Ore Cluster Research Articles

Mineral Chemistry and In Situ LA-ICP-MS Titanite U-Pb Geochronology of the Changba-Lijiagou Giant Pb-Zn Deposit, Western Qinling Orogen: Implications for a Distal Skarn Ore Formation

The giant Changba-Lijiagou (Ch-L) Pb-Zn deposit is in the northeast part of the Xicheng ore cluster, Western Qinling Orogen. The ore genesis remains controversial; it could be either a sedimentary exhalative genetic type or an epigenetic hydrothermal genetic type. Here, in situ titanite U-Pb dating for the two kinds of titanite is presented, yielding ages of 212.8 ± 3.0 Ma in the mineralized skarn ore and 214.6 ± 5.1 Ma in the host rock. These ages conform to the previously reported magmatic zircon age (229–211 Ma) based on the in situ zircon U-Pb dating of plutons in this district and the time of large-scale magmatic–hydrothermal activities in Western Qinling Orogen (229–209 Ma). Titanites occurring in mineralized skarn and those that are calcite-hosted are similar to hydrothermal-origin titanites in major element characteristics. The Eu anomalies in the two types of titanite record oxidizing conditions during the mineralization process. A mineral assemblage of garnet, pyroxene, riebeckite, biotite, and potash feldspar, replacing the albite, is well-developed in the deposit. The mineralogical and geochronological characteristics indicate that the Ch-L Pb-Zn deposit is a distal skarn deposit and the result of intensive tectonomagmatic processes in the Xicheng ore cluster during the process of the Late Triassic orogeny.

РЕЗУЛЬТАТЫ НАУЧНЫХ ЭКСПЕДИЦИОННЫХ ГЕОЛОГО-ГЕОФИЗИЧЕСКИХ ИССЛЕДОВАНИЙ ПОЛЕЗНЫХ ИСКОПАЕМЫХ МОРЕЙ ДАЛЬНЕВОСТОЧНОГО РЕГИОНА РОССИЙСКОЙ ФЕДЕРАЦИИ И ТИХОГО ОКЕАНА (ПРОЕКТ «ГЕОМИР»)

The paper presents a brief overview of the results of integrated geological, geophysical and oceanographic studies for the period 2017–2023, for which interregional generalizations were made on some promising areas of study of underwater mineral resources and the environment. The data on geological underwater objects, in particular, manganese ores of the Sea of Japan and the Sea of Okhotsk and adjacent water areas; rare-earth ores of the Tomtor ore cluster, ancient and modern coastal-marine placers of the Laptev Sea coast are presented; barite ore occurrences “Barite Hills” (in the Sea of Okhotsk); ferromanganese formations of the Eastern Arctic shelf of Russia; coastal marine placers of the shelf and coast of the Far Eastern seas, including gold-bearing placers. including gold-bearing placers of the shelf zone of the south of Primorye and north of Sakhalin, titanomagnetite placers of the Kuril Islands, gold-bearing placers of the North Sakhalin Plain and others. Direct signs of hydrocarbons were obtained in areas previously considered unpromising (including the South China Sea), gas hydrate accumulations were mapped and studied in the Sea of Okhotsk and the Sea of Japan, prospecting for gas hydrates in the Bering Sea was prepared, and comparative studies of hydrate-bearing capacity of the marginal seas of the NW Pacific and the Indian Ocean were carried out. The main features of the distribution of lithologic and gas-geochemical indicators of hydrocarbon gases in bottom sediments of the southwestern sector of the East Siberian Sea, which is the least studied in terms of oil and gas content, were studied. Based on the data of gas-geochemical studies, the prospects of oil and gas content of the eastern shelf of the Arctic were assessed. The results of geomicrobiological studies in the seas of the Far East region are described. In some cases deepsea sediments themselves (peloid-like sediments, etc.) appear to be a separate huge mineral resource. At present, the “continent-ocean” transition zone and neutral waters can become the most important source of replenishing the mineral resource base of these mineral components. The presented research corresponds to the main objectives of the GEOMIR project of the national action plan within the UN Decade of Ocean Sciences for Sustainable Development (2021–2030) and was carried out mainly in accordance with the directions of the state assignment. Studies of gas hydrates were carried out within the framework of the WESTPAC working group “Gas hydrates and methane fluxes in the Indo-Pacific region” (CoSGas, 2021–2024), established on the initiative and under the leadership of Russia.

Identification of new objects promising for porphyry molybdenum-copper mineralization when creating the State geological map 1000/3: Sheets O-55, O-56 (Northern Priokhotye, Magadan region) as an example

The Motykleisky, Chistoozerny, and Pavlovichsky new ore clusters promising for porphyry molybdenum-copper mineralization have been identified in the Magadan region due to results of creation of the State Geological Map 1000/3, sheets O-55, O-56. The porphyry-type mineralization is associated with the Priokhotsky plutonic belt of Albian-Cenomanian granitoids of the Magadan suite of the calcareous-alkaline series (K/Na <1). The granitoids are dominated by porphyritic tonalites and quartz diorites of type I magnetite series, often adakitic in composition. The mineralization is accommodated by the Jurassic-Lower Cretaceous island-arc sedimentary-volcanic formations. Relationship between the mineralization and granitoids is substantiated by the U-Pb SIMS SHRIMP and Re-Os TIMS dating. In potential ore clusters, the mineralization is manifested by extensive fi lds of hydrothermal-metasomatic alterations (propylites and quartz-sericite-pyrite metasomatites). Recommendations are given for follow-up large-scale geological survey and prospecting in the area of the potential ore clusters.

Rare earth mineralization in ores of the Gurvunur apatite-magnetite deposit (Ozerny ore cluster, Western Transbaikalia)

The Gurvunur apatite-magnetite deposit is located within the Ozerny ore cluster in Wes-tern Transbaikalia. A peculiarity of this object is the presence of rare-earth mineralization in the ores. The main REE concentrator minerals include monazite, allanite, apatite, and epidote. One of the main concentrators of REE is apatite, where the content of REE sum reaches 2.6 wt. %. The REE are mainly represented by light lanthanides, with La up to 1.8 wt. % and Ce up to 2.08 wt. % predominating. Monazite- (Ce) is formed in the process of apatite refining, leading to the monazite fine-grained dissemination and veinlets occurring. Epidote is found in nests and vein-like formations of skarn aggregates. The mineral mainly contains light lanthanides (La up to 5.11 wt. %, Ce up to 2.47 wt. %) and forms gradual transitions to allanite that, in its turn, is also found in the form of isolated segregations or as a part of aggregates of epidote-allanite composition. Light lanthanides with Ce up to 14.35 wt. % and La up to 9.16 wt. % pre-dominate in the allanite composition. The study of the mineral composition and distribution of REE in ores and minerals allows us to conclude that rare-earth mineralization in the ores of the Gurvunur apatite-magnetite deposit was formed as a result of skarning of the carbonate-bearing volcanogenic-sedimentary rocks, and the source of rare-earth mineralization was granodiorites of the Vitimkan intrusive suite.

Авландинский палеовулкан и золото-серебряное оруденение

The article describes the geological structure and composition of the Avlandya stratovolcano, composed of cover and intrusive volcanites of the Late Devonian - Early Carboniferous Kedonian series. The paleovolcano area corresponds to the Avlandya ore cluster. The sector block on the southwestern periphery of the paleovolcano is the Kubaka ore field, which contains the large Kubaka gold and silver deposit and a number of occurrences. Textural features, the composition of ores and native gold indicate that the Kubaka deposit belongs to the volcanogenic gold-silver formation. The geological criteria of the Kubaka's Middle Paleozoic age have been determined.

Enhancing Geological Understanding and Identifying Gold Anomalies in the Ailaoshan Orogen

AbstractThe Ailaoshan Orogen in the southeastern Tibet Plateau, situated between the Yangtze and Simao blocks, underwent a complex structural, magmatic, and metamorphic evolution resulting in different tectonic subzones with varying structural lineaments and elemental concentrations. These elements can conceal or reduce anomalies due to the mutual effect between different anomaly areas. Dividing the whole zone into subzones based on tectonic settings, ore cluster areas, or sample catchment basins (Scb), geochemical and structural anomalies associated with gold (Au) mineralization have been identified utilizing mean plus twice standard deviations (Mean + 2STD), factor analysis (FA), concentration‐area (C‐A) modeling of stream sediment geochemical data, and lineament density in both the Ailaoshan Orogen and the individual subzones. The FA in the divided 98 Scbs with 6 Scbs containing Au deposits can roughly ascertain unknown rock types, identify specific element associations of known rocks and discern the porphyry or skarn‐type Au mineralization. Compared with methods of Mean + 2STD and C‐A model of data in the whole orogen, which mistake the anomalies as background or act the background as anomalies, the combined methods of FA and C‐A in the separate subzones or Scbs works well in regional metallogenic potential analysis. Mapping of lineament densities with a 10‐km circle diameter is not suitable to locate Au deposits because of the delineated large areas of medium‐high lineament density. In contrast, the use of circle diameters of 1.3 km or 1.7 km in the ore cluster scale delineates areas with a higher concentration of lineament density, consistent with the locations of known Au deposits. By analyzing the map of faults and Au anomalies, two potential prospecting targets, Scbs 1 and 63 with a sandstone as a potential host rock for Au, have been identified in the Ailaoshan Orogen. The use of combined methods in the divided subzones proved to be more effective in improving geological understanding and identifying mineralization anomalies associated with Au, rather than analyzing the entire large area.

Carboniferous magmatic activity in the Aqishan–Caixiashan polymetallic ore cluster, eastern Tianshan, NW China: implications for tectonic evolution and regional metallogeny

Carboniferous magmatic activity in the Aqishan–Caixiashan polymetallic ore cluster, eastern Tianshan, NW China: implications for tectonic evolution and regional metallogeny

Genesis of the Dongtangzi Zn-Pb Deposit of the Fengxian–Taibai Ore Cluster in West Qinling, China: Constraints from Rb-Sr and Sm-Nd Geochronology, and In Situ S-Pb Isotopes

The large Dongtangzi Zn-Pb deposit is located in the southwest of the Fengxian–Taibai (abbreviated as Fengtai) ore cluster in the west Qinling orogen. The origin of the deposit is controversial, positing diverse genesis mechanisms such as sedimentary-exhalative (SEDEX), sedimentary-reformed, and epigenetic-hydrothermal types. This study combines systematic ore geology observations with high-precision Rb-Sr and Sm-Nd ages of 211 Ma and in situ S-Pb isotopes to constrain the timing and origin of mineralization. In situ S-Pb isotopic studies show that the sulfide ores display a narrow range of δ34S values from 1.1‰ to 10.2‰, with 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of 18.07 to 18.27, 15.64 to 15.66, and 38.22 to 38.76, respectively. On the other hand, pyrites of the sedimentary period and the granite porphyry dike have δ34S values ranging from 15.8 to 21.4‰ and from 2.1 to 4.3‰ (with 206Pb/204Pb ratios of 18.09 to 18.10, 207Pb/204Pb ratios of 15.59 to 15.61, and 208Pb/204Pb ratios of 38.17 to 38.24), respectively. The above-mentioned S-Pb isotopic compositions indicate that the metallic materials involved in ore formation originated from a mixture of Triassic magmatic hydrothermal fluid and metamorphic basement. By integrating the regional geology, mineralization ages, and S-Pb isotopic studies, we propose that the Dongtangzi Zn-Pb deposit is the product of epigenetic hydrothermal fluid processes, driven by Late Triassic regional tectono-magmatic processes.

Compositional balance analysis: A novel method for tectono-geochemical anomaly identification and blind ore deposit prediction

Tectono-geochemical exploration always involves the study of tectono-geochemical primary halos. From the perspective of compositional data analysis, this study introduced how to use compositional balance analysis (CoBA) method to recognize tectono-geochemical anomalies and infer blind ore deposits in the deep. A case study for prediction of concealed Pb–Zn ore deposits based on tectono-geochemical data in the Huangzhuguan ore cluster, Gansu Province, China, was employed to demonstrate the potential applications of the CoBA method. First, an optimal element combination (i.e., Pb–Zn –Cd) related to near-ore halo was determined by means of CoBA method and receiver operating characteristic curve analysis. Then, according to the element zonation sequences of the primary halo in the hydrothermal deposit, the front halo element combination (i.e., As–Sb–Hg) and the tail halo element combination (i.e., W–Sn–Mo–Bi) were selected for compositional balance analysis. Finally, based on knowledge-driven CoBA method, three types of tectono-geochemical primary halos were customized to evaluate blind Pb–Zn deposits in the Huangzhuguan ore cluster. The results indicate that the CoBA method combined with the superimposed characteristics of tectono-geochemical primary haloes, proves to be effective and straightforward in interpreting Pb–Zn mineralization-related anomalies and predicting hidden Pb–Zn targets.

Magmatic-hydrothermal fluid evolution of the tin-polymetallic metallogenic systems from the Weilasituo ore district, Northeast China

The large Weilasituo Sn-polymetallic deposit is a recent exploration discovery in the southern Great Xing’an Range, northeast China. The ore cluster area shows horizontal mineralization zoning, from the inner granite body outward, consisting of high-T Sn–W–Li mineralization, middle-T Cu–Zn mineralization and peripheral low-T Pb–Zn–Ag mineralization. However, the intrinsic genetic relationship between Sn-W-Li mineralization and peripheral vein-type Pb–Zn–Ag–Cu mineralization, the formation mechanism and the deep geological background are still insufficiently understood. Here, we use fluid inclusions, trace elements concentrations in quartz and sphalerite, and H–O isotope studies to determine the genetic mechanism and establish a metallogenic model. Fluid inclusion microthermometry and Laser Raman spectroscopic analysis results demonstrates that the aqueous ore-forming fluids evolved from low-medium salinity, medium–high temperature to low salinity, low-medium temperature fluids. Laser Raman spectroscopic analysis shows that CH4 is ubiquitous in fluid inclusions of all ore stages. Early ore fluids have δ18OH2O (v–SMOW) values from + 5.5 to + 6.2‰ and δD values of approximately − 67‰, concordant with a magmatic origin. However, the late ore fluids shifted toward lower δ18OH2O (v–SMOW) (as low as 0.3‰) and δD values (~ − 136‰), suggesting mixing between external fluids derived from the wall rocks and a contribution from meteoric water. Ti-in-quartz thermometry indicates a magmatic crystallization temperature of around 700 °C at a pressure of 1.5 kbar for the magmatic ore stage. Cathodoluminescence (CL) imaging and trace element analysis of quartz from a hydrothermal vug highlight at least three growth episodes that relate to different fluid pulses; each episode begins with CL-bright, Al-Li-rich quartz, and ends with CL-dark quartz with low Al and Li contents. Quartz from Episode 1 formed from early Sn-(Zn)-rich fluids which were likely derived from the quartz porphyry. Quartz from episodes 2 and 3 formed from Zn-(Sn)-Cu-rich fluid. The early magmatic fluid is characterized by low fS2. The SO2 produced by magma degassing reacted with heated water to form SO42−, causing the shift from low fS2 to high fS2. The SO42− generated was converted to S2– by mixing with CH4-rich, Fe and Zn-bearing external fluid which led to late-stage alteration and dissolution of micas in vein walls, thus promoting crystallization of pyrrhotite, Fe-rich sphalerite and chalcopyrite and inhibiting the precipitation of anhydrite. This study shows that ore formation encompassed multiple episodes involving steadily evolved fluids, and that the addition of external fluids plays an important role in the formation of the later Cu–Zn and Ag–Pb–Zn mineralization in the Weilasituo ore district.

Paleovolcanism and the prospecting indicators and outlooks for discovery of new economic-grade copper-zinc massive sulfide ore deposits in the Verkhneuralsk ore region, Southern Urals

The principal regularities of distribution of the VMS type mineralization in the Verkhneuralsk ore region in the Southern Urals are characterized. Metallogenic factors of the first kind (stratigraphic, magmatic, lithological, and tectonic) and of the second kind (geotectonic and paleovolcanic) are
 shown. A combined convective-postmagmatic ore formation model for the VMS is briefly described, that takes into account a genetic relationship of the VMS ore formation to silicic magmatism of the basalt-rhyolite (“contrast”) volcanic formation, four types of such relationship being distinguished, the spatial, temporal, energetic, and compositional ones. The geological, geochemical, and geophysical prospecting indicators for the Ural type VMS mineralization are presented separately for various classes of forecasting metallogenic areas (ore regions, ore clusters, and ore fields and deposits). In the southern portion of the ore district, a site promising for revealing a new ore deposit has been identified, for which the category P2 forecasted resources have been estimated and a recommendation has been given for the geological exploration.

СТРУКТУРЫ ЦЕНТРАЛЬНОГО ТИПА В ЮЖНОМ СИХОТЭ-АЛИНЕ В ВЕРОЯТНОСТНЫХ ГРАВИТАЦИОННЫХ МОДЕЛЯХ: ГЛУБИННОЕ СТРОЕНИЕ, РЕОЛОГИЯ, ИЕРАРХИЯ, ФРАКТАЛЬНОСТЬ И МЕТАЛЛОГЕНИЯ

As a result of the analysis of 3D-distributions of density contrast in the crust of the South Sikhote-Alin, connections are established between ore districts, ore clusters, and ore fields, on the one hand, and hierarchically subordinate structures of the central type of three taxonomic levels, on the other. Based on the coincidence of the areas of spatial distribution of ore mineralization with the projections of deep density heterogeneities, the probable depth of occurrence of fluid-magmatic sources of ore mineralization and vertical extent of ore-magmatic systems of different specialization were determined: tin (depth of 2‒6 km), tin-polymetallic (4‒12 km), polymetallic (6‒20 km), and gold-tungsten (14‒24 km). The spatial distribution of central-type structures and the associated areas of ore mineralization are coincident with viscous shear zones, within which subsidence of the crustal upper layer is observed (Samarkinsky terrane, Kavalerovsky district and Soboliny ore cluster), as well as displacement of the contours of density heterogeneities in different depth sections (Dalnegorsky region). Deep boundaries of the ancient continental crust and Mesozoic island-arc wedges subducted under accretionary-fold complexes were determined. The joint of these structures is characterized by distinct features of a transform fault.

A «necklace» of large clusters of strategic raw materials over a stagnant oceanic slab in East Asia

<p>An analysis of geological-geophysical, metallogenic, geochronological, and seismic tomographic studies in territories joining Southeast Russia, East Mongolia, and Northeast China led to the conclusion that deep geodynamics significantly influenced the formation of highly productive ore-magmatic systems in the Late Jurassic-Early Cretaceous. This influence was likely manifested through the initiation of decompression processes around stagnant slab boundaries in the Late Mesozoic. Decompression and advection, which are particularly active near the natural boundaries of the slab, act as triggers for the intense interaction of under and over subduction asthenospheric fluids with adjacent sections of the mantle and for the directed upwelling of powerful flows of matter and energy into the lithosphere. These flows determine the locations of intermediate and peripheral magma chambers: Primary chambers in the lower lithosphere among the metasomatized mantle and lower crust and associated chambers in the middle and upper cratonized parts of the lithosphere. Large ore clusters containing noble metals (Au, PGE), uranium, fluorite, and Cu-Mo-porphyry deposits are associated with late- and postmagmatic derivatives of the emerging magma chambers over the frontal and peripheral (paleotransform) boundaries of a stagnant Pacific slab. These large Late Mesozoic ore clusters and districts form a distinctive "necklace" of strategic materials in East Asia.</p>

Mineralogical, geochemical characteristics and formation mechanism of skarns in Banlun magnetite ore cluster area, southeastern Yunnan

Mineralogical, geochemical characteristics and formation mechanism of skarns in Banlun magnetite ore cluster area, southeastern Yunnan

Диарсениды и сульфоарсениды Fe, Co, Ni, пространственно связанные с Лево-Сеймканским гранитным плутоном (Магаданская область, Россия)

The Ni-Co mineralization in the Levo-Seimkan ore cluster has been studied. In xenoliths of gabbro-diorites from of the Levo-Seimkan granite massif, the disseminated sulfoarsenide and sulfoantimonide mineralization with predominant antimonial nickeline and with the gersdorfitekrutovite series minerals has been revealed, with a constant Sb admixture in gersdorfite (from 1.1 to 2.4 wt. %) and nickeline (Sb 3.2-12.2 wt. %) in association with pyrrhotite. In a new ore occurrence (Puglivy Creek, Arman River basin, 2 km from the mouth), in a stockwork of quartz-chlorite veins localized directly in the granites of the Levo-Seymkan massif, the Co-As-Bi-Te-Au mineralization has been established. Ore mineral nests and inclusions are represented by glaucodote (Ni under 3.28 wt. %), associated with native Bi, bismuthine, tellurovismuthite, hedleyite, and native Au. Ni-Co mineralization of disseminated ores from gabbro-diorite xenoliths from the Levo-Seymkan massif and from the stockwork localized in the massif granites (roof outshot in the Puglivy Creek), as well as from veins and veinlets in contact hornfelses (Puglivoye and Obkhod deposits). It has been found that mineral phases are not as characteristic for mineralization in granites and Ni hornfelses, and that the Co/Ni increases with distance from the Levo-Seimkan massif due to the lower migration ability of Ni relative to that of Co in the course of successive geochemical differentiation.

Predicting copper-polymetallic deposits in Kalatag using the weight of evidence model and novel data sources

Abstract The Kalatag Ore Cluster Area, located in the Eastern Tianshan metallogenic belt of Xinjiang, stands out as a notable copper polymetallic mineralization zone, recognized for its diverse ore types and untapped potential. Despite the foundational nature of traditional exploration methods, they have not fully exploited this potential. Addressing this, our study leverages modern geospatial technologies, especially ArcGIS, combined with multi-source geoscience data to refine ore formation predictions in Kalatag. We identified key ore-controlling factors: the ore-bearing strata of Daliugou and Dananhu Groups, buffer zones around faults and intrusions, and geophysical anomalies. From these, a conceptual model was developed using the weight of evidence model. This model pinpointed four ‘A’ class and three ‘B’ class targets for mineral exploration, highlighting the central role of faults in ore control. Significantly, all known ore deposits were encompassed within these targets. Our approach not only paves the way for improved ore prediction in Kalatag but also offers a blueprint for other mineral-rich areas. Merging traditional geology with advanced technology, we elevate mineral exploration’s precision, emphasizing the synergy of an integrated method, especially in geologically complex areas. The effectiveness of our model provides insights for future exploration, particularly in mining areas’ deeper zones.

Extraction of gravity components related to W-Sn polymetallic deposits using Bi-dimensional empirical mode decomposition (BEMD) in the Laojunshan Ore Cluster Region, SW China

The Laojunshan ore cluster region is situated at the north Song Chay dome, which is the junction of the Yangtze, the Cathaysia, and the Indo-China Blocks. The north Song Chay dome characterized by the Laojunshan metamorphic core complex is an important ore-forming region for W-Sn-Pb-Zn-In elements related to the Late Cretaceous granitic magmatism. In this paper, the Bi-dimensional empirical mode decomposition (BEMD) is applied to separate gravity components from the original gravity data, combined with the known geological and mineralized information, to explore the relationships between the gravity components and various ore-controlling factors at different depths. Four intrinsic mode functions (IMFs) and a residue are obtained. They may imply the spatial distribution of the geological bodies with featured gravity components at different depths. The results are shown as follows:(1) The low-pass filtering gravity component (BIMF4) implies the deeply buried geological units in the study region. The Cretaceous Laojunshan granitic complex and the Nanwenhe gneissic granite display negative gravity components and weak positive gravity components, respectively. The former is closely related to Sn-Zn-In mineralization, the latter is closely related to W polymetallic deposits. Therefore, the negative gravity components showing the Laojunshan granitic complex are the prospecting targets for deeply buried Sn-Zn-In deposits. The weak positive gravity components displaying the Nanwenhe gneissic granite are the prospecting targets for deeply buried W polymetallic deposits.(2) The band-pass filtering gravity component (BIMF3) implies the geological units at middle depth. The skarn-type Sn-W polymetallic deposits are observed in the transition zones from the positive to the negative gravity components, which coincide with the contact metasomatic zones between the Cretaceous granite and the Cambrian-Devonian carbonate rocks. Some small quartz vein W deposits occur within the Cretaceous Laojunshan granite with negative gravity components, and some layered W deposits occur in the Silurian gneissic granite with a weak positive gravity component.(3) High-pass filtering gravity component (BIMF2) implies geological units at the shallow crust, which shows that most of the deposits (occurrences) are located within the positive gravity component zones. These positive gravity component zones should be ore-finding targets for further prospecting for the undiscovered Sn and W polymetallic deposits.(4) The gravity components separated by BEMD coincide with the spatial distribution of the granites associated with various types of mineralization and alteration zones at different depths, which will give insights for further prospecting for concealed ore bodies in this study region.

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.

Precious-Metal Mineralization and Formation Conditions of the Biche-Kadyr-Oos Epithermal Au-Ag Ore Occurrence (Eastern Sayan, Russia)

The Biche-Kadyr-Oos epithermal Au-Ag ore occurrence is a prospective object in the Ak-Sug porphyry copper ore cluster (Eastern Sayan) in the northern part of the Central Asian orogenic belt (CAOB). The mineralization consists of gold-sulfide-quartz and gold-polysulfide-carbonate-quartz veins with argillic zones in the Lower Cambrian volcanic-sedimentary rocks. The origin of the Au-Ag ore occurrence is still debatable. To determine the origin, we examined the mineralogical and geochemical features, conditions of formation, and fluid sources of the Biche-Kadyr-Oos ore. A mineralogical and geochemical investigation outlines three stages of mineral formation: early argillic stage; gold-sulfide-quartz stage with pyrite, marcasite, pyrrhotite, arsenopyrite, chalcopyrite, less frequently sphalerite, hessite, gold, and electrum; and late gold-polysulfide-carbonate-quartz stage with gold, electrum, Hg-electrum, Se-acanthite, Se-galena, bornite, tennantite, tetrahedrite, hessite, tellurobismuthite, bismuthinite, matildite, jamesonite, ourayite, native Bi, and barite. Fluid inclusion study (thermometry, Raman spectroscopy) in quartz and mineral thermometry (electrum and sphalerite paragenesis) determined that ore veins were formed at P~0.5 kbar from CO2-water Na-K-chloride fluid (4.9–9.6 wt % NaCl eqv) and temperatures from 300 to 200 °C (early gold-sulfide-quartz veins at 300–230 °C, and late gold-polysulfide-carbonate-quartz veins at 290–200 °C) and variations in fO2, fS2, fSe2 and fTe2. The S isotopic composition in sulfides and δ34SH2S values of the fluid are +1.3‰ and +4.7‰, respectively, (T = 300–275 °C) indicating magmatic S in ore formation. The oxygen isotope data indicate that during the formation of veins, the magmatic fluid mixed with meteoric water (δ18Ofluid is from +3.4 to +6.4‰). The isotopic data that were obtained combined with mineralogical and geochemical features and conditions of ore formation indicate the similarity of Biche-Kadyr-Oos ore occurrence with epithermal Au-Ag deposits of intermediate sulfidation (IS) type. The presence of epithermal Au-Ag mineralization of the Biche-Kadyr-Oos IS type in ore cluster of the Ak-Sug Cu-Au-Mo porphyry deposit indicates the existence of a single porphyry-epithermal ore-magmatic system.

Problems of the Genesis of Deposits of the Ozerninsky Polymetallic Ore Cluster, Western Transbaikalia, Russia

Problems of the Genesis of Deposits of the Ozerninsky Polymetallic Ore Cluster, Western Transbaikalia, Russia