Gold Fineness Research Articles

Mineralogy and mineral chemistry of Bi-Te minerals: Constraints on mineralization process of the Dulanggou gold deposit, Dadu River Metallogenic Belt, China

There is a widely recognized association of bismuth (Bi)-tellurium (Te) minerals with gold in many hydrothermal gold deposits. However, the specific process for gold enrichment related to Bi-Te minerals remains enigmatic. The Dulanggou gold deposit, located on the southeastern margin of the Songpan-Garzê orogenic belt, China, provides an opportunity to research this process. Gold in the deposit is mainly associated with coarse-grained Bi-Te minerals and bismuth-rich polyphase metal droplets. Three mineralization stages are identified in the deposit. In Stage 1, a small amount of gold was deposited within dominate pyrrhotite. In Stage 2, a large amount of visible gold grains were precipitated with coarse-grained Bi-Te minerals. The various Bi-Te phases are mainly tsumoite, pilsenite, unnamed minerals (Bi3Te2, Bi2Te), joséite-B and trace hedleyite, which have a common characteristics of 2 ≥ Bi/Te > 1. In stage 3, around the Stage 2 large Bi-Te phase patches, bismuth-rich polyphase metal droplets pervasively occurred with Bi/Te ≥ 2. Other Bi-Te minerals in Stage 3 include hedleyite, unnamed minerals (Bi3Te, Bi8Te3, Bi5Te), joséite-B, and joséite-A, all intergrowth with gold and maldonite in the metal droplets. Mineral chemistry and phase diagrams of the Bi-Te mineral assemblages indicate that the mineralization temperatures at Stages 2 and 3 are > 325 ℃ and around 235 ℃ respectively, and the fTe2 and fS2 gradually decrease from Stage 2 to Stage 3. Importantly, a large amount of native gold was deposited with native Bi during Stage 3 and Bi contents in Bi-Te minerals increase with gold fineness from 799 ∼ 876 at Stage 2 to 833 ∼ 939 at Stage 3. These indicate that the metal droplets could be Bi-rich melts which were separated from Bi-Te phase patches and scavenged gold from earlier mineral assemblages to enhance gold enrichment.

Features of the Tanalyk gold placer and its primary sources (the Baymak ore-placer cluster, Southern Urals)

The article presents the results of a study of the Tanalyk placer, which is part of the Baymak ore-placer cluster. It is shown that gold is predominantly bright yellow in color and has lump-shaped, wedge-shaped, plate-shaped and wire-rod-shaped forms. In terms of granulometric composition, it belongs to the large and medium class and is characterized mainly by medium roundness. The uniformity of morphological varieties of gold in different lithological and stratigraphic horizons indicates the inheritance of gold from ancient deposits to young ones.
 Placer gold is of high quality and has a fairly consistent composition; the main impurity here is silver, the content of which varies from 0.2 to 9%. The average fineness of gold in the placer in the following areas: Baymak pond – 938, Shurinsky log – 935, Aktash log – 943, Tanalyk (lines 1502-1559) – 917. Hypergene new formations on the surfaces of gold grains are represented by high-fineness rims. A common feature for gold of all size classes is the presence in the depressions and on their surface of films of iron and manganese hydroxides, crusts of fine-grained quartz, chlorite, and less commonly biotite, in which a large number of microparticles of very high-fine gold measuring 0.1–0.5 μm were found.
 The typomorphism of schlich gold, its composition and features of the internal structure indicate that the main source of gold was gold-quartz mineralization in the zones of wall-metasomatites of the Kul-Yurt-Tau gold-pyrite deposit, gold-polymetallic and gold-barite deposits Grafskoye, Troitsk and Novo-Troitsk. The junction points of diagonal neotectonically active lineaments with meridional magma- and ore-supplying faults form polychronic and polygenic through ore-concentrating structures. Dispersed gold occurrences in these structures are placer-forming and serve as the main source of the formation of large placers.

Mineralogy and Geochemistry of the Mupane and Shashe Gold Deposits of the Tati Greenstone Belt (NE Botswana): Implications for Mineral Deposit Models and Exploration

Abstract The Archean Tati greenstone belt is located at the southwestern margin of the Zimbabwe craton (northeast Botswana) and hosts numerous Cu-Ni ± platinum group element (PGE) and Au ± Ag occurrences and deposits. Gold occurrences/deposits are poorly studied, and key questions pertaining to their genesis remain unclear, including the mode of occurrence(s) of gold, the relative timing of gold introduction with respect to the evolution of the greenstone belt, the number of gold mineralization events, the alteration patterns, and the relationships between each alteration pattern and gold mineralization. A detailed study that includes sulfide and gold grain chemistry using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and electron probe microanalysis (EPMA), respectively, and X-ray diffraction (XRD) of mineralized rock samples of three Tati greenstone belt gold deposits was carried out to constrain the genesis of gold mineralization and formulate exploration guidelines in the Tati greenstone belt. Gold in the Tati greenstone belt is the result of multiple events, is mainly associated with arsenopyrite, pyrite, and sphalerite, and occurs as (1) microinclusions within sulfides, (2) intergrowth with sulfides, (3) minute particles (<2–10 µm) within the silicate matrix, (4) microfractures and microvug infills, and (5) lattice-bound and sulfide-hosted refractory gold. The first gold event (as electrum) is premetamorphic and associated with sphalerite-quartz veins. The second stage is a postmetamorphic high-grade gold event that is accompanied by extensive carbonatization and propylitization of host rocks. The third stage of gold mineralization is marked by the dissolution of gold in the early formed stages 1 to 2 and subsequent reprecipitation within cracks, fractures, and vugs. Auriferous pyrite composition suggests that Au-bearing mineralizing fluids are predominantly of magmatic origin and that their physicochemical compositions changed during the mineralization process, as supported by chemically zoned Au-bearing arsenopyrite, various alteration types containing gold, and variation in gold fineness across the several gold deposits in the Tati greenstone belt. Gold deposition in the Tati greenstone belt mainly occurred through sulfidation, as indicated by the closest spatial association between gold and Fe-bearing sulfides and ferromagnesian silicates. Gold in the Tati greenstone belt is closely correlated with As, Sb, Pb, Bi, Ni, Hg, Tl, Cd, In, Mo, W, Zn, and Te and moderately to weakly associated with Sn, Se, Cr, Co, Ge, Cd, Mn, V, Ga, and Ag. The correlation between Au and fluid mobile elements, i.e., Te, Sb, Se, As, Hg, and Bi, can be used as a vectoring tool during the exploration of gold within the Tati greenstone belt, as these elements likely form halos that are much broader than the primary footprint of gold mineralization.

Overview of early cretaceous gold mineralization in the orogenic belt of the eastern margin of the Siberian craton: geological and genetic features

The giant Verkhoyansk-Kolyma gold province, producing more than∼ 3700 t of gold, is one of the most important metallogenic provinces for orogenic gold deposits in the world. The province is located on the eastern margin of the Siberian craton. The main types here are multistage orogenic Au-As and orogenic-like Au-Sb types of mineralization, related to the Late Jurassic-Early Cretaceous metallogeny and the evolution of the convergent margin. These deposits were formed in the environment of late orogeny during two metallogenic stages—the Late Jurassic-Early Cretaceous collision-related (early stage/stage one, 135–150 Ma) and the Early Cretaceous subduction-related (late stage/stage two 114–130 Ma). The common features, differences and genetic nature of the deposits of these two metallogenic stages have been debated for a long time. To improve the understanding of these problematic issues and the genesis of deposits, and control over them by the mantle lithosphere, we consider here the Early Cretaceous orogenic belts of the eastern margin of the Siberian craton. Orogenic belts are related to the development of the paleo-Arctic and paleo-Pacific margins of Siberia. The tectonic, geochronological, mineralogical and geochemical specificity of the deposits of the orogenic belts are shown. A regional metallogenic overview of gold deposits is performed using data on the age of mineralization and the isotopic composition of sulfur sulfides. A preliminary model of the origin of late stage mineralization is proposed in connection with the processes of the Okhotsk-Koryak orogenic belt formation. Increased concentrations of siderophilic and chalcophilic elements, the Ni, Bi minerals presence in the ores, relatively high fineness of gold, predominance of juvenile sulfur in the isotopic composition of sulfide sulfur, аnd the control by large trans-crustal faults as well as spatial and chronological association with initial (dike) magmatism indicate mantle sources of ore fluids. This mineralization within the orogenic belts of the eastern margin of the Siberian craton assumingly appeared due to dehydration of the submerged slab and local upwelling in the mantle in the rear of the active continental margin. The possibility of the gold-bearing fluids existence in such conditions is estimated. The metallogenic specific nature of collision-related and subduction-related orogenic Au is defined. The proposed model can be useful for the analysis of polychronous orogenic Au-As and orogenic-like Au-Sb metallogeny of orogenic belts on craton margins globally.

A rare sellaite-bearing orogenic gold deposit at Pianyanzi, Yangtze Craton: Ore genesis as implied from in-situ studies of pyrite

The Pianyanzi gold deposit is situated at the western margin of the Yangtze Craton, and represents a rare sellaite-bearing orogenic gold deposit. This deposit belongs to the Dauduhe gold belt of southwestern China and remains poorly documented. In this paper we present first petrographic and in-situ geochemistrical and sulfur isotope data from pyrite as well as results of multielement mapping. The deposit is dominated by native gold (average gold fineness = 980.8) filling fractures in minerals (e.g., pyrite, quartz, sellaite and hematite) or also emplaced along the contact interface between mineral grains. Pyrite is the most abundant sulfide mineral of this deposit. We identified five generations of pyrite: Py1, Py2a, Py2b, Py3, and Py4. Gold occurs in sellaite- and hematite-bearing mineral assemblages formed simultaneous with the formation of Py2a&b and Py4, respectively. Py1 formed in the Au-poor ore stage, while Py3 formed during the late galena-dominated sulfide stage. All generations of pyrite exhibit low concentrations of gold with an average value of less than 2 ppm. Py2a&b possess distinctive textures and chemical zonation, with trace elements displaying greater variations compared to Py1, Py3 and Py4. The δ34S values vary from −0.52 ‰ to 7.08 ‰, which is consistent with those of orogenic deposits of the Daduhe gold belt. The deep metasomatized mantle lithosphere acted as a potential source of ore fluids. We conclude that the co-precipitation of native gold and sellaite was triggered by the interaction between auriferous fluids and dolomite.

Algama Gold Ore Cluster (Aldan–Stanovoi Shield): Mineralogy, Formation Conditions, Sources of Ore Matter, and Age of Mineralization

Abstract —The paper presents results of research into the conditions of formation of ores in the poorly studied Algama ore cluster (Bodorono deposit and Dyvok ore occurrence) located at the junction of the Aldan Shield and the Stanovoi area. We have established that Bi and Se minerals (bismuthinite, lillianite, native bismuth, tellurobismuthite, tetradymite, hedleyite, pilsenite, and laitakarite) are present in the ores of the Bodorono deposit. Two successive productive stages of mineral formation have been distinguished: Au–polymetallic and Au–Bi–Te. The corresponding minerals are products of the evolution of a hydrothermal system, during which a gradual decrease in fluid temperature (from 300 to 145 °C) and salinity (from 5 to 1.9 wt.% NaCl equiv.) took place. The fineness of native gold gradually increases from early (~840‰) to late (~940‰) stages and changes in passing from simple sulfides to sulfosalts. The evolution of the ore system is accompanied by a change in the composition of the vapor phase of fluid inclusions from CH4–CO2 to CO2 with an impurity of N2 and CH4. The results of 40Ar/39Ar dating of pre-ore metasomatites point to ore-forming processes at the Bodorono deposit ca. 150 ± 1.8 Ma. Analysis of the isotopic composition of lead in galena shows the leading role of the ancient crustal source of ore matter. The calculated isotopic composition of oxygen (δ18OH2O) in ore-bearing quartz varies from 1.0 to 7.3‰, which corresponds to an aqueous fluid of a mixed source. The Dyvok ore occurrence differs from the Bodorono deposit in the mineral composition of ores and the physicochemical parameters of ore formation. Four mineral stages have been established within the ore occurrence: gold–arsenopyrite–pyrite–quartz, pyrite–chalcopyrite–sphalerite, quartz–boulangerite, and telluride. The telluride stage is represented by hessite, altaite, volynskite, merenskyite, melonite, and rucklidgeite. Gold-bearing mineralization formed from a fluid of medium salinity (0.9–9.2 wt.% NaCl equiv.) with a predominance of CO2 and an impurity of CH4 in the vapor phase at moderate temperatures (310–360 °C). The calculated values of δ34S and δ18O varied from 2.2 to 3.0‰ and from 0.6 to 12.0‰, respectively. The 40Ar/39Ar age of gold mineralization is 124.0 ± 1.5 Ma, which corresponds to the stage of tectonomagmatic activity in the Aldan Shield.

Typification of gold occurences in the Phuoc Thanh - Phuoc Son area, Central Vietnamccurences in the Рhuoc Тhanh — Рhuoc Son area, Сentral Vietnam

Background. Substantiation for the expediency of typification of gold occurrences in the Phuoc Thanh–Phuoc Son area, Central Vietnam.Aim. To classify and evaluate the prospects of gold mineralization in the Phuoc Thanh–Phuoc Son area, Central Vietnam.Materials and methods. The data of geological mapping and exploration of 20 deposits and ore occurrences in the Phuoс Son and Phuoc Thanh ore fields, collected in the 2001–2019 period, were analyzed.Results. The deposits and ore occurrences of gold-sulfide-quartz and low-sulfide gold-quartz formations of the Late Mesozoic age were established to be common within the Phuoc Thanh– Phuoc Son area. These deposits differ in terms of reserves, ore body morphology, gold-silver ratio, and gold fineness. Conclusion. The results obtained can be used when forecasting the largest gold deposits in Central Vietnam.

Epithermal Deposits of Kamchatka, Russia

The results of studying the epithermal deposits of Kamchatka, one of the most promising gold-mining provinces of the Russian Federation, are generalized. The deposits are divided into acid–sulfate (Ac-Sul) and adularia–sericite (Ad-Ser) types (Heald et al., 1987). The disadvantages of the scheme, which is the most popular in the English-language literature and is based on the sulfidation state of mineral parageneses in ores (LS, IS, and HS types), are shown. The classification that we proposed includes differences in mineral associations in circum–ore metasomatites, which are determined by the acidity–alkalinity and an oxidation state of mineral-forming fluids, and are clearly diagnosed at the first stages of studying the deposits. Kamchatka epithermal deposits of the Ad-Ser-type are associated with andesite volcanism of the volcanic belts. Gold ore associations are concentrated in quartz, carbonate–quartz, and adularia–quartz veins, as well as in sericitized metasomatites, which are replaced by argillizites and propylites towards the periphery. The Ad-Ser-type is characterized by combination with polysulfide (Pb, Zn) (Amethyst, Kumroch, Vilyuchinskoe deposits), sulfosalt (Ag, Sb, As, Bi, Sn) (Ozernovskoe, Baranyevskoe), and selenide (Ag, Se) (Amethyst, Asachinskoe, Rodnikovoe) assemblages. Low-fineness native gold (220–310‰) is typical of the early polysulfide assemblage. With an increase in the fugacity of Te and Se, the gold fineness increases to 510–740‰, and with the progressive activity of Sb, As and Bi and the formation of sulfosalt associations, it reaches 998‰. The homogenization temperatures of primary fluid inclusions in quartz from gold-bearing associations of the Ad-Ser-type are 260–250°C; the minerals crystallize from solutions containing no more than 3 wt % NaCl eq. Maletoyvayam, the only Ac-Sul-type deposit in Kamchatka, is localized in quartz, secondary quartzites, and alunite–sericite–kaolinite–quartz metasomatites. Gold-bearing parageneses indicate the leading role of selenium in mineral formation, contain high-fineness native gold, sulfoselenotellurides, tellurides, and selenides of Au, which crystallize from acidic fluids with salinity of 1–5 wt % NaCl eq. at temperatures of 290–175°C.

3D Plotting of Gold Solubility and Gold Fineness: Quantitative Analysis of Ore-Forming Conditions in Hydrothermal Gold Deposits

Abstract The 3D plotting of gold solubility and gold fineness aims to illustrate how to quantify their correlations with ore-forming conditions in hydrothermal gold deposits. The thermodynamic calculation of the Au-Ag solid solutions in Mathematica and the 3D plotting in MATLAB are used to build isopleths of gold solubility and gold fineness at different temperatures (200℃, 400℃), pressures (0.1, 5 kbar), salinities (1, 40 wt% NaCl eq.), and sulfur concentrations (0.01, 0.5 mol/kg). The plot indicates that the ore-forming conditions have different correlations with gold solubility and gold fineness. Average rates of change for the correlations are quantified, showing distinct values in the four pH-logfO2 fields of (I) HSO4−, (II) SO42−, (III) H2S, and (IV) HS−, where dominant gold and silver complexes have different dependencies on the conditions. The quantification of the plots illustrates that a decrease in gold solubility by one order of magnitude is possibly caused by a decrease in temperature of ≥40℃, the salinity of ≥9.6 wt% NaCl eq. or sulfur concentration of ≥0.14 mol/kg, or an increase in pressure of ≥3 kbar, while a decrease in gold fineness by 100 units is possibly caused by a decrease in temperature of ≥14 ℃, pressure of ≥1.4 kbar, or salinity of ≥4 wt% NaCl eq., or an increase in sulfur concentration of ≥0.07 mol/kg. Quantification results suggest that a sharp decrease in temperature may result in large-scale gold mineralization and a great variation in gold fineness. In addition, the quantification reveals that the correlation between gold solubility and gold fineness can be expressed by a function, providing a rapid method for 3D plotting.

Tourmaline occurrence and gold mineralization at a granitoid-metasediment contact in the Upper Lom Basin, east Cameroon

Gold mineralization of the Upper Lom Basin in the eastern Cameroon goldfield is spatially associated with tourmaline. The goldfield belongs to the Adamawa-Yadé Domain of the Central African Fold Belt and is characterized by eluvial, alluvial and lode gold deposits of Pan-African age. This paper examines the chemistry and morphology of saprock gold and its link with tourmaline in the host rock. Tourmaline chemistry was obtained using the electron microprobe analysis (EMPA) technique while gold grains were examined for morphology and microchemistry using the EMPA equipped with scanning electron microscopy and energy dispersive spectrum instruments. The tourmaline compositional data plot in the dravite field, and belongs to the alkali group showing major element variations that are typical of tourmaline associated with granite-related orogenic gold deposits common along shear zones. Gold alloy composition (Ag, Cu) suggests multiple gold precipitation events due to episodic fluid influx, with a range of 572–1000 gold fineness. We infer that tourmaline development and gold deposition were coeval within the aureole around the pluton and involved reduced hydrothermal fluids with low salinity. The high δ11B in the tourmaline also points to fluid derivation from the Pan African granitic basement widely recognized to be fertile in gold in eastern Cameroon. Tourmaline textural-chemical features such as low Na content and gold microchemistry point to granite-related hydrothermal style of primary gold mineralization, and has implications for exploration as tourmaline-rich rocks in the vicinity of the felsic plutons in the Lom Basin would be optimal target areas for future exploration.

Ore Mineralogy and Typomorphism of Native Gold of the Spokoininsky Cluster of the Aldan–Stanovoy Gold Province

The ore mineralogy of a new promising target of the Aldan–Stanovoy gold province—the Spokoininsky cluster—is considered. Gold mineralization is represented by a volumetric, nonlinear type, unconventional for the region; it is related to elements of fold structures and reverse fault in the enclosing metamorphic basement rocks. Vein-disseminated sulfide–(pyrite)–quartz ores build up deposit-like bodies in beresites from gneisses and granite gneisses and are associated with Mesozoic igneous rocks of subalkaline formations. Mineralization is characterized by polysulfide (Fe-Cu-Pb); gold–bismuth (Au-Bi) and gold–silver–telluride (Au-Ag-Te) mineral types. Different mineral types have their own typomorphic minerals and typochemistry (fineness and impurities) of native gold. The widespread distribution of telluride mineralization and its great importance in the formation of gold mineralization on the Aldan shield is confirmed. The distribution area of bismuth (including tellurium–bismuth) mineralization in the southern part of the Aldan shield, in the zone of influence of the Stanovoy deep fault, has been identified.

Gold endowment and unloading along pathway for giant gold mineralization: Insights from spatiotemporal variations of in-situ pyrite geochemistry and gold fineness from the Jiaodong gold deposits, north China Craton

Over 5000 tonnes of gold were accumulated in the Jiaodong Peninsula at the early Cretaceous, the sources and critical ore-forming processes of which are still controversial. Here, we conducted comprehensive in-situ textural, elemental and isotopic analyses on pyrite and gold grains from the different mineralization styles, hydrothermal stages and depths for three representative gold deposits (Linglong, Xiadian and Jiangjiayao) from the northwestern Jiaodong Peninsula, with the aim to exactly constrain the sources and ore-forming processes. Three groups of δ34Spyrite were identified in the studied deposits, of which the Group 1 shows stable and low δ34S (4.8–7.6‰) throughout the hydrothermal evolution while the Group 2 has elevated δ34S (6.0–12.8‰) coupled with increasing As and Au concentrations. The Group 3 shows moderate δ34S (5.2–9.8‰) accompanied by high Al and Si concentrations. The Group 1 suggests a low-δ34S primary auriferous fluid derived from a mantle-related source, whereas the Group 2 indicates the primary auriferous fluid leaching additional S, As and Au from the Precambrian metasedimentary rocks along pathway. The Group 3 is petrographically coupled with numerous silicate inclusions, indicating enhanced fluid-rock interaction between the auriferous fluids and the granitic wallrcoks. Gold fineness decreases from the early to the late hydrothermal stages, combined with increasing deposition of polymetallic sulfides, suggesting an increase of pH resulting in efficient Au deposition. Gold fineness and Bi concentrations in pyrite decrease with shallowing, suggesting that cooling affected Au deposition as well. Bismuth-Te-S minerals were identified in the deep depths, combined with the well correlated Bi and Ag, implying that Bi-Te complexes might play a role in transporting Au and Ag at high-temperature conditions. The above results corroborate that multiple sources and ore-forming processes were responsible for the giant gold mineralization, of which the gold endowment from Precambrian wallrocks needs to be further concerned.

Mineralogical constraints on the genesis of an alkalic-type epithermal Au-Te deposit: Tuvatu, Fiji

To study the characteristics and genetic constraints on alkalic-type epithermal Au mineralisation, here we use the example of the Tuvatu Au-Ag deposit in Fiji, with an emphasis on detailed, quantitative mineralogy. Tuvatu mineralisation is hosted in a weakly altered potassic monzonite in parallel sided-veins of K-feldspar, biotite, sericite, calcite, and quartz, with epidote-bearing propylitic or sericite-rich selvages. Petrographic study of core and automated SEM-based mineralogical mapping of thin sections have been utilised to update previous parageneses of the deposit. Automated SEM techniques enable identification of small amounts of obscure minerals that form minuscule grains, which would otherwise be very difficult to identify and measure. As a result, our data show that gold fineness is extremely high, with the mean and median Au content of native-Au and Au-Ag alloy being 96.7% and 100% respectively, yet precious-metal tellurides make up the majority of the Au deportment. Tellurides show evidence of multiple phases and zoning with depth. For the first time at Tuvatu, Pt- and Pd-tellurides have been identified. Tuvatu has a number of features in common with alkalic systems elsewhere, including quartz-poor, carbonate-rich veins and alteration, abundant and varied telluride minerals, high gold grades, and Pt-Pd occurrences. We suggest these characteristics are a result of relatively high temperature (250–300 °C) fluids and immiscible semi-metal melts fluxing into the shallow epithermal environment. High pH fluids lead to quartz-poor alteration, but mildly acidic conditions dominate in areas of high fluid flux, where the lower pH causes precipitation of tellurides with quartz. Boiling of the fluids produces zonation of tellurides with depth but leaves relatively subtle textural evidence compared to boiling in most epithermal systems, in common with other quartz poor, carbonate-rich alkalic epithermal deposits around the world.

ԴՐԱՄԱԿԱՆ ԱՆՎԱՆՈՒՄՆԵՐԻ ԱՐՏԱՑՈԼՈՒՄԸ ՀԱՅԿԱԿԱՆ ՎԻՄԱԳՐԵՐՈՒՄ (ՀԱՅ.) / REFLECTION OF MONETARY NAMES IN ARMENIAN LAPIDAR INSCRIPTIONS

Based on the rich Armenian epigraphic material, which has come down to us mainly from the developed Middle Ages, we see that money is most often embodied in the following terms: DAHEKAN (DEKAN), DUCAT, DRAM, SPITAK (SPITAK SULTANI), STAK, TANGKA, KINEIN (K), TUMAN, DIAN. Spitak sultani, tanga, kineyin(k), dian are found in the lapidary inscriptions known to us only once. Dram is mainly mentioned from the period of the Bagratuni kingdom (874/885 – 1045) until the tenth years of the 13th century. It was Arabic silver ﻡﻫﺭﺩ (dirham) weighing 2.97 grams. Since the reign of Bagratuni, the gold coin of the Dahekan (4.20 – 4.40 g) was used along with the dram until the first half of the 14th century. The ratio of dahekans to dram was 1:10. Since the middle of the 11th century, in addition to the dram and dahekan, we have seen in circulation in Armenia the European gold ducat coin (weight: 3.5 g, gold fineness: 980). During this period, the ducat had a ratio of 1:1.5 to dahekan. The ducat was also used in lapidary inscriptions at the end of the 13th century. In the 13th – 14th centuries, the most popular currency in Armenia was Spitak (white), which, as the name suggests, was originally a silver coin. Spitak was certainly a Mongolian coin that weighed 2.74 – 2.83 grams of silver. Seljuk silver coins (spitak sultani) and Mongolian copper coins (weighing 3 – 5 g) were also in circulation. From the middle of the 15th century to the middle of the 17th century, stak was mainly in circulation in Armenia. True, the name stack, according to Hr. Acharyan, comes from the word spitak (white), which suggests that it was a silver coin, but it had an unprecedented and unique value. With a comparative epigraphic study, it is revealed that 1 stak was equal to 15 – 20 ducats, 20 – 25 dahekans, 100 – 150 spitaks, 200 – 250 drams, and also 4 tumans. The latter is most often found in Armenian lapidary inscriptions of the mid-17th – mid-19th centuries.

Geological Constraints on the Genesis of Jagpura Au-Cu Deposit NW India: Implications from Magnetite-Apatite Mineral Chemistry, Fluid Inclusion and Sulfur Isotope Study

The Jagpura Au-Cu deposit is situated within the Aravalli craton in the northwestern part of India. In the present work, petrography, mineral chemistry, fluid inclusion and sulfur isotopic compositions were used to study the Jagpura Au-Cu deposit. The ore mineral association of the deposit is arsenopyrite, loellingite, chalcopyrite, pyrrhotite and pyrite, along with native gold, magnetite and apatite. The gold fineness ranges from 914–937‰ (avg. 927‰). The presence of Au-Bi-Te phases, pyrite (>1 Co/Ni ratio), magnetite (≥1 Ni/Cr ratio, <1 Co/Ni ratio) and apatite (>1 F/Cl ratio) suggest the hydrothermal origin Au-Cu mineralization. A fluid inclusion study indicates the different episodes of fluid immiscibility with the homogenization temperatures varying between 120–258 °C and salinities range within the 8.86–28.15 wt% NaCl eq. The sulfur isotopic composition of sulfides varies from 8.98 to 14.58‰ (avg. 11.16‰). It is inferred that the variation in the sulfur isotopic compositions of sulfides is due to the cooling and dilution of the metalliferous fluid of mixed origin, derived from the basement meta-sedimentary rocks and the high saline basinal fluid. The iron oxide-copper-gold-apatite associations, structural control of mineralization, pervasive hydrothermal alteration, fluid salinity and sulfur isotope compositions indicate that the Jagpura Au-Cu deposit is similar to the iron oxide-copper-gold (IOCG)-iron oxide-apatite (IOA)types of deposits. Based on the ore geochemistry and the trace elements systematic of magnetite, the deposit is further classified as an IOCG-IOA type: IOCG-Co (reduced) subtype.

Occurrence State and Properties of Gold Minerals from the Gold Deposits on the North China Platform

By studying both the microscopic physical and chemical typomorphic characteristics of gold minerals associated with representative gold deposits on the north-central margin of the North China Platform, this paper seeks to identify macroscopic metallogenic mechanisms of gold deposits. The majority of the gold minerals from the gold deposits are native gold with minor electrum and calaverite. The form and grain size of gold minerals from the representative gold deposits reflect the metallogenic properties of medium-deep and medium-high temperature deposits. The projected gold fineness of the Xiaoyingpan gold mine all falls in the medium-temperature area in the figure and tends to be in the high-temperature area, while that of the Zhangquanzhuang gold mine mostly falls in the middle-temperature area, showing the difference in the metallogenic conditions of the two deposits. Both Xiaoyingpan and Zhangquanzhuang gold deposits show the following rules: poor in Zn, Pb, Sb and Se, but rich in Cu, Fe without Mn, indicating that both deposits are of medium-deep origin. The three representative gold deposits all show high gold fineness characteristics, and the general rules are as follows: Dongping-type gold deposit (934.8-969.7) > Xiaoyingpan-type gold deposit (900.0) > Zhangquanzhuang type gold deposit (824.0), showing that the representative gold deposits were formed at higher temperature and deeper depth, and the gold in the ores inherited the characteristics of high gold fineness originating from the Archean metamorphic rock series, which implying that the metallogenic material originated from the ancient metamorphic rock series; the long metallogenic period and multiple metallogenic stages made gold fully transformed, purified and enriched. There are three main occurrence states of gold minerals in the study area, from primary to secondary, they are respectively inclusion gold, gold minerals between other mineral crystals and those filled in the fractures of other minerals.

Episodic ore-forming fluid evolution processes in the Jiudian gold deposit, Jiaodong Peninsula: Constrains from texture, trace element and S isotope composition of pyrite

Jiudian is a representative quartz vein-type gold deposit in the Jiaodong world-class gold province, southeast of the North China Craton. Four stages and ten pyrite generations can be identified based on the paragenetic relationships: (1) pyrite (Py1)-milky quartz, (2) pyrite (Py2-1 and Py2-2)-smoky grey quartz, (3) siderite-pyrrhotite-pyrite (Py3, Py3-1 and Py3-2)-quartz, (4) quartz-polysulfide-siderite-marcasite (Py4-mc)-pyrite (Py4-1, Py4-2 and Py4-3), suggesting the complex and multistage ore-forming processes.The course-grained euhedral Py1 from the pre-ore stage 1 quartz veins is enriched in lattice-bound Co, Ni, and Se with relatively low δ34S values (+4.7 to + 5.5‰), precipitated from the equilibrated fluid environment with higher temperature (ca. 400 ℃). The dissolution-reprecipitation textures are characterized by the pristine As-rich Py2-1 as parent phase and porous Py2-2 as product phase hosting abundant microscale galena enriched in low-melting chalcophile elements (LMCE, e.g., Pb, Bi, Ag, Te, and Sb) and minor electrum. Both of Au-HS and Ag-Cl complexes destabilized by decompression would result in the precipitation of electrum with low gold fineness (672 to 713). Py3 is a poor host for majority of trace elements coexisting with pyrrhotite, precipitated from the late second pulse fluid.Py3 was overprinted by the third ore fluid pulse and replaced by siderite into sieve-shaped Py3-1 and anhedral aggregates Py3-2. Subsequently, fluid oxidation caused by pyrite replacement and meteoric water influx would result in the precipitation of marcasite (Py4-mc). Furthermore, euhedral pyrite aggregates were directly deposited from this ore-forming fluid, characterized by the Co-rich core (Py4-1) with abundant inclusions of LMCE-dominant sulfosalt (lillianite homologues) and galena, overgrown by pristine As-rich rim (Py4-2). The decoupled As and Co in Py4-1 and Py4-2 were probably attributed to abrupt temperature drop due to meteoric water influx. Nevertheless, the precipitation of visible gold with higher gold fineness in siderite or intergrown with Py4-mc was primarily resulted from fluid oxidation which has significant effect on the stabilities of Au-HS complexes but little on those of Ag-Cl complexes. The last generation Py4-3 was the post-oxidation product, evidenced by the extremely negative δ34S values (-34.3 to −28.4‰).Hence, the textural and geochemistry characteristics of different pyrite generations of Jiudian have revealed the presence of three fluid pulses as well as the distinctive evolution processes and changes of physicochemical conditions leading to the characteristic mineral assemblages and multiple-stage gold mineralization, which could provide implications for the genesis of siderite-rich gold deposits in the Jiaodong district.

Золотое оруденение Нижне-Мякитского рудно-россыпного узла (Северо-Восток России)

A comprehensive study of native gold and ore mineral parageneses of the Berental intrusive-dome structure in the southeastern part of the Yano-Kolyma gold-bearing belt has been carried out. The zonality of mineralization is shown: from the central part (in the Berental stock endocontacts) with the Au-Bi-Te mineralization "style" to - As-Au (in the exocontacts of the stock) and, further, to Ag-Pb-Zn on the periphery. In the same direction changes the fineness of native gold in ores, from high and medium to low fineness. Antimony mineralization was noted at the final stage of ore formation. Vertical zoning is expressed in the silver-polysulfide type of mineralization changing with depth to sulfide-sulfoarsenide and, lower, bismuth-sulfotelluride. A rare mineral, maldonite (Au2Bi), is relatively widespread. The end-to-end ore minerals are pyrrhotite, native bismuth, and its tellurides. The obtained facts permitted to attribute the hydrothermal system of the Berental stock to the RIRGD type, i. e. to gold deposits associated with restored intrusives, which can contribute to the improvement of the methodology for prospecting and evaluation works at deposits of this type and to the discovery of large occurrences in terms of reserves.

Increased recovery of free fine gold in the leaching process

The current state of world mineral resources is characterized by a decrease in the quality of minerals. An increase in production and processing volumes is possible only through the development of new deposits and the involvement of off-balance ores, dumps and tailings, slags and other industrial wastes in the integrated mining process. More increasing the need for involving raw materials of complex composition, refractory, low-grade, with small reserves, technogenic mineral waste. It becomes more and more relevant as the discovery and exploitation of new deposits, allowing to increase the gold reserve of the Republic of Kazakhstan. The article presents the results of sorption leaching of ore in order to extract gold associated with sulfides, the processes of opening gold. A representative sample was taken and the phase composition of an additional explored ore body was studied at one of the deposits in Kazakhstan. The ore sample was prepared for research: three-time mixing by the ring-cone method, in general, three-stage quarting and mixing were performed. It should be noted that the methods for processing gold-bearing ore raw materials depend on many parameters, including the material composition and technological properties. Samples from the last quarting materials were selected for chemical, sieve and phase analyzes. It was found that the test sample contained 6.04 g / t Au and 7.9 g / t Ag, as well as fineness of gold within 0.01-0.25 mm phase analysis. Mineral gold formations can be easily soluble in cyanide solutions (native gold, electrum), partially soluble (maldonite, or practical are insoluble (tellurides). Gold in ores is present in the form of gold-colored sizes and shapes. Both physical (gravity, flotation) and chemical (cyanide, etc.) methods are used to extract it. Rational analysis also found that gold in the ore under study, crushed to a particle size of 90%, class 0.071 mm, gold is free and in intergrowths is 81.46%, gold associated with sulfides is 14.40%, in rock-forming minerals 1.66%. Based on the data obtained, it can be stated that when cyanidating ore, one should expect rather high rates of gold dissolution (80% or more). Gold extraction from ore with a content of 85% fraction -0.071mm-90.2%, with a content of 85% fraction- 0.071mm-98% with oxidative leaching. Full extraction of gold from ore is possible with sorption cyanide leaching with their preliminary oxidation. The paper considers economically feasible existing and promising technologies for gold extraction at the leading factories of Kazakhstan and abroad.

New data on the mineralogy of the gold-sulfide ore type
 of the Karalveem deposit, Chukotka

In this paper, we present the results of a mineralogical
 study of the ores of the Karalveem deposit in
 the northeast of Russia (Central and Ruslovy areas).
 Gold mineralization is characterized by two types of
 ores: gold-quartz-arsenopyrite (quartz veins with native
 gold and sulfide mineralization) and gold-sulfide (metasomatites)
 in gabbrodolerite. In most samples, both types
 of ores are combined, making these complex ores
 are of particular interest. The main ore mineral is arsenopyrite;
 secondary and accessory minerals include
 pyrite, rutile, ilmenite, galena, chalcopyrite, monazite,
 sphalerite, and native gold. Native gold in quartz-sulfide
 and gold-sulfide ore types is present in a free form as
 microveinlets, micron-size segregations in the host rock,
 or as microinclusions in sulfides. Both ore types are
 characterized by the similar chemical composition of ore
 minerals: the fineness of gold in the gold-sulfide type
 is 870–900 ‰, in veins – 840–910 ‰. The trace element
 composition of pyrite and arsenopyrite from metasomatites
 and quartz veins is also alike. Based on this,
 it was concluded that the productivity of gold-sulfide and
 gold-quartz-arsenopyrite ores was formed by a single
 impulse.