Monzogranite Intrusions Research Articles

Geochronology, Geochemistry, and Lu-Hf Isotopic Compositions of Monzogranite Intrusion from the Chang’anpu Mo Deposit, NE China: Implications for Tectonic Setting and Mineralization

The Chang’anpu Molybdenum deposit occurs in the monzogranite intrusions in the Lesser Khingan Mountains-Zhangguangcai Mountains metallogenic belt. Previous work focused on the study of deposits, including geological characteristics, mineralization time, S-Pb isotope, etc. However, systematic petrogeochemical study of monzogranite intrusion and comparative analysis with other porphyry deposits in the region are lacking. Three monzogranite dating samples yield LA-ICP-MS zircon weighted mean 206Pb/238U ages of 174.7 ± 1.3 Ma, 174.9 ± 1.4 Ma, and 174.3 ± 1.8 Ma, respectively, indicating that the magmatism occurred in the middle Jurassic of Mesozoic. The 14 monzogranite samples show alkali rich and relatively high silica content (up to 84.39%) with the differentiation index (DI) ranges from 86 to 96, showing that monzogranite have been subjected to fractional crystallization during its evolution; the depletion of Ba, Sr, P, Nb, Ti, and Eu also indicates that the rock has undergone crystallization fractionation, the monzogranite belong to the highly fractionated I-type. Positive εHf(t) values (6.72–8.85) and young TDM2 (551–673 Ma) of the monzogranite indicate that the formation of Chang’anpu monzogranite intrusion is related to the partial melting of juvenile lower crust, originated from the Mesoproterozoic depleted mantle. The magmatism and related Mo mineralization in the Chang’anpu deposit occurred in an active continental margin setting associated with westward subduction of the Paleo-Pacific plate beneath the Eurasian plate.

Zircon U–Pb age, whole-rock geochemistry and Nd–Sr–Pb isotope constraints on petrogenesis of the Eocene Zajkan gabbro–monzogranite intrusion, Tarom-Hashtjin magmatic belt, NW Iran

The late Eocene high-K to shoshonitic Zajkan intrusion, situated in the Tarom-Hashtjin magmatic belt (THMB), NW Iran, ranges in composition from gabbro to pyroxene quartz monzodiorite, pyroxene quartz monzonite and monzogranite, and is classified as an I-type metaluminous granitoid. On the primitive mantle-normalised spider diagram, these rocks demonstrate negative high field strength element (HFSE) anomalies, large-ion lithophile element (LILE) enrichment, and positive Pb anomaly, indicating a subduction-related signature. Furthermore, the granitoids are characterised by coherent chondrite-normalised rare earth element patterns with high light rare earth elements/heavy rare earth elements (LREE/HREE) and moderate to weakly negative Eu anomalies (Eu/Eu* = 0.6–0.86). LA-ICP-MS zircon U–Pb dating demonstrates that the Zajkan intrusion crystallised at ca 36.5 Ma. Relatively low to moderate 87Sr/86Sr ratios (0.7046–0.7061) and positive εNd(t) values (1.52–1.88) of the Zajkan samples are consistent with an enriched lithospheric mantle source that was metasomatised by an earlier subducted slab. Geochemical features show that the parental magma of the Zajkan intrusion likely resulted from a partial melting of metasomatised amphibole-bearing mantle source. Sr–Nd isotope modelling is consistent with the Zajkan intrusion formed from a mix of ∼80% of a mantle-derived magma and ∼20% of a juvenile lower crustal-derived magma. Partial melting of the metasomatised mantle may have resulted from late Eocene lithospheric thinning and hot asthenospheric upwelling through slab roll-back or lithospheric delamination. KEY POINTS The late Eocene high-K to shoshonitic Zajkan intrusion is located within the Tarom-Hashtjin magmatic belt, NW Iran. U–Pb zircon dating revealed an age of ca 36.5 Ma for emplacement of the Zajkan intrusion. Sr–Nd isotope modelling is consistent with the Zajkan intrusion formed from a mix of ∼80% of mantle-derived magma and ∼20% of juvenile lower crustal-derived magma.

Metallogeny of the continental collision-related Jiagang W-Mo deposit, Tibet: Evidence from geochronology and petrogenesis

The Jiagang W-Mo deposit is the first greisen-type tungsten deposit recognized in the Lhasa terrane, and thus it has important genetic implications for understanding the regional tungsten mineralization potential. Greisen-type orebodies dominate in the deposit. Ores characterized by veinlets and dissemination are located in intensively altered monzogranite and contact zones between the monzogranites and sedimentary rocks. The minor quartz vein-type orebodies occuring as large quartz veins mainly precipitated in the sedimentary rocks. Intrusions associated with the Jiagang deposit are monzogranites, which can be subdivided into medium-grained monzogranite (MMG), porphyritic monzogranite (PMG), and fine-grained monzogranite (FMG). The zircon U-Pb ages of the PMG and MMG are 18.2 ± 0.2 Ma and 18.6 ± 0.1 Ma, respectively. These ages are consistent with the muscovite 40Ar-39Ar plateau ages (18.7 ± 0.2 Ma, 18.5 ± 0.2 Ma) and the molybdenite Re-Os isochron age (19.0 ± 0.3 Ma) within errors, indicating that the Jiagang W-Mo mineralization took place during the post-collisional stage of the Indo-Asian continental collision. The mineralization is temporally, spatially and genetically associated with the monzogranitic intrusions. The FMGs have the lowest SiO2 contents (70.8–71.5 wt%), lowest differentiation index (DI = 85.7–86.3) and least obviously negative Eu anomalies (Eu/Eu* = 0.22–0.42). The PMGs and MMGs have higher SiO2 contents (72.6–76.3 wt%), higher differentiation index (DI = 89.3–92.7) and more negative Eu anomalies (Eu/Eu* = 0.11–0.24). Almost all of the rocks are strongly peraluminous (A/CNK = 1.02–1.29), enriched in LILEs and depleted in HFSEs. Concentrations of K2O, CaO, FeOT and TiO2 of the three types of monzogranites show negative correlations with SiO2, while P2O5 exhibits the opposite trend. Values of Nb/Ta decrease with SiO2 contents, and those of (La/Yb)N increase with La contents. Whole rock εNd(t) of the FMGs range from −11.3 to −11.1 with two-stage Nd isotopic model ages (TDM2) of 1741–1797 Ma, which are similar to those of the PMGs and MMGs (εNd(t) = −10.9– −10.6; TDM2 = 1709–1816 Ma). Zircon εHf(t) values of the PMG and MMG range from −13.8 to −5.3 with two-stage Hf isotopic model ages of 1439–1979 Ma. These data suggest that the ore-forming monzogranites are strongly peraluminous S-type granites, which should be derived from anatexis of the Proterozoic metagreywackes underneath the central Lhasa subterrane. The PMG and MMG are highly fractionated through various degrees of fractional crystallization of plagioclase, K-feldspar, biotite, monazite and allanite from the parental melts represented by the FMG. Zircon trace elements suggest that oxygen fugacity of the ore-forming magmas is relatively low and decreased as the magmas evolved, which is favorable to remove substantial tungsten from melts into the tungsten-mineralizing hydrothermal fluids. A high degree of fractional crystallization of the crustally-derived magmas with relatively low magmatic oxidation state are the critical factors determining the generation of the tungsten mineralization in the Jiagang deposit. Combined with the existing breakthroughs in prospecting exploration, we propose that the central Lhasa subterrane has great metallogenic potential in W-(Mo) mineralization associated with the Indo-Asian continental collision.

Integrated ophiolite and arc evolution, southern Brasiliano Orogen

Integrated study of Tonian ophiolite mélanges and intra-oceanic arc of the São Gabriel juvenile terrane exposes a key geotectonic unit in the evolutionary history of Gondwana during Brasiliano Orogeny. LA-ICP-MS U-Pb geochronology in rutile and zircon were combined with Lu-Hf and rare earth elements in zircon. We report the first rutile dating of ultramafic rock in the Brazilian Shield of 787.6 ± 2.6 Ma for the Cambaizinho ophiolite magnesian schist. Dating of rutile corresponds to the metamorphic age of the mantle section of the ophiolite. São Gabriel arc infrastructure is represented by the Cambaí Complex, including the Vila Nova Suite metatonalite with zircon U-Pb age of 724.6 ± 3.2 Ma and late Sanga do Jobim Suite monzogranite intrusions with two main pulses at 698.9 ± 4.2 Ma and 673.9 ± 6.8 Ma. Zircon εHf(t) values are positive for both rocks and range between +10.1 and +7.4 in metatonalite and +9.2 to +2.5 in monzogranite. Detrital zircon from metasedimentary rocks support superstructure arc investigation. Ages range from 817 to 650 Ma, with strong concentration between 750 and 730 Ma. Positive εHf(t) values and Rare Earth Elements (REE) signature point to main source of metasedimentary rocks in the arc, with ophiolitic contribution. Therefore, geotectonic processes in the Brasiliano Orogeny include the construction of São Gabriel terrane with Tonian oceanic crust evolving to intra-oceanic subduction until 650 Ma to final development along the margin of continental crust. Overthrusting of the São Gabriel terrane onto the Rio de La Plata Craton occurred at 650–620 Ma. Our data correlate with Tonian intra-oceanic arcs from Brasilia belt (Goiás arc ca. 862–630 Ma) and Ribeira belt (Serra da Prata arc – 856–838 Ma; Rio Negro arc – 790–620 Ma). Oceanic crust generation combined with subduction to form Tonian arcs along the Brasiliano Orogen were most significant for construction of West Gondwana.

Precambrian basement rocks of Wadi-Khuda-Shut area, South Eastern Desert of Egypt: Geology and remote sensing analysis

Wadi Khuda-Wadi Shut area in the South Eastern Desert (SED) of Egypt is mainly made up of gneisses, ophiolitic serpentinites and intermediate schistose metavolcanics. These metamorphic rock units are intruded by syn-late-tectonic diorite, granodiorite, ultramafic-mafic, and monzogranite intrusions. The gneisses comprise biotite hornblende gneiss, hornblende gneiss and migmatites. They are of granodiorite and diorite composition. The ophiolitic serpentinite with talc carbonate rocks were thrusted over the metavolcanics with NW-SE thrust contact. The late tectonic ultramafic-mafic rock units are represented in the study area by Dahanib pluton, which is consisted of layered peridotite-dunite associated with olivine gabrro, normal gabbro and gabbro-norite as well as rare hornblende gabbro. These varieties are related to the layered intrusions rather than Alaskan-types, and formed by magmatic differentiation. The granodiorite and monzogranite represent the youngest basement rock units in the study area. The principal components and band ratios of ASTER and Landsat-8 data were successfully used for the first time in lithological discrimination and geological mapping of the study area. This study concluded that, the interpreted data of ASTER and Landsat-8 combined with field study and petrographic investigation clearly discriminated the exposed rock units. Accordingly, a detailed geological map emphasizing the lithological units in Khuda-Shut area has been presented.

Albian–Cenomanian A-type granite-related Ag–Pb–Zn veins in the central Yidun Terrane, SW China: constraints from the Xiasai deposit

The Xiasai–Lianlong metallogenic belt in the central Yidun Terrane (China) hosts several Sn–Ag and (Sn–) Ag–Pb–Zn deposits, which are spatially associated with Cretaceous granites. The Xiasai Ag–Pb–Zn deposit (about 0.27 Mt Pb+Zn, 1028 t Ag, and 20,000 t Sn) is the largest deposit in the belt and is related to a monzogranite intrusion. The deposit consists of sulfides in hydrothermal veins, resulting from three successive mineralization stages (I–III). A Rb–Sr isochron of sphalerite samples yielded an age of 99 ± 3 Ma, and zircon U–Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) dating of the Xiasai monzogranite gave ages between 102 ± 1 and 101 ± 1 Ma. The Xiasai monzogranite has a weakly peraluminous A-type granite composition, with high SiO2, alkali, and FeOt contents and low CaO, MgO, and TiO2 contents. It is marked by enrichments in Rb, Th, and U, with depletions in Ba, Nb, Sr, P, and Ti relative to the primitive mantle. The REE patterns show a negative slope due to LREE enrichment with negative Eu anomalies (Eu/Eu* = 0.1–0.3). The Xiasai monzogranite, with variable eHf(t) values (− 2.7 to 0.6) and Meso- to Neoproterozoic two-stages Hf model ages (TDM2 = 925–1095 Ma), was probably derived from mixing of melts derived from partial melting of the Paleoproterozoic crustal basement and the Early Cretaceous mantle in an extensional tectonic setting. Hydrothermal fluids are characterized by high temperatures (423–481 °C) and salinities (14.9–19.0 wt% NaCl) for Sn mineralization (stage I), moderate temperatures (285–386 °C) and salinities (3.5–8.0 wt% NaCl) for the Cu–Zn mineralization (substage II-2), and low temperatures (158–242 °C) and salinities (3.4–5.7 wt% NaCl) for the Ag–Pb mineralization (substage II-3). The H–O isotopes indicate that the hydrothermal fluid likely has a magmatic component that mixed over time with infiltrating meteoric water and organic matter during fluid–rock interactions. The δ34S values of sphalerite range from − 9.7 to − 3.1‰ and those from galena from − 10.5 to − 4.9‰. The estimated δ34S value of the hydrothermal fluid is − 8.5‰, using the sulfur isotopic fractionation of sphalerite–galena pairs that are interpreted to be in equilibrium. Sulfides from substages II-2 and II-3 have relatively homogeneous Pb isotopic compositions, which are similar with those of K-feldspars from the Xiasai monzogranite. Geochronological and isotope data support a magmatic–hydrothermal origin for the Xiasai Ag–Pb–Zn deposit.

Origin of cordierite-bearing monzogranites from the southern Central Iberian Zone – Inferences from the zoned Sierra Bermeja Pluton (Extremadura, Spain)

Voluminous peraluminous (biotite, biotite–cordierite and cordierite–muscovite-bearing) granitic plutons were emplaced in the southern part of the Central Iberian Zone (Iberian Massif) during the waning stages of the Variscan Orogeny. The role of the mantle and the nature of the crustal sources involved in the generation of these remarkable granites are still a matter of discussion. To address these issues, a detailed study of the Sierra Bermeja Pluton, a ~60 km2 cordierite-bearing monzogranite intrusion representative of the regional Nisa–Alburquerque–Los Pedroches Magmatic Alignment, has been carried out. This pluton was formed by an inward sequence of three distinct but near contemporaneous magma pulses: Outer Unit (OU), Middle Unit (MU) and Inner Unit (IU). The nested pluton is cut by a number of syn-plutonic vaugneritic dykes, while lamprophyres were distinctly later.The age of the Pluton has been established at ca. 306 Ma (309 ± 3 to 304 ± 3 Ma) by LA-ICP-MS U–Pb dating of zircon and monazite. The peraluminosity (A/CNK = 1.01–1.33) and P2O5 contents (0.19–0.35 wt%) of the monzogranitic units increase inwards (OU → MU → IU). This is accompanied by an overall decrease in TiO2, MgO, CaO, and FeOt, and most trace-elements, including REE. The three units display similarly low 87Sr/86Sr306Ma ratios (0.7033–0.7046) but decreasing εNd306Ma (OU: ~ −2.7, MU: ~ −3.8, IU: −7.5 to −4.7). Vaugneritic rocks have homogeneous composition with similar 87Sr/86Sr306Ma ratios (~0.7043) to those of the monzogranites but higher εNd306Ma (~ +1.1) values. Whole-rock geochemical data imply a partial melting of mainly Cambro–Ordovician felsic metaigneous rocks (OU) with increasing proportion of Neoproterozoic–Lower Cambrian metasediments of the Schist–Greywacke Complex (MU) that formed, almost exclusively, the source of the IU. Thermobarometric data suggest that melting processes progressed upward through the geological record and magma emplacement took place at <3 kbar, with crystallization temperatures of 710–810 °C. Geochemical modelling implies that each monzogranitic unit could have evolved independently at the emplacement level by a 20–26% fractional crystallization of a mineral assemblage constituted by Kfs + Pl > Bt >> Ap + Mnz + Xtm. The present results could be extensible to other cordierite-bearing granites of the southern Central Iberian Zone although forthcoming experimental work and detailed comparisons are required to confirm such extrapolation.

The composite Sierra Bermeja Pluton (southern Iberian Massif): science, heritage and geoconservation

ABSTRACT The Sierra Bermeja Pluton (∼60 km2 surface area) exemplifies a type of controversial granites of the Iberian Massif (European Variscan Belt), the cordierite-bearing ‘Serie Mixta’ (mixed series) monzogranites. The pluton is included almost completely in the Cornalvo Natural Park (Badajoz, Spain), a relevant target area in Roman times. The geological mapping summarised in the presented map at 1:10,000 scale has revealed a complex intrusive assemblage. Three main cordierite-bearing monzogranite types that show local varieties constitute most of the massif. Monzogranite intrusions are younger towards the centre of the pluton and gave rise to outstanding mappable mingling/mixing zones in some areas. A NE–SW trending reduced dyke complex composed by vaugnerite series rocks, lamprophyres, aplites and quartz dykes, completes the lithological assemblage of the pluton. An inventory of Geologic Points of Interest to promote the geological knowledge of this remarkable protected area and its geoconservation is also presented.

Granite-related Yangjiashan tungsten deposit, southern China

The Yangjiashan scheelite-bearing deposit (38,663 metric tons of WO3 with an average ore grade of 0.70% WO3) is hosted in quartz veins in a biotite monzogranite intrusion and surrounding slate in the Xiangzhong Metallogenic Province of southern China. The monzogranite has a zircon SHRIMP U–Pb age of 406.6 ± 2.8 Ma (2σ, n = 20, MSWD = 1.4). Cassiterite coexisting with scheelite yields a weighted mean 206Pb/238U age of 409.8 ± 5.9 Ma (2σ, n = 30, MSWD = 0.20), and molybdenite intergrown with scheelite yields a weighted mean Re–Os age of 404.2 ± 3.2 Ma (2σ, n = 3, MSWD = 0.10). These results suggest that the Yangjiashan tungsten deposit is temporally related to the Devonian intrusion. The δD and calculated δ18OH2O values of quartz intergrown with scheelite range from − 87 to − 68‰, and − 1.2 to 3.4‰, respectively. Sulfides have a narrow range of δ34S values of − 2.9 to − 0.7‰ with an average value of − 1.6‰ (n = 16). The integration of geological, stable isotope, and geochronological data, combined with the quartz–muscovite greisen style of ore, supports a magmatic–hydrothermal origin for the tungsten mineralization. Compared to the more common tungsten skarn, quartz–wolframite vein, and porphyry tungsten deposits, as well as orogenic gold deposits worldwide, the Yangjiashan tungsten deposit is an unusual example of a granite-related, gold-poor, scheelite-bearing quartz vein type of deposit. The calcium needed for the formation of scheelite is derived from the sericitization of calcic plagioclase in the monzogranite and Ca-bearing psammitic country rocks, and the relatively high pH, reduced and Ca-rich mineralizing fluid may be the main reasons for the formation of scheelite rather than wolframite at Yangjiashan.

Controls on different mineralization styles of the Dongbulage Mo and Taibudai Cu-(Mo) porphyry deposits in the Great Xing’an Range, NE China

The Dongbulage porphyry Mo-dominant and Taibudai Cu-(Mo) deposits are located in the central–southern Great Xing’an Range, Inner Mongolia, northeastern China, and are associated with granite porphyry and monzogranite intrusions, respectively. Re–Os isotope data for five molybdenite samples from the Dongbulage Mo deposit give a weighted mean model age of 164.3 ± 1.2 Ma, which is in accordance with a zircon U–Pb age of 164.5 ± 1.7 Ma for the host granite porphyry, indicating that the deposit formed at the end of the Middle Jurassic. The zircon U–Pb age of the Taibudai ore-bearing monzogranite is 137.9 ± 1.7 Ma, indicating that the deposit formed in the Early Cretaceous.Whole-rock geochemical data indicate that the Dongbulage granite porphyry and the Taibudai monzogranite are high-K calc-alkaline, and have REE patterned light rare earth elements (LREEs) enriched and heavy rare earth elements (HREEs) depleted. Both plutons show Ba, Nb, and Ti depletions on normalized trace element diagrams, and the Dongbulage granite porphyry shows strongly negative Eu anomalies which are absent in the Taibudai intrusion. The geochemical differences between the two intrusions suggest that the Dongbulage granite porphyry is the result of more advanced fractional crystallization, which led to the formation of a Mo-dominant deposit, whereas the lesser degree of crystal fractionation in the Taibudai monzogranitic magma resulted in the formation of a Cu deposit. The relatively listric-shaped REE patterns of Taibudai rocks suggest more hydrous parental magmas than that of Dongbulage rocks. Therefore, fractional crystallization and magma water content exert a significant control on the styles of mineralization (Mo- versus Cu-dominant) in the central–southern Great Xing’an Range.

Genesis of the Wurinitu W-Mo deposit, Inner Mongolia, northeast China: Constraints from geology, fluid inclusions and isotope systematics

The Wurinitu W–Mo deposit is located in the Erlian-East Ujimqin metallogenic belt in the Great Xing’an Range, NE China. Tungsten and molybdenum mineralization generally occurs as veins in quartz hosted by the Middle to Lower Ordovician wall rocks or as disseminations in the Early Cretaceous monzogranite intrusions. Fluid inclusion studies and multiple isotope analyses, provide systematic evidence to determine the evolution of the hydrothermal fluids, the source of metals and fluids, as well as mineral precipitation mechanisms, which are significant for the magmatic-hydrothermal system but are poorly understood. Three types of fluid inclusion assemblages (FIAs), including L (liquid-rich two-phase FIAs), V (vapor-rich two-phase FIAs), and L-V (liquid–vapor two-phase FIAs), have been identified in quartz veins from the W-mineralization (I), Mo-mineralization (II), and quartz – carbonate (III) stages at Wurinitu. The ore-forming fluids evolved from a high- to moderate-temperature and moderate- to low-salinity H2O–NaCl ± CO2 system in the W- and Mo- mineralization stages to a low-temperature and low-salinity H2O–NaCl system in the quartz-carbonate stage; they were trapped at temperatures of ∼365 °C, ∼266 °C, and ∼198 °C. The results of hydrogen and oxygen isotope analyses (δ18OH2O = −4.0 to +7.7‰; δDH2O = −116 to −92‰) indicate that the stage I fluids dominantly originated from magmatic water, and the stages II and III show addition of meteoric water. Sulfur (δ34SVCDT = 1.9–4.0‰) and lead isotope values (206Pb/204Pb = 18.099–18.728, 207Pb/204Pb = 15.527–15.616, and 208Pb/204Pb = 38.019–38.465) suggest that the ore metals in the hydrothermal fluids were derived from the granitic magma. All these observations reveal that (1) the Wurinitu W–Mo deposit is a magmatic-hydrothermal ore system, (2) W- and Mo- mineralization occurred under lithostatic pressure of 203–294 bars, and hydrostatic pressure of ∼102 bars, respectively, and (3) fluid boiling and mixing with meteoric water might be the key factors controlling the large-scale ore deposition at Wurinitu.

Granitoid-associated gold mineralization in Egypt: a case study from the Atalla mine

Gold-bearing sulfide-quartz veins cutting mainly through the Atalla monzogranite intrusion in the Eastern Desert of Egypt are controlled by subparallel NE-trending brittle shear zones. These veins are associated with pervasive sericite-altered, silicified, and ferruginated rocks. The hosting shear zones are presumed as high-order structures of the Najd-style faults in the Central Eastern Desert (~ 615–585 Ma). Ore minerals include an early pyrite-arsenopyrite (±pyrrhotite) mineralization, partly replaced by a late pyrite-galena-sphalerite-chalcopyrite (±gold/electrum ± tetrahedrite ± hessite) assemblage. Gold occurs as small inclusions in pyrite and arsenopyrite, or more commonly as intergrowths with galena and sphalerite/tetrahedrite in microfractures. Arsenopyrite geothermometry suggests formation of the early Fe-As-sulfide mineralization at 380–340 °C, while conditions of deposition of the late base metal-gold assemblage are assumed to be below 300 °C. Rare hessite, electrum, and Bi-galena are associated with sphalerite and gold in the late assemblage. The early and late sulfide minerals show consistently a narrow range of δ34S ‰ (3.4–6.5) that overlaps with sulfur isotopic values in ophiolitic rocks. The Au-quartz veins are characterized by abundant CO2 and H2O ± CO2 ± NaCl inclusions, where three-dimensional clusters of inclusions show variable aqueous/carbonic proportions and broad range of total (bimodal) homogenization temperatures. Heterogeneous entrapment of immiscible fluids is interpreted to be caused by unmixing of an originally homogenous, low salinity (~ 2 eq. mass % NaCl) aqueous-carbonic fluid, during transition from lithostatic to hydrostatic conditions. Gold deposition occurred generally under mesothermal conditions, i.e., 1.3 kbar and ~ 280 °C, and continued during system cooling to < 200 °C and pressure decrease to ~ 0.1 kbar. Based on the vein textures, sulfur isotope values, composition of ore fluids, and conditions of ore formation, we suggest that the Atalla monzogranite intrusion acted only as a competent structural host for ore deposition from shear-related, metal-rich fluids migrated up from depth. This model is also presumed for most granitoid-associated Au deposits in the region, considering the similarity in their structural control, alteration pattern and mineralogy, and chemistry of the ore fluids.

Geology, geochronology, geochemical characteristics and origin of Baomai porphyry Cu (Mo) deposit, Yulong Belt, Tibet

The Baomai porphyry Cu-Mo deposit is a newly discovered deposit located in the northern section of the Yulong porphyry Cu belt, eastern Tibet. It is associated with Eocene biotite monzogranite intrusions that were emplaced into Paleoproterozoic Ningduo Group and Middle-Upper Triassic sedimentary rocks. A biotite monzogranite porphyry with a zircon U-Pb age of 42.7 Ma was intruded by several post-ore diorite porphyry dikes (ca. 37.8 Ma). Alteration mineral assemblages consistent with argillic, phyllic, and hornfels were identified in ore-bearing porphyries and host rocks at Baomai. Argillic and phyllic alteration assemblages are spatially related to high-grade Cu and Mo mineralization, whereas hornfels alteration is accompanied by weak Cu mineralization. Molybdenite from the mineralized porphyry returned a Re-Os isochron age of 42.6 Ma, and is considered to represent the age of porphyry-style mineralization at the deposit. Ore-bearing porphyries in Baomai are high-K (K2O/Na2O >1), alkaline-rich intrusions rich in LREE, LILE (e.g., Rb, U, K), depleted in HFSE (e.g., Nb, Ta, P and Ti) and contain absent or slightly negative Eu anomalies and no significant Ce anomalies. Slightly high 87Sr/86Sr ratios (0.7064–0.7076), low εNd(t) values (−2.5 to −4.6), uniform (206Pb/204Pb)i ratios (18.70–18.75) and positive εHf(t) values (0–5.3) of ore-bearing porphyries at Baomai indicate that they share the same or similar petrogenesis to other mineralized porphyries within the Yulong porphyry Cu belt. The porphyries were likely generated from partial melting of phlogopite-bearing amphibolite or amphibolite eclogite with a low degree of crystal fractionation, and related to enrichment mantle (EMII) transformed or mixed by older subducted slab-derived fluid. Actually, there are no significant three stages of ore-bearing magmatic activities in Yulong porphyry Copper belt (Hou et al., 2003b), Eocene intrusions (37–43 Ma) and regional strike slip faulting were all important factors in controlling the formation of these Cu-polymetallic deposits during the Eocene India-Tibetan collision.

Environmental issues of the Island of Giglio, Tuscan Archipelago, Italy

The Island of Giglio consists of the lower Pliocene monzogranite intrusion (91.5% of the territory) and Mesozoic–lower Miocene metamorphic and sedimentary tectonic units (8.5% of the territory) of the Ligurian-Piemontese and Tuscan domains in the Franco Promontory. Climatic data recorded from 1993 to 2015 highlight that the average annual temperature and rainfall have increased overall. The main morphological characteristics of the island are: (1) the landslides that affect either the geological formations, above all along the coastal belt, in particular in the Franco Promontory, or the widespread eluvium–colluvium deposits and numerous piles of rock blocks originating from the monzogranite intrusion; (2) the several torrents that cut across the monzogranite intrusion with high gradients resulting in considerable erosion. The island, which includes some very small perennial springs, is covered mainly by short brush and garrigue and subordinately by forests. Six environmental issues have been detected: the high geomorphological and hydraulic risk, respectively, along the coastline, and in the urban areas of Cala delle Cannelle, Giglio Campese, and Giglio Porto; the abandoned quarries showing unstable fronts; the landfill of municipal solid waste, lacking remediation aimed at its safety; the protection and set up of the perennial springs; the safety of paths; and the mining of pyrite started in 1875 until the closure of works in 1962. Suitable suggestions to solve the environmental issues are provided.

Lithostratigraphy of the Friersdale Charnockite (Keimoes Suite), South Africa

The Friersdale Charnockite is a late-Mesoproterozoic (1078 ± 10 Ma), fine- to medium-grained to porphyritic orthopyroxene-bearing monzogranite intrusion with characteristic opalescent quartz that outcrops in the Keimoes-Upington region of the Northern Cape, South Africa. The weakly to undeformed, northwest-southeast trending granitoid body represents the most extensive member of the Keimoes Suite and intruded across the tectonic boundary between the granulite facies Kakamas and Areachap Terranes of the Namaqua-Natal Metamorphic Province during the final stages of the main Namaqua orogeny. The Friersdale Charnockite is a metaluminous, ferrous and potassic monzogranite with major, trace, REE and isotope chemistries suggesting a mixed crustal source with significant input from both Paleoproterozoic- and Mesoproterozoic-aged source regions.

Tin–rare-earth element greisens of the Solnechnoe cassiterite–silicate deposit, Russian Far East

The paper considers for the first time the morphology, composition, and conditions of formation of the greisens of the Solnechnoe deposit (Komsomol’sk ore district), a typical cassiterite–silicate assemblage. The greisens are localized in the root parts of the deposit and represent a system of veins and veinlets formed in the contraction fractures of the metasomatically altered roof of the monzogranite intrusion (age of 94–92 Ma). The cassiterite–chlorite–carbonate–muscovite–quartz composition of the greisens with admixture of topaz, fluorite, and apatite reflects the composition of the monzogranites. The greisens are close in age (85.3 Ma on muscovite) to the granitic aplites (80–85 Ma on the whole-rock and biotite) of the final phase of the intrusive magmatism. The fluid regime of their formation differs from that of the economic ores in higher temperature, pressure, and salinity. One distinguishing feature of the greisens is elevated contents of LREE, U, and Th, which are incorporated in the REE fluorcarbonates, thorite, and uranothorite crystallizing together with cassiterite.

Geochronology and lithostratigraphy of the Siguiri district: Implications for gold mineralisation in the Siguiri Basin (Guinea, West Africa)

Geochronology and lithostratigraphic characterisation of the Siguiri district in the Palaeoproterozoic Birimian terrane of West Africa has provided a reappraisal of the Siguiri Basin stratigraphy. This new insight into the evolution of the central part of the basin further highlights first order controls on the location of the world class Siguiri orogenic gold district. Three metasedimentary formations occur in the Siguiri district: the Balato, Fatoya and Kintinian formations. These formations consist of fine-grained organic-rich shales, mudstone and siltstone/greywacke/limestone interbeds, decimetre- to metre-thick graded greywacke beds and debris flow deposits. The Balato Formation displays low-energy, hemipelagic marine or lake sediments, whereas the Fatoya Formation consists of distal turbidite deposits (thin-bedded turbidites and channel-fill deposits). Altogether they form a basal regressive sequence. The overlying Kintinian Formation is shale-rich, and contains a stack of polymict conglomeratic interbeds (up to 100m in thickness) around the base of the Formation in the Siguiri district. This conglomerate unit transects the whole Siguiri Basin and is interpreted to be the product of repeated subaqueous debris flow deposits and represent olistostromes (or mélanges of sedimentary origin) with various autochthonous and allochthonous clasts. The youngest detrital zircon age population for each of the Balato, Fatoya and Kintinian formations yields ages of 2113±10Ma, 2113±5Ma and 2124±7Ma respectively, thus constraining the maximum age of deposition for each of these formations. The minimum age of deposition of these sedimentary rocks is constrained by a crosscutting volcanic breccia dated at 2092±5Ma, and by the Maléa monzogranite intrusion dated at 2089±12Ma. Comparison of the sedimentary facies and geochronology of the Siguiri sedimentary rocks with other sedimentary basins in the West African Craton, suggests that the Kintinian Formation is part of the Lower Tarkwa Group, best described as “late orogenic basin” sediments. The Kintinian olistostromes are inferred to highlight the onset of renewed tectonic activity associated with the first phases of compression during the Eburnean Orogeny in the Siguiri Basin at ca. 2115Ma. The peculiar morphology of these olistostromes compared to the bulk of the Siguiri Basin sedimentary rocks, illustrates a major change in lithofacies. This change is interpreted to have developed along fundamental basement structures, controlling the early architecture of the Siguiri Basin as well as the location of world-class gold mineralisation in the Siguiri district. These fundamental structures are thought to have acted as first order fluid pathways during the E-W progressive compressional event responsible for orogenic gold mineralisation in the Siguiri district.

Geochronology, geochemistry, and geological implications of late Carboniferous – early Permian mafic and felsic intrusive rocks from Urad Zhongqi, western Inner Mongolia

AbstractThe mafic and felsic Haertaolegai intrusions crop out in Urad Zhongqi, western Inner Mongolia and are dominated by monzogranite, porphyritic granite, and gabbroic diorite intrusions. We investigate the tectonic setting, geochronology, and anorogenic characteristics of the western Inner Mongolia through field investigation, microscopic and geochemical analyses of samples from the Haertaolegai bimodal intrusions and laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) zircon U–Pb dating of gabbroic diorite and adakitic granites. Petrographic and geochemical studies of the bimodal intrusions indicate that the gabbroic diorites formed from a primary magma generated by the partial melting of lithospheric mantle material that had previously been modified by subduction-related fluids. The felsic rocks are high-K calc-alkaline and metaluminous, have characteristics of adakitic rocks and were generated during the partial melting of juvenile crustal material. Zircon U–Pb dating indicates that the felsic portion of this pluton was emplaced during late Carboniferous – early Permian time, with the mafic portion of the pluton emplaced during early Permian time. The zircons of adamellites have ɛHf(t) values andTDM2ages of +1.0 to +2.7 and 1032–1128 Ma, respectively, suggesting that they formed from magmas generated by partial melting of juvenile Mesoproterozoic lower crust. These data, combined with the geology of the region, indicate that the late Carboniferous – early Permian bimodal intrusive rocks in western Inner Mongolia record a transitional period from collisional compression to post-collisional extension. These results indicate that the Paleo-Asian Ocean in western Inner Mongolia closed before 300 Ma.

Geochemistry and petrogenesis of Mashhad granitoids: An insight into the geodynamic history of the Paleo-Tethys in northeast of Iran

Mashhad granitoids in northeast Iran are part of the so-called Silk Road arc that extended for 8300km along the entire southern margin of Eurasia from North China to Europe and formed as the result of a north-dipping subduction of the Paleo-Tethys. The exact timing of the final coalescence of the Iran and Turan plates in the Silk Road arc is poorly constrained and thus the study of the Mashhad granitoids provides valuable information on the geodynamic history of the Paleo-Tethys. Three distinct granitoid suites are developed in space and time (ca. 217–200Ma) during evolution of the Paleo-Tethys in the Mashhad area. They are: 1) the quartz diorite–tonalite–granodiorite, 2) the granodiorite, and 3) the monzogranite. Quartz diorite–tonalite–granodiorite stock from Dehnow–Vakilabad (217±4–215±4Ma) intruded the pre-Late Triassic metamorphosed rocks. Large granodiorite and monzogranite intrusions, comprising the Mashhad batholith, were emplaced at 212±5.2Ma and 199.8±3.7Ma, respectively. The high initial 87Sr/86Sr ratios (0.708042–0.708368), low initial 143Nd/144Nd ratios (0.512044–0.51078) and low εNd(t) values (−5.5 to −6.1) of quartz diorite–tonalite–granodiorite stock along with its metaluminous to mildly peraluminous character (Al2O3/(CaO+Na2O+K2O) Mol.=0.94–1.15) is consistent with geochemical features of I-type granitoid magma. This magma was derived from a mafic mantle source that was enriched by subducted slab materials. The granodiorite suite has low contents of Y (≤18ppm) and heavy REE (HREE) (Yb<1.53ppm) and high contents of Sr (>594ppm) and high ratio of Sr/Y (>35) that resemble geochemical characteristics of adakite intrusions. The metaluminous to mildly peraluminous nature of granodiorite from Mashhad batholiths as well as its initial 87Sr/86Sr ratios (0.705469–0.706356), initial 143Nd/144Nd ratios (0.512204–0.512225) and εNd(t) values (−2.7 to −3.2) are typical of adakitic magmas generated by partial melting of a subducted slab. These magmas were then hybridized in the mantle wedge with peridotite melt. The quartz diorite–tonalite–granodiorite stock and granodiorite batholith could be considered as arc-related granitoid intrusions, which were emplaced during the northward subduction of Paleo-Tethys Ocean crust beneath the Turan micro-continent. The monzogranite is strongly peraluminous (Al2O3/(CaO+Na2O+K2O) Mol.=1.07–1.17), alkali-rich with normative corundum ranging between 1.19% and 2.37%, has high initial 87Sr/86Sr ratios (0.707457–0.709710) and low initial 143Nd/144Nd ratios (0.512042–0.512111) and εNd(t) values (−5.3 to −6.6) that substantiate with geochemical attributes of S-type granites formed by dehydration-melting of heterogeneous metasedimentary assemblages in thickened lower continental crust. The monzogranite was emplaced as a consequence of high-temperature metamorphism during the final integration of Turan and Iran plates. The ages found in the Mashhad granites show that the subduction of Paleo-Tethys under the Turan plate that led to the generation of arc-related Mashhad granites in late-Triassic, finally ceased due to the collision of Iran and Turan micro-plates in early Jurassic.

Mineralization and fluid evolution of the Jiyuan polymetallic Cu–Ag–Pb–Zn–Au deposit, eastern Tianshan, NW China

The newly discovered Jiyuan Cu–Ag–(Pb–Zn–Au) deposit is located in the southern section of the eastern Tianshan orogenic belt, Xinjiang, northwestern China. It is the first documented deposit in the large Aqikekuduke Ag–Cu–Au belt in the eastern Tianshan orogen. Detailed field observations, parageneses, and fluid inclusion studies suggest an epithermal ore genesis for the main Cu–Ag mineralization, accompanied by a complicated hydrothermal alteration history most likely associated with the multi-stage tectonic evolution of the eastern Tianshan. The Jiyuan Cu–Ag ore bodies are located along the EW-striking, south-dipping Aqikekuduke fault and are hosted by Precambrian marble and intercalated siliceous rocks. Early-stage skarn alteration occurred along the contact zone between the marble layers and Early Carboniferous diorite–granodiorite and monzogranite intrusions; the skarns are characterized by diopside–tremolite–andradite–pyrite–(magnetite) assemblages. Local REE-enriched synchysite–rutile–arsenopyrite–(clinochlorite–microcline–albite) assemblages are related to K–Na alteration associated with the monzogranite intrusions and formed under conditions of high temperature (310°C) and high salinity (19.9 wt.% NaCl). Subsequent hydrothermal alteration produced a series of quartz and calcite veins that precipitated from medium- to low-temperature saline fluids. These include early ‘smoky’ quartz veins (190°C; 3.0 wt.% NaCl) that are commonly barren, coarse-grained Cu–Ag mineralized quartz veins (210°C; 2.4 wt.% NaCl), and late-stage unmineralized calcite veins (140°C; 1.1 wt.% NaCl). Tremolite and Ca-rich scapolite veins formed at an interval between early and mineralized quartz veins, indicating a high-temperature, high-salinity (>500°C; 9.5 wt.% NaCl) Ca alteration stage. Fluid mixing may have played an important role during Cu–Ag mineralization and an external low-temperature Ca-rich fluid is inferred to have evolved in the ore-forming system. The Jiyuan auriferous quartz veins possess fluid characteristics distinct from those of the Cu–Ag mineralized quartz veins. CO2-rich fluid inclusions, fluid boiling, and mixing all demonstrate that these auriferous quartz veins acted as hosts for the orogenic-type gold mineralization, a common feature in the Tianshan orogenic belt.