Quartz chemistry is important for revealing fluid sources and evolution in hydrothermal deposits, but such information is lacking for many epithermal systems and deposit types. To investigate quartz chemistry in this system further, we collected representative samples of quartz from adularia-sericite epithermal Ag deposits in China and determined their chemical compositions. In adularia-sericite epithermal Ag-bearing systems, magmatic quartz from porphyry intrusions and host subvolcanic rocks displays SEM-CL spectral peaks at 360 and 415 nm and exhibits homogenous CL or weak zonal textures (alternating growth zones within individual quartz crystals). Trace elements in magmatic quartz have the lowest Sb concentrations (median = 0.1 ppm; n = 80). Hydrothermal quartz can be classified into type I and type II by CL false color and CL spectral peaks. Hydrothermal type I quartz has spectral peaks at 360 and 415 nm; it exhibits zonal or sector textures and is associated with base metal sulfides and minor Ag mineralization. Such hydrothermal type I quartz has low Sb concentrations (median = 4.5 ppm; n = 839), contains liquid-rich fluid inclusions, and is formed by cooling. The cooling trend is indicated by a positive correlation between the concentrations of Sb and Al, as well as between Li and Al. Hydrothermal type I quartz has an Fe center by electron spin resonance, whereas other centers are missing or weak at room temperature. In general, hydrothermal type II quartz mantles type I quartz. Hydrothermal type II quartz has an ultrahigh-intensity peak (by several orders of magnitude) at 580 nm, zonal textures, and is associated with abundant Ag mineralization. Hydrothermal type II quartz has the highest Sb concentrations (median = 71 ppm; n = 185), which remain constant as Al decreases on an Sb vs. Al plot. This quartz has colloform, bladed, or zonal textures and contains coexisting liquid- and vapor-rich fluid inclusions indicative of boiling. Additionally, this quartz has a significantly higher E'1 center intensity, suggesting a high concentration of oxygen vacancies associated with rapid crystallization. The mineral paragenesis, analytical results, and geochemical models show that, in these Ag-bearing epithermal systems, hydrothermal type I quartz associated with base metal sulfides precipitated during cooling, whereas subsequent growth-zoned hydrothermal type II quartz with high Sb concentrations and Ag-minerals precipitated during boiling. These results suggest that the CL texture and spectra, trace elements, and electron spin resonance data of quartz could identify veins with potential for Ag mineralization in epithermal systems.

The formation of bonanza Au-Ag-telluride ores in adularia-sericite epithermal deposits is hypothesized to be attributed to the input of magmatic fluid into flow systems dominated by barren meteoric water. However, understanding of the role and importance of magmatic fluids in the formation of bonanza ores remains limited. To address these concerns, we conducted Cu isotope analyses of chalcopyrite, which coexists with Au-Ag-tellurides in the Te-rich Sandaowanzi deposit located in northeastern China, as well as ore-bearing quartz veins, coeval igneous rocks, and older igneous rocks that underlie the deposit. To aid interpretation, we use geochemical modeling techniques along with O isotope data from calcite and quartz, as well as thermal outputs from modern geothermal systems.At Sandaowanzi, the delta 65Cu values of chalcopyrite vary widely, ranging from 0.48 to 0.86 parts per thousand. These values are higher than underlying Early Jurassic monzogranite (-0.06 to 0.27 parts per thousand), as well as coeval Early Cretaceous andesite and basaltic andesite (0.01 to 0.11 parts per thousand) and Early Cretaceous dacite and granodiorite (0.33 to 0.52 parts per thousand). The O values of calcite vary from -3.2 to 6.7 parts per thousand. The present isotope data, together with previous delta 18O analyses of quartz, support the idea that the fluids responsible for ore formation at Sandaowanzi were derived from a magmatic source. Progressive input of magmatic fluids into convecting meteoric water explains the telluride precipitation. Subsequent boiling can explain Au, Ag, and Cu precipitation in the upwelling limb of convection cells. Injection of high-temperature magmatic fluids (similar to 300 degrees C) into shallow meteoric groundwater (similar to 250 degrees C) and formation of Au-Ag-telluride ores can take place over a relatively short timeframe, typically around 1000 years. In contrast, the process of electrum precipitation occurs at a later stage compared to the formation of Au-Ag-telluride ores in the boiling zones (<300 degrees C). These findings indicate that Au-Ag-telluride precipitation occurs at the mixing interface under high temperatures (>300 degrees C), suggesting that it is located at greater depths compared to typical Au-Ag mineralization in adularia-sericite epithermal systems.

ABSTRACTThe tectonic position of the North China Craton within the Rodinia supercontinent remain unclear due to the scarcity of early Neoproterozoic magmatic rocks in the region, resulting in limited paleomagnetic data. In this study, we report the discovery of a Neoproterozoic metamorphic gabbro intrusion within the Bayan Obo Group, located in the northwestern Bayan Obo rift zone at the northern margin of the North China Craton. This finding offers crucial geological insights into addressing this key scientific question. We utilised petrography, whole‐rock geochemistry, zircon U–Pb geochronology, and Sr‐Nd isotopic analysis to investigate the genesis and source of the gabbroic rock and its tectonic setting. The metamorphosed gabbro has a zircon 206Pb/238U weighted mean age of 925.9 ± 7.2 Ma, with low SiO2 (46.46%–48.28%), high Na2O (2.95%–3.56%), and low K2O (0.761%–1.41%), and has the signature of sub‐alkaline tholeiitic basalt. It is enriched in large‐ion lithophile elements (Rb, Ba, Th, U, K, Pb) and depleted in high‐field‐strength elements (Nb, Ta). The rock is also enriched in light rare earth elements, shows a negative Eu anomaly, and has a positive εNd(t) value (+0.1 ~ +0.8). The metamorphosed gabbro shares geochemical characteristics and Nd isotopic compositions with contemporaneous mafic intrusions, including the 945–890 Ma mafic sills in southeastern North China Craton, the ~925 Ma Dashigou mafic dike swarm in central North China Craton, the ~925 Ma gabbro in Guyang, northern North China Craton, and the 827–819 Ma gabbro in Langshan, western North China Craton. This age suggests that the gabbro may represent a response to a large‐scale mafic magmatic event in central‐eastern North China Craton during the early Neoproterozoic, potentially linked to the initial breakup of the Rodinia supercontinent.

Late Triassic–Jurassic orogenic and Early Cretaceous epithermal Au deposits are significant producers of Au, Ag, and potentially critical elements (e.g., Te, Se and Sb) in the North Heilongjiang Belt in the Xing'an Block, NE China. However, the preservation mechanism of these Au deposits associated with tectonic evolution is unclear. Here, we conducted zircon U–Pb, sericite Ar–Ar, zircon and apatite (U–Th)/He dating as well as whole‐rock geochemistry in the Xing'an Block. Zircon U–Pb dating shows the ages of 174.1 ± 2.4 Ma for the granodiorite, 169.9 ± 1.6 Ma for the tonalite, 154.0 ± 2.0 Ma for the monzogranite and ca.122 Ma for the diorite. Sericite Ar–Ar dating presents plateau and isochron ages of 163.2 ± 1.8 Ma and 163.4 ± 2.8 Ma. The average apatite (U–Th)/He (AHe) and zircon (U–Th)/He (ZHe) ages from the Jurassic rocks have the ranges of ca. 146–89 Ma and ca. 150–116 Ma and from the Cretaceous are ca. 109–76 Ma and ca. 117–111 Ma, respectively. The Early‐Middle Jurassic intrusions are featured by the tonalite‐trondhjemite‐granodiorite (TTG) rock type. Late Jurassic monzogranite has the geochemical signature of adakitic rocks. The Early Cretaceous granitoids are classified as volcanic arc granites with a part of the Early Cretaceous granodiorite featured by adakitic. These new results reveal five group ages associated with tectonic evolution, Au mineralization and the preservation of the Au deposits. (i) Magmatic events were related to the subduction of the Mongolia‐Okhotsk Ocean during the Early Jurassic (ca. 177–170 Ma) and then the compressional settings with regional deformation (ca. 167–163 Ma). (ii) Thickening crust and orogenic Au mineralization were related to the closure of the Mongolia‐Okhotsk Ocean (ca. 154–145 Ma). (iii) The transformation was from compressional to extensional settings followed by exhumation during the Early Cretaceous (ca. 145–120 Ma), which is the factor of the exhumation of the orogenic Au deposits formed from the Late Triassic to Late Jurassic. (iv) Epithermal Au–Ag mineralization was associated with an extension related to the subduction of the Palaeo‐Pacific Plate (ca. 120–100 Ma). (v) Thermal history shows one thermal event during the Late Cretaceous (ca. 89–76 Ma). The Au deposits have been preserved since the Late Cretaceous.

Magmatic-related epithermal silver-rich polymetallic deposits are among the most important sources of Ag in the world, and they are found associated with magmatic systems with striking differences. Most of the time, they are associated either with I -type oxidized (magnetite-series granite) intermediate to evolved intrusions or with S-type/A-type reduced (ilmenite-series granite) highly evolved intrusions. To better understand these associations, the Ag evolution has been tracked during the magmatic differentiation and the magmatic-hydrothermal transition stage of A -type highly evolved porphyritic granites associated with the giant Shuangjianzishan Ag-Pb-Zn-(Sn) epithermal deposit, the largest known Ag deposit of Asia (145 million tonnes at 128.5 g/t Ag and 2.2 wt % Pb + Zn) located in the largest known metallogenic province for Ag in China (the southern Great Xing'an Range). At the Shuangjianzishan deposit, the porphyritic granite complex consists of three temporally distinct intrusions-a coarse-grained monzogranite porphyry, a fine-grained syenogranite porphyry, and a fine-grained syenogranite-having crystallized at similar to 2 kbar and similar to 750 degrees C and recording a continuous magmatic differentiation trend. The silicate melt that generated the last highly differentiated intrusion (fine-grained syenogranite) is interpreted as the source of the mineralizing fluids forming the Shuangjianzishan Ag-Pb-Zn(Sn) epithermal deposit, as it is the only intrusive unit that reached fluid saturation, as indicated by cotrapped fluid and melt inclusions in quartz phenocrysts and by the occurrences of unidirectional solidification textures (USTs). Silver evolution in the different porphyritic granite facies was reconstructed with laser ablation-inductively coupled plasma-mass spectrometry analyses of quartz-hosted silicate melt inclusions, amphibole-hosted magmatic sulfide inclusions, and chemical modeling. The silicate melt forming the porphyritic granite complex was sulfide saturated during the first crystallization stage, as shown by the occurrence of Ag-rich monosulfide solid solution (MSS) inclusions hosted in amphibole phenocrysts from the coarse-grained monzogranite porphyry and from mafic microgranular enclaves hosted in the coarse-grained monzogranite porphyry. However, these Ag-rich MSSs had only a minimal impact on the Ag budget of the magmatic system, as shown by the increase of the Ag concentration (similar to 100-1,000 ppb) in quartz-hosted silicate melt inclusions during the further evolution of the system until fluid exsolution was reached. These results combined with mass balance modeling suggest that Ag and Sn are efficiently transferred to the evolving residual melt during crystallization and crystalmelt segregation. The results of this study indicate that highly Ag endowed epithermal polymetallic deposits can be formed from the exsolution of Ag-rich mineralizing fluids from relatively low volume, highly evolved, reduced melts, similar to those responsible for the formation of Sn-rich greisen deposits.

Mineral assemblages containing Cu-Bi sulfosalts, Bi chalcogenides, and Ag-(Au) tellurides have been identified in the mid-Miocene Zhibula Cu skarn deposit, Gangdese Belt, southern Tibet. Different mineral assemblages from three locations in the deposit, including proximal massive garnet skarn, proximal retrogressed pyroxene-dominant skarn in contact with marble, and distal banded garnet–pyroxene skarn hosted in marble, are studied to constrain the evolution of the mineralization. Hypogene bornite contains elevated Bi (mean 6.73 wt.%) and co-exists in proximal andradite skarn with a second bornite with far lower Bi content, carrollite, Au-Ag tellurides (hessite, petzite), and wittichenite. This assemblage indicates formation at relatively high temperatures (>400 °C) and high fS2 and fTe2 during prograde-stage mineralization. Assemblages of Bi sulfosalts (wittichenite, aikinite, kupčíkite, and paděraite) and bismuth chalcogenides (e.g., tetradymite) in proximal pyroxene skarn are also indicative of formation at relatively high temperatures, but at relatively lower fTe2 and fS2 conditions. Within the reduced distal skarn (chalcopyrite–pyrrhotite-bearing) in marble, cobalt, and nickel occur as discrete minerals: cobaltite, melonite and cobaltic pentlandite. The trace ore mineral signature of the Zhibula skarn and the distributions of precious and critical trace elements such as Ag, Au, Co, Te, Se, and Bi support an evolving magmatic–hydrothermal system in which different parts of the deposit each define ore formation at distinct local physicochemical conditions. This is the first report of kupčíkite and paděraite from a Chinese location. Their compositions are comparable to other occurrences, but conspicuously, they do not form nanoscale intergrowths with one another.

Most high-grade U ores are mined from quartz veins hosted in granites. The veins formed at shallow depths during episodic hydrothermal activity, however, the evolution of multiple stage fluids is not well constrained. In this study, we collected 56 quartz samples from the world-class, granite-related, Zhuguangshan U district (>17,000 t U from seven deposits) in southern China. Their textures and compositions were analyzed using scanning electron microscope cathodoluminescence (SEM-CL, n = 98) and laser ablation-induction coupled plasma-mass spectrometry (LA-ICP-MS, n = 643). Four types of quartz were identified, including magmatic quartz, early hydrothermal euhedral quartz, ore stage hydrothermal quartz (U-rich), and late hydrothermal quartz. New quartz textures and chemical compositions show that the transition of early hydrothermal quartz from the magmatic to hydrothermal stages is discontinuous, unlike the continuous trend observed in most magmatic-hydrothermal systems. Ore stage quartz is CL dark (with a peak at 650 nm), occurs as rims on early barren quartz, and has high contents of Mn, Al, and Sb. Altered textures of magmatic quartz developed through fluid-rock reactions at low temperatures, while rimmed textures of hydrothermal quartz formed during subsequent late-stage U-bearing fluid events, which played a crucial role in U mineralization. Quartz in the Zhuguangshan U district has distinct features compared to other magmatic-hydrothermal systems that can guide exploration for high-grade ore in this, and perhaps other, granite-related U systems.

Tellurium (Te)-bearing adularia-sericite epithermal Au-Ag deposits are widely distributed in calc-alkaline magmatic arcs and are an important current and future source of precious and critical metals. The source of ore-forming fluids in these deposits remains unclear due to the lack of in situ isotopic evidence on Au-, Ag-, and Te-bearing minerals. To advance the understanding of the source and evolution of Te and precious metals, herein, we combine in situ Pb isotope analysis with He, Ne, and Ar isotope and microthermometric analysis of fluid inclusions in ore and gangue minerals from two Te-rich and two Te-poor epithermal Au-Ag deposits that occur in an Early Cretaceous magmatic arc in the North Heilongjiang Belt, northeastern China. Ore minerals (hessite, petzite, calaverite, altaite, pyrite, chalcopyrite, and galena) from Te-rich Au-Ag deposits, including Sandaowanzi and Yongxin, have the least radiogenic Pb isotope compositions (Pb-206/Pb-204 from 18.1 to 18.3) and the lowest mu 1 values (the U-238/Pb-204 ratio of the lead source down to 9.14) of the deposits studied. For these Te-rich deposits, noble gas isotope data show that fluid inclusions in ore minerals contain a large proportion of mantle He (up to 25%), whereas barren early-stage minerals do not (<1%). The Pb, noble gas isotope, and fluid inclusion microthermometric results suggest that Te-rich ore-forming fluids were likely discharged from mafic magmas into convecting meteoric flow systems at shallow levels (<2 km). In contrast to the Te-rich deposits, ore minerals from the Te-poor Dong'an Au-Ag deposit have radiogenic Pb isotope compositions (Pb-206/Pb-204 from 18.8 to 18.9) and the highest mu 1 values (up to 10.54). Fluid inclusions in ore minerals contain a small proportion of mantle He (1% to 5%). The results suggest that metals and ore-forming fluids in these deposits were discharged from either more crustally contaminated intermediate-felsic magmas or leached from upper crustal rocks by convecting meteoric flow systems. Although the Te-poor Tuanjiegou Au-Ag deposit has a non-radiogenic Pb isotope composition consistent with a mafic magma source, Te is much less abundant (electrum [>95%] is the major gold- and silver-bearing mineral) than Au. The main exploration implication of these results is that unexplored volcano-plutonic centers in the northeast Xing'an Block with less radiogenic Pb isotope compositions (Pb-206/Pb-204 < 18.3) and containing fluids with a high proportion of mantle He are more likely to generate Te-rich epithermal Au-Ag deposits than other volcano-plutonic centers in NE China.

The origin of propylitic fluids in intermediate sulfidation mineralization has not been investigated in detail. Here, we present an extensive petrographic, geochemical, and isotopic (O-H-Sr) study of propylitic epidote, chlorite, and calcite from the Zhengguang intermediate sulfidation epithermal Au-Zn deposit, NE China. Propylitic minerals can be divided into three main types based on their different textural occurrences, namely interstitial cement of clasts of hydrothermal breccia, replacement of primary plagioclase or hornblende, and vein infill of cracks, with late, minor calcite as amygdules in vesicles of andesite representing a fourth textural occurrence. The H-O isotope compositions and mass balance calculations suggest that most propylitic epidote records a dominant (> 50 O_H_2O values equilibrated with different types of epidote (cement 6.8 ± 0.7‰, replacement 5.1 ± 1.1‰, vein 4.5 ± 1.4‰, 1 SD), and the decreasing content of high-temperature elements (e.g., Cu-Mo) from cement, through replacement to vein epidote and chlorite, collectively indicates a decreasing role of magmatic fluids. Replacement epidote and chlorite are enriched in Sr-Mn-Y-Sb, whereas replacement epidote and calcite record similar (87Sr/86Sr)i values to the andesitic host rock, suggesting that replacement minerals inherit certain elements from plagioclase and hornblende, and the Sr isotope signature of the wall rocks. We highlight that propylitic alteration in epithermal deposits can involve significant proportions of magmatic fluids and texturally different alteration mineral types should be considered when using mineral isotopic or chemical compositions to track fluid sources or to vector towards the location of intrusive centers.

The La’erma and Qiongmo Au–Se deposits are characterized by a paragenetic Au–Se association hosted in the siliceous formation of the Cambrian Taiyangding Group in the western Qinling Orogen, central China. The La’erma and Qiongmo Au–Se deposits, which are considered to be the Carlin gold deposits, comprise a variety of selenides, native gold, and stibnite coexisting with baryte. Four stages have been recognized: sage I comprises pyrite and quartz with minor stibnite; stage II is composed mainly of sulfides; stage III is composed mainly of selenides; and stage IV is dominated by quartz–baryte–dickite. Stages II and III are the main metallogenic stages. Based on changes in mineral assemblages, combined with fluid inclusions and thermodynamic data, we evaluated the physicochemical conditions of the main metallogenic stages. The logfS2 values of ore-forming fluids at stage II ranged between −10.44 and −14.60 with logfSe2 being less than −10.70. Comparably, during stage III, which is characterized by numerous selenides, the logfS2 and logfSe2 ranged from −7.13 to −12.20 and −13.98 to −8.82, respectively. The occurrence of baryte during the mineralization suggests a consistently oxidizing condition, which can effectively remove Au from fluids. More importantly, this study emphasizes that the oxidizing condition was only a fundamental prerequisite for the deposition of selenides, and a high ∑Se/S ratio of the fluid ultimately controlled the precipitation of selenides. In the La’erma and Qiongmo deposits, intense water–rock reactions occurred as ore-forming fluids flowed into the Se-rich siliceous formations, resulting in an increase in the ∑Se/S ratio of the fluid and in the precipitation of selenides.

The Lianzigou deposit, which has an Au–Te paragenetic association, is hosted in plagioclase gneiss of the Qincanggou Formation in the Taihua Group in the Xiaoqinling region, central China. This quartz vein-type Au deposit comprises native Au and a variety of tellurides. The latter include calaverite (AuTe2), krennerite (Au3AgTe8), petzite (Au3AgTe2), hessite (Ag2Te), melonite (NiTe2), and altaite (PbTe). Four stages have been recognized in this deposit: stage I consists of K-feldspar and quartz; stage II is of milky quartz veins accompanied by coarse-grained disseminated and lumps of pyrite with weak Au mineralization; stage III is composed mainly of Au, tellurides, and sulfides; and stage IV is characterized by abundant carbonate and quartz. Based on mineral assemblage and thermodynamic data, we estimated the physicochemical conditions of the main metallogenic stages. Based on thermodynamic modelling, the physicochemical conditions of Au–Ag–Te mineral associations were estimated. The Au–Ag–Te minerals from stage III formed mainly under conditions of logƒO2 = −43.15 to −33.31, logƒH2S = ~−9.29, pH < 7, logfTe2 = −10.6 to −9.8 and logαAu+/αAg+ = −7.2 to −6.5. In contrast, the physicochemical conditions of stage II were higher, specifically pH (8.3–8.5) and logƒO2 (−34.90−31.96). In the ore-forming fluids of the Lianzigou deposit, the dominant Au species was Au(HS)2− while the dominant Te species were HTe−(aq) and Te22−(aq). Moreover, the Au–Ag–Te metal associations in the Lianzigou Au deposit were derived from mantle materials related to lithospheric thinning of the eastern North China craton in the Early Cretaceous under an extensional tectonic system.

Oxygen fugacity ( f O 2 ) is a key intensity variable during the entire magmatic‐hydrothermal mineralization courses. The redox state and its variations between different stages of the ore‐forming fluids of intermediate sulfidation epithermal deposits are rarely deciphered due to the lack of appropriate approaches to determine f O 2 of the fluids. Here, we reported the δ 34 S of the sulfides from three different stages (stage I, II, III) of Zhengguang, an Early Ordovician Au‐rich intermediate sulfidation (IS) epithermal deposit, to decipher the redox evolution of the ore‐forming fluids. The increasing δ 34 S values from stage I pyrite (py1, average –2.6‰) through py2 (average –1.9‰) to py3 (average –0.2‰) indicates a decrease of the oxygen fugacity of the ore‐forming fluids. A compilation of δ 34 S values of sulfides from two subtypes of IS deposits (Au‐rich and Ag‐rich) from NE China shows that the δ 34 S values of sulfides from Au‐rich IS deposits are systematically lighter than those of Ag‐rich IS Ag‐Pb‐Zn deposit, indicating the ore‐forming fluids of the former are more oxidized than the latter. We highlight that sulfur isotopic composition of hypogene sulfides is an efficacious proxy to fingerprint the oxygen fugacity fluctuations of epithermal deposits and could potentially be used to distinguish the subtypes of IS deposits.

Quartz trace elements record information about fluid evolution as well as metal migration and precipitation. Here, we summarize most of the reported (including this study) quartz trace element data (N = ~4,600) generated by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) on various textural types and paragenetic stages of quartz in I-type porphyry-epithermal (Cu-Mo-Au-Ag-Te) and S- and A-type granitegreisen (Sn-W and rare metal) systems in the world. The results show that Li versus Al diagrams, combined with Ti-Ge-As-Sb contents, can be used to decipher the source and evolution of fluids in magmatic-hydrothermal systems. In I-type porphyry-epithermal systems, magmatic quartz has low Li/Al ratios from 0.001 to 0.173 (N = 483) with a mean of 0.039 ± 0.032. Hydrothermal quartz has progressively higher Li and Al concentrations that are dominated by cooling along fluid pathways. Quartz evolves from Ti rich to Ge rich from early to late stages in porphyry hydrothermal veins and is As and Sb rich in epithermal veins. In S- and A-type granite-greisen systems, magmatic quartz has high Li/Al ratios from 0.007 to 0.502 (N = 604) with a mean of 0.130 ± 0.063 and from 0.009 to 0.327 (N = 325) with a mean of 0.126 ± 0.065, respectively. Hydrothermal quartz has progressively lower Li and Al concentrations that are dominated by fluid-rock reactions and cooling along fluid pathways. Quartz evolves with decreasing Ti concentrations from magmatic to hydrothermal stages. Ge is abundant in pegmatite quartz in S-type systems. Variations in pH or precipitation rate along fluid pathways have a small influence on Li/Al ratios. The variation of quartz trace elements with elevation in individual systems suggests that they can be used as a vector to guide exploration in magmatic-hydrothermal systems.

The Inner Mongolia Plateau is located in the north of the Late Palaeozoic Hegenshan ophiolitic mélange belt, and its Mesozoic magmatism impacts our understanding of the tectonic evolution affected by the closing of the Mongol‐Okhotsk Ocean and Palaeo‐Pacific Ocean. Here, we present new U–Pb ages, whole‐rock geochemistry and Hf isotopes from the Late Mesozoic magmatic rocks in the Dalai area along the northeastern margin of the Inner Mongolia Plateau. The Late Jurassic rock types include medium‐fine‐grained phenocryst‐bearing and porphyritic monzogranites as well as medium‐fine‐grained monzogranites with the precise age range of 167.7–159.8 Ma. The Early Cretaceous rock types consist of fine‐grained biotite monzogranite and medium‐fine‐grained biotite monzogranite with the precise age range of 140.9–130.7 Ma. The geochemistry data show that the Late Jurassic and Early Cretaceous rocks are peraluminous granites and high‐K calc‐alkaline series and can be classified as A‐type granite. These granites are enriched in large‐ionlithophile elements such as Rb, Th and U, depleted in the high‐field‐strength elements such as Nb, Sr, P, and Ti. Rare earth elements have high total concentrations and present the light rare earth elements enriched with the heavy rare earth elements depleted. Zircon Hf isotopes show that ε Hf( t ) ranges from +8.0 to +15.9 from the Late Jurassic rocks and +6.9 to +13.5 from the Early Cretaceous rocks. Our new results reveal that the Late Jurassic and the Early Cretaceous magmas were derived from partial melting of the younger lower crust, and the Early Cretaceous rocks are more strongly contaminated than the Jurassic intrusions. The Late Jurassic rocks in the Dalai area were formed from a post‐collisional setting related to the closure of the Mongol‐Okhotsk Ocean in the Early‐Middle Jurassic. The Early Cretaceous intrusions were formed from a transition setting from post‐collision to syn‐collision associated with the superposition of the Mongol‐Okhotsk Ocean and the Palaeo‐Pacific Ocean tectonic domain.

Tellurium-bearing low-sulfidation epithermal Au-Ag deposits are significant producers of gold, silver, and potentially strategic elements if mineral processing methods are optimized for recovery. Although these deposits are generally related to alkaline magmatism, our study documents an unusual occurrence of Te-rich low-sulfidation epithermal systems in the North Heilongjiang Belt in northeast China that is spatially and temporally associated with calc-alkaline magmatism and tectonic extension in a continental arc-setting. In the North Heilongjiang Belt, Te-bearing Au-Ag deposits are usually sited in dilatant zones, mostly along extensional NW structures or at their intersections with deep-seated NE-striking faults such as the NenjiangHeihe and Jiayin-Mudanjiang lineaments. Of these deposits, Sandaowanzi is well-known for its bonanza gold grades. These faults localized andesitic to rhyolitic volcano-plutonic centers that evolved from mantle-derived mafic melts to intermediate compositions due to differentiation and crustal assimilation as documented by their mineralogy and Sr, Nd, and Pb isotope compositions. During assimilation of country rocks, fluids containing 3He and other volatiles derived from mantle magmas displaced or mixed with external groundwater containing radiogenic 4He derived from country rocks. In this belt, the bulk metal content of Au, Ag and Te was probably introduced by deep mantle-derived mafic-intermediate calc-alkaline intrusions. However, our study does not exclude input of metals leached from underlying metasedimentary rocks and older Te-bearing Au mineralization. The noble gas, hydrogen, oxygen and lead isotope compositions of fluid inclusions and ore minerals suggest that the deposits formed by mixing between magmatic fluids and convecting meteoric ground waters containing lead leached from surrounding country rocks. At deeper levels, isotopic evidence suggests that Au-Ag-Te (Bi) precipitated with pyrite, quartz, sericite, and carbonate minerals due to mixing with Te-rich fluids. At shallower levels, Au and Ag precipitated contemporaneously with base-metal sulfides, hydrothermal quartz and sericite during episodic boiling as evidenced by silica morphology and mineral textures. The relatively uniform spacing of epithermal systems along NW- and NE-trending structures in the North Heilongjiang Belt was used to identify unexplored spaces within this mineral belt that are prospective for concealed low-sulfidation epithermal gold deposits. Although some of the Au-Ag deposits in this belt are enriched in Te, there is a lack of coeval alkaline igneous rocks that are commonly associated with Te-bearing gold deposits elsewhere in the world (e.g., Cripple Creek, Emperor, and Lihir Island).

The Jiawula-Chaganbulagen (Jia-Cha) super-large, magmatic-hydrothermal Ag-Pb-Zn ore field in the southern Erguna Block, northeast China, is characterized by a large and well-developed alteration and metallic zonation (similar to 56 km(2)) that is centered on porphyry Mo-Cu mineralization. The ore field includes two intermediatesulfidation epithermal Ag-Pb-Zn deposits, which are located at Jiawula and Chaganbulagen. A weighted-mean molybdenite Re-Os age of 135.1 +/- 2.1 Ma (MSWD = 0.16) and a molybdenite Re-187-Os-187 isochron age of 135.4 +/- 2.3 Ma (MSWD = 0.44) were obtained for the Mo-Cu mineralization, and the host quartz monzonite porphyry yielded a weighted-mean zircon U-Pb age of 141.9 +/- 2.4 Ma (MSWD = 0.044). Geochronological data suggest that the epithermal mineralization occurred at 135 to 133 Ma, and the porphyry age is little older than the porphyry-epithermal mineralization. The porphyry Mo-Cu mineralization is interpreted as the hydrothermal center of the ore field, based on the metal zonation:Mo-Cu. Zn-Cu -> Zn-Cu-Pb-(Ag) -> Zn-Pb-Ag-(Cu) -> Ag (Au)-Pb-Zn -> Ag, with vertical ore minerals zonation from deeper molybdenite-chalcopyrite to shallower sphalerite-galena-chalcopyrite through molybdenite-chalcopyrite-sphalerite. Trace element analyses by LA-ICP-MS of pyrite and pyrrhotite show that micro-inclusions exhibit similar "ore field-scale" trace element zonation: Bi-Ag -> Bi-Sb-Ag -> Sb-Ag. Geological and geochronological evidence indicates that the Jia-Cha epithermal system is genetically related to the adjacent porphyry Mo-Cu mineralization. XRF element mappings of the replaced ores revealed that late ore stage oxidizing fluids dissolved the early chalcopyrite at depth, and then replaced the sulfides in the main ore stage. Porphyry-epithermal mineralization system in the Jia-Cha ore field is significant for further exploration for porphyry Mo-Cu and epithermal Ag-Pb-Zn deposits in northeast China.

Solid solution decomposition texture, melt annealing texture, mineral-melt dihedral texture, dissolution-reprecipitation texture are also characteristic textures of LMCE melts involved in mineralization.The low-melting point chalcophile elements (LMCE), including As, Sb, Bi, Hg, Pb, Se, Te, Tl, Sn and so on, have characteristics of chalcophile behavior, low melting point and semi-metallic properties, which can form LMCE melt during mineralization process and play an important role for the efficient enrichment and precipitation of Au, Ag, PGE and other precious metals. In this paper, the previous research data and the LMCE thermodynamic phase diagrams were analyzed. Combining research results of epithermal, orogenic, Carlin to Carlin-like and alkaline to meta-alkaline intrusion-related gold deposits, the authors discussed the formation and type of LMCE melts and their mechanisms for the enrichment of Au, Ag, PGE and other precious metals, and summarized mineral compositions and characteristic textures of mineralization that benefited by LMCE melts. The LMCE melts can be formed during magmatic, (magmatic-) hydrothermal and metamorphic processes, and belong to one of the important metallogenic mechanisms for precious metal deposits. There are many ion clusters in the LMCE melts, and aggregation between the clusters precludes the melt to reach phase equilibrium, which results in many non-equilibrium mineral combinations, including the coexistence of native LMCE, intermetallic compounds and multiphase minerals containing LMCE. Gold could also exist as ion clusters in the LMCE melt that gather to form spherical or flakes native gold, and form the super-rich ore bodies. The minerals formed by LMCE melt often exist as single or group combinations of emulsion droplets, beads, and bubbles in round, nearly round, and irregular particle inclusions in sulfides, selenides, tellurides, oxides and silicates, or distribute along fractures of minerals. These LMCE micro-inclusions are derived from melt disturbance that result in melt-melt or melt-liquid emulsification. Fluid boiling should be the main mechanism that causes the melt disturbance since the LMCE melt cannot be quenched and crystallized quickly at this process. It is usually cooled slowly at low temperature to achieve phase equilibrium and form complex mineral compositions. This feature is significant even in micro- to nano-scale mineral particles. Melt-fluid inclusions are the most direct evidence for the involvement of LMCE melts during mineralization.

Abstract Tellurium-rich (Te) adularia-sericite epithermal Au-Ag deposits are an important current and future source of precious and critical metals. However, the source and evolution of ore-forming fluids in these deposits are masked by traditional bulk analysis of quartz oxygen isotope ratios that homogenize fine-scale textures and growth zones. To advance understanding of the source of Te and precious metals, herein, we use petrographic and cathodoluminescence (CL) images of such textures and growth zones to guide high spatial resolution secondary ion mass spectroscopy (SIMS) oxygen isotope analyses (10 μm spot) and spatially correlated fluid inclusion microthermometric measurements on successive quartz bands in contemporary Te-rich and Te-poor adularia-sericite (-quartz) epithermal Au-Ag vein deposits in northeastern China. The results show that large positive oxygen isotope shifts from –7.1 to +7.7‰ in quartz rims are followed by precipitation of Au-Ag telluride minerals in the Te-rich deposit, whereas small oxygen isotope shifts of only 4‰ (–2.2 to +1.6‰) were detected in quartz associated with Au-Ag minerals in the Te-poor deposits. Moreover, fluid-inclusion homogenization temperatures are higher in comb quartz rims (avg. 266.4 to 277.5 °C) followed by Au-Ag telluride minerals than in previous stages (~250 °C) in the Te-rich deposit. The Te-poor deposit has a consistent temperature (~245 °C) in quartz that pre- and postdates Au-Ag minerals. Together, the coupled increase in oxygen isotope ratios and homogenization temperatures followed by precipitation of Au-Ag tellurides strongly supports that inputs of magmatic fluid containing Au, Ag, and Te into barren meteoric water-dominated flow systems are critical to the formation of Te-rich adularia-sericite epithermal Au-Ag deposits. In contrast, Te-poor adularia-sericite epithermal Au-Ag deposits show little or no oxygen isotope or fluid-inclusion evidence for inputs of magmatic fluid.

根据金矿床中碲、硒赋存特点与富集程度,可将Au-(Ag)-Te-Se成矿系统的矿床成因类型划分为:(1)浅成低温热液型金银矿床;(2)造山型金矿床;(3)卡林类卡林型金矿床;(4)碱性偏碱性侵入岩型金矿床;(5)斑岩型(铜)金矿床;(6)夕卡岩型(铜)金矿床;(7)VMS型金多金属矿床.碲、硒都是亲地幔的元素,侵入岩与火山岩是Au-(Ag)-Te-Se成矿系统中碲、硒的重要来源,黑色岩系也是硒的重要来源.温度、pH、氧逸度等是控制Te、Se的迁移与富集的重要因素.Au-(Ag)-Te-Se成矿系统的成矿机制与岩浆脱气、流体熔体分离、水岩反应、流体沸腾与混合、有机作用密切相关.其中岩浆脱气、流体熔体分离、流体沸腾与流体混合是碲化物型金矿床的重要成矿机制,而水岩反应、流体混合、有机作用是硒化物型金矿床的重要成矿机制.在成矿过程中,先期形成一些亚稳定或不稳定的过渡态矿物易发生固溶体分离作用,或是不饱和流体与已形成的矿物发生溶解再沉淀作用,导致矿石具有丰富的物质组成和结构特点.

The newly discovered Shangmachang epithermal gold (> 11 t Au; Heilongjiang province, NE China) and Beidagou epithermal tellurium-gold (> 5 t Au) deposits are located at the northeastern margin of the Central Asian Orogenic Belt and are hosted in Early Cretaceous volcanic rocks. At the Shangmachang deposit, gold occurs largely as electrum microparticles (5-120 mu m) with a fineness of approximately 401-697 in quartz, calcite, and pyrite. Silver-bearing minerals include electrum, polybasite, and minor argentite. The main mineral paragenetic assemblages consist of pyrite-electrum and galena-polybasite, while the hydrothermal alteration minerals include quartz, calcite, sericite, chlorite, and pyrite. Trace elements in the gangue minerals show that the Al contents of gold-bearing quartz veins are lower than those of pure quartz veins (early stage). Fluid inclusions in quartz and calcite mainly comprise liquid-vapor, and the components contain a liquid phase consisting of Na+, Cl-, and SO42- and a gas phase consisting of N-2, CO2, and CH4. The Shangmachang fluid inclusions homogenize at 142.8 degrees-303.0 degrees C and are of low salinity (0.2-8.8 wt% NaCl equiv.),while the Au mineralization formed at 150 degrees-225 degrees C. The calcite delta O-18(fluid) values range from -17.8%(0) to -13.1%(0), and the carbon isotope compositions range from -8.2%(0) to -4.5%(0). Zircon U-Pb dating of the Longjiang Formation andesite yields 119.4 +/- 1.9 Ma, and the granite yields 118.6 +/- 1.2 Ma, suggesting that local magmatism occurred during the Early Cretaceous. Calcite Sm-Nd dating suggests that the Au mineralization has an age of approximately 113.6 +/- 4.0 Ma. At the Beidagou deposit, the main mineral paragenetic assemblages consist of sphalerite-galena-hessite and chalcopyrite-altaite-petzite-hessite, while the hydrothermal alteration minerals include quartz, calcite, anhydrite, chlorite, and pyrite. The components of the fluid inclusions in quartz contain a fluid phase consisting of Na+, K+, Cl-, and SO42- and a gas phase consisting of N-2, CO2, CH4, and C2H6. The Beidagou fluid inclusions homogenize at 133.8 degrees-370.1 degrees C and are of low salinity (0.2-8.7 wt% NaCl equiv.), while the Au mineralization formed at 175 degrees-250 degrees C. The delta O-18(fluid) and delta D-SMOW values of the quartz samples from Beidagou range from -8.2%(0) to -5.0%(0) and -101.6%(0) to -92.8%(0), respectively. The Al contents of gold-bearing quartz veins are higher than those of pure quartz veins. Rb-Sr dating of ore-bearing quartz veins suggests that the Te-Au-Ag mineralization has an age of about 115.5 +/- 4.4 Ma. In summary, the interpretation of new data from the geological setting, fluid inclusions, O-H-C isotopes, and geochronology, suggests that the ore-forming fluids predominantly comprised meteoric fluids, while the metal content was derived from a mantle source at both the Shangmachang and Beidagou deposits. A geochemical model suggests that the fluids responsible for quartz deposition had a neutral pH and that adiabatic boiling and mixing triggered the gold, silver and tellurium precipitation. Both Shangmachang and Beidagou are interpreted as low-sulfidation epithermal gold deposits.