Tectonic transition in the Aqishan-Yamansu belt, Eastern Tianshan: Constraints from the geochronology and geochemistry of Carboniferous and Triassic igneous rocks

A combination of zircon U-Pb ages, whole-rock geochemistry, Sr-Nd isotopes, and in situ zircon Hf isotope, for newly found felsic igneous rocks from the Hongshanliang copper deposit district in the Aqishan-Yamansu belt, NW China, are presented to investigate the petrogenesis and tectonic or even crustal evolution of the Eastern Tianshan during the Late Paleozoic to the Early Mesozoic. Zircon U-Pb ages show two phases of igneous activity in the Early Carboniferous (348.8 +/- 2.1 Ma and 343.3 +/- 2.3 Ma for rhyolite and granite porphyry) and the Triassic (250.2 +/- 3.5 Ma and 235.7 +/- 2.4 Ma for (monzonitic) granodiorite and monzogranite) in the Hongshanliang copper deposit district. The Carboniferous granitic rocks are enriched in Rb, Ba, and Pb, and depleted in Nb and Ta, with low WY ratios, showing arc-related affinities. Dominantly positive epsilon(Hf)(t) values ( +2.55 to +7.15 and +1.54 to +5.03 for the rhyolite and granite porphyry, respectively), crustally-derived geochemical elements ratios (e.g., Nb/Ta, Th/U, Ta/U, and Th/La) and Mg-# values (< 37), combined with epsilon(Nd)(t) values (-0.1 to +0.6 and 03 for the rhyolite and granite porphyry), suggest the Carboniferous granitic rocks were derived from partial melting of the Mesoproterozoic lower crust with mantle-derived magmas involvement. The Triassic (monzonitic) granodiorite and monzogranite are medium-K calc-alkaline, enriched in LILE, and depleted in HFSE, with high SiO2, Al2O3, Sr, and Sr/Y, and low Y and HREE values, characteristic of adakite-like rocks. The Triassic granitoids have low MgO, TiO2, Cr, Co, and Ni contents and high Fe2O3T/MgO ratios (3.07-3.23), with geochemical features of juvenile crust (e.g., low Nb/U and Ta/U ratios and depleted epsilon(Hf)(t) values) and mantle-derived magmas (e.g., high Th/U and Th/La ratios and Mg-# values), which suggests that the Triassic granitoids were derived from partial melting of thickened juvenile lower crust with minor mantle-derived components. Integrating published cognition and our work, we propose that the Aqishan-Yamansu belt underwent a tectonic transition from an Early Carboniferous fore-arc basin extensional setting to a Triassic within-plate one. Early Carboniferous granitic magmas were emplaced during the southward subduction of the Kangguer oceanic slab and Triassic granitoids were formed after later collision between the Dananhu-Tousuquan island arc and the Yili-Central Tianshan block. Moreover, we also conclude that the major crustal growth in the Eastern Tianshan occurred at ca. 444-270 Ma and was accompanied by abundant Fe-Cu-Ni-Au mineralization, with crustal reworking at ca. 250-200 Ma. (C) 2019 Elsevier B.V. All rights reserved

The multiple granitic magmatism in the giant Huayangchuan uranium polymetallic ore district: Implications for tectonic evolution of the southern margin of North China Craton in the Qinling Orogen

The giant Huayangchuan U-Nb-Pb deposit in the Qinling Orogen is a newly verified carbonatite-hosted deposit in the southern margin of the North China Craton (NCC), central China. Granitic magmatism is extensively developed in the Huayangchuan deposit area, but their ages and petrogenesis are not well constrained. The exposed granitic rocks are mainly biotite monzogranite porphyry, granite pegmatite, granodiorite, and biotite monzogranite with zircon U-Pb ages of 1808 +/- 10 Ma, 1807 +/- 14 Ma, 233 +/- 1.4 Ma, and 132 +/- 0.6 Ma, respectively. The Paleoproterozoic biotite monzogranite porphyry belongs to shoshonite and metaluminous series, showing enrichment of LREE and LILE and depletion of HREE and HFSE, with high Zr + Y + Nb + Ce values and Ga/Al ratios, which are consistent with A-type granite. Whereas, the contemporaneous granite pegmatite dykes with weak mineralization are also cala-alkaline to shoshonite and peraluminous series, enriched in Rb, Ba, and LREE, and depleted in Nb, Ta, Ti and HREE. The shoshonite and weakly peraluminous Triassic granodiorite is slightly enriched in LREE with flat HREE patterns, enriched in Ba and Sr and depleted in Nb, Ta, P, and Ti, with similar geochemical characteristics to adakite-like rocks. The Early Cretaceous biotite monzogranite is characterized by LREE enrichment and flat HREE patterns, belonging to shoshonite and metaluminous to weakly peraluminous I-type granite, with U and LILE enrichment, and HFSE-depleted. The high initial Sr-87/Sr-86 ratios and enriched Nd (epsilon(Nd)(t) = -17.5 to -17.1) and epsilon(Hf) (t) = -33.2 to -14.6) isotopes reveal that the Huayangchuan granitic rocks are obviously sourced from crustal-derived magmas. Combined with regional geology and this study, we proposed that: (1) the Paleoproterozoic biotite monzogranite porphyry and granite pegmatite were generated from ancient lower crust during post-collisional extension setting; (2) the granodiorite was likely sourced from partial melting of thickened lower crust with pelagic sediments materials addition during the Triassic although the mineralization-related carbonatite having similar age with granodiorite may derive from mantle; and (3) the Early Cretaceous biotite monzogranite was mainly sourced from the partial melting of lower crust induced by the underplating of the mafic magma. We suggest that the first phase of magma occurred in the Huayangchuan district during the Paleoproterozoic following the amalgamation of the Eastern and Western blocks along the Trans-North China Orogen. Since the Mesozoic, the ongoing northward subduction of the Yangtze Craton (YZC) resulted in the crust thickening, developing the Triassic granitic magmatism and major mineralization associated with carbonatite. The widespread Cretaceous granite and deposit in the southern margin of NCC indicate that intracontinental extension and lithospheric thinning occurred in response to the tectonic regime transition from NS-trending to EW-trending subduction

Late Paleozoic magmatism and metallogenesis in the Agishan-Yamansu belt, Eastern Tianshan: Constraints from the Bailingshan intrusive complex

The Aqishan-Yamansu belt in the Eastern Tianshan (NW China) contains many intermediate to felsic intrusive rocks and spatially and temporally associated Fe (-Cu) deposits. Zircon U-Pb dating of the Bailingshan granitoids, including diorite enclaves (in granodiorite). diorite, monzogranite and granodiorite, and andesitic tuff from the Shuanglong F-Cu deposit area yielded ages of 329.3 +/- 2.1 Ma, 323.4 +/- 2.6 Ma, 313.0 +/- 2.0 Ma. 307.5 +/- 1.7 Ma and 318.0 +/- 2.0 Ma, respectively. These new ages, in combination with published data can be used to sub-divide magmatism of the Bailingshan intrusive complex into three phases at ca. 329-323 Ma, ca. 318-313 Ma and ca. 308-297 Ma. Of the analyzed rocks of this study, the Shuanglong diorite enclave, diorite and andesitic tuff show calc-alkaline affinities, exhibiting LILE enrichment and HFSE depletion, with negative Nb and Ta anomalies. They have high MgO contents and Mg-# values, with depleted epsilon(Hf)(t) and positive epsilon(Nd)(t) values, similar crustal-derived Nb/Ta and Y/Nb ratios, low Th/Yb and Th/Nb, and high Ba/La ratios. which are consistent with them being sourced from a depleted mantle wedge metasomatized by slab-derived fluids and crustal contamination. However, the monzogranite and granodiorite are metaluminous with characteristics of low- to high-K calc-alkaline I-type granites. The granitic rocks are enriched in LILE, depleted in HFSE and have significant Eu anomalies, with high Y contents and low Sr/Y ratios, resembling typical of normal arc magmas. Depleted epsilon(Hf)(t) and positive epsilon(Nd)(t) values with corresponding young T-DM(C) ages of zircons, as well as Nb/Ta, Y/Nb, Th/U and La/Yb ratios suggest that the granitic rocks were probably formed by re-melting of juvenile lower crust or pre-existing mantle-derived mafic-intermediate igneous rocks. Integrating published data, we conclude that the Bailingshan granitoids (excluding the Shuanglong diorite and diorite enclave) were derived from re-melting of juvenile lower crust and mantle-derived mafic-intermediate igneous rocks, with mantle components playing a more prominent role in the formation of the younger and more felsic rocks. A comprehensive review, including our new data, suggests that the Aqishan-Yamansu belt formed as a fore-arc basin during the Carboniferous (ca. 350-300 Ma) when the Kangguer oceanic slab subducted beneath the Yili-Central Tianshan block. The ongoing southward subduction of the slab resulted in the closure of the Aqishan-Yamansu fore-arc basin (ca. 320-300 Ma), due to slab steepening and rollback followed by slab breakoff and rebound. During the Aqishan-Yamansu fore-arc basin inversion, the main phase of the Bailingshan granitoids emplaced in the Aqishan-Yamansu belt, accompanied by contemporary Fe and Fe -Cu mineralization. (C) 2018 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved

Magnetite Geochemistry of the Jinchuan Ni-Cu-PGE Deposit, NW China: Implication for Its Ore-Forming Processes

The Jinchuan Ni-Cu-PGE deposit is the single largest magmatic Ni-sulfide deposit in the world, with three different hypotheses on its ore-forming processes (e.g., in-situ sulfide segregation of sulfide-bearing magma, deep segregation with multiple injections of magma, and hydrothermal superimposition) mainly based on study of whole-rock geochemistry and isotopes (e.g., S-Sr-Nd-Hf). In this study, we mainly concentrated on magnetite textural and geochemical characteristics from different sulfide ores to clarify the genetic types and geochemical difference of the Jinchuan magnetite, and to explore a new credible ore-forming process by magnetite formation process when combined with detailed deposit geology. Three types of magnetite from massive and disseminated sulfide ores were observed by different textural analysis, and they were shown to have different genetic types (mainly in geochemistry) and trace elemental features. Type I magnetite is subhedral to anhedral from massive Ni- (or Fe-) and Cu-rich sulfide ores, with apparent magmatic origin, whereas Type II (dendritic or laminar crystals) and III magnetite (granular crystals as disseminated structures) from disseminated Cu-rich sulfide ores may have precipitated from late stage of melts evolved from a primitive Fe-rich and sulfide-bearing system with magmatic origin, but their geochemistry being typical of hydrothermal magnetite, videlicet, depletions of Ti (&lt; 20 ppm), Al (&lt; 51 ppm), Zr (0.01&ndash;0.57 ppm), Hf (0.03&ndash;0.06 ppm), Nb (0.01&ndash;0.14 ppm), and Ta (0.01&ndash;0.21 ppm). Such different types of magnetite can be clearly distinguished from concentrations and ratios of their trace elements, such as Ti, V, Co, Ni, Zn, Zr, Sn, Ga, and Ni/Cr. Those different types of Jinchuan magnetite crystallized from (evolved) sulfide-bearing systems and their geochemistries in trace elements are controlled mainly by evolution of ore-related systems and geochemical parameters (e.g., T and fO2), with the former playing a predominant role. Combining the previous literature with this study, we propose that the Jinchuan deposit formed by multiple pluses of sulfide-bearing magma during fractional crystallization, with the emplacing of more fractionated and sulfide-bearing magma during sulfide segregation playing a predominant role. During this multiple emplacement and evolving of sulfide-bearing systems, Type I magmatic magnetite crystallized from primitive and evolved Fe-rich MSS (monosulfide solid solution), while Type II and III magnetite crystallized from evolved Fe-rich MSS to Cu-rich ISS (intermediate solid solution) during sulfide fractionation, with those Type II and III magnetite having much higher Cu contents compared with that of Type I magnetite

Magnetite geochemistry of the Longqiao and Tieshan Fe-(Cu) deposits in the Middle-Lower Yangtze River Belt: Implications for deposit type and ore genesis

Magnetite is a common mineral in many ore deposits and their host rocks, and contains a wide range of trace elements (e.g., Ti, V, Mg, Cr, Mn, Ca, Al, Ni, Ga, Sn) that can be used for deposit type fingerprinting. In this study, we present new magnetite geochemical data for the Longqiao Fe deposit (Luzong, ore district) and Tieshan Fe-(Cu) deposit (Edong ore district), which are important magmatic-hydrothermal deposits in eastern China. Textural features, mineral assemblages and paragenesis of the Longqiao and Tieshan ore samples have suggested the, presence of two main mineralization periods (sedimentary and hydrothermal) at Longqiao, among which the hydrothermal period comprises four stages (skarn, magnetite, sulfide and carbonate); whilst the Tieshan Fe-(Cu) deposit comprises four mineralization stages (skarn, magnetite, quartz-sulfide and carbonate). Magnetite from the Longqiao and Tieshan deposits has different geochemistry, and can be clearly discriminated by the Sn vs. Ga, Ni vs. Cr, Ga vs. Al, Ni vs. Al, V vs. Ti, and Al vs. Mg diagrams. Such difference may be applied to distinguish other typical skarn (Tieshan) and multi-origin hydrothermal (Longqiao) deposits in the MLYRB. The fluid-rock interactions, influence of the co-crystallizing minerals and other physicochemical parameters, such as temperature and fO(2), may have altogether controlled the magnetite trace element contents of both deposits. The Tieshan deposit may have had higher degree of fO(2), but lower fluid-rock interactions and ore-forming temperature than the Longqiao deposit. The TiO2-Al(2)o(3)-(Mgo + Mno) and (Ca + Al + Mn) vs. (Ti + V) magnetite discrimination diagrams show that the Longqiao Fe deposit has both sedimentary and hydrothermal features, whereas the Tieshan Fe-(Cu) deposit is skarn-type and was likely formed via hydrothermal metasomatism, consistent with the ore characteristics observed

The Late Paleozoic magmatic evolution of the Aqishan-Yamansu belt, Eastern Tianshan: Constraints from geochronology, geochemistry and Sr-Nd-Pb-Hf isotopes of igneous rocks

The Aqishan-Yamansu belt in the Eastern Tianshan (Xinjiang, NW China) is an important mineralization belt. The belt mainly comprises Carboniferous volcanic, volcaniclastic and elastic rocks, and hosts many intermediate-felsic intrusions and Fe (-Cu) deposits. The biotite diorite, felsic brecciated tuff, granodiorite and syenite from the western Aqishan-Yamansu belt are newly zircon U-Pb dated to be 316.7 +/- 1.4 Ma, 315.6 +/- 2.6 Ma, 305.8 +/- 1.9 Ma and 252.5 +/- 1.4 Ma, respectively. The mafic rocks (mafic brecciated tuff and diabase porphyry) are tholeiitic to talc-alkaline series, LILE-rich (e.g., Rb, Ba and Pb), HFSE-depleted (e.g., Nb and Ta), and have high Mg-#(44-60), Nb/Ta (15.0-20.0), Ba/La (&gt; 30) and Ba/Nb (&gt; 57) values/ratios, and low Th/Yb ratios (&lt; 1), probably originating from mantle wedge metasomatized by slab-derived fluids. The intermediate-felsic igneous rocks are LILE-rich, HFSE-depleted, with high Sr and Y contents showing typical of normal arc magma affinity. Moreover, the depleted epsilon(Hf)(t) (&gt; 2.10) and positive epsilon(Nd)(t) (&gt; 5.7), combined with variable Nb/Ta ratios (9.52-21.4), Y/Nb ratios (1.47-39.7) and Pb isotopes (Pb-206/Pb-204 = 16.225-17.640, Pb-207/Pb-204 = 15.454-15.520, Pb-208/Pb-204 = 37.097-38.025) suggest that these rocks were magma mixing products between juvenile crustal-derived magmas and minor mantle-derived magmas. Combined published works with our new ages, geochemical and isotopic data, we propose that the Aqishan-Yamansu belt was an Early Carboniferous fore-arc basin during the southward subduction of the Kangguer oceanic slab beneath the Yili-Central Tianshan block. With the continuing southward subduction, the Aqishan-Yamansu fore-arc basin initiated to close, which generated the mafic and intensive intermediate-felsic magmatism associated with regional Fe (-Cu) mineralization

Deciphering fluid origins in the Paleozoic Laoshankou Fe-Cu-Au deposit, East Junggar: Constraints from noble gases and halogens

To constrain the ore-fluid source(s) of the Laoshankou Fe-Cu-Au deposit (Junggar orogen, NW China), we analyzed the fluid inclusion (FI) noble gas (Ar, Kr and Xe) and halogen (Cl, Br and I) compositions in the hydrothermal epidote and quartz. Four hypogene alteration/mineralization stages, including (I) pre-ore Ca-silicate, (II) early-ore amphibole-epidote-magnetite, (III) late-ore pyrite-chalcopyrite, and (IV) post-ore hydrothermal veining, have been identified at Laoshankou. Stage II FIs have salinity of 15.7 wt.% (NaCl eq.), I/Cl molar ratios of 75 × 10−6–135 × 10−6, and Br/Cl molar ratios of 1.4 × 10−3–2.1 × 10−3. The moderately-high seawater-corrected Br*/I ratios (0.5–1.5) and low 40ArE/Cl slope (~10−5) indicate the presence of sedimentary marine pore fluid, which was modified by seawater reacting with the Beitashan Fm. volcanic rocks. Stage III fluid is more saline than their stage II and IV counterparts, reaching up to 23.3 wt.% (NaCl+CaCl2 eq.) close to halite saturation (~26 wt.%). The fluid has I/Cl ratios of 75 × 10−6–90 × 10−6 and Br/Cl ratios of 1.5 × 10−3–1.8 × 10−3. Considering the increasing 40ArE/Cl trend toward bittern brine and the higher 36Ar content than air-saturated water (ASW), a bittern fluid source is inferred from seawater evaporation, which was modified by interaction with organic-rich marine sedimentary rocks. Stage IV FIs have lower temperature (110–228 °C) and Br/Cl (0.90 × 10−3–1.2 × 10−3), but higher 36Ar content than ASW, indicative of dissolved evaporite or halite input. Considering also the low δDfluid (−114‰ to −144‰) and δ18Ofluid (2.1‰–3.5‰) values, meteoric water (with minor dissolved evaporites) likely dominated the stage IV fluid. The evaporites may have formed through continuous evaporation of the stage III surface-derived bittern. Involvement of non-magmatic fluids and different ore-fluid origins in stages II and III suggest that the ore-forming process was different from a typical magmatic-hydrothermal fluid-dominated skarn mineralization, which was previously proposed for Laoshankou. Our noble gas and halogen study at Laoshankou provide new insights on the fluid sources for the Paleozoic Fe−Cu (−Au) deposits in the Central Asian Orogenic Belt (CAOB), and our non-magmatic fluid source interpretation is consistent with the basin inversion setting for the mineralization

Genesis of the Paleozoic Aqishan-Yamansu arc-basin system and Fe (-Cu) mineralization in the Eastern Tianshan, NW China

The formation of the Eastern Tianshan orogen (northern Xinjiang, NW China) with a number of EW-trending mineralization belts was closely linked to the evolution of the Junggar and South Tianshan oceans, probably part of the Paleo-Asian Ocean. Among these Eastern Tianshan mineralization belts, the Carboniferous Aqishan-Yamansu Fe (-Cu) belt hosts a total reserve of 207 Mt Fe and economic Cu endowments for many deposits. These Fe (-Cu) deposits are hosted in submarine volcanic rocks (Lower Carboniferous Yamansu Formation and Upper Carboniferous Tugutublak Formation) and are featured by the presence of extensive skarn alteration without apparently-causative intrusive rocks, which leads to debates over their genesis. In this paper, we have summarized the ore deposit geology, geochemistry and stable isotopes of the Aqishan-Yamansu Fe (-Cu) deposits and discuss their genesis under the regional tectonic framework. We suggest that the Carboniferous Aqishan-Yamansu belt may have been a forearc basin formed by the south-dipping subduction of the Kangguer Ocean beneath the Central Tianshan massif. The Yamansu Formation volcanic rocks and some syngenetic Fe deposits may have formed during the opening of the forearc basin. The Tugutublak Formation volcanic rocks and most Fe (-Cu) deposits may have formed during the subsequent Late Carboniferous basin inversion. In these Aqishan-Yamansu Fe (-Cu) deposits, the Fe mineralization occurred earlier and was likely formed directly from the magmatic-hydrothermal fluids, whereas the subsequent Cu mineralization was likely caused by the gradual increase of seawater or basinal brine influx into the fluid system (external sulfur). The probable external sulfur input, the absence of clear plutonic link, and the temporal coincidence of peak mineralization and basin inversion for the Carboniferous Aqishan-Yamansu Fe -Cu mineralization are comparable to the Mesozoic IOCG mineralization in the Central Andes

Magnetite geochemistry of the Heijianshan Fe-Cu (-Au) deposit in Eastern Tianshan: Metallogenic implications for submarine volcanic-hosted Fe-Cu deposits in NW China

The Heijianshan Fe-Cu (-Au) deposit is located in the Aqishan-Yamansu belt in Eastern Tianshan, NW China. As a typical Fe-Cu deposit in the region, Heijianshan is hosted in the Upper Carboniferous Matoutan Formation submarine volcanic/volcaniclastic rocks. Alteration styles, mineral assemblages and vein crosscutting relationships divide the hydrothermal alteration and mineralization processes into seven stages, namely the chromite (Stage I), epidote (Stage II), magnetite (Stage III), pyrite (Stage IV), Cu (-Au) (Stage V), late veins (Stage VI) and supergene (Stage VII) alteration/mineralization stages. Magnetite mineralization comprises the hematite (Stage III-A) and main magnetite (Stage Ill-B) mineralization sub-stages. The Heijianshan magnetite ores consist of massive (with mushketovite (MOM) or sulfides (MOS)), disseminated (DO) and magnetite clasts (with chromite (MWC) or without chromite (MNC)) ores. Magnetite in massive- and disseminated ores is featured by (1) depletion in Zr, Nb and Ta; (2) low Ti (&lt;2 wt.%) and Al (&lt;1 wt.%); and (3) Ni/Cr &gt;= 1, which all reflect a hydrothermal origin. Moreover, magnetite in massive-and disseminated ores has lower Cr (MOM: 0-13.2 ppm; MOS: 0-12.9 ppm; DO: 3.57-133 ppm) than magnetite clasts ores (MNC: 849-2544 ppm; MWC: 835-44,132 ppm). However, the high Cr in the magnetite clasts ores may have been inherited from the chromite they replaced. From the magnetite clasts to disseminated/massive ores, formation temperature decreased and fO(2) increased, which may represent the major controls on the formation of the various magnetite ore types. Compositions of the ore fluids and host rocks, formation of coexisting minerals and other physicochemical parameters (such as T and fO(2)) may have variably influenced the magnetite geochemistry in the different Heijianshan ore types, with fluid compositions probably playing the most important role. Discrimination diagrams, for instance, Cr vs. Co/Ni, Cr vs. Ti, V vs. Cr and Ni vs. Cr, may be useful for magnetite mineralization type differentiation in other submarine volcanic-hosted Fe/Fe-Cu deposits in the Aqishan-Yamansu belt. Geochemical discrimination diagrams, alteration and mineralization paragenesis indicate that the Heijianshan Fe-Cu (-Au) deposit is best classified as an IOCG-like deposit, which offers a new insight for classifying and characterizing ore genetic types for similar Fe and Fe-Cu deposits in Eastern Tianshan. (C) 2016 Elsevier B.V. All rights reserved