Olga Valentinovna Yakubovich

This study presents a new analytical approach to (U,Th)-He dating of individual pyrite grains. We demonstrate that a widely available commercial fiber-laser marking system operated in scanning mode can efficiently extract radiogenic He from pyrite encapsulated in quartz ampoules. The ampoules retain the thermal decomposition products and associated parent nuclides, allowing U and Th to be subsequently determined in the same material from which He was extracted. The proposed extraction technique was validated using pyrite from two gold-bearing sites in the Russian Far East: the Pavlik orogenic gold deposit in the Magadan Region and the Upryamoe gold occurrence, Chukotka. The resulting pyrite (U,Th)-He ages are 139.3 ± 1.7 Ma (MSWD = 2.5; n = 7) and 125.4 ± 2.1 Ma (MSWD = 0.87; n = 5), respectively. Compared with the previously developed high-vacuum furnace procedure, the scanning fiber-laser approach increases the analytical throughput of pyrite (U,Th)-He dating by approximately an order of magnitude, allowing up to eight samples to be analysed per day. By making individual-grain age determinations faster and operationally simpler, the method enables larger datasets to be acquired and thereby improves the statistical characterization of pyrite ages from a range of geological settings.

This study presents a new analytical approach to (U,Th)-He dating of individual pyrite grains. We demonstrate that a widely available commercial fiber-laser marking system operated in scanning mode can efficiently extract radiogenic He from pyrite encapsulated in quartz ampoules. The ampoules retain the thermal decomposition products and associated parent nuclides, allowing U and Th to be subsequently determined in the same material from which He was extracted. The proposed extraction technique was validated using pyrite from two gold-bearing sites in the Russian Far East: the Pavlik orogenic gold deposit in the Magadan Region and the Upryamoe gold occurrence, Chukotka. The resulting pyrite (U,Th)-He ages are 139.3 ± 1.7 Ma (MSWD = 2.5; n = 7) and 125.4 ± 2.1 Ma (MSWD = 0.87; n = 5), respectively. Compared with the previously developed high-vacuum furnace procedure, the scanning fiber-laser approach increases the analytical throughput of pyrite (U,Th)-He dating by approximately an order of magnitude, allowing up to eight samples to be analysed per day. By making individual-grain age determinations faster and operationally simpler, the method enables larger datasets to be acquired and thereby improves the statistical characterization of pyrite ages from a range of geological settings.

The main techniques used for gas extraction from solid geological samples for geochronological studies are their thermal destruction either in an isothermal mode, for example in a double vacuum furnace, or under the action of laser radiation. Approaches based on the use of laser technologies are more express and have a low-background. The article describes an original high-vacuum experimental setup based on an ytterbium fiber optic laser for gas extraction from milligram samples of rocks and minerals in a scanning mode. In the proposed configuration, a static vacuum of 10^–8 Torr can be achieved in the high vacuum laser cell. Heating of individual mineral grains to a temperature of over 1800°C is ensured. Using the example of the international standard for (U,Th)–He dating—Durango apatite—it is demonstrated that the laser installation ensures complete extraction of radiogenic helium from the mineral and can be used for isotope-geochronological studies.

During the geological survey, conducted between 2017 and 2021 in the western part of the Kolyma–Omolon microcontinent, a zone of structural transformations was identified within the southeastern margin of the Middle Jurassic Rassokhinsky (Rassoshinsky) granitoid massif. Quartz veins and veinlets containing native gold are associated with this zone. Research revealed that the sulfur isotope composition in sulfides from this zone (δ³⁴S ~ –15 ‰) is significantly lighter compared to that in molybdenite from the central part of the granitoid massif (δ³⁴S ~ 5 ‰). In addition, (U,Th)-He dating of idiomorphic pyrite crystals, extracted from hydrothermally altered trachytes near a large quartz vein, gave an age of 65 ± 2 Ma (n = 4). The obtained data, combined with geological observations, point to the Early Paleogene tectonic-thermal activity in the region, which has led to the redistribution of ore components.

Prospecting efforts to located Au mineralization within the Altai-Sayan fold area (ASFA) over previous decades have revealed that Devonian epithermal Au-Ag mineralization is more widespread than previously recognized. The preservation of this type of mineralization in Paleozoic rocks offers new prospects for the exploration of Au-Ag deposits in the underexplored region of Gornaya Shoria. The Kalarskoe epithermal Au-Ag occurrence represents Devonian epithermal mineralization within the Kaburchak cluster, Gornaya Shoria, Russia. This occurrence is confined to zones of argillic alteration that were superimposed on previously formed propylites. The argillic-altered rocks host quartz-sulfide veinlet zones. The mineralization of the Kalarskoe site is characterized by a high abundance of sulfide minerals: commonly, 5%–10%; often, up to 20%; and in some cases, up to 60%–70%. The ore minerals are represented by pyrite, arsenopyrite, sphalerite, galena, chalcopyrite, fahlores, native Au, and electrum, as well as by the sulfosalts Pb, Bi, Ag, Cu, and the tellurides of Au, Ag, and Pb. Based on mineralogical observations, at least four generations of sulfide mineral formations are distinguished within the ore occurrence. The mineralization of the Kalarskoe ore occurrence may be assigned to the intermediate sulfidation (IS) type. The results of the (U,Th)-He dating of pyrite from the pyrite-arsenopyrite massive body (pyr-3 and 4) revealed the protracted history of the mineralization in the intervals from ~399 to ~371 Ma. The obtained results substantially enhance the prospecting models for the exploration of epithermal Au-Ag deposits in the western part of the Altai-Sayan fold area (ASFA).

We propose a new analytical approach for (U-Th)/He dating of Fe-hydroxides, that includes sealing samples in quartz ampoules and demonstrates its suitability as a reliable tool for the investigation of geological processes. The (U-Th)/He ages of goethite clasts and vein from Fe- and Mn-oxide mineralization rocks recovered from the slope of Chukchi Borderland in the Amerasia Basin demonstrate remarkable reproducibility, yielding a weighted mean age of 8.6 ± 0.3 Ma (n=4) and 4.8 ± 0.4 Ma (n=2), respectively, providing insights into the Neogene mineralization history of the region. This study also focuses on the sample preparation technique, that might influence the (U-Th)/He ages. Our data indicate that a significant fraction of U can be leached from the goethite during sonication by distilled water which might result in over-dispersed (U-Th)/He ages.

We propose a new analytical approach for (U-Th)/He dating of Fe-hydroxides, that includes sealing samples in quartz ampoules and demonstrates its suitability as a reliable tool for the investigation of geological processes. The (U-Th)/He ages of goethite clasts and vein from Fe- and Mn-oxide mineralization rocks recovered from the slope of Chukchi Borderland in the Amerasia Basin demonstrate remarkable reproducibility, yielding a weighted mean age of 8.6 ± 0.3 Ma (n=4) and 4.8 ± 0.4 Ma (n=2), respectively, providing insights into the Neogene mineralization history of the region. This study also focuses on the sample preparation technique, that might influence the (U-Th)/He ages. Our data indicate that a significant fraction of U can be leached from the goethite during sonication by distilled water which might result in over-dispersed (U-Th)/He ages.

We propose a new analytical approach for (U-Th)/He dating of Fe-hydroxides, that includes sealing samples in quartz ampoules and demonstrates its suitability as a reliable tool for the investigation of geological processes. The (U-Th)/He ages of goethite clasts and vein from Fe- and Mn-oxide mineralization rocks recovered from the slope of Chukchi Borderland in the Amerasia Basin demonstrate remarkable reproducibility, yielding a weighted mean age of 8.6 ± 0.3 Ma (n=4) and 4.8 ± 0.4 Ma (n=2), respectively, providing insights into the Neogene mineralization history of the region. This study also focuses on the sample preparation technique, that might influence the (U-Th)/He ages. Our data indicate that a significant fraction of U can be leached from the goethite during sonication by distilled water which might result in over-dispersed (U-Th)/He ages.

We propose a new analytical approach for (U-Th)/He dating of Fe-hydroxides, that includes sealing samples in quartz ampoules and demonstrates its suitability as a reliable tool for the investigation of geological processes. The (U-Th)/He ages of goethite clasts and vein from Fe- and Mn-oxide mineralization rocks recovered from the slope of Chukchi Borderland in the Amerasia Basin demonstrate remarkable reproducibility, yielding a weighted mean age of 8.6 ± 0.3 Ma (n=4) and 4.8 ± 0.4 Ma (n=2), respectively, providing insights into the Neogene mineralization history of the region. This study also focuses on the sample preparation technique, that might influence the (U-Th)/He ages. Our data indicate that a significant fraction of U can be leached from the goethite during sonication by distilled water which might result in over-dispersed (U-Th)/He ages.