Geochemistry and geochronology of granitoid rocks of the Taatsiin Gol pluton of the Khangai Complex, Central Mongolia

The Taatsiin Gol pluton is one of the major constitute the intrusive body of the Khangai Complex, and is composed the first phase of diorite, the second phase of porphyritic granite, biotite-hornblende granite, and granodiorite, and the third phase of biotite granite and alkali granite. This paper presents new geochemical and U-Pb zircon age data from intrusive rocks of the Taatsiin Gol pluton. Geochemical analyses show that the granitoid rocks of the pluton are high-K calc-alkaline, and metaluminous to weakly peraluminous I-type granites, depleted in HFSE such as Nb, Ta, Ti and Y and enriched in LILE such as Rb, Cs, Th, K and LREE, where some variations from early to later phases rock. Zircon U-Pb dating on the biotite granite of the third phase yielded weighted mean ages of 241.4±1.2 Ma and 236.7±1.4 Ma. Based on the new and previous researchers’ age results, the age of the Taatsiin Gol pluton of the Khangai Complex is 256-230 Ma consistent with the late Permian to mid-Triassic time. Although showing variated geochemical features, the rocks of the three phases are all suggested to form at an active continental margin setting, probably related to the southwestward subduction of the Mongol-Okhotsk Ocean plate during the late Permian to mid-Triassic period.

Constraints of magmatism on the Ergu Fe–Zn polymetallic metallogenic system in the central Lesser Xing’an Range, NE China: evidence from geochronology, geochemistry and Sr–Nd–Pb–Hf isotopes

The medium-sized Ergu Fe–Zn polymetallic skarn deposit is located in the central Lesser Xing’an Range, NE China. The ore bodies are mainly hosted in the contact zone between granodiorite intrusions and lower Cambrian dolomitic crystalline limestones or skarns. To reveal the magmatic influence on the mineralization, resource potential and metallogenic geodynamic process of this deposit, a systematic study of the geology, petrology, zircon U–Pb dating, element geochemistry, amphibole geochemistry and Sr–Nd–Pb–Hf isotopes of the Ergu deposit intrusives was conducted. The results show the following: (1) The major rock types in the mine area are medium-grained granodiorite and porphyritic granite, and the rock related to mineralization is medium-grained granodiorite. Zircon U–Pb dating suggests that the granodiorite and porphyritic granite formed at 181.9–183.8 Ma and 182.7 Ma, respectively. Thus, an Early Jurassic magmatic event led to the formation of the Ergu deposit. (2) The granodiorite and porphyritic granite are high-K calc-alkaline I-type granites that formed by comagmatic evolution with varying degrees of fractional crystallization and were likely derived from partial melting of the lower crust. The Ergu deposit occurred in an active continental-margin tectonic setting. (3) The high water content (5.69 wt % H2O), high oxygen fugacity (ΔFMQ = +1.75 to +1.82) and intermediate-plutonic emplacement (3.13 km) of the granodioritic magma are key factors in the formation of the Ergu deposit. The porphyry granite is characterized by high water content (>4 wt % H2O), reduced oxygen fugacity (ΔFMQ = −0.47) and shallow emplacement (<3 km).

Petrographic Studies of Rocks around Arum and Its Environs, North Central Nigeria

A detailed geological mapping of the area around Arum and environs part of Kurra sheet 189 SW was carried out on the scale of 1: 12, 500. Geologic field mapping and petrographic study (both megascopic and microscopic) were the methodology used. The geologic mapping of the area identified four rock units which are; granite, porphyritic granite, granitic gneiss and Porphyroblastic gneiss. These rock types were distributed such that the granite at the north-eastern part covered about 25%, the north –western portion was occupied by the porphyritic granite which occupied the largest portion of about 30% of the area. The third rock unit is the granitic gneiss which covered only about 20%. The fourth (last) and the oldest rock unit is the Porphyroblastic gneiss covering about 25% of the total area at the south-eastern corner. Megascopic and microscopic study revealed that the rocks in the area comprised of minerals such as; quartz, biotite, muscovite, microcline, feldspar, hornblende, garnet, etc. Structures that were clearly evident in the area included fault, foliation, joints, and veins. Structural analysis showed that their rose diagrams proved a NW-SE, NNE-SSW and NE-SW trends to be dominant.

Generation of Cretaceous high-silica granite by complementary crystal accumulation and silicic melt extraction in the coastal region of southeastern China

It is generally hypothesized that high-silica (SiO2 &gt; 75 wt%) granite (HSG) originates from crystal fractionation in the shallow crust. Yet, identifying the complementary cumulate residue of HSG within plutons remains difficult. In this work, we examine the genetic links between the porphyritic monzogranite and HSG (including porphyritic granite, monzogranite, and alkali feldspar granite) from the coastal area of southeastern China using detailed zircon U-Pb ages, trace elements, Hf-O isotopes, and whole-rock geochemistry and Nd-Hf isotopic compositions. Zircon U-Pb ages indicate that the porphyritic monzogranite and HSG are coeval (ca. 96−99 Ma). The HSG and porphyritic monzogranite have similar formation ages within analytic error, identical mineral assemblages, similar Nd-Hf isotopic compositions, and consistent variations in their zircon compositions (i.e., Eu/Eu*, Zr/Hf, and Sm/Yb), which suggests that their parental magma came from a common silicic magma reservoir and that the lithological differences are the result of melt extraction processes. The porphyritic monzogranite has relatively high SiO2 (70.0−73.4 wt%), Ba (718−1070 ppm), and Sr (493−657 ppm) contents, low K2O and Rb concentrations and low Rb/Sr ratios (0.1−0.2), and it displays weak Eu anomalies (Eu/Eu* = 0.57−0.90). Together with the petrographic features of the porphyritic monzogranite, these geochemical variations indicate that the porphyritic monzongranite is the residual silicic cumulate of the crystal mush column. The HSG (SiO2 = 75.0−78.4) has variable Rb/Sr ratios (2−490) and very low Sr (1−109 ppm) and Ba (9−323 ppm) contents. Zircon from the HSG and porphyritic monzogranite overlap in Eu/Eu*, Zr/Hf, and Sm/Yb ratios and Hf contents; however, some zircon from the HSG show very low Eu/Eu* (&lt;0.1) and Zr/Hf ratios. These features suggest that the HSG represents the high-silica melt that was extracted from a crystal-rich mush. The injection of mantle-derived hotter mafic magma into the mush column and the exsolution of F/Cl−-enriched volatiles (or fluids) from the interstitial melt rejuvenated the pre-existing highly crystalline mush. Subsequent extraction and upward migration of silicic melt resulting from compaction of the mush column formed the HSG at shallow crustal levels, which left the complementary crystal residue solidified as porphyritic monzogranite at the bottom.

Genesis of Dulong Sn-Zn-In Polymetallic Deposit in Yunnan Province, South China: Insights from Cassiterite U-Pb Ages and Trace Element Compositions

The Dulong Sn-Zn-In polymetallic deposit in the Yunnan province, SW China, hosts a reserve of 5.0 Mt Zn, 0.4 Mt Sn, and 7 Kt In. It is one of the most important polymetallic tin ore districts in China. Granites at Dulong mining area include mainly the Laojunshan granite (third phase), which occurs as quartz porphyry or granite porphyry dikes in the Southern edge of the Laojunshan intrusive complex. Granites of phases one and two are intersected at drill holes at depth. There are three types of cassiterite mineralization developed in the deposit: cassiterite-magnetite ± sulfide ore (Cst I), cassiterite-sulfide ore (Cst II) within the proximal skarn in contact with the concealed granite (granites of phases one to two and three), and cassiterite-quartz vein ore (Cst III) near porphyritic granite. Field geology and petrographic studies indicate that acid neutralising muscovitization and pyroxene reactions were part of mechanisms for Sn precipitation resulting from fluid-rock interaction. In situ U–Pb dating of cassiterite samples from the ore stages of cassiterite-sulfide (Cst II) and Cassiterite-quartz vein (Cst III) yielded Tera-Wasserburg U–Pb lower intercept ages of 88.5 ± 2.1 Ma and 82.1 ± 6.3 Ma, respectively. The two mineralization ages are consistent with the emplacement age of the Laojunshan granite (75.9–92.9 Ma) within error, suggesting a close temporal link between Sn-Zn(-In) mineralization and granitic magmatism. LA-ICPMS trace element study of cassiterite indicates that tetravalent elements (such as Zr, Hf, Ti, U, W) are incorporated in cassiterite by direct substitution, and the trivalent element (Fe) is replaced by coupled substitution. CL image shows that the fluorescence signal of Cst I–II is greater than that of Cst III, which is caused by differences in contents of activating luminescence elements (Al, Ti, W, etc.) and quenching luminescence element (Fe). Elevated W and Fe but lowered Zr, Hf, Nb, and Ta concentrations of the three type cassiterites from the Dulong Sn-Zn-In polymetallic deposit are distinctly different from those of cassiterites in VMS/SEDEX tin deposits, but similar to those from granite-related tin deposits. From cassiterite-magnetite ± sulfide (Cst I), cassiterite-sulfide ore (Cst II), to cassiterite-quartz vein ore-stage (Cst III), high field strength elements (HFSEs: Zr, Nb, Ta, Hf) decrease. This fact combined with cassiterite crystallization ages, indicates that Cst I–II mainly related to concealed granite (Laojunshan granites of phases one and two) while Cst III is mainly related to porphyritic granite (Laojunshan granites of phase three).

Kivilompolo Mo mineralization in the Peräpohja belt revisited: Trace element geochemistry and Re-Os dating of molybdenite

The Kivilompolo molybdenite occurrence is located in the northern part of the Peräpoh jabelt, within the lithodemic Ylitornio nappe complex. It is hosted within a deformed porphyritic granite belonging to the pre-orogenic 1.99 Ga Kierovaara suite. The minerali-zation occurs mostly as coarse-grained molybdenite flakes in boudinaged quartz veins, with minor chalcopyrite, pyrite, magnetite, and ilmenite. In this study, we report new geochemical data from the host-rock granite and Re-Os dating results of molybdenite from the mineralization. For the whole-rock geochemistry, the mineralized granite is similar to the Kierovaara suite granites analyzed in previous studies. Also, the ca. 2.0 Ga Re-Os age for molybdenite is equal, within error, to the U-Pb zircon age of the Kierovaara suite granite. In addition, similar molybdenite and uraninite ages have been reported from the Rompas-Rajapalot Au-Co occurrence located 30 km NE of Kivilompolo. We propose that the magmatism at around 2.0 Ga ago initiated the hydrothermal circulation that was responsible for the formation of the molybdenite mineralization at Kivilompolo and the primary uranium mineralization associated with the Rompas-Rajapalot Au-Co occurrence or at least, the magmas provided heating, and in addition potentially saline magmatic fluids and metals from a large, cooling magmatic-hydrothermal system.

Cogenetic Dykes the Key to Identifying Diverse Magma Batches in the Assembly of Granitic Plutons

This study demonstrates that dykes that are coeval and cogenetic with plutons can provide an important tool for recognizing discrete batches of magma with similar overall chemical compositions and physical attributes, but different isotopic characteristics, and which contributed to pluton formation. The Qianlishan granitic pluton, located in the Qin–Hang fault zone separating the Yangtze block from the Cathaysia block in South China, was emplaced at 155 Ma to 152 Ma in the Late Jurassic. It consists of a central zone of strongly differentiated zinnwaldite-bearing equigranular granite surrounded by a less differentiated porphyritic granite. The pluton is spatially associated with an extensive granitic dyke swarm dated here at 153–152 Ma, demonstrating a coeval relationship. Amongst the dykes, two discrete end-member sources can be identified from the bimodal nature of their zircon hafnium and oxygen systematics, with one group showing a range in εHf(t) of − 11.9 to − 8.0 and in δ18O of 9.0–10.4‰, whereas in the other group the ranges are from −7.3 to − 4.1 and 8.4–9.4‰, respectively. This contrasts with the two phases of the Qianlishan pluton, which record wide ranges in εHf(t) of − 11.1 to − 5.1 and in δ18O of 8.3‰ to 10.4‰, but without bimodality. Hence, the overlapping Hf–O isotopic profiling shows the dykes and pluton to be cogenetic. Small-volume magma batches, with their rapid transport through the crust and quick cooling, are all typical features of dyke generation, thus preserving the original heterogeneous Hf–O isotopic signatures that are characteristic of two distinct crustal sources. However, although the pluton was formed from similar sources to the dykes, the bimodal source identity was lost during its assembly through mixing of the magma batches. These findings also provide a potential explanation for the wide range of zircon hafnium isotopic systematics typical of granitic plutons, as shown by sampling at all scales.

Concentration Mechanisms of Rare Earth Element-Nb-Zr-Be Mineralization in the Baerzhe Deposit, Northeast China: Insights from Textural and Chemical Features of Amphibole and Rare Metal Minerals

The Early Cretaceous Baerzhe deposit in Inner Mongolia, Northeast China, hosts a world-class resource of rare earth elements (REEs), niobium, zirconium, and beryllium. In contrast to previous interpretations of the deposit as a multiphase, miaskitic alkaline granite, our observations of the relationships of various rock phases, the textural features and chemical evolution of amphibole, and the distribution of primary and secondary mineral assemblages suggest that the igneous phases evolved from a hypersolvus porphyritic granite, through a variably altered transsolvus granite, both of which are miaskitic, to a strongly altered, agpaitic, transsolvus granite that contained primary elpidite. All of these phases share a common igneous lineage. The Baerzhe deposit is characterized by five stages of rare metal mineralization, starting with the magmatic crystallization of elpidite (stage I). Elpidite was subsequently hydrothermally replaced by zircon and quartz to form pseudomorphs in stage II. Stage II is also characterized by Na metasomatism (albite and aegirine alteration of alkali feldspar and amphibole, respectively) and by snowball quartz that contains inclusions of albite, aegirine, and zircon. Sodium metasomatism, Zr mineralization, and snowball quartz are restricted to the agpaitic rocks. REEs, Nb, and Be occur as a variety of minerals that are disseminated through all the altered rocks and were precipitated in three sequential stages (stages III-V), with the formation of heavy REE-dominant phases generally preceding light REE-dominant phases. Moderate to pervasive hematization, which altered much of the transsolvus miaskitic granite and all the agpaitic granite, initiated late in stage II and accompanied most of the REE-Nb-Be mineralization in stage III. The stage-III mineralization, represented by hingganite-(Y), hingganite-(Ce), aeschynite-(Y), and columbite-(Fe), developed in two substages, with hingganite-(Y) preceding hingganite-(Ce); these REE-Nb-Be minerals are mainly contained in quartz-rich pseudomorphs (REE-Nb-Be–rich pseudomorphs) but also occur as partial replacement of earlier minerals. Stages IV and V represent a transition from F-absent assemblages that are characterized by euxenite-group minerals and monazite-(Ce) in stage IV-A, to light REE and F-rich minerals: bastnäsite-(Ce) in stage IV-B and fluocerite-(Ce) and synchysite-(Ce) in stage V. The low REE, Nb, and Be concentrations in amphibole and the fact that REE-Nb-Be assemblages never contain zircon as a constituent preclude leaching of preexisting amphibole or zirconosilicates as significant sources of REEs, Nb, or Be. Rather, these elements may have inherently been present in magmatic-hydrothermal fluids or have been leached from crystallized fluoride melts.

Petrogenesis and geodynamic setting of granitoids at Machangqing Cu–Mo (Au) deposit, western Yangtze craton, southwestern China: constraints from zircon U–Pb and molybdenite Re–Os geochronology, Lu–Hf isotopes, and geochemistry

The Machangqing Cu–Mo (Au) deposit is located in the central part of the Jinshajiang – Red River belt in the Sanjiang orogen, which lies across the Qiangtang terrane and western Yangtze craton, southwestern China. Zircon U–Pb dating constrains that the granite porphyry and porphyritic granite emplacements occurred at 35.92 ± 0.31 Ma and 34.92 ± 0.31 Ma, respectively. The Re–Os model ages of molybdenite are 34.94 ± 0.38 Ma. The new ages presented here, along with previously published data in the region, define a short duration of potassic magmatism and mineralization from 37 Ma to 34 Ma in the Jinshajiang – Red River belt. Zircon Ce4+/Ce3+ values of the porphyritic granite and granite porphyry vary from 50.32 to 1579.20 (averaging 481.01) and 33.18 to 1511.80 (averaging 452.98), respectively, and the log(fo2) values vary from –6.66 to −23.86 and −9.88 to −25.18, respectively, which plot within the range of the fayalite–magnetite–quartz buffer curve to the magnetite–hematite buffer curve, indicating an oxidized magma source, which may have facilitated the Cu–Au enrichment. Zircons from granitoids show εHf(t) values ranging from −0.75 to +2.33 and crustal model ages between 0.9 and 1.1 Ga. The features of Lu–Hf isotopes and wide range of Mg#, Cr, and Ni contents imply that the magmas of the Machangqing granitoids were probably derived from partial melting of juvenile lower crust and mixed with some mantle melts. Combined with the features of the Machangqing granitoids, the following evolution process are concluded. During the Cenozoic, the India–Asia continental collision triggered upwelling of hot asthenosphere and underplating of the thickened juvenile lower crust, which caused the formation of mafic and felsic magmas. Those magmas ascended, mixed, crystallized, and formed Machangqing ore-bearing granitoids in an intracontinental extension setting.

Petrogenesis of the post-collisional porphyritic granitoids from Jhalida, Chhotanagpur Gneissic Complex, eastern India

The Jhalida porphyritic granitoid pluton is exposed in a regional shear zone belonging to the Chhotanagpur Gneissic Complex of the Satpura Orogen (c. 1.0 Ga), regarded as the collisional suture between the South and North Indian blocks. The pluton intruded the migmatitic gneisses, metapelites, calc-silicate rocks and amphibolites belonging to the amphibolite facies. The mineral assemblage indicates the calc-alkaline nature of the granitoids. Mafic (Pl–Qz–Bt±Hbl) schists occur as xenoliths within the pluton. The granitoids are classified as alkali-calcic to alkalic, dominantly magnesian grading to ferroan, metaluminous to slightly peraluminous, and shoshonitic to ultrapotassic. Geochemically, the granitoids are enriched in large-ion lithophile elements (LILE), particularly K, and light rare earth elements (LREE), but are comparatively depleted in Nb, Ta, and heavy rare earth elements (HREE). The strong negative correlation between SiO2 and P2O5, metaluminous to weakly peraluminous character, high liquidus temperature (798–891°C) and high fO2 (ΔQFM +0.8 to +1.6) of the melt suggest their I-type nature. Field relations and tectonic discrimination diagrams imply their post-collisional emplacement. Low Nb/U (average 8.5), Ce/Pb (average 9.0), and Al2O3/(Al2O3 + FeO(t) + MgO + TiO2) ratios and relatively low Mg number (average 0.15) of these granitoids indicate a crustal mafic source. Batch melting (at 825–950°C) of 10–20% of an old, incompatible elements-rich high-K high-alumina hornblende granulite can generate the porphyritic granite melt. The heat source for melting was an upwelling of the asthenospheric mantle in the post-collisional set-up. Textural and chemical characteristics of the mafic xenoliths show that invading porphyritic granitoid magma metasomatized the amphibolite protoliths.