Vol 61, No 5 (2019)

ARTICLES
Selenga ore district in Western Transbaikalia: structural and mineragenetic zoning, genetic types of deposits and geodynamic settings of ore localization
Gordienko I.V., Badmatsyrenova R.A., Lantseva V.S., Elbaev A.L.
Abstract

Based on complex structural, geological, and mineragenetic metallogenic studies, taking into account the results of earlier subject-specific, prospecting, mapping, and exploration works, it has been established that Upper Paleozoic and Early Mesozoic tectono-magmatic structures are widely developed within the ore district. They are associated with the development of the transregional Upper Paleozoic Selenga-Vitim volcano-plutonic belt of riftogenic type as well as with the formation of the Early Mesozoic Western Transbaikalian zone of intraplate magmatism. The main commercially important mineral raw material resources of the Selenga ore district which are located in the ore clusters (the Kunaley, Kizhinga, Cheremshanka-Oshurkovo, Tashir et al.) and beyond their bounds are associated with the Late Paleozoic-Mesozoic magmatic activity. It is shown that molybdenum and beryllium are the main ore mineral resources within the investigated ore district which establish its mineragenetic features. The new material characteristics of the Upper Paleozoic and Early Mesozoic intraplate magmatic complexes and the associated deposits of mineral raw materials (Mo, Be, Ti, quartz, fluorite and apatite raw materials) and other promising ore objects of gold, uranium and rare-earth-barium-strontium mineralization are obtained. The geodynamic conditions of their formation and the main age boundaries of the ore-forming processes are revealed, the prospects of mining in the Selenga ore district and the involvement of this ore potential in the program of the region’s economic modernization are estimated.

Геология рудных месторождений. 2019;61(5):3-36
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“Invisible” gold in synthetic and natural arsenopyrite crystals (Vorontsovka deposit, Northern Urals)
Kovalchuk E.V., Tagirov B.R., Vikentyev I.V., Chareev D.A., Tyukova E.E., Nickolsky M.S., Borisovsky S.E., Bortnikov N.S.
Abstract

In many types of hydrothermal ore deposits Au occurs in “invisible” state in most common minerals of the Fe-As-S system. It is supposed that the state of the “invisible” Au may be either non-structural (nano-sized inclusions of metal and its compounds) or chemically bound (isomorphous solid solution). Here we report results of investigation of the state and the concentration range of “invisible” Au in synthetic and natural arsenopyrites FeAsS (Vorontsovka deposit, North Urals, type Carlin). Conditions that favor the formation of Au-bearing arsenopyrite were identified. The synthesis experiments were carried out in Au-saturated system by means of salt flux method with a stationary temperature gradient. The temperature at the cold end of the ampole was 400–500 °С. The chemical composition of arsenopyrite was determined by electron probe microanalysis. The composition of the synthesized arsenopyrite varied within [at.%]: Fe from 32.6 to 34.4, As from 30.0 to 36.5, S from 29.4 to 36.0. The Au content in arsenopyrite varied from the detection limit (< 45 ppm) to 3 wt.%. A strong negative correlation between the concentrations of Au and Fe was observed in the synthesized arsenopyrite grains. The slope of the correlation lines corresponds to the formation of the Au-bearing solid solution where Au isomorphically substitutes for Fe at the parameters of the synthesis experiments. In addition, there is a weaker positive correlation between Au and As: higher Au concentrations are characteristic of arsenic-rich compositions (As/S [at.%] > 1) and those close to stoichiometric arsenopyrite, whereas in sulfur-rich arsenopyrite the concentration of Au is lower and does not exceed 0.25 wt.%. The positive Au-As correlation appears not only on a local level within a single crystal of synthetic and natural arsenopyrite, but is valid on the Vorontsovka deposit scale: As-rich arsenopyrite formed at lower temperature and sulfur fugacity (t = 250–370 °C, log f S2 = –12 ÷ –17) contains more Au than the As-poor early arsenopyrite (t = 270–400 °C, log f S2 = –7 ÷ –9). Comparison of these results with the literature data shows that the positive correlation between the concentrations of Au and As in arsenopyrite and the negative correlation between the concentrations of Au and Fe are the common features of ores of the Carlin-type deposits. We suggest that, in contrast to negative correlation Au-Fe, the positive correlation Au-As cannot be explained in terms of crystal chemistry, but can result from the effect of external factors among which are the difference in composition of ore-forming hydrothermal fluids and the sulfur fugacity.

Геология рудных месторождений. 2019;61(5):62-83
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Age, composition and sources of rocks and ores of the Okunevskoe fluorite-leucophanite deposit, Western Sayan: assessment of the contribution of magmatism to ore mineralization
Lykhin D.A., Yarmolyuk V.V., Vorontsov A.A.
Abstract

The paper presents data on the structure of the Okunevskoe fluorite-Leucophanite deposit, located within the Early Paleozoic rare-metal East Sayan rare metal metallogenic zone. The deposit is controlled by alkali granitoids, with ore mineralization concentrated at the contact of granitoids and host carbonates. It is represented by leucophanite-fluorite and pyroxene-fluorite ore types. The Ar-Ar age of granitoids is established at ~485 Ma. Geochemical characteristics of igneous rocks, ores, and host carbonates are determined. It is shown that in geochemical parameters leucophanite-fluorite ores are close to alkaline granites, while pyroxene-fluorite ores are close to alkaline syenites. The characteristics of the Nd isotop composition in rocks and ores of the deposit are given. Igneous rocks (granitoids and basite dikes) are characterized by åNd (t) values from +4 to +5.5. The åNd (t) values in ores range from +1.2 to +4.2, in skarns it is +4.8. The host carbonates have abruptly contrasting values åNd (t) = –4.2. Based on these data, which demonstrate a high compositional similarity between granitoids and ores, a conclusion is drawn about the leading contribution from magmatic processes to the ore mineralization of the Okunevskoe deposit.

Геология рудных месторождений. 2019;61(5):37-61
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Akkalkan deposit of bentonite clays (Southeast Kazakhstan): formation conditions and prospects for technological use
Nasedkin V.V., Boeva N.M., Vasiliev A.L.
Abstract

The article presents the results of the bentonite clays study of Akkolkanskoye deposit, located in South-Eastern Kazakhstan. Based on the mapping, four main types of bentonites were identified: light gray argillite-like clay; dark gray clay lamellar and crushed stone morphology; waxy light brown and pale yellow clay lamellar texture; black plastic clay. Mineralogical study of these varieties allowed to establish the relationship of crystal-morphological features of the main rock-forming mineral in clays with the conditions of their formation and with the technological properties of bentonite raw materials for use in various industries.

Геология рудных месторождений. 2019;61(5):84-95
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Geology of Chernogorskoe gem-quality skapolite deposit (Central Pamirs, Tajikistan)
Litvinenko A.K., Moiseeva S.B., Odinaev S.A., Utenkov V.A.
Abstract

The Montenegrin jewel scapolite deposit, which relates to a new genetic type, is characterized. It is located in the Central Pamirs (Tajikistan) and is localized in the sarydzhilginsk formation of the muzkol series (PR1). The enclosing rocks are metamorphosed basite-ultrabasic formations of the kukurt complex, among which harzburgites were first discovered.

Jewel scapolite mineralization contains albitite lenses. They were formed by the metasomatic replacement of nepheline syenites. The reaction occurred with a negative volume effect with a decrease in the volume of solid phases 14%, which caused the appearance of voids. Albitite bodies form a lenticular nesting structure. They have cross-cutting contacts. They are accommodated by amphibolites, which metasomatically replace melanocratic gabbroids and partially altered harzburgites. Jewelry scapolite is localized in 28 albitite lenses, the walls of the voids of which are inlaid with columnar purple scapolite. The sequence of processes at the field corresponds to the following scheme: formation of melanocratic gabbroids with small bodies of nepheline syenites → metasomatic development in the first amphibolites, and in the second – albitites with voids → growth on the walls of the hollows of the hollow scapolite → crystallization in the voids of the jewelry scapolite.

Геология рудных месторождений. 2019;61(5):96-108
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