Gold Province Research Articles

Deep gold mineralization features of Jiaojia metallogenic belt, Jiaodong gold Province: Based on the breakthrough of 3000 m exploration drilling

ABSTRACT Recently, continuous breakthroughs have been made about deep gold prospecting in the Jiaodong gold province area of China. Approximately 5000 t of cumulative gold resources have been explored in Jiaodong, which has thus become an internationally noteworthy gold ore cluster. The gold exploration depth has been increased to about 2000 m from the previous

Ore-forming processes in the Wang’ershan gold deposit (Jiaodong, China): Insight from microtexture, mineral chemistry and sulfur isotope compositions

The microtexture, trace element characteristics and sulfur isotopic features of ore-related minerals provide important clues to trace physico-chemical conditions and source characteristics of ore formation. In this study, we investigate the Wang’ershan gold deposit in the Jiaodong gold province of eastern North China Craton where three hydrothermal stages were distinguished. Stage I is characterized by K-feldspar, sericite, quartz with minor pyrite precipitation (Py-I); sericite, quartz (Qtz-a) and pyrite (Py-II) with minor gold precipitated during stage II; and stage III involved quartz (Qtz-b), gold, and polymetallic sulfides with minor pyrite (Py-III). In situ δ34S results show a decreasing trend from 21.7 to 14.6‰ (Py-I) to 9.2–8.3‰ (Py-II) and 8.9–8.6‰ (Py-III). The Py-II and Py-III are poor in mineral inclusions and porous microtextures, and have no oscillatory composition zoning. The Co content is 1–2 order of magnitudes higher in Py-I (371.2 – 823.2 ppm, av. 597.2 ppm) than late stage pyrites (0.4 – 524.2 ppm, av. 95.4 ppm). Qtz-a show cataclastic breccia cemented by Qtz-b with little dissolution during the injection of stage III ore-forming fluids. The Al contents decrease from Qtz-a (49.0 – 426.6 ppm) to Qtz-b (18.2 – 46.8 ppm). Based on the sulfur isotope, trace element and microtextural characteristics in Py-II and Py-III, combined with previous fluid inclusion studies, we infer that the ore-forming fluids of stage II and III experienced gentle immiscibility and were suggested to be of different evolutionary stages of a single ore-forming fluid sharing common sources with similar and near-equilibrium physicochemical conditions. The trace element characteristics with lack of oscillatory compositional zoning in the two stages of quartz suggest gentle cooling with lack of any abrupt change of physicochemical conditions during fluid immiscibility. The decoupling of Au and As contents in Py-II and Py-III was likely controlled by chemisorption of gold in pyrite structure. Complex variation in geochemical features of ore-forming fluids from early alteration to main mineralization period is indicated by the large range of δ34S and Co contents in Py-I and late stage pyrites, and the differences in alteration processes. Based on a comparison of the Co/Ni, Ni and As among pyrites from the Wang’ershan gold deposit, typical porphyry deposits and orogenic gold deposits, together with the large positive deviation of δ34S relative to mantle values, we propose that ore-forming materials of the Wang’ershan gold deposit were derived from mixed sources involving magmatic hydrothermal-related and sedimentary strata-related components.

IN SITU DATING OF HYDROTHERMAL MONAZITE AND IMPLICATIONS FOR THE GEODYNAMIC CONTROLS ON ORE FORMATION IN THE JIAODONG GOLD PROVINCE, EASTERN CHINA

AbstractThe Jiaodong gold province, the largest gold producer in China, formed in a setting dominated by a 30-m.y. episode of Izanagi plate rollback and widespread extension, concomitant with late Mesozoic craton destruction. This study presents new high precision in situ sensitive high-resolution ion microprobe (SHRIMP) U-Th-Pb and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb ages for hydrothermal monazite from the largest of the Jiaodong gold deposits, which were previously dated as indicating ore formation over a few tens of millions of years when applying sericite Ar-Ar, zircon U-Pb, and less robust analytical techniques. Our U-Pb dating on monazite from the Jiaojia and Linglong deposits in western Jiaodong yielded consistent ages at ca. 120 Ma. The new geochronologic results, coupled with recently reported in situ monazite dates from smaller deposits in western Jiaodong, reveal that the deposits that host most of the ≥4,000-t Au resource formed during a relatively brief period at ca. 120 Ma. In eastern Jiaodong, the much smaller resource may have formed about 5 m.y. later, recorded by 114.2 ± 1.5 Ma gold mineralization at the Rushan deposit. The postsubduction opening of a slab gap at ca. 120 Ma is the most likely cause of the extensive gold mineralization in Jiaodong. The gap induced a local and rapid devolatilization of the hydrated mantle wedge at submelt temperatures. The transient event included release of a major volume of gold-transporting aqueous-carbonic fluid that was stored in the wedge into major NNE-trending structures in the overlying lithosphere.

In-situ sulfur isotopes analysis as an exploration tool for orogenic gold mineralization in the Granites-Tanami Gold Province, Australia: Learnings from the Callie deposit

Orogenic gold deposits are commonly associated with a small alteration and geochemical footprint that often hinders the exploration process. In the Granites-Tanami Gold Province; however, we demonstrate that sulfur isotope analyses represent a powerful exploration tool for orogenic gold mineralization. The Granites-Tanami Gold Province, situated in the Northern Territory (Australia), hosts numerous gold occurrences including the world-class Callie deposit (c. 14.2 Moz Au). In this paper, we use sulfur isotopes to: 1) characterize the δ34S signature of the sulfides associated with gold mineralization in order to assist with exploration in the Granites-Tanami Gold Province, and 2) monitor the temporal fluid evolution of the Callie deposit. We present in-situ sulfur isotope analyses of sulfides associated to gold mineralization, diagenetic sulfides, and sulfides associated to a barren, post-mineralization hydrothermal event. Our results show that the sulfides associated with mineralization yield δ34S values that range from +4‰ to +11.5‰ (n = 114), the diagenetic sulfides yield δ34S values that range from +0.0‰ to +1.7‰ (n = 41) and the post-mineralization sulfides yield δ34S values that range from +2.3‰ to +3.3‰ (n = 20). The range of δ34S values obtained from mineralized samples at the Callie deposit coincides with δ34S values reported in sulfides associated to other orogenic gold deposits of the Granites-Tanami Gold Province. The mineralization-related δ34S signature in the Granites-Tanami Gold Province is distinct from both diagenetic and post-mineralization sulfides providing a unique isotopic signature for the sulfides associated to gold mineralization. Therefore, we propose that the application of routine sulfur isotope analysis may represent a valuable tool for mineral exploration in the area. We also report a temporal shift toward lighter δ34S values from various sulfides associated to the stratabound mineralization at the Callie deposit. We interpret the shift in δ34S values as the expression of a progressive increase in the oxygen fugacity of the ore fluid resulting from progressive alteration of the host-rock.

Pyrite textures and compositions in Jiangshan gold deposit, Bengbu Uplift, southeastern North China Craton: Implications for ore genesis

Many Phanerozoic gold deposits in East China, e.g., those in the Jiaodong Peninsula, hosted either in granitoids of the same age or Precambrian basement rocks of the North China Craton, have been well documented. The Bengbu Uplift along the southeastern margin of the North China Craton is believed to be the western extension of the Jiaodong gold province, separated by the large-scale sinistral Tan-Lu Fault Zone. However, no deposits with more than 10 t gold resources have been discovered in the Bengbu Uplift, and it is unclear whether the timing and genesis of gold deposits in the Bengbu Uplift are similar to those in the Jiaodong gold province.In this study, laser ablation inductively coupled plasma mass spectrometry trace element analyses, mapping, and in situ sulfur isotope analyses were used to determine the source and process of gold mineralization in Jiangshan gold deposit, the largest in the region. The wall rocks in the Jiangshan gold deposit are metamorphic rocks of the Neo-Archaean Wuhe Group, and the ore bodies are controlled by the eastern part of the Guangou–Xiajijia Fault. Four stages were identified from cross-cutting relationships and textural and mineralogical characteristics: pre-ore stage (stage I), quartz–pyrite–muscovite alteration (stage II), pyrite–quartz veins (stage III), and quartz–pyrite veinlets (stage IV). Each of the four stages is characterized by a different type of pyrite, here named Py1, Py2, Py3 and Py4. Py1 formes the core of Py2, has elliptical and irregular shapes, contains low gold and arsenic concentrations, and has δ34S values of 0.86–2.86‰. Py2 is hosted in quartz–pyrite–muscovite-altered rocks with disseminated and aggregated euhedral to subhedral textures. It has elevated arsenic content and the lowest gold content, with some rhythmic zones and fractures. Stage II was crosscut by stage III. Py3 has anhedral textures with brittle deformation and occupies fractures in stage III pyrite–quartz veins. The gold content of Py3 is slightly higher than that of Py1 and Py2, but its arsenic content is extremely low. Py4 in the quartz–pyrite veinlets has cataclastic textures with the highest gold and chalcophile element contents. Native gold and electrum also formed in stage IV, which is the main gold stage in the Jiangshan deposit. The δ34S values of Py2–Py4 are broadly similar (5.79–7.98‰), suggesting a common sulfur source. Based on previous studies and higher δ34S values of hydrothermal pyrite, the fluid sulfur isotopes are interpreted to relate to degassing of the mantle wedge metasomatized by slab fluids during the westward subduction of the palaeo-Pacific plate beneath the North China Craton during the early Cretaceous. Based on the geological characteristics of the deposit, we classify the Jiangshan gold deposit as a Jiaodong fracture-disseminated-type gold deposit which occurs as disseminated veinlets and disseminated mineralization in wallrocks along fracture zones. Tectonic events may be the most important factor in gold mineralization in fracture-disseminated type gold deposits.

Genesis of the Zhangquanzhuang gold deposit in the northern margin of North China Craton: Constraints from deposit geology and ore isotope geochemistry

The genesis of orogenic gold deposits in the northern margin of the North China Craton (NCC) is still ambiguous, and this is addressed in this case study on the Zhangquanzhuang gold deposit. This deposit shows features typical of orogenic gold deposits, including quartz vein-type mineralization controlled by shear zones, sericite-quartz-pyrite-carbonate alteration along shear zones, absence of connection to any magmatic intrusion, and occurrence of native gold and electrum. The Zhangquanzhuang gold deposit, which is hosted in Archean high-grade metamorphic rocks, was formed in Mesozoic and largely later than the regional metamorphism. In this deposit, the Pb isotope compositions of sulfides in ores have low 206Pb/204Pb ratios of 16.874–17.007, 207Pb/204Pb ratios of 15.368–15.410, and 208Pb/204Pb ratios of 37.023–37.215, and these are much less radiogenic than those of regional metamorphic and magmatic rocks. This finding precludes the possible derivation of ore fluid from regional magmatism and metamorphism. In pyrite-hosted fluid inclusions in the ores, the 3He/4He and 40Ar/36Ar ratios are 1.26–1.75 Ra and 1622–2816, respectively, showing prominent signature of mantle sources. These geochemical features, together with the large temporal discrepancy between regional metamorphism and mineralization, suggest that ore fluid and metal had a subcrustal source similar to the gold deposits in the Jiaodong gold province in the southeastern margin of the NCC. The calculated δ34SH2S values for the ore fluid are 2.31–4.48‰, which are heavier than the δ34S of depleted mantle. The δ18O of ore-related quartz mostly cluster around 11‰, implying high δ18O of subcrust-derived ore fluid. The stable O and S isotope data indicate that the subcrustal source has been metasomatized by subducted crustal sediments.

Magnetotelluric exploration of deep-seated gold deposits in the Qingchengzi orefield, Eastern Liaoning (China), using a SEP system

The Liaodong Peninsula in northern China has undergone multi-stage magmatic and tectonic modifications, similar to those recorded by the Jiaodong gold province that is the largest gold-producing district in China, indicating that Liaodong Peninsula has great potential for new discoveries. However, no significant gold deposit has been discovered thus far at depths below 1.5 km, the typical depth of the gold-bearing system in the comparable Jiaodong gold province. This study focused on the Qingchengzi orefield on the northern Liaodong Peninsula. Qingchengzi recorded multiple post-magmatic hydrothermal gold-mineralizing events along the Jianshanzi fault zone, the main ore-controlling structure in the orefield. Given the potential for undiscovered, deep-seated gold mineralization along the Jianshanzi fault zone, we performed a magnetotelluric (MT) study designed to identify any deeper exploration targets. The surface electromagnetic prospecting (SEP) system, a portable instrument suitable for use in electromagnetically mountain environments, was employed for the purpose of acquiring the MT data. Shallow conductive anomalies identified in the vicinity of the Jianshanzi fault zone were tested by known drilling recorder. The survey not only helped to generate a detailed map of the deep geological architecture, but also allowed us to estimate the vertical extent of the known gold orebody to a depth of more than 2 km.

Two-stage gold deposition in response to H2S loss from a single fluid in the Sizhuang deposit (Jiaodong, China)

The material source, fluid evolution and mineralizing mechanism in the Jiaodong gold province have been hotly debated for several decades. The Sizhuang gold deposit provides an excellent object for studying these issues. Gold in this deposit mainly precipitated in the quartz–Au–pyrite (stage II) and quartz–Au–polymetallic (stage III) stages. Stage III can be further subdivided into the early stage III (chalcopyrite, galena with minor amounts of electrum, pyrrhotite, pyrite, siderite and sphalerite) and the late stage III (chalcopyrite, magnetite, siderite with a little pyrrhotite). Pyrite from stage II and stage III contains consistent δ34S signatures (8.1‰–9.6‰ and 7.5‰–9.8‰, respectively) as well as trace elements (e.g. Co: 8.19 vs. 2.63 ppm, Ni: 3.54 vs. 0.74 ppm, As: 29.95 vs. 5.78 ppm, and Bi: 3.18 vs. 7.81 ppm). These consistent geochemical features combined with previous fluid inclusion and C-H-O isotope studies argue for a common source for ore-forming materials and fluids of the stage II and III at Sizhuang deposit. During the stage II and III, reduced sulfur species may have been lost from ore-forming fluids in response to pyrite precipitation (HS- being scavenged by pyrite) and fluid immiscibility (H2S entering vapor phase), which led to the total sulfur concentration (∑Stotal) decrease in the ore-forming fluids. Thermodynamic calculations at different ∑Stotal and constant pressure (2000 bar) and temperature (300 °C) in Fe-Cu-O-S-H system reveal that ∑Stotal decrease can lead to first enlargement and then shrinkage of pyrrhotite stability field with magnetite stability field being broadened to more acidic field; that sulfur species is dominated by H2S (>90 mol%) under the bornite–pyrite phase boundaries in the acidic ore-forming fluids; and that decreases in H2S concentration can efficiently cause gold precipitation by reducing gold bisulfide solubility up to 2–3 orders of magnitude while ∑Stotal just decreases ~50 times. Pyrrhotite and magnetite precipitated due to enlarged stability field during this physicochemical process, which is in line with geologic observations. It is proposed that the two-stage gold deposition by H2S loss from a single ore-forming fluid could account for gold precipitation coupling with occurrence of pyrrhotite and magnetite in the mineral assemblage at Sizhuang deposit.

Mesozoic Orogenic Gold Mineralization in the Jiaodong Peninsula, China: A Focused Event at 120 ± 2 Ma During Cooling of Pregold Granite Intrusions

AbstractJiaodong gold deposits are mainly sited along faulted contacts between Upper Jurassic Linglong granite and Precambrian basement metamorphic rocks or Lower Cretaceous Guojialing granite. Long-standing controversies relate to timing of gold mineralization and granite-gold relationships. In this study, gold-related muscovite consistently provides concordant 40Ar/39Ar plateau ages of 120 ± 2 Ma (2σ) for the Jiaojia, Sizhuang, and Luoshan deposits. Analogous 40Ar/39Ar timing constraints from gold-related muscovite are provided by total gas and high-temperature ages from Fushan, concordant high-temperature ages from Rushan, and fusion-step ages from Xiadian deposits. These new 40Ar/39Ar ages, when combined with previous reliable 40Ar/39Ar and U-Pb age constraints for mineralization, including ages of pre- and postgold dikes, define a widespread gold mineralization event at 120 ± 2 Ma (2σ). Published zircon U-Pb ages for Guojialing and Aishan granite magmatism suggest an ~8-m.y. lag between peak intrusive activity and gold mineralization. This, together with lack of both high-temperature alteration assemblages and alteration and/or metal zonation, indicates that the structurally controlled Jiaodong deposits are orogenic rather than intrusion-related deposits. Despite this, granite intrusions are considered to have provided suitable fluid trap sites. New 40Ar/39Ar analyses of biotite from the Linglong and Guojialing granites show they had cooled to about ~300° ± 50°C by ca. 123 to 124 Ma, providing pressure-temperature conditions similar to those under which most orogenic gold deposits formed close to the ductile-brittle transition. This enabled the effective ingress of fluids at supralithostatic pressures at 120 ± 2 Ma, leading to intensive brecciation, alteration, and deposition of both vein-type and disseminated gold ores. New zircon (U-Th)/He dates together with apatite fission-track data indicate that preservation of the gold province is due to slow postmineralization uplift and exhumation.

NOBLE GASES FINGERPRINT THE SOURCE AND EVOLUTION OF ORE-FORMING FLUIDS OF CARLIN-TYPE GOLD DEPOSITS IN THE GOLDEN TRIANGLE, SOUTH CHINA

Abstract Precise constraints on the source and evolution of ore-forming fluids of Carlin-type gold deposits in the Golden Triangle (south China) are of critical importance for a better understanding of the ore genesis and a refined genetic model for gold mineralization. However, constraints on the source of ore fluid components have long been a challenge due to the very fine grained nature of the ore and gangue minerals in the deposits. Here we present He, Ne, and Ar isotope data of fluid inclusion extracts from a variety of ore and gangue minerals (arsenian pyrite, realgar, quartz, calcite, and fluorite) representing the main and late ore stages of three well-characterized major gold deposits (Shuiyindong, Nibao, and Yata) to provide significant new insights into the source and evolution of ore-forming fluids of this important gold province. Measured He isotopes have R/RA ratios ranging from 0.01 to 0.4 that suggest a maximum of 5% mantle helium with an R/RA of 8. The Ne and Ar isotope compositions are broadly comparable to air-saturated water, with a few analyses indicating the presence of an external fluid containing nucleogenic 38Ar and radiogenic 40Ar. Plotted on the 20Ne/4He vs. helium R/RA and 3He/20Ne vs. 4He/20Ne diagrams, the results define two distinct arrays that emanate from a common sedimentary pore fluid or deeply sourced metamorphic fluid end-member containing crustal He. The main ore-stage fluids are interpreted as a mixture of magmatic fluid containing mantle He and sedimentary pore fluid or deeply sourced metamorphic fluid with predominantly crustal He, whereas the late ore-stage fluids are a mixture of sedimentary pore fluid or deeply sourced metamorphic fluid bearing crustal He and shallow meteoric groundwater containing atmospheric He. Results presented here, when combined with independent evidence, support a magmatic origin for the ore-forming fluids. The ascending magmatic fluid mixed with sedimentary pore fluid or deeply sourced metamorphic fluid in the ore stage and subsequently mixed with the meteoric groundwater in the late ore stage, eventually producing the Carlin-type gold deposits in the Golden Triangle.

Textural and geochemical investigation of pyrite in Jacobina Basin, São Francisco Craton, Brazil: Implications for paleoenvironmental conditions and formation of pre-GOE metaconglomerate-hosted Au-(U) deposits

The Jacobina Basin has a well-preserved sedimentary record, including continental and marine deposits, and hosts Au-(U)-Py mineralization in metaconglomerate beds similar to the Witwatersrand gold province. Based on petrographic observations, in situ trace-elements, and multiple sulfur isotope analyses (32S, 33S, 34S, and 36S) on pyrite from alluvial and marine facies, several types of pyrite were recognized. The pyrite grains identified in the alluvial metaconglomerates resemble those found in several pre-GOE gold-bearing metaconglomerates, including detrital and epigenetic varieties. Detrital inclusion-bearing pyrite is enriched in several redox-sensitive trace-metals as well as Au, which indicate an association with carbonaceous shales. On the other hand, the sources of detrital massive pyrite are more variable and include igneous, metamorphic, and hydrothermal sources from the Paleoarchean hinterland of Jacobina Basin. Epigenetic pyrite in metaconglomerates formed during metamorphism by the recrystallization of detrital pyrite with negligible contributions from external hydrothermal fluids to the basin. Diagenetic and epigenetic pyrite are found in marine lithologies. In a metapelite sample, the pyrite grains formed near the sediment-water column interface, with S sourced from the photolytic sulfate (SO42−, Δ33S < 0) dissolved in the water column. A quartzite sample, in turn, has detrital pyrite grains that were likely reworked from continental deposits, as well as pyrite formed by the assimilation of elemental sulfur (S8, Δ33S > 0) that accumulated in sediment pore water during diagenesis. Significantly, the pyrite associated with terrestrial metasediments shows a wide range in δ34S values but quite restricted ranges in Δ33S and Δ36S values, whereas pyrite associated with the marine metasedimentary rocks exhibits limited δ34S values but has a wide range in Δ33S values and correlated Δ36S values close to the Archean array. These data suggest distinct preservation routes for MIF-S from atmospheric SO42− and S8 in terrestrial and marine environments. Conditions on the terrestrial surface resulted in re-equilibration of distinct S sources, diminishing the amplitude of the Archean atmospheric signal. In contrast, SO42− dissolved in shallow marine settings while S8 settled to the floor, favoring the preservation of MIF-S isotopic signatures. Such processes may also explain the apparent differences in interpretations of atmospheric conditions derived from uncharacterized pyrites from Archean sources. Our data suggest that the Earth’s atmosphere remained anoxic, and terrestrial conditions were such as to allow the syngenetic accumulation of gold, as recently proposed for the Witwatersrand gold deposits.

Geochronology, isotopic chemistry, and gold mineralization of the black slate-hosted Haoyaoerhudong gold deposit, northern North China Craton

The Haoyaoerhudong gold deposit is the largest gold deposit in the north margin of the North China Craton gold province, and contains over 7 Moz of gold at an average grade of 0.62 g/t. The deposit is hosted in the carbonaceous and pyritic slate, phyllite, and schist and is controlled by a tight syncline and shear zones. The high-grade orebodies contains abundant pyrite veins and pyrite-quartz veins. Three stages of pyrite have been identified, including the diagenetic disseminated pyrite, pyrite veins caused by peak matamorphism, and pyrite-quartz veins forming during post-peak metamorphism. Native gold has been observed in pyrite veins and pyrite-quartz veins.The 40Ar/39Ar plateau age of a biotite separate from a tails of boudinaged pyrite-quartz veins is 260.1 ± 2.9 Ma. Combined with previously published 40Ar/39Ar mica age data and low closure temperature of mica, these results suggest that pyrite veins and pyrite-quartz veins were formed during the peak, to post-peak metamorphism during 285–260 Ma, respectively. The lower limit of the formation age of sedimentary disseminated pyrites has constrained to 1670–1560 Ma by the intruded mafic–ultramafic dikes.Disseminated pyrite separates have δ34S values ranging from −39.40‰ to + 17.85‰, 206Pb/204Pb of 19.144–21.892, 207Pb/204Pb of 15.681–15.864, and 208Pb/204Pb of 37.502–38.925, suggesting they were formed from seawater sulfate and has experienced strong sulfur isotopic fractionation. In contrast, hydrothermal pyrites from pyrite veins and pyrite-quartz veins have δ34S values ranging from +6.8‰ to +16.47‰, 206Pb/204Pb of 18.566–18.922, 207Pb/204Pb of 15.645–15.684, and 208Pb/204Pb of 38.924–38.983, which may reflect dissolution-reprecipitation of disseminated sulfides from the pre-existing organic-rich sediments. The mineral paragenetic, geometric, and cross-cutting relationships of pyrite veins and pyrite-quartz veins at Haoyaoerhudong suggest that gold was most likely introduced into pyrite, accompanying sedimentation of the organic-rich shales, and then became enriched during diagenesis. Subsequently, the hydrothermal fluids following metamorphism and shear zone activity make dissolution of the gold in the diagenetic pyrite and precipitated in the intersection of shear zone and tight syncline.

Characteristics and evolution of ore-fluids of the Dayingezhuang gold deposit, Jiaodong gold province

Characteristics and evolution of ore-fluids of the Dayingezhuang gold deposit, Jiaodong gold province

U-Th-Pb Shrimp dating of hydrothermal monazite from the Trairão Gold Deposit - Alta Floresta Gold Province (Amazon Craton)

Abstract Alta Floresta Gold Province occurs in the center-south portion of the Amazon Craton. Trairao gold deposit, which is located in the Alta Floresta Gold Province, is hosted by 1878 to 1854 Ma arc-related granites. Two important Au deposits take place in the region, the Trairao and Chumbo Grosso, which are structurally controlled by N80°W/S80°E trending lineament and associated with quartz veins and disseminated sulfides in a strong phyllic alteration zone of the host granite. Hydrothermal monazite grains formed during the Au mineralization event occur as fine anhedral crystals filling fractures or as isolated grains associated with Ag, Au, molybdenite, barite, pyrite, galena, and sphalerite. The hydrothermal monazite grains contain very low U, relatively low Th, and moderate Nd and La contents. SHRIMP U-Th-Pb dating of these crystals yielded an age of 1798 ± 12 Ma for Trairao and 1805 ± 22 Ma for Chumbo Grosso Au-deposits, whereas magmatic zircon grains of the granitic host rocks yielded an age of 1854 ± 8 Ma. The ages obtained in this paper are similar to those reported by Assis (2015), who studied Pe Quente (Re-Os in molybdenite, 1792 ± 9 Ma and 1784 ± 11) and Francisco deposits (40Ar-39Ar ages from sericitic halo: 1779 ± 6.2 and 1777 ± 6.3 Ma). Serrato et al. (2014) acquired Re-Os dating in pyrite and molybdenite from Juruena gold deposit. The results show isochronous ages at 1786 ± 1 Ma, with a model age at 1787 ± 3.2 Ma, suggesting a major Statherian gold metallogenic event at the Alta Floresta Gold Province region. Regional fluids-flow has a close relationship with the generation and concentration of several important economic deposits in the Eastern border of Alta Floresta Gold Province, including Pe Quente, Francisco, Juruena, Chumbo Grosso, and Trairao Au-deposits.

Linking Mesozoic lode gold deposits to metal-fertilized lower continental crust in the North China Craton: Evidence from Pb isotope systematics

The source(s) of lode gold deposits formed in Precambrian cratons related to accretion/collision and cratonic reactivation, formerly attributed to either supercrustal volcano-sedimentary sequences or deep crustal/sub-crustal origin, remain controversial largely because gold deposits are spatially related to metamorphosed rocks, but geochemical data somewhat indicate a poorly understood deep source. Reconciling such conflicts is important to better understand the main factor controlling the formation of ore deposits and their genetic link with specific tectonic settings. Giant Late Mesozoic lode gold provinces in the North China Craton (NCC) were formed ca. 1.7 Ga later than cratonization metamorphism, and contemporaneous with intensively felsic to mafic magmatism related to cratonic reactivation. In this study, we conduct a comprehensive Pb isotope study on major gold deposits from the eastern Yanshan belt, northern margin of the NCC. In order to constrain the source(s) of gold, we attempt to map regional Pb isotope variations of lower continental crust (LCC), and develop a two stage quantitative model (punctuated by three prominent geological events at 2.80 Ga, 1.85 Ga and 0.16 Ga) to reproduce time-integrated Pb isotopic signatures of deep-seated lithospheric reservoirs to make a comparison with Pb isotopic signatures of the gold mineralization. Gold-bearing pyrites within different types of host rocks have relatively uniform Pb isotopic ratios, which are significantly different to high-grade metamorphosed host rocks, but similar to those of spatially associated Late Mesozoic granitic rocks. Our data show that the Pb isotopic signatures of gold deposits vary consistently with presumed regional Pb isotopes of the LCC during the Late Mesozoic. Lead isotopic heterogeneity of the LCC was likely caused by underplating of mafic magmas derived from mantle sources. During underplating, highly chalcophile elements (e.g. Au, Ag and Cu) were concentrated at the base of the LCC due to sulfide saturation from mafic magmas. Integrating petrological, geochemical, geochronological, and considering chalcophile element solubility, we propose a new genetic model to describe the formation of Late Mesozoic gold deposits in the NCC: (1) early formation of sulfide-bearing cumulates with high Au/Cu ratios during magma differentiation at the base of the LCC; (2) subsequent fluid-fluxed remelting of these cumulates at the onset of lithospheric extension and release and ascent of ore-forming fluids to the site of precipitation. Considering the metallogenic characteristics of other Au ore-forming systems, we suggest that metal fertilization in deep-seated reservoirs and subsequent tectonic decompression are important factors controlling the development of Au-rich ore deposits worldwide. This study demonstrates how Pb isotope can be employed to trace source(s) of gold deposits.

Textures of auriferous quartz-sulfide veins and 40Ar/39Ar geochronology of the Rushan gold deposit: Implications for processes of ore-fluid infiltration in the eastern Jiaodong gold province, China

The Rushan gold deposit, located in the eastern part of the world-class Jiaodong gold province, contains the largest gold resource within a single fault-controlled quartz vein in China. Processes involved in auriferous quartz vein deposition are not clear, and the precise gold mineralization age remains controversial for this deposit. New 40Ar/39Ar dating data on sericite from ores and altered rocks suggest that the Rushan gold deposit formed between ca. 122 Ma and 117 Ma, which overlap or are slightly younger than those of gold deposits in northwestern Jiaodong province. The age differences between samples from different locations indicate that the quartz veins on the margin of the orebody may be younger than those in the center, suggesting a single and protracted gold mineralization event lasting for about 5 My. Differences between gold mineralization ages and emplacement/cooling ages of the ore-hosting Kunyushan granite imply that they are not genetically related and that the Kunyushan granite is unable to provide any thermal input to the mineralization system. This also applies to the Sanfoshan monzonite as it marginally postdated gold mineralization and lacks any spatial association with it.Internal textures of high-angle shear veins and low-angle extension veins indicate that episodic fluctuations from supralithostatic to hydrostatic fluid pressure triggered the multiple ore-controlling fault ruptures induced by breach of supralithostatic fluids under a seismogenic regime. In this model, the controlling fault starts to slip with both reverse and sinistral kinematics, and dilatational zones are created. The ore-forming fluids then migrate upwards along the fault, due to the large pressure difference between the dilatational zones and the deep parts of the fault, causing hydraulic fracture in the host rocks and earlier quartz veins. Large volumes of quartz, pyrite, and other ore components are precipitated due to fluid immiscibility caused by pressure fluctuations, and new quartz veins form along both sides of the earlier quartz veins. The fault is now sealed by these new quartz veins and the fluid pressure starts to build until the next breach cycles. Orebodies with complex internal textures were thus deposited incrementally in these cycles, closely fitting the classic fault-valve model, in this case under a weak regional NW-SE transpressional stress.

Carlin-style gold province linked to the extinct Emeishan plume

Carlin-style gold deposits constitute one of the most important types of Au resources in the world. Previous studies on these deposits correlated the source of Au with metal-enriched sedimentary formations or metasomatized subcontinental lithospheric mantle (SCLM) associated with oceanic subduction. The role of mantle plumes in generating Carlin-style deposits has remained enigmatic due to lack of adequate evidence. Here we investigate the second largest Carlin-style Au province in the world, after Nevada in USA, within the Youjiang basin in the eastern part of the ∼260 Ma Emeishan large igneous province (LIP) of southwestern China. We present a novel model for the genesis of this ore province based on thermodynamic modeling, which envisages that cumulates formed by high degree (over ∼80 wt.%) of crystal fractionation from the Emeishan plume-derived magmas under low oxygen fugacity conditions generated an enriched juvenile lower crust. Our new results from integrated in situ zircon geochronology and oxygen isotopes of mineralized tuffs from the Au deposits hosted in the Emeishan volcanic rocks reveal zircon growth at ∼129–136 Ma and ∼239 Ma with δ18OVSMOW values of +5.9‰ to +6.9‰, suggesting that the gold mineralization events in the Youjiang basin followed the Emeishan plume activity and that the ore-forming fluids were of magmatic origin. In conjunction with evidence from the Emeishan LIP for native gold grains that precipitated in the early fractionation stage under low oxygen fugacity, we propose a model involving juvenile lower crust beneath the eastern Emeishan province as a potential Au reservoir, the reactivation of which by later magmatic-hydrothermal activity associated with oceanic subduction events generated the large auriferous province in the Youjiang basin. We therefore conclude that the crustal magmatic underplate generated by mantle plume has the potential to contribute to the formation of Carlin-style Au deposits, thus offering new insights into the possible link between mantle plumes and various types of Au deposits such as porphyry, sediment-hosted and orogenic Au deposits associated with LIPs.

Multistage exhumation of the Anjiayingzi gold deposit, northern North China Block: Geodynamic settings and exploration implications

Post-mineralisation exhumation is pivotal because of its strong effects on the preservation of ore deposit. The Jiguanzi quartz monzonite hosts the Anjiayingzi Au deposit at the centre of the Kalaqin Antiform (or Kalaqin metamorphic core complex) in the northern North China Block (NCB). We can link the exhumation of the deposit with regionally geodynamic events and evaluate its exploration implications using low-temperature thermochronology from the quartz monzonite host. Sericite 40Ar/39Ar dating of auriferous quartz-sulphide veins indicates that gold mineralisation timing is 130 ± 1 Ma. Zircon fission track ages of fresh samples from the host quartz monzonite vary from 118 ± 6 to 99 ± 4 Ma, and apatite fission track ages vary from 99 ± 6 to 66 ± 5 Ma. A four-stage post-mineralisation exhumation history is revealed by combining the binomial peak fitting of single-grain ages and low-temperature thermal history inverse modelling. The first exhumation event is dated at ca. 130–100 Ma, and characterised by the most rapid exhumation rate of 167 m/Ma and ca. 5 km rise. This movement is related to the top-to-NW and a SE ductile-brittle extensional deformation of the Kalaqin Antiform. Regionally, it is also contemporaneous with the formation of extensional metamorphic core complexes, development of basins, and increasing heat flow and decreasing thermal lithospheric thickness in the eastern NCB. All of these synchronous events can be linked to the back-arc setting of the subducting Izanagi Oceanic Plate and resulted geodynamic changes beneath the NCB. The relatively slow stage 2 exhumation, dated at ca. 100–65 Ma with an exhumation rate of 20 m/Ma, was triggered by the collision between the Izanagi Oceanic Plate and eastern China at ca. 100 Ma and following change in the drift direction of the Izanagi Oceanic Plate. Sedimentation of basins in the NCB was continuous during this period. Resumed stage 3 exhumation (ca. 65–45 Ma, 27 m/Ma) and synchronous sedimentary inversion are products of regional compression event related to the collision between India and the Eurasian plates. Change of the Pacific Oceanic Plate drifting direction at ca. 50 Ma finally induced the monotonic cooling and exhumation of stage 4 (19 m/Ma). The estimated post-mineralisation exhumation is ~7.1 km, and the ore-forming depth of the Anjiayingzi Au deposit is between 5.1 and 10.1 km. In combination with previously published data, the differential exhumation history, exhumation degree and preservation potential of major gold provinces in NCB are confirmed, which further indicate that their gold prospectivity must be assessed individually.

The genesis of the Mesozoic alkaline intrusions of the Khokhoi ore field (Upper Amga gold-mining district, Aldan Shield, North Asian Craton)

The article discusses petrography and features of the chemical composition of the Mesozoic alkaline intrusions of the Khokhoi ore field located within the Upper Amga gold-mining district in the Aldan Shield. This gold-mining district is located in the Aldan-Stanovoy Province rich in gold. Tectonic position and magmatic events of this Province are close to those positions and events of Shandong Gold Province of Sino-Korean Craton. The investigation of the genesis of the magmatic rocks and comparison of the Provinces can shed light on the genesis and regularity of location of the gold deposits in them. Intrusions of the Upper Amga gold-mining district passed through the metamorphic rocks of the Precambrian and intruded into the Cambrian carbonate rocks and the Jurassic sandstones. Petrographic observations found that large intrusive massifs of the ore field consist mainly of potassic feldspar and plagioclase. Mineral composition, structure and texture of the rocks correspond to syenite and monzonite. Blocks of melanocratic rocks – presumably tephrites are rare on the surface. Several generations of feldspar and dark-colored minerals are observed within all these rocks, indicating melt fractionation. High Sr and K contents were identified in the rocks. Contents decrease in the series of tephrite-syenite-monzonite. This feature, judging by other petrochemical data, can be associated not only with magmatic differentiation, but also with the melting and interaction of the lithosphere. In sienites, ovoids of quartz and the first-generation potassic feldspar melting margin were found. It could be possibly resulted from the capture of surrounding rock material and changes in the thermodynamic conditions of crystallization. It is found out that potassium and silicon contents in rocks depend inversely on calcium content. Interaction of melts and the host carbonate rocks with removal of silicon and potassium and formation of gold-bearing sericite-quartz and feldspar-quartz metasomatites is assumed. The loss of potassium probably has led to potassium metasomatism at the contacts of intrusions. This metasomatism produced the gold ores.

Remobilization of metasomatized mantle lithosphere: a new model for the Jiaodong gold province, eastern China

The ~ 120 Ma Jiaodong province in the North China Craton, composed of abundant Mesozoic granites that intrude Precambrian metamorphic basement, is bordered by the Sulu orogenic belt, which formed through the collision between the North China and Yangtze cratons in the Triassic. Insights on the geodynamic setting and source of gold and fluids in the Jiaodong gold province are based on a detailed study of the Sanshandao deposit. The δ13CPDB and δ18O values of hydrothermal calcite from this deposit range from − 4.3 to − 6.5‰ and 11.4 to 15.1‰, respectively, which are compatible with a mantle source. Pre-ore mafic dykes in the deposit show typical arc-like geochemical features, suggesting that the mantle source was metasomatized prior to the basic magmatism. The δ34S values of gold-related pyrite from Sanshandao and other large deposits in the province range from 10.9 to 11.5‰ and are higher than those of the country rocks, but consistent with the signature of orogenic gold deposits sourced from a Neoproterozoic sedimentary reservoir. These high positive δ34S values are interpreted to be inherited from auriferous Neoproterozoic sedimentary rocks of the northern Yangtze Craton, which were subducted into the mantle lithosphere beneath the North China Craton during the formation of eclogite in the adjacent Sulu orogenic belt in the Triassic. The syn-ore Lower Cretaceous mafic dykes display oceanic island basalt-like geochemical features, suggesting that asthenosphere upwelling triggered the release of gold and sulfur from an enriched and fertilized mantle lithosphere, contributing to the auriferous fluid which formed the widespread gold mineralization in the Jiaodong province at ca. 120 Ma.