Ar Plateau Research Articles

Geochronology and geochemistry of the Banjiaoyuan tin deposit, southern Hunan Province and its geological implications

Situated in the central part of the Southern Hunan segment of the Nanling Metallogenic Belt, the Banjiaoyuan tin deposit represents a significant Indosinian quartz vein type tin deposit. Based on field geological surveys and petrographic observations, the mineralization in the area can be divided into three stages: (I) early greisen stage, (II) cassiterite-quartz vein stage, and (III) late barren quartz vein stage. The dating results show that the 40Ar-39Ar plateau age of muscovite in stage I is 215.51 ± 0.87 Ma, and the Rb-Sr isochronous age of quartz mineral in stage II is 214.2 ± 3.1 Ma (MSWD = 1.3), both of which are coincide with the cassiterite U-Pb lower intercept age (215.7 ± 1.3 Ma, MSWD = 1.2), confirming the existence of metallogenic events in this region during the late Indosinian. The δD and δ18O of quartz in stage II range from −66.2 to −80.2 ‰, and 3.71 to 6.17 ‰, respectively, indicating that the ore-forming fluid is mainly derived from a mixture of magmatic-hydrothermal fluids and a small amount of meteoric water. We applied LA-ICP-MS chemical mapping and trace elements analysis to cassiterites, found that they underwent a transition from oxidation to reduction during precipitation when the fluids tend to be more volatile-rich and highly fractionated. The formation of the Banjiaoyuan tin deposit is closely related to the late Indosinian magmatic activity in the Yangmingshan region. Besides, the deep and peripheral parts of the mining area also have the potential for large-scale vein-type and greisen-type W-Sn mineralization.

40Ar-39Ar dating, fluid inclusion, and isotopic constraints on the timing, fluid evolution, and deposition of the polymetallic Nuocang Pb–Zn deposit in the western Nyainqêntanglha belt

The Nyainqêntanglha polymetallic belt (NPB) is western China's foremost skarn Pb–Zn metallogenic belt. Significant progress has been made in determining these ore deposits' age and origin. However, the precipitation mechanisms and mineralization controls for these deposits remain unresolved. 40Ar/39Ar dating, fluid inclusion (FI), and H-O-S-Pb isotopic data are presented for the Nuocang deposit, a newly discovered polymetallic Pb-Zn skarn deposit in the western NPB, with the goal to trace age and, especially, the major fluid processes associated with hydrothermal evolution leading to the precipitation of ore. The muscovite yields an 40Ar-39Ar plateau age of 59.68 ± 0.60 Ma, which closely resembles typical skarn deposits within the NPB, indicating that it formed during the main collisional stage of the India–Eurasia continent. In the Nuocang base-metal skarn deposit, three ore-related stages can be discerned and subdivided: 1) the pre-ore stage, containing the prograde and early retrograde metasomatic skarn minerals, 2) the syn-ore stage, including the late retrograde metasomatic minerals and sulfides, and 3) the post-ore stage of quartz, calcite, and chlorite alteration. Correspondingly, three types of FI (L, V, and S type) have been identified. The ore-forming fluids evolved from moderate to high temperature between 340 and 440 °C primarily, but up to 571 °C, and moderate to high salinity (concentrated ∼8–18 wt% NaCl-equiv., but up to 48.1 wt% NaCl equiv.) in the pre-ore stage. During the syn-ore stage, the fluids were at low to moderate temperature (between 200 and 320 °C) and low salinity (∼2 to 12 wt% NaCl-equiv.) and developed in low temperature (∼120–200 °C) and low salinity (∼2–8 wt% NaCl equiv.) in the post-ore stage. The calculated δDH2O values of the transparent minerals were −180 to −106 ‰ during the pre-ore stage, −141 to −59 ‰ during the syn-ore stage, and −152 to −105 ‰ during the post-ore stage. The δ18OH2O values were −1.2 to 3.8 ‰ during the pre-ore stage, −4.7 to −2.3 ‰ during the syn-ore stage, and −10.9 to −5.0 ‰ during the post-ore stage, respectively.Based on these results, the magmatic fluids appeared to have gradually evolved into meteoric. Meteoric water is believed to play a significant role in metal deposition within magmatic-hydrothermal systems. Locally, boiling is also considered another key mechanism for ore precipitation. The S-Pb isotope values of the sulfide metals indicate that the metallogenic materials were predominantly derived from an upper crustal source mixing with minor amounts of mantle–derived components. This study suggests that the fluid mixing is related to geostatic pressure variations and infiltration of meteoric waters into the hydrothermal system and are key mechanisms triggering Pb-Zn ore deposition in the NPB.

Petrology, geochemistry and Ar-Ar geochronology of eclogites in Jinshajiang orogenic belt, Gonjo area, eastern Tibet and restriction on Paleo-Tethyan evolution

As one of the important Paleo-Tethys suture zones in eastern Tibet, the Jinshajiang orogenic belt is of great significance to study the tectonic evolution of the main suture zone of Paleo-Tethys. In this paper, eclogites developed in the Jinshajiang suture zone in Gonjo area, eastern Tibet, are selected as specific research objects, and petrological, geochemical and Ar-Ar geochronological analyses are carried out. The major element data of the whole rock reveals that the eclogite samples have the characteristics of picritic basalt-basalt and belong to the oceanic low potassium tholeiites. The results of rare earth elements and trace elements of the samples show that the protoliths of eclogites have characteristics similar to oceanic island basalt (OIB) or normal mid ocean ridge basalt (N-MORB). Muscovite (phengite) from two eclogite samples yield the Ar-Ar plateau ages of 247 ± 2 Ma and 248 ± 2 Ma respectively, representing the peak metamorphic age of eclogite facies and the timing of complete closure of the Jinshajiang Paleo-Tethys Ocean. Muscovite and biotite selected from the hosting rocks of eclogite yield the Ar-Ar plateau ages are 238 ± 2 Ma and 225 ± 2 Ma respectively, reflecting the exhumation age of eclogites and their hosting rocks. Combined with the zircon U-Pb dating data (244 Ma) of eclogites obtained in previous work, it can be concluded that the Jinshajiang Paleo-Tethys ocean was completely closed and arc-continent collision was initiated at about 248–244 Ma (T₂¹). Subsequently, due to the large-scale arc (continent)-collision orogeney between Deqin-Weixi continental margin arc and Zhongza block (T₃¹–T₃²), the eclogites were rapidly uplifted to the shallow crust.

Muscovite 40Ar-39Ar and cassiterite U-Pb dating of the Indosinian Aotou quartz-vein type tin deposit, southern China and its geological significance

The determination of deposit age is fundamental in economic geology, while the result is often disappointing because of the difficulties in selection of suitable minerals. In this study, on the base of detailed field investigation, we successfully combined the muscovite 40Ar-39Ar dating and cassiterite LA-ICP-MS U-Pb dating in the Aotou tin deposit, Jiangxi province, South China. The result of the muscovite 40Ar–39Ar plateau ages (228.7 ± 1.5 Ma) and the cassiterite U-Pb lower intercept ages (227.4 ± 6.9 Ma) are consistent, accurately defined that the Aotou tin deposit was formed during late Indosinian. With the gradual discovery of another Indosinian W-Sn deposit, we have taken this opportunity to discuss the prospecting index of the Indosinian granite by compiling data of relevant plutons. The result reflects that the Indosinian metallogenic plutons are mainly acidic rocks and produced in the form of small rock mass, with index minerals of muscovite and volatile-rich minerals such as tourmaline and fluorite. Geochemically, they show that the higher SiO2 content (71.51–78.14%), A/CNK (1.13–1.66), Rb/Sr (21.94 in average), but lower Nb/Ta (4.03 in average) and ΣREE (85 ppm in average), which could be useful indexes for identifying the metallogenic pluton. Furthermore, the negative correlation between SiO2 and ΣREE, K2O and Na2O can be used as important ore-prospecting indexes, as a result of they indicate the differentiation of ore-bearing hydrothermal fluids.

Early Cambrian high pressure/low temperature metamorphism in the southeastern Tarim craton in response to circum-Gondwana cold subduction

The circum-Gondwana subduction initiated by the early Cambrian has been suggested to reflect the establishment of the modern plate tectonics. The metamorphic rocks with low thermobaric (T/P) ratios indicative of cold subduction in the present tectonic regime have not been well investigated. To better understand the circum-Gondwana subduction and to test its possible link with the emergence of the modern plate tectonics, this study focused on blueschist-facies metamorphic rocks in the Altyn Tagh of the southeastern Tarim craton. Mineral assemblage and chemistry, phase equilibrium modelling, and quartz-in-garnet Raman elastic geobarometry reveal that the zoisite blueschist and glaucophane (Gln)-bearing quartz schist in northern Altyn Tagh were metamorphosed to lawsonite to epidote blueschist-facies at 520–545 °C and 16–19 kbar. It reflects high-pressure (HP)/low temperature (LT) metamorphism with low T/P ratios of <300 °C/GPa and thermal gradients of <10 °C/km. These blueschist-facies metamorphic rocks underwent rapid decompression starting at P-T conditions of <495 °C and <9.6 kbar during exhumation. Ar-Ar geochronology records paragonite Ar-Ar plateau ages of 520–506 Ma for the zoisite blueschist samples and phengite Ar-Ar plateau ages of 522–516 Ma for the Gln-bearing quartz schist samples, suggesting that the peak HP/LT metamorphism occurred prior to ca. 522 Ma. Based on new results and available data from the major Gondwana blocks, cold subduction was suggested to profoundly operate along circum-Gondwana in the early Cambrian after the amalgamation of Gondwana. The extensive circum-Gondwana subduction represents the earliest global cold subduction in Earth’s history associated with the establishment of the modern plate tectonics, as directly recorded by the studied early Cambrian blueschist-facies metamorphic rocks and a dramatic drop in the mean T/P of metamorphism since the early Paleozoic.

Early Yanshanian metallogenesis of the Banjing tungsten deposit in Ganxian, Jiangxi province, China: Constraints from geochemistry, Sr–Nd isotopes, zircon U–Pb, molybdenite Re–Os, and mica 40Ar–39Ar dating

The Banjing tungsten deposit, which has been discovered recently, is located in the northernmost part of the Dabu pluton, southern Jiangxi Province, China. In this study, zircon LA‐ICP‐MS U–Pb dating of the fine‐grained porphyritic biotite granite indicate that it was formed in the early Yanshanian (159.4 ± 2.5 Ma–161.6 ± 0.8 Ma). Whole‐rock geochemical studies have shown the fine‐grained porphyritic biotite granite has SiO2 of 75.82%–76.84%, Al2O3 12.50%–12.87%, MgO 0.07%–0.20%, and CaO 0.64%–1.09%, with A/CNK of 1.017–1.038. It has a total rare earth elements content of 93.9–118.9 ppm with strong negative Eu anomalies (δEu = 0.021–0.081). The biotite granite is enriched in Rb, Th, U, Nd and depleted in Ba, Sr, Nb, Ti. These data suggest the Dabu pluton belongs to S‐type granite. This pluton has ISr of 0.71212–0.72929 and εNd(t) from −9.60 to −10.62 with Nd model ages concentrated in 1732–1838 Ma. These isotopic data in combination with zircon Hf isotopes suggest the biotite granite originated from partial melting of the Middle Proterozoic metamorphic supracrustal rocks in South China, with a minor contribution from juvenile crust. Meanwhile, this study has obtained Re–Os isochron ages of the intrusion‐related and quartz vein‐type molybdenum mineralization are 156.3 ± 2.7 Ma and 157.0 ± 1.1 Ma in the Banjing tungsten deposit, respectively. Sericite from the greisen‐type tungsten‐molybdenum ore has an 40Ar–39Ar plateau age of 156.4 ± 1.0 Ma, interpreted as the formation age of this deposit. Collectively, the Banjing tungsten deposit is considered as a product of the early Yanshanian large‐scale peak mineralization in South China, which was formed in an extensional intracontinental environment caused by the subduction of the Palaeo‐Pacific Plate.

Cretaceous intraplate volcanism of Govorov Guyot and formation models of the Magellan seamounts, Pacific Ocean

ABSTRACT The OIB-type volcanic rocks of Govorov Guyot in Magellan Seamounts (Pacific Ocean) include basalts, trachybasalts, basaltic trachyandesites, and trachyandesites dated by the 40Ar-39Ar plateau from 121 ± 2.8 to 98.5 ± 1.4 Ma. Some rocks bear amphibole-spinel wehrlite xenoliths and clinopyroxene-amphibole (Cpx-Amp) mantle vein fragments in xenoliths and xenocrysts, which are remnants of metasomatized oceanic lithosphere. The pressure and temperature crystallization for pargasitic amphibole were the highest (1170–1130°C and 2.5–1.6 GPa, 73–53 km depth) in wehrlite peridotite and the lowest (1.6–1.1 GPa, shallower than 52 km, and 1070–980°C) in Cpx-Amp metasomatic mantle veins. Ti-bearing Amp phenocrysts and microlites crystallized from the parent melts of basaltic rocks at 1060–910°C and 1.2–0.4 GPa (40–15 km). The ascending basaltic melts lost H2O from 8.6 ± 1.2 to 2.6 ± 0.4 wt% upon decompression. Amphibole mantle xenocrysts became replaced by Ti-magnetite- and rhönite-bearing mineral assemblages in intermediate magma chambers within oceanic crust (3–7 km). Pargasitic Amp in wehrlite and metasomatic mantle veins may have crystallized at different depths from hydrous (6–4.5 ± 0.7 wt% H2O) mafic melts that percolated through peridotite. The sources of heat and metasomatic agents (silicate melts and/or fluids enriched in volatiles) most likely had no relation to the Pacific Plate subduction but may be associated with the Southern Pacific Superplume in the South Pacific Thermal and Isotopic Anomaly region, or may be located at the Lithosphere-Asthenosphere Boundary (LAB) level in the plume absence. Repeated events of Cretaceous intraplate volcanism in the Magellan guyots can be explained in terms of plume (hotspot) activity or decompression partial melting of enriched or metasomatized asthenosphere and/or metasomatized oceanic lithosphere caused by Pacific Plate deformation and fracturing from the LAB level.

Ages, H[sbnd]O[sbnd]C[sbnd]S[sbnd]Pb isotopes, and fluid inclusion study of the Daolundaba Cu–Sn–W–Ag deposit in Inner Mongolia, NE China

The medium-sized Daolundaba Cu–Sn–W–Ag deposit is located in the southern Great Xing'an Range (SGXR), being one of the representative deposits in this area. The vein orebodies of the deposit occur within the NE-trending fracture zones, which are developed in the Early Permian silty slate and Late Variscan biotite monzogranite. However, its mineralization age remains controversial, which affects the understanding of Sn–polymetallic mineralization in the SGXR. To determine the mineralization age and reveal the sources of fluid and ore-forming material, sericite and monazite dating, fluid inclusion microthermometry, and isotopic analysis were carried out in this study. The ore-forming process at the deposit can be divided into four stages: quartz–fluorite–muscovite–tourmaline–cassiterite–wolframite–arsenopyrite stage (stage I), quartz–fluorite–wolframite–chalcopyrite–arsenopyrite–pyrrhotite stage (stage II), quartz–fluorite–sericite–chalcopyrite–pyrite–pyrrhotite–silver mineral stage (stage III), and quartz–calcite–fluorite–pyrite stage (stage IV). The sericite sample yielded a 40Ar–39Ar plateau age of 138.8 ± 0.7 Ma and an isochronal age of 140.0 ± 1.1 Ma, and the LA-ICP-MS U–Pb age of three monazite samples was 136.0 ± 2.3–134.7 ± 2.8 Ma, indicating that the Daolundaba deposit formed in the Early Cretaceous. Liquid-rich, gas-rich, and daughter mineral-bearing inclusions have been identified in quartz, fluorite, and calcite. Homogenization temperatures and salinities of the fluid inclusions (FIs) in the stage I vary from 309 °C to 389 °C and 6.2 wt% to 46.3 wt% NaCl eqv., respectively. Homogenization temperatures and salinities of the FIs in the stage II vary from 242 °C to 339 °C and 5.3 wt% to 41.4 wt% NaCl eqv., respectively. Homogenization temperatures and salinities of the FIs in the stage III vary from 153 °C to 268 °C and 3.5 wt% to 35.4 wt% NaCl eqv., respectively. There are only liquid-rich inclusions in quartz, fluorite, and calcite of the stage IV; their homogenization temperatures and salinities vary from 114 °C to 188 °C and 2.1 wt% to 7.6 wt% NaCl eqv., respectively. The ore-forming fluids of the Daolundaba deposit are characterized by moderate–high temperature and great fluctuating salinity, belonging to an H2O–NaCl ± CO2 ± CH4 system. The δ18Owater and δD values of the stages I and II vary from 2.5 ‰ to 7.2 ‰ and − 127 ‰ to − 106 ‰, respectively; the δ18Owater and δD values of the stage III vary from − 3.0 ‰ to − 0.3 ‰ and − 126 ‰ to − 94 ‰, respectively; the δ18Owater and δD values of the stage IV vary from − 10.9 ‰ to − 4.7 ‰ and − 102 ‰ to − 81 ‰, respectively; indicating that the ore-forming fluids of the stages I and II mainly consist of magmatic water, that the ore-forming fluid in the stage III is a mixture of magmatic and meteoric water, and that the fluid in the stage IV is meteoric water. The δ13C values for calcite of the stage IV vary from − 9.8 ‰ to − 6.7 ‰, suggesting that the carbon was mainly from a magmatic source. The δ34S values range from − 7.4 ‰ to − 1.3 ‰ with an average of − 4.7 ‰. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of the metallic minerals are in the ranges of 18.293–18.612, 15.519–15.706, and 38.078–38.826, respectively. Both S and Pb isotopic systems indicate that the ore-forming metals primarily came from Mesozoic felsic magma. Fluid boiling and mixing were two main mechanisms for the deposition of ore-forming materials.

Repeated brittle reactivations of a pre-existing plastic shear zone: combined K–Ar and 40Ar–39Ar geochronology of the long-lived (&gt;700 Ma) Himdalen–Ørje Deformation Zone, SE Norway

AbstractBrittle reactivation of plastic shear zones is frequently observed in geologically old terranes. To better understand such deformation zones, we have studied the &gt;700 Ma long structural history of the Himdalen–Ørje Deformation Zone (HØDZ) in SE Norway by K–Ar and 40Ar–39Ar geochronology, and structural characterization. Several generations of mylonites make up the ductile part of HØDZ, the Ørje Shear Zone. A 40Ar–39Ar white mica plateau age of 908.6 ± 7.0 Ma constrains the timing of extensional reactivation of the Ørje mylonite. The mylonite is extensively reworked during brittle deformation events by the Himdalen Fault. 40Ar–39Ar plateau ages of 375.0 ± 22.7 Ma and 351.7 ± 4.4 Ma from pseudotachylite veins and K–Ar ages of authigenic illite in fault gouge at c. 380 Ma are interpreted to date initial brittle deformation, possibly associated with the Variscan orogeny. Major brittle deformation during the Early–Mid Permian Oslo Rift is documented by a 40Ar–39Ar pseudotachylite plateau age of 294.6 ± 5.2 Ma and a K–Ar fault gouge age of c. 270 Ma. The last datable faulting event is constrained by the finest size fraction in three separate gouges at c. 200 Ma. The study demonstrates that multiple geologically significant K–Ar ages can be constrained from fault gouges within the same fault core by combining careful field sampling, structural characterization, detailed mineralogy and illite crystallinity analysis. We suggest that initial localization of brittle strain along plastic shear zones is controlled by mechanical anisotropy of parallel-oriented, throughgoing phyllosilicate-rich foliation planes within the mylonitic fabric.

Hydrothermal evolution from porphyry- to epithermal-style mineralization in the Naozhi deposit, NE China

The Naozhi deposit in the Yanbian district of northeastern China contains polymetallic epithermal veins and subeconomic porphyry-style Cu mineralization within 2 km of each other. These two mineralization styles are genetically associated with 130–126 Ma andesites and dioritic–granitic intrusions. Isotopic ages determined on sericite (128.2 ± 2.9 Ma; 40Ar–39Ar plateau age) and sulfide (124.6 ± 2.7 Ma; Rb–Sr isochron) associated with the epithermal mineralization constrain the hydrothermal activity to at approximately 128 Ma. Three types of fluid inclusions, including halite-bearing, vapor-rich, and liquid-rich inclusions were trapped in quartz from porphyry-style veinlets associated with an assemblage of K-feldspar–biotite–magnetite. Based on microthermometry and the homogenization behavior of halite-bearing inclusions, they were trapped at lithostatic pressures of > 500 bars and at temperatures of ≥ 350 °C, whereas the vapor- and liquid-rich inclusions were trapped at pressures and temperatures of 110 ± 35 bars and ≤ 350 °C.Epithermal mineralization comprises four vein stages, which, from oldest to youngest, are quartz–pyrite, quartz–base metal sulfide, quartz–precious metal, and quartz–carbonate. The ore assemblage precipitated from low-salinity fluids (<10 wt% NaCl equiv.) at temperatures and pressures of ≤ 350 °C and ≤ 100 bars. The δ18OH2O (2.5 to −2.4 ‰) and δDH2O (−85 to −114 ‰) compositions of fluids related to porphyry- and epithermal-style mineralization indicate a mixture of magmatic and meteoric waters. The δ34SH2S (−3.1 to 4.5 ‰) values of fluids become isotopically heavier from the quartz–pyrite stage to the quartz–base metal sulfide stage, reflecting continuous reduction during epithermal mineralization. The mineral assemblage and chemical composition of sulfide minerals indicate a transition from oxidizing, high sulfidation porphyry-style fluids to reducing, intermediate–low sulfidation epithermal fluids, with log ƒO2 values ranging from −31 to > −33, and log ƒS2 values ranging from −7.0 to ≤ −13.4 during the epithermal veining stage. Metal deposition in the Naozhi magmatic–hydrothermal system resulted from cooling, sulfidation, neutralization, and boiling of predominantly magmatically sourced hydrothermal fluids that mixed with meteoric water.

Intraplate Volcanism of the Alba Guyot: Geodynamic Formation Models of the Magellan Seamounts in the Pacific Ocean for 100 million years

Abstract -We report data on 9 samples of basaltic rocks and a spinel lherzolite xenolith collected during dredging in the area of Alba Guyot (Magellan Seamounts, Pacific Ocean). The data include 40Ar–39Ar ages of five samples and mineral chemistry of rock-forming and accessory minerals and glasses, with implications for the formation conditions of Ti-amphibole in basaltic melts. The upper slope parts at Alba Guyot and its satellite Oma Vlinder at sea depths of 3600 to 2200 m, are composed of ~1400 m thick basaltic rocks that formed within the 112 to 86 Ma interval (40Ar–39Ar plateau ages). Later, in its 60 Myr history postdating the Cretaceous volcanism, the guyot was exposed to erosion, which produced a plateau-like flat top, and underwent another pulse of volcanism in the Cenozoic. Miocene (&amp;lt;20 Ma) eruptions of basanitic magma on the Alba Gyot plateau were associated with petit-spot volcanoes. Judging by the absence of hyaloclastic deposits around those volcanoes and the age of the lavas, the Cenozoic eruptions occurred in subaerial conditions before the guyot submerged below the sea level. The Alba volcanics have greater contents of incompatible elements than typical oceanic island basalts (OIB), apparently, because they formed by low-degree partial melting of different sources: pargasite-bearing spinel peridotite of the metasomatized oceanic lithosphere, mainly for Cretaceous basaltic rocks, and/or garnet peridotite for Miocene petit-spot basanites. Multiple eruptions at Alba Guyot for 100 Myr may have been maintained either by the Southern Pacific Superplume in the region of the South Pacific Thermal and Isotopic Anomaly (SOPITA) in the Mesozoic or by translithospheric faulting originated at the lithosphere-asthenosphere boundary (LAB) in the Cenozoic.

Genesis of the Lishupo gold deposit in the Jiangnan Orogen, NE Hunan (South China): Biotite Ar-Ar, zircon U-Pb ages and H-O-S-Pb isotopic constraints

The Lishupo gold deposit is located in the central Jiangnan Orogen (South China). Gold ore occurs mainly as quartz veins and altered slates, hosted by faults and shear zones in the low-grade metamorphosed Neoproterozoic Lengjiaxi Group. Metallic minerals include pyrite, arsenopyrite, pyrrhotite, chalcopyrite, sphalerite and galena, and the major alteration styles include silicification, sericitization, chloritization and carbonatization. Based on its vein crosscutting relationships and mineral assemblages and paragenetic sequence, mineralization at Lishupo comprises three stages: (1) quartz (Q1)–dolomite–pyrite (Py1)–arsenopyrite; (2) quartz (Q2)–dolomite–pyrite (Py2)–polymetallic sulfides; (3) quartz (Q3)–carbonate. Biotite from the sulfide-bearing ores of Stage 2 yielded a 40Ar–39Ar plateau age of 208.67 ± 1.25 Ma, and pre-ore granodiorite yielded a zircon U-Pb age of 430.8 ± 3.2 Ma. The dating results indicate that the Lishupo gold mineralization occurred at ∼ 210 Ma, coeval with the Late Triassic regional gold mineralization event in NE Hunan. Stage 1 to 3 quartz has δ18OVSMOW = +15.5 to + 17.6‰ and δDVSMOW = –81.2 to –70.3‰, and the ore-fluids were calculated to have δ18OFluid = +2.9 to + 10.9‰. This suggests that the ore-forming fluids were derived from a metamorphic source with magmatic input. The auriferous sulfides (pyrite containing invisible gold) have δ34SCDT = –13.7 to –4.6‰, 206Pb/204Pb = 18.230–18.642, 207Pb/204Pb = 15.615–15.755, and 208Pb/204Pb = 38.582–39.100. These isotopic data indicate that the ore-forming fluids and metals were derived from a deeper metamorphic source. The Lishupo deposit exhibits many features of orogenic gold mineralization, such as control by ductile shear zones, mineralization styles (quartz veins with abundant sulfide minerals), and H–O–S–Pb isotopic features indicating deeper metamorphic source. Based on similarities to other orogenic gold deposits, the Lishupo deposit is best classified as orogenic type formed at ∼ 210 Ma, in response to the Late Triassic extensional tectonics caused by the Paleo-Pacific plate, or the post-orogenic tectonics after the South China-Indochina and/or North China-South China collision.

Ta-Nb mineralization in the shallow-level highly-evolved P-poor Shihuiyao granite, Northeast China

The Shihuiyao granite district in the southern Great Xing'an Range, Northeast China, is a newly discovered area of rare-metal-bearing granites (RMG). The latest Jurassic Shihuiyao granitic pluton, emplaced into the Lower Permian Linxi Formation, comprises porphyritic granite, leucogranite, and amazonite-bearing pegmatite, all enriched in rare metals (mainly Ta, Nb, Rb). The Shihuiyao granites are peraluminous (A/CNK = 1.02–1.27), characterized by high contents of SiO2 (69.4–78.0 wt%), Al2O3 (12.7–16.9 wt%) and total alkalis (6.8–12.8 wt%), enriched in Ta, Nb, Rb, Cs, and Sn, but depleted in Ba and Sr. They have strong negative Eu anomalies (Eu/Eu⁎ = 0.02–0.42) and show the M-type REE tetrad effect. Low Nb/Ta (<4) and Zr/Hf (<8) values indicate high degree of magmatic fractionation. Whole-rock and mineral compositions variations indicate that the Shihuiyao granites are a typical low pressure and P-poor RMG, which experienced intensive magmatic fractionation followed by intensive hydrothermal reworking. The narrow range of δ7Li values (−0.86‰ to 0.88‰) and Rayleigh distillation modeling suggest that the porphyritic granite and leucogranite represent products of the same magma source, but evolved independently at depth. LA-ICP-MS UPb dating of monazite from the porphyritic granite and leucogranite yield lower-intercept ages of 150.2 ± 0.6 Ma and 147.0 ± 1.7 Ma, respectively. The 40Ar39Ar plateau ages of mica from leucogranite (146.3 ± 1.1 Ma) and an ore-bearing quartz vein (145.6 ± 1.0 Ma), and the UPb age of columbite (146.7 ± 4.7 Ma) further identify this as a latest Jurassic magmatic-hydrothermal mineralization event in NE China. Rapid crystallization and chemical quenching of magma resulted in neutralization of the acid fluoride solution, and a loss of the fluoride ligand during fluid evolution. This further triggered the subsequent crystallization of NbTa oxides. As revealed from geochemical and textural characteristics of the columbite group minerals, the high-degree of fractional crystallization and Ta-rich hydrosilicate fluid metasomatism are the main factors leading to the enrichment of TaNb within Shihuiyao RMG. In general, we conclude that rare metal-hosted magmatism took place in two episodes in NE China, namely, (i) Latest Jurassic to Early Cretaceous (150–130 Ma) peraluminous to metaluminous Ta-Nb-Sn-W RMG, and (ii) Early Cretaceous (130–120 Ma) alkaline Nb-Ta-Be-REE-Zr RMG, which highlight the prospecting fertility for Nb-Ta-REE (SnW) mineralization in NE China.

Cassiterite U–Pb, mica 40Ar–39Ar dating and cassiterite trace-element composition of the Furong tin deposit in the Nanling Range, South China

The Furong tin deposit (530,000 t Sn @ 0.8% Sn) is located in the southern part of the Mid–Late Jurassic, multiphase, granitic Qitianling batholith in the Nanling Range, South China. The spectrum of tin mineralization comprises skarn, chloritized granite, greisen, and quartz vein types, of which the skarn type is the most important. Cassiterite U–Pb dating provided Tera-Wasserburg lower intercept ages of 157.1 ± 1.5 Ma and 156.3 ± 1.5 Ma for skarn-type mineralization, 158.1 ± 1.4 Ma and 158.7 ± 1.6 Ma for chloritized granite-type mineralization, 155.8 ± 3.4 Ma for greisen-type mineralization, and 160.1 ± 1.7 Ma for quartz vein-type mineralization. These ages overlap with each other and define a pooled weighted mean age of 157.9 ± 1.1 Ma (2σ) for the tin ore system. Hydrothermal phlogopite from tin skarn and muscovite from tin greisen yielded younger 40Ar–39Ar plateau ages of 154.3 ± 1.9 Ma and 150.0 ± 1.5 Ma, respectively, which may reflect resetting due to post-ore fluid circulation. Distinctive cathodoluminescence textures and trace-element patterns of various cassiterite types indicate that the four ore types resulted from pulsed ore-forming fluids and changes in temperature in a single magmatic-hydrothermal system. In combination with the geological characteristics, the geochronological and trace-elemental data of cassiterite indicate that the formation of different ore types at Furong was associated with the most fractionated and latest alkali-feldspar granite of the Qitianling batholith, and resulted from the specific interactions of the ore-forming fluids with their granite and limestone host rocks.

Geochronology and geochemistry of the Late Jurassic Wujiaping Sn deposit, Dayishan ore field, South China: Implications to the petrogenesis and Sn mineralization

The Wujiaping Sn deposit is located at the northern Dayishan ore field, South China, whose ore veins are mainly hosted in the Dayishan pluton. LA–ICP–MS zircon U–Pb dating for the medium-fine grained- and medium-coarse grained-biotite monzogranite of Dayishan pluton yields emplacement ages of 154.5 ± 1.6 Ma (MSWD = 2.0) and 155.5 ± 0.5 Ma (MSWD = 1.9), respectively, which are consistent with the muscovite 40Ar-39Ar plateau age of 150.4 ± 0.9 Ma for the quartz vein type ore veins. It is indicated that the Sn mineralization in the Wujiaping deposit is related to the Late Jurassic granitic magmatism. These granites show the geochemical features of highly fractionated S-type granite: 1) low Zr + Nb + Ce + Y contents (<209 ppm); 2) high A/CNK ratios (>1.1); 3) low crystallization temperature (mean = 688 °C); 4) high Rb/Sr ratios (mostly > 48); 5) high differentiation index (DI > 90); and 6) low CaO, P2O5, Sr, and Eu contents. Whole rocks isotopes show that these granites shows variable initial 87Sr/86Sr ratios (0.70251–0.71208), negative εNd(t) values (−7.94–5.62) and old two stage Nd model ages of 1491–1563 Ma. LA–MC–ICP–MS zircon Lu–Hf isotopes show that the medium-fine-grained monzogranite have positive εHf(t) values of 0.37–8.5 and two stage Hf model ages of 662–1180 Ma, whereas the medium-coarse grained-biotite monzogranite have negative εHf(t) values of −6.42–3.55 and two stage Hf model ages of 1431–1599 Ma. It is proposed of that these granites are originated from melts mixed by crustal- and mantle-constituents and are formed in an extensional setting caused by the subduction of the Palaeo-pacific plate. The low LogfO2 values calculated through zircons (−21.2–13.1) and high F contents (3630–5120 ppm) indicate the granites derived from reduced and F-rich melts. Therefore, the reduced melt is highly fractionated and enriched in Sn and F, resulting in the large scale Sn mineralization in the Dayishan ore field.

Genesis and fluid evolution of the Huangtan Au-Cu deposit in the Kalatag district, Eastern Tianshan, NW China: Constraints from geology, geochronology, fluid inclusions, and H-O-S-Pb isotope geochemistry

The newly discovered Huangtan Au-Cu deposit is located in the central Dananhu - Tousuquan arc of Eastern Tianshan, southern Central Asian Orogenic Belt (CAOB). It is the first Au-dominated volcanogenic massive sulfide (VMS) polymetallic deposit in the Eastern Tianshan. Veinlet-disseminated and massive orebodies are hosted within Early Silurian pyritic phyllic tuff and volcanic breccia and controlled by a secondary fracture zone of the Kalatag fault with extensive hydrothermal alteration. Four primary alteration/mineralization stages have been recognized as follows: (1) Early ore stage (S1), forming mainly ore-barren fine quartz veins with minor gold-bearing sulfides; (2) main ore stage (S2), forming mainly thick quartz veins with abundant coarse-grained subhedral pyrite (S2-1), and plentiful chalcopyrite, sphalerite, barite and Au-bearing sulfide veins (S2-2); (3) late ore stage (S3), which is characterized by plenty of barren quartz–calcite veins with few sulfides; and (4) supergene stage (S4), accompanied by abundant oxide mineralization, including malachite, jarosite and other supergene minerals. From S1 to S3, microthermometric data of fluid inclusions show homogenization temperatures of 263–379 °C (mean = 308 °C), 188-292 °C (mean = 240 °C), and 118-198 °C (mean = 158 °C), respectively, and salinities of 5.3–14.2 (mean = 10.8) wt.% NaCl equiv., 2.8–10.7 (mean = 7.6) wt.% NaCl equiv., and 0.3–14.1 (mean = 2.6) wt.% NaCl equiv., respectively. The ore-forming fluids are characterized by middle-low temperature, low salinity, relatively reduced condition, and an H2O-NaCl ± CO2 ± CH4 system.The δ34S values (−5.25‰ to 0.50‰) and Pb isotopic ratios (206Pb/204Pb = 17.868–19.495, 207Pb/204Pb = 15.446–15.575, and 208Pb/204Pb = 37.350–38.491) suggest that the ore-forming materials came predominantly from a deep-seated magma source with a minor contribution of lower continental crust. The δ18OH2O and δDV-SMOW values of fluid inclusions in each metallogenic stage range from −6.1 to 5.6‰ and −66.8 to −53.9‰, respectively, suggesting the dominant role of magmatic water mixed with convectively circulating heated seawater during fluid evolution. Fluid cooling dilution, local boiling, and fluid mixing were considered as the main mechanisms of metal precipitation. The 40Ar-39Ar plateau age of hydrothermal muscovite from the late ore stage (S3) is 414.4 ± 0.4 Ma, which represents the upper limit age of shallow hydrothermal alteration and Au-Cu mineralization. It is also consistent with the Early Silurian polymetallic metallogenic event in the Kalatag district. The auriferous Huangtan and adjacent Cu-Zn-rich Huangtupo VMS deposits show obvious ore-forming element differences, and constitute a unique VMS metallogenic system in the Eastern Tianshan Orogenic Belt (ETOB), which provides an important research object and new insight for ore prospecting in the peripheral Gobi Desert area.

In-situ hydrothermal zircon U–Pb and phlogopite 40Ar–39Ar geochronology of uranium mineralisation in Luzong ore district scientific drilling (LTZK01), Anhui Province, SE China: Constraints on the mineralisation process

The economically important Luzong ore district, located at the north-eastern margin of the South China Block, developed numerous Fe–Cu–Pb–Zn–U deposits during the Early Cretaceous. The identified uranium deposits are primarily granite-related vein-type deposits distributed in the exposed granites and adjacent Jurassic sediments along the SE edge of the Luzong volcanic basin. Recently, new uranium mineralisation has been discovered by scientific drilling in concealed syenite in the centre of the Luzong basin. In this study, we conducted detailed studies of geological characteristics and determined the geochronology of the uranium mineralisation to constrain the ore-forming process. Luzong scientific drilling (LTZK01) penetrated Quaternary loose surface deposits (0–2 m), Cretaceous volcanic rocks (2–1488.84 m), concealed syenite and monzonite (1488.84–2012.35 m), and uranium mineralisation (1506–1742 m). Uranium mineralisation predominantly occurs as uranothorite in hydrothermal veins along the intragranitic fractures and breccias, which are associated with a pyrite-quartz-albite-tourmaline-phlogopite gangue assemblage. LA-ICPMS U–Pb dating of zircons from syenite and monzonite yields crystallisation ages of 131.4 ± 1.6 (MSWD = 0.45) and 131.7 ± 1.0 Ma (MSWD = 0.87), respectively. Based on the close textural relationship with other hydrothermal minerals, morphology, and trace element features, the zircons from the uraniferous veins are of a hydrothermal origin. In-situ LA-ICPMS U–Pb dating of hydrothermal zircons yielded a weighted mean age of 131.1 ± 1.6 Ma (MSWD = 3.6), which is consistent with the hydrothermal phlogopite 40Ar–39Ar plateau age of 129.25 ± 1.51 Ma (MSWD = 7.70). These ages indicate that uranium mineralisation in LTZK01 is marginally younger than the crystallisation of the host igneous rocks and might be associated with the post-magmatic hydrothermal process. Based on the magmatic and mineralisation ages obtained in this study and previous researches, we propose that the uranium was probably fractionated from the felsic melt into F-rich magmatic fluids to form uraniferous veins in LTZK01 as the pressure and/or temperature decreased.

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.

Geochemistry and geochronology of the Jawornik granitoids, Orlica-Śnieżnik Dome, Sudetes, Poland

The Jawornik granitoids intrude, in vein-like form, a sequence of a polymetamorphic metavolcanic and metapelitic rocks of the Orlica-Śnieżnik Dome, Sudetes, Poland. This paper provides whole-rock geochemical data, sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon geochronological data as well as 40Ar-39Ar age determinations to constrain the genetic and temporal relationships of the different rock types forming these veins. Based on macroscopically visible features of the granitoids and their relationship with tectonic structures visible in the country rocks, four varieties of the Jawornik granitoids have been distinguished: amphibole- and biotite-bearing granites (HBG), biotite-bearing granites (BG), biotite- and muscovite-bearing granites (BMG) and muscovite-bearing granites (MG). The Jawornik granitoids as a whole show a limited but significant variation in major element chemical composition, with SiO2 ranging from 65 to 76 wt.% (average 69.16 wt.%, n = 24). They are subalkalic, peraluminous and calc-alkaline [average A/CNK = 1.07, average (Na2O + K2O) = 7.75, average (Fe2O3t/(Fe2O3t + MgO) = 0.59]. Close inspection of their geochemical parameters showed that the samples investigated can be subdivided into two groups. The first group, the HBG, BG, and BMG varieties, comprising most of the granitoids in the Złoty Stok-Skrzynka Tectonic Zone, were formed by melting of greywackes or/and amphibolites. The MG, belonging to the second group, were formed by partial melting of a more felsic source. The HBG yielded a zircon U-Pb age of 351 ±1.3 Ma and well-defined 40Ar-39Ar plateau ages for hornblende (351.1 ±3.9 Ma) and coexisting biotite (349.6 ±3.8 Ma), indicating probably the oldest magmatic event in this region. Zircons from the MG, the youngest rock variety on the basis of their relationship with the tectonic structures in the host rocks, yielded a U-Pb age of 336.3 ±2.4 Ma, though based on three points only. The biotites and muscovites from the BMG have 40Ar-39Ar plateau ages of 344.1 ±4.7 Ma and 344.6 ±3.8 Ma, respectively. These data, in combination with already published isotopic ages, suggest that the Jawornik granitoids intruded host rocks of the Orlica-Śnieżnik Dome in three stages, at ~350, ~344 and ~335 Ma.

Structural and thermochronologic constraints on skarn rare-metal mineralization in the Cenozoic Cuonadong Dome, Southern Tibet

Abstract The Cuonadong super-large Be-W-Sn rare metals deposits are hosted by skarns and marbles in the middle unit of the Cuonadong Dome. Rocks in the Cuonadong Dome record four major deformational events: D1, top-to-S thrust; D2, top-to-N extension; D3, approximately E–W extensional deformation; and D4, late collapse structural deformation. Skarns and/or marbles featured by the directional alignment of skarn minerals are exposed in garnet-staurolite-bearing mica schist, and are closely related to the deformed leucogranites and pegmatites. The boundary between leucogranites and skarns is locally gradual or sharp, which suggests that skarns and the deformed leucogranites resulted from the synkinematic magmatism and the strong activity of the STDS. Ar-Ar dating of muscovite from the deformed granites in the middle unit and biotite from granitic gneiss in the core yielded Ar-Ar plateau ages of 15.0 ± 0.2 Ma and 13.9 ± 0.4 Ma, respectively, which reflects the age of syntectonic magmatism, and the activity time of the STDS at the Cuonadong Dome, respectively. Ar-Ar dating of biotite from marble in the middle unit yielded Ar-Ar plateau age of 16.1 ± 0.2 Ma, which was interpreted as the formation age of the synkinematic skarns. Skarns in the Cuonadong Dome were related to the detachments and formed in association with the emplacement of leucogranites. Therefore, we suggest that the formation of the Cuonadong Be-W-Sn skarn deposit was contemporaneous with the intrusion of leucogranitic magma and the top-to-north extensional deformation along the STDS.