Stratiform base-metal deposits in the Eastern province of the Southern Urals, Russia

The stratiform base-metal Biksizak and Amur deposits, Kolpakovsky and Andree-Yul??evsky group of ore occurrences localized in the Eastern province of the Southern Urals and the adjacent Central Urals are considered in this paper. Their geology, composition of ore, and orebody morphology are characterized. These objects and occurrences occupy different geological positions, being hosted in (1) Ordovician, Silurian, and Devonian limestones formed in an island-arc setting (Biksizak deposit, Kolpakovsky occurrence); (2) Middle and Upper Devonian flyschoid sequences at a distance from the active volcanic zone (Amur deposit); and (3) Riphean (?) platform cover (Andree-Yul??evsky group of occurrences). The objects considered differ in origin. The hydrothermal Pb-Zn ores of the Biksizak deposit and the Kolpakovsky occurrence are epigenetic with respect to the host rocks. They were formed in the Early Carboniferous and related to early collisional minor andesite and quartz diorite porphyry intrusions. The hydrothermal-sedimentary Amur massive sulfide Zn deposit of the Filizchai type was formed at the end of Middle Devonian. Zinc occurrences of the Andree-Yul??evsky group are probably products of regeneration of older stratiform lodes.     

Combining fractal analysis of mineral deposit clustering with weights of evidence to evaluate patterns of mineralization: Application to copper deposits of the Mount Isa Inlier, NW Queensland, Australia

The clustering of mineral occurrences and their spatial associations with particular geological features are critical aspects of mineral distributions for exploration and understanding ore genesis. Variations in the degree of clustering of mineral occurrences or geological features can be measured by fractal dimensions, obtained from a shifting box counting method. Spatial associations between mineral occurrences and geological features can be quantified by the weights of evidence (WofE) method using the contrast value, which increases with the strength of the spatial relationship. A new method is proposed to evaluate mineral occurrence distributions by combining the power of fractal analysis of clustering with the WofE approach. The method compares the correlation between the variation in degree of clustering of mineral occurrences and a geological feature in a study area, with the contrast value of the same feature. The possible outcomes can be simplified into four scenarios, depending on whether the correlation in variation of clustering and the contrast are high or low, respectively. Each outcome has specific exploration implications. If either a high correlation in variation of clustering or a high contrast value is obtained, the geological feature can be used for exploration targeting.The integrated fractal and WofE approach is applied to copper occurrences in the Proterozoic Mount Isa Inlier, NW Queensland, Australia, which hosts large numbers of copper deposits (1,869 occurrences), including the world class Mount Isa copper deposit. Variation in clustering of copper occurrences has a positive correlation with variation in clustering of fault bends (R = 0.823), fault intersections (R = 0.862) and mafic rocks (R = 0.885). WofE results indicate that the copper occurrences are spatially associated with fault intersections and bends and with mafic rocks. Analyses were carried out separately for the two major lithostratigraphic sequences in the Inlier, the Eastern and Western Successions. The Western Succession copper occurrences are apparently more clustered than those of the Eastern Succession, which may reflect a lower degree of exploration and/or geological factors. The association of copper occurrences with mafic rocks compared with fault bends and intersections is greater in the Eastern Succession, which may reflect genetic factors. Correlations in the variation of clustering of mineral occurrences and geological features have a linear relationship with the contrast values, and the spatial association between all geological features and copper occurrences constitute high correlation/high contrast cases. The linear relationship suggests that the geological features that control the clustering of the copper occurrences could be the same features that control their localization.     

Variscan ore formation and metamorphism at the Felbertal scheelite deposit (Austria): constraining tungsten mineralisation from Re–Os dating of molybdenite

The Felbertal scheelite deposit in the Eastern Alps has been regarded as the type locality for stratabound scheelite deposits. It is hosted by a Cambro-Ordovician metavolcanic arc sequence with minor Variscan granitoids (∼ 340 Ma) in the central Tauern Window. Re–Os model ages for molybdenite from the Felbertal tungsten deposit range between ∼ 358 and ∼ 336 Ma and record several pulses of magmatic-hydrothermal-metamorphic molybdenite formation. Molybdenite ages from the K2 orebody, a scheelite-rich quartz mylonite in the Western ore field, indicate that both mineralisation and mylonite are Variscan in age and suggest that the shear zone was active for ∼ 20 million years. Early stage tungsten mineralisation (Scheelite 1) in quartzitic ores in the Eastern ore field, which is free of molybdenite, yielded very low to near blank levels of Re and Os and thus could not be dated. However, molybdenite from scheelite–quartz stringers, previously interpreted as a feeder stockwork to quartzitic scheelite ore of presumed Cambrian age, yielded Variscan Re–Os ages of ∼ 342 and ∼ 337 Ma. Dating of molybdenite contained in scheelite ores thus far provides no indication of a Cambrian component to the tungsten mineralisation. Our data are consistent with a model of either granite intrusion-related ore formation and coeval metamorphic overprint during the Early Carboniferous or, alternatively, molybdenite formation may be exclusively attributed to Variscan metamorphism (see Stein 2006).     

Source of Pb in orogenic lode-gold mineralisation: Pb isotope constraints from deep crustal rocks from the southwestern Archaean Yilgarn Craton, Australia

Southern Cross was one of the earliest gold mining centres in Western Australia. Over 142 tonnes of gold have been produced from the district, and, on a gold per hectare basis, the Southern Cross greenstone belt in the southwestern Yilgarn Craton is the most productive of Western Australia's Archaean greenstone belts. The SW Yilgarn Craton is characterised by high-grade (amphibolite- to granulite-facies) metamorphism, extensive granitoid magmatism and older greenstone volcanism ages, compared to the well-known greenschist-facies metamorphism and younger (2.7 Ga) eruption ages which dominate in the Eastern Goldfields Province. The Pb-isotope compositions of deep-seated granitoids in the SW Archaean Yilgarn Craton, which were emplaced coeval with a craton-wide major orogenic lode-gold mineralization event at about 2.64–2.63 Ga, have been determined for 96 whole-rock and 24 K-feldspar samples. The Pb isotope data of the granitoids are consistent with a crustal origin for their genesis, probably by reworking (partial melting) of older continental crust. The Pb isotope composition of greenstones, which are the main host rocks for gold mineralisation, and pyrites from the komatiite-hosted syngenetic Ni deposits in the amphibolite-facies Forrestania greenstone belt, have also been determined, with initial Pb-isotope ratios higher than that for the Eastern Goldfields Province. The Pb isotopic character of the orogenic lode-gold deposits in the region is intermediate between coeval granitoid and greenstone Pb, indicating that the ore fluids contained metals from both reservoirs. The Pb in the ore fluid of the most deeply formed deposit, Griffin's Find, overlaps the isotopic composition of coeval granitoids, indicating the deep-seated granitoid magmatism was the primary source for Pb in the ore fluids. Received: 8 October 1998 / Accepted 22 December 1998     

Geology and mineralogy of ore at the hidden Engteri Au-Ag deposit,the Magadan Region

The Engteri is a new hidden Au-Ag deposit in the Russian segment of the Pacific ore belt. The discovery of this deposit merits special attention, because it involves repeated attempts to reappraise a lowprospective ore occurrence, which were crowned with success as a result of fulfillment of large-scale drilling project. The average Au grade is 18.6 gpt. The deposit is classified as the gold geochemical type of Au-Ag deposits. The major ore mineral is pyrite, which amounts to no less than 95% of the total ore minerals. The native phases comprise electrum and to a lesser extent native gold of low fineness (730). The homogenization temperature of fluid inclusions is 125–255°C with a distinct maximum at 145–150°C. Despite blind localization of some orebodies, the Engteri deposits bears evidence for a deep erosion level: (1) small vertical range of economic mineralization (50–100 m); (2) predominant occurrence of massive sugarlike quartz with a low sulfide content; (3) prevalence of massive and brecciated textures above rhythmically banded textures; and (4) lack of low-temperature propylites. The southern part of the ore field distinguished by occurrence of rhythmically banded, framework-tabular, and brecciated texture has the best prospect for revealing new orebodies. The Engteri deposit allowed us to outline the following prospecting guides and methods of prospecting for hidden Au-Ag deposits: (1) these deposits are regularly arranged in ore clusters between heavy concentrate anomalies of cinnabar and gold-silver or silver-base-metal occurrences (method of missed link); (2) findings of fragments of ore mineral assemblages with sporadically high Au and Ag contents in barren calcite-quartz veins (method of indicators); (3) linear zones of ankeritization in the fields of low- and mediumtemperature propylites (mapping of metasomatic rocks); and (4) pyrite-quartz veinlets with rhythmically banded pockets (mineralogical mapping of halos of stringer-disseminated mineralization).     

Mineralogy and formation conditions of ores in the Bereznyakovskoe ore field,the Southern Urals,Russia

The Bereznyakovskoe ore field is situated in the Birgil’da-Tomino ore district of the East Ural volcanic zone. The ore field comprises several centers of hydrothermal mineralization, including the Central Bereznyakovskoe and Southeastern Bereznyakovskoe deposits, which are characterized in this paper. The disseminated and stringer-disseminated orebodies at these deposits are hosted in Upper Devonian-Lower Carboniferous dacitic-andesitic tuff and are accompanied by quartz-sericite hydrothermal alteration. Three ore stages are recognized: early ore (pyrite); main ore (telluride-base-metal, with enargite, fahlore-telluride, and gold telluride substages); and late ore (galena-sphalerite). The early and the main ore stages covered temperature intervals of 320–380 to 180°C and 280–300 to 170°C, respectively; the ore precipitated from fluids with a predominance of NaCl. The mineral zoning of the ore field is expressed in the following change of prevalent mineral assemblages from the Central Bereznyakovskoe deposit toward the Southeastern Bereznyakovskoe deposit: enargite, tennantite, native tellurium, tellurides, and selenides → tennantite-tetrahedrite, tellurides, and sulfoselenides (galenoclausthalite) → tetrahedrite, tellurides, native gold, galena, and sphalerite. The established trend of mineral assemblages was controlled by a decrease in $ f_{S_2 } $ f_{S_2 } , $ f_{Te_2 } $ f_{Te_2 } and $ f_{O_2 } $ f_{O_2 } and an increase in pH of mineral-forming fluids from early to late assemblages and from the Central Bereznyakovskoe deposit toward the Southeastern Bereznyakovskoe deposit. Thus, the Central Bereznyakovskoe deposit was located in the center of an epithermal high-sulfidation ore-forming system. As follows from widespread enargite and digenite, a high Au/Ag ratio, and Au-Cu specialization of this deposit, it is rather deeply eroded. The ore mineralization at the Southeastern Bereznyakovskoe deposit fits the intermediate- or low-sulfidation type and is distinguished by development of tennantite, a low Au/Ag ratio, and enrichment in base metals against a lowered copper content. In general, the Bereznyakovskoe ore field is a hydrothermal system with a wide spectrum of epithermal mineralization styles.     

蒙古国伊罗河铁矿床地质特征及找矿标志

蒙古国伊罗河铁矿床属于华力西晚期形成的接触交代型铁矿床,探获资源量近10×10⁸t,矿床平均品位＞50%,外围有多个探明铁矿产地及找矿远景区,周边潜在资源量30×10⁸~40×10⁸t。为探讨该区域接触交代型铁矿床的成矿地质规律,本文从伊罗河铁矿的成矿地质背景、矿区地层、构造、岩浆岩、变质作用分析入手,以其东矿段Ⅰ号矿体为例详细论述矿体形态、规模、产状、赋矿岩性特征,通过矿石样品测试分析阐述矿物组成特征、化学成分、矿石结构构造、磁铁矿粒度及成矿阶段等,初步总结了矿床成因和找矿标志。     

Mineralogy, chemistry and genesis of Nishikhal manganese ores of South Orissa, India

Manganese ores of Nishikhal occur as distinctly conformable bands in the khondalite suite of rocks belonging to the Precambrian Eastern Ghats complex of south Orissa, India. Manganese minerals recorded are cryptomelane, romanechite, pyrolusite, with minor amounts of jacobsite, hausmannite, braunite, lithiophorite, birnessite and pyrophanite. Goethite, graphite, hematite and magnetite are the other opaque minerals and quartz, orthoclase, garnet, kaolinite, apatite, collophane, fibrolite, zircon, biotite and muscovite are the gangue minerals associated with these ores. The mineral chemistry of some of the phases, as well as the modes of association of phosphorous in these ores have been established. The occurrence of well-defined bands of manganese ore; co-folding of manganese ore bands and associated metasedimentary country rocks; the min-eral assemblage of spessartite-sillimanite-braunite-jacobsite-hausmannite; the geochemical association of Mn-Ba-Co-Ni-Zn together with the Si versus Al and Na versus Mg plots of the manganese ores suggest that the Nishikhal deposit is a metamorphosed Precambrian lacustrine deposit. Continental weathering appears to be the source for manganese and iron. After deposition and probable diagenesis, the manganese-rich sediments were metamorphosed along with conformable psammitic and pelitic sediments under granulite facies conditions, and subsequently underwent supergene enrichment to produce the present deposit. Received: 14 March 1995 / Accepted: 11 April 1996     

Structural,lithological, and geochemical constraints on the dynamic magma plumbing system of the Jinchuan Ni–Cu sulfide deposit,NW China

Eastern and western portions of the Jinchuan ultramafic intrusion have previously been interpreted as dismembered segments of a single elongate intrusion by late faults. However, the different stratigraphic sequences of the two portions indicate that they are originally two separate intrusions, referred to as Eastern and Western intrusions in this study. The Eastern intrusion is characterized by a concentric distribution of rock types with a core of sulfide dunite enveloped by lherzolite, whereas the Western intrusion is composed of the Upper and Lower units, interpreted as magmatic mega cycles with regular variations in lithology and chemistry. In the Western intrusion, the Upper unit consists of fine-grained dunite, lherzolite, and pyroxenite from its base to its top. The MgO contents decrease upward from the dunites (42–45 wt.%) to the lherzolites (36–41 wt.%), while Al₂O₃ and incompatible elements increase upward. In contrast, the Lower unit consists of coarse-grained dunites and lherzolites containing 37–40 and 28–35 wt.% MgO, respectively. Sharp contacts between the Upper and Lower units and fine-grained dunite xenoliths at the top of the Lower unit indicate that the Lower unit intruded along the base of the Upper unit. Disseminated and net-textured sulfides primarily occur in the Lower unit and comprise the no. 24 ore body. Very low S contents (<100 ppm) of the wall rocks at Jinchuan indicate that they were not the source of S causing sulfide immiscibility. Sulfide segregation more likely occurred in deep-seated magma chambers, and sulfides were deposited in the Western intrusion when sulfide-bearing magmas passed through the intrusion. In contrast, the Eastern intrusion was formed by injections of sulfide-free and sulfide-bearing olivine-crystal mushes, respectively, from another deep-seated staging magma chamber. The Eastern and Western intrusions and the deep-seated magma chambers comprise a complicated magma plumbing system at Jinchuan. Normal faults played a significant role in the formation of the magma plumbing system and provided pathways for the magmas.     

湘西-黔东下寒武统清虚洞组藻灰岩沉积特征及其找矿意义

铅锌矿是湘西-黔东地区的优势矿种,资源丰富,开发历史悠久,找矿潜力巨大。综合分析前人有关湘西-黔东生物礁的资料,介绍了藻灰岩的沉积特征,并结合大量实际地质资料,对藻灰岩控矿进行了论述。结果表明: 成矿物质主要来源于藻类及碳酸盐泥对Pb²⁺、Zn²⁺离子的吸取,矿床成因属于沉积成岩矿床类型,兼有成岩期后矿床性质; 藻礁灰岩与不同岩性的接合部位及其附近等微地球化学障区,往往就是铅锌富矿体产出部位; 藻礁灰岩与礁间通道的薄层泥质白云质灰岩呈指状交叉接触处,也常有铅锌富矿体产出; 铅锌富矿体基本上产于清虚洞组灰岩段中,且明显受该段藻礁灰岩控制。为满足国内外对铅锌矿日益增长的消费需要,深入研究区内铅锌矿的地层岩相岩石控矿因素及其富集规律,指导该地区藻灰岩中铅锌矿找矿工作,具有重要的现实意义。     

Ag-Sb mineralization of the Yana-Kolyma belt, Northeast Russia

The mineral assemblages of the Ag-Sb deposits from the Yana-Kolyma Foldbelt were studied. The compositions of ore minerals, the isotopic compositions of sulfur in ore minerals, and the carbon and oxygen in carbonates are given. Arsenopyrite of the deposits is significantly enriched in Sb (1–16 wt %), which is related to the primary enrichment of the ore-hosting sequences in Sb and the ore formation at shallow depths. Based on the fluid inclusions study, the deposits were formed at T = 329–149°C and P = 0.30–1.04 kb from low-salinity chloride-sulfate-bicarbonate solutions enriched in Sb and Ag. The sequence of precipitation of Ag-Sb minerals was mainly controlled by the Sb concentration and the sulfur fugacity and potential in the fluid.     

Rhenium–osmium systematics of the Mount Isa copper orebody and the Eastern Creek Volcanics,Queensland, Australia: implications for ore genesis

The syn-tectonic breccia-hosted Mount Isa Cu deposit in northwest Queensland is the largest sediment-hosted Cu deposit in Australia. Whole-rock samples of chalcopyrite-rich Cu ore form an isochron with a Re–Os age of 1,372 ± 41 Ma. This age is more than 100 Ma younger than the previously accepted age of Cu ore formation, an Ar–Ar mineral age for biotite separated from the host rocks within the alteration envelope to the Cu orebody. This discrepancy cannot be unequivocally resolved due to a lack of other absolute geochronological constraints for Cu mineralisation or the deformation event associated with Cu emplacement. The 1,372 ± 41 Ma date may reflect (a) the time of Cu deposition, (b) the time of a hydrothermal event that reset the Re–Os signature of the Cu ore or (c) mixing of the Re–Os isotope systematics between the host rocks and Cu-bearing fluids. However, a range of published Ar–Ar and Rb–Sr dates for potassic alteration associated with Cu mineralisation also records an event between 1,350 and 1,400 Ma and these are consistent with the 1,372 Ma Re–Os age. The 1.8 Ga Eastern Creek Volcanics are a series of tholeiitic basalts with a primary magmatic Cu enrichment which occur adjacent to the Mount Isa Cu deposit. The whole-rock Os isotopic signature of the Eastern Creek Volcanics ranges from mantle-like values for the upper Pickwick Member, to more radiogenic/crustal values for the lower Cromwell Member. The Re–Os isotope signature of the Cu ores overlaps with those calculated for the two volcanic members at 1,372 Ma; hence, the Os isotope data are supportive of the concept that the Os in the Cu ores was sourced from the Eastern Creek Volcanics. By inference, it is therefore postulated that the Eastern Creek Volcanics are the source of Cu in the Mount Isa deposit, as both Os and Cu are readily transported by oxidised hydrothermal fluids, such as those that are thought to have formed the Cu orebody. The Pickwick Member yields a Re–Os isochron age of 1,833 ± 51 Ma, which is within error of previously reported age constraints. The initial ¹⁸⁷Os/¹⁸⁸Os isotopic ratio of 0.114 ± 0.067 (γOs = −0.7) is slightly subchondritic, and together with other trace element geochemical constraints, is consistent with a subcontinental lithospheric mantle source. The Pickwick Member records a minimum age of ca. 1.95 Ga for melt depletion in the subcontinental lithospheric mantle beneath the Mount Isa Inlier prior to the extraction of the magmas which formed the Eastern Creek Volcanics. This corresponds with the end of subduction-related magmatism along the eastern margin of the Northern Australian Craton, which included the Mount Isa Inlier.     

山东玲珑金矿石英成因矿物学研究及其找矿远景的确定

玲珑金矿是我国目前最大、开采历史最久的含金石英脉型金矿之一。已有许多地质学者对其多方面进行了大量研究,但对最重要的脉石矿物—石英,仍有必要系统研究,为这个老矿山的远景找矿和那些尚未勘探的石英脉的含矿性评价提供有用信息。     

Geological and fluid inclusion studies of the Dongpo tungsten skarn ore deposit,China

The Dongpo tungsten ore deposit, the largest scheelite skarn deposit in China, is located at the contact of a 172-m. y. biotite granite with a Devonian marble. The mineralization associated with the granite includes W, Bi-Mo, Cu-Sn and Pb-Zn ores. Several W mineralization stages are shown by the occurrence of ore in massive skarn deposits and in later cross-cutting veins. The high garnet/pyroxene ratio, the hedenbergite and diopside-rich pyroxene and the andradite-rich garnet show the deposit belongs to the oxidized skarn type. Detailed fluid inclusion studies of granite, greisen, skarn and vein samples reveal three types of fluid inclusion: (1) liquid-rich, (2) gas-rich and (3) inclusions with several daughter minerals. Type (3) is by far the most common in both skarn and vein samples. The dominant daughter mineral in fluid inclusions is rhembic, highly birefringent, and does not dissolve on heating even at 530°C. We assume that this mineral is calcite. The liquid phase in most of the fluid inclusions has low to moderate salinities: 0–15 wt. %; in a few has higher salinities (30–40 wt. % NaCl equivalent). The homogenization temperatures of inclusions in the skarn stage range from 350°C to 530°C, later tungsten mineralization-stage inclusions homogenize between 200°C and 300°C, as do inclusions in veins. Fluid inclusions in granite and greisen resemble those of the late tungsten mineralization stage, with low salinity and homogenization temperatures of 200°–360°C. The tungsten-forming fluids are probably a mixture that came from biotite granite and the surrounding country rocks.     

The Late Paleozoic porphyry–epithermal spectrum of the Birgilda–Tomino ore cluster in the South Urals,Russia

The Birgilda–Tomino ore cluster in the East Uralian zone, South Urals, Russia, hosts a variety of Late Paleozoic porphyry copper deposits (Birgilda, Tomino, Kalinovskoe, etc.), high- and low sulfidation epithermal deposits (Bereznyakovskoe, Michurino), and skarn-related base metal mineralization (Biksizak) in carbonate rocks. The deposits are related to quartz diorite and andesite porphyry intrusions of the K–Na calc-alkaline series, associated to a subduction-related volcanic arc. We report microprobe analyses of ore minerals (tetrahedrite–tennantite, sphalerite, Bi tellurides and sulfosalts, Au and Ag tellurides), as well as fluid inclusion data and mineral geothermometry. On the basis of these data we propose that the Birgilda–Tomino ore cluster represents a porphyry–epithermal continuum, with a vertical extent of about 2–3 km, controlled by temperature decreases and fS₂ and fTe₂ increase from deeper to shallow levels.     

Mineralogy and geochemistry of the sodium metasomatism-related uranium occurrence of Aricheng South, Guyana

The Aricheng South uranium occurrence is associated with Na metasomatism that affected the granitoids of the Kurupung Batholith in western Guyana. The mineral paragenesis indicates that late-magmatic albitization was followed by chlorite alteration of biotite. A minor amount of uraninite occurs in fractures in the newly formed albite crystals, often in company of calcite. The main mineralization stage occurred later than albitization and chloritization and is represented by brannerite disseminated in a groundmass of fine-grained hydrothermal zircon. Whole rock geochemistry supports the temporal dissociation of albitization from the main ore stage. Brannerite, zircon, and uraninite are often partially altered to secondary brannerite, zircon, and coffinite, respectively. Stable oxygen (chlorite, calcite) and hydrogen (chlorite) isotope compositions suggest that a highly evolved meteoric fluid, or at least one corresponding to a very high rock/fluid ratio (δ¹⁸O of approx. 3.4% to 4‰ and δD of approx. −80‰) may have caused the pre-ore alteration assemblage. The fluids in equilibrium with main ore stage zircon have δ¹⁸O of approx. 6.8‰ and appear to be of magmatic origin. The Aricheng occurrence geochemically, mineralogically, thermally, and paragenetically resembles the Valhalla U deposit in northern Australia despite differences between the deposits’ host lithologies, whereas the Lagoa Real and Espinharas U deposits in Brazil have host rock lithology that resembles that of Aricheng.     

The Ribeira fluorite district,southern Brazil

The origin and evolution of different ore deposits grouped in the same district are often complex and may involve inheritance from crustal or mantle geochemical anomalies, remobilization of former ore deposits and a polyphase hydrothermal history. Localized in a Proterozoic basement in the Parana state, the Ribeira fluorite district is such an example composed of three deposit types with distinct geological and geochemical characters. Emplaced at different periods from the late Proterozoic to the Cretaceous, they are roughly aligned along a belt nearly 10 km in width and 50 km in length, the southern boundary of which is a transcurrent fault. Two main ore facies are present: (1) microcrystalline ore (< 0.1 mm grains) and (2) macrocrystalline ore (with a grain size of several millimetres). The former results from the replacement of metalimestones or internal karstic sediments and the latter from microcrystalline ore dissolution and pore precipitation or recrystallization. At least two different groups of source rocks can be proposed for the trapped REE in CaF₂: (1) fluorite samples associated with the Mato Preto carbonatitic rocks display a slightly negative ɛNd compatible with a mantle source and a REE pattern with the higher ΣREE and La/Yb ratio in the district; (2) other fluorites have a strongly negative ɛNd (− 14 to − 20) which indicates a crustal source. That fluorine and REE have the same source is possible in strata-bound and fracture-filling deposits, but is doubtful at Mato Preto, the only economic fluorite deposit associated with carbonatite rocks in Brazil. This occurrence within a Precambrian fluorite belt suggests that remobilization of a former strata-bound deposit was a more significant metallogenic process than magmatic differentiation. Editorial handling: DR     

Gold and silver tellurides in the Shirokinsky ore-and-placer cluster,the Sette-Daban Ridge,Yakutia

The first findings of Au and Ag tellurides (sylvanite and petzite) in sulfide-quartz ore of the Shirokinsky ore and placer cluster located in the Sette-Daban Horst-Anticlinorium are described. These minerals were found for the first time at the gold deposits of East Yakutia. The chemical compositions (wt %) of sylvanite (23.65–24.61 Au, 12.7–13.13 Ag, 59.3–59.97 Te, 96.26–97.97 in total) and petzite (23.17–25.24 Au, 42.27–44.40 Ag, 31.26–33.37 Te, 98.19–102.55 in total) are reported. Galena as a host mineral is associated with native gold, electrum, hessite, and stützite. The finding of Au-Ag and Ag tellurides provides evidence for the development of Au-telluride mineralization in the Sette-Daban Horst-Anticlinorium.     

Topical issues of the theory of gold deposit formation

The issues of the theory of gold deposit formation are considered. These issues were crucial in the works by N.V. Petrovskaya. The systematics of gold deposits based on stable mineral assemblages and mineral and geochemical types of ores and their families characteristic of certain groups of gold deposits is consonant with contemporary analogue classifications of ore deposits, which, however, require improvement by means of developing their genetic version. Petrovskaya’s proposed subdivision of gold deposits into families distinguished by depth of their formation is such a version, because in Petrovskaya’s understanding, the factor of depth integrates genetic features of deposits formed at shallow, medium, and great depths. According to recent data, the depth interval of localization of ore deposits is estimated at 15–20 km instead of 6–10 km suggested earlier; thus, the intervals of medium and great depths increase. Attention is called to the Petrovskaya’s ideas of stadial progressive development of ore formation with change in pyrite-arsenopyrite mineralization by base-metal and telluride mineralization along with advanced and concomitant deposition of quartz. The stadial formation of shallow-seated deposits and colloidal mineral formation therein, as well as the concept of gel metasomatism and mechanisms of accompanying destruction of preceding mineral assemblages developed by Petrovskaya, are considered and their implications are illustrated by specific deposits. Petrovskaya’s views on sources of ore matter and the polygenetic character of gold and Au-bearing deposits are discussed.     

Constraints on the composition of ore fluids and implications for mineralising events at the Cleo gold deposit,Eastern Goldfields Province,Western Australia

The Cleo gold deposit, 55 km south of Laverton in the Eastern Goldfields Province of Western Australia, is characterised by banded iron‐formation (BIF)‐hosted ore zones in the gently dipping Sunrise Shear Zone and high‐grade vein‐hosted ore in the Western Lodes.There is evidence that gold mineralisation in the Western Lodes (which occurred at ca 2655 Ma) post‐dates the majority of displacement along the Sunrise Shear Zone, but it remains uncertain if the ore in both structures formed simultaneously or separately. Overall, the Pb, Nd, Sr, C, O and S isotopic compositions of ore‐related minerals from both the Western Lodes and ore zones in the Sunrise Shear Zone are similar. Early low‐salinity aqueous‐carbonic fluids and late high‐salinity fluids with similar characteristics are trapped in inclusions in quartz veins from both the Sunrise Shear Zone and the Western Lodes. The early CO₂, CO₂–H₂O, and H₂O‐dominant inclusions are interpreted as being related to ore formation, and to have formed from a single low‐salinity aqueous‐carbonic fluid as a result of intermittent fluid immiscibility. Homogenisation temperatures indicate that these inclusions were trapped at approximately 280°C and at approximately 4 km depth, in the deeper epizonal range. Differences between the ore zones are detected in the trace‐element composition of gold samples, with gold from the Sunrise Shear Zone enriched in Ni, Pb, Sn, Te and Zn, and depleted in As, Bi, Cd, Cu and Sb, relative to gold from the Western Lodes. Although there are differences in gold composition between the Sunrise Shear Zone and Western Lodes, and hence the metal content of ore fluids may have varied slightly between the different ore zones, no other systematic fluid or solute differences are detected between the ore zones. Given the fact that the ore fluids in each zone have very similar bulk properties, the considerable differences in gold grade, sulfide mineral abundance, and ore textures between the two ore zones most likely result from different gold‐deposition mechanisms. The association of ore zones in the Sunrise Shear Zone with pyrite‐replaced BIF suggests that wall‐rock sulfidation was the most significant mechanism of gold precipitation, through the destabilisation of gold‐bisulfide complexes. The Western Lodes, however, do not exhibit any host‐rock preference and multistage veins commonly contain coarse‐grained gold. Fluid‐inclusion characteristics and breccia textures in veins in the Western Lodes suggest that rapid pressure changes, brought about by intermittent release of overpressured fluids and concomitant phase separation, are likely to have caused the destabilisation of gold‐thiocomplexes, leading to formation of higher‐grade gold ore zones.