Quartz Syenite Research Articles

Gold Mineralization at the Syenite-Hosted Anwangshan Gold Deposit, Western Qinling Orogen, Central China

The Anwangshan gold deposit is located in the northwestern part of the Fengtai Basin, Western Qinling Orogen (WQO). The gold ore is hosted within quartz syenite and its contact zone. The U–Pb weighted mean age of the quartz syenite is 231 ± 1.8 Ma. It is characterized by high potassium (K2O = 10.13%, K2O/Na2O > 1) and high magnesium (Mg# = 55.31 to 72.78) content, enriched in large ion lithophile elements (Th, U, and Ba) and light rare earth elements (LREE), with a typical “TNT” (Ti, Nb, and Ta) deficiency. The geochemical features and Hf isotope compositions (εHf(t) = −6.68 to +2.25) suggest that the quartz syenite would form from partial melting of an enriched lithospheric mantle under an extensional setting. Three generations of gold mineralization have been identified, including the quartz–sericite–pyrite (Py1) stage I, the quartz–pyrite (Py2)–polymetallic sulfide–early calcite stage II, and the epidote–late calcite stage III. In situ sulfur isotope analysis of pyrite shows that Py1 (δ34S = −1.1 to +3.8‰) possesses mantle sulfur characteristics. However, Py2 has totally different δ34S (+5.1 to +6.7‰), which lies between the typical orogenic gold deposits in the WQO (δ34S = +8 to +12‰) and mantle sulfur. This suggests a mixed source of metamorphosed sediments and magmatic sulfur during stage II gold mineralization. The fluid inclusions in auriferous quartz have three different types, including the liquid-rich phase type, pure (gas or liquid)-phase type, and daughter-minerals-bearing phase type. Multiple-stage fluid inclusions indicate that the ore fluids are medium-temperature (concentrated at 220 to 270 °C), medium-salinity (7.85 to 13.80% NaCleq) CO2–H2O–NaCl systems. The salinity is quite different from typical orogenic gold deposits in WQO and worldwide, and this is more likely to be a mixture of magmatic and metamorphic fluids as well. In summary, the quartz syenite should have not only a spatio-temporal but also a genetical relationship with the Anwangshan gold deposit. It could provide most of the gold and ore fluids at the first stage, with metamorphic fluids and/or gold joining in during the later stages.

MINERALOGICAL, PETROGRAPHIC AND GEOCHEMICAL EVIDENCE FOR ZIRCON FORMATION CONDITIONS WITHIN THE BURPALA MASSIF, NORTHERN BAIKAL REGION

This paper reports investigation on zircons from quartz syenite, alkaline and foid syenite, as well as metasomatic rock from the fenitization zone hosted by the Burpala massif. It is performed by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), cathodoluminescence (CL), laser ablation inductively coupled plasma mass spectrometry (LA ICP MS), and Raman spectroscopy. Generally, all zircons from igneous rocks show rhythmic, crystal growth zoning or sector zoning (type I) except for some zircons from alkaline syenites (type II) showing patchy zoning. They systematically contain pores or cavities. The REE patterns of magmatic zircons share similar features: e.g. depletion of LREE ((Yb/La)N up to 35000), large positive Ce (Ce/Ce* 6–427) and small negative Eu (Eu/Eu* 0.37–0.93) anomalies. Zircons crystallized from quartz syenites at 830±30 °C at the early stage of rock formation, while zircons from alkaline and foid syenites crystallized at the later stage of rock formation (680–750 °C). Meanwhile, crystallization of zircons with rhythmic zoning (type I) occurs at later magmatic stage, while the formation zircons of type II is probably related to the separation of the highly fluorinated aqueous fluid from the residual melt.Zircons from fenites have a bipyramidal habit holding a heterogeneous mosaic core and a homogeneous (or rhythmic zoning) rim. The cores of zircon show flat REE patterns without significant anomalies, while the rims are characterized by noticeable fractionation of REE ((Yb/La)N 85–615) and show a positive Ce anomaly (Ce/Ce* 4–18). The Raman spectra of the cores show a higher degree of crystallinity than the rims, and their flat REE spectra are probably related to the contamination by micro inclusions. The discordant U-Pb age of 295±3 Ma was obtained for zircon rims, which is consistent with the age of formation of igneous rocks of the Burpala massif (298–291 Ma). The latter supports the syngenetic origin of metasomatic ore mineralization with the main stage of massif formation.

Late Palaeozoic high-K calc-alkaline to shoshonitic series magmatism and related W(–Mo–Cu–Au) metallogeny of the Kyrgyz Tien Shan, Central Asia

In the Kyrgyz Tien Shan, numerous high-K calc-alkaline to shoshonitic series intrusions are associated with the large fault system known as the ‘Major structural line of Tien Shan’, or ‘Nikolaev Line’. During the Carboniferous, this lineament represented a zone of intracontinental, possibly back-arc rifting associated with a north-dipping subduction, whereas in the Late Carboniferous to Permian it was part of a larger continental collision structure. These Late Paleozoic high-potassic intrusions comprise numerous intrusive phases that vary in composition from the early mafic (monzogabbro, monzodiorite) through intermediate (monzonite, syenite, quartz syenite) to late stage and more evolved (quartz monzonite, granodiorite, monzogranite, leucogranite–alaskite) members locally intersected by monzodiorite–porphyry and lamprophyre dykes. They can be related to low degrees (from ∼1–2 to 2–2.5 vol%) of partial melting of metasomatically enriched upper mantle followed by magma fractionation and emplacement at shallower crustal levels. In summary, the high-K magmas formed in continental- and post-collisional arc settings with a progressive input of crustal material. From the west to the east, the potassic intrusions contain progressively higher Nb and Y concentrations, reflecting their derivation in a post-collisional setting. The A-type granite signatures also become more distinct in this direction. This is consistent with the tectonic model implying the ‘scissor-like’ closure of the Late Paleozoic Turkestan palaeo-ocean from east to west. These high-potassic intrusions are accompanied by W–Mo–Cu–Au skarn/porphyry to Au(–W) replacement-style deposits, which are part of the extended Au (Au–W–Mo–Cu) metallogenic belt of Tien Shan. The association of skarn and porphyry-style W–Mo to Mo–Cu–Au–W mineralization defines these ‘porphyry–skarn’ systems as a distinct group containing strongly oxidized andradite-dominant skarns. An early W partitioning into magmatic–hydrothermal fluid, together with Mo and Cu, is typical of this magmatic–hydrothermal system and can be explained by an early H 2 O saturation of the parental magma. The late-stage mafic dykes including lamprophyres probably reflect the presence of another, but concealed, mafic intrusion releasing CO 2 and metals, such as Au, As, Sb, Bi and Te, into the hydrothermal mineral system.

Late Paleozoic potassic igneous rocks of the Kensu and Dzholkolot plutons in the eastern Kyrgyz Tien Shan: Petrology, geochemistry, U-Pb zircon geochronology, and related skarn-porphyry W-Mo-Cu-Au mineralization

The Kensu and Dzholkolot multiphase intrusions are situated in the eastern part of the “Main Structural Line of Tien Shan”, or the “Nikolaev Line”. The plutons comprise mafic to intermediate (monzogabbro, monzonite, syenite, quartz syenite) and silicic (quartz monzonite, monzogranite, and leucogranite-alaskite) members, together with the interim (camptonite) and final monzodiorite-porphyry dikes. Geochemical signatures of the igneous rocks correspond to high-K calc-alkaline to shoshonitic series intrusions, with a strong A-type affinity, emplaced in post-collisional setting. Magmatic evolution included a generation of shoshonitic magma by a low-degree partial melting of the metasomatically-enriched upper mantle, followed by amphibole fractionation in a deep (lower crustal?) magma chamber. This was followed by a generation of mantle-induced granitic magmas in a crustal protolith, with possible mixing/mingling of various magmas. The rocks crystallized at shallow levels, in an oxidized environment, under decreasing pressure and temperature toward the younger (granitic) intrusion phases.Isotopic U-Pb (LA-ICP-MS) zircon dating of the igneous rocks indicates their Late Carboniferous age (ca. 325–302 Ma). The magma emplacement included a number of intrusion phases from monzogabbro (321 ± 4 Ma), monzonite (319 ± 4 Ma), and camptonite (306 ± 4 Ma), to quartz syenite (305.5 ± 2 Ma to 302 ± 3.7 Ma), quartz monzonite (305 ± 3 Ma) and subsequent granitic phases. Although the ages identified correspond to those of the subduction-related magmatism in the western part of the Middle Tien Shan, geochemical characteristics of the rocks supporting rather post-collisional setting of the plutons are in agreement with a “scissor-like” closure of the Turkestan paleoocean, starting from the east. Zircon xenocrysts dated at ca. 1.9 Ga suggest the presence of an underlying old continental crust.The skarn-porphyry W-Mo(−Cu-Au) mineralization complements the group of similar deposits associated with high-K calc-alkaline to shoshonitic series intrusions in the Middle Tien Shan and globally. The high endowment in W and Mo can be related to the fertilization of subduction-modified subcontinental lithospheric mantle in these metals, together with more common fertilization in Cu and Au, with its subsequent involvement in the magma generation in post-collisional setting. The endowment in W and Mo can also reflect a greater involvement of an ancient continental crust as the magma source(s). The oxidized paragenesis of hydrothermal alteration assemblages and mineralization corresponds to the respective affinities of the igneous rocks.

Geology, fluid inclusion, 40Ar-39Ar geochronology, and isotope constraints on the ore genesis of the Ershiyizhan Cu–Au deposit, Heilongjiang Province, China

The Ershiyizhan Cu–Au deposit, located in the eastern part of the upper Heilongjiang metallogenic belt, north of the Great Xing'an Range, is composed of orebodies from the Mesozoic magmatic rocks and the Ershierzhan group. There are three metallogenic stages of this deposit, (1) Quartz-K-feldspar-polymetallic sulfide stage (stage Ⅰ), (2) quartz-polymetallic sulfide stage (stage II), and (3) quartz-calcite ± pyrite stage (stage Ⅲ). Three types of fluid inclusions (FIs) were discovered in the vein mineral assemblages, liquid-rich two-phase aqueous FIs (L-type), vapor-rich aqueous FIs (V-type), and multi-phase FIs (S-type) with daughter minerals, including S1-type inclusions homogenized through vapor disappearance and S2-type inclusions homogenized by halite dissolution. Quartz of stage I and stage II contains all of these FIs. In contrast, the L-type fluid inclusions of stage III veins are the only ones present in the calcite. The homogenization temperatures and salinities obtained from FIs in stages I, II, and III range from 330 to 563 °C, 223 to 423 °C, and 108 to 225 °C, and 0.88 to 66.18 wt%, 2.41 to 48.59 wt%, and 0.18 to 3.23 wt% NaCl equiv., respectively. δ18O and δD values obtained from stable isotope analyses of K-feldspar and quartz samples collected from stages I, II, and III range from −2.31 to 7.89 and −133.2 to −98.2, respectively. Microthermometry and H-O isotope data from FIs suggest that the ore-forming fluids of the deposit had a magmatic origin, characterized by high temperatures, low–high salinities, an H2O-NaCl fluid system and this fluid system evolved to a low temperature, low salinities fluid through the gradual combination of meteoric water from stages II to III. Trapping pressures estimated from boiling L-type, V-type, and S1-type fluid inclusions in stage Ⅰ were 100–500 bars, corresponding to a mineralization depth of 1.0 to 5.0 km, with fluid boiling and mixing likely being responsible for the precipitation of sulfides and gold. K-feldspar from an auriferous vein of stage I yielded an 40Ar/39Ar isotopic plateau age of 131.21 ± 0.52 Ma, suggesting that the mineralization of the deposit is closely associated with the Early Cretaceous quartz monzonite porphyry. The analysis of the S isotope of metal sulfides in this deposit demonstrate that the sulfur reservoir is primarily derived from a hybrid magma source consisting of both mantle-derived and crustal-derived materials. Lead radioactive isotopic analysis for metal sulfides and various wall rocks also implies the lead source is a mixed source of upper crust and mantle. Thus, S-Pb isotope studies indicate that a crust-mantle mixed source for the mineralization of the deposit, and ore-forming material may originate from both quartz monzonite porphyry and various surrounding rocks including Late Triassic-Early Jurassic monzogranite, granite, quartz syenite, and the Ershierzhan Formation. Considering the geology, geochronology, FI, and H-O-S-Pb isotopic characteristics, the Ershiyizhan Cu–Au deposit is classified as a porphyry deposit formed in an extensional environment due to the delamination of the thickened lower crust following the Mongolian-Okhotsk Ocean closure.

Geochemical characteristics, hazards impact assessment and radiogenic heat production of the alkaline rocks.

This study primarily investigates the natural radioactivity level in alkaline rocks collected from the Wadi El-Dib ring complex (WDRC) in North Eastern Desert of Egypt, and assesses potential health risks associated with their use as decorative building materials. The work was accomplished using a high-purity germanium detector as well as ICP-MS and ICP-AES techniques. The WDRC composed essentially of trachyte, quartz syenite, granite and syenite. Geochemically, these rocks contain high SiO2 and alkalis with metaluminous to slightly peraluminous features. All rocks contain high concentrations of rare earth elements (∑REEs = 109-1075ppm), with clear enrichment in light REEs compared to heavy REEs [(La/Yb)N = 8.3-25.3. Radiometrically, the concentrations of the natural radioisotopes (238U, 232Th, and 40K) in the studied rock types surpassed the worldwide average values assigned for building materials by UNSCEAR. This elevation of the radioisotope concentration values is due to the presence of supplement minerals such as monazite, zircon, allanite, and rutile. Granites exhibit the highest mean concentrations of 238U (av. 164.24 ± 14.76Bq/kg) and 232Th (av. 214.37 ± 23.33Bq/kg), while trachytes demonstrate the highest 40K (av. 1352.56 ± 65.56Bq/kg) concentrations. In contrast, syenites exhibite the lowest mean concentrations for 238U (av. 54.51 ± 6.81Bq/kg) and 232Th (av. 56.76 ± 6.25Bq/kg), while quartz syenites display the lowest mean concentration of 40K (av. 1144.78 ± 96.19Bq/kg). The radiogenic heat production (RHP) associated with U, Th, and K range between 1.41 to 9.33μW/m3, exceeding the typical crustal mean value of 0.8 to 1.2μW/m3. The radiological parameters and indices evaluating risks of the outdoor and indoor radiation doses due to the investigated rocks were assessed. The results indicated that these rocks meet globally accepted values and safety standards (approved by UNSCEAR, ICRP, and EC) for surface building materials, as well as they underscore the importance of adhering to safety protocols to safeguard workers from radiation exposure within the WDRC area. Ultimately, the data herein provide a valuable database for assessing the compatibility of geochemical data and natural radioactivity level in WDRC rocks. Additionally, it reveals that from the radiological perspective, the investigated rocks are considered safe for use as decorative construction materials.

Late Paleozoic potassic igneous rocks of the Adyrtor intrusions in the eastern Kyrgyz Tien Shan: geochemistry, isotope U-Pb zircon geochronology, and related W-Mo(-Cu-Au) mineralization

ABSTRACT The Adyrtor multiphase pluton is situated in the easternmost part of the ‘Main Structural Line of Tien Shan’, or the ‘Nikolaev Line’, and intrudes the Paleoproterozoic metamorphic sequence representing the oldest (1.8–2.5 Ga) continental basement fragment in the Tien Shan orogenic belt. The intrusions comprise mafic to intermediate (monzodiorite, monzonite, quartz syenite) and silicic (quartz monzonite, monzogranite, and leucogranite-alaskite) rocks. Geochemical signatures of the igneous rocks correspond to high-K calc-alkaline to shoshonitic series intrusions, with a strong A-type granite affinity, emplaced in post-collisional setting. Based on the isotopic U-Pb data, quartz syenite from the Adyrtor intrusions crystallized at 330.7 ± 4.3 Ma, and quartz monzonite – at 329.5 ± 5.8 Ma. Although the ages identified correspond to those of the subduction-related magmatism in the western part of the Middle Tien Shan, geochemical characteristics of the rocks support rather post-collisional setting of the plutons, principally due to a ‘scissor-like’ closure of the Turkestan paleoocean, starting from the east. Magmatic evolution included a generation of shoshonitic magma by low-degree partial melting of the metasomatically-enriched upper mantle, followed by amphibole fractionation in a deep (lower crustal ?) magma chamber. Then, under the influence of mantle-supplied fluids and heat, granitic magmas in the crustal protolith could have been generated, with further mixing/mingling of the mantle-derived mafic (shoshonitic) magma and mantle-induced crustal granitic magma, followed by the magma fractionation and emplacement at shallower crustal levels. Assimilation of an old continental crust is also envisioned, consistent with the presence of the xenocrystic zircons dated at ca. 1.6 Ga to 2.5 Ga and the A-type granitoid affinity of the igneous rocks. The associated skarn-porphyry W-Mo(-Cu-Au) mineralization is consistent with post-collisional setting of the productive intrusions. This mineralization complements the group of similar deposits and occurrences associated with high-K calc-alkaline to shoshonitic series intrusions in the Middle Tien Shan and globally. The high endowment in W and Mo can be explained by the fertilization of subduction-modified subcontinental lithospheric mantle in these metals, with its further involvement in the magma generation in post-collisional setting. Also, a stronger W-Mo mineralization can reflect a greater role of a crustal protolith in the magma generation, as revealed by the distinct A-type affinity of the igneous rocks.

Syenites

Syenites are felsic plutonic igneous rocks characterized by the lack of quartz (<5 percent) or feldspathoids (<10 percent), although quartz syenites have 5–20 percent quartz. Typically they consist of feldspars, predominantly alkali feldspar with minor ferromagnesian minerals, usually pyroxene, amphibole or biotite. Syenites are overwhelmingly rocks of extensional environments and generally occur in areas of continental rifting, such as the African Rift Valley, and also on oceanic islands, such as the Canary archipelago. The extrusive equivalent of syenite is trachyte. As examples, we will look at two plutonic complexes containing syenites: the little‐known Kangerlussuaq intrusion in East Greenland and the more familiar Larvik Plutonic Complex in the Oslo region of Norway. Syenites occur in association with both oversaturated (quartz syenites and granites) and foid‐bearing rocks (typically nepheline syenites). Agpaitic syenites are highly evolved types with titano‐zircono‐silicates such as eudialyte. Syenites find use as dimension stones and countertops.

Nd isotope systematics of Late Paleozoic granitoids from the Western Transbaikalia (Russia): Petrological consequences and plume model testing

Late Paleozoic granites of the Angara-Vitim batholith (AVB) occupy an area of 200,000 km2 in Western Transbaikalia (the eastern part of the Central Asian fold belt). Batholith granitoids form a sheet-like body with an average thickness of 7–10 km and a volume of about 1 million km3. The granitoid massifs that make up the batholith are composed of high-potassium calc-alkaline and subalkaline quartz monzonites, quartz syenites, amphibole-biotite granodiorites, and biotite granites of autochthonous and allochthonous facies. An extremely high heterogeneity of the batholith isotopic structure was established, which basically corresponds to the parameters of uneven-aged crustal metaterrigenous protoliths. There are significant variations in εNd(Т) and accordingly T(DM-2) in granitoids of different complexes. It is assumed that the isotopic heterogeneity of AVB was formed due to the melting of a limited protoliths number that are maximally contrasting in isotopic and lithological composition: the Paleoproterozoic continental crust with εNd(Т) ≈ -20 ÷ -22 and T(DM-2) = 2.9–2.5 Ga and Neoproterozoic mafic granulites of increased potassium alkalinity, enriched in the juvenile component (εNd(Т) ≈ -3.0; T(DM-2) = 1.2–1.3 Ga). The latter were the main magmas source of postbatholitic alkali granites. Melts from these contrasting protoliths were only in some cases complementary to the salic melts sources. The main mechanism that determined the isotopic composition of AVB granitoids was the mixing of isotopically contrasting magmas in different proportions. Mingling dikes, mafic inclusions in granitoids, and synplutonic mafic intrusions in the AVB indicate an additional mixing component. It was mafic magma from an enriched mantle reactivated in the Late Paleozoic under the mantle plume influence on the heated plastic crust of a young (Hercynian) orogen.

Material composition of the Mesozoic igneous rocks of the Mikhailovsky massif and small bodies of the Evotinskiy ore district (Southern Yakutia, Aldan-Stanovoi shield)

The petrographic and geochemical characteristics of the Mesozoic igneous rocks of the Mikhailovsky massif, including the sills and dikes of the Evotinsky ore district located in the central part of the Nimnyr terrane of the Aldan-Stanovoy shield, were examined. This study revealed for the first time that the Mikhailovsky Massif is composed of quartz monzonites, while the sills and dikes are composed of quartz syenites. These rocks are geochemically close to the shoshonite-latite series of island arc rocks and are enriched in LREE and depleted in HREE, characterized by aweak negative Eu-anomaly. The sequence of magmatism development in the Mesozoic has been established: the formation of rocks of the Mikhailovsky massif and most small bodies occurred in the post-collision period, followed by the intrusion of quartzsyenite dike bodies in theanorogenicstages of territorial development.The study suggeststhat all the studied igneous rocks of the northeastern part of the Evotinsky region are characterized by a duality of geochemical composition,which indicates either intense mantle-crustal interactionor the existence of two sources of both mantle and crustal originat that time.

Geochemical evolution of the REE-enriched Cave Peak porphyry Mo-deposit, Trans-Pecos Texas, USA

The Cave Peak deposit is a rift-related, breccia-hosted, fluorine-rich porphyry molybdenum deposit that is enriched in Nb, REE, and other critical minerals. Cave Peak is the easternmost member of a northwest-trending group of Paleogene intrusions in the Diablo Plateau along with the Marble Canyon stock, an unmineralized, petrogenetically related, compositionally zoned mafic alkaline pluton. The Cave Peak intrusions show within-plate geochemical affinity and is the product of a highly differentiated magma series. Curvilinear trends in Harker variation and trace element diagrams record magma differentiation from mafic to intermediate (44–69 wt% SiO2) to felsic (70–76 wt% SiO2) compositions at Marble Canyon and Cave Peak, respectively. Quartz syenite and monzonite from the Marble Canyon stock yielded zircon UPb ages of 36.2 ± 0.15 Ma and 36.1 ± 0.09 Ma, respectively. The youngest major intrusion at Cave Peak, an alkali feldspar granite porphyry, has a zircon UPb age of 34.8 ± 0.4 Ma, supporting that these intrusions represent a magma differentiation trend. The δ98Mo of Cave Peak molybdenites range between −0.39 ± 0.06 ‰ and + 0.52 ± 0.06 ‰ with a total Mo isotope range of 0.91 ‰. Cave Peak samples predominantly fractionated towards heavier δ98Mo. The Cave Peak data are distinctly heavier than data obtained from the nearby subduction-related Red Hills porphyry Cu deposit which has δ98Mo values of −0.25‰ to −0.51‰.

Mid-Mesoproterozoic (ca. 1.37 Ga) anorogenic magmatism in the Dabie orogen, northern Yangtze Craton: Response to the breakup of Columbia

It is evident that the Yangtze Craton was involved in the formation and breakup of the Columbia supercontinent. However, due to the scarcity of Mesoproterozoic geological records and reliable paleomagnetic data, little is known about the timing, paleogeographic position, and geological processes of the Yangtze Craton. We conducted detailed geological mapping, petrographic, geochemical, and in situ zircon U-Pb and Lu-Hf isotopic investigations on newly recognized Mesoproterozoic quartz syenite and monzogranite in the Dabie orogen, northern Yangtze Craton. The results show that the quartz syenite and the monzogranite were emplaced at 1369 ± 12 Ma and 1372 ± 5 Ma, respectively. Both rocks are high in total alkali (K2O + Na2O) content and FeOt/(FeOt + MgO), with elevated diagnostic 10,000*Ga/Al ratios and Zr + Nb + Ce + Y concentrations, and enrichment in light rare earth elements. They are also depleted in heavy rare earth elements with significant negative Eu anomalies but remarkably low Sr, Cr, and Ni contents. These compositions define affinity to A1-type granite. In addition, the quartz syenite displays variable zircon Hf and homogeneous whole-rock Nd isotopic compositions with positive εHf(t) values of +0.7 to +5.7 (average +2.4) and εNd(t) values of −0.1 to +2.5 (average +1.0). In contrast, the monzogranite has homogeneous zircon Hf and whole-rock Nd isotopic compositions with negative εHf(t) values of −5.7 to −2.6 (average −4.8) and εNd(t) values of −3.5 to −1.5 (average −2.2). We propose that the quartz syenite was likely generated by the partial melting of juvenile, crust-derived melt with involvement of minor mantle-derived material, while the monzogranite was likely derived from the partial melting of ancient crust in an extensional tectonic regime (e.g., continental rift). Based on the newly recognized ca. 1.37 Ga granitic magmatism and previously reported magmatic events, we argue that the mid-Mesoproterozoic (ca. 1.37 Ga) magmatism in the Yangtze Craton occurred in response to the breakup of Columbia, and represents the separation of the Yangtze Craton from Columbia. Furthermore, according to comparable magmatic and sedimentary events, we propose that the Yangtze Craton, along with central Hainan Island, may have been linked to northwestern Laurentia, southwestern Siberia, and northeastern Australia during 1.6−1.4 Ga.

Petrogenesis of Neoproterozoic high-K intrusion in the southwestern Yangtze Block, South China: Implication for the recycled subducted-sediment in the mantle source

The study of K-enriched intrusive rocks is essential for deciphering mantle metasomatism beneath active continental arcs. In this contribution, high-precision zircon U–Pb–Hf isotope, whole-rock geochemistry, Sr–Nd isotope, and mineral chemistry analyses were performed to evaluate the petrogenesis and geodynamic system of the Yunnongfeng intrusion on the southwestern margin of the Yangtze Block. The Yunnongfeng intrusion consists of a high-K to shoshonitic rock assemblage with variable lithology from gabbro-diorite to granite. Zircon U–Pb dating gives concordant crystallization ages of ca. 782.5 ± 3.8 Ma for gabbro-diorite, ca. 774 ± 4.1 and 776 ± 4.1 Ma for diorite, ca. 770 ± 4.7 Ma for quartz monzonite, ca. 763 ± 3.4 Ma for quartz syenite, and ca. 764 ± 16 Ma for granite. These samples also show similar Sr–Nd, and Lu–Hf isotopic compositions, implying a common magma source. The similar crystallization age and regular variation of major and trace element contents suggest that these rocks were formed through fractional crystallization of cogenetic primitive mantle magmas. The enriched εNd(t) (−5.7 to − 5.1) and εHf(t) (−6.7 to − 1.2) values, high Rb/Y and Th/La ratios, slight Nd–Hf decoupling, and high-K and Th contents demonstrate that their lithospheric mantle source was enriched by slab-related fluid and sediment-related melt. The samples also exhibit remarkable enrichment in large-ion lithophile elements and depletion in high-field-strength elements, indicative of subduction-related arc magmatism. Taking into account previous studies, we suggest that the western margin of the Yangtze Block experienced a long-term subduction process during the Neoproterozoic, and the Yunnongfeng intrusion formed in an extensional back-arc basin. Based on the K-enriched mafic–intermediate rocks from the western margin of the Yangtze Block commonly show high K2O/Na2O, Rb/Sr, low Ba/Rb ratios, and enriched εNd(t) values, our study, coupled with numerous previous reports, proposes that the K-enrichment resulted from the breakdown of phlogopite, owing to subduction-related sediment melt reacting with peridotite in the mantle source area.

Discovery, geological setting and mineralization of the Shuvuutai molybdenum deposit, central-southern Mongolia

We document the newly discovered Shuvuutai Molybdenum (Mo) porphyry deposit located in the central-east Mongolian volcanic/-plutonic belt of the southern Altaids. The deposit is characterized by quartz vein- and veinlet-disseminated-type Mo ore bodies mainly hosted in a Late Permian-Early Triassic granitic intrusion. In this study, we provide a detailed study that integrates detailed geology with petrographic, mineralogic, geochemical, and geochronologic date to determine the tectonic setting of the deposit. Fluid inclusion analysis is used to reconstruct the fluid evolution history of the Shuvuutai Mo mineralization system and to understand the origin of the deposit. The ore bodies occur mainly as veins, lenses, and pods in positions from inner intrusions through contact zones to the host rocks distal to causative intrusions. The host rocks are variable in lithology, including granites, porphyries, volcanic breccias and tuffs, and sedimentary rocks. Outward from ore bodies to host rocks, the wall rock alteration is zoned from potassic (K-feldspar-quartz-mica), through phyllic (quartz-sericite-chlorite-epidote), to propylitic or argillic alterations. Two samples from porphyry stock intrusions at Shuvuutai were selected for U–Pb zircon geochronology and trace element composition studies, including the ore-hosting monzodiorite porphyry and quartz syenite porphyry. Our new ages are consistent with, or slightly postdate published zircon U-Pb ages of early phase of monzodiorite porphyry (268–232 Ma) and the main phase of quartz syenite porphyry (251.6 ± 1.7 Ma). Hydrothermal mineralization generally includes four stages, from early to late, represented by (1) potassic feldspar-quartz veins or veinlets, (2) quartz-molybdenite stockworks, (3) quartz-sulfide stockworks, and (4) quartz ± carbonate veins or veinlets. The ore-forming fluids were initially magmatic in origin and show high-temperature and high-salinity, containing daughter mineral and CO2-bearing fluid inclusions; and eventually evolved to low-temperature, low-pressure, low-salinity and CO2-poor meteoric water. S isotopic compositions of sulfides from the Shuvuutai Mo porphyry deposit indicate that the source of the ore-forming material was derived from the felsic magma. The Central-Eastern Mongolian volcanic-plutonic belt continues from Mongolia into northeast China, where similar Mo deposits are not yet recognized, suggesting that a new exploration strategy, based on the characteristics and history of the Shuvuutai discovery, is needed for the Chinese segment of the Altaids.

Eocene (∼ 53 Ma) alkaline complex in the southern Lhasa subterrane, Tibet: Implications for Neo-Tethyan slab breakoff

The Eocene alkaline magmatism in the southern Lhasa subterrane provides insights into the timing and dynamic mechanism of the Neo-Tethyan oceanic slab breakoff. Here, we present a combined study of whole-rock geochemistry, zircon U–Pb ages and Sr–Nd–Hf isotopes for the Mayum alkaline complex in the southern Lhasa subterrane. The complex is composed of amphibole syenites, quartz syenite, alkali feldspar granites and mafic microgranular enclaves (MMEs) in the host quartz syenites. Their crystallization ages are 52.2 ± 0.8 Ma, 52.2 ± 1.0 Ma, 49.6 ± 0.5 Ma and 53.1 ± 1.6 Ma, respectively, indicating that these rocks were simultaneously generated in the early Eocene. The hosted alkaline rocks are shoshonic with high SiO2 (64.32–70.49 wt.%), Na2O+K2O (6.63–9.43 wt.%) and low MgO (0.57–2.47 wt.%) contents. They are enriched in large-ion lithophile elements (LILEs: e.g., Rb, K), light rare earth elements (LREEs), Th and U, and are depleted in high field-strength elements (HFSEs) (such as Nb, Ta, and Ti) with strongly negative Eu anomalies (Eu/Eu* = 0.33–0.75). They have homogeneous whole-rock (87Sr/86Sr)i ratios (0.7051–0.7056), low εNd(t) values (–1.7 to –0.9), and positive zircon εHf(t) values (+1.69 to +7.72). Thus, the host alkaline rocks were generated from partial melting of the juvenile lower crust under the southern Lhasa subterrane, and went through a fractional crystallization process during magma ascending emplacement. Compared with the host alkaline complex, the MMEs have lower SiO2 contents (55.16–63.67 wt.%), very higher Fe2O3T (4.08–6.58 wt.%) contents with variable Cr (3.45–226.00 ppm), V (46–107 ppm) and Ni (2.66–6.16 ppm) contents. Meanwhile, the MMEs have similar patterns in trace and rare earth elements (such as obviously Eu anomalies, Eu/Eu* = 0.24–0.38) and similar whole-rock Sr-Nd isotopes ((87Sr/86Sr)i = 0.7051–0.7056, εNd(t) = –2.1 to –1.4) with the host alkaline rocks. Thus, the MMEs might be derived from a mantle source, and magma mixing occurred between the MMEs and the host alkaline rocks. The Mayum alkaline rocks and associated MMEs were generated under an extensional tectonic setting related to the Neo-Tethyan oceanic slab breakoff at ca. 53 Ma.

Gravimetric inversion and three-dimensional geological modelling of the Piquiri Syenite Massif, southern Brazil

The Pelotas Batholith corresponds to the eastern margin of the Dom Feliciano Belt in southernmost Brazil. It comprises multiple intrusions formed by successive tectonic-magmatic processes during the Brasiliano / Pan-African Cycle. One of these intrusive igneous bodies is the Piquiri Syenite Massif (PSM), recently described as a multi-intrusive body formed by three successive pulses, dated by LA-MC-ICP-MS (U-Pb in zircon), with the oldest pulse located at the margins and the youngest in the centre of the intrusion. Pulse 1 (609.3 ± 1.5 Ma) comprises fine- to medium-grained equigranular syenite to quartz syenite and alkali-feldspar quartz syenite, with colour index M′15–30. Pulse 2 (603.4 ± 3.9 Ma) comprises medium- to coarse-grained equigranular alkali-feldspar syenite and alkali-feldspar quartz syenite, with colour index M′ 5–15 and fragments of Pulse 1 varieties. Pulse 3 (588.8 ± 3.1 to 583.2 ± 1.8)comprises medium- to coarse-grained inequigranular quartz syenites, with colour index M′ 2–10, containing fragments of pulses 1 and 2 varieties. As defined by the AMS data, the PSM magnetic fabric is concordant with the magmatic fabric, parallel to the outer edges of the body, dipping towards the centre. However, the construction and emplacement of the body have been the subject of different interpretations. The main objective of this work is to relate the general morphology of the massif and the behaviour of the pulses within the massif with the processes of formation and ascent of the magmas that have built it. For this, terrestrial geophysical surveys were carried out to obtain gravimetric data, with which the Bouguer Anomaly map was generated. Modelling by gravimetric inversion was carried out in nine profiles using tools from the Oasis Montaj software, which was the basis for constructing a three-dimensional geological model using the Leapfrog Geo software. Associating the geological model with the magmatic and magnetic foliations, including the magnetic lineation, it was possible to determine a change in behaviour between the youngest and the two oldest pulses related to the ascension process. In addition, the body’s general shape, with the greatest depths located in the eastern region, allowed us to relate the rise of magma to a structure in the region.

Geochemistry and Geochronology (U-Pb and Lu-Hf) of the Soarinho Alkaline Massif (Brazil): Implications on Mantle versus Crustal Signature of Syenitic Magma

The Soarinho Alkaline Intrusion, southeastern Brazil, makes up part of the Serra do Mar Igneous Province, and it is composed of alkali feldspar syenite, alkali feldspar trachyte, quartz syenite, and monzonite. Geochemical and geochronological analyses of the Soarinho were compared with data from its neighbors, Rio Bonito and Tanguá. Zircon U-Pb Laser Ablation ages show that Soarinho is younger than Rio Bonito and Tanguá. Ages obtained from the monzonite (60 ± 2 Ma), alkali feldspar syenite (58 ± 2 Ma), and quartz syenite (58 ± 2 Ma) are indistinguishable within error. One nepheline syenite sample from Tanguá gives an age equal to those of Rio Bonito already published (65 ± 1 Ma). Petrographic and geochemical data show a clear contrast among Soarinho, Rio Bonito, and Tanguá. Lu-Hf isotopic data for the three alkaline intrusions (all negative) point to some similarities in their sources. The data suggest an enriched mantle source for Soarinho; however, an older continental crust contribution cannot be discarded.

Geochronology and Geochemistry of Wangjiadashan Quartz Syenite Porphyry in Suizao Area of Hubei Province in the Tongbai-Dabie Orogenic Belt

Geochronology and Geochemistry of Wangjiadashan Quartz Syenite Porphyry in Suizao Area of Hubei Province in the Tongbai-Dabie Orogenic Belt

Bureya−Jiamusi−Khanka superterrane linked to the Kuunga-Pinjarra interior orogen of East Gondwana and its drift toward Northeast Asia

There is general agreement that a series of East Asian blocks has always lain outboard of both India and Australia along the North Indo−Australie peripheral orogen. However, whether the East Asian blocks were involved in the interior orogens of East Gondwana remains equivocal. The geochronology and geochemistry of Neoproterozoic−Late Triassic rocks in the Russian Far East, together with existing paleontological and detrital zircon data, offer an opportunity to determine the tectonic origin and drift history of the Bureya−Jiamusi−Khanka superterrane. Biotite and amphibole 40Ar/39Ar dating results define a distinctive episode of Late Pan-African (ca. 550 Ma) metamorphism and a local Late Triassic (ca. 219−200 Ma) episode of deformation for the Bureya−Jiamusi−Khanka superterrane. Zircon U−Pb ages and whole-rock geochemical data indicate that the Early Ordovician (483 ± 3 Ma) highly fractionated I-type monzogranites were emplaced in a post-collisional setting linked to the collapse of a Late Pan-African orogen, while the Late Triassic (ca. 234−223 Ma) A-type quartz syenites and I-type granite aplite dikes were formed in a slab-pull−induced passive continental margin of the subducting Mudanjiang oceanic plate. These crucial archives, complemented by data from the literature, reveal that the Bureya−Jiamusi−Khanka superterrane made up the northernmost Kuunga-Pinjarra interior orogen during the final assembly of East Gondwana. As a result of Devonian rifting after Early Ordovician orogen collapse, the Bureya−Jiamusi−Khanka superterrane escaped from the Kuunga-Pinjarra interior orogen and subsequently migrated to Northeast Asia by the Late Triassic to Jurassic due to the subduction and closure of the Paleo-Tethys and Paleo-Pacific oceans.

Late Paleozoic alkaline granitoids of the southwestern and Northern Mongolia: U–Pb ID TIMS zircon dating, petrogenesis and implications for post-accretion and anorogenic activity of the Central Asian Orogenic Belt

In tectonic history of many orogenic belts, alkaline granitoids with A-type affinity mainly reveal lithosphere extension events. However, precise dating of these rocks is often hampered by several problems either due to absence of accessory zircon or due to high U and Th contents disturbing the U–Pb isotope system. This study reports results of chemical abrasion isotope dilution–thermal ionization mass spectrometry (CA ID TIMS) U–Pb dating of zircon from five plutons of aegirine- and/or alkaline amphibole-bearing alkali-feldspar granites and quartz syenites from the Trans-Altai Gobi (SW Mongolia) and Northern Mongolia in the Central Asian Orogenic Belt and reveals their close petrogenesis in different tectonic position. In the SW Mongolia the earliest Carboniferous alkaline granitoids (ca. 358–346 Ma) were formed during the post-accretion extensional event suggesting the Late Devonian accretion of the Trans-Alai Gobi–Eastern Junggar oceanic island arc to the Mongolian–Chinese Altai peri-Siberian continental margin. Alkaline granitoids of the Northern Mongolia were emplaced in the Early Permian during two independent geographically overlapping anorogenic near-coeval igneous pulses. The earliest pulse (ca. 285 Ma) related to evolution of the western half of the Northern Mongolia–Western Transbaikalia volcano-plutonic belt of alkaline granitoids with the bimodal volcanic sequences, is ascribed to the most significant Early Permian magmatic event throughout the Central Asian Orogenic Belt. The latest pluton (276 ± 1 Ma) identifies the initial emplacement stage of the Middle Permian–Early Triassic Khangai granitoid batholith.Alkaline granitoids from the Trans-Altai Gobi and Northern Mongolia possess similar ferroan, mainly peralkaline, A2-type granite geochemical characteristics, but differ in Nd isotopic signatures. For the Trans-Altai Gobi plutons εNd(t) = +6.7; for Northern Mongolian plutons εNd(t) varies between –1.7 to + 0.6. These values are consistent with the Nd isotopic evolution of the continental crust of the hosting terranes, ‘Hercynian’ isotope province for the Trans-Altai Gobi and ‘Caledonian’ province with a pre-Ediacaran microcontinent crust for the Northern Mongolia. Thereby studied alkaline granitoids were formed manly though anatexis of the host terrane crust during post-accretion and anorogenic extension events in different parts of the Central Asian Orogenic Belt.