Zircon Geochemistry Research Articles

Dating the Sedimentary Protolith of the Daldyn Group Quartzite, Anabar Shield, Russia: New Detrital Zircon Constraints

Quartzites and paragneisses of the Archean granulite series of the Anabar Shield (Siberian Craton, Russia) are described geochemically. The Sm-Nd isotope systematics of the rocks and the U-Pb age (SHRIMP II) and geochemistry of zircons from quartzites and paragneisses are studied. Newly formed zircons from quartzites display geochemical characteristics of the magmatic type and were produced by rock anatexis upon granulite-facies metamorphism. The Paleoproterozoic age of the latest detrital zircons, 2250 ± 24 Ma, constrains the maximum age of sedimentary rock deposition. The anatectic rims around detrital zircons were formed ca. 2000 ± 9 Ma ago. The time of deposition of the sedimentary protolith of gneisses and quartzites falls within the age interval of the above-mentioned dates and is tentatively accepted as 2.1 Ga. The presence of Paleoproterozoic metasedimentary rocks in the Daldyn Group implies the tectonic heterogeneity of the series and the existence of Paleoproterozoic rock bodies among the predominant Archean rock sequences.

The contribution of charnockite magmatism to achieve near-ultrahigh temperatures in the Namaqua–Natal Metamorphic Province, South Africa

Aluminous metapelitic granulites from the central Namaqua Sector of the Namaqua–Natal Metamorphic Province, South Africa, host partly retrogressed hercynite–quartz assemblages. These assemblages record peak P–T conditions of 860–890 °C and 5–5.5 kbar, estimated via thermodynamic modelling and ternary feldspar thermometry. In-situ U–Pb geochronology and geochemistry of anatectic zircon and monazite constrains this event as part of the main Namaqua Orogeny affecting the terrane at c. 1040–1035 Ma. Detrital zircon age spectra span from about 1860 to 1100 Ma, peaking at c. 1800–1700 and 1400–1300 Ma, suggesting detritus was sourced from nearby Paleoproterozoic- and Mesoproterozoic terranes. Thin sections reveal narrow monomineralic coronae of garnet, cordierite or sillimanite separating formerly coexisting hercynite and quartz. Calculated chemical potential relationships show that coronae have developed in response to very minor, near-isobaric cooling shortly after the thermal peak, involving limited diffusion down gradients of μFeO–μMgO. Corona formation occurred in distinct compositional domains, controlled by neighbouring porphyroblasts such as garnet and/or sillimanite. Isolated hercynite–quartz pairs distal from porphyroblasts developed thin rinds of sillimanite, requiring no additional compositional gradients. Cordierite inclusions in garnet, limited melt production and extraction and corona-textures are consistent with an anticlockwise evolution, involving burial and concomitant heating to near-ultrahigh temperature conditions followed by near-isobaric cooling at mid-crustal depths. The hercynite–quartz equilibria record the highest metamorphic temperature affecting the Namaqua Sector, requiring a crucial component of advective heating via voluminous pre- to syn-metamorphic felsic-charnockitic magmatism of the Spektakel Suite. Namaqua-aged granulite facies metamorphism at the terrane scale was driven by a combination of mafic underplating and radiogenic heating. Calculated temperature–enthalpy profiles suggest that advective heating locally increased the suprasolidus enthalpy budget by a third which allowed peak temperatures to be some 50 °C higher than would otherwise have been achieved.

Granite-Related Tin Metallogenic Events and Key Controlling Factors in Peninsular Malaysia, Southeast Asia: New Insights from Cassiterite U-Pb Dating and Zircon Geochemistry

Abstract Permian-Triassic granites and associated tin deposits are widespread in the Eastern and Western belts of Peninsular Malaysia. The ages and key controlling factors of tin mineralization, however, are poorly constrained. Cassiterite separates from the Sintok and Rahman tin deposits in the Western belt, and Bandi, Setahum, Lembing, and Cherul tin deposits in the Eastern belt have U-Pb ages of 218.9 ± 3.4 and 226.8 ± 7.6 Ma, and 213.1 ± 3.9, 270.6 ± 4.6, 282.7 ± 4.6, and 281.3 ± 3.5 Ma, respectively. These ages directly constrain the tin mineralization in Peninsular Malaysia to two separate periods: 290 to 270 Ma and 230 to 210 Ma. Zircon crystals from tin-bearing granites in the Cherul and Sintok deposits have U-Pb ages of 276.0 ± 1.9 and 221.9 ± 0.6 Ma, respectively, consistent with the cassiterite U-Pb ages within uncertainties. Zircon crystals from barren granites of the Kuantan pluton in the Eastern belt have a U-Pb age of 260.5 ± 0.7 Ma, which is between the two tin mineralization periods. Zircon from these barren granites have εHf(t) values from −5.4 to 3.6, two-stage Hf model ages (TDM2) from 1.4 to 1.0 Ga, and Ce4+/Ce3+ ratios from 40 to 120. By comparison, zircon crystals from the tin-bearing granites have low εHf(t) values (−9.7 to −3.2) and Ce4+/Ce3+ ratios (4–67) and high TDM2 (1.8–1.4 Ga). Zircon ages, Hf isotopes, and trace elements indicate that the tin-bearing granitic magmas in Peninsular Malaysia had relatively low oxygen fugacity and were derived from reworking of Paleo- to Mesoproterozoic sedimentary rock-dominated crust in response to the Paleo-Tethyan subduction and continental collision. This study confirms that the nature of magma sources and redox states of magmas were key in the formation of the tin-rich granites and associated tin deposits and that the granite-related tin mineralization in Peninsular Malaysia was closely related to the evolution of the eastern Paleo-Tethys.

Source rejuvenation vs. re-heating: Constraints on Siberian kimberlite origin from U[sbnd]Pb and Lu[sbnd]Hf isotope compositions and geochemistry of mantle zircons

We have studied a suite of mantle zircons from several differently aged pipes of the Siberian kimberlite province via UPb and LuHf isotope analyses and trace element compositions. The UPb ages we obtained confirmed four main episodes (Silurian, Devonian, Triassic and Jurassic) of kimberlite activity on the Siberian craton. The Druzhba pipe had two populations of zircons dating from the Silurian and Devonian, respectively. The geochemical features of our suite of mantle zircons show low concentrations of U, Th and heavy rare earth elements (REEs), positive Ce anomalies, and weak or absent Eu anomalies, which is in accord with the mantle-derived nature of the zircon. Despite having broadly similar geochemistry, zircons from differently aged kimberlites had some clear differences arising from variations in the composition of the protokimberlite metasomatic melt and from peculiarities of fractional crystallization. The Th/U ratios were highest in the Silurian zircons and sharply decreased toward the Devonian. The Triassic zircons had elevated and highly variable Ce/Nb ratios with low and nearly constant Th/U ratios.Zircons from Siberian kimberlites with different UPb ages showed systematic variations in their initial Hf isotope compositions. The oldest Silurian kimberlite field, Chomurdakh, had two zircon populations: Silurian zircons, with ɛHft values in the range of +2.8 to +5.9 units, and Devonian zircons, with ɛHft values in the range of +1.6 to +2.0 units. Zircons from the Devonian field kimberlites were in the range of +5.6 to +9.6 ɛHft units. The Triassic kimberlitic zircons had the most juvenile Hf isotope composition, at +9.3 to +11.2 ɛHft units, while the Jurassic zircons had +6.9 ɛHft units. The combination of the UPb and LuHf isotope data suggests a periodic rejuvenation of the lithospheric mantle roots by low-volume melts from the asthenospheric mantle, resulting shortly after in kimberlite emplacements. Some Devonian and Jurassic kimberlites may have been melted by re-heating the Silurian and Triassic age sources, respectively, about 60 Myr after they were formed.

Zircon geochemistry of Edong granitoids in the Middle-Lower Yangtze Metallogenic Belt (Eastern China): Constraints on W-Cu-Fe skarn mineralization

It has long been established that skarn deposits of different metals are associated with intrusions of different compositions. Intermediate-felsic granitoids in the Edong district of the Middle-Lower Yangtze Metallogenic Belt host skarn deposits with varying W-Cu-Fe proportions, yet previous whole-rock geochemical studies could not distinguish between the magmatic suites that formed the different skarn deposits. In this study, LA-ICP-MS zircon geochemical data are presented for the Ruanjiawan W skarn (60300 t WO3), Tongshankou Cu skarn (0.6 Mt Cu), Tonglushan Cu-Fe skarn (1.1 Mt Cu and 56.8 Mt Fe) and Jinshandian Fe skarn (200 Mt Fe) deposits in the Edong district. Zircons from the ore-forming intrusions of these skarn deposits are all characterized by heavy rare earth element (HREE) enrichments and light rare earth element (LREE) depletions, with positive Ce anomalies and slightly negative Eu anomalies. Tungsten contents in zircons from the W ore-forming intrusion (0.02–3.16 ppm W; avg. 1.14 ppm) are generally higher than in zircons from the Cu ore-forming intrusion (0.00–0.24 ppm W; avg. 0.03 ppm). Copper content in zircons from the Cu ore-forming intrusion is higher than in those from the W ore-forming intrusion. Fertile intrusive rocks from the four skarn deposits contain zircons with high calculated Ce4+/Ce3+ ratios (Ruanjiawan: 71.7; Tongshankou: 207.5; Tonglushan: 263.6; Jinshandian: 189.0. Fluorine content of the Ruanjiawan intrusion is higher than the Tonglushan and Jinshandian intrusions, followed by the Tongshankou intrusion. Chlorine contents show the opposite trend. We propose that the different source regions for the ore-fertile intrusions is the critical factor that controls the metal content, oxygen fugacity and volatile components. Our studies suggest that zircon geochemistry is a good indicator to distinguish tungsten causative intrusions from copper- and iron ore related intrusions (i.e. W content ≧ 1.14 ppm and Ce4+/Ce3+ ratios ≦ 207.5).

Rare sapphire-bearing syenitoid pegmatites and associated granitoids of the Hamedan region, Sanandaj–Sirjan zone, Iran: analysis of petrology, lithogeochemistry and zircon geochronology / trace element geochemistry

AbstractPegmatites and associated granitoids are integral parts of the Alvand plutonic complex in the Sanandaj–Sirjan zone, Iran. Whole rock major- and trace-element lithogeochemistry together with zircon U–Pb geochronology and zircon geochemistry are examined to evaluate the petrogenesis of sapphire-bearing pegmatites and other peraluminous pegmatites in the region. Pegmatites vary in their chemical compositions from mostly peraluminous, high-K calc-alkaline to shoshonitic signatures. A rare variety of extremely peraluminous sapphire-bearing syenitoid pegmatite (Al2O3> 30 wt %; A/CNK > 2) exists. This silica-undersaturated pegmatite and its sapphire crystals have a primary igneous origin. U–Pb zircon geochronology of three separate samples from this pegmatite indicates the following ages: 168 ± 1 Ma, 166 ± 1 Ma and 164 ± 1 Ma. The zircon grains have notable amounts of Hf (up to 17 200 ppm), U (up to 13 580 ppm), Th (up to 5148 ppm), Y (up to 4764 ppm) and ∑REE (up to 2534 ppm). There is a positive correlation between Hf and Th, Nb and Ta, U and Th, and Y and HREE and a negative correlation between Hf and Y values in the zircons. These zircons exhibit pronounced positive Ce anomalies (Ce/Ce* = 1.15–68.06) and negative Eu anomalies (Eu/Eu* = 0.001–0.56), indicative of the relatively oxidized conditions of the parent magma. Ti-in-zircon thermometry reveals temperatures from as low as ~683 °C up to ~828 °C (average = 755° ± 73 °C). Zircon and monazite saturation equilibria are also consistent with these temperatures. Zircon grains are magmatic (average La < 1.5, (Sm/La)N> 100 and Th/U > 0.7), with chemical characteristics similar to zircons from continental crust.

Trace Element Geochemistry of Zircons from the Early Paleozoic Granites of the Angara–Vitim Batholith

Abstract—Analysis of zircons from Early Paleozoic calc-alkaline granitoids in the central part of the Angara–Vitim Batholith revealed two geochemically different zircon varieties. Central unaltered domains have homogenous BSE images, “magmatic” REE distribution pattern, and the moderate content of trace elements. Altered zones of zircon are characterized by more gentle patterns owing to the growth of LREE and MREE, as well as by the elevated contents of U, Th, Ca, Sr, and Ba. Such compositional peculiarity could be related to the influx of fluid, which caused a metasomatic alteration of granites during their microclinization. Geochemical features of zircons, together with their internal structure, should be taken into account during geochronological study of zircon.

The Geochronology and Geochemistry of Zircon as Evidence for the Reconcentration of REE in the Triassic Period in the Chungju Area, South Korea

The Chungju rare-earth element (REE) deposit is located in the central part of the Okcheon Metamorphic Belt (OMB) in the Southern Korean Peninsula and research on REE mineralization in the Gyemyeongsan Formation has been continuous since the first report in 1989. The genesis of the REE mineralization that occurred in the Gyemyeongsan Formation has been reported by previous researchers; theories include the fractional crystallization of alkali magma, magmatic hydrothermal alteration, and recurrent mineralization during metamorphism. In the Gyemyeongsan Formation, we discovered an allanite-rich vein that displays the paragenetic relationship of quartz, allanite, and zircon, and we investigated the chemistry and chronology of zircon obtained from this vein. We analyzed the zircon’s chemistry with an electron probe X-ray micro analyzer (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The grain size of the zircon is as large as 50 µm and has an inherited core (up to 15 µm) and micrometer-sized sector zoning (up to several micrometers in size). In a previous study, the zircon ages were not obtained because the grain size was too small to analyze. In this study, we analyzed the zircon with laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) for dating purposes. The REE patterns and occurrence of zircon in the quartz–allanite vein match well with previous reported recrystallized zircon, while the behavior of the trace elements shows differences with magmatic and hydrothermal zircon. The 206Pb/238U ages obtained from the zircon in the quartz–allanite vein are from 240.1 ± 2.9 to 257.1 ± 3.5 Ma and this age is included in the tectonic evolution period of the study area. Therefore, we suggest that the quartz–allanite veins in the Gyemyeongsan Formation were formed during the late Permian to early Triassic metamorphic period and the zircon was recrystallized at that time. The Triassic age is the first reported age with zircon dating in the Gyemyeongsan Formation and will be an important data-point for the study of the tectonic evolution of the OMB.

The Chemical Evolution from Older (323–318 Ma) towards Younger Highly Evolved Tin Granites (315–314 Ma)—Sources and Metal Enrichment in Variscan Granites of the Western Erzgebirge (Central European Variscides, Germany)

The sources and critical enrichment processes for granite related tin ores are still not well understood. The Erzgebirge represents one of the classical regions for tin mineralization. We investigated the four largest plutons from the Western Erzgebirge (Germany) for the geochemistry of bulk rocks and autocrystic zircons and relate this information to their intrusion ages. The source rocks of the Variscan granites were identified as high-grade metamorphic rocks based on the comparison of Hf-O isotope data on zircons, the abundance of xenocrystic zircon ages as well as Nd and Hf model ages. Among these rocks, restite is the most likely candidate for later Variscan melts. Based on the evolution with time, we could reconstruct enrichment factors for tin and tungsten starting from the protoliths (575 Ma) that were later converted to high-grade metamorphic rocks (340 Ma) and served as sources for the older biotite granites (323–318 Ma) and the tin granites (315–314 Ma). This evolution involved a continuous enrichment of both tin and tungsten with an enrichment factor of ~15 for tin and ~7 for tungsten compared to the upper continental crust (UCC). Ore level concentrations (>10–100 times enrichment) were achieved only in the greisen bodies and dykes by subsequent hydrothermal processes.

Using zircon geochemistry to map alteration in the Gawler Craton, South Australia

Zircon is a refractory mineral that is able to crystallize within hydrothermal, igneous and metamorphic environments, resulting in extreme variability in its external morphology, internal textures ...

Tectonomagmatic evolution of the Sveconorwegian orogen recorded in the chemical and isotopic compositions of 1070–920 Ma granitoids

The Sveconorwegian Province in Southern Norway and Sweden hosts at least four granitoid suites, representing apparently continuous magmatism at the SW margin of the Fennoscandian Shield between 1070 and 920 Ma. This study presents a compilation of published and new zircon LA-ICP-MS U-Pb geochronology, whole-rock and zircon geochemistry and Sm-Nd isotope data for the granitoid suites and demonstrates the granitoids’ ability to record changes in the tectonomagmatic evolution of this orogenic Province. The Sirdal Magmatic Belt (SMB, ca. 1070–1010 Ma) represents the earliest magmatism, west in the Province, followed by two hornblende-biotite granitoid suites (HBG, ca. 1000–920 Ma) and the Flå–Iddefjord–Bohus suite (FIB, ca. 925 Ma), in central and eastern parts of the Province, respectively. The SMB and the HBG bodies located outside of the SMB (referred to as HBGout) are chemically similar, whereas the HBG bodies located in the same region as the SMB (referred to as HBGin) are more ferroan, enriched in incompatible elements and have higher zircon saturation temperatures. Isotopically, the SMB and both HBG suites fall on an evolutionary trend from widespread 1.5 Ga crust in the region, suggesting this was the dominant crustal contribution to magmatism. The FIB suite is more peraluminous, rich in inherited zircon, and has isotopic compositions suggesting a more evolved source than both the HBG suites and the SMB. Trace element modelling shows that the SMB and HBGout suites could have formed by 50% partial melting of 1.5 Ga crust, whereas 5–10% remelting of the dehydrated and depleted SMB residue accounts for the geochemical composition of the HBGin suite. The available data suggest a scenario where the 1.5 Ga lower crust underwent melting due to long-lived mafic underplating giving rise to the SMB suite. After ca. 1000 Ma, regional-scale extension may have led to more widespread mafic underplating causing remelting of the residue following SMB melt extraction, forming the HBGin suite, with lower-crustal melting farther east forming the HBGout suite. Changes in melt composition over this 150 Myr time interval may thus be ascribed to an evolving melt source rather than fundamental changes in tectonic regime. Deep continental subduction at ca. 990 Ma, east in the orogen, provided an isotopically evolved crustal source for the FIB suite. The data underline the difference in tectonic processes across the orogen, with long-lived, high temperatures in the western and central parts and colder, high-pressure events in the eastern parts of the orogen.

Geochemistry and origin of zircon in chlorite schists of the Ronda peridotites (Betic Cordilleras, southern Spain)

AbstractThis work deals with scarce chlorite schists scattered through the Ronda peridotites (Betic Cordilleras, Spain). These schists have unusually high zircon contents, which contrast with the usual lack of this mineral in ultramafic rocks. From field data and detailed petrographic, geochemical, and geothermometric studies, we focused on the origin of the zircon, a relevant issue for the interpretation of geochronological results. The chlorite schists appear as concordant sheets with granite dikes and as blackwall zones between dikes and serpentinized peridotites. As the intrusion age of the dikes and chlorite schist zircon crystallization (ca. 22 Ma) is slightly older than the age of serpentinization and related chlorite schist formation (ca. 19 Ma), we propose that the chlorite schists are tied to the intrusion of the granite dikes and the subsequent serpentinization of peridotites. Trace and rare earth elements alone are not indicative of the magmatic or hydrothermal origin of the zircon, but the combination of information about zircon morphology, melt inclusions, geothermometry, and the structural relationships between granite dikes and chlorite schists points to late magmatic melts for the zircon origin. We suggest that high-temperature melts saturated in F and Cl acted as Zr carriers under low-pH conditions. A change of the pH conditions, due to hydrothermal alkaline fluids incoming for the concomitant peridotite serpentinization, would have led to zircon crystallization and concentration at the apical zones of the dikes, and to rodingitization before the extensive observed chloritization.

Hf and Nd Isotopic Constraints on Pre‐ and Syn‐collisional Crustal Thickness of Southern Tibet

AbstractIn Southern Tibet, voluminous granitoids emplaced between 225‐20 Ma provide a spatiotemporal window into the geochemical and tectonic evolution of the crust. Hf and O isotope geochemistry of whole rocks and constituent zircons together with whole‐rock chemistry reveal a coherent magmatic history of Gangdese granitoids, and by extension, crustal thickening history of S. Tibet. We observe a spatial isotopic gradient with N‐S distance from the Indus‐Tsangpo Suture (ITS), with younger, more εHf‐positive granitoids adjacent the ITS. Zircons range from εHf = ‐13 to +11 in a broadly systematic fashion from north to south, generally independent of 206Pb/238U age. Adjacent to the ITS, syncollisional (<50 Ma) rocks have generally more heterogeneous εHf than precollisional (>70 Ma) and early syncollisional (50‐70 Ma) granitoids, likely reflecting increased assimilation of crustal material in syncollisional magmas as the crust thickened. Zircon δ18O ranges between +4 and +8‰; syncollisional samples have exclusively mantle‐like values (+5.5 to +6‰), with greater heterogeneity in precollisional samples. Zircon and whole‐rock εHf data reported here are consistent with previous Nd‐based thermoisotopic models indicating that the Lhasa block maintained a wedge‐shaped crustal geometry from the early Jurassic until the onset of collision. Given evidence of minimal post‐50 Ma upper‐crustal shortening, these results support earlier findings that the Tibetan crust reached its present ~75 km thickness via a roughly equal mixture of upper plate accretion and juvenile magmatic inflation on top of the ~30 km‐thick of Indian crust underthrust beneath the Lhasa block.

Timing of high-grade metamorphism in the Kontum Massif, Vietnam: Constraints from zircon–monazite multi-geochronology and trace elements geochemistry of zircon–monazite–garnet

Metamorphic rocks in the Kontum Massif, including the Kannak, Ngoc Linh and Kham Duc Complexes are characterized by amphibolite- to granulite-facies metamorphism and their mono- versus poly-metamorphic evolution is a matter of debate. In this study, we constrained on the timing of high-grade metamorphism in this massif by combining laser ablation inductively coupled plasma mass spectrometry U–Pb zircon and electron microprobe chemical U–Th–Pb monazite ages with geochemical relation of trace elements between zircon–monazite–garnet. The results indicated that the analyzed pelitic and mafic granulites in the western Kannak Complex experienced the high temperature metamorphism at ca. 250 Ma with subsequent decompression. However, in the western Ngoc Linh Complex two high-grade metamorphic events were recorded in one of analyzed pelitic gneisses. The first high temperature metamorphism began at ca. 440–450 Ma with the attainment of the peak condition at ca. 430 Ma, overprinted by the second one at ca. 240–250 Ma with following decompression and exhumation stage at ca. 230 Ma. The other pelitic gneiss and mafic granulite detected only younger single event. Pelitic gneisses in the Kham Duc Complex recorded medium pressure metamorphism occurred at ca. 240 Ma without any traces of early metamorphic event.

Geochemistry and geochronology of zircons from granite-hosted gold mineralization in the Jiaodong Peninsula, North China: Implications for ore genesis

Large-scale quart-vein and structurally-controlled gold mineralization is intensely developed in the Jiaodong Peninsula, North China Craton and is typified by the Linglong and Jiaojia deposits, respectively. In this work, zircons from typical gold-bearing ores of the Sanshandao Northern Sea (SNS), Jiuqu (JQ) and Canzhuang (CZ) gold deposits were compared in terms of texture, U–Pb age, trace element content and Hf isotopic signatures in order to discern whether zircon from ore samples can be used as an indicator of ore genesis and grade. Most studied zircons are magmatic in origin with a hydrothermal overprint (i.e., zircons with core-rim assemblages, fractured-dissolution textures and hydrothermal activity-related fluid/mineral inclusions). Three zircon age clusters were differentiated: ~120 Ma, ~150 Ma and >2000 Ma. The ~120 Ma zircons show evidence of hydrothermal alteration (dark in cathodoluminescent images with hydrothermal rim textures) and are characterized by high LREE, P, Ti and εHf(t) (−21 to −15) and young TDMC (2100–2500 Ma). This suggests an interaction between the mantle and crust at the magma source, and that a P/Ti-rich, Al-poor, high temperature, high fO2, wet late-stage residual granitic melt and intense hydrothermal alteration played an important role in the formation of gold mineralization. The ~150 Ma zircons have high Y, Nb, Ta and U contents, low εHf(t) (−26 to −20) and old TDMC (2300–3000 Ma) ages, and HREE-enriched patterns with pronounced Ce and Eu anomalies. These features indicate a reduced, cool and Al-rich magma which did not favor gold mineralization, even though it was highly evolved. This also implies that the degree of magma differentiation is not the key factor that led to gold mineralization in the Jiaodong gold province. The >2000 Ma zircons are primarily limited to gold ores with high Pb contents, HREE-enriched patterns and variable Ce and Eu anomalies, indicating that they were inherited from the Paleoproterozoic (2000–2200 Ma) basement. In addition, the SNS high-grade ores yielded zircon with the greatest U-Pb age range (mainly 110–180 Ma) and the most pronounced hydrothermal overprinting, indicating that large-scale mineralization resulted from multi-stage granitic intrusion, with intense fluid dissolution and metasomatism. This research highlights that correlations between zircon age populations, Hf isotope signatures, internal structures and trace element patterns can provide insights into ore genesis and fluid evolution in gold mineralization systems.

Multistages of original sapphire formation related to basaltic magmatism in the Bo Phloi basaltic gem field, Kanchanaburi, Western Thailand: Evidence from trace elements and ages of zircons

Trace element geochemistry of zircons in the Bo Phloi basaltic gem deposit, Kanchanaburi, Western Thailand indicates that majority of the sapphires and associated minerals appear to have crystallized in an environment related to highly alkaline felsic melt with subordinate collaboration of contact metamorphism at the lower crust. The U-Pb dating of a zircon inclusion in sapphire and zircons in two sapphire-bearing gravels yielded the average ages of 24 ± 0.9, 10.86 ± 0.14 and 4.4 ± 0.4 Ma, respectively. These dates are concordant with the timing of the Cenozoic basaltic volcanism in Thailand and Southeast Asia which span from late Oligocene to Pleistocene. These ages are, however, mostly pre-dated (one is close to) ~4–3 Ma ages of the Bo Phloi basalt. Therefore, the original sapphire formations appear to have the same thermal history when partial melting in the upper mantle had occurred extensively and led to early state of Cenozoic basaltic eruption in this region. These also indicate that the formation of sapphire from bi-modal origins (felsic melt and contact metamorphism) occurred episodically earlier during ~24–4 Ma as a result of the hybrid interplay of (lower) crustal and (upper) mantle materials. Later, the eruption of mantle-derived alkaline basalt carried the sapphire from both origins along with other xenoliths and xenocrysts to the surface during ~4–3 Ma.

Whole-rock and zircon geochemistry of the Xiaoliugou granites, North Qilian Orogen (NW China): Implications for tectonic setting, magma evolution and W–Mo mineralization

Ordovician W–Mo polymetallic mineralization-related granites are widely developed in the western section of the North Qilian Orogen, NW China. In order to shed light on the tectonic setting, magma evolution and genesis of mineralization in the orogeny, highly evolved granitic rocks (monzogranites) from the Qibao and Qiqing deposits in the Xiaoliugou ore field were studied. Typical of subduction-related A-type granites, the Xiaoliugou granitic rocks are enriched in SiO2, Rb, Th, U, Ta, Nd, Zr and Hf but relatively depleted in Ba, Sr, P and Eu. The variable initial whole rock 87Sr/86Sr ratios (0.62937–0.70543) and wide range of zircon εHf(t) values (−18 to 6) suggesting mantle–crust interaction and mixing of depleted mantle and deep crust in the source area. Whole-rock elemental and Rb–Sr isotopic geochemistry suggest slow cooling, significant fractional crystallization, weak wall-rock assimilation/contamination and intense fluid differentiation/metasomatism during the genesis of the Xiaoliugou granitic rocks. Zircon U–Pb dating yielded three age clusters: Precambrian (>540 Ma) (n = 32), Ordovician (~450 Ma) (n = 40), and Cretaceous (~135 Ma) (n = 18). Zircon internal textures indicate a range of sources including residual/detrital zircons from the magma source region and local sediments, magmatic and fluid-altered zircons, and late stage hydrothermal zircons. Zircon trace element and Lu–Hf isotopic compositions suggest fluid metasomatism during granite emplacement in the Ordovician and overprinting by a more evolved, oxidized fluid in the Cretaceous. Involvement of a late, high-temperature, highly fractionated, F-rich fluid could have enhanced W–Mo mineralization. Consequently, a two-stage genetic model is proposed for the Xiaoliugou granitic-minerogenic system involving primary mineralization in the Ordovician (~450 Ma), followed by a Cretaceous magmatic hydrothermal overprint (~135 Ma).

Bulk rock and zircon geochemistry of granitoids from the Chotanagpur Granite Gneissic Complex (CGGC): implications for the late Paleoproterozoic continental arc magmatism in the East Indian Shield

The north-eastern part of the Chotanagpur Granite Gneissic Complex (CGGC) exposes a vast expanse of felsic orthogneisses (~ 1450 Ma magmatic crystallization age) containing a variety of metamorphosed supracrustal rocks and augen gneiss. However, origin and timing of emplacement of the protolith of the augen gneiss are not well constrained. Owing to lack of detailed study and paucity of exposures, the antiquity of the basements of the CGGC also remains poorly understood. To address this issue, we present bulk rock geochemical data and the U–Pb and Lu–Hf isotope composition of zircon from augen gneisses from two adjoining areas within the CGGC. Our obtained data suggest that the augen gneiss have been derived from hybrid source involving older crustal rocks and metasomatised mantle. The bulk rock and zircon geochemistry also suggest that the protolith of the augen gneiss was emplaced in an early Paleoproterozoic basement in a continental arc setting. U–Pb ages of the magmatic zircon grains constrain the age of intrusion at ca. 1710 Ma and ca. 1635 Ma. The timing of this late Paleoproterozoic felsic magmatism overlaps with the timing of the regional high-to-ultrahigh-temperature granulite facies metamorphism in the CGGC.

Thickening and partial melting of the Northern Qinling Orogen, China: insights from zircon U–Pb geochronology and Hf isotopic composition of migmatites

The widespread migmatites in the Precambrian basement of the North Qinling Belt are products of partial melting of the Earth's crust and record the tectono-thermal response to Late Paleozoic collision along the Shangdan suture. The morphology and trace element geochemistry of zircons from the migmatites suggest a metamorphic origin related to partial melting. The zircons from leucosome, melanosome and banded migmatites yield U–Pb weighted mean ages of 408 ± 2, 403 ± 2 and 400 ± 2 Ma, respectively, constraining the timing of migmatization. The granitic dyke intruded into the migmatites gives a zircon U–Pb weighted mean age of 396 ± 2 Ma, constraining the minimum time of migmatization. Zircons from the melanosome and banded migmatite yield upper intercept ages of 1088–1061 Ma, representing the protolith ages of the basement of the North Qinling Belt. The zircon rims of the melanosome and banded migmatite predominantly display negative and positive ε Hf ( t ) values, respectively, suggesting the variable input of mantle material. Together with the regional geology and previous geochronological data, we propose that the thickening and partial melting in the North Qinling Belt was induced by the collision along the Shangdan suture between the North and South China Blocks from c. 408 to 400 Ma. Supplementary material: LA-ICP-MS U–Pb data, Lu–Hf isotopic compositions and trace element geochemistry data of the zircons and Ti-in-zircon thermometry are available at https://doi.org/10.6084/m9.figshare.c.4521389

Zircon at the Nanoscale Records Metasomatic Processes Leading to Large Magmatic–Hydrothermal Ore Systems

The petrography and geochemistry of zircon offers an exciting opportunity to better understand the genesis of, as well as identify pathfinders for, large magmatic–hydrothermal ore systems. Electron probe microanalysis, laser ablation inductively coupled plasma mass spectrometry, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging, and energy-dispersive X-ray spectrometry STEM mapping/spot analysis were combined to characterize Proterozoic granitic zircon in the eastern Gawler Craton, South Australia. Granites from the ~1.85 Ga Donington Suite and ~1.6 Ga Hiltaba Suite were selected from locations that are either mineralized or not, with the same style of iron-oxide copper gold (IOCG) mineralization. Although Donington Suite granites are host to mineralization in several prospects, only Hiltaba Suite granites are considered “fertile” in that their emplacement at ~1.6 Ga is associated with generation of one of the best metal-endowed IOCG provinces on Earth. Crystal oscillatory zoning with respect to non-formula elements, notably Fe and Cl, are textural and chemical features preserved in zircon, with no evidence for U or Pb accumulation relating to amorphization effects. Bands with Fe and Ca show mottling with respect to chloro–hydroxy–zircon nanoprecipitates. Lattice defects occur along fractures crosscutting such nanoprecipitates indicating fluid infiltration post-mottling. Lattice stretching and screw dislocations leading to expansion of the zircon structure are the only nanoscale structures attributable to self-induced irradiation damage. These features increase in abundance in zircons from granites hosting IOCG mineralization, including from the world-class Olympic Dam Cu–U–Au–Ag deposit. The nano- to micron-scale features documented reflect interaction between magmatic zircon and corrosive Fe–Cl-bearing fluids in an initial metasomatic event that follows magmatic crystallization and immediately precedes deposition of IOCG mineralization. Quantification of α-decay damage that could relate zircon alteration to the first percolation point in zircon gives ~100 Ma, a time interval that cannot be reconciled with the 2–4 Ma period between magmatic crystallization and onset of hydrothermal fluid flow. Crystal oscillatory zoning and nanoprecipitate mottling in zircon intensify with proximity to mineralization and represent a potential pathfinder to locate fertile granites associated with Cu–Au mineralization.