Quartz Diorite Research Articles

Tourmaline as an indicator of ore-forming processes: Evidence from the Laodou gold deposit, Northwest China

A detailed textual and geochemical study of tourmaline is presented to trace fluid evolution and ore genesis of the Laodou gold deposit in West Qinling Orogen, Northwest China. Based on petrographic observations and relationships to gold mineralization, three generations and five types of tourmaline were identified. The pre-ore tourmaline generation (Tur A) occurs as phenocryst replacement within quartz diorite porphyry (Tur A1) and metasomatic filling in hydrothermal breccia (Tur A2). It shows intense oscillatory zoning and variable Mg/(Mg + Fe) ratios (0.30–0.67), implying rapid compositional changes controlled by host-rock composition and fluid-rock interaction. The syn-ore tourmaline generation (Tur B) forms as open-space filling (Tur B1) and peripheral overgrowth (Tur B2) of Tur B1. It occurs in quartz-tourmaline and quartz-stibnite-sphalerite-tourmaline veins. Narrow Mg/(Mg + Fe) range (0.48–0.76), poor chemical zoning and more homogeneous compositions of Tur B reflect a higher fluid flux. The post-ore tourmaline generation (Tur C) occurs as monopolar overgrowths developed at the − c pole of previous tourmaline within granitoids and hydrothermal veins. This has a composition between dravite and foitite with Mg/(Mg + Fe) from 0.65 to 0.95 and no zoning, which reflect formation under low-temperature conditions. Relatively high Sn, Nb and Ta concentrations, LREE enrichment accompanied by strong positive Eu anomalies of Tur A mostly support a magmatic-hydrothermal origin. Slight LREE enrichment and low abundances of ΣREE of Tur B are caused by progressive input of meteoric waters. Tur C shows relative enrichment in Ba, depletions in V and Ni, and a flat REE pattern with negative Eu anomalies, suggesting a metamorphic source. Boron isotope compositions suggest that boron of Tur A (δ11B average − 6.49 ‰) is sourced from an I-type melt involved with the Laodou quartz diorite porphyry, while the lighter δ11B values in paragenetically younger tourmaline (Tur C with δ11B average − 9.10 ‰) support cooling and a metamorphic input sourced from argillaceous slate of the Lower Permian Daguanshan Group. The variations in textural characteristics, chemical and boron isotope compositions from Tur A to Tur C support a fluid mixing between a magmatic-hydrothermal fluid and meteoric waters leaching metasedimentary rocks. Typical morphology, core-to-rim decrease in Mg/(Mg + Fe), Fe3+Al−1, (□XAl)(NaR2+)−1 and (AlO)(R2+OH)−1 vectors, decreasing Na, Ca concentrations and Eu anomalies of tourmaline may record cooling, oxidation and dilution during fluid evolution. This process is possibly caused by fluid mixing and results in gold precipitation. Boron sources, as well as fluid provenance and evolution interpreted by tourmaline provide insight into the Laodou deposit as an intrusion-related gold deposit.

Characteristics and Genesis of Laterite Bauxite in Sompak District and Surrounding Areas, Landak Regency, West Kalimantan

West Kalimantan has very large bauxite resources, reaching 2.07 billion tons, equivalent to 57.32% of the total bauxite resources in Indonesia with bauxite reserves of 0.84 billion tons or equivalent to 66.77% of the total national mineral reserves. The researched area covers Sompak District and surrounding areas, Landak Regency, West Kalimantan. This research aims to determine geological conditions, laterization, and characteristics of laterite bauxite in the studied area. Methods used in this research are geological mapping, lateritic mapping, and petrographic and geochemical analyses. The lithology of the researched area is composed of granodiorite, porphyry quartz diorite, granite, porphyry andesite, porphyry basalt, alluvial, and swamp deposits. Laterite profiles in the researched area generally consist of topsoil, latosol, bauxite, and clay zone. The laterite bauxite derived from granodiorite is classified as a medium grade, laterite bauxite from porphyry quartz diorite is classified as high-grade bauxite, laterite bauxite from andesite porphyry is classified as low-medium grade bauxite, and laterite bauxite from porphyry basalt in the studied area is classified as high grade bauxite. Laterite bauxites in the researched area were formed from weathered parent rocks which were intermediate - alkaline igneous rock.

Petrogenesis of Middle Triassic Adakite-like Intrusions in the Asiha Orogenic Gold Deposit, East Kunlun Orogenic Belt, China

The East Kunlun Orogenic Belt is considered as one of the important gold mineralization regions in the Tethys tectonic domain. These orogenic gold deposits are related to intermediate-acid intrusions formed at the end of Paleo-Tethys evolution, but the petrogenesis is controversial. This paper presents a new study on the geochemistry of zircon U-Pb, O, S, and Pb isotopic compositions of Asiha quartz diorite, granite porphyry, and sulfides. The geochemical features of quartz diorite and granite porphyry are consistent with the modern adakite, with high content of Sr but low content of Y, Yb, and MgO. Magmatic zircons from these two types of intrusion yielded U-Pb ages of 238.4 ± 1.4 Ma and 240 ± 1.7 Ma, respectively. The high O isotopic composition of Asiha complex may reflect that crust or crustal derivates were incorporated into the magmatic melt, and the Pb isotope characteristics indicates a lower crust origin. The δ34S values of pyrites range from 4.9‰ to 11.6‰. This study infers that the Asiha complex perhaps formed by partial melting of the Paleo-Tethys subducted oceanic crust with seafloor sediments and is markedly different from the traditional adakite. Asiha deposit is an orogenic gold deposit related to adakite-like rocks, which formed in Triassic in the East Kunlun Orogenic Belt.

Magnetic susceptibility, mineral chemistry, and geothermobarometry of granitoids from Lohit Plutonic Complex, Arunachal Trans‐Himalaya, Northeast India: Implications on emplacement and crystallization conditions of oxidized calc alkaline magmatic arc system

AbstractThe Lohit Plutonic Complex (LPC) of Arunachal Trans‐Himalaya represents the northeast extension of Trans‐Himalayan magmatic arc system located in the north of Indus Tsangpo Suture Zone (ITSZ). Field relation, magnetic susceptibility (MS), and phase petrology on the granitoids of LPC was conducted in order to assess the granite series (magnetite, oxidized vs. ilmenite, reduced types), and physico‐chemical conditions of the LPC granitoid magmas. The studied granitoids are well‐exposed in the Dibang and Lohit valleys, and their MS values indicate a bi‐modal patterns corresponding to ilmenite (reduced) series (71%) and magnetite (oxidized) series (29%) granites. The variation of MS in the LPC granitoids is related to the alteration of ferromagnetic minerals, and later tectonic and deformational processes that acted upon them. The amphiboles from the LPC granitoids are calcic (CaB >1.5, Si = 6.30–7.06 apfu) and exhibit tschermak substitutions typical to their evolution in a calc alkaline, metaluminous (I‐type) felsic magmas. Al‐in‐hornblende rims estimate the emplacement of quartz diorite and granodiorite magmas at shallow (~5 km) and mid (~16 km) crustal depths. Geothermometric results point to a regime of magmatic crystallization (940–837°C for quartz diorite; 882–829°C for granodiorite) sufficiently above the solidus of respective melts. Biotites from LPC granitoids are primary to re‐equilibrated, and transitional between magnesio‐ and ferri‐biotites. Quartz diorite and granodiorite biotites evolved under oxidizing magmas (log ƒO2−14 to log ƒO2−13) in a temperature range of ~750–950°C, typical to their formation in a calc alkaline magma of subduction zone environment. However, the biotites from leucogranite appear to have evolved under a mildly reducing magma environment, most likely attained in a collisional setting. The obtained results suggest that the oxidized nature of calc alkaline, subduction‐related magmatic arc rocks of the LPC is largely modified and reduced by post‐magmatic, and later tectonothermal and deformational events that operated during Himalayan and Trans‐Himalayan orogenesis.

МЕДНО-ПОРФИРОВАЯ МИНЕРАЛИЗАЦИЯ ТАЛЬНИКОВОГО РУДНОГО ПОЛЯ (ОХОТСКИЙ СЕГМЕНТ ОХОТСКО-ЧУКОТСКОГО ВУЛКАНОГЕННОГО ПОЯСА)

The Talnikovoye ore field where previous academic research and exploration work revealed porphyry copper mineralization is described. Our data show that mineralization is confined to the intrusions of Turonian granodiorite and quartz diorite (91 Ma, U-Pb metohod), as well as the accompanying hydrothermal-explosive breccias. Biotite-epidote-chlorite propylites are widespread within the ore field; in the southern part, phyllic alteration is superimposed on the halo of K-feldspar alteration. The ore occurs in zones of intense quartz, chlorite-epidote-quartz (with chalcopyrite and molybdenite), sulfide-potassium feldspar-quartz (with chalcopyrite and bornite), and sulfide-quartz-sericite (with chalcopyrite) stockwork veining with copper-molybdenum mineralization. They are characterized by moderate concentrations of Cu (0.1–0.3 %, reaching 1.1 %) and Mo (up to 0.1 %), low concentrations of Au (up to 0.1 g/t) and Ag (up to 2.6 g/t) and have a Cu-Mo-(Au, Ag, Pb, Zn, Sb, As) geochemical signature. Fluid inclusion data suggest the formation of mineralized veinlet quartz during the magmatic-hydrothermal transition (430–150 °С) with solutions at high (50 wt % NaCl equiv.), medium and low concentration (5–18.9 wt % NaCl equiv.) involved under the cooling-dilution scenario. Values of the main geochemical indicators, such as Cu/Mo (30–60) and Cu/Au (> 1 × 105) ratios allowed us to assign the Tal’nikovoye ore field to the porphyry copper-molybdenum type characteristic of continental-margin volcano-plutonic belts formed at the mafic island-arc basement. The geochemical parameters of porphyry granitoids indicate their formation in a setting of subduction-to-transform plate boundary transition.

Petrogenesis of the quartz diorite porphyry in the Zaozigou, West Qinling and its geological implications

西秦岭造山带位于华北板块和华南板块之间,是我国中央造山带的重要组成部分,记录了东亚古特提斯洋东北支的演化历史,对于探讨华北板块和华南板块的碰撞过程具有重要意义。西秦岭广泛发育的早-中三叠世火成岩与勉略洋壳向北俯冲有关,但勉略洋壳的闭合时限仍有争议。因此本文对采自早子沟地区的石英闪长玢岩进行锆石U-Pb年代学、Lu-Hf同位素和全岩主微量地球化学分析,查明早子沟石英闪长玢岩成因及其构造演化背景,并进一步约束勉略洋壳闭合时间。锆石LA-ICP-MS U-Pb定年结果表明,石英闪长玢岩侵位年龄为~232Ma,为中三叠世岩浆活动的产物。石英闪长玢岩含有较高的SiO₂(56.18%~68.26%),K₂O为1.82%~3.70%,A/CNK值为0.73~1.07,是准铝质-弱过铝质的钙碱性-高钾钙碱性岩石。其富钾的特征,与中高钾基性下地壳部分熔融产生的熔体成分一致。轻重稀土分异明显,(La/Yb)_N比值为8.10~61.2,富集大离子亲石元素(K、Sr、Ba、Cs),亏损高场强元素Nb、Ta,具有弱负铕异常(<i>δ</i>Eu=0.65~0.93),显示了典型的大陆地壳岩石特征。石英闪长玢岩较高的Mg^#值(47.57~70.35)意味着有一定幔源物质的加入。<i>ε</i>_Hf(<i>t</i>)在-12.9~-7.2之间,对应的二阶段Hf模式年龄(<i>t</i>²_DM)为1.70~2.10Ga,表明岩浆来自于古元古代下地壳的重熔。本文认为石英闪长玢岩形成于勉略洋壳向北俯冲背景下的活动大陆边缘环境,具有碰撞前花岗质岩石特征,即勉略洋壳在~232Ma仍处在俯冲阶段。

Geology, mineralization and calcite‐rich potassic alteration at the Humpa Leu East (HLE) porphyry Cu‐Au prospect, Hu'u district, Sumbawa Island, Indonesia

AbstractThe Humpa Leu East (HLE) prospect is one of the newly discovered porphyry Cu‐Au prospects in the Hu'u district, Sumbawa Island, Indonesia. The HLE prospect was formed by calc‐alkaline magmatic activity in an active continental margin setting. The prospect is typical calc‐alkaline porphyry Cu‐Au mineralization related to multiphase diorite and quartz diorite porphyry intrusions, which are hosted by andesitic crystalline tuff, volcanic breccia, and andesite lava. Hydrothermal alteration recognized at the surface includes potassic, propylitic, advanced argillic, intermediate argillic, and argillic alteration. Two styles of Cu‐Au mineralization were identified in the HLE prospect, that is, quartz‐sulfide veins and sulfide dissemination, formed in the early, intermediate, and late stages. The early stage is associated with M (magnetite ± bornite ± chalcopyrite), A (quartz + magnetite), and AB (quartz + magnetite + chalcopyrite ± pyrite) veins. These veins were mainly formed in the potassic alteration zone. The intermediate stage is characterized by B (quartz + chalcopyrite + pyrite) and C (chalcopyrite ± pyrite) veins and mainly associated with the chlorite‐sericite and sericite alteration zones. The late stage is mainly associated with D (calcite + gypsum + quartz + pyrite ± chalcopyrite ± sphalerite ± galena) veins with sericite‐chlorite alteration halo. Petrography and electron microprobe analyses indicate that calcite mainly replaced Ca‐rich plagioclase. Fluid inclusion petrography and Raman spectroscopy revealed that monophase vapor inclusions, as well as two‐phase (V + L) and multiphase (V + S + L) fluid inclusions contain CO2 gas. The potassic alteration with significant amounts of calcite is indicative of CO2‐rich fluids, which is uncommon in other porphyry Cu‐Au deposits. On the basis of textural and fluid inclusion analyses, calcite formed by a reaction between Ca‐rich plagioclase and CO2‐rich hydrothermal fluids. The CO2 in the hydrothermal fluids of the HLE prospect was likely derived from the magma.

Petrogenesis and geochronology of the bronze fox porphyry Cu-Au deposit: Implications for the geodynamic evolution of the Gurvansaykhan Island arc, southern Mongolia

ABSTRACT A diversity of Devonian-Carboniferous volcanic arcs and granitoid intrusions are exposed in the Gurvansaykhan arc terrane of southern Mongolia. Several giant porphyry Cu-Au-Mo deposits are associated with intrusions within these arcs. The Bronze Fox deposit located in the central part of the Gurvansaykhan arc terrane is an example of a potentially economic deposit with affinity of adakite-like granitoid porphyry (i.e. 428 Mt grading 0.26% to 0.30% Cu for up to 2,437 Mlb of copper and 0.84 Moz gold). The genesis and magmatic evolution of the causative rocks of the Bronze Fox porphyry Cu-Au hosting rocks are poorly understood, and different models are still under debate. In the current study, we present new field observations and petrographic, geochemical, and geochronological data to describe the magmatic evolution and geodynamic settings. In addition, the mineral chemical data are reported from some selected rock-forming minerals to identify crystallization conditions of the studied rock suites by employing geothermobarometric methods. Zircon chronological data reveal the emplaced age at 331 ± 3.4 Ma for the volcanic lava, followed by mineralized granodiorite and monzodiorite with intruded ages of 326.5 ± 3.4 Ma and 326.5 ± 2.7 Ma, respectively. The studied intrusive and extrusive rocks are high-K-alkaline and metaluminous, characterized by high Mg#. They are enriched in large ion lithophile elements (Sr and Ba) and light rare earth elements (LREEs) and depleted in high field strength elements (Nb, Ta, and Ti) and heavy rare earth elements (HREEs). The highly mineralized granodiorite intrusion yields zircon crystallization temperatures ranging from 631.8 to 779.4°C, and the monzodiorite intrusion, which contains relatively low-grade mineralization, has a wider range (599.0 to 803.4°C). The formation pressures of the former range from 0.5 to 0.2 kbar, which is equivalent to a depth of 1.38 km based on amphibole geochemical calculations. The results of mineral chemistry indicate that the unmineralized diorite unit was formed under medium pressure (~50 MPa) and high temperature (~750°C) at depths of 6.8 to 7.5 km. Similarities in geochemistry and petrographic features suggest that the igneous rocks probably originated from a similar magma source (i.e. from the melting of ancient oceanic crust and sediments) but experienced different degrees of partial melting or mixing with lower juvenile crust melts. The estimated fO2 values obtained by amphibole chemistry in the granodiorite and quartz diorite of the Bronze Fox copper-gold mineralization range from −13.0 to −11.8 and −13.2 to −10.8, respectively, confirming that these igneous rocks probably crystallized under relatively oxidized conditions above the nickel-nickel oxide (NNO) buffer. Such results yield an overall range between NNO +2.6 and NNO +1.4, which are characterized by high oxygen fugacities and high Ce4+/Ce3+ ratios that reflect oxidizing magma, thus indicating quite promising potential for porphyry Cu-Au mineralization in the region. Based on the findings of this work, we suggest a new tectonic model of arc magmatism that is a response to the subduction of the Paleo-Asian Ocean in the early Carboniferous period.

Geochronology (U-Pb and Re-Os) and H[sbnd]O[sbnd]S isotopes reveal ore fluid origin and crucial role of meteoric water for Laozuoshan quartz-vein-hosted gold metallogeny in Jiamusi, NE China

The Laozuoshan auriferous sulfide-quartz veins, which are hosted in the granodiorite, monzogranite, and quartz diorite, are the only Early Cretaceous gold deposit discovered in the central Jiamusi Massif, but its origin and ore-forming processes remain unclear. Here, we integrate mineralogy, HOS isotopes, and U-Pb and Re-Os geochronology to unravel the formation of the Laozuoshan quartz-vein gold mineralization. Zircon and molybdenite from the monzogranite wallrock and gold ores yield weighted mean U-Pb and isochron Re-Os dates of 259.9 ± 2.1 Ma and 103.3 ± 2.3 Ma, respectively. Our radiometric dating suggests that the Laozuoshan quartz-vein gold mineralization was coeval with the quartz diorite (105–103 Ma) but after the monzogranite emplacement. Quartz grains from the auriferous veins of different stages yielded scattered δ18O values (5.4 to 13.0 ‰), with the δD values (fluid inclusions) ranging from –99.9 to –74.9 ‰. The δ18O values of quartz (10.9–13.3 ‰) and feldspar (9.4–11.0 ‰) from the unaltered wallrocks are similar to those (δ18Oquartz = 11.2–13.2 ‰ and δ18Ofeldspar = 10.0–10.4 ‰) from the potassic alteration halos. Meanwhile, the sericite-altered rocks have δ18O values of 12.4–12.9 ‰ (quartz) and 3.4–5.2 ‰ (sericite). Sulfides from the gold ores yielded decreasing δ34S values from 5.3 to 6.9 ‰ (early stage), through 1.0–3.5 ‰ (intermediate stage), to –4.9 to –4.4 % (late stage). The isotope data reflect a largely magmatic source for the early ore fluids, whilst the sulfur was possibly derived from the Mashan Group migmatite. The results, in combination with geologic evidence, indicate that the Laozuoshan quartz-vein gold mineralization was spatially, temporally, and genetically related to the Early Cretaceous quartz diorite, and thus can be classified as intrusion-related, magmatic-hydrothermal-vein type. In the ore-forming processes, the ascending Early Cretaceous magma may have acquired most of their sulfur and gold through assimilation of the Mashan Group migmatite. The early ore fluids derived from the quartz diorite magma may have initially focused into narrow cracks/fractures in the quartz diorite margin and then flow along the fracture system. Subsequently, meteoric water incursion led to temperature drop, boiling, oxygen fugacity increase, and chemical exchange of the resultant fluids, which facilitated gold scavenging by bismuth-rich melts and rapid precipitation as arsenopyrite-hosted electrum and gold-bismuth mineral eutectic assemblage. This study highlights the crucial role of meteoric water in formation of the magmatic-hydrothermal-vein type gold deposit.

Multiple Sources of Indosinian Granites and Constraints on the Tectonic Evolution of the Paleo-Tethys Ocean in East Kunlun Orogen

Numerous Indosinian granitoids occur in the East Kunlun Orogen (EKO). The Indosinian was a key transitional period associated with the evolution of the Paleo-Tethys Ocean. Here, we study the relationship between the petrogenesis of the granitoids and the regional tectonic setting based on a comprehensive analysis of the petrology, geochronology, and geochemistry of typical granitoids in the eastern part of the EKO. The Indosinian granitoid compositions are dominated by quartz diorites, granodiorites, monzogranites, porphyritic monzogranites, and syenogranites. Early Indosinian granitoids are large, granitic batholiths, while the middle and late Indosinian granitoids are smaller in size. From the early Indosinian to late Indosinian, the granitoids show a transition from a medium-K calc-alkaline to high-K calc-alkaline composition. They are enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) and depleted in high-field-strength elements (HFSEs), especially for the Helegangxilikete and the Kekeealong plutons. The late Indosinian granitoids have relatively low Y and Yb contents, high Sr contents, and high La/Yb and Sr/Y ratios, which suggests adakitic affinity. The zircon saturation temperatures of the early Indosinian syenogranite and the Keri syenogranite are above 800 °C. The zircon saturation temperatures of other Indosinian granites (average 749 °C) are lower than those of the biotite and amphibole partial melting experiment. In the early Indosinian (255–240 Ma), numerous granitoids were the products of the partial melting of the juvenile lower crust by mafic magma underplating. This underplating is geodynamically related to the continuous subduction of a branch of Paleo-Tethys Ocean, with slab break-off, rapid upwelling, and mantle decompression. In the middle Indosinian (240–230 Ma), the compression that accompanied the continent–continent collision was not conducive to fluid activity, and hence, the formation of magma could be attributed to dehydration partial melting of muscovite, biotite, or amphibole. In the late Indosinian (230–200 Ma), the delamination of thickened crust would provide heat and channels for fluid migration, leading to a flare-up of the magmas. The composition and petrogenesis of the Indosinian granitoids in the eastern EKO are the result of processes associated with the subduction, collisional, and post-collisional stages, during the evolution of the Paleo-Tethys Ocean.

Mineralogy and Geochemistry of Diorites and Quartz Diorites of the Bolshoi Karan Gold–Porphyry Deposit in the Southern Urals

Mineralogy and Geochemistry of Diorites and Quartz Diorites of the Bolshoi Karan Gold–Porphyry Deposit in the Southern Urals

“Scissors‐type” closure of the A'nyemaqen Ocean: Geochronological and geochemical constraints of Late Permian–Triassic granitoids in the East Kunlun Orogen

The East Kunlun Orogen (EKO) is located in the western part of China and has witnessed the Late Permian–Triassic tectonic evolution involving the A'nyemaqen Ocean (a part of the Palaeo‐Tethys Ocean). In this study, geochronology, geochemistry, and Hf isotope analysis of Late Permian–Triassic granitoids were carried out. Zircon U–Pb dating of Dachagou granodiorite and monzogranite in the western part of the EKO (W–EKO) is 233.4 ± 1.1 and 225.8 ± 1.2 Ma, respectively. The Dachagou granodiorite and monzogranite are characterized by low values of 10, 000 Ga/Al ratios (1.75–2.06, 1.42–1.60) similar to those of I‐type granite. The εHf (t) (−2.4 to +0.1, −3.0 to +0.2) indicate that the magma forming these granites was derived from a mafic Mesoproterozoic lower crust. Zircon U–Pb age of Lalingzaohuo quartz diorite is 244.5 ± 2.6 Ma, and its εHf(t) values (−0.7 to +2.5) indicate the origin of crust–mantle mixing. Zircon U–Pb ages for Nagengkangqieer granodiorite and monzogranite in the eastern part of the EKO (E–EKO) are 250.1 ± 2.8 and 238.9 ± 2.2 Ma, respectively. These rocks are also characterized by low 10, 000 Ga/Al ratios (2.37–2.66 and 2.49–2.63) again similar to I‐type granite. The εHf(t) (−3.9 to 0.4, −3.3 to 1.1) indicate that the magma was derived from the crustal materials. As contemporaneous rocks, the Dachagou and Nagengkangqieer granodiorites and the Lalingzaohuo quartz diorites are formed in a subduction environment. However, the Dachagou and Nagengkangqieer monzogranites are formed in a collision environment. Based on this result, the closure time of the W–EKO and E–EKO of the A'nyemaqen Ocean had an age gap of ~15 Ma, hence the closure mode of the A'nyemaqen Ocean should be a “scissor‐type” closure.

Growth of early Paleozoic continental crust linked to the Proto-Tethys subduction and continental collision in the East Kunlun Orogen, northern Tibetan Plateau

The East Kunlun Orogen (EKO) in the northern Tibetan Plateau records two continental collisional orogenic events and magmatism in early Paleozoic and early Mesozoic. However, possible magmatic additions to the continental crust growth of the EKO in different tectonic stages of early Paleozoic collisional orogeny have been overlooked. Three phases of early Paleozoic plutons from the Xiangride-Kuhai area in the east of the EKO have been chosen for detailed investigation and the results are reported here. The oldest magmatic suite (Stage 1) includes the ca. 471 Ma Qurelong Monzodiorite and ca. 454 Ma granodiorite in the Zhiyu Intrusive Complex. The monzodiorite has a sanukitoid-like composition with high TiO2 and Y contents and is interpreted as being derived from partial melting of metasomatized mantle wedge lherzolite. The granodiorite is typified by its high SiO2 content, high Sr/Y ratio, and depleted Hf isotope, and is interpreted as an adakite-like melt derived from the melting of a subducted Proto-Tethys oceanic crust. The magmatism can be linked to northward subduction of the Proto-Tethys Ocean between 520 and 450 Ma. Stage 2 magmatism is represented by a plutonic suite emplaced during ca. 450−431 Ma with an I-type granitic composition. Of these, the ca. 447 Ma Kengdenongshe Intrusion composed of peraluminous granite with enriched Nd-Hf isotopes is indicative of a Mesoproterozoic igneous source in the orogen. The ca. 450−434 Ma monzogranite and granodiorite in the Walega and Zhiyu intrusive complexes exhibit variable element and isotope compositions. They would have been generated by magma mixing of felsic melts from the old crust and mafic magmas derived from the metasomatized lithospheric mantle, with a mafic melt proportion of &amp;gt;30%. The ca. 431 Ma quartz diorite in the Walega Intrusive Complex is formed through crustal assimilation and fractional crystallization of mafic magmas derived from the metasomatized lithospheric mantle, with a mafic melt proportion &amp;gt;60%. Stage 2 suite was emplaced during the closure of Proto-Tethys oceanic branches and subsequent continental collision during 450−426 Ma. Magmatism diminished between ca. 426 and 410 Ma during exhumation of the continental lithosphere as indicated by the presence of retrograde eclogites in the EKO. Stage 3 magmatic suite includes the ca. 408 Ma Langmuri Intrusion and ca. 403 Ma Niantang Syenogranite. These plutons are adakite-like or have an A-type granitic composition and are enriched in Nd-Hf isotopes. They might have been derived from the remelting of old and juvenile continental crust in a post-collisional extensional setting during 410−390 Ma. Identification of partial melts, derived from the subducted Proto-Tethys oceanic crust and metasomatized lithospheric mantle in stage 1 and 2 plutons, show that the subcrustal materials have been significantly transferred to the overlying continental crust. Hence the magmatism in oceanic subduction (Stage 1) and continental collision (Stage 2) settings contributes to the early Paleozoic juvenile continental crust growth of the EKO. The post-collisional extensional setting (Stage 3) is dominated by the reworking of a pre-existing continental crust. The early Paleozoic continental crust growth processes in the EKO are different from the previous view in which the continental collision orogens have no crust growth, and inconsistent with the proposal that crust growth is significant only in a continental collision setting.

Petrogenesis and Metallogenesis of Granitoids in the Yangla Cu-W Polymetallic Deposit, Southwest China: Evidence from Zircon Trace Elements and Hf Isotope

Magmatic zircon tends to present characteristic trends in trace element compositions in response to magma petrogenesis and metallogenesis, such that zircon may provide a window into melt evolution not accessible by whole rock chemistry. The Yangla large Cu deposit is located in the central part of the Jinshajiang Suture Zone, southwest China, constrained between the Jinshajiang and Yangla Faults. In this study, the trace elements and hafnium isotopic compositions of zircons from quartz diorite were studied. Previous published relevant data of Yangla granitoid plutons (i.e., dioritic enclave, granodiorite, and quartz monzonite porphyry) also have been systematically cited and discussed. The result shows that the crystallization temperature and two-stage Hf mode ages (tCDM; the age of the source rocks for the magmas) gradually increased while the oxygen fugacity (fO2) and εHf(t) values gradually decreased, corresponding to the diorite enclave (~232 Ma), through granodiorite (~208 Ma) and quartz monzonite porphyry (~202 Ma), and to quartz diorite (~195 Ma). It is suggested that four plutons were from the same three-component mixing of upper crust + lower crust + mantle magmas, while the upper crustal metasediments ratios were gradually increased from the early to late stage. The increasing upper crust inputs resulted in higher melting temperatures and compositions of the initial magma. All melts experienced distinct fractional crystallization of apatite, titanite, and amphibole, and the later granite melts experienced higher assimilation and fractional crystallization degrees than the early ones in the evolution processes four stages of intrusive rocks. These Yangla granitoids are the products of large-scale acid magmatic emplacement activities in the Triassic-early Jurassic and have a good metallogenic potential of the Cu-W polymetallic deposit.

Early-Middle Devonian adakitic magmatism generated by slab retreat in southern West Junggar, NW China: implications for tectonic correlation with central and East Kazakhstan

ABSTRACT The West Junggar terrane (WJT) is known to tectonically correlate with the Central and East Kazakhstan terrane; however, the Middle Palaeozoic magmatism has rarely been reported in the southern WJT, leading to significant uncertainties on the tectonic evolution and correlation of the southwestern Central Asian Orogenic Belt (CAOB). Here, we present the adakitic quartz diorites with zircon U-Pb ages of 390–394 Ma in the Alashankou region to demonstrate the presence of Early-Middle Devonian magmatism in the southern WJT for the first time. They are characterized by low Yb (1.00–1.41 ppm) and Y (8.9–14.4 ppm) but high Sr (301.5–475.9 ppm), Sr/Y (23–41), and (La/Yb)N (8.1–11) values, typical of modern adakites. As suggested by the relatively high SiO2 (64.96–67.71 wt.%), moderate K2O (1.53–3.19 wt.%), but low MgO (1.56–2.31 wt.%), TiO2 (0.28–0.42 wt.%), Cr (≤13.7 ppm), Co (2.7–9.9 ppm), Ni (8.0–18.7 ppm), and Th (3.7–4.8 ppm) concentrations as well as the high positive ɛHf(t) values (+5.6 to +10.3) and low Nb/Ta ratios, the adakitic quartz diorites were probably generated by the partial melting of a slightly thickened lower crust, which consisted mainly of the Ediacaran-Middle Palaeozoic intra-oceanic arc rocks in the southern WJT. Combined with regional data, our new results support that the southern WJT probably evolved as the eastern extension of the Kazakhstan Early-Middle Devonian outer volcanic belt during the Middle Palaeozoic. The Early-Middle Devonian tectonic extension and resultant lower crust melting may thus be related to the slab retreat of the Junggar-Balkhash Ocean.

Development of Open Transport of Aqueous Fluid from Pegmatite Revealed by Trace Elements in Garnet

We investigated the fluid flow and elemental transport from a granitic body to the middle crust by determining the trace element compositions of garnet in pegmatites related to a quartz diorite intrusion and metamorphic rocks on Kinkasan Island, northeast Japan. Garnet in the pegmatites and biotite schists is characterized by spessartine– (Sps–) almandine- (Alm-) rich compositions of Sps14–69Alm22–70Prp2–14Grs1–13 and Sps16–30Alm54–66Prp9–16Grs3–6, respectively. A garnetite pod in the metamorphic unit has grossular- (Grs-) rich compositions (Sps1–4Alm8–11Prp0.1–0.4Grs80–87Adr3–4). The peak temperature ( T ) and pressure ( P ) conditions of the biotite schist during contact metamorphism were 600–650°C and 0.27–0.41 GPa, respectively. The primary fluid inclusions in quartz crystals within the pegmatites hosted by the quartz diorite and hosted by the metamorphic rocks have a wide range of homogenization temperatures (200–380°C). These correspond to the trapping temperature of 500–700°C, assuming a salinity of 4 wt.% NaClequivalent at pressure of the crystallization of the quartz diorite. Chondrite-normalized rare earth element (REE) patterns of garnets in the pegmatites in the quartz diorite and metamorphic unit are generally characterized by enrichment of heavy REEs and negative Eu anomalies with the REE contents in the schists which are systematically lower than in the pegmatites. However, garnet in the biotite schists close to the pegmatites has similar REE contents to garnet in the adjacent pegmatites. These geochemical features suggest that garnet in the biotite schists grew in response to fluid infiltration from the pegmatites. Besides, the Grs-rich garnet in the garnetite pod and its host quartz schist have flat heavy REE patterns and no Eu anomalies, which probably reflect a metasomatic process related to plagioclase replacement that produced Ca-Al-rich fluids. Our results suggest that the infiltration of pegmatitic fluids enhances elemental transport and metamorphic reactions in the middle crust.

Subduction‐related mafic to felsic magmatism in the Xiangpishan concentric calc‐alkaline complex, Northeast Tibetan Plateau

The Xiangpishan complex in the Zongwulong‐Qinghainanshan Tectonic Belt, Northeast (NE) Tibetan Plateau, is a composite concentric pluton consisting of a felsic core (granodiorite) surrounded by quartz diorite in the middle to diorite and minor gabbro at the margin with locally less volume of monzogranite. Many dioritic enclaves are unevenly distributed within host granitoids. We evaluate the petrogenesis of the complex by geochemical, geochronological, and Hf isotopic data in tandem with regional data in the belt. The results show that felsic rocks were emplaced during the Late Permian (ca. 262–256 Ma); whilst gabbros yielded a younger age of ca. 249 Ma. As the hybrid phase from mixing between felsic and mafic magmas, enclaves and diorites have analogous ages (ca. 257–254 Ma) to both. Zircons from gabbro and enclaves are marked by higher εHf(t) value up to +1.82; whilst granodiorites have lower εHf(t) value of −5.48, consistent with hybrid diorites possessing intermediate εHf(t) values of −3.14 to 0.34. Furthermore, the quantitative calculation from Mass Balances Modelling suggests that the mass of mafic magma (ca. 67%–79%) is involved to achieve the hybridization. Geochemically, these rocks crystallized from calc‐alkaline magma with different sources, but demonstrated consistent arc‐like signatures, as they are enriched in large‐ion lithophile elements and light rare earth element (LREE), and depleted in high‐ field‐strength elements and heavy rare earth element (HREE). Besides, they present negative Nb–Ta anomalies together with significant P and Ti troughs. Finally, an evolutional model has been proposed that the asthenosphere‐lithosphere interaction played an important role during the emplacement of the complex, where the limited volumes of mantle‐derived melt act as the suppliers of heat and mass (mainly volatile components) to induce partial melting of the juvenile mafic lower crust and mixed (or mingled) with the produced crust‐derived magma during the oceanic subduction, which led to the generation of diorites as well as mafic microgranular enclaves.

The Mesoarchean plutonic complex from the Carajás province, Amazonian craton: Petrogenesis, zircon U[sbnd]Pb SHRIMP geochronology and tectonic implications

This study investigates the origin of the different Mesoarchean granitoids of the Ourilândia plutonic complex from the Carajás province (northern Brazil), as well as their geodynamic significance. This complex integrates interdigitated plutons of 2.88 Ga biotite granite (BG) and sanukitoid (SNK), with subordinate high-K calc-alkaline (HKCA) granodiorite-granite and tonalite-trondhjemite-granodiorite (TTG). (i) The BG is represented by equigranular monzogranite, which can be formed by 18% melting from TGG-type trondhjemite. (ii) The SNKs are composed of granodiorites (equigranular, heterogranular and porphyritic), with subordinate tonalite, quartz monzodiorite and quartz diorite, all with mafic microgranular enclaves. The different SNK-type granitoids and quartz monzodiorite were generated by 18–33% melting from mantle previously enriched by 20–40% TTG-type melt in the garnet stability zone. On the other hand, quartz diorite and mafic enclaves formed from fluid-metasomatized mantle at lower depths. (iii) The HKCA granodiorite-granite group (also called high-Ti SNK) is composed of porphyritic granodiorite and heterogranular monzogranite. The granodiorite can be formed by 30% melting from mantle enriched by 40% TTG-type melt under oxidizing conditions, with the participation of a component enriched in HFSEs. The heterogranular monzogranite is a hybridization product between 60% metasomatized mantle-derived magmas (high-Ti granodiorite) and 40% crust-derived magmas (equigranular monzogranite). (iv) The TTG-type tonalitic xenolith and porphyritic trondhjemite were formed by partial melting of hydrous metabasalts; however, the trondhjemite petrogenesis involves hybridization with enriched mantle-derived magmas. The BG and SNK provided coeval crystallization ages of 2881 ± 10 Ma and 2886 ± 14 Ma, respectively. In addition, in the BG, three more crystal populations were identified with ages of 3040 ± 40 Ma, 2976 ± 09 Ma and 2934 ± 21 Ma. The first two are interpreted as xenocrystals, and the latter is interpreted as inherited crystals. ∼2.88 Ga represents the main period of crustal growth in the Ourilândia do Norte area, with emplacement of juvenile magmas and crustal reworking. The studied rocks were formed in a post-subduction collision setting with coeval mantle and crust-derived magma generation over a short time span (∼2.88 Ga), where shear zones conditioned the ascent and emplacement of the Ourilândia magmas.

Petrogenesis and metal fertility of Yinzu pluton in the Daye district, eastern China: Insights from whole-rock and mineral (zircon, apatite and amphibolite) geochemistry

The Daye district in eastern China is featured by numerous granitoid intrusions of Early Cretaceous ages that intrude Paleozoic to Early Triassic marine carbonate and clastic rocks. Several dozen skarn Cu-Fe-Au deposits occur along the intrusive contact zones of the Echeng, Tieshan, Jinshandian, Lingxiang, Tongshankou and Tonglushan intrusions. However, no economic skarn mineralization has been recognized in other intrusions and whether or not these intrusions are metal fertile remain unresolved. In this paper, we use whole-rock and mineral (zircon, apatite and amphibole) geochemistry to provide significant new insights into the petrogenesis and metal fertility of the Yinzu granitoid pluton.The Yinzu pluton mainly consists of quartz diorite and diorite phases that have zircon U-Pb ages of 148.4 ± 1 Ma and 146.6 ± 1.6 Ma, respectively. Whole-rock Sr-Nd isotopic compositions ((87Sr/86Sr)i = 0.70635 to 0.70741; εNd(t) = −8.74 to −3.73) and zircon hafnium isotopes (εHf(t) = −9.1 to −4.8) overlap with values of the Cu-fertile Tongshankou and Tonglushan granitoids, implying a common enriched lithospheric mantle source. The whole-rock geochemical data suggest that both the diorite and quartz diorite have experienced variable degrees of fractional crystallization of olivine, amphibole, titanite and magnetite. The Ce4+/Ce3+ ratios (16–445) and oxygen fugacity (logfO2) calculated using trace element concentrations of zircon (ΔFMQ = +0.2 to +2.4) suggest that both intrusive phases crystalized from oxidized melts similar to Cu-fertile magmas in the world, with the quartz diorite being well comparable to the Tongshankou and Tonglushan granitoids. Based on available melt-apatite partitioning models, the estimated S and Cl contents for the magmas parental to the Yinzu pluton are akin to those of the Cu-fertile granitoids in the Daye district. Rocks of the Yinzu pluton display high apatite Sr/Y (0.38–3.01) and Eu/Eu* (0.35–0.71) ratios as well as high zircon Eu/Eu* (0.51–0.86) and 10000*(Eu/Eu*)/Y (2–27) ratios, indicating significant fractionation of amphibole with limited plagioclase fractionation and high magmatic water contents (>4 wt% H2O). This view is consistent with the calculated melt H2O content of 4.3–6.1 wt% based on the amphibole compositions.Collectively, results presented here indicate that magmas generating the Yinzu pluton are hydrous, oxidized and S-rich, characters similar to the Cu-fertile granitoids in Daye and elsewhere. Thus, the Yinzu pluton is considered to be Cu-(Au) fertile. This consideration is partially supported by occurrences of several vein-type Cu prospects within and disseminated Au ores in Silurian clastic sedimentary rocks immediately to the southeast of this pluton. Based on the regional metallogeny and results of this study, we suggest that the Yinzu pluton is a promising target of future Cu-(Au) exploration.

Mineralogy and Mineral Chemistry of Dioritic Dykes, Quartz Diorite Enclaves and Pyroxene of the Sungun Cu-Mo Porphyry Deposit, East Azerbaijan, Iran

The Sungun Cu-Mo porphyry deposit forms part of the Ahar–Arasbaran Magmatic Belt (AAMB). Its host Miocene porphyry stock is quartz monzonitic in composition and is cut by intermediate dykes that post-date mineralization. These dykes contain pyroxene and enclaves of ambiguous origin. Dykes of microdiorite are observed within quartz diorite dykes, whereas later diorite dykes contain three different kinds of enclaves (diorite, quartz diorite and hornfels) of sizes between 1 and 10 cm. Enclaves consist of plagioclase, hornblende and biotite, with accessory sphene, quartz and apatite. Chlorite compositions in microdiorite are within the chamosite range, whereas they are within the clinochlore range in diorite enclaves. Microprobe analyses of pyroxene indicate an augitic composition (Fs13.38-22.79Wo29.1-33.57En48.53-56.61), consistent with an igneous origin. Hornblende of the diorite enclaves formed at pressures ranging between 3 and 5.3 kilobars and temperatures between 714 and 731 °C. Average oxygen fugacity during rock formation is −14.75. Such high oxygen fugacities suggest that the diorite formed near the boundaries of a convergent margin. Amphibole compositions suggest that the diorite enclaves are sub-alkaline to mildly alkaline, consistent with reported whole-rock chemistry of the Sungun magmas. Pyroxenes were formed at pressures ranging between 11 and 15 kilobars (33–45 km) and temperatures between 1100 and 1400 °C. The amount of Fe3+ in clinopyroxene is also consistent with high oxygen fugacity within their environment of crystallization. Overall, these results have implications for our understanding of the origin of the Sungun Cu-Mo porphyry magmas and their mineral deposits in a lower-crustal setting.