Vol 61, No 6 (2019)

ARTICLES
Gold deposits in the Earth's history
Goryachev N.A.
Abstract

The distribution of the main gold deposits in the history of the Earth is considered. Primary heterogeneity of the Archean crust by gold bearing is shown. The main gold ore metallogenic epochs are characterized. Links of gold deposits with VMS and Cu-Ni in the early periods of the Earth (Archaean-Proterozoic) and, in addition, with deposits of W, Mo, Cu, Sb, Hg and Sn in the Phanerozoic are shown. An analysis of the distribution of mineralogical and geochemical types of the actual Au mineralization also showed significant diversity for the Phanerozoic compared with Precambrian. These data reflect the mantle-crustal origin of Au mineralization as a whole and indicates an increase in the contribution of the crust matter to the balance of Au mineralization with the age of the Earth. The well-known interruption in the formation of Au deposits (1.7–0.8 billion years) was discussed, which was caused by the stable craton regime of the long-existing Columbia (Nuna) – Rodinia supercontinent.

Геология рудных месторождений. 2019;61(6):3-18
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Global metallogeny of tantalum through geological time
Tkachev A.V., Rundqvist D.V., Vishnevskaya N.A.
Abstract

The distribution of tantalum-bearing mineral deposits and their tantalum resources are analyzed on the geological time scale. The sampling list includes 65 mineral deposits with their individual resource estimations above two thousand tonnes of Ta2О5. The used classification of the deposits includes five types: pegmatitic, granitic, alkaligranitic, foidic, and carbonatitic ones. Placers and ore-bearing weathering crusts are considered together with their endogenous hard ore sources. The geohistorical variability in tantalum metallogeny is presented through a comparison of supercontinent cycles. The Rodinian cycle gives the most significant amount of the resources with the lion’s share concentrated in exceptionally voluminous deposits of the foidic type. In descending order, it is followed by the Pangean and Columbian cycles, with the alkaligranitic and foidic types dominating in their resources. The Kenoran cycle, which is next in our resource ranging, stands out for its monotypic presentation, because only pegmatite tantalum deposits were generated in it. The current Amasian cycle has the smallest resource amount which is accounted for by the cycle’s incompleteness. The Amasian-aged resources are distributed between the alkaligranitic, granitic, and pegmatitic deposit types more or less evenly. In general, the pegmatitic and granitic types resources are of primary importance for tantalum extraction due to their mineralogical peculiarities. The pegmatitic type tantalum deposits were generated in all the cycles, while the granitic type objects were formed in the Pangean and Amasian cycles only. The most considerable resources concentrated in these two deposit types belong to the Kenoran and Pangean cycles.

Геология рудных месторождений. 2019;61(6):19-37
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Coupled dissolution–precipitation reactions of tennantite-tetrahedrite minerals in the Darasun gold deposit (Eastern Transbaikalia, Russia)
Lyubimtseva N.G., Bortnikov N.S., Borisovsky S.E., Vikent’eva O.V., Prokofiev V.Y.
Abstract

Heterogeneous rhythmic-zonal aggregates of tennantite-IV replaced partly or completely early homogeneous Zn-tetrahedrite-I and euhedral (Fe-Zn)-tennantite-I crystal were found in ores of the Darasun gold deposit. Different replacement stages of fahlore were observed. It initiates at grain boundaries and is terminated by a complete transformation into pseudomorphic newly formed (Zn-Fe)-tennantite-IV aggregates rimed with Zn-tetrahedrite-IV. These aggregates associated intimately with bournonite and galena and their deposition initiated the pseudomorph formation. EMPA revealed that (Fe-Zn)-tetrahedrite richer in As relative to Zn-tetrahedrite-I was deposited at initial stage. Tennantite with wide variation in Sb/(Sb + As) and Fe/(Fe + Zn) ratios predominantes in heterogenous zonal aggregates of (Fe-Zn)-tetrahedrite-tennantite-IV. A negative correlation between the Sb/(Sb + As) and Fe/(Fe + Zn) was found in these minerals. In each site at the contact between Zn-tetrahedrite-I and newly formed (Fe-Zn)-tetrahedrite-tennantite-IV a miscibility gap between As and Sb a sharp drop in the Sb/(Sb + As) ratio and an increase in Fe/(Fe + Zn) ratio occur. Sharp saw-shape boundaries between Zn-tetrahedrite-I and tennantite-IV and voids in newly formed aggregates are considered to be evidence for couple dissolution-precipitation reactions. The dissolution was initiated due disequilibrium between Zn-tetrahedrite-I and an undersaturated fluid resulted from deposition of galena and bournonite. Precipitation of tetrahedrite-tennantite-IV occurred under oscillation in Sb/(Sb + As) and Fe/(Fe + Zn) ratios due to the metal and semimetal contents in the fluid. Crystallization temperature of zonal-heterogenous tennantite-IV aggregates was calculated by sphalerite-fahlore geothermometer which shows (134–161) ± 20 °С. Instability of early Zn-tetrahedrite-I resulted from fluid cooling, decreasing in fluid salinity, changing in tetrahedrite and tennantite solubility due to an evolution of migration conditions of semimetals.

Геология рудных месторождений. 2019;61(6):38-57
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A new model of a unique Schlema-Alberoda five-element deposit, Federal Republic of Germany
Naumov G.B., Vlasov B.P., Mironova O.F.
Abstract

This article concludes a series of works detailed the data on the Schlema-Alberoda unique deposit in order of sources of ore and gangue minerals, their association with retrograde metamorphism of rocks from the contact metamorphism zone. The relationship of stages of mineral formation is presents, as well as, their directed replacement. A general scheme of formation stages of hydrothermal ores is given, which results the joint analysis of geological and geochemical evolution of potentially ore-bearing provinces.

Геология рудных месторождений. 2019;61(6):58-66
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Scheelite of the Bystrinsky skarn-porphyry Cu-Au-Fe deposit (Eastern Transbaikalia, Russia): genetic implications
Kovalenker V.A., Plotinskaya O.Y., Kiseleva G.D., Minervina E.A., Borisovskii S.E., Zhilicheva O.M., Yazykova Y.I.
Abstract

The first results of the study (methods of mineragraphy, cathodoluminescence (CL), electron-probe microanalysis (EPMA) and laser-ablation inductively-coupled plasma-mass spectrometry (LA-ICPMS)) of scheelite from quartz-molybdenite and quartz-carbonate-sulfide vein-veinlet (porphyry type) are considered, as well as the magnetite-sulfide massive, veinlets and disseminated (skarn type) mineralization of the skarn-porphyry Cu-Au-Fe deposit of Bystrinskoye (East Transbaikalia) – one of the largest gold-copper porphyry ore-fields in Russia. It has been established that scheelite, being not the main mineral of the deposit ores, is found almost everywhere, which makes it possible to identify its key features reflecting the specific features of the genesis, both of different types of mineralization and the deposit as a whole. It is shown that scheelite from different types of ore mineralization has clearly determined individual characteristics, differing in prevalence, ensembles of associated minerals, color of CL and fluorescence in the UV-light, composition and concentrations of macro- and microelements, as well as the nature of REE-spectra. These distinctive features testify to a significant difference in the conditions for the formation of the studied ore types and reveal the dependence on the physicochemical and compositional parameters of the mineral-forming medium, which makes it possible to consider scheelite as a fundamentally important genetic indicator of the evolution of mineral formation patterns. Concentrations of Mo in scheelite, the type and form of REE-spectra, which are generally, determined both by the inheritance of the mineral-forming fluid chemistry and the peculiarities of isomorphic occurrence of REE in the structure of the mineral, and variations in the redox properties of the mineral-forming fluid, are of key importance.

Геология рудных месторождений. 2019;61(6):67-88
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