Geochemical peculiarities of ores from the largest Natalka gold deposit in Northeastern Russia

This study of the behavior of trace and rare earth elements in ores from the Natalka gold deposit allows us to draw several conclusions. It is suggested that ore formation is related to the regional metamorphism of the host terrigenous carbonaceous rocks, which could be the major source for trace and rare earth elements. Minor enrichment of the Natalka ores in W is evidence of the contribution of magmatic fluid, which could be superimposed on early quartz veins, in ore formation. Our results support the metamorphic–magmatic model of formation of economic gold–quartz deposits of the Yana–Kolyma Belt. The similarity of metasomatites of the Natalka deposit with disseminated gold–sulfide refractory ores from the Nezhdaninskoe and Bakyrchik deposits points to the possible presence of such ores in the Natalka deposit. Our data are important for forecasting regional metallogenic reconstructions, search, and evaluation of gold deposits.     

Tectono-metallogenic settings of the formation and convergence of disseminated Au–sulfide mineralization

Large Au-sulfide deposits (GSDs) of disseminated ores occur worldwide in metallogenic provinces of various ages (from Precambrian to Pliocene). The studies performed showed that the great genetic diversity of GSD is determined by the similar oregenesis conditions that appear in different tectono-metallogenic settings (TMSs). A GSD is included in a certain TMS by the respective changes in the mineral and geochemical assemblages of ores. However, in the majority of cases, the GSDs of different TMSs are convergent (quasi-identical) in the texture, structure, and mineral composition of ores. All types of the above TMSs are found in Russia, which allows forecasting the discovery of new GSDs in each setting.     

Formation conditions of high-grade gold–silver ore of epithermal Tikhoe deposit,Russian Northeast

The Tikhoe epithermal deposit is located in the Okhotsk–Chukotka volcanic belt (OChVB) 250 km northeast of Magadan. Like other deposits belonging to the Ivan’insky volcanic–plutonic depression (VTD), the Tikhoe deposit is characterized by high-grade Au–Ag ore with an average Au grade of 23.13 gpt Au and Au/Ag ratio varying from 1: 1 to 1: 10. The detailed explored Tikhoe-1 orebody is accompanied by a thick (20 m) aureole of argillic alteration. Pyrite is predominant among ore minerals; galena, arsenopyrite, sphalerite, Ag sulfosalts, fahlore, electrum, and küstelite are less abundant. The ore is characterized by abundant Sebearing minerals. Cu–As geochemical specialization is noted for silver minerals. Elevated Se and Fe molar fractions of the main ore minerals are caused by their formation in the near-surface argillic alteration zone. The veins and veinlets of the Tikhoe-1 ore zone formed stepwise at a temperature of 230 to 105°C from Nachloride solution enriched in Mg and Ca cations with increasing salinity. The parameters of the ore-forming fluid correspond to those of epithermal low-sulfidation deposits and assume the formation of high-grade ore under a screening unit of volcanic rocks. In general, the composition of the ore-forming fluid fits the mineralogy and geochemistry of ore at this deposit. The similarity of the ore composition and parameters of the ore-forming fluid between the Tikhoe and Julietta deposits is noteworthy. Meanwhile, differences are mainly related to the lower temperature and fluid salinity at the Julietta deposit with respect to the Tikhoe deposit. The fluid at the Julietta deposit is depleted in most components compared with that at the Tikhoe deposit except for Sb, Cd, and Ag. The results testify to a different erosion level at the deposits as derivatives of the same ore-forming system. The large scale of the latter allows us to predict the discovery of new high-grade objects, including hidden mineralization, which is not exposed at the ore field flanks and beyond them.     

Detection of the 2020 Geomagnetic Jerk Using near Real-Time Data from the “St. Petersburg” and “Klimovskaya” Magnetic Observatories

Doklady Earth Sciences - Highly accurate observations of the Earth’s total magnetic field vector promptly derived from the data recorded at the “St. Petersburg” (Leningrad oblast)...     

On the Need for Accurate Monitoring of the Geomagnetic Field during Directional Drilling in the Russian Arctic

Izvestiya, Physics of the Solid Earth - Abstract—The readings of well magnetometers used in directional drilling may be distorted by geomagnetic storms and substorms. These distortions occur...     

A New Solid Solution with Garnet Structure: Berzeliite–Schäferite Isomorphic Series from the Fumarole Exhalation of the Tolbachik Volcano,Kamchatka

Geology of Ore Deposits - An extended isostructural solid solution (isomorphic series) between arsenate and vanadate of the garnet supergroup — berzeliite (NaCa2)Mg2(AsO4)3 and...     

Golʼtsovoe Ag–Pb–Zn Deposit (Northeastern Russia): Geological Setting,Mineralogy, Geochemistry,and Ore Formation Conditions

Geology of Ore Deposits - The Gol’tsovoe Ag–Pb–Zn-deposit (1600 t silver in ores with an average grade of 1025 g/t Ag) is located on the southeastern flank of the Dukat mining...     

“Postmineral” basaltoids and ore-bearing hydrothermal mineralizations

Contrasting volcanism (rhyolite-basalt) is typical of volcanogenic ore-bearing zones. At the same time, it has not been considered correct to regard contrasting volcanism as an exploration criterion for such zones, since the basaltoid member of volcanism is frequently postmineral. However, there is sufficient reason to consider subvolcanic bodies of postmineral basaltoids as the latest (terminating) formations of an approaching front of basic magmas, which is the cause of upper crustal granitoid magmatism and hydrothermal anomalies. Naturally enough, all volcanism ceases after the basaltoid effusions, and the hydrothermal systems also gradually disappear. Relicts of these systems are frequently reliably identified as quartz carbonate geodes in basaltic andesite sheets and dikes.     

Distribution and Formation of Mississippi Valley–Type Lead–Zinc Deposits on the Eastern Margin of the Siberian Platform (Results of GIS Analysis of the Global Crust Model)

Doklady Earth Sciences - Recent studies of the lithosphere based on the gravity data from the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) were used for the first time to...     

Three principal types of the Earth’s lithosphere and their metallogenic specialization

It is shown in this paper that, according to the data of Russian and non-Russian specialists, three characteristic “lines” (“polychronic formation arrays”) of metallogeny absolutely correspond to the idea of the existence of three principal types of the Earth’s lithosphere. Two of these types are well known, the “classical” oceanic and continental types; the third, marginal-sea type, with the so-called modified type of mineralization, is still underestimated. In the same time, this type of the lithosphere, usually considered as intermediate or transitional, is nearly the most determinative in the Earth’s evolution both in tectonics (generation of new portions of juvenile continental crust and formation of supercontinents) and in the metallogenic aspects (diverse and high industrial potential of ore occurrences).