels of medium-chrome and aluminous chromitites of the Voikaro-Syninsky massif

2021 ◽  
pp. 39-47
Author(s):  
Pavel Borisovich SHIRYAEV ◽  
◽  
Nadezhda Vladimirovna VAKHRUSHEVA ◽  
Keyword(s):  
Oxidation State ◽  
Chromium Content ◽  
Ultramafic Rocks ◽  
Work Study ◽  
Chemical Zoning ◽  
Polar Urals ◽  
The Core ◽  
Ore Bodies ◽  
Scientific Papers ◽  
The Polar Urals

Relevance of the work. The conditions for the formation of chromium ores in alpine-type ultramafites remain a topical subject of research. In recent years, scientific papers have focused on the issue of changing the chemical composition of ore-forming minerals and chromium ores under the influence of deformation and dynamic recrystallization processes accompanying metamorphism. The results of such studies make it possible to formulate a new model of the formation of chromium mineralization taking into account a significant amount of geological data indicating that alpine-type ultramafic rocks are “mantle tectonites”. In our work, we have studied zonal ore-forming spinels from chrome ores of the Polar Urals. The results of the study make it possible to associate the formation of chemical zoning in minerals and ore bodies with recrystallization under the influence of stress tension. Purpose of the work – study of the conditions for the formation of chemical zoning of chromium spinels from alumina and medium chromium ores of the Voikaro-Syninsky massif. Results. Zonal ore-forming spinels from medium-chromium and aluminous chromitites of the Voikaro-Syninsky massif (Polar Urals) have been studied. It was found that replacement rims are developed along the grains of oreforming spinels with an increased content of Cr2 O3 and an oxidation state of iron in relation to the core, as well as a reduced content of Al2 O3 . The oxidation state of iron in the rims of most grains does not exceed the values typical for unaltered ore-forming spinels. T–fO2 parameters of zoning formation in spinels were determined by oxythermobarometry. Comparison with zoned chrome spinels of the Golyamo Kamenyane massif (Bulgaria). Conclusion. Metamorphic transformations of alumina and medium-chromium chromitites of the Voikaro-Syninsky massif, occurring under subcrustal conditions under the action of directional stress at relatively constant T–fO2 parameters, lead to an increase in the chromium content of the ore mineral.

Magmatic activity at the Silurian/Devonian boundary in the Brunovistulia and Małopolska Terranes (S Poland): possible link with the Rheic Ocean closure and the onset of the Rheno-Hercynian Basin

2019 ◽  
Vol 157 (2) ◽  
pp. 119-133
Author(s):  
Jerzy Nawrocki ◽  
Magdalena Pańczyk ◽  
Piotr Szrek
Keyword(s):  
Sedimentary Rocks ◽  
Detrital Zircons ◽  
Magmatic Activity ◽  
Ion Microprobe ◽  
Rheic Ocean ◽  
Models Of Development ◽  
Regional Tectonic ◽  
Single Grain ◽  
S Poland ◽  
Tectonic Extension

AbstractThe age of granophyric diorite from the Sosnowiec IG-1 borehole (Brunovistulia Terrane) was studied by means of U–Pb single-grain zircon analysis performed on a SHRIMP (sensitive high-resolution ion microprobe) IIe device. The isotope ages and provenance of zircons from the Emsian tuffs cropping out in the southern part of the Holy Cross Mountains (Małopolska Terrane) were also investigated using the same method. The age of the diorite intrusion (420 ± 2 Ma) is comparable with the combined Ar–Ar/magnetostratigraphic age of the Bardo diabase intrusion from the northern part of the Małopolska Terrane. These intrusions were emplaced during the same event of regional tectonic extension associated with the Rheic Ocean closure and the onset of processes creating the Rheno-Hecynian Basin near the Silurian/Devonian boundary. A negative Nb anomaly characteristic of both intrusions could be linked with the subduction of the Rheic oceanic crust under the SE margin of the Old Red Continent. Emsian magmatic activity in the distant Rheno-Hercynian Zone provided several tuff layers in the northern part of the Małopolska Terrane. As can be inferred from zircon ages, these tuffs were derived from mafic eruptions that cut sedimentary rocks containing detrital zircons transported from Baltica. This interpretation fits the existing models of development of the Rheno-Hercynian Basin in the Emsian.

Geology and footwall alteration of the South Bay massive sulphide deposit, northwestern Ontario, Canada

1983 ◽  
Vol 20 (12) ◽  
pp. 1862-1879 ◽  
Author(s):  
Tetsuro Urabe ◽  
S. D. Scott
Keyword(s):  
Lava Dome ◽  
Isotopic Ratio ◽  
Massive Sulphide Deposit ◽  
Sulphide Deposit ◽  
Ore Formation ◽  
Northwestern Ontario ◽  
Alteration Halo ◽  
Oxygen Isotopic ◽  
Bulk Chemistry ◽  
Kuroko Deposits

South Bay is an Archean volcanogenic massive Cu–Zn sulphide deposit having many features in common with the Kuroko deposits of Japan. The ore lenses overlie a quartz–feldspar porphyritic rhyolite (QFP) lava dome and are covered by or occur within rhyolitic tuff breccia that, together with rhyolite tuffs and lavas, is contained within a caldera-like structure.Footwall hydrothermal alteration at South Bay is detectable for several hundred metres from ore. "Unaltered" footwall QFP lava dome contains a mineral assemblage of quartz + two feldspars + two micas + epidote + calcite + ilmenite. Closer to the orebodies, K-feldspar, epidote, and biotite disappear first, followed by consumption of calcite, ilmenite, and albitized plagioclase. The most altered QFP has an assemblage of quartz + paragonite + phengitic muscovite + chlorite + dolomite + sphene + rutile. The ratio Fe/(Fe + Mg) in dolomite, muscovite (phengite), and chlorite decreases consistently towards the orebodies. Neither bulk chemistry (except for Na2O) nor oxygen isotopic ratio shows consistently systematic lateral changes within the alteration halo. Quartz from the stringer zone, from lenses in massive ore, and from ore-horizon chert all have a very narrow δ18O range of +9.0 to +11.3‰. The δ18O of the QFP is +9.3 to +9.4‰, regardless of the degree of alteration.The temperature of ore formation is estimated to have been around 300 °C based on the paragonite–muscovite geothermometer and the carbonate geothermometer. The δ18O value of the ore-forming solution at 300 °C would have been between +2.1 and +4.4‰, which is similar to that of the Kuroko deposits.

GOLD POTENTIAL OF MANITANYRDSKY AREA AND PROSPECTS FOR RESOURCE POTENTIAL RAMP-UP, POLAR URALS

2020 ◽  
pp. 39-51
Author(s):  
L. I. Efanova ◽  
S. K. Kuznetsov ◽  
M. B. Tarbaev ◽  
T. P. Mayorova
Keyword(s):  
Geological Structure ◽  
General Information ◽  
Economic Interest ◽  
Resource Potential ◽  
Ore Formation ◽  
Polar Urals ◽  
Quartz Veins ◽  
Gold Sulfide

General information on geological structure and gold potential of Manitanyrdsky area located in the western Polar Urals is provided. Niyayuskaya ore zone is revealed, Verkhneniyayuskoye-2, Niyakhoiskoye-2 and Yagodnoye mineral occurrences are characterized. It is shown that, aside from vein gold-sulfide-quartz mineralization, disseminated and veinlet-disseminated mineralization separated from quartz veins is widespread, which is also of economic interest. Gold in ores occurs as ultrafine inclusions in arsenopyrite and pyrite; it is also found in cross fractures as overgrown with later sulfides, which suggests two ore formation stages - gold-pyrite-arsenopyrite and gold-chalcopyritesphalerite-galena. Lithochemical prospecting results are presented, gold-enriched areas are identified. Prospects for the area’s resource potential ramp-up are assessed.

scholarly journals 3D Numerical Simulation-Based Targeting of Skarn Type Mineralization within the Xuancheng-Magushan Orefield, Middle-Lower Yangtze Metallogenic Belt, China

Lithosphere ◽  
2020 ◽  
Vol 2020 (1) ◽  
Author(s):  
Xunyu Hu ◽  
Xiaohui Li ◽  
Feng Yuan ◽  
Simon M. Jowitt ◽  
Alison Ord ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Numerical Modeling ◽  
Mineral Exploration ◽  
Sedimentary Cover ◽  
Volumetric Strain ◽  
Skarn Deposit ◽  
3D Numerical Simulation ◽  
Ore Formation ◽  
Metallogenic Belt ◽  
Simulation Based

Abstract Recent exploration has identified a series of Cu-Mo skarn deposits within the Xuancheng-Magushan orefield. The orefield forms part of the Nanling-Xuancheng mining district, which is located within the Middle-Lower Yangtze River Metallogenic Belt (MLYRMB) of central-eastern China. However, this area contains thick and widespread unprospective sedimentary cover sequences that have impeded traditional approaches to mineral exploration. This study presents the results of 3D numerical simulation modeling that identifies possible mineral exploration targets within the entire Xuancheng-Magushan orefield. This modeling enables the identification of unexplored areas with significant exploration potential that are covered by thick sedimentary sequences that cannot be easily explored using traditional exploration approaches. This study outlines the practical value of 3D numerical simulation-based targeting in areas with thick sedimentary cover sequences and uses the Flac3D software package to couple processes involved in ore formation such as stress, pressure, and heat transfer. Here, we use volumetric strain increments calculated during numerical modeling as the thermodynamic representation of the generation of space during prograde skarn formation, with this space filed by sulfides either penecontemporaneously or soon after magmatism. This process occurred during retrograde hydrothermal ore formation and the genesis of the skarn-type mineralization in this area. The results of the volumetric strain increment calculated during this numerical modeling study matches the distribution of known mineralization as well as delineating eight potential targets that have not yet been explored but represent areas of significant exploration potential within the Xuancheng-Magushan orefield, indicating these targets should be considered prospective for future mineral exploration. One of these targets was also identified during our previous Comsol-based numerical modeling of the formation of the Magushan Cu-Mo skarn deposit. The fact that this area has been identified as prospective using two different numerical modeling methods indicates that this area should be prioritized for future exploration and also validates the numerical modeling approaches used here and in our previous research that more specifically focused on the Magushan skarn deposit. Overall, our study indicates that prospectivity modeling using 3D numerical simulation-based approaches can be both effective and economical and should be considered an additional tool for future mineral exploration to reduce exploration risks when targeting mineralization in areas with thick and unprospective sedimentary cover sequences.

A Novel Approach for Representing Ice Microphysics in Models: Description and Tests Using a Kinematic Framework

2008 ◽  
Vol 65 (5) ◽  
pp. 1528-1548 ◽  
Author(s):  
Hugh Morrison ◽  
Wojciech W. Grabowski
Keyword(s):  
Water Vapor ◽  
Vapor Deposition ◽  
Mass Fraction ◽  
Gradual Transition ◽  
New Approach ◽  
Ice Particles ◽  
Novel Approach ◽  
Conversion Rates ◽  
Mass Dimension ◽  
Ice Microphysics

Abstract This paper documents the development of a novel approach for representing ice microphysics in numerical models. In this approach, the ice particle mass–dimension and projected-area–dimension relationships vary as a function of particle size and rimed mass fraction. All ice microphysical processes and parameters are calculated in a self-consistent manner in terms of these mass–dimension and area–dimension relationships. The rimed mass fraction is predicted locally by separately predicting the ice mixing ratios acquired through water vapor deposition and through riming. The third predicted variable is the number concentration of ice particles. This approach allows representing in a natural way the gradual transition from small to large ice particles due to growth by water vapor deposition and aggregation and from unrimed crystals to graupel due to riming. In traditional approaches, these processes are treated by separating ice particles into predefined categories (such as cloud ice, snow, and graupel) using fairly arbitrary thresholds and conversion rates. With some modifications, the new approach can be employed in either bin or bulk microphysical models. In this paper, the new approach is implemented in a bulk two-moment microphysical scheme representing both warm-rain and ice processes and it is applied to an idealized 2D kinematic framework mimicking a shallow mixed-phase cumulus. The size distributions of cloud droplets, drizzle/rain drops, and ice particles are represented using gamma distributions. The new scheme is compared to a version of the scheme that uses the traditional approach for ice microphysics; that is, unrimed ice/snow and graupel are separate species, with threshold-based conversion rates between the former and the latter. The new and traditional schemes produce similar results, although the traditional scheme, unlike the new scheme, produces a distinct double maximum in the surface precipitation rate, corresponding to precipitation shafts consisting of either ice/snow or graupel. The relative magnitude of these peaks, as well as the ice water path and optical depth of the simulated cloud, is highly sensitive to the threshold for converting unrimed ice to graupel. In contrast, the new scheme does not require any conversion threshold and predicts formation of ice particles with wide range of rimed fractions.

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