Low-sulfide Gold-quartz Research Articles

Age and Sources of Low-Sulfide Gold–Quartz Mineralization of the Karalon Ore Field, North Transbaikalia, Russia: Results of Isotopic–Geochemical (Rb–Sr and Pb–Pb) Studies

Age and Sources of Low-Sulfide Gold–Quartz Mineralization of the Karalon Ore Field, North Transbaikalia, Russia: Results of Isotopic–Geochemical (Rb–Sr and Pb–Pb) Studies

Трансформации геофизических полей и геолого-геофизические признаки золото-кварцевого оруденения на примере Средне-Урканской перспективной площади (Амурская область)

In this paper, the results of the analysis of geophysical fields and their transformants (statistical, filtration) of gold mineralization areas are presented and some of their features are established. A set of geophysical studies and methodological processing techniques that can solve the problems of forecasting gold mineralization are presented. Based on the interpretation of a set of geophysical data and available geological materials, prospecting geological and geophysical signs of raremetal low-sulfide gold-quartz mineralization in the hierarchical sequence ore field - ore zone are offered.

TECHNOLOGY FOR PROCESSING LOW-SULFIDE GOLD-QUARTZ ORE

Link for citation: Fedotov P.K., Senchenko A.E., Fedotov K.V., Burdonov A.E., Vlasova V.V. Technology for processing low-sulfide gold-quartz ore. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2022, vol. 333, no. 6, рр.178-189. In Rus.
 The relevance of the research is caused by the necessity to acquire new knowledge about the enrichment of gold-bearing ores and the need to develop the resource base of the Russian Federation, namely involve subsoil use objects in economic circulation. The purpose of the study is to study the processing of low-sulfide gold-quartz ore using an integrated technology for the enrichment of mineral raw materials. Object: gold ore raw materials with an average gold grade of 11,88 g/t. The silver content is negligible – 2,43 g/t. The main ore minerals in the sample are pyrite and pyrrhotite. The average content of these minerals in the ore, according to mineralogical and X-ray diffraction analysis, was about 6 % (in total). The main rock-forming minerals of the original ore are: quartz – 60,1 %; quartz-chlorite-mica aggregates – 3,8 %; carbonates – 7,1 %. Methods. The research methodology was based on the theoretical foundations of mineral processing. The study of the material composition of the ore, and enrichment products, was carried out using chemical, assay, thermal, spectrometric methods, as well as atomic emission spectrometry and other methods. The study of washability was carried out by the methods of gravity and flotation enrichment, namely: GRG test, stage test of the Institute TOMS (Russia) (determination of the optimal size of ore grinding and the number of enrichment stages), modeling of gold extraction in the grinding cycle, determination of the optimal degree of grinding, study of the choice of flotation reagents, study of the kinetics of the process and the implementation of a complex of technological studies. Results. It was found that the gold recovery when performing the GRG test was 72,75 % with a total concentrate yield of 1,34 % and a content of Au 664,78 g/t. At the same time, the gold content in the tailings was 3,29 g/t. A stage test showed that for ore processing only by gravity technology, it is advisable to use a two-stage scheme. The first stage is in the grinding cycle with the ore size of 60–70 % and the second stage – with the final size of the discharge of the classification 90 % size of –0,071 mm. Centrifugal separation, as a free gold recovery operation in a grinding cycle, works efficiently. A concentrate with a gold content of 2426 g/t was obtained with an output of 0,31 % and an extraction of 63,74 %. The enrichment of the first stage tailings crushed to 90 % size of –0,071 mm at the KC-CVD concentrator (modeling) made it possible to extract gold into a total gravity concentrate (KC-MD+KC-CVD) of 87,25 % with a concentrate yield of 22,63 %. The gold content in the tailings was 1,97 g/t. The results of gravity and flotation concentration of the original ore indicate the feasibility of using a combined gravity-flotation technological scheme. In a closed experiment of the initial ore beneficiation according to the gravity-flotation scheme at a natural pH of the pulp (without adding acid), the following products were obtained: gravity concentrate with a gold content of 2426 g/t at a yield of 0,31 % and an extraction of 64,06 %; flotation concentrate (after the II cleaning) with a gold content of 122 g/t with a yield of 2,90 % and recovery of 33,01 %; the total gold recovery in the gravity-flotation concentrate was 94,07 % with a yield of 3,21 % and Au content of 345,87 g/t, the gold content in the flotation tailings was 0,72 g/t.

Коренное золотопроявление на «Территории» Олега Куваева (север Чукотского нагорья)

A sample of a gold-bearing quartz vein from the Upper-Ichuveem ore occurrence, discovered in the Triassic terrigenous complex in the north of the Chukotka Upland, the Oleg Kuvaev's “Territory”, had been comprehensively studied. The gross gold grade was estimated at 3–4 g / t. The vein includes quartz, native gold, sulfide-goldsilver solid solutions, alumoseladonite, aluminium-sulfate-phosphates Fe-Pb-Mg-Ca compound, apatite, pyrite, iron-titanium oxides, litharge, native phases composed of Fe (Ni), Ag-Pb-Bi, Fe-Al-PS-As, multicomponent ocher of hypergene origin. Native gold ranges from medium to fine. The vein contains particles of non-crystalline organic matter, which is close in composition of organic groups to polysaccharides. It is possible that the carbon particles found in the gold-quartz vein are of an abiogenic nature and can be compared with abiogenic condensed organelles in the products of modern volcanism. The data obtained make it possible to attribute the Upper- Ichuveem gold ore occurrence to a low-sulfide gold-quartz formation, but with additional signs of gold-silver and polymetallic formations, which can be regarded as a favorable prerequisite for prospecting and exploration in Oleg Kuvaev's «Territory» not only of gold-placer deposits, but also of lode gold deposits.

Geological-structural control and criteria of forecasting the types of primary sources of placer gold on the East of Siberian platform

Identification of indicators on placer gold allowed predicting formation types of primary sources of gold and their location in the East Siberian platform, overlapped by thick cover of Meso-Cenozoic deposits, where traditional methods of prospecting of gold deposits are ineffective. Each gold-ore formation is known to have the corresponding geological-structural control. Based on study of mineralogical-geochemical features of placer gold and regularity of its distribution, it has been determined that primary sources of low-sulfide gold-quartz, gold-copper-porphyritic, gold-ferruginous-quartzite, gold—rare-metal and gold-platinoid formations are confined to basement outcrops and their framings; gold-sulfide-quartz formation — to metasomatites, developed within the zones of deep faults, tracing the terrigenous-carbonate series; and manifestations of gold-silver formation are localized in the zones of intracontinental paleorifts. In general, identification of geological-structural location of specific types of gold sources favors more correct selection of prospecting methods for gold deposits in areas with thick sedimentary cover, and evaluating their potential.

Indicative features of placer gold for the prediction of the formation types of gold deposits (east of the Siberian Platform)

Prediction and search for gold deposits in the east of the Siberian Platform are problematic because the study area is overlain by a thick cover of MZ-KZ deposits. Search for gold deposits by the largest geological institutions using conventional methods have not yielded positive results, because the main attention was focused on the discovery of ancient gold-bearing conglomerates of the Witwatersrand type and on the evaluation of the gold ore potential of basic magmatism. Typomorphism of placer gold bears huge information about the genesis of native gold, both its primary endogenous origin and its exogenous transformation, which makes it possible to identify the formation type of mineralization, increases the reliability of the prediction of gold deposits, and ensures their purposeful search in the platform areas. The revealed indicative features of placer gold made it possible to substantiate the formation of the gold ore sources of Precambrian low-sulfide gold-quartz, gold-iron-quartzite, porphyry gold-copper, and gold-PGE mineralization and Mesozoic gold-silver, gold-rare-metal, and gold-sulfide-quartz mineralization in the east of the Siberian Platform. We have established that high-fineness placer gold with microinclusions of pyrite, arsenopyrite, quartz, and carbonates with recrystallized structures and lines of plastic deformation is specific to the ore sources of low-sulfide gold-quartz mineralization. A high content of Cu (up to 4%) in flaky high-fineness gold is one of indicators of porphyry gold-copper mineralization. The angular shape of gold grains, the fine fraction and high fineness of gold, its completely recrystallized and regrown internal structure, and the permanent presence of Fe, Bi, and Cu microimpurities and hematite, ilmenite, and corundum microinclusions are typical of gold-iron-quartzite mineralization. Flaky and laminated high-fineness gold particles with steady Pt, Pd, and Ni impurities and Pt-mineral phases and Au-Pt intergrowths in them testify to the ore sources of gold-PGE mineralization. Laminated and cloddy gold fractions of >0.25-2.0 mm, the medium and low fineness of gold, its single-crystal or, sometimes, porous internal structure, the wide range of microimpurities (Pb, Zn, As, Sb, Cu, Te, etc.), and microinclusions of native Ag, adularia, Sr-barite, and calcite are indicators of gold-silver mineralization. Laminated, dendritic, and cloddy-angular gold grains, wide variation in gold fineness (307-950‰), and the presence of microinclusions of native bismuth, maldonite, arsenopyrite, and silver tellurides are indicative of gold-rare-metal mineralization. Laminated and cloddy gold grains, their size varying from dust to >0.25 mm, their mono- and coarse-grained internal structure, wide variation in gold fineness (600-900‰), and the presence of Hg microimpurities (up to 6% and more) and microinclusions of quartz, calcite, pyrite, arsenopyrite, tellurides, selenides, and REE phosphates point to gold-sulfide-quartz mineralization. The established placer gold indicators of the particular formation types of ore sources in the east of the Siberian Platform made it possible to predict Precambrian gold deposits with low-sulfide-gold-quartz mineralization similar to the Kirkland Lake and Porcupine mines and gold deposits with Mesozoic gold-silver mineralization similar to the Cripple Creek mine. The developed criteria for determining the types of mineralization by indicative features of placer gold give an insight into the ore genesis and can be successfully applied to prediction and search for gold deposits and to evaluation of their gold resources.

Ore-bearing fluids of the Eldorado gold deposit (Yenisei Ridge, Russia)

The Eldorado low-sulfide gold-quartz deposit, with gold reserves of more than 60 tons, is located in the damage zone of the Ishimba Fault in the Yenisei Ridge and is hosted by Riphean epidote-amphibolite metamorphic rocks (Sukhoi Pit Group). Orebodies occur in four roughly parallel heavily fractured zones where rocks were subject to metamorphism under stress and heat impacts. They consist of sulfide-bearing schists with veins of gray or milky-white quartz varieties. Gray quartz predominating in gold-bearing orebodies contains graphite and amorphous carbon identified by Raman spectroscopy; the contents of gold and amorphous carbon are in positive correlation. As inferred from thermobarometry, gas chromatography, gas chromatography-mass spectrometry, and Raman spectroscopy of fluid inclusions in sulfides, carbonates, and gray and white quartz, gold mineralization formed under the effect of reduced H2O-CO2-HC fluids with temperatures of 180 to 490 °C, salinity of 9 to 22 wt.% NaCl equiv, and pressures of 0.1 to 2.3 kbar. Judging by the presence of 11% mantle helium (3He) in fluid inclusions from quartz and the sulfur isotope composition (7.1-17.4‰ δ34S) of sulfides, ore-bearing fluids ascended from a mantle source along shear zones, where they “boiled”. While the fluids were ascending, the metalliferous S- and N-bearing hydrocarbon (HC) compounds they carried broke down to produce crystalline sulfides, gold, and disseminated graphite and amorphous carbon (the latter imparts the gray color to quartz). Barren veins of milky-white quartz formed from oxidized mainly aqueous fluids with a salinity of <15 wt.% NaCl equiv at 150-350 °C. Chloride brines (>30 wt.% NaCl equiv) at 150-260 °C impregnated the gold-bearing quartz veins and produced the lower strata of the hydrothermal-granitoid section. The gold mineralization (795-710 Ma) was roughly coeval to local high-temperature stress metamorphism (836-745 Ma) and intrusion of the Kalama multiphase complex (880-752 Ma).

ISOTOPE-GEOCHEMICAL AND GEOLOGICAL-GENETIC CRITERIA FOR SEARCH OF URAN AND GOLD DEPOSITS OF THE INGUL MEGABLOCK OF THE UKRAINIAN SHIELD

The system of isotope-geochemical criteria of forecasting and prospecting for the Early Proterozoic deposits of albitite (sodium-carbonate) and low-sulfide gold-quartz (with telluride's) ore formations was elaborated for the first time. The first is represented by Severinovsky, Michurinsky, Yuryevsky, Vatutinsky and Novokonstantinovsky deposits of uranium, the second – by the East-Yuryevsky gold deposit. The basis of isotope-geochemical criteria (regional and local) is laid, given in the development of geo-genetic features of mineralization. Regional features equally characterize the deposits of both formations, to which we can refer the geological factors of ore control for the entire Ingul block. Local criteria characterize individual ore zones or even ore bodies; their isolation requires a detailed study of ore matter and is therefore given separately for gold and uranium ores.Key words: isotopic and geochemical criteria, albitite formation, little sulphide gold-quartz formation, Ingul megablock, Ukrainian Shield.

Сульфидная минерализация, самородное золото и его геохимические связи в рифейских отложениях Авзянского рудного района (Южный Урал)

In the Avzyan ore-bearing region the sulfides from the low-sulfide gold-quartz deposits (Ulyuk-Bar, Kurgashly) are characterized by higher concentrations of As, Co, Ni, Cu, Pb in comparison with sulfides from sediments outside of ore-bearing zones. The gold is associated with As and sometimes - with S and Co. Gold-bearing sulfides are situated mostly in sandstones, where they were formed as a result of replacement of early formed ore-free pyrites by arsenopyrite and its association with arsenic pyrite during fluid movement ( Т = 250-450°С, Р = 26-360 bar) through fault zones. This process is fixed in the zonal distribution of arsenic pyrite and in varying behavior of total As in rocks. The proportion of p-type conduction pyrite increases with the depth, and zones of its development and high content of As in rocks are controlled by faults. The strong positive correlation of Au with S, Cu, Co, Pb, Ni, Zn is marked at the gold-sulfide (Bogryashka) and gold-sulfide-quartz (Gorny Priisk) occurrences. The connection of Au with As is not clear. At the Bogryashka occurrence pyrites are characterized by high concentrations of Sb, at the Vostochno-Aktashskoe occurrence - by Co and V. The gold in the Gorny Priisk ore deposit and in the Bogryashka occurrence is characterized by high ratio Au/Ag (>21) and impurity of Bi (0.4-1.2 wt %). The ratio Au/Ag is 5-8 in the gold from the Ulyuk-Bar and the Vostochno-Aktashskoe occurrences. Native gold in the Ulyuk-Bar and the Bogryashka occurences is associated with uranium-thorium minerals.

Porphyry-Style Petropavlovskoe Gold Deposit, the Polar Urals: Geological Position, Mineralogy, and Formation Conditions

Geological and structural conditions of localization, hydrothermal metasomatic alteration, and mineralization of the Petropavlovskoe gold deposit (Novogodnenskoe ore field) situated in the northern part of the Lesser Ural volcanic–plutonic belt, which is a constituent of the Middle Paleozoic island-arc system of the Polar Urals, are discussed. The porphyritic diorite bodies pertaining to the late phase of the intrusive Sob Complex play an ore-controlling role. The large-volume orebodies are related to the upper parts of these intrusions. Two types of stringer–disseminated ores have been revealed: (1) predominant gold-sulfide and (2) superimposed low-sulfide–gold–quartz ore markedly enriched in Au. Taken together, they make up complicated flattened isometric orebodies transitory to linear stockworks. The gold potential of the deposit is controlled by pyrite–(chlorite)–albite metasomatic rock of the main productive stage, which mainly develops in a volcanic–sedimentary sequence especially close to the contacts with porphyritic diorite. The relationships between intrusive and subvolcanic bodies and dating of individual zircon crystals corroborate a multistage evolution of the ore field, which predetermines its complex hydrothermal history. Magmatic activity of mature island-arc plagiogranite of the Sob Complex and monzonite of the Kongor Complex initiated development of skarn and beresite alterations accompanied by crystallization of hydrothermal sulfides. In the Early Devonian, due to emplacement of the Sob Complex at a depth of approximately 2 km, skarn magnetite ore with subordinate sulfides was formed. At the onset of the Middle Devonian, the large-volume gold porphyry Au–Ag–Te–W ± Mo,Cu stockworks related to quartz diorite porphyry—the final phase of the Sob Complex— were formed. In the Late Devonian, a part of sulfide mineralization was redistributed with the formation of linear low-sulfide quartz vein zones. Isotopic geochemical study has shown that the ore is deposited from reduced, substantially magmatic fluid, which is characterized by close to mantle values δ34S = 0 ± 1‰, δ13C =–6 to–7‰, and δ18O = +5‰ as the temperature decreases from 420–300°C (gold–sulfide ore) to 250–130°C (gold–(sulfide)–quartz ore) and pressure decreases from 0.8 to 0.3 kbar. According to the data of microanalysis (EPMA and LA-ICP-MS), the main trace elements in pyrite of gold orebodies are represented by Co (up to 2.52 wt %), As (up to 0.70 wt %), and Ni (up to 0.38 wt %); Te, Se, Ag, Au, Bi, Sb, and Sn also occur. Pyrite of the early assemblages is characterized by high Co, Te, Au, and Bi contents, whereas the late pyrite is distinguished by elevated concentrations of As (up to 0.7 wt %), Ni (up to 0.38 wt %), Se (223 ppm), Ag (up to 111 ppm), and Sn (4.4 ppm). The minimal Au content in pyrite of the late quartz–carbonate assemblage is up to 1.7 ppm and geometric average is 0.3 ppm. The significant correlation between Au and As (furthermore, negative–0.6) in pyrite from ore of the Petropavlovskoe deposit is recorded only for the gold–sulfide assemblage, whereas it is not established for other assemblages. Pyrite with higher As concentration (up to 0.7 wt %) is distinguished only for the Au–Te mineral assemblage. Taking into account structural–morphological and mineralogical–geochemical features, the ore–magmatic system of the Petropavlovskoe deposit is referred to as gold porphyry style. Among the main criteria of such typification are the spatial association of orebodies with bodies of subvolcanic porphyry-like intrusive phases at the roof of large multiphase pluton; the stockwork-like morphology of gold orebodies; 3D character of ore–alteration zoning and distribution of ore components; geochemical association of gold with Ag, W, Mo, Cu, As, Te, and Bi; and predominant finely dispersed submicroscopic gold in ore.

Kysylga gold–silver deposit in the terrigenous sequences of the Verkhoyansk–Kolyma mesozoides

The paper reports the mineralogical and geochemical features of the Kysylga gold deposit located in the hornfelsed Norian sedimentary rocks and classified with low-sulfide gold–quartz type of deposits typical of the Verkhoyansk–Kolyma metallogenic province. Detailed typomorphic study of the major minerals (quartz, arsenopyrite, and gold) of the ore veins shows that the deposit is assigned to the gold–silver type. Mineralogical and geochemical data substantiate this conclusion.

Gold mineralization of the Khaak-Sair gold-quartz ore occurrence in listwanites (western Tuva)

We consider mineral assemblages and mineralogical and geochemical peculiarities of hypogene gold from the Khaak-Sair multistage low-sulfide gold-quartz ore occurrence in listwanites. Three productive substages of Au-and Ag-mineral formation have been recognized on the basis of mineralogical studies: gold-sulfosalt-sulfide-quartz, gold-mercury-quartz, and gold-selenide-telluride-sulfide-quartz. These substages were characterized by the following sequences of mineral formation: (1) ultrahigh-fineness gold → high-fineness gold → argental gold (medium- and low-fineness gold) → electrum + Ag-bearing and argental fahlores (up to 50 wt.% Ag) ± acanthite ± hessite; (2) high-fineness gold → Hg-bearing and mercurian gold → mercurian electrum → mercurian kustelite → Au-bearing mercurian silver; and (3) high-fineness gold → mercurian gold → mercurian electrum + naumannite + Te-bearing naumannite + fischesserite + tiemannite + hessite + coloradoite + Ag-bearing minerals of the galena-clausthalite series (up to 6 wt.% Ag) ± Se-cinnabar ± Se-imiterite. Productive mineral assemblages of the ore occurrence formed in the hypabyssal facies (depth ~1.5 km, P ~0.5 kbar) on the background of a temperature decrease from 290 to 160 °C and variations in f(O2), f(S2), f(Se2), and f(Te2).

Structures, mineralogy, and fluid regime of ore formation in the polygenetic Malo-Taryn gold field, Northeast Russia

Detailed structural study of ore zones and deformations in host rocks reveals the multistage tectonic evolution of the Malo-Taryn ore field. Gold–quartz mineralization is confined to the interstratal and longitudinal thrust faults, where vein–stringer bodies are systematically oriented relative to the structures of the thrust stage. Antimony mineralization is superposed on gold–quartz mineralization in the same structures, being associated with veins formed during the shear stage of deformations. It is determined that the types of mineralization were formed in the following sequence: gold–bismuth, low-sulfide gold–quartz, berthierite–antimonite, and silver–antimony. Data on mineral assemblages and typomorphic features of minerals are reported. The isotope composition of minerals, temperature conditions, and composition of orebearing fluids are studied. It is established that the same minerals ascribed to different types of mineralization sharply differ in typomorphic features, which is caused by the different composition and genesis of the hydrothermal fluids. The superposition of different types of mineralization on one another within repeatedly activated tectonic structures that were fluid-permeable for a long time is an important indication of large-scale deposits.

Sources and fluid regime of quartz-carbonate veins at the Sukhoi Log gold deposit, Baikal-Patom Highland

Complex (δ18O, δ13C, 87Sr/86Sr, 143Nd/144Nd, and REE composition) data were obtained on quartz-carbonate veins in metasedimentary rocks to elucidate the material sources and to evaluate fluid regime during low-sulfide gold-quartz ore mineralization at the Sukhoi Log deposit. In order to use an oxygen isotopic thermometry for quartz veins, we calibrated empirical dependence of fractionation factors between vein quartz and altered wall rocks. The temperature range of quartz equilibration with wall rocks was evaluated at 380–190°C. Independent temperatures obtained using this thermometer indicate that the vein ankerite can be both earlier and later than vein quartz. The isotopic systematics (δ13C and δ18O) of ankerite in the quartz-carbonate veins, carbonates in the ore-hosting shales of the Khomolkho and Imnyakh formations both within and outside mineralized zones at the deposit indicate that the ore-hosting rocks and veins in the mineralized zone contain incoming carbonate, which was most probably borrowed from the carbonate rocks of the Imnyakh Formation. REE composition of vein ankerite shows that these elements were transported by fluid as carbonate complexes. The behavior of the Eu/Eu* and (La/Yb)n ratios and Mn of the vein ankerite suggest that during carbonate crystallization the system was closed with respect to fluid. Sr-Nd isotope systematics indicates that the isotopic parameters of the vein ankerite were formed with the participation of metasedimentary host rocks of both the Imnyakh and Khomolkho formations, which are contrastingly different in Nd isotopic composition. A fluid/rock ratio during metasomatic processes in the wall rocks was calculated for two scenarios of their thermal history: with a continuously operating heat source beneath the Sukhoi Log structure and with a linear cooling of the structure. The effective integral W/R ratios calculated lie within the range of 0.046–0.226 and suggest that the veins were produced with the metamorphic fluid. Low W/R ratios are inconsistent with the mechanism of vein quartz crystallization due to fluid oversaturation with respect to SiO2 at decreasing temperature. We believe that the main mechanism responsible for the origin of these veins was variations of fluid oversaturation due to pressure variations (pressure solution mechanism). This hypothesis is consistent with the reported isotopic-geochemical characteristics of the wall rocks at the Sukhoi Log deposit.

Gold resource potential of the eastern Siberian Platform: Placers and their feeding sources

The data on typomorphism of placer gold and its localization in the eastern Siberian Platform have been integrated for the first time. The alluvial, pseudolode, and eolian morphology of gold determines the origin of placers, which is explained not only by hydrodynamic but also by eolian processes. The recent and older alluvial (Au-bearing reservoir rocks in the second case), as well as eolian (unconventional type), genetic types of placers are recognized in the given territory. Precambrian and Mesozoic stages of ore formation are distinguished by the set of typomorphic attributes of placer gold (chemical composition, microinclusions, internal structure, etc.). On the basis of distinguishing features of placer gold, Precambrian lode deposits of great depth spatially related to outcrops of the basement have been forecasted for the first time and classified into low-sulfide gold-quartz, Au-bearing banded iron formation, Au-Cu porphyry, and Au-PGE types. The inferred shallow-seated gold-silver and gold-sulfide-quartz disseminated deposits occur locally and are related to the Mesozoic tectonomagmatic reactivation. The elaborated methods and approaches to the study of placer gold typomorphism in the eastern Siberian Platform also could be helpful in providing insights into placer origin, and forecasting and prospecting gold deposits on the East European Platform, which is close to the Siberian Platform in geological evolution.

Geochemistry of native gold from deposits of various types

The ICP-MS-analyzed 490 samples of lode and placer gold allowed us to detect a wide spectrum of trace elements in native gold from the most abundant gold-polysulfide-quartz, low-sulfide gold-quartz, and gold-silver deposits from various gold provinces and districts of the Russian Federation. The typical set of elements in gold of each deposit type has been determined. The distribution of REE, rare alkali and alkaline earth metals in native gold is estimated for the first time, and a geochemical index has been proposed to typify gold occurrences. Compositional differences of native gold are also caused by regional metallogenic features of gold provinces. The results obtained make it possible to determine a type of lode and placer gold occurrences at early stages of geological exploration.

The Sarylakh and Sentachan gold-antimony deposits, Sakha-Yakutia: A case of combined mesothermal gold-quartz and epithermal stibnite ores

New mineralogical, thermobarometric, isotopic, and geochemical data provide evidence for long and complex formation history of the Sarylakh and Sentachan Au-Sb deposits conditioned by regional geodynamics and various types of ore mineralization, differing in age and source of ore matter combined in the same ore-localizing structural units. The deposits are situated in the Taryn metallogenic zone of the East Yakutian metallogenic belt in the central Verkhoyansk-Kolyma Fold Region. They are controlled by the regional Adycha-Taryn Fault Zone that separates the Kular-Nera Terrane and the western part of the Verkhoyansk Fold-Thrust Belt. The fault extends along the strike of the northwest-trending linear folds and is deep-rooted and repeatedly reactivated. The orebodies are mineralized crush zones accompanied by sulfidated (up to 100 m wide) quartz-sericite metasomatic rocks and replacing dickite-pyrophyllite alteration near stibnite veinlets. Two stages of low-sulfide gold-quartz and stibnite mineralization are distinguished. The formation conditions of the early milk white quartz in orebodies with stibnite mineralization at the Sarylakh and Sentachan deposits are similar: temperature interval 340–280°C, salt concentration in fluids 6.8–1.6 wt % NaCl equiv, fluid pressure 3430–1050 bar, and sodic bicarbonate fluid composition. The ranges of fluid salinity overlapped at both deposits. In the late regenerated quartz that attends stibnite mineralization, fluid inclusions contain an aqueous solution with salinity of 3.2 wt % NaCl equiv and are homogenized into liquid at 304–189°C. Syngenetic gas inclusions contain nitrogen 0.19 g/cm3 in density. The pressure of 300 bar is estimated at 189°C. The composition of the captured fluid is characterized as K-Ca bicarbonatesulfate. The sulfur isotopic composition has been analyzed in pyrite and arsenopyrite from ore and metasomatic zones, as well as in coarse-, medium-, and fine-grained stibnite varieties subjected to dynamometamorphism. The following δ34S values, ‰ have been established at the Sarylakh deposit: −2.0 to −0.9 in arsenopyrite, −5.5 to −1.1 in pyrite, and −5.5 to −3.6 in stibnite. At the Sentachan deposit: −0.8 to +1.0 in arsenopyrite, +0.5 to +2.6 in pyrite, and −3.9 to +0.6 in stibnite. Sulfides from the Sentachan deposit is somewhat enriched in 34S. The 18O of milk white quartz at the Sarylakh deposit varies from +14.8 to 17.0‰ and from +16.4 to + 19.3‰ at the Sentachan. The δ18O of regenerated quartz is +16.5‰ at the Sarylakh and +17.6 to +19.8‰ at the Sentachan. The δ18O of carbonates varies from +15.0 to 16.3% at the Sarylakh and from +16.7 to +18.2‰ at the Sentachan. The δ13C of carbonates ranges from −9.5 to −12.1‰ and −7.8 to −8.5‰, respectively. The calculated \( \delta ^{18} O_{H_2 O} \) of the early fluid in equilibrium with quartz and dolomite at 300δC are +7.9 to +10.1‰ for the Sarylakh deposit and +9.5 to +12.4‰ for the Sentachan deposit (+4.9 and 6.0‰ at 200°C for the late fluid, respectively). Most estimates fall into the interval characteristic of magmatic water (°18O = +5.5 to +9.5‰).

First data on distribution of REE, Li, Rb, Cs, Sr, and Ba in native gold from deposits of the main gold-bearing provinces of Russia

Seventy chemical elements were analyzed in more than 350 samples of native gold from deposits of some goldbearing provinces of Russia by the ICP Ms method. Analyses were performed in the Section of Analytical Investigations, Central Exploration and Research Institute for Nonferrous and Precious Met� als, on the Elan 6100 apparatus (Perkin Elmer), ana� lyst I.V. Grigor'eva. Samples of pure native gold with a weight of ~5 mg were used for analysis. The control was performed by repeated analysis of selected sample duplicates and demonstrated good convergence of the results. Samples were distinguished into three types of deposits from the whole data massif: gold-polysul� fide-quartz, lowsulfide gold-quartz, and gold-silver (1). These types included ore objects and placers with established or assumed sources of ore material. The relationships between ore and placer objects in the samples are different. Gold-silver deposits of the Okhotsk-Chukotsk volcanogenic belt (OCVB) and Kamchatka comprise only ore objects, because up to now placers, the formation of which is related to this type of deposits, with rare exceptions, are not known. Placers with deposits of the gold-polysulfide-quartz type as an assumed source of gold are included in the sample for the Sikhote-Alin province. The presence of REEs (from La to Lu) and rare alkaline (Li, Rb, Cs) and alkalineearth (Sr, Ba) ele� ments was established as stable admixtures in native gold for the first time. Their average concentrations in gold from deposits of the types considered from ten goldbearing provinces of Russia are presented in the table.