Ore Formation Research Articles

Brine reflux as a possible first order control on the alkali geochemistry of baseline sedimentary rocks in the Proterozoic North Australian Zinc Belt

The Proterozoic McArthur Basin is economically significant because it contains the world-class McArthur River camp of stratiform Zn-Pb deposits hosted in shales in the c. 1640 Ma Barney Creek Formation. Despite periods of strong interest from minerals explorers and research groups over the past forty years, significant additional resources have not yet been discovered in the terrane. High potassium (K) concentrations in rocks in the McArthur Basin are noted since the earliest literature. One hypothesis for high K concentrations in the Barney Creek Formation is the development of authigenic K-feldspar (K-feldspathisation) by exposure to a low temperature brine reflux flow system during early diagenesis. This is significant to minerals exploration because the genetic link between low temperature brine reflux and sediment-hosted ore formation is an emerging topic in economic geology. K-feldspathisation of sedimentary sequences may be a key identifier of regional potential for development of McArthur River type mineralisation.Gianfriddo et al. (2022) characterise K-feldspathised and non-feldspathised Barney Creek Formation using SEM imagery and whole rock inorganic geochemistry. Here we demonstrate that public domain geochemistry data for basinal sedimentary rocks in wider Proterozoic northern Australia broadly conform to the same K-feldspathised and non-feldspathised fields defined by Gianfriddo et al. (2022). Based on the assumption that the alkali signature in the regional data reflects the presence/absence of authigenic K-feldspar analogous to that described in the Barney Creek Formation case study, and the interpretation that this is controlled by K-feldspathisation during brine reflux, these data indicate a preliminary framework for extensive fluid flow that is geographically coherent and consistent with current understanding of the tectono-sedimentary evolution of Proterozoic northern Australia.We caution that our model is speculative at this stage and requires detailed studies of the mineralogy and facies of the samples for validation. While readers are encouraged to consider this approach in their mineral exploration or academic work, other components such as lithology, facies, mineralogy, diagenesis, and provenance need necessarily also be considered especially at the local scale.

A metasomatised mantle origin for post‐collisional porphyry ore‐forming magmas in the Sanjiang metallogenic belt, Southwest China

AbstractWe constrain the magma sources of representative post‐collisional ore‐associated and barren suites in the Sanjiang metallogenic belt, Southwest China. The ore‐associated suites generally have higher Mg# and Cr and Ni contents than the crustal melts. Also, they show wide ranges of whole‐rock Nd and zircon Hf isotopes that are similar to the subduction‐modified mantle‐derived alkaline volcanic rocks in the region. Combing with the geochemical model, we suggest that the ore‐associated suites dominantly originated from partial melts of subduction‐metasomatised mantle by fractional crystallisation. In contrast, the barren suites are mainly characterised by low Mg# and Cr and Ni contents that are comparable to the crustal melts and they have enriched whole‐rock Nd and zircon Hf isotopes, indicating a metasomatised lower crustal origin. The different magma sources play an important role in controlling the fertility of contemporary ore‐associated and barren magmatic suites during post‐collisional porphyry ore formation.

Diffusion of Sm‐Nd in Scheelite and its Significance to Isotopic Dating and Tracing

AbstractAs the principal ore mineral in various tungsten (‐gold) deposits, scheelite (CaWO4) plays an important role in directly dating the timing of ore formation, and in tracing associated material sources through the study of its Sm‐Nd geochronology and Nd isotopic characteristics. Since the retention of Sm‐Nd systematics within scheelite is presently unconstrained, equivocal interpretations for isotopic data resulting from this method have occurred quite often in previous studies that apply these isotopic data. In order to better elucidate the closure of Sm‐Nd in scheelite, the kinetics of Sm and Nd within this mineral lattice were investigated through calculation of diffusion constants presented herein. The following Arrhenius relations were obtained: urn:x-wiley:10009515:acgs15005:equation:acgs15005-math-0001 showing diffusion rate of Nd is near identical to Sm in scheelite when at the same temperature. However, compared to other rare earth elements (REEs), which have markedly different atomic radii to either Nd or Sm, these are shown to exhibit a great variation in diffusivities. The observed trends in our data are in excellent agreement with the diffusion characteristics of REEs in other tetragonal ABO4 minerals, indicating that ionic radius is a key constraint to the diffusivity of REEs in the various crystal lattices. With this in mind, the same substitution mechanism and a very slight discrepancy in radii will allow us to infer that significant Sm/Nd diffusional fractionation in scheelite is unlikely to occur during most geological processes.Based upon the diffusion data determined herein, Sm and Nd closure temperatures and retention times in scheelite are discussed in terms of diffusion dynamics. Those results suggest that closure temperatures for Sm‐Nd within this mineral are relatively high in contrast to the temperature ranges of ore‐formation responsible for scheelite‐related deposits, and any later thermal environments. It is likely, therefore, that relevant isotopic information could be easily retained under most geological conditions, since initial crystallization of the scheelite. In addition, comparison of this mineral‐element pair over a range of temperatures with some other common minerals used as geochronometers (e.g., zircon and apatite) indicates that Sm‐Nd system has a slower diffusive rate in scheelite than for Sr in apatite or Ar in quartz, and only a little faster than for Pb in zircon. It should be noted, within most hydrothermal deposits where zircon has crystallized, its size is typically no more than 100 μm, whereas scheelite commonly occurs as macroscopic grains. For this reason, the larger dimensions of scheelite would provide a robust Sm‐Nd system more able to resist perturbations, relating to any later thermal process. As such Sm‐Nd investigations of scheelite are akin to U‐Pb within zircon samples used in isotopic dating. These observations indicate that Sm‐Nd age and isotopic information can provide reliable data in all but the most extreme case, especially when data are extracted from macroscopic grains of scheelite that are chosen to be “pristine” (i.e., free of surface alteration and/or fractures).

Вещественный состав золоторудного месторождения Среднеканская дайка (Северо-Восток России)

The article comprehensively describes host rocks and ores of the Srednekanskaya Dike gold deposit. Ore formation was found to include several stages: metamorphogenic, hydrothermal-metasomatic (productive), and hypergenic. Characteristic features of gold mineralization have been revealed. The bulk of the gold is confined to vein quartz (1); gold fills interstitia in quartz, arsenopyrite, and pyrite (2); in quartz veins and quartz-carbonate-feldspar breccias, localized in microdiorites, gold is deposited in arsenopyrite and pyrite, and associated with diorite-porphyry - only in arsenopyrite (3); the decisive role in the formation of gold mineralization is played by structural control expressed by brecciation and hydrothermal metasomatosis of rocks and by resulting gold sedimentation in weakened zones (4).

The Use of Typomorphic Features of Placer Gold of the Anabar Region for Determining Its Sources

Typomorphic features of placer gold of the Anabar region were studied as predictive-exploration criteria. The target of the study was to determine the typomorphic features of placer gold related to the intermediate sources (paleo-placers) and the supposed nearby primary ore occurrences. Two varieties of placer gold were identified. The first variety is well-rounded high-fineness lamellar gold with a highly modified internal structure. This native gold is associated with intermediate sources, Neogene–Quaternary watershed pebble beds. The second type includes slightly rounded gold with a wide variation in fineness (494‰–999‰). Its indicator is a block heterophase internal structure. The set of typomorphic features of this variety of placer gold indicates the vicinity of the primary source, what was the prerequisite for constructing prospecting traverses in order to find ore occurrences. As a result of these studies, hydrothermal-metasomatic formations with gold-sulfide mineralization were identified. The main primary substrate for them is fractured near-fault carbonate rocks of the Cambrian and Vendian–Cambrian age. Along with this, hydrothermalites developed on slightly cemented fine-pebble quartz conglomerates of the Middle Permian age were found in the core of exploration wells. Two types of metasomatic rocks are identified: quartz-potassium feldspar and jasperoid. The main ore minerals were galena and pyrite, different ratios by sites were revealed. Gold was identified in the form of small particles in the carbonate and siliceous substrate of hydrothermal-metasomatic formations. The lithological factor was one of the leading favorable factors for the ore formation due to the presence of near-fault highly permeable fractured carbonate and slightly cemented terrigenous rocks. The structural control of the studied ore occurrences is determined by their localization in the Mayat–Logoy and Dogoy–Kuoy faults of the Molodo–Popigay system of discontinuous faults. We assume a two-stage formation of the gold ore occurrences: during the first stage, the ore components in the form of primary hydrothermal-sedimentary ores in the near-gault zones were formed. The second stage was related to the processes of the Mesozoic tectonic-magmatic activation, when the intrusion of basite dikes initiated the mobilization of ore components the gold-sulfide occurrences were formed in the near-fault zone as a result of silicic-potassic metasomatosis of the carbonate and terrigenous rocks.

Circular economy landfills for temporary storage and treatment of mineral-rich wastes

Many countries face serious strategic challenges with the future supply of both aggregates and critical elements. Yet, at the same time, they must sustainably manage continued multimillion tonne annual arisings of mineral-dominated wastes from mining and industry. In an antithesis of circular economy principles, these wastes continue to be landfilled despite often comprising valuable components, such as critical metals, soil macronutrients and mineral components which sequester atmospheric carbon dioxide (CO2). In this paper, the authors aim to introduce a new concept for value recovery from mineral-rich wastes where materials are temporarily stored and cleaned in landfill-like repositories designed to be mined later. The time in storage is utilised for remediating contaminated materials and separating and concentrating valuable components. It is proposed that this could be achieved through engineering the repository to accelerate ‘lithomimetic’ processes – that is, those mimicking natural supergene processes responsible for the formation of secondary ores. This paper summarises the concept and justifications and outlines fundamental aspects of how this new concept might be applied to the design of future repositories. The proposed concept aims to end the current ‘linear’ landfilling of mineral-rich wastes in favour of reuse as aggregates and ores.

In situ LA–ICP–MS analyses of muscovite: Constraints on granite-type Li mineralization in northwestern Jiangxi, South China

Giant granite-type lithium (Li) deposits in northern Jiangxi province (South China), such as the Shiziling–Baishuidong (1.1Mt @ 0.3 wt% Li2O) and Yichun #414 (0.6 Mt @ 0.39 wt% Li2O), are tectonically located in the Jiangnan Orogen. The concentration and enrichment mechanism of rare metals (incl. Li) in northern Jiangxi is still unclear. Mica is widely distributed in this Li-ore type and is closely ore-related. Therefore, we used mica geochemistry to determine the mineralization process and mechanism of the Shiziling-Baishuidong and Yichun #414 deposits. At Shiziling-Baishuidong, lithium mineralization is concentrated along the intrusive endo-contact of Early Cretaceous highly-fractionated S-type muscovite granite. Early albite and muscovite (with Li-rich mica) alterations, and late greisen (muscovite and quartz) alterations are common in the Shiziling-Baishuidong and Yichun #414 deposits. The hydrothermal and magmatic muscovite is mostly lepidolite and zinnwaldite, respectively. At Yichun, the biotite- or two-mica granite may have altered by F- and Na-rich magmatic–hydrothermal fluids, leaching the Li-Nb-Ta-W for the subsequent mineralization in the muscovitization and greisenization stages. The re-equilibrated muscovite (M2r), a metasomatic(altered) equilibrated muscovite in the altered granite, has the lowest Li (663 ppm), Nb (15.2 ppm), Ta (16.7 ppm), and W (6.12 ppm) contents. At both Shiziling–Baishuidong and Yichun, the magmatic muscovite has the highest Nb/Ta (mostly > 8) but lower Li/Rb (mostly 1.5), whereas the hydrothermal muscovite has the lowest Nb/Ta (mostly ∼ 4) but higher Li/Rb (mostly > 1.5). The re-equilibrated muscovite has Nb/Ta = 4 to 8 and a wide Li/Rb range (0.1 to 2.0). When lithium was precipitated, the re-equilibrated and hydrothermal muscovite mineralogy and chemistry show that hydrothermal alteration was essential in the granite-type Li ore formation at Shiziling–Baishuidong.

Gold, antimony and mercury ore formation and metallogenic link in the Sandu-Danzhai area, Jiangnan Orogen, SW China

The turbidite-hosted Au-Sb-Hg deposits in the Sandu-Danzhai area are distributed along the southwestern marginal fault of the Jiangnan Orogen, yet any genetic link among the Au, Sb and Hg mineralization and their respective ore-forming process remain unclear. Here, we investigate the Paiting Au(-Hg) and Miaolong Au-Sb deposits and present a new metallogenic model based on detailed petrographic observations, and in-situ trace element (EPMA and LA-ICP-MS) and sulfur isotope (fs-LA-MC-ICPMS) analyses on sulfide minerals. Our results show that the ore formation in the Sandu-Danzhai metallogenic belt (SDMB) can be divided into Au (pyrite + arsenopyrite + dolomite), Au-Sb (pyrite + arsenopyrite + stibnite + quartz), Sb (stibnite + native antimony + barite + dolomite + quartz) and Hg (cinnabar + calcite) stages, based on mineral paragenetic and vein crosscutting relationships. Trace element compositions suggest that progressive As enrichment in pyrite is accompanied by increasing Au, Sb and Cu contents, implying that these elements may have been leached from the same source via fluid-rock reactions. Sulfur isotope compositions of the sulfates and sulfides in the Au-Sb-Hg ores reveal that the sulfur was originated from thermal-chemical sulfate reduction (TSR) of marine sulfates in the Cambrian ore-bearing strata. Thus, we propose that deep metamorphic fluids (as evidenced from the high fluid CO2 and CH4 contents) may have promoted ore-material (e.g., Au, Sb, As, Hg) mobilization in the metamorphic basement and/or Cambrian strata. As for the metal transport and precipitation mechanism, fluid-rock interaction may have decreased the ore-fluid As content and caused auriferous pyrite precipitation. Meanwhile, changes in temperature and oxygen-sulfur fugacity may have significantly decreased Sb solubility, leading to extensive stibnite precipitation. Cinnabar associated with calcite was likely deposited via carbonate dissolution in the Cambrian strata in late hydrothermal (waning) stage. Overall, we propose that the Au-Sb-Hg deposits in the SDMB are best classified as orogenic type, and the metallogeny was controlled by boundary faults of the Jiangnan Orogen.

Combination model-based numerical simulation of the mineralizing processes within iron oxide-apatite systems

Iron oxide-apatite (IOA) deposits are high grade iron magmatic-hydrothermal mineral deposits having significant economic values and extremely complex and coupled forming processes. The combination model of ore deposits is a model integrating characteristics of several deposits with the same genetic type or sharing close temporal-spatial correlations. This research highlights the usage of numerical simulation method and combination model of deposits in quantitatively analyzing ore-forming processes during the formation of IOA systems and views the future developments of numerical modeling in ore geology research. Our numerical model couples heat transfer, pressure, fluid-flow, chemical reactions and migration of ore-forming materials. Results match the fact that temperature reduction and pressure variation are two key factors controlling the temporal-spatial distribution of iron mineralization, and results of cooling process indicates that a single period of ore formation of IOA deposits may last no more than 12,200 years, a timespan much shorter than previously estimated. These results are obtained based on the concept of combination model of IOA systems, providing quantitative information reflecting the generation of IOA deposits. However, the methods in our research are stills limitations remained, such as uncertainty of pre-metallogenic conditions and restriction from elementary reactions. Future advances in analytical methods and mathematical models will definitely improve the practicality of combination model of deposits and numerical modeling of ore formation, and provide quantitative answers for existing problems related to mineral deposits.

Scientific achievements of USMU employees in the field of searches and exploration of deposits of piezo-optical and vein quartz

The study of deposits of piezo-optical and vein quartz in the Middle and Southern Urals by employees of the Ural State Mining University (Sverdlovsk Mining Institute) took place in two stages. The period of active introduction of scientific achievements of the Sverdlovsk school of quartzists under the guidance of Professor G. N. Vertushkov lasted more than 30 years – from 1950 to 1980. As a result, a method of field observations and laboratory studies of vein quartz was developed, namely, quartzometric survey, the effectiveness of which was proved by its use for 50 years. The second period of scientific study of quartz deposits proceeded from 1992 to 2020. The creative scientific team of the Department of Geology, consisting of Doctors of Geological and Mineralogical Sciences V. N. Sazonov, V. N. Ogorodnikov, Yu. A. Polenov and Candidate of Geological and Mineralogical Sciences A. N. Savicheva continued a detailed study of gold and quartz deposits. The subject of the closest attention of the authors was the connection between the processes of ore formation and changing geodynamic conditions. It has been established that many ore fields of the Ural deposits are polychronous and polygenic.

To the features of the mechanism of ore formation

To date, there is no doubt that in the Paleozoic the crust of the Urals was formed in a setting of tangential compression as a result of manifestations of several tectonic cycles, each of which was due to the thrust of the oceanic crust on the continental base. As a result, the geochemical interaction of the compositions of volcanogenic-sedimentary formations, which evolved in accordance with the increase in tectonic compression from minimum to maximum values, was determined. Significantly increased tectonic loads lead to squeezing of eruption channels, cessation of magmatic activity, widespread development of flysch and olistostromal strata, massive thrusting and digging of previously formed formations, and the appearance of anatectic granite intrusions. The first half of the tectonic cycle, as a rule, evolutionary, led to the development of igneous rocks — the main carriers of ore components in a dispersed state. The second half is deformation, in addition to the listed processes, it contributed to the concentration of useful components in one way or another in the deposit. In accordance with the model of the formation of the earth’s crust, the epochs of ore formation are simultaneous with the thrusting and are genetically determined by it.

Mineralogy of ores of the Vosneenskoe gold deposit (Southern Ural)

The mineralogical features of the ores of the Voznesenskoye gold deposit located in the zone of the Main Ural Fault at the northern end of the Magnitogorsk megazone of the Southern Urals have been studied. The chemical composition of minerals was determined using a Tescan Vega Compact scanning electron microscope with an Oxford Instruments Xplorer 15 energy dispersive analyzer. Two stages of ore formation have been identified and characterized. On the early of them, arsenic pyrite (0.38–0.84% As), which is the main mineral of ores, was first formed, and later sulfurous arsenopyrite (S/As = 1.12–1.19), molybdenite enriched in Fe (7.25–8.07%), and chalcopyrite. Using an arsenopyrite geothermometer, it was found that the formation of sulfides at an early stage occurred approximately in the temperature range of 318–380°C. At a late stage, an association was formed that united pyrite containing Sb (0.28–0.31%), Zn-Fe-tetrahedrite (Cu9.1–9.4 (Fe1.2–1.3 Zn1.1–1.4)2.4–2.6 (As0.2–0.4 Sb3.7–4.1)4.2–4.3 S12.9–13.2) and native high-grade gold (952–997‰) with impurities Ag and Cu. Minerals of this association, which have an insignificant distribution, are found in crushing zones developed in arsenic pyrite. In terms of chemical composition, the studied tetrahedrite is close to the fahlores of the subepithermal mineralization of the Mikheevka porphyry Cu deposit. Based on the results of the studies performed, a preliminary conclusion was made that the Voznesenskoye deposit belongs to the subepithermal type of gold mineralization.

Equilibrium fractionation of REE isotopes in nature: Insights from NRIXS and DFT+U studies of Eu and Dy phonon density of states

Rare Earth Elements (REEs) are commonly utilized in Earth and environmental sciences to study a variety of geological processes due to their distinct patterns and radioactive-radiogenic decay systems (147Sm-143Nd, 146Sm-142Nd, 138La-138Ce). Advances in analytical techniques now enable the use of REE stable isotopic fractionations to clarify lingering ambiguities in REE systematics. In this study, we employed Nuclear Resonant Inelastic X-ray Scattering (NRIXS) to study the phonon density of states of 151Eu and 161Dy in several pure compounds, as well as in synthetic basalt and andesite glasses, and rhyolite glasses produced under various redox conditions, to determine equilibrium isotopic fractionation factors for the REEs. We additionally utilized Density Functional Theory with a Hubbard U correction (DFT+U) to calculate these factors. Our findings indicate that the directionally averaged mean force constant of Dy3+ is ∼270 N/m across various compounds, while those of Eu2+ and Eu3+ are ∼83 and 214 N/m, respectively, in geologically relevant glasses and other pure compounds. These force constants were then used to estimate those of all REEs using scaling arguments. The results suggest that equilibrium isotopic fractionation should be limited for REEs in igneous rocks, allowing for the interpretation of REE isotopic fractionation in these rocks and minerals as a result of kinetic effects. This could facilitate understanding the role of diffusion in igneous rocks and ore formation. Additionally, our results imply that significant Eu isotopic fractionation could exist in hydrothermal fluids, which could aid in understanding the formation of ore deposits and REE cycling in the oceans.

Origin and evolution of the ore-forming fluids in the southern Abbas Abad iron skarn deposit, NE Isfahan, Central Iran: Insights from geology, fluid inclusions, and C[sbnd]O isotopes

The southern Abbas Abad iron skarn deposit is located in the western part of the Central Iran zone, SW edge of the Urumieh˗Dokhtar magmatic arc. The skarn alteration occurred mainly at the contact of the Abbas Abad gabbro and Triassic Nayband Formation. The Triassic Nayband Formation in the southern Abbas Abad area consists of limestone, shale, siltstone, and marl with interlayers of tuff. The Abbas Abad gabbro is calc˗alkaline with adakitic signatures and continental arc setting affinity. Four iron ore bodies occur along the NW˗SE trending normal fault along the southern margin of Abbas Abad gabbro within sedimentary host rocks of the Nayband Formation. Three main paragenetic stages of skarnification and ore deposition have been recognized: i) prograde stage, ii) retrograde stage, and iii) supergene stage. Spinel, garnet, and pyroxene formed during the prograde stage. Epidote, tremolite˗actinolite, calcite and ore minerals, such as magnetite, hematite-I, pyrite, and minor chalcopyrite formed the retrograde stage assemblage. Magnetite is the main economic ore mineral, which is diverse in terms of fabric and texture, including massive, disseminated, needle˗like, blade˗like, prismatic, crustification, and cubes. Stable isotope data from Abbas Abad iron skarn deposit indicated that the interaction of non-magmatic brine (connate) fluids with Triassic carbonate host rocks at high temperature and its mixing with meteoric water has led to changes in the isotopic composition of the mineralizing fluid. Subsequently, garnet and magnetite with relatively high estimated fluid δ18O values (average 12.3 and 14.6 ‰, respectively) formed from this modified fluid. The estimated δ18O values of fluid in equilibrium with calcite decreased as a result of the greater influx of the meteoric water into the hydrothermal system in the late stages of ore formation. Fluid inclusion data from this iron skarn deposit are consistent with minor boiling during the prograde stage, although cooling and dilution seem to be principally responsible for Fe precipitation. The petrogenetic model proposed for the Southern Abbas Abad iron skarn deposit suggests that during the Eocene a gabbroic stock intruded the sedimentary rocks of the Nayband Formation and acted as a heat source for the non-magmatic brine (connate and meteoric) fluids convection cells, then reacted with cooler Triassic carbonate rocks. In this model, leaching of the gabbroic rock provided the iron, whereas carbon came from degassing and dissolution of carbonate rocks during contact metamorphism-metasomatism.

Hydrological controls on base metal precipitation and zoning at the porphyry-epithermal transition constrained by numerical modeling

Ore precipitation in porphyry copper systems is generally characterized by metal zoning (Cu–Mo to Zn–Pb–Ag), which is suggested to be variably related to solubility decreases during fluid cooling, fluid-rock interactions, partitioning during fluid phase separation and mixing with external fluids. Here, we present new advances of a numerical process model by considering published constraints on the temperature- and salinity-dependent solubility of Cu, Pb and Zn in the ore fluid. We quantitatively investigate the roles of vapor-brine separation, halite saturation, initial metal contents, fluid mixing and remobilization as first-order controls of the physical hydrology on ore formation. The results show that the magmatic vapor and brine phases ascend with different residence times but as miscible fluid mixtures, with salinity increases generating metal-undersaturated bulk fluids. The release rates of magmatic fluids affect the location of the thermohaline fronts, leading to contrasting mechanisms for ore precipitation: higher rates result in halite saturation without significant metal zoning, lower rates produce zoned ore shells due to mixing with meteoric water. Varying metal contents can affect the order of the final metal precipitation sequence. Redissolution of precipitated metals results in zoned ore shell patterns in more peripheral locations and also decouples halite saturation from ore precipitation.

Case Histories of Orogenic Gold Deposits

This review compares genetic parameters of 12 orogenic gold deposits. The set of examples is considered to represent largely the variability of orogenic gold deposit (OGD) characteristics. The data are presented in tables and include following definitive parameters: regional geologic settings, nature of hosts rocks and mineralization, ore controlling structures, ages of host rocks and mineralization and timing of mineralization relative to metamorphism, hydrothermal alteration mineralogy and ore mineral assemblages, isotopic signatures, physical conditions of ore formation and proposed origin of ore fluids aa well as gold reserves, production, and grades. This allows comparison of deposits from different geologic terrains having different ages and formed under different P-T conditions. The data are further discussed before the background of the orogenic gold system and the crustal metamorphic models that provide different scenarios to explain the source of ore fluids. The orogenic gold system model advocates a metal and fluid source external to the terrain in which mineralization occurred, but the model applies only for 3 of the 12 deposits studied. All other deposits formed most likely from a crustal source, which would favor the crustal metamorphic model. However, the formation of hypozonal OGDs cannot be accounted for by the crustal metamorphic model or by the metamorphic devolatilization model. The data identify a set of coherent signatures in OGDs, but there seem to be no unified model for all possible environmental conditions and facets of ore formation and fluid sources, tectonic and lithologic setting, and scale of gold endowment.

Геохимические особенности Ag-Au рудопроявления Кыплатап (центральная Чукотка)

The article considers the geochemical features of unconventional mineralization in secondary quartzite’s of the Kyplatap ore occurrence, located on the southeastern flank of the volcanic dome structure (VDS) of the same name, complicating the Palyavaam-Pykarvaam volcanotectonic depression (VTD) in the Chaun zone of the Central Chukotka sector of the Okhotsk-Chukotka volcanic Belt (OChVB). The Kyplatap VDS was formed due to the intrusion into the Late Cretaceous Alkaquun volcanites of a large laccolith-like subvolcanic body composed of rhyolite-trachyriolite-trachydacites. Based on the geochemical studies of the Kyplatap ore occurrence, the authors compiled a representative database of geochemical data, including the results of analyses of express-RFA, PKSA and XSA with coordinates and composition of ores and rocks. Correlation analysis of the database showed a positive relationship between Au and Ag, as well as Sb for ore mineralization, and a negative correlation of these elements with the association of the rock group of elements (Ti, Y, Zr, Nb and Yb) that were removed during ore formation. The authors also distinguished the second rock group of elements (K, Ga, Sn, Ba, V, W, Pb, Sc, La and B), characterized by medium and weak correlation of the first group of elements. They calculated the coefficients of enrichment and deficiency of ore-forming elements for the samples taken within the ore zones of the Kyplatap ore occurrence. The extreme enrichment group includes elements Au, Ag, Sb, Bi, As, the average contents of which are 100 times or more, and the minimum concentrations are at least 2-10 times higher than the average contents in the upper crust. The normal enrichment group includes elements S, Sn, Cu, Zn, Mn, Mo and Pb, the average contents of which are 2-10 times, and the maximum concentrations are 5-100 times higher than the average concentrations of the upper crust. The obtained values of the enrichment coefficients indicate a sufficiently intensive metensomatoses and ore formation within the Kyplatap ore occurrence.

Origin of Upper Cretaceous marine ironstones of Ayat Formation (Turgay depression, Northern Kazakhstan)

This work studies the mineralogical and geochemical features of ooidal ironstone formation of the Upper Cretaceous Ayat Formation located in the Turgay depression (Kazakhstan). The origin of ooidal ironstone deposits has been the subject of many discussions for a long time. These results present diagenetic conditions of the marine ironstone precipitation in the Ayat Formation. Various authigenic minerals, such as siderite, glauconite, goethite, pyrite, hydroxylapatite, wurtzite, and barite indicate fluctuations in the different geochemical conditions during the diagenesis of marine sediments of the Ayat Formation. The precipitation of in situ pyrite and wurtzite was controlled by an oxygen-deficient environment at the interface between water and sediment, which was accompanied by bacterial sulphate reduction under seabed conditions and, in consequence, by the concentration of sulfides. The authigenic assemblage of siderite, wurtzite, and barite indicates an integrated process of their input to site the sedimentation. The stable isotopic composition of siderite supports the microbial carbonate origin by decomposing the organic matter. However, geochemical features (the pattern Co/Zn vs (Co + Ni + Cu)) evidence the hydrogenous precipitation of iron. It involves the interaction of two central in situ processes to form Ayat ooidal ironstones. One of them is the iron precipitation from the bottom water, and the second is the microbial generation of hydrocarbons. Marine Ayat and channel Lisakovsk ironstones have similar features of bulk rock geochemistry. It reflects the exact environments of the ooidal iron ore formation, while the wall rocks have distinctive facies conditions.

Geodynamic aspects of the metallogeny-magmatic zonality relationship of orogenic volcanic-plutonic belts

Research subject. The orogenic marginal-continental and collisional volcanic-plutonic belts, and the zonality of magmatism and metallogeny within them, as well as the relationship of endogenous metallogeny with magmatic zonality and geodynamics of belt formation.Materials and methods include the long-term studies of the Devonian and Upper-Paleozoic belts of Kazakhstan and the Cretaceous-Paleogenic belt of Sikhote-Alin; an analysis of the alterations in the material parameters of magmatites; the identification of the front and rear parts of the belts and the arrangement features of metallogenic zones within their limits; and the data on other belts of the world.Results. For the marginal continental belts, an asymmetric change of the tholeiitic and low-potassium magmatites of the calcareous-alkaline petrochemical series of the frontal zone of the belt into the magmatites of the high-potassium branch of the calcareous-alkaline and shoshonite series of the rear zone (Devonian and Upper Paleozoic belts of Kazakhstan) has been established. In the same direction, the elemental, as well as the genetic type of deposits changes: pyrite copper-polymetallic frontal zones are replaced by molybdenum-copper-porphyry rear zones (near the border with the frontal zone) and then by rare metal ones. This is also characteristic of the Andean and Okhotsk-Chukchi belts. The collision belts are characterised by symmetrical zonality with a change from rare metal deposits in the centre to copper-polymetallic deposits at the edges (Mongolia). In some cases (Sikhote-Alin and Japan), the continuity of the marginal-continental belt is disrupted as a result of the mantle diapir (or plume), symmetrical magmatic and metallogenic zonality occurs with the change of polymetallic manifestations (near the ocean–continent boundary) to rare-metal ones in the distance. Conclusions. The change in the material parameters of the magmatites of the marginal-continental belts correlates with the removal of their ranges from the ocean–continent transition zone to the interior of the latter. In this case, copper-polymetallic pyrite ore formations are replaced by copperporphyry and then by rare metal ones in this direction. This is due to subduction processes. The collision situation is characterised by a symmetrical zonality of material magmatic parameters with respect to the crowding zone and a symmetrical arrangement of metallogenic zones with a change of rare metal deposits in the crowding zone to copper and polymetallic along the frame. These data are important for metallogenic prediction, as well as for palaeotectonic reconstructions.

Peculiarities of the formation of the Zhailma volcano-tectonic deep

Purpose. Studying the features of the Zhailma volcano-tectonic depression formation, as well as the principles and factors affecting this structure’s ore formation. Methodology. Analysis of the results of isotope dating of rocks, critical analysis of literature and fund materials, analysis of the genesis and specificity of the Zhailma structure mineralization, features of the volcano-tectonic depression formation. Findings. The Zhailma graben syncline formation is associated with subsidence after ejections of significant masses of acidic magmatic material from stratovolcanoes concentrated on the Zhailma structure. The initiation and development of the graben-syncline is closely related to the processes of tectonomagmatic evolution of the Devonian volcano-plutonic belt. Originality. The search model for stratiform deposits of the Atasu type has been revised, taking into account the original theory of the volcano-tectonic origin of the structure, formed at the final stages of the formation and development of the Devonian volcano-plutonic belt. The genesis of the Atasu-type deposits is considered as sedimentary-hydrothermal one, associated with the processes of diagenesis and catagenesis occurring within sedimentary basins. The presence of two large volcanoes on the northern side of the caldera structure was substantiated: North Zhairem and Ustanynzhal. Practical value. It is recommended to carry out predictive metallogenic and, accordingly, prospecting work for deposits of the Atasu type within the graben-synclines of the Sarysu-Teniz segment of the Devonian volcanic belt, where such deposits of ferromanganese ores as Tur, Bogach and Karaadyr are already being developed in the Aydagarly graben-syncline.