Largest Gold Deposits Research Articles

Metallogenic characteristics and tectonic setting of the Jiaodong gold deposit, China

Jiaodong is the largest gold deposit concentration area in China. In recent years, great breakthroughs have been made in deep prospecting, and it has become the third largest concentration area of gold deposits in the world. A series of prospecting discoveries in the Jiaodong area provided the basic conditions for summarizing the regional metallogenic law, constructing the deposit model, carrying out research on the genesis of the deposit and innovating metallogenic theory. The Jiaodong gold deposits are mainly distributed in Northwest Jiaodong, Qi-Peng-Fu and Mu-Ru metallogenic regions, and mainly occur in Precambrian metamorphic rock series, Jurassic Linglong-type granite, Early Cretaceous Guojialing-type granite and Laiyang group. The orebodies are controlled by Sanshandao, Jiaojia, Zhaoping, Xilin-Douya, Jinniushan and other major ore-controlling fault zones. The main mineralization types include altered rock-type, quartz vein-type, stockwork type, sulfide quartz vein-type, interlayer detachment zone-type, altered conglomerate-type, basin margin fault breccia-type and pyrite carbonate vein-type and so on. The important progress of deep prospecting is summarized: two super giant deposits have been evaluated in the Sanshandao and Jiaojia areas; the amount of altered rock-type gold resources identified by deep prospecting has exceeded that of quartz vein-type gold deposits in the Linglong gold deposit field; the Hushan large scale gold deposit has been discovered in Qixia gold deposit field; and the Liaoshang large-size gold deposit is a new discovery of deep prospecting in Pengjiakuang gold deposit field. The ore-controlling faults of gold deposits have several changing steps with dip angle varying from steep to gentle along the dip angle. The gold ore bodies are mainly enriched in sections along the steep, gentle turning points and relatively gentle parts of the fault dip angle, forming a stepped distribution pattern. In the Early Cretaceous, the subduction and rollback of the Paleo-Pacific plate induced crust mantle interaction, resulting in large-scale magmatic and fluid activities. The crust tension and magma uplift form the dome extension structure of granite, which provides a channel for the migration of ore-forming fluid and also provides favorable space for the deposition of ore-forming fluid.

The Neglected Involvement of Organic Matter in Forming Large and Rich Hydrothermal Orogenic Gold Deposits

Orogenic gold deposits have provided most of gold to humanity. These deposits were formed by fluids carrying dissolved gold at temperatures of 200–500 °C and at crustal depths of 4–12 km. The model involves gold mobilization as HS− complexes in aqueous solution buffered by CO2, with gold precipitation following changes in pH, redox activity (fO2), or H2S activity. In this contribution, the involvement of carbonaceous organic matter is addressed by considering the formation of large and/or rich orogenic gold deposits in three stages: the source of gold, its solubilization, and its precipitation. First, gold accumulates in nodular pyrite within carbonaceous-rich sedimentary rocks formed by bacterial reduction of sulfates in seawater in black shales. Second, gold can be transported as hydrocarbon-metal complexes and colloidal gold nanoparticles for which the hydrocarbons can be generated from the thermal maturation of gold-bearing black shales or from abiotic origin. The capacity of hydrocarbons for solubilizing gold is greater than those of aqueous fluids. Third, gold can be precipitated efficiently with graphite derived from fluids containing hydrocarbons or by reducing organic-rich rocks. Black shales are thus a key component in the formation of large and rich orogenic gold deposits from the standpoints of source, transport, and precipitation. Unusual CO2-rich, H2O-poor fluids are documented for some of the largest and richest orogenic gold deposits, regardless of their age. These fluids are interpreted to result from chemical reactions involving hydrocarbon degradation, hence supporting the fundamental role of organic matter in forming exceptional orogenic gold deposits.

Structural and dynamic conditions for the formation of large orogenic gold deposits in Central and Northeast Asia

Research subject. Large orogenic gold deposits in the fold belts of Central and Northeast Asia.Materials and methods. Geological mapping of various scales on a number of large orogenic gold deposits was conducted using the methods of structural-paragenetic analysis of metamorphic strata, accompanied by obligatory linking of ore mineralization manifestations to specific structures. In a number of cases, various statistical methods were used to geometrize mineralization, identify patterns of its location and determine the paths of paleofluid flows. Available publications on the objects under consideration were reviewed. The geological and structural features of large orogenic gold deposits – Muruntau, Kokpatas, Sukhoi Log and Pavlik – were considered.Results. The Muruntau, Kokpatas and the Sukhoi Log ore deposits are of shariyage-thrust type. Compared to these objects, the Pavlik field is confined to a zone of volumetric fracturing between a series of reverse faults, feathering a large deep fault and belonging to the transpression type. At the Muruntau and Pavlik deposits, the analysis of the location of the most intensive mineralization substantiated the paths of paleofluid flows, along which the fluid migration and ore formation took place.Conclusions. The distribution of ore mineralization in the Muruntau deposit obeys the orientation of planar (cleavage) and linear (orientation of fold hinges) elements. Apparently, the former (main) direction may indicate the orientation and position of the main migration route of ore-bearing fluids, while the latter corresponds to secondary channels, the position of which is due to the intersection of syn-napping structures with favourable lithological horizons. For the Pavlik deposit, the position of ore pillars is compared with the paths of paleofluid flows, the root parts of which are promising for identifying the most powerful and intense mineralization.

Gold in Paleoproterozoic (2.1 to 1.77 Ga) Continental Magmatic Arcs at the Tapajós and Juruena Mineral Provinces (Amazonian Craton, Brazil): A New Frontier for the Exploration of Epithermal–Porphyry and Related Deposits

This review paper aims to integrate geological, tectonic and metallogenetic data, including new data, and propose a regional model for the gold (and base metal) mineralization in the south Amazonian Craton to support the mineral exploration concerning magmatic–hydrothermal deposits. The Proterozoic evolution of the Amazonian Craton comprises the accretion of terrains to the Archean Carajás Mineral Province. In the Tapajós and Juruena mineral provinces, located at the south part of the Amazonian craton, a long-lived ocean–continent subduction event produced ca. 2.0 to 1.77 Ga continental magmatic arcs. Extensive lava flows, volcaniclastic, sedimentary, and plutonic rocks were originated during at least four major orogenic magmatic events (ca. 2.1, 1.9, 1.88, and 1.80 Ga) and two post- to anorogenic events (ca. 1.87 and 1.77 Ga). Gold mineralization occurs in: (i) alluvial/colluvial occurrences, (ii) orogenic carbonate–sulfide-rich quartz veins in shear zones, (iii) stockworks, veins, and dissemination in granites, (iv) contact of basic dikes, (v) well-preserved high-, intermediate- and low-sulfidation epithermal mineralization, and (vi) porphyry-like and intrusion-related gold systems associated with late- to post-orogenic epizonal granites. The estimated historical gold production, mainly in secondary deposits, is over 27 Moz at the Tapajós and 6 Moz at the Juruena provinces. A total resource of over 5 Moz Au is currently defined in several small to large primary gold deposits. Andesite to rhyolite, volcaniclastic, and clastic sedimentary rocks (1.96–1.88 Ga) host epithermal (high-, intermediate-, and low-sulfidation) Au–(Ag–Pb–Zn) mineralization, whereas Au–Cu and Cu–Mo–Au mineralization is hosted in sub-volcanic tonalitic to granitic plutons. Advanced argillic alteration (alunite, pyrophyllite, enargite) associated with high-sulfidation mineralization occurs in ring volcanoes around nested volcanic calderas. This zone grades outward to propylitic or chlorite alteration, often covered by silica caps with vuggy silica. Lava flows and volcaniclastic rocks within faults or associated with volcanic edifices and rhyolitic domes host low- and intermediate-sulfidation mineralization. Low-sulfidation alteration zones typically have adularia and illite or sericite. Chalcopyrite, sphalerite, galena, pyrite, digenite, and manganiferous calcite are related to intermediate-sulfidation gold mineralization. Late- to post-orogenic evolved oxidized I-type granitoids host alkalic-type epithermal and porphyry-like gold mineralization. Porphyry-style hydrothermal alteration is analogous to those of modern systems, with inner sodic and potassic (potassic feldspar ± biotite or biotite) alterations grading to propylitic, muscovite-sericite, chlorite–sericite, and chlorite alterations. Potassic alteration zones are the locus of Cu–Mo mineralization, and gold-rich zones occur in muscovite/sericite–quartz–pyrite alteration. The Paleoproterozoic epithermal and porphyry-like mineralization in these large provinces defines a new frontier for the exploration of world-class gold deposits in the worldwide Proterozoic arc-related magmatic terrains.

Erratum to: Crustal Source of Pb and S at the Yubileynoe Porphyry Gold Deposit (Southern Urals, Kazakhstan): High Precision Pb–Pb and δ34S Data

The Yubileinoe large gold deposit, located at the southern end of the Magnitogorsk megazone, is the only known representative of the Au–porphyry systems in the Southern Urals. It is genetically related to granitoids formed in a suprasubduction setting under mature oceanic island arc environment/setting. The obtained isotope (Pb–Pb and δ34S) data indicate the input of mineral-forming components into the Au–porphyry system of the deposit, mainly from granitoid melts, confirming a common source of ore material and ore-bearing granitoids. The geochemical and isotopic characteristics of granitoids indicate the leading role in their genesis of the crustal source, which is considered Late Precambrian continental crust.

Thermochronological constraints on the exhumation history of the Carboniferous Katebasu gold deposit, western Tianshan gold belt, NW China

Abstract The western Tianshan Gold Belt hosts numerous giant and large gold deposits that have been formed during the late Paleozoic amalgamation of the Tianshan orogen. However, little is known about their exhumation histories during the Mesozoic to Cenozoic intracontinental evolution of the orogen. The Carboniferous Katebasu orogenic gold deposit in northwestern China is a new gold discovery within the western Tianshan Gold Belt, and it shares many similarities with other orogenic gold deposits in the belt. In this contribution, new 40 Ar/ 39 Ar and (U–Th)/He ages were combined with previous geochronology and numerical modelling to quantify its post-Carboniferous cooling and exhumation history. The results revealed a three-phase cooling history and two phases of post-mineralization exhumation. We suggest that a large volume ( c. 0.8 km) of the mineralized roof parts of the Katebasu deposit might have been removed during uplift and erosion, whereas significant ore reserves could still exist at depth. The large erosion depth of the Katebasu gold deposit in the Nalati Range of the Chinese western Tianshan also signifies that shallow-emplaced porphyry and epithermal systems that formed prior to Permo-Triassic uplift might have been largely eroded.

Geochronological Constraint on the Evolution of the Aktyuz Terrane, Kyrgyz North Tianshan, and the Fate of the Taldybulak Levoberezhny Gold Deposit

The Aktyuz Terrane in Kyrgyz North Tianshan is of particular interest due to the occurrence of high and ultrahigh pressure (HP–UHP) rocks and it containing the third largest gold deposit in Kyrgyz North Tianshan, i.e., Taldybulak Levoberezhny (abbreviated to Taldybulak Lev.). To constrain the ages of the host Kemin Complex and its auriferous monzogranite porphyry, detailed zircon U–Pb dating [by laser ablation inductively coupled plasma-mass spectrometry (LA-ICPMS) and secondary ion mass spectroscopy (SIMS)] and Lu–Hf isotopic analyses were carried out. The intensively altered auriferous monzogranite porphyry yielded two weighted mean ages of 444 ± 3 Ma (n = 14, mean squared weighted deviation (MSWD) = 0.49, by LA-ICPMS) and 440 ± 5 Ma (n = 8, MSWD = 0.82, by SIMS) that are indistinguishable within error ranges. Such ages are consistent with a previously reported sulfide Re–Os isochron age of 434 ± 18 Ma, supporting a Silurian porphyry gold mineralization. The granitic gneiss yielded a protolith age of 773 ± 7 Ma (n = 7, MSWD = 0.04) and two metamorphic ages of 514 ± 4 Ma (n = 8, MSWD = 0.09) and 483 ± 3 Ma (n = 11, MSWD = 0.04). Detrital zircons from one fuchsite schist sample yielded highly variable ages from 729 ± 13 Ma to 2,463 ± 30 Ma, with 12 data points weighted at 740 ± 5 Ma (MSWD = 0.95). The metamorphic overgrowth yielded a weighted mean age of 460 ± 4 Ma (n = 4, MSWD = 0.15). Detrital zircons in the migmatitic amphibolite are aged from 788 ± 7 Ma to 3,447 ± 32 Ma, with two major concentrations at 941 ± 7 Ma (n = 13, MSWD = 0.95) and 794 ± 5 Ma (n = 8, MSWD = 0.19). The metamorphic overgrowth yielded an average age of 555 ± 4 Ma (n = 8, MSWD = 0.65). The detrital and xenocryst zircons, and evolved εHf(t) values (−20.9 to −7.8) and old two-stage Hf model ages (1,367–3,159 Ma), revealed the presence of a Precambrian basement that may be dated back to the Archean Eon. The two metamorphic ages may correlate with oceanic subduction and continental collision, respectively.

Crustal Source of Pb and S at the Yubileynoe Porphyry Gold Deposit (Southern Urals, Kazakhstan): High Precision Pb\u2013Pb and \u03b434S Data

The Yubileinoe large gold deposit, located at the southern end of the Magnitogorsk megazone, is the only known representative of the Au–porphyry systems in the Southern Urals. It is genetically related to granitoids formed in a suprasubduction setting under mature oceanic island arc environment/setting. The obtained isotope (Pb–Pb and δ34S) data indicate the input of mineral-forming components into the Au–porphyry system of the deposit, mainly from granitoid melts, confirming a common source of ore material and ore-bearing granitoids. The geochemical and isotopic characteristics of granitoids indicate the leading role in their genesis of the crustal source, which is considered Late Precambrian continental crust.

Pyrite Rb-Sr geochronology, LA-ICP-MS trace element and telluride mineralogy constraints on the genesis of the Shuangqishan gold deposit, Fujian, China

The Shuangqishan gold deposit is the largest gold deposit in the Dehua ore cluster of Fujian Province. The gold orebodies are located in the metamorphic rock of Neoproterozoic Daling Formation. Representative genetic models of Shuangqishan gold deposit include epithermal gold deposit, orogenic gold deposit and granitoid-related gold deposit. Based on the comprehensive research of pyrite Rb-Sr geochronology, telluride mineralogy and pyrite LA-ICP-MS trace element, we intend to discuss the genesis of the Shuangqishan gold deposit. The Rb-Sr isotopic dating of gold-bearing pyrite indicates thatmineralization age of the Shuangqishan gold deposit is 153.5 ± 2.4 Ma, which is the same as that of the granite porphyry dyke (zircon U-Pb age = 153.4 ± 1.2 Ma) in the mining area. The main gold-bearing mineral is native gold, with a fineness of >920, additional gold-bearing mineral is electrum, with a fineness of 677 ~ 741. The gold-bearing polymetallic sulphide quartz veins contain a large amount of tellurbimuth (Bi2Te3), rucklidgeite (PbBi2Te4) and tetradymite (Bi2Te2S). The Shuangqishan gold deposit’s characteristic combination of Au-Bi-Te elements is analogous to that of typical magmatic-hydrothermal deposit. The estimated log f Te2 versus log f S2 conditions of telluride mineralization at 250 °C are –13.0 ~ –9.5, –14.7 ~ –10.5, respectively. LA-ICP-MS trace element analysis of gold-bearing pyrite shows that the pyrite is As-poor and has high content of Te, Bi, Pb, Co and Ni, but has low content of Au and As. The typical As-poor pyrite indicates that the Shuangqishan gold deposit is the magmatic hydrothermal gold deposit. Te displays a high positive correlation with Bi and Pb, indicating that Te, Bi and Pb occur as Bi-telluride micro-inclusion in pyrite. Our research shows that the Shuangqishan gold deposit is the magmatic hydrothermal gold deposit formed in the late Jurassic.

Genesis of the Hebaoshan gold deposit in Fujian Province of Southeast China: constraints from a combined fluid inclusion, H-O-C-S-Pb-He-Ar isotope and geochronological study

The large Hebaoshan gold deposit (41.5 t Au, average grade: 3.5 g/t) is located in a hitherto poorly documented gold province in the northeastern part of the South China Block. It is hosted by Precambrian metasedimentary rocks that experienced Triassic greenschist- to amphibolite-facies metamorphism. Three hydrothermal stages can be distinguished: quartz + sericite + pyrite + pyrrhotite (stage I), quartz + magnetite + sulfide (stage II), and quartz + carbonate + pyrite + hematite (stage III). Auriferous pyrite samples yielded a Rb-Sr isochron age of 234 ± 3 Ma (2σ, MSWD = 0.24), and ore-related hydrothermal sericite yielded a 40Ar-39Ar plateau age of 226.4 ± 2.0 Ma (2σ, MSWD = 1.01), which are distinctly younger than ca. 430 Ma granitic rocks in the mining district and older than 170–130 Ma granites in the region, ruling out any genetic link between granite emplacement and gold mineralization. The mineralizing fluid system can be described as carbonic-aqueous with low to moderate salinity (2.2–10.1 wt% NaCl equiv.) and medium temperature of 290 to 350 °C (stage I) and 230 to 280 °C (stage II). The δ18O quartz ranges from 13.3 to 15.4 ‰, and the δD values for fluid inclusions in quartz range from − 97 to − 60 ‰. The calcite has C-isotopes ranging from − 6.1 to − 3.8 ‰ and O-isotopes from 2.8 to 13.6 ‰. H-O-C isotope data are consistent with a metamorphic fluid derived from devolatilization of Neoproterozoic basement rocks during regional metamorphism in the Late Triassic Indosinian period. The δ34S values of sulfides for stages I, II, and III are 0.1 to 7.8 ‰, − 10.6 to 5.1 ‰, and − 18.9 to − 14.1 ‰, respectively, indicating an increase in oxygen fugacity during fluid ascent which resulted in more negative sulfur isotope values of sulfides and precipitation of gold. Pyrite separates have 206Pb/204Pb ratios of 17.340 to 17.687, 207Pb/204Pb ratios of 15.539 to 15.604, and 208Pb/204Pb ratios of 37.749 to 38.094. The S-Pb isotope data suggest derivation of S and Pb from the Precambrian metasedimentary country rocks. Auriferous pyrite yielded elevated 3He/4He ratios (0.78–1.46 Ra), which suggest a mantle component as can be expected from fluids derived from a subduction setting. It is concluded that Hebaoshan is an orogenic gold deposit that formed during Triassic flat-slab subduction of the paleo-Pacific plate beneath the South China Block and thus constitutes the first Triassic deposit of this type recognized in the coastal area of Southeast China.

A magmatic‐hydrothermal origin of the Xinfang gold deposit, Liaodong Peninsula, China, revealed by in‐situ S–Pb isotopes and trace element analyses of pyrite

AbstractThe Xinfang deposit is a large gold deposit (>20 t of Au) on the southern edge of the Liaodong Peninsula, China. A total of 37 gold‐bearing orebodies are identified along NS‐ and NW‐striking faults and are mainly hosted by the Archean and Neoproterozoic metamorphic rocks. Three stages of hydrothermal mineralization are distinguished, including Stage I of dominant quartz ± pyrite (Py1), Stage II of quartz‐polymetallic sulfide (Py2), and Stage III of quartz‐calcite ± pyrite (Py3). Gold primarily occurs at the Stage II in association with intensive silicification, pyritization, and sericitization. Here, we report on high‐precision in‐situ LA‐MC‐ICP‐MS analyses of S and Pb isotopic compositions of the sulfide minerals and LA‐ICP‐MS analyses of trace element signature of the pyrite from the Xinfang gold deposit. The δ34S values of the sulfides range from 1.3 to 5.3‰, which is consistent with a magmatic origin of S. The sulfides yield 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb ratios of 37.497–37.773, 15.323–15.410, and 17.004–17.229, respectively, which deviate from the values of the wall rocks, suggesting an external Pb source. The in‐situ LA‐ICP‐MS spot analyses of the pyrite reveals that gold occurs in two generations of pyrite (Py2 and Py3) but at low concentrations (≤0.06 ppm for Py2, ≤0.24 ppm for Py3). Visible gold, however, only occurs in the Stage II assemblage as inclusions in pyrite and quartz, and is distributed along the margins or within the fractures of the sulfides. The Py2 shows high Co, Ni, and As concentrations and is depleted in other trace elements typical of a magmatic‐hydrothermal derivation. In contrast, Py3 exhibits low concentrations in most trace elements. Trace element mapping of Py2 revealed correlations between Fe and Co, as well as Ni and As, indicating their couped substitution in the pyrite structure. The available geological, petrographic and geochemical data consistently suggest that the Xinfang gold deposit formed during the Early Cretaceous by hydrothermal fluids of magmatic contribution.

Bioleaching: Validation of the Extraction of Precious Metals Through Selective Recovery of Iron, Copper and Zinc

In Ecuador, large gold deposits were discovered in the areas of Nambija and Ponce Enríquez, but they contain metal sulfides that, when exposed to the action of air and water, intervene in a series of physical, chemical and biological phenomena. The oxidation of sulfides to sulfates occurs by the catalytic action of bacteria, in addition to the production of sulfuric acid that dissolves heavy metals such as iron, copper and zinc; a process known as bioleaching. These solutions, with a high level of acidity, are carried away by water currents or runoff, becoming a great contaminant of water and soil of the surrounding sector. Acid mine drains are one of the main problems of environmental pollution; the mining deposits are located in areas of great biodiversity. In these areas there are births of water used for human consumption, agriculture and mining work; the mismanagement of tailings, tailings and sands that are discharged into rivers and streams generate serious environmental damage. The objective of the work is to use selective precipitation to recover iron, copper and zinc from acid solutions produced by bioleaching during the extraction of precious metals at the laboratory level and from acid drainage of natural mine, to comply with environmental regulations regarding the discharge of effluents and reduce the effect of environmental pollution produced by acid mine drains. This investigation presents the conditions for a successful individual recovery of the main base metals contained in a bioleaching solution with high copper, zinc, and iron concentrations by pH-based selective precipitation. Tests were made with standard solutions of known concentrations of copper, iron, lead, and zinc and by titration the concentrations were checked, which allowed to validate the volumetric titration method. The selective precipitation of heavy metals was carried out in three phases using real acid main drainage and bioleaching solutions generated at the laboratory. The first phase in a pH range of 2 to 4 to recover iron; the second phase in a pH range of 4 to 6 to recover copper; and the third phase in a pH range of 6 to 10 to recover zinc. The selective precipitation allowed the heavy metals to be completely removed from the solution or to achieve concentrations below the maximum allowable limit to be discharged to a body of water or public sewer. Validation of SOLBIO 2 and Orenas bioleaching solutions was performed.

Resource potential of one of Earth's final remaining frontiers: the Siberian Platform

The Siberian Platform, covering a vast area of East Siberia (Russian Federation), represents one of the largest underexplored regions in Asia. Previous expeditions and regional surveys in the twentieth century, however, suggest that the Siberian Platform and adjacent orogenic belts hold significant potential for large undiscovered gold, copper, diamond and industrial mineral deposits, along with extensive oil and gas fields. The remoteness of the region, its inhospitable winter climate, and a major lack of modern infrastructure and mining methods have long hampered exploration in this area. These factors, along with the additional investment required and political uncertainties involved with operating in Russia, have deterred many international mining companies from considering the Siberian Platform as a viable region for exploration and mining. However, as mining industry paradigms change into a green, battery metals‐driven commodity sector, and modern mining methods are developed, increasing efficiency at a lower cost, the significant undiscovered mineral potential of the Siberian Platform could elevate the region to the forefront of mineral exploration and mining in the future.

К ВОПРОСУ О ЗОЛОТОНОСНОСТИ КОР ВЫВЕТРИВАНИЯ УЧАСТКА РЫБАЧИЙ (ЗАПАДНЫЙ СИХОТЭ-АЛИНЬ)

The author addresses an issue of gold presence in pre-Quaternary crusts of weathering that are widespread in sub-mountain areas of the doming-block geomorphological structures of the Amur Region, the Khabarovsk and Primorsky Territories along the periphery of large- and medium-sized Cenozoic basins and depressions. For a more detailed mining and geological study and assessment of the gold content of the weathering crusts, we recommended the Rybachy site as one of these objects (insufficiently studied), and the entire Mukhenskaya area as a promising one. These sites are located in the zone of articulation of the eastern side of the Middle Amur Depression with the folded structures of the West Sikhote-Alinsky volcanic belt. The author gives examples of large gold deposits, related to weathering crusts with their brief description (Olympiada, Kuranakh), as well as a brief description of alluvial deposits of weathering crust (sub-basalt cl.Paskhalny, an eluvial-alluvial placer of the Bolotisty Stream). The search work of the DVIMS (Far Eastern Institute of Mineral Raw Materials) in 2002 indicated the potential of weathering crusts within the Rybachy prospect for gold mineralization. This is supported by elevated gold in heavy mineral concentrates from the linear weathering crusts and residual blankets, as well as from non-commercial placers (from 0.01 to 4.0 g/t and higher); the occurrence of fracture zones, brecciation, secondary silicification close by fractures, and abundant Late Cretaceous silicic and intermediate dikes. Zones of hydrothermally altered rocks (silicification, chloritization, sericitization, argillization) are widespread here.

Multistage Thrust and Nappe Tectonics in the Southeastern Part of East Sayan and Its Role in the Formation of Large Gold Deposits

Abstract ––Comprehensive studies of structural geology and metallogeny, taking into account the authors’ previous works started as early as the last century, have shown that the southeastern part of East Sayan formed mainly in the Neoproterozoic–early Paleozoic in the settings of multistage thrust and nappe tectonics and tectonomagmatic restructuring of autochthonous and overthrust allochthonous oceanic (ophiolitic), island arc, and ocean-marginal terranes as well as amalgamation of accretion–collision and postcollisional igneous complexes that formed during the opening and subsequent closure of the Paleoasian Ocean marginal structures. In the middle and late Paleozoic, active intraplate volcanic and plutonic processes continued in the thrust/overthrust fault setting, which led to the formation of new dome-shaped nappe structures and the redistribution of ore matter (gold etc.) in large mineral deposits. The final structure of the East Sayan region formed during the late Cenozoic as a result of mountain uplifting and volcanic eruptions, including those in the valley of the Zhombolok River.

Hydrothermal alteration and mineralization of Baiyun gold deposit in Liaodong Peninsula, North China Craton

Baiyun deposit is a large gold deposit in the Liaodong Peninsula (North China Craton), containing over 31.7 t of gold. Silicic alteration, K‐feldspar alteration, and pyritization are well developed and closely related with mineralization in Baiyun deposit. Based on field and optical microscopic observations, the alteration styles include quartz + K‐feldspar zone, pyrite + sericite +quartz zone, and chlorite zone from orebody outward. In this study, the quartz, K‐feldspar, and pyrite of pre‐ore, syn‐ore stages 1 and 2 were selected for LA‐ICP‐MS trace element analysis and electron probe microanalysis (EPMA) to reveal the alteration‐mineralization link. Results show that the albite was altered to mainly K‐feldspar and minor secondary quartz at syn‐ore stage 1. Fluid‐rock reaction of the silicic‐potassic alteration may have decreased the fluid oxygen fugacity (fO2), which triggered the gold precipitation. Most of invisible gold occurred in the form of solid solution. At syn‐ore stage 2, albite altered to mainly quartz and minor K‐feldspar. The syn‐ore stage 1 K‐feldspar also altered to minor secondary quartz at syn‐ore stage 2. In addition, the release of sulphur from the syn‐ore stage 1 pyrite was likely another trigger for the gold precipitation. Most of syn‐ore stage 2 invisible gold occurred as nano‐particles. The ore‐forming fluids consist mainly of primary magmatic fluids mixed with minor metamorphic fluids. The ore metals may have sourced mainly from the magmatic fluid and the sillimanite‐mica schist of the Gaixian Formation.

An Archean Porphyry-Type Gold Deposit: The Côté Gold Au(-Cu) Deposit, Swayze Greenstone Belt, Superior Province, Ontario, Canada

Abstract The Archean low-grade, large-tonnage Côté Gold Au(-Cu) deposit is the first large gold deposit discovered in the Swayze greenstone belt, Ontario, Canada. The deposit is hosted by the Chester Intrusive Complex, a low-Al composite, subvolcanic intrusion composed of tonalite, quartz diorite, and diorite that was previously constrained to ca. 2741 to 2739 Ma (U-Pb zircon). Presented here is the first detailed study of the mineralization and related alteration, along with the relative and absolute age (U-Pb, Re-Os) constraints on gold mineralization. The earliest hydrothermal stage is represented by rare Au-bearing amphibole-rich veins and breccias. The main ore stage consists of biotite-rich alteration centered on an Au(-Cu)–bearing magmatic-hydrothermal biotite breccia body with spatially related disseminated biotite and veins of both sheeted and stockwork type. Extensive fracture-controlled and replacement-style Au ± Cu-bearing muscovite alteration overprints biotite-altered rocks in the core of the deposit. Barren fracture-controlled and disseminated epidote alteration is localized to the north of the deposit and above the magmatic-hydrothermal biotite breccia. Late, texturally destructive albite alteration overprints the mineralized hydrothermal alteration in the deposit core. U-Pb isotope dilution-thermal ionization mass spectrometry and laser ablation-inductively coupled plasmamass spectrometry ages for hydrothermal titanite from amphibole (2745 ± 3 Ma) and albite (2737.5 +2.2/–1.8, 2745 ± 9, and 2736 ± 7 Ma) alteration assemblages constrain hydrothermal activity to ca. 2740 Ma. The timing of gold and sulfide mineralization is also constrained by two Re-Os molybdenite ages of 2736.1 ± 11.4 (biotite alteration) and 2746.8 ± 11.4 Ma (muscovite alteration). These new ages overlap with the ca. 2741 to 2739 Ma magmatism for the Chester Intrusive Complex, thereby suggesting a synintrusion, magmatic-hydrothermal origin for the gold mineralization and related alteration. This is significant, as it represents a new gold metallogenic event in the Abitibi subprovince, for which regional importance remains to be defined. Considering the spatial association of the deposit with a dioritic intrusion and the temporal overlap of igneous activity with alteration (i.e., amphibole, biotite, sericite) and mineralization (i.e., breccias, veins, disseminations), the deposit is interpreted as an Archean magmatic-hydrothermal ore system sharing analogies with Phanerozoic Au-Cu porphyry deposits. It suggests that Archean porphyry-type deposits can form in low-Al composite intrusions, which are known to host Cu-Mo-Au breccia, vein, and disseminated mineralization and underlie temporally and genetically related felsic to intermediate volcanic rocks that host volcanogenic massive sulfide deposits.

Petrography of the Mesozoic Alkaline Rocks of the Medvedev Massif (South Yakutia, Aldan-Stanovoy Shield, Leglier Ore Cluster)

The article considers petrographic compositions of the Mesozoic alkaline magmatic rocks of the Medvedey massif. The latter is a part of the Central Aldan ore district and is spatially located in the central part of the Nymnyr block. The massif is a multiphase structure, of the most productive stage of development of the territory – the Mesozoic tectonic-magmatic activation of the Aldan-Stanovoy shield. The main purpose of this work was to identify qualitative quantitative-mineralogical characteristics of the massif rocks, potential for gold mineralization, using crystal-optical methods. As a result of the field works and petrographic studies of the Mesozoic alkaline magmatic rocks, it was determined that, The Medvedev massif has a zonal structure and is represented by three phases of intrusion with distinct contacts between the latter, which rocks differ in structural and material features. The rocks of the first phase of the massif are composed considerably of leucocrate (the content of dark-colored minerals is up to 9%) syenite-porphyry with elements of the monzonite structure. Magmatic formations of the second phase of the massif differ from those of the first phase primarily in structural features and are represented by hypidiomorphic granular differences with an increased content of dark-colored minerals in the rocks up to 15%. The rocks of the final phase have a noticeable difference from the first two phases and are represented by mesocratic monzonite porphyry with a clearly expressed monzonite structure with a dark-colored mineral content up to 20%. Within the Central Aldan ore region, the large Samolazovskoye gold deposit is associated with similar multiphase massifs, in particular with the Yukhtin massif. During field works, it was found that gold-ore mineralization is associated with the massif, which formation is related to an intensively occurred contact-metasomatic effect on the host rocks. Hydrothermal-metasomatic transformations of the latter are the products of multi-stage alkali-silicate metasomatism, associated with the second and especially the first phases of intrusion of the massif, as well as with further weathering processes, disintegration of gold-ore metasomatites and formation of an oxidation zone. Based on the petrographic study of the material composition of the rocks of the massif, it is concluded that gold ore occurrences of commercial scale can be associated with such massifs of multi-phase intrusion.

Estimates of pit-lake evaporation and its potential effects on groundwater interactions with the Humboldt River

The Humboldt River, in northern Nevada supplies water mostly for irrigation of nearby croplands. Groundwater pumping both near and distant from the river has increased over the past 50 years. The primary use of groundwater is for irrigation of croplands but it is also an important source for municipalities, mining and other industries. Large gold deposits that require dewatering were discovered in the mountains of the central part of the drainage basin in the 1970’s and 1980’s. Much of the water pumped to dewater the mines is recharged back to groundwater in the valleys or is released to the Humboldt River or one of its tributaries. Of concern is the long-term loss of groundwater from pit-lake evaporation and how those losses could affect groundwater interactions with the Humboldt River once mine operations cease. Flows in the Humboldt River are mostly dependent on snowmelt runoff from the mountains, particularly from mountains in the drainage area upstream of the Palisade gaging station. The mean flow increases with drainage area between the gaging stations upstream of Elko and at Palisade, whereas the mean flow decreases downstream of the Palisade gaging station. Much of the decrease in mean flow downstream of Palisade is caused by: (1) minimal additional contributions from runoff and groundwater flow; (2) spreading of water to native pastures on the floodplain; and (3) infiltration of river water into its associated alluvium. During low-flow periods, particularly during periods of drought, the Humboldt River between Battle Mountain and Comus gaging stations often has flows less than 1 cubic foot per second (cfs) even before there was any mine dewatering. Estimated groundwater loss to evaporation for the five largest pit lakes in the drainage area between the Palisade and Comus gaging stations is about 5,400 acre-feet per year (afy) (7.6 cfs or five times less than the estimated net annual evaporation loss from the Rye Patch and the Pitt-Taylor Reservoirs upstream of Lovelock, Nevada. The groundwater loss to three of the pit lakes (Goldstrike Mine, Cortez operations, and Twin Creeks Mine) is unlikely to affect river flow because even prior to mine dewatering, groundwater flow from the low-lying mountains was lost to evapotranspiration near the base of the alluvial fans and did not contribute flow to the river. The Lone Tree Mine ceased dewatering in December 2006 and since then a lake has formed in the pit. The floodplain of the Humboldt River in the reach between Battle Mountain and Comus is underlain by a layer of blue clay at shallow depth. Between 2007 and 2019, the net mean annual streamflow loss between Palisade and Comus is nearly the same as during a period of little groundwater pumping from 1946 to 1969 suggesting that even the relatively large amount of water pumped from the mine has had a little effect on Humboldt River flows. Groundwater evaporation from the eventual pit-lake at the Gold Quarry Mine is estimated at 740 afy (about 1 cfs) and could perhaps decrease the gain in the Humboldt River upstream of Palisade. How much of a decrease is uncertain because some of it could be lost to evapotranspiration at the edge of the floodplain prior to reaching the river. Even if the groundwater loss from the pit lake at Gold Quarry Mine were to reduce the gain of river flow between Carlin and Palisade, the loss would be too little to measure accurately.

The large Bakyrchik orogenic gold deposit, eastern Kazakhstan: Geology, mineralization, fluid inclusion, and stable isotope characteristics

The large (>13 Moz Au, averaging 5–6 g/t Au) Bakyrchik Au deposit in eastern Kazakhstan is part of a district-scale mineralized zone, situated in an accretionary terrane. The deposit is localized within a shear zone in carbonaceous sedimentary rocks, which crosscuts the stratigraphy and comprises subconcordant dikes of high-K calc-alkaline (to shoshonitic?) rocks (lamprophyre to monzogabbro to monzodiorite). The tectonized/cataclased carbonaceous rocks contain numerous banded (bedded?) pyrite clasts and bands and abundant disseminated auriferous sulfides (pyrite and acicular arsenopyrite); the latter overprint pyritic clasts and occur proximal to (although mostly outside of) the concordant quartz veins and associated quartz-cemented hydrothermal breccias. Late granodiorite-plagiogranite dikes postdate auriferous sulfides and associated quartz veins/hydrothermal breccia but are overprinted by the late quartz veins containing free native gold and some Cu-Zn-Pb sulfides. This mineralization, however, is minor at the deposit.The most abundant stylolitic quartz veins accompanied by auriferous sulfide mineralization were formed from a homogenous and then boiling aqueous-carbonic fluid at temperatures of >315–300 to 265–240 °C and pressures of 0.8 to 1.2 kbar. Boiling was a dominant process during the formation of hydrothermal breccias accompanied by most intense auriferous sulfide (pyrite, arsenopyrite) mineralization at the temperatures of 250–230 °C and pressures of ~1.1 kbar. The late quartz veins were also formed from a homogenous and then boiling aqueous-carbonic fluid at temperatures of >350–315 to 235–225 °C and pressures of 1.1 to 1.3 kbar. The stable isotope data support a variable – from sedimentary to magma-derived - source of sulfur (δ34S = −20 to ~0‰), with a dominantly sedimentary to metamorphic source of carbon (δ13C = −27.4 to −22.5‰).The deposit is polygenetic and exhibits combined synsedimentary-exhalative, metamorphic to intrusion-related, magmatic-hydrothermal signatures, with strong structural control and close association with various dikes. Most of auriferous sulfide mineralization occurred after or nearly coeval to the intrusion of mafic to intermediate dikes, with a strong positive correlation of Au with As, Ssulf, Ag, Sb, and Hg. Homogenized δ34S values of auriferous pyrite and arsenopyrite (from −2.4 to −0.5‰), close to the meteorite standard, indicate dominantly magma-derived sulfur. Late quartz veins with free native gold and minor Cu-Zn-Pb sulfides are more distinctly related to granodiorite-plagiogranite intrusions.