Quartz Monzonite Research Articles

Characteristics of the Late Devonian Tsagaan Suvarga Cu–Mo deposit, Southern Mongolia

The Late Devonian Tsagaan Suvarga deposit (255 Mt at 0.55% Cu, 0.02% Mo) is located on the NW margin of the Tsagaan Suvarga Complex (TSC), which extends ENE over 15 × 10 km and comprises mainly medium-grained equigranular hornblende-biotite quartz monzonite and monzodiorite. Distinct mineralized intrusions are inferred from distribution of Cu–Mo mineralization but are not clearly discernible. The Tsagaan Suvarga Complex is a window within Carboniferous volcanic and sedimentary rocks, and wall rocks to the TSC are not known or exposed in the nearby district. Whole-rock analyses and Sr–Nd isotopes, 87Sr/86Sr0 = 0.7027 to 0.7038 (n = 12) and eNd0 = + 4.26 to + 2.77 (n = 12), show that the granitoids are subduction-related I-type, high K-calc-alkaline to shoshonitic series and derived from a mantle source. They exhibit fractionated light rare earth elements, without depleted Eu and depleted middle heavy rare earth elements and Y, typical of oxidized, fertile porphyry magmatic suites. Early porphyry-style quartz veins include A- and B-type. Molybdenite occurs in monomineralic veins (1–5 mm) or A veins. Copper mineralization occurs mainly as chalcopyrite and subordinate bornite, disseminated and associated with quartz–muscovite veins. Pyrite (vol%) content is less than chalcopyrite and bornite combined. Deep oxidation to about 50 m depth has formed zones of malachite and covellite in late fractures. The most important alteration is actinolite–biotite–chlorite–magnetite replacing hornblende and primary biotite. Quartz–K-feldspar alteration is minor. Late albite replaces primary K-feldspar and enhances sodic rims on plagioclase crystals. Quartz–muscovite (or sericitic alteration) overprints actinolite–biotite and porphyry-type quartz veins. Field observations and petrographic studies suggest that the bulk of the chalcopyrite–bornite mineralization at the Tsagaan Suvarga formed together with coarse muscovite alteration.

Comparative study of mineral chemistry of four biotite types as geochemical indicators of mineralized and barren intrusions in the Sungun Porphyry Cu-Mo deposit, northwestern Iran

The Sungun Porphyry copper-molybdenum deposit, in the northwestern part of the post-collisional Urumieh-Dokhtar magmatic arc, developed as a consequence of hydrothermal alteration related to the emplacement of the Sungun quartz monzonite porphyry stock into Eocene volcanic rocks. Based upon petrographic characteristics, back-scattered electron images, and compositional attributes, biotite from the Sungun Porphyry copper-molybdenum deposit was grouped into least-altered magmatic biotite (LA-Mbt), least-altered equilibrated magmatic biotite (LA-Eq Mbt), equilibrated magmatic biotite (Eq-Mbt), and secondary hydrothermal biotite (S-Hbt) types. The LA-Mbt from the mineralized zone have high TiO2 (3.92–4.33 wt%) compared to LA-Eq Mbt (3.81–4.20 wt%), Eq-Mbt (2.75–3.85 wt%), and S-Hbt (0.27–3.00 wt%). The LA-Mbt of the barren dike is also characterized by high TiO2 (4.17 wt% on average). Na2O, SiO2, and MnO (wt%) of biotite are systematically different between mineralized intrusions and barren ones. The highest amounts of Na2O (0.39–0.58 wt%) and MnO (0.11–0.18 wt%) are found in the LA-Mbt of the barren dike, which contrast with LA-Mbt of the mineralized zone having 0.08–0.15 wt% Na2O and 0.03–0.14 wt% MnO. Low SiO2 values (36 wt% on average) are characteristic of LA-Mbt from the barren dike in comparison with LA-Mbt of the mineralized zone (37 wt% on average). The SO3 contents in LA-Mbt of the mineralized zone (0.03–0.12 wt%) are much higher than those for LA-Mbt of the barren dike (0.01–0.04 wt%). The fluctuations in SO3 content of S-Hbt reflect a complex history of formation of S-Hbt in two stages. One group of S-Hbt has SO3 > 0.04 wt% and are principally related to the potassic (medium–high)/phyllic (low) assemblage, forming with magnetite at high oxygen fugacity, whereas the second group has SO3 < 0.04 wt% and is related to the phyllic (high)/argillic (low) assemblage, having formed during a stage of sulfide mineralization. The calculated oxygen fugacities (ƒO2) of 10−15.4–10−13.8 for the mineralized zone of the Sungun Porphyry Cu-Mo deposit lie completely within the domain of logƒO2 > ΔFMQ+2 (where FMQ is the fayalite–magnetite–quartz oxygen buffer), typical of oxygen fugacities associated with Cu-Mo porphyry mineralization. Altered biotite types have higher Cl contents than the least altered varieties, indicating that Cl may be used as an indicator of post-magmatic hydrothermal processes. The range of F contents (0.336–0.621 wt%) for the LA-Mbt of the mineralized zone is higher than those of the LA-Mbt types of the barren dike (0.219–0.347 wt%). Fluorine in biotite may be used as an exploration vector to characterize mineralized versus subeconomic porphyry Cu-Mo systems.

Late Carboniferous adakitic porphyries in the Huangliangzi pluton, West Junggar (Xinjiang), NW China: Petrogenesis and their tectonic implications

Late Carboniferous to Early Permian granitic rocks are widely distributed in the Western Junggar (Xinjiang, NW China), but their petrogenesis and tectonic contexts remain controversial. In this paper, we present new zircon U–Pb age, major element, trace element data for the Huangliangzi pluton from the southern West Junggar. The pluton mainly consists of granodiorite porphyry, biotite monzonitic granite porphyry, and quartz monzonite diorite porphyry. Laser‐ablation inductively‐coupled mass‐spectrometry (LA‐ICP‐MS) zircon U–Pb obtained the age of 321.7 ± 1.3 Ma, indicating the granodiorite porphyry was emplaced in the early Late Carboniferous, coeval with abundant magmatic rocks in the region. Geochemically, these rocks are moderately peraluminous high‐K calc‐alkalic and characterized by relatively high SiO2 (64.31–66.69 wt.%), Al2O3 (15.82–16.73 wt.%), and Sr (379–489 ppm) contents and low MgO (1.08–2.46 wt.%; Mg# = 39–55), Y (7.61–9.64 ppm), and Yb (0.95–1.23 ppm) contents, along with positive Eu anomalies (Eu/Eu* = 1.01–1.34) and high Sr/Y (47.7–57.1) ratios. These are compositional features of adakites that are commonly assumed to have been produced through partial melting of subducted oceanic crust. In addition, the adakitic rocks are relatively enriched in light rare‐earth elements (LREEs), large ion lithophile elements (LILEs: e.g., Rb, Ba, Sr, and K), and depleted in high‐field‐strength elements (HFSEs: e.g., Nb, Ta, and Ti) and are also characterized by high εNd(t) value and low initial (87Sr/86Sr)i ratio. The most plausible mechanism for the Huangliangzi adakitic porphyries is the partial melting of subducted oceanic crust interacting with a mantle wedge. Combined with the geological setting and previous studies, therefore, we suggest that the southern West Junggar was in a subduction‐dominated island‐arc setting in the early Late Carboniferous, and multistage subduction–accretionary orogeny may be the main mechanism for the difference between the north and the south subduction duration in the Western Junggar.

Geochemistry and U–Pb–Hf zircon data for plutonic rocks of the Troia Massif, Borborema Province, NE Brazil: Evidence for reworking of Archean and juvenile Paleoproterozoic crust during Rhyacian accretionary and collisional tectonics

Rhyacian (c. 2.30–2.05 Ga) subduction-accretion and collisional processes are thought to represent an important event of crustal growth and reworking, often reported in the so-called Tranzamazonian/Eburnean granite-greenstone terranes of N/NE Brazil and West African craton. In this work, we present whole-rock geochemistry and U–Pb–Hf zircon ages for Rhyacian plutonic rocks that intrude Paleoproterozoic granite-greenstone terranes and Archean basement rocks of the Troia Massif, Borborema Province, NE Brazil. U–Pb SHRIMP zircon age of 2185 ± 4 Ma was obtained for a metatonalite sample (Mirador metatonalites). The metatonalites show geochemical affinity similar to those of adakites-like rocks, with all “classic” (slab-derived) adakitic signature (e.g. high Sr/Y, La/Yb and low HREE), but more akin to those evolved from partial melting of the metasomatized mantle wedge, followed by fractional crystallization. Zircon Hf crustal model ages of the metatonalite sample range between 2800 and 2660 Ma, evidencing that Archean crustal components contributed to its magma genesis, probably via subduction of continental-derived sediments to the mantle wedge. For potassic plutons of the Troia Massif (Bananeira suite) we obtained U–Pb SHRIMP zircon age of 2079 ± 4 Ma for a deformed quartz-monzonite with geochemical affinities similar to those derived from low-pressure partial melting of a K-rich mafic protolith. For less-deformed equigranular granites, we obtained a U–Pb LA-ICPMS zircon age of 2068 ± 5 Ma. They are high-K calc-alkaline and slightly peraluminous granites that probably derived from low-pressure partial melting of tonalitic crustal sources (metatonalites) and/or metagraywackes. Zircon Hf crustal model ages of a granite sample range from 2713 to 2535 Ma, evidencing Archean crustal contribution to magma genesis. However, two analyzed c. 2307 Ma inherited zircon grains show εHf(t) values of c. +4.87, indicating that crustal reworking of less-radiogenic Paleoproterozoic sources also participated in its genesis. Regional correlations of our results with the Paleoproterozoic record of the Troia Massif, Borborema Province and surrounding cratonic domains, suggest that the studied plutons are related to the c. 2.2–2.0 Ga Transamazonian/Eburnean orogenic cycle. The c. 2185 Ma metatonalites are associated to pre-collisional setting, while the c. 2079–2068 Ma quartz monzonites and granites evolved during collisional setting.

The Shah-Ali-Beiglou Zn-Pb-Cu (-Ag) Deposit, Iran: An Example of Intermediate Sulfidation Epithermal Type Mineralization

The Shah-Ali-Beiglou epithermal base metal-silver deposit is located in the Tarom-Hashjin metallogenic province (THMP) in northwestern Iran. This deposit is hosted by quartz monzonite dikes of Oligocene age and surrounded by andesite to trachyandesite volcanic and volcaniclastic rocks of Eocene age. The subvolcanic rocks in the study area vary in composition from quartz-monzonite to monzonite and have metaluminous, calc-alkaline to shoshonitic affinity. These rocks have I-type geochemical characteristic and are related to post-collisional tectonic setting. The mineralization occurs as NE-SW and E-W-trending brecciated veins controlled by strike-slip and normal faults, which are associated to the Late Oligocene compressional regime. The mineral paragenesis of the vein mineralization is subdivided into pre-ore stage, ore stage, post-ore stage, and supergene stage. Pre-ore stage is dominated by quartz, sericite, and subhedral to anhedral pyrite as disseminated form. Ore-stage is represented by quartz, sphalerite (from 0.1 mol % to 4 mol % FeS), galena, chalcopyrite, tetrahedrite-tennantite, minor seligmannite and enargite, as vein-veinlet, cement and clast breccias. Post-ore stage is defined by deposition of quartz and carbonate along with minor barite, and supergene stage is characterized by bornite, chalcocite, covellite, hematite, goethite, and jarosite. The ore mineralization is associated with the silicic alteration. The styles of alteration are silicic, carbonate, sericitic, chloritic, and propylitic. Fluid inclusions in sphalerite have a wide range of salinities between 0.35 wt % and 21.4 wt % NaCl equivalent and homogenization temperatures range from 123 to 320 °C. The isotopic values of sulfides vary from 2.8‰ to 6.7‰ suggesting a magmatic source for the sulfur. In the present study, based on geological setting, alteration style of the host and wall rocks, main textures, mineral assemblages, composition of ore minerals, and structural features, it is suggested that the mineralization in the Shah-Ali-Beiglou is similar to intermediate-sulfidation style of epithermal deposits.

Petrogenesis of Early Cretaceous granitoids from southwest Zhejiang, NE South China Block and its geodynamic implication

In situ zircon U–Pb ages, whole-rock major and trace elements, and Sr–Nd isotopic compositions of the Sucun, Yunfeng, and Jingning intrusions from southwest Zhejiang, NE South China Block, are presented to trace their petrogenesis and shed light on its lithosphere evolution. LA–ICP–MS U–Pb zircon dating shows that the Sucun quartz monzonite and Jingning monzogranite were emplaced at ~135 Ma, and the Yunfeng quartz monzonite and Jingning granite were emplaced at 104 and 112 Ma, respectively. All these intrusions are metaluminous to weakly peraluminous and lie within high-K calc-alkaline to shoshonite series field (SiO2 = 66–76 wt%, A/CNK = 0.95–1.09, K2O/Na2O = 0.78–1.77). The Yunfeng quartz monzonite clearly have lower K2O and total REE contents, and higher CaO, Na2O, Al2O3, P2O5, MgO, and TiO2 contents, and relatively less enriched Sr–Nd isotopic compositions than those of the Sucun quartz monzonite, indicating that the Yunfeng quartz monzonite were derived from partial melting of a more juvenile lower crust sources compared with the magma source of the Sucun quartz monzonite. The Jingning monzogranite exhibit similar major elements covariations and Nd isotopic compositions, but higher Ba, Sr, and Eu contents and lower Rb, Th, and U contents than those of the Jingning granite. The geochemical features imply that the Jingning monzogranite and granite were fluid-present and fluid-absent anatexis products of the same Paleoproterozoic crustal source, respectively. Whole-rock Sr–Nd isotopic data imply that the estimated amounts of juvenile mantle-derived melts input into the mature crust show southeastward decreasing trend away from the Jiangshan–Shaoxing fault. We propose that roll-back and retreat of the Paleo-Pacific subducting plate might cause extensive asthenosphere mantle upwelling in East China, and the mantle-derived melts tend to rise through the regional main fault zones and preferentially modify the lithosphere nearby these faults.

Mesozoic multiple magmatism and porphyry–skarn Cu–polymetallic systems of the Yidun Terrane, Eastern Tethys: Implications for subduction- and transtension-related metallogeny

Most mineralized porphyries associated with large to giant oxidized porphyry Cu deposits show an affinity with relatively high Sr/Y features. The Mesozoic porphyry–skarn Cu–polymetallic systems of the Yidun Terrane hosted by the Late Triassic and Late Cretaceous intrusions provide chances to investigate the spatial and genetic relationships between subduction- and transtension-related magmatism and mineralization, and determine the petrogenesis and fertility of magmatic rocks. Zircon U–Pb ages indicate that the Late Triassic pre-ore quartz diorite porphyries and syn-ore quartz monzonite porphyries were emplaced at ~225 and ~215Ma, respectively. The Late Cretaceous syn-ore monzogranite porphyries were emplaced at 83–78Ma. Our new data, combined with previously published geochronological data, show the spatially overlapping distribution of the multiple Mesozoic porphyry systems in the Yidun Terrane. Although all the Late Triassic intrusive rocks share similar geochemical characteristics, the pre-ore quartz diorite porphyries have normal arc-related chemical features with low Sr/Y and (La/Yb)N ratios, high Y and Yb abundances, while the syn-ore quartz monzonite porphyries exhibit high Sr/Y and (La/Yb)N ratios, low Y and Yb abundances. All samples show similar Sr–Nd–Hf isotopic compositions [(87Sr/86Sr)i=0.7060–0.7117, εNd(t)=−6.7 to 0.0, zircon εHf(t)=−4.0 to +3.0], suggesting that they were probably derived from partial melting of juvenile lower crust. Trace-element patterns and partial melt modeling indicate that the quartz diorite porphyries were likely formed by partial melting of normal thick lower crust, while the causative quartz monzonite porphyries were probably formed by partial melting of eclogitized, thickened lower crust. We propose that pre-ore quartz diorite porphyries were probably generated earlier via the subduction of Garze–Litang oceanic crust, and syn-ore quartz monzonite porphyries were formed later by partial melting of sulfide-enriched, thickened juvenile lower crust. Thus, these high Sr/Y quartz monzonite porphyries host several economically important porphyry Cu deposits, such as Pualng, Xuejiping and Songnuo. However, the Late Cretaceous syn-ore monzogranite porphyries have lower εHf(t) values (−8.4 to −2.9) and εNd(t) values (−7.5 to −3.8) than the Late Triassic porphyries, indicating that the former mainly originated from ancient crustal materials. New dataset and previous studies suggest that the Late Cretaceous post-collisional transtension triggered the asthenospheric upwelling and the underplating of mafic magmas, induced the partial melting of garnet-bearing amphibolite and thus caused the emplacement of monzogranite porphyries and associated porphyry–skarn Cu–Mo deposits.

Origin of dioritic magma and its contribution to porphyry Cu–Au mineralization at Pulang in the Yidun arc, eastern Tibet

The giant Pulang porphyry Cu–Au deposit in the Yidun arc, eastern Tibet, formed due to westward subduction of the Garze–Litang oceanic plate in the Late Triassic. The deposit is hosted in an intrusive complex comprising primarily coarse-grained quartz diorite and cored quartz monzonite. Here, we investigate a suite of simultaneous (216.6 ± 1.9 Ma) diorite porphyries within the complex. The diorite porphyries are geochemically similar to mafic magmatic enclaves (MME) hosted in coarse-grained quartz diorite, and both are characterized by low SiO2 (59.4–63.0 wt%) and high total alkali (Na2O + K2O = 7.0–9.2 wt%), K2O (3.5–6.4 wt%), MgO (3.2–5.5 wt%), and compatible trace element (e.g., Cr = 72–149 ppm) concentrations. They are enriched in large-ion lithophile and light rare earth elements (LILE and LREE, respectively), but depleted in high field-strength and heavy rare earth elements (HFSE and HREE, respectively), and yield variably high (La/Yb)N ratios (17–126, average 65) with weak to negligible Eu anomalies. Furthermore, they yield low (87Sr/86Sr)i ratios (0.7054–0.7067), weakly negative εNd(t) (−2.8 to −0.8) values, and variable zircon εHf(t) (−5.4 to +0.8) and δ18O (6.0‰–6.7‰) values. These geochemical features indicate that the diorite porphyry and MME formed through crustal assimilation of a magma produced during low-degree partial melting of metasomatized phlogopite-rich subcontinental lithospheric mantle. In contrast, the coarse-grained quartz diorite and quartz monzonite have relatively high concentrations of SiO2 (61.1–65.3 wt%), K2O (4.1–5.4 wt%), and total alkali (Na2O + K2O = 7.1–8.1 wt%), and low concentrations of MgO (generally <3.0 wt%) and compatible trace elements (e.g., Cr = 38–61 ppm). They yield high Sr/Y ratios (50–63) that indicate an adakitic affinity, and are enriched in LILE, depleted in HFSE, and yield lower (La/Yb)N values (13–20, average 17) than the diorite porphyry and MME. They yield low (87Sr/86Sr)i ratios (0.7046–0.7066), negative εNd(t) (−3.3 to −1.7) values, and zircon εHf(t) and δ18O values of −2.9 to −0.1 and 5.7‰–6.5‰, respectively, suggesting that they represent high-K calc-alkaline to shoshonitic adakitic magmas that were sourced from subduction-modified juvenile lower crust. Observations of the newly identified diorite porphyry and previously reported MME suggest that input of such dioritic magma into the upper crustal porphyry magma chamber would have contributed not only the necessary metals (e.g., Cu and Au), sulfur, but also H2O to the system, thus aiding in the generation of the giant Pulang porphyry Cu–Au deposit.

Petrogenesis of the Pulang porphyry complex, southwestern China: Implications for porphyry copper metallogenesis and subduction of the Paleo-Tethys Oceanic lithosphere

The Pulang complex is located in the southern segment of the Yidun Arc in the Sanjiang Tethys belt, southwestern China. It is composed of quartz diorite, quartz monzonite and granodiorite porphyries, and hosts the super-large Pulang deposit. This study presents new U-Pb geochronological, major-trace elemental and Sr-Nd-Hf isotopic data to constrain the petrogenesis of the Pulang complex and to evaluate its significances for porphyric mineralization and tectonic evolution of the Paleo-Tethys Ocean. The zircon U-Pb dating yields ages ranging from 208Ma to 214Ma. Geochemically, the Pulang complex has high Sr and MgO contents, and high Sr/Y and La/Yb ratios, but low Yb and Y contents, displaying adakitic affinities. However, it has moderate Sr/Y and La/Yb ratios, and high Rb contents (32 to 202ppm). The Pulang samples plot into the transitional field between adakites and normal arc rocks, differing from typical adakites. It is attributed to the assimilation of 10–15% crustal components. The zircon εHf(t) (−4.6 to −2.5), whole-rock (87Sr/86Sr)i (0.7052 to 0.7102), εNd(t) (−0.62 to 2.12) values and adakitic affinities suggest that the Pulang complex was derived from a basaltic slab-melt source and reacted with peridotite during ascending through an enriched asthenospheric mantle wedge. The basaltic slab-melts likely resulted from the westward subduction of the Ganzi-Litang oceanic plate (a branch of the Paleo-Tethys). As far as the metallogenesis concerned, three factors in mineralization are proposed in this paper. The country rock, quartz diorite porphyry, has higher Cu contents than the mantle (average 30ppm), suggesting that ore-forming magma was derived from a Cu-enriched source, which is a crucial contribution to the late mineralization to form the super-large Pulang deposit. In addition, the barren quartz diorite, granodiorite, and ore-bearing quartz monzonite porphyries are all characterized by high oxygen fugacity, which is another important factor for the mineralization. Moreover, the separation/exsolution of the quartz monzonite from the quartz diorite is vital to the enrichment of Cu in the Pulang deposit. The emplacement of the Pulang pluton, posterior to the closure of the Jiangshajiang Ocean (a branch of the paleo-Tethys), is consistent with the igneous rocks associated with the westward subduction of the Ganzi-Litang oceanic plate during late Triassic Time. The Zhongdian Arc in the southern segment of the Yidun Arc was close to the arc front that was conducive to Cu mineralization in the porphyry system.

Jurassic granitoids in the northwestern Sanandaj–Sirjan Zone: Evolving magmatism in response to the development of a Neo-Tethyan slab window

Voluminous Jurassic granitoids within the Sanandaj–Sirjan Zone (SSZ) provide insight into the magmatic arc formed in the active margin of Eurasia. Here, we present new in situ zircon U–Pb, whole-rock major and trace element, and Sr–Nd isotopic data for the Gorveh Plutonic Complex (GPC) of the northwestern SSZ in Iran. Six samples from the plutons within the GPC yielded zircon U–Pb ages that range from 151 to 146Ma. These plutons can be subdivided into two groups based on their geochemistry. Group 1 rocks (the Mobarak Abad diorites and the Gorveh gabbros and diorites) contain relatively high concentrations of the high field strength elements (HFSE; Nb, Ta, Zr, and Ti) and have low Th/Nb (0.20–0.56) and moderate Sm/Yb ratios (1.51–2.32), low (87Sr/86Sr)i values (0.70354–0.70622), and high εNd(t) values (2.3–5.4). These features indicate that the Group 1 rocks formed from magmas derived from a subduction-modified region of the subcontinental lithospheric mantle. The Group 2 plutons (the Bolban Abad granites and the Gorveh quartz monzonites) have A-type granites affinities, including high K2O+Na2O and Zr+Nb+Ce+Y concentrations, and high FeOtot/MgO and 10,000×Ga/Al ratios. These A-type rocks are enriched in Rb, Th, and K, and depleted in Ba, U, Nb, Ta, Sr, P, and Ti. The Group 2 plutons have different Sr–Nd isotopic compositions to each other, indicating they were derived from different sources and record different igneous processes. The Gorveh quartz monzonites have high (87Sr/86Sr)i ratios (0.70552–0.70617), negative εNd(t) values (−1.1 to −5.4), and extremely low concentrations of MgO (0.32–0.35wt%), suggesting they were derived from an igneous quartzo-feldspathic crustal source. In comparison, the Bolban Abad granites have positive εNd(t) values and contain high concentrations of SiO2 and low concentrations of MgO, suggesting that they formed from Group 1 magmas that subsequently underwent assimilation and fractional crystallization processes. Combining these new data with the results of previous research, we conclude that this Jurassic magmatism was the result of the formation of a slab window within the subducting Neo-Tethys slab, a process that caused the partial melting of overlying continental lithospheric material.

Upper Triassic mafic dykes of Lake Nyos, Cameroon (West Africa) I: K-Ar age evidence within the context of Cameroon Line magmatism, and the tectonic significance

The hydrodynamic fragmentation that formed Lake Nyos in northwest Cameroon did not only make it the most unpopular lake in the world from a gas disaster perspective, it also opened a rare and formidable window through which much of the geology of Cameroon can be studied in a single locality. The Cambrian quartz monzonite cliff excavated by the maar-forming explosion and exposed in its northeastern shore is intruded by mafic dykes, two of which we dated. Even though close to one another, the dykes are different in composition. The alkaline dyke yields a slightly older (Carnian) K-Ar fedspar age of 231.1 ± 4.8 Ma, while the sub alkaline dyke yields an age of 224.8 ± 4.7 Ma (Norian). Based on radioisotopic age data available over the last 48 years (347 data) for the Cameroon Line magmatism comprising eruptives and volcano-plutonic complexes, the Nyos dykes are way older than the Cameroon Line, and even pre-date the Lower Cretaceous initiation of west Gondwana fragmentation in Equatorial Atlantic domain. They would therefore not have been directly linked to the formation of the Cameroon Line. Alternatively, they might be associated with the development of intra-continental rift systems in West Central Africa that pre-dated west Gondwana breakup to form the Atlantic Ocean.

Devonian alkaline magmatic belt along the northern margin of the North China Block: Petrogenesis and tectonic implications

Some Devonian magmatic rocks have been identified from the northern margin of the North China Block (NCB) in recent years. However, their petrogenesis and tectonic setting are still highly controversial. Here we present new geochronological, Sr-Nd-Hf isotopic and whole-rock chemical data on several newly identified and previously reported Devonian alkaline complexes, including mafic-ultramafic rocks (pyroxenites and gabbros), alkaline rocks (syenites, monzonites) and alkaline granites in the northern NCB. We firstly identified some mafic-ultramafic rocks coeval with monzonite and quartz monzonite in the Sandaogou and Wulanhada alkaline intrusions. New zircon U-Pb dating of 16 samples from the Baicaigou, Gaojiacun, Sandaogou, Wulanhada and Chifeng alkaline intrusions combined with previous geochronological results indicate that the Devonian alkaline rocks emplaced during the early-middle Devonian at around 400–380 Ma and constitute an E–W-trending alkaline magmatic belt that extend ca. 900 km long along the northern margin of the NCB. Whole-rock geochemical and Sr-Nd-Hf isotopic data reveal that the Devonian alkaline rocks were mainly originated from partial melting of a variably enriched lithospheric mantle with different involvement of ancient lower crustal component and fractional crystallization. The Devonian alkaline magmatic belt rocks in the northern NCB are characterized by very weak or no deformations and were most likely related to post-collision extension after arc-continent collision between the Bainaimiao island arc and the northern margin of North China Craton during the latest Silurian. Partial melting of subcontinental lithospheric mantle to produce the Devonian alkaline magmatic rocks suggests that the northern North China Craton has an inhomogeneous, variably enriched subcontinental lithospheric mantle and was characterized by significant vertical crustal growth during the Devonian period.

Late Palaeozoic igneous rocks of the Great Xing’an Range, NE China: the Tayuan example

ABSTRACTThe Tayuan plutons located at the boundary of the Erguna and Xing’an blocks expose a coexisting mafic–felsic association that is made of monzogranite and gabbro-monzodiorite as well as subordinate quartz monzonite. LA–ICP–MS U–Pb zircon dating revealed a synchronous emplacement of the monzogranite (314–317 Ma), gabbro (308–315 Ma), and quartz monzonite (310 ± 3 Ma). The majority of these intrusions are characterized by an enrichment in light rare earth elements relative to heavy rare earth elements and a depletion of high strength field elements (e.g. Nb, Ta, Ti). Zircons from the gabbro and monzogranite have εHf(t) values of 1.1–9.6 and −3.0–3.3, respectively. Geochemical data show that the gabbro-monzodiorite may have been generated by the melting of a fluid-metasomatized lithospheric mantle, while the monzogranite may have been formed by a partial melting of the Mesoproterozoic crust. The quartz monzonite has similar whole-rock geochemical and Hf isotopic compositions to those of the gabbros and could have been produced from the same mantle source as that from which the gabbros were extracted. The Tayuan plutonic rocks have high contents of K2O and total alkalis and show a northwestward polarity like that of the continental margin plutonic rocks along the Hegenshan–Heihe suture zone. Combined with data from published studies, our data indicate that the Tayuan intrusive rocks were generated by the northwestward subduction of the Hegenshan–Heihe Oceanic plate.

Latest Cretaceous “A2-type” granites in the Sakarya Zone, NE Turkey: Partial melting of mafic lower crust in response to roll-back of Neo-Tethyan oceanic lithosphere

An integrated study of comprehensive geochronological, geochemical, and Sr-Nd-Hf isotopic data was undertaken for the A-type Topcam pluton that intruded within the Sakarya Zone (NE Turkey) with the aims of elucidating its origin and tectonic significance and gaining new insights into the generation of aluminous A-type granites. New LA-ICP-MS zircon U-Pb crystallization ages of 72 and 73Ma indicate emplacement in the Late Cretaceous time, just after extensive metaluminous I-type magmatism in the area. The pluton consists mainly of alkali feldspar, quartz, plagioclase, amphibole, and biotite with accessory minerals such as magnetite, apatite, and zircon. The outcrop is composed of granite, syenite, monzonite, and quartz monzonite and possesses a wide range of SiO2 content (57–70wt%) with elevated Ga/Al ratios and low Mg# (mostly <43). The pluton is metaluminous to weakly peraluminous, with aluminium saturation index (ASI) (molar Al2O3/[CaO+K2O+Na2O]) values of 0.82 to 1.18, and belongs to the shoshonitic and ultra-potassic series. All the samples exhibit relative enrichment in light rare earth elements (LREE) and significant negative Eu (Eu/Eu*=0.31 to 0.86) anomalies on the chondrite-normalized REE diagram. The rocks are enriched in some large ion lithophile elements (e.g., Rb, Th and Ba), and spidergrams show a relative depletion in Nb, Ti, and Sr. The granitic rocks of the pluton have identical 87Sr/86Sr(i) ratios ranging from 0.70518 to 0.70716, relatively low εNd (t) values varying from −5.5 to −0.4, and TDM ages (0.82–1.19Ga). In situ zircon analyses show that the rocks have variable negative and positive εHf (t) values (−5.5 to 5.9) and Hf two-stage model ages (742 to 1468Ma), which are indicative of minor addition of juvenile material. Sr-Nd isotope modelling suggests mixing of 70–90% of lower crustal-derived melt with ~10–30% of mantle-derived melt at lower crust depths. The heat source for partial melting is provided by upwelling of hot asthenosphere triggered by slab roll-back events. Geochemical and isotopic data reveal that metaluminous A2-type granites were derived from partial melting of the Paleozoic lower continental crust dominated by mafic rocks in amphibolitic composition, with minor input of subcontinental lithospheric mantle-derived magma followed by subsequent limited fractional crystallization to generate a variety of rock types. From integrating all available data with the regional tectonic evolution in the Sakarya Zone and adjacent regions, we attribute generation of aluminous A2-type granites to a back-arc extension in the subduction zone, which is induced by the roll-back of the Neo-Tethyan oceanic slab around 72Ma. Consequently, we conclude that these A-type granites were related to intensive extension tectonic, which peaked during the late Cretaceous (Maastrichtian) in response to the roll-back of the Neo-Tethyan oceanic slab, which is indicative of the final-stage subduction-related magmatism in the Sakarya Zone.

Highly differentiated magmas linked with polymetallic mineralization: A case study from the Cuihongshan granitic intrusions, Lesser Xing'an Range, NE China

The genetic link between granitoids and polymetallic skarn mineralization has remained equivocal. The Cuihongshan skarn-porphyry W-Mo-Pb-Zn-(Fe-Cu) deposit in the eastern part of the Central Asian Orogenic Belt provides a unique example to address this issue. The major rock types in the mine area are Early Paleozoic intrusions composed of biotite syenogranite and biotite porphyritic granite and Early Mesozoic intrusions represented by porphyritic quartz monzonite, biotite monzogranite, and porphyritic granite. The diagnostic mineralogical and geochemical features indicate that the rocks belong to A2-type granites. The Early Paleozoic suite shows zircon U-Pb ages of ~501Ma, and εHf(t) values of −4.4 to +2.7 and +2.4 to +7.6, respectively. In combination with their coherent geochemical trends, these rocks are inferred to be products of in-situ differentiation. Although the Mesozoic suite shows crystallization ages of 194–196Ma, εHf(t) values are in the range of −2.5 to +7.5 for the porphyritic quartz monzonite, the −1.8 to +4.5 values for the monzogranite and the +2.3 to +8.0 range for the porphyritic granite. The porphyritic quartz monzonite displays distinct mineral assemblage and shows significant compositional gap with the other two lithofacies. In contrast, the monzogranite and porphyritic granite have similar geochemical features, and are thus inferred to be co-magmatic. Considering the high SiO2 contents, variable εHf(t) (−4.4 to +8.0) and εNd(t) values (−8.4 to +0.28) for the two suites, we infer that both episodes of granitoid magmatism resulted from partial melting of crustal materials with a mixed source containing varying proportions of juvenile and Precambrian crustal components. The Early Mesozoic porphyritic granite shows a highly evolved F-rich geochemical affinity, and experienced magma-fluid interaction. Cassiterite from the calcic skarn and the magnesian skarn that coexists with magnetite orebodies shows a mean U-Pb age of 195.4±1.9Ma and 191.2±7.5Ma respectively, indicating that the mineralization is genetically related to the Mesozoic granitic rocks. We infer that halogen-rich magmatic-hydrothermal fluids were derived from the Early Mesozoic highly fractionated magma, and the spatial association of the metallic elements with different geochemical behavior in the Cuihongshan deposit is correlated to multiple stages of evolution of halogen-rich magmatic-hydrothermal fluids.

Evaluation of granitic rocks as feldspar source: Al Madinah, Western Part of Saudi Arabia

ABSTRACTThe source of the feldspar is found in the Late-Precambrian granitoid rocks of Al Madinah area, which covers about 2000 km2 within a 44,000 km2 area of the western part of Saudi Arabia. Petrographical and geochemical study shows that the granitic rocks have a considerable compositional range from quartz monzonite, quartz syenite, syenite, alkali granite to alkali feldspar granite. Mineralogical and petrographical results have revealed that Al Madinah granites are composed of quartz, K- feldspar, Na-plagioclase and muscovite. Geochemical data for the feldspar samples show average SiO2, Al2O3, K2O, Na2O, CaO, Fe2O3, MgO and TiO2 contents of 71.33, 13.71, 4.78, 5.93, 1.17, 1.89, 0.34 and 0.31 wt.%, respectively, while mineralogical results reveal average K-feldspar and Na-plagioclase contents of 28.53% and 39.66%, respectively. They are almost invariably composed of metaluminous, calc-alkaline and shoshonite, with respect to alumina saturation. These deposits are characterized and evaluated for their potential as a source of feldspar.

Mineralized breccia clasts: a window into hidden porphyry-type mineralization underlying the epithermal polymetallic deposit of Cerro de Pasco (Peru)

Cerro de Pasco (Peru) is known for its large epithermal polymetallic (Zn-Pb-Ag-Cu-Bi) mineralization emplaced at shallow level, a few hundred meters below the paleo-surface, at the border of a large diatreme–dome complex. Porphyry-style veins crosscutting hornfels and magmatic rock clasts are found in the diatreme breccia and in quartz–monzonite porphyry dikes. Such mineralized veins in clasts allow investigation of high-temperature porphyry-style mineralization developed in the deep portions of magmatic–hydrothermal systems. Quartz in porphyry-style veins contains silicate melt inclusions as well as fluid and solid mineral inclusions. Two types of high-temperature (> 600 °C) quartz–molybdenite–(chalcopyrite)–(pyrite) veins are found in the clasts. Early, thin (1–2 mm), and sinuous HT1 veins are crosscut by slightly thicker (up to 2 cm) and more regular HT2 veins. The HT1 vein quartz hosts CO2- and sulfur-rich high-density vapor inclusions. Two subtypes of the HT1 veins have been defined, based on the nature of mineral inclusions hosted in quartz: (i) HT1bt veins with inclusions of K-feldspar, biotite, rutile, and minor titanite and (ii) HT1px veins with inclusions of actinolite, augite, titanite, apatite, and minor rutile. Using an emplacement depth of the veins of between 2 and 3 km (500 to 800 bar), derived from the diatreme breccia architecture and the supposed erosion preceding the diatreme formation, multiple mineral thermobarometers are applied. The data indicate that HT1 veins were formed at temperatures > 700 °C. HT2 veins host assemblages of polyphase brine inclusions, generally coexisting with low-density vapor-rich inclusions, trapped at temperatures around 600 °C. Rhyolitic silicate melt inclusions found in both HT1 and HT2 veins represent melt droplets transported by the ascending hydrothermal fluids. LA-ICP-MS analyses reveal a chemical evolution coherent with the crystallization of an evolved rhyolitic melt. Quartz from both HT1 and HT2 veins also contains secondary, low-temperature (~ 300 °C) brine and aqueous fluid inclusions that record the cooling of the system. Both vein types are locally crosscut and/or reopened by a pre-diatreme polymetallic event consisting of pyrite, sphalerite with “chalcopyrite disease,” galena, chalcopyrite, tetrahedrite–tennantite, and minor quartz. LA-ICP-MS analyses of mineral and high-temperature fluid inclusions hosted in HT1 and HT2 veins and in situ secondary-ion mass spectrometry oxygen isotope analyses of vein quartz indicate a magmatic signature for the mineralizing fluids with no major meteoric water input and allow reconstruction of the source and chemical evolution of fluids that formed these porphyry-style veins as snapshots of the early and deep mineralizations at Cerro de Pasco. This detailed study of the porphyry-type mineralization hosted in clasts offers a unique opportunity to reconstruct the late magmatic and early hydrothermal evolutions of porphyry mineralization underlying the world-class Cerro de Pasco epithermal polymetallic (Zn-Pb-Ag-Cu-Bi) deposit.

Caracterización de parámetros en la concentración de circones para andesitas, monzogranitos, riolitas, cuarcitas y cuarzomonzonitas

The Medellin chemical laboratory of the Servicio Geologico Colombiano (Colombian Geological Survey) is conducting research to characterize the different parameters involved in the process of concentrating zircons for U-Pb LA-ICP-MS geochronology analysis. This methodology was applied to five different rock types, including andesites, rhyolites, quartzites, monzogranites and quartz monzonites; the stages of this process were as follows: grinding (crushing, pulverizing and screening), gravimetric concentration on a Wilfley table, magnetic concentration in an isodynamic Frantz separator, separation using LST dense liquids (lithium polytungstate), zircon picking and detailed sample mount preparation. The methodology consisted of performing tests on five samples of each rock type in order to find the best particle size during the grinding stage, the best forward and side angles on the Wilfley table and the best side and forward angles for the isodynamic Frantz separator to obtain the largest amount of zircons for U-Pb LA-ICP-MS geochronology analysis.

Zircon U–Pb geochronology and geochemistry of the Cerro Colorado porphyry copper deposit, northern Chile

Porphyry Copper Deposits (PCDs) dominantly form in convergent plate margins genetically related to volcanic arcs. However, their temporal relationships with active volcanism are less clear. Active volcanic activity is often considered to impede the formation of PCDs and some workers have concluded that PCD formation must take place at times of volcanic quiescence or at a waning stage of volcanism. However, several studies have documented evidence suggesting syn-eruption PCD formation. A combination of radiometric dating, geochemistry studies and observations of rock cores from the Cerro Colorado PCD, a BHP Billiton property located in N. Chile, provides evidence compatible with syn-volcanic PCD formation within a volcanic edifice.Textural observations at both hand specimen and microscopic scales combined with new LA-ICPMS and SHRIMP dating of zircons suggest the intrusive history of the Cerro Colorado area can be separated into two main units: a porphyritic tonalite ca. 53.5 Ma and a porphyritic quartz monzonite ca. 50 Ma. There is also evidence for crystallisation at ca. 60 Ma, but a corresponding distinct lithology was not identified. A quartz porphyry unit previously identified as the youngest intrusive body is reinterpreted as an altered equivalent of the monzonite. The youngest intrusive units are represented by porphyritic granodiorite with an age 51–50 Ma. These units only show minor metal mineralisation suggesting that the main phase of mineralisation in the Cerro Colorado mine occurred over a few million years, bracketed by the two main pulses of igneous intrusion, which are consistent with documented Ar–Ar ages. Re–Os ages reported by previous studies suggest an earlier phase of mineralisation at ca. 56–54 Ma. U–Pb dating of zircon from a volcanic-related breccia that cuts the host rocks of the Cerro Colorado Mine reveals a phase of volcanic activity at ca. 57 Ma, after formation of the regional Cretaceous Cerro Empexa Formation. This age range overlaps the ages derived for the intrusive porphyry units suggesting a close temporal relationship between volcanism and the ore-forming subvolcanic intrusions in Cerro Colorado. A link between active volcanism and mineralisation is reinforced by the ultrafine-grained matrix and the presence of strong brecciation associated with the monzonite-quartz porphyry stock suggesting decompression and volatile release have taken place during emplacement.

Geochemical constraints on the link between volcanism and plutonism at the Yunshan caldera complex, SE China

The Yunshan caldera complex is part of a larger scale, ca. 2000-km-long volcanic–plutonic complex belt in the coastal region of SE China. The volcanic rocks in the caldera complex are characterized by high-silica peraluminous and peralkaline rhyolites associated with an intracaldera porphyritic quartz monzonite pluton. In this study, we present zircon U–Pb, Hf and stable O isotopes along with geochemical data of both volcanic and plutonic rocks to evaluate the potential petrogenetic link between volcanism and plutonism in the Yunshan caldera complex. SHRIMP zircon U–Pb geochronology of both volcanic and plutonic rocks yields almost identical ages ranging from 95.6 to 93.1 Ma. The peraluminous and peralkaline rhyolites show negative anomalies of Sr, P, Ti and Ba and to a lesser extent negative Nb and Ta anomalies, along with positive Rb anomalies and ‘seagull-like’ rare earth element (REE) patterns with negative Eu anomalies and low (La/Yb)N ratios. The intracaldera porphyritic quartz monzonite displays minor negative Rb, Nb, Ta, Sr, P and Ti anomalies and a positive Ba anomaly with REE patterns characterized by relatively high (La/Yb)N ratios and lack significant Eu anomalies. The peraluminous and peralkaline rhyolites and the porphyritic quartz monzonite exhibit consistent e Nd(t) of − 3.7 to − 2.2 and display zircon e Hf(t) values of − 2.1 to 3.7. They further have similar, mantle-like, zircon oxygen isotopic compositions (δ18OVSMOW mainly = 4.63 to 5.76‰). We interpret these observations to be in agreement with a crystal mush model in which the parental magma of the volcanic and plutonic rocks of the Yunshan caldera complex was likely produced by interaction of asthenosphere melts with subduction-influenced enriched mantle wedge. The peralkaline rhyolites are interpreted to represent the most differentiated magma that has subsequently experienced significant fluid–melt interactions, whereas the porphyritic quartz monzonite may be representative of the residual crystal mush. The Yunshan rhyolites typically match the geochemical characteristics of ‘hot-dry-reduced’ rhyolites indicating that, during the late Cretaceous, the tectonic setting of SE China changed from a compressional environment to an extensional environment, i.e., from an arc into a back-arc setting. Our results imply that volcanic and plutonic rocks in caldera systems may provide unique constraints on the evolution of the magmatic system in which both the erupting melt and the residual crystalline material are being preserved.