Intercept Age Research Articles

Caledonian Sn Mineralization in the Yuechengling Granitic Batholith, South China: Geochronology, Geochemistry, Zircon Hf Isotopes, and Tourmaline Chemistry and B Isotopes of the Lijia Sn Deposit and Its Hosting Granites

The Lijia Sn deposit, located in northeastern Guangxi Zhuang Autonomous Region of south China, occurs on the eastern margin of the Yuechengling granite batholith. The Sn deposit contains quartz vein type and greisen type ores and is spatially associated with the medium-coarse-grained biotite granite and the fine-grained tourmaline-bearing biotite granite. LA-ICP-MS zircon U-Pb dating gave an emplacement age of 431.7 ± 2.5 Ma for the medium-coarse-grained biotite granite and of 430.2 ± 2.4 Ma for the fine-grained tourmaline-bearing biotite granite. LA-ICP-MS cassiterite U-Pb dating yielded Tera-Wasserburg lower intercept ages of 429.1 ± 3.4 Ma and 425.7 ± 3.3 Ma for the quartz vein type and greisen type ores, respectively. The ages demonstrate near coeval Caledonian granitic emplacement and Sn mineralization events that have been considered uncommon in south China. Both granites might be derived from partial melting of the Paleoproterozoic basement, as evidenced from zircon ɛHf(t) values of −3.13 to −10.31 and TDM2 from 1627 Ma to 2134 Ma. Three different types of tourmalines have been identified, including (1) tourmaline in quartz–tourmaline nodules in the fine-grained tourmaline-bearing biotite granite (Tur 1), (2) tourmaline in quartz veins (Tur 2a), and (3) tourmaline in greisen (Tur 2b). Most of the tourmalines belong to the alkali group and the schorl-dravite solid-solution series. The hydrothermal tourmalines of Tur 2a and Tur2b showed similar δ11B values to those of the Tur 1 tourmalines in the fine-grained tourmaline-bearing biotite granite, suggesting ore-forming materials derived from granitic magmas. The hydrothermal tourmalines of Tur 2b had slightly lower δ11B values than Tur 1 and Tur 2a tourmalines as a result of progressive 11B depletion during early tourmaline crystallization.

Differentiating Triassic W–Sn ore-bearing and ore-free plutons in the Xitian Ore Field (South China) using apatite geochemistry

Though the metallogenic process of the Xitian W–Sn deposit has been established, the key factors distinguishing Triassic W–Sn ore-bearing granites from ore-free granites remain uncertain, leaving an important gap in understanding the controls on Triassic W–Sn mineralization. In this study, we present a comprehensive investigation of apatite from the Triassic Longshang W–Sn ore-bearing and Goudalan ore-free granites, to trace the nature of parental magma and to provide constraints on the processes related to Triassic W–Sn mineralization in Xitian Ore Field (South China). Apatites from ore-bearing (AOB) granites and apatites from ore-free (AOF) granites exhibit distinct Cathodoluminescence (CL) images: AOB samples feature darker cores and brighter rims, with concentric oscillatory growth zoning in the rim sections, whereas AOF samples exhibit chaotic textures in CL images. The U–Pb age dating of AOB and AOF yield a lower intercept age of 227.3 ± 4.3 Ma (1σ, MSWD = 3.9) and 227.1 ± 7.8 Ma (1σ, MSWD = 2.4) on the Tera-Wasserburg diagrams, respectively. The similar εNd(t) values (−10.91 to −9.82 for AOB; −10.42 to −8.77 for AOF) (expressed as deviation in parts per 10,000 from CHUR composition), relatively low Cl contents (<0.05 wt%), and high F (~3 wt%) of studied apatites, suggest that W–Sn ore-bearing and ore-free granitic magmas were both generated by melting of old continental crust. The texture and high concentration of REE + Y and Th in AOB could be assumed as the result of fluid exsolution. The chaotic texture, broad variation in 147Sm/144Nd ratios, may imply that AOF might have experienced metasomatic modification. Lower Eu/Eu* value together with higher Ce/Ce* value in AOB suggests a more reduced environment for W–Sn ore-bearing granites. Lower Sr, Mg content, and higher Y contents suggest that W–Sn ore-bearing granites have a higher degree of fractionation than ore-free granites. We propose that the mobilization and transport ability of W and Sn by hydrothermal fluids play an important role in the enrichment of W and Sn, and redox state of magma and the degree of magma differentiation determine the final enrichment level of tungsten and tin.

A Cryogenian impact structure lurking in the shadows of northern Sweden

AbstractHere we report on findings for four rock samples with melt texture found in a gravel pit within a glaciofluvial deposit near the small town of Kitkiöjärvi in northernmost Sweden. The samples are comprised of granitic clasts embedded in a brown fine‐grained melt matrix. The samples all contain quartz grains and/or clasts exhibiting multiple sets of planar deformation features oriented parallel to crystallographic planes characteristic of shock metamorphism. The samples also contain Former Reidite In Granular Neoblastic (FRIGN) zircon. We therefore conclude that the investigated samples represent impact melt rock. We interpret a U‐Pb concordia age of 658.9 ± 6.9 Ma (Cryogenian) derived using secondary‐ion mass spectrometry analysis of shocked zircon, as the best estimate for the age of the impact event that formed the melt rocks. Zircon grains from two of the samples yield younger lower intercept ages, raising the possibility that the samples came from multiple impact events of different ages. Although we cannot exclude this possibility, we interpret the younger ages from the clast‐rich melt rocks to reflect non‐impact‐related Pb loss events and suggest that all samples likely came from the same structure. Analysis of the glaciofluvial history of the region, along with the relatively high frequency of finds (five in total, as one similar melt rock was found in the pit in 2018), points to a short‐distance glacial transportation of the samples from the southwest. Since there are no known impact structures in Sweden within that area and/or of similar age, we conclude that an old (the oldest known yet) impact structure in Sweden potentially is yet to be discovered somewhere in the vicinity of the gravel pit.

Zircon and garnet U-Pb dating reveals the mineralization history of volcanic-related skarn iron deposits

The genesis of skarn garnet in volcanic-related skarn iron deposits is controversial because of the absent or ambiguous spatiotemporally related intrusions. In this study, we present combined LA-ICP-MS garnet U-Pb and SHRIMP zircon U-Pb ages to determine the spatiotemporal relationship between skarn garnet and a potentially related intrusion or causative volcanic rock. Three types of garnet (Grt1, Grt2, and Grt3) are identified in the Yamansu deposit, and Grt1 yields a lower intercept age of 326 ± 9 Ma (n = 32, MSWD = 0.3). SHRIMP zircon U-Pb dating of the associated volcanic rock yields a weighted mean age of 327 ± 3 Ma (n = 10, MSWD = 1.4), suggesting an isochronous relationship between the volcanic rock and Grt1. Grt2 and Grt3 yield lower intercept ages of 316 ± 6 Ma (n = 22, MSWD = 1.4) and 315 ± 6 Ma (n = 35, MSWD = 1.5), respectively. However, the zircon U-Pb weighted mean age of 252 ± 4 Ma (n = 5, MSWD = 0.8) obtained from the associated intrusion is obviously younger than the skarn age and the previously reported ore-forming age, implying no temporal relationship between mineralization and the intrusion. More significantly, precise 206Pb/238U weighted mean ages of 325 ± 9 Ma (n = 15, MSWD = 0.3), 316 ± 8 Ma (n = 11, MSWD = 0.4), and 319 ± 7 Ma (n = 12, MSWD = 0.5) were obtained from Grt1, Grt2, and Grt3, respectively, and we find that andradite-rich garnet with high U and ΣREE concentrations has the potential to yield the more precise U-Pb ages. The combined garnet and zircon U-Pb ages reveal that the hydrothermal skarn and mineralization in volcanic-related skarn iron deposits are related to volcanic activity rather than intrusions. Multiple episodes of volcanic-related hydrothermal activity may have caused multiple phases of skarn formation and mineralization in volcanic-related skarn iron deposits.

New insights on the petrogenesis of the Koktokay No.3 pegmatitic dyke: Petrological and zirconological evidence from the Aral granitic complex (Xinjiang, China)

The Koktokay No.3 pegmatite dyke (KPD), containing numerous Li–Be–Nb–Ta–Cs mineral resources, is among the world’s most famous rare-metal deposits, and attracted much attention. Up to now, over thirty geochronological data have been reported ranging from 332 Ma to 120 Ma for the KPD, which causes uncertainty about the origin and petrogenesis of the pegmatite. In this contribution, whole-rock geochemistry and zircon geochronology have been conducted on the Aral biotite monzogranite (BMG), the Koktokay muscovite alkali-feldspar granite (MAG), and the KPD. Petrological and whole-rock geochemistry results reveal that the BMG is normal granite with medium SiO2 (mean of 67.23 %), enriched in compatible trace elements such as Ba, Sr and Zr, and slight negative Eu anomalies, while the MAG belongs to highly-fractionated granite with high SiO2 (mean of 73.92 %) and extensive negative Eu anomalies, and enriched in incompatible trace elements such as Rb, Ta, and U. Zircon morphology and LA–ICPMS analysis reveal that magmatic zircons from the BMG, hydrothermal zircons from the MAG and KPD yield lower intercept ages at 217.3 ± 2.4 Ma, 197.8 ± 4.7 Ma, and 195.4 ± 2.0 Ma, respectively. Combining with tectonic information and geochronological data of granitic activity and its mineralization in the Altay, this study explains the petrogenetic mechanism of the KPD after Wang et al. (2021)‘s metallogenic model: (1) In late stage of Middle Triassic, the collision between the Siberian plate and the Kazakhstan–Junggar plate caused a large number of thrust nappe faults and crust thickening in the Altay orogenic belt; At ∼217 Ma, the compression reached its peak, the crustal anatexis produced syn-collisional BMG (i.e., the Aral BMG); After the compressive peak, huge amount of granitic magma in deep-seated magma chamber underwent over 20 Myr of fractional crystallization, and the residual magma enriched in ore-forming materials (rare metal elements, volatile components, and aqueous fluids) occurred at the top of the magma chamber; (2) When the regional stress converted from compression to extension, the highly-fractionated residual magma ascended rapidly from the long-lived magma chamber along extensional faults at ∼195 Ma; The huge amount of melt-bearing fluids were exsolved from the residual magma in the course of its emplacement due to sharply decreasing pressure, and intruded into a large cavity generated by extensional fault; Along with slowly decreasing temperature, the melt-enriched fluids crystallized outside-in as (quasi-) concentric pegmatitic zones (i.e., KPD); (3) The residual magma which lost huge amount of fluid filled the lower space of the extensional system, and crystallized as post-collisional MAG (i.e., the Koktokay MAG). Based on the genetic relationship among tectonics, petrogenesis, and metallogeny, the proposed model shows material and energetic conversion processes from syn-collisional granites to post-collisional granites with granitic–pegmatitic deposits

The origin of ∼ 2.5 Ga arc-related magmatic charnockites of Karimnagar, SE India, and implications for tectonic assembly in the Dharwar craton

In the Indian peninsula, the Singhbhum, Bastar, and Dharwar cratons in the South India Block (SIB) constitute a contiguous mass of >2.5 Ga crystalline rocks. Did the cratons develop as a coherently evolved mass since their origin, or do these cratons constitute an assembly of disparately evolved cratons? Variably-deformed charnockites in the Karimnagar granulite belt and associated blastoporphyritic granitoids at the NE fringe of the Eastern Dharwar Craton (EDC) contain enclaves of mafic granulites, high-Al metapelites and anatectic quartzofeldspathic gneisses. The charnockites are demonstrably intrusive into the enclave suite. The enclave suite exhibits steeply-plunging reclined folds; the axial planes of the folds coincide with the N-striking tectonic fabrics in the Karimnagar charnockite/granitoids. The foliated charnockites display magmatic flow texture defined by trains of euhedral alkali feldspar, contain euhedral-subhedral pyroxene phenocrysts, and the quartz grains exhibit abundant chessboard microstructure. The weakly-strained euhedral laths of feldspars and pyroxenes phenocrysts share high-energy boundaries between themselves, and with quartz. Emplacement temperatures of the magmatic charnockites at ∼900 °C are obtained from Al-in-Opx thermometry. Whole rock chemistry is consistent with an arc-related origin for most charnockites. In zircons within charnockites, variably zoned cores yield ages of 2680 ± 15 Ma and 2504 ± 12 Ma in the UPb Concordia plot. Recrystallized domains in zircon grains yielded upper intercept ages constrained between 2510 ± 4 Ma and 2509 ± 3 Ma, identical with the U-Th-Pb chemical ages (2502–2508 Ma) retrieved from monazites. The zircon εHf(t) values (− 4.85 to 1.31) suggest the ∼2.5 Ga magmatic charnockites were derived from <3.0 Ga crustal sources. The late Neoarchean magmatic charnockites in the EDC margin were emplaced in a 2.7–2.5 Ga convergent tectonic setting, and the high-T magmatic charnockites formed due to delamination of a subducting (E-W shortening) oceanic crust. The subduction possibly relates to the late Neoarchean growth of the Dharwar craton involving the assembly of disparately-evolved crustal blocks, now parts of the Dharwar craton. The findings suggest that the emplacement of Karimnagar magmatic charnockites in a contractional setting is unrelated to an accretion between the Eastern Dharwar and the Bastar cratons, as suggested by earlier workers.

Petrogenesis of Montana, USA Sapphires Inferred from Oxygen Isotopes and Zircon Inclusions

Abstract Montana hosts the largest sapphire deposits in the US, but the genesis of and connection among the various secondary and primary sapphire occurrences remains cryptic. In situ SIMS measurements of oxygen isotopes in sapphires and zircon inclusions in sapphires provide an opportunity to study the isotope and trace element geochemistry in order to understand sapphire-forming protoliths (i.e. crustal setting and alteration). Sapphire from Montana was transported as xenocrysts in carrier (host) magmas that resorbed sapphire exteriors during transport. The timing and nature of sapphire genesis is elucidated by SIMS measurements of trace elements and U–Pb from discrete zones in zircon inclusions with rims that are interpreted to be syngenetic with host sapphire. Montana sapphires exhibit a large range of δ18O values, from −3‰ to +12‰ VSMOW. However, all but two anomalous crystals fall in the range of 0‰ to 8‰. There is significant crystal-to-crystal variability yet averages at most deposits are consistent with high-temperature equilibration with the mantle (δ18O(Crn) = 4.4‰ to 5.7‰), with the exception of the commercial sapphire deposits at Rock Creek that average 2.7‰. Ruby analyses are limited, but typically have lower δ18O values compared to sapphires from the same detrital localities. Homogeneity within individual crystals (avg. 2 s = ±0.2‰) indicates the absence of isotopically distinct fluid or melt during crystallization. But intercrystalline δ18O ranges by up to 7‰ at a single locality, suggesting sapphire variability at a deposit reflects heterogeneity in the original protolith. Oxygen isotope fractionations between zircon rims and surrounding sapphire suggest comagmatic zircon inclusions and corundum equilibrated at high temperature. No correlation is seen for the degree of radiation damage and alteration of δ18O(Zrc) when zircon inclusions are surrounded and armored by sapphire. U–Pb ages and trace elements were measured in a small subset of syngenetic zircon inclusions in Dry Cottonwood Creek sapphires, revealing a Proterozoic (1778 ± 9 Ma) age for the protolith of sapphires at this locality and a likely polygenetic history. Previous work has suggested formation of these sapphires through partial melting of anorthosites and several anorthosites occur locally and match the age of zircon inclusion cores—the Boehls Butte anorthosite (~180 km NW of Rock Creek) and the Bitterroot anorthosite (~55 km W of Rock Creek) could correlate with Al-rich protoliths at depth. Proterozoic U–Pb ages of zircon from the Boehls Butte anorthosite (1787 ± 2 Ma) match well with the age of zircon inclusion cores in Dry Cottonwood Creek sapphires and suggest genesis in these or similar protoliths. Zircon rims with Tera-Wasserburg lower intercept ages of 110 ± 9 Ma are consistent with previous observations of a xenocrystic relationship to the ~50 Ma Eocene volcanic rocks. Corundum that formed over 50 Ma prior to being scavenged by Eocene magmas likely originated by the anatexis of Precambrian anorthosites and possibly other aluminum-rich rocks at depth.

The genesis of intersection-type uranium deposits in south China: Insights from zircon and pitchblende U-Pb geochronology and pyrite sulfur isotopes of the Egongtang uranium deposit, southern Jiangxi

Intersection-type uranium deposits refer to the uranium deposits that are located at the intersection of mafic dykes and silicified faults and are an important type of granite-related uranium deposits in South China. However, the genesis of these deposits still remain poorly understood. The Egongtang uranium deposit is a typical intersection-type uranium deposit in the Huangsha uranium ore district (southern Jiangxi) that bears a number of NWW-trending mafic dykes, thus providing an excellent opportunity to study the genesis of intersection-type uranium deposits. In this study, the mineralization age and genesis of this deposit were constrained using in situ zircon and pitchblende U-Pb geochronology, whole-rock geochemistry, and pyrite sulfur isotope data. The zircon U-Pb dating constrains the crystallization ages of 240.4 ± 1.3 Ma and 160.7 ± 1.6 Ma for granites in the Huangsha ore district. The samples (including altered and unaltered) of the granites are characterized by variable whole-rock U contents of 5.8–14.1 ppm and Th/U ratios of 2.4–7.7, which favor the crystallization of uraninite in the granites and suggest U leaching from the granites during alteration. In situ U-Pb dating on pitchblende from the Egongtang uranium deposit yielded a lower intercept age of 89.8 ± 1.1 Ma, indicating that the uranium mineralization took place at the Late Cretaceous. Pyrite associated with pitchblende has δ34S values ranging from 1.6‰ to 3.8‰, suggesting a magmatic source. This study indicates that granites in this area might have represented the source of uranium for the Egongtang deposit, and that the uranium mineralization was probably related to the Late Cretaceous crustal extension in South China.

Pan-African and Early Paleozoic Orogenic Events in Southern Tibet: Evidence from Geochronology and Geochemistry of the Kangbuzhenri Gneissic Granite in the Zhegu Area

The Zhegu area in southern Tibet is situated in the central and eastern part of the Tethys Himalayan tectonic belt, with the Kangbuzhenri area being abundant in gneissic granites. This study examines the petrology, chronology, and geochemistry of the Kangbuzhenri gneissic granite, providing insights into its Pan-African and Early Paleozoic geological evolution. The zircon U-Pb chronology indicates an upper intercept age of ~539 Ma, reflecting Pan-African orogenic events in the eastern part of the Tethys Himalayan tectonic belt, and a lower intercept age of ~144 Ma, representing a late tectonic–thermal event. Geochemically, the gneissic granites are calc-alkaline peraluminous rocks with high SiO2 and Al2O3 contents and low TiO2, P2O5, MgO, and FeOT contents. The gneissic granites are enriched in LREE and LILEs (Rb, Pb, Th, U, etc.), but relatively depleted in HREE and HFSEs (Nb, Ti, P, etc.). Most of them show a weak negative δEu anomaly, except for two samples which show a significant negative δEu anomaly due to the crystallization of plagioclase. Based on the above study, most of the gneissic granites exhibited the characteristics of an I-type granite, while two of the samples were a highly differentiated I-type granite with S-type affinities. All the above characteristics indicate that the gneissic granite likely originated from the partial melting of crustal materials and sediments with a minor involvement of mantle-derived materials. Combined with the previous chronological studies, the Kangbuzhenri gneissic granites were formed in an extensional tectonic environment during post-collision orogeny and then they were influenced by the Kerguelen mantle plume tectonic–thermal event around ~144 Ma and the subsequent Southern Tibet Detachment System (STDS).

Magmatic-hydrothermal evolution and rare metal enrichment of the Huoshibulake B-rich rare metal granite in the Southern Tianshan: Insights from texture, geochemistry, and Hf[sbnd]O isotopes of zircon

Deciphering magmatic-hydrothermal evolution and rare metal mineralization mechanisms in granitic systems is always challenging, particularly when elucidating the intricate details of magmatic-hydrothermal transition, the critical stage when the system changes from melt-driven to fluid-driven with associated metal extraction. Here we present a case study of the Huoshibulake Nb-REE-mineralized alkali pluton in the north margin of the Tarim Carton, China. The pluton exhibits abundant tourmaline-quartz orbicules and tourmaline-quartz veins, which are the products of immiscible B-rich melt exsolved during the magmatic-hydrothermal transition. Three types of zircon crystals with different morphology have been recognized in the pluton: antecrystic, autocrystic and hydrothermal zircons, the latter two representing the melt and fluid parts of the system. LA-ICP-MS UPb dating of autocrystic zircon from granite and orbicule samples (206Pb/238U ages of 274.8 ± 1.5 and 273.6 ± 2.0 Ma, respectively) and cassiterite from the vein sample (lower 206Pb/238U intercept age of 271.4 ± 4.1 Ma) overlap within error. The similar trace-element patterns and near-identical O-isotopic compositions between hydrothermal and autocrystic zircons indicate that the hydrothermal zircons were crystallized from magmatic fluids. Zircon HfO isotopic systematics suggests that the coeval A1-type granites in the Halajun area evolved from a single parental magma chamber which originated from ∼30% of the upper crustal material mixed with ∼70% mantle-derived mafic magma. Whole-rock compositional trends reveal that fractional crystallization of felsic minerals contributed to the rare metal enrichment. The rare metal mineralization in the veins and the close association of rare metal mineralization with fluorite indicate the critical role of F-rich hydrosilicate liquids in rare metal mineralization, which is also recorded by the significant increase of rare metal concentrations from the autocrystic to the hydrothermal zircon grains.

Garnet and Zircon U‐Pb Geochronology and Geochemistry Reveal Genesis of the Dafang Au‐Pb‐Zn‐Ag Deposit, Southern Hunan

AbstractGarnet is a primary mineral in skarn deposits and plays a significant role in recording copious mineralization and metallogenic information. This study systematically investigates the geochemistry and geochronology of garnet and zircon in the Dafang Au‐Pb‐Zn‐Ag deposit, which represents prominent gold mineralization in southern Hunan, China. Garnet samples with distinct zoning patterns and compositional variations were identified using various analytical techniques, including Backscattered Electron (BSE) imaging, Cathodoluminescence (CL) response, textural characterization, and analysis of rare‐earth elements (REE), major contents, and trace element compositions. The garnet was dated U‐Pb dating, which yielded a lower intercept age of 161.06 ± 1.93 Ma. This age is older than the underlying granodiorite porphyry, which has a concordia age of 155.13 ± 0.95 Ma determined by zircon U‐Pb dating. These results suggest that the gold mineralization may be related to the concealed granite. Two groups of garnet changed from depleted Al garnet to enriched Al garnet, and the rare earth element (REE) patterns of these groups were converted from light REE (LREE)‐enriched and heavy REE (HREE)‐depleted with positive europium (Eu) anomalies to medium REE (MREE)‐enriched from core to rim zoning. The different REE patterns of garnet in various zones may be attributed to changes in the fluid environment and late superposition alteration. The development of distal skarn in the southern Hunan could be a significant indicator for identifying gold mineralization.

Early Orosirian belts of the central Guiana Shield, northern Amazonian Craton: U-Pb geochronology and tectonic implications

The Cauarane-Coeroeni Belt (CCB), the Orocaima Igneous Belt (OIB) and the Rio Urubu Belt (RUB) are the main tectonic features of the central part of the Guiana Shield. The CCB is a sinuous NW-SE/NE-SW/NW-SE trending high-grade supracrustal belt, bordered to the north by the OIB, formed by volcanics and high-crustal level granitoids, and to the south by the RUB, made up of deeply emplaced granitoids and gneisses. We present 27 new U-Pb SHRIMP and LA-ICP-MS zircon ages for these belts.The geochronological data obtained for 10 granitoid samples of the OIB indicate that magma pulses of different typologies were coeval along the belt and confirm its continental scale extension. Crystallization ages obtained for the high-K calc-alkaline granitoids vary from 1990 ± 5 Ma to 1957 ± 17 Ma and those of reduced A-type granites vary from 1980 ± 14 Ma to 1974 ± 8 Ma.Only four samples of granitoids and gneisses of the RUB were analysed. Crystallization ages of 1964 ± 7 Ma and 1956 ± 8 Ma were calculated respectively for a granodiorite and for an orthogneiss and are in agreement with the 1.96–1.92 Ga age period regionally considered for the evolution of the RUB. However, an age of 1973 ± 7 Ma was calculated for a foliated S-type granite, indicating that slightly older granitoid rocks are also present within the RUB. In addition, an age of 1935 ± 10 Ma was calculated for the high-grade metamorphism along the belt.A microgranitic dyke that crosscuts the foliation of a gneiss of the RUB was dated at 1884 ± 7 Ma, and probably represents one of the feeder dykes for the large 1.89–1.87 Ga Uatumã magmatic event.Twelve samples of the CCB were analysed. The data for the detrital nuclei of the zircon crystals of the paragneisses and schists suggest an overall similar inheritance pattern along the length of the CCB, recording the contribution of Archean to early Orosirian sources, with a major participation of Rhyacian domains.The oldest detrital zircon crystals yielded an age of 3.65 Ga, but the age of most of the Archean zircon grains fall in the 3.50–2.50 Ga range and they were probably derived from the Imataca and Amapá blocks. Results in the 2.50–2.30 Ga age interval were obtained for detrital zircon grains of many samples, indicating the contribution of Siderian source-areas, possibly the Bacajá Domain, located outside the shield. Those terranes formed within the shield during the Rhyacian phase of the Transamazonian Cycle were probably the source of the 2.30–2.05 Ga detrital zircon grains. In addition, zircon grains with ages between 2.05 Ga and 2.03 Ga were possibly derived from the Trairão-Anauá terranes.The U-Pb SHRIMP zircon dating allowed to better constrain the metamorphic events along the CCB. The syn-kinematic M1 high-grade metamorphic phase could not be directly dated, and we suggest it occurred between 2025 Ma and 2000 Ma. The imprint of the thermal M2 metamorphic event is recorded by the presence of rims and cores of zircon crystals with very low Th/U ratios (<0.1), showing secondary texture. Upper intercept ages of 1983 ± 9 Ma, 1978 ± 9 Ma and 1967 ± 27 Ma were obtained for M2. Zircon grains with secondary textures and very low Th/U ratios (<0.1) from a sample collected in the vicinities of the RUB yielded an upper intercept age of 1955 ± 14 Ma, tentatively interpreted as reflecting M3.The ages obtained for the M2 and M3 metamorphic phases coincide, respectively with those measured for the rocks of the OIB and for the high-grade metamorphism in the RUB. We envisage that the M2 and M3 metamorphic overprints in the paraderived rocks of the CCB reflect important fluid input and thermal perturbation respectively during the emplacement of the OIB granitoids to the north, and the assemblage of granitoid bodies of slightly different ages, deformation and high-grade metamorphism within the RUB, south of the CCB.The early Orosirian terranes of the central part of the Guiana Shield were formed during Akawai Orogeny. The 2.04–2.03 Ga Trairão-Anauá terranes and the CCB supracrustal rocks represent the pre-collisional and collisional stages of the orogeny, the OIB records post-collisional, late-orogenic magmatism. The RUB is probably reflecting a post-collisional setting associated with transpressive deformation. The Akawai Orogeny is interpreted as the late stage of the Transamazonian Cycle, after the main Rhyacian orogeny of the cycle, and was responsible for the final amalgamation of this part of the Columbia paleocontinent.

Multiple isotopic dating constraints on diverse W metallogeny in the Baiyunxian ore field, South China

The Baiyunxian ore field, a large tungsten ore filed in the Nanling Metallogenic Belt of South China, hosts a variety of tungsten deposits such as the Dapu (quartz wolframite vein type), Chashanjiao (skarn type), Toutianmen (greisen type), and Dashan (quartz scheelite vein type). However, precise mineralization ages of these deposits remain poorly constrained and this has long vexed a better understanding of genetic relationships between diverse W mineralization types and the spatially associated Jiufeng granitic complexes. Here, we report firsthand zircon U–Pb, monazite U–Pb, garnet U–Pb, cassiterite U–Pb, and molybdenite Re–Os ages of different granites and ores from the Baiyunxian ore field. The Jiufeng granitic complexes consists of phase Ⅰ biotite granite (P1), phase Ⅱ two-mica granite (P2), and phase Ⅲ granitic dikes (P3, including greisen W ore). Zircons from P1 granite define a concordant U–Pb age of 166.0 ± 0.9 Ma (MSWD = 1.1). Monazites from P2 granite yielded a Tera–Wasserburg lower intercept age of 159.2 ± 0.7 Ma (MSWD = 0.45). In addition, zircons and monazites from P3 granite in the Toutianmen deposit yield a concordant U–Pb age of 154.7 ± 1.3 Ma (MSWD = 1.3) and a Tera–Wasserburg lower intercept age of 156.6 ± 1.9 Ma (MSWD = 0.14), respectively, suggestive of multi-stage emplacement processes of the Jiufeng complexes. Ten molybdenite samples from the Dapu deposit generate an isochron age of 156.0 ± 3.0 Ma (MSWD = 0.93). In situ garnet and cassiterite LA-ICP-MS U–Pb dating results of the Chashanjiao skarn deposit yield lower Tera–Wasserburg intercept ages of 155.3 ± 1.2 Ma (MSWD = 1.6) and 153.4 ± 3.7 Ma (MSWD = 1.3), respectively. These dating results indicate that different W mineralization events in the Baiyunxian ore field intensively occurred in the Late Jurassic (∼159–153 Ma). Despite a close spatial relationship between various W orebodies and P1 granite, the geochronological results demonstrate that extensive W metallogeny in the Baiyunxian ore filed likely occurred later than P1 granite and contemporaneous with P2–3 granites. In addition, scheelites from the four deposits have similar REE patterns that are characterized by weak MREE enrichment, despite few exceptions being found in scheelites from the Dashan and Chashanjiao deposits. This suggests that the diverse W metallogeny in the Baiyunxian ore field were derived from the same magmatic hydrothermal system and changed as the ore-forming fluid evolved. Multidisciplinary evidence indicates that the Late Jurassic highly evolved P2–3 granites of the Jiufeng complexes were crucial to W mineralization in the Baiyunxian ore field and the lithology of wall rocks exerted first-order control of W mineralization types.

Tracing fluid exsolution and hydrothermal alteration signature of the Mufushan Nb–Ta–(Li–Be–Cs) deposit, South China: an apatite perspective

The appearance of hydrous magmas and the following separation of volatile-rich fluids through hydrothermal alteration are intricately linked to the formation of granitic rare-metal deposits, the principal source of worldwide Li, Be, Nb, Ta and Cs production. The lack of mineralogical information from the developing magmatic–hydrothermal system has, however, prevented a thorough comprehension of these processes. Apatite occurs as an accessory mineral in the metasedimentary (schist)–magmatic (muscovite monzogranite)–pegmatite (ore-free or ore-bearing pegmatite) rocks in the Mufushan Complex (MFSC) rare-metal ore field of northeastern Hunan, South China, potentially providing insights into Nb–Ta–(Li–Be–Cs) mineralization. To demonstrate that apatite can potentially record the magmatic–hydrothermal evolution of metasedimentary–magmatic–pegmatite systems, this study presents a combined textural and geochemical study of apatite from the MFSC granitic pegmatite-type rare-metal mineralization. The MFSC apatite textures and compositions have changed since it first crystallized (i.e. post-crystallization alteration). Apatite from the schist shows a homogeneous rim or homogeneous textures with cracks or inclusions (S-ap1) and a patchy core (S-ap2), indicative of a magmatic–hydrothermal origin. Apatite from the muscovite monzogranite (G-ap) displays altered and distinctive core–rim textures, with visible voids, mineral inclusions and cracks, suggestive of overprinting of early magmatism texture by hydrothermal fluid. However, compared with S-ap1, S-ap2 and G-ap, the pegmatite apatite shows more complicated textures; that is, P-ap1 (homogeneous bright and dark areas) and P-ap2 (replacement texture involving alteration rim, growth zonation, patchy and complex zoning patterns). P-ap1 underwent early magmatism and weaker post-hydrothermal overprinting, and P-ap2 reflects a magmatic–hydrothermal product. S-ap1 and S-ap2 yield lower intercept ages of 130.6 ± 1.8 and 128.4 ± 3.8 Ma, respectively, which are consistent with the transitional age of the magmatic–hydrothermal metallogenic environment in northeastern Hunan. G-ap and P-ap1 yield older ages of 136.3 ± 2.8 and 141.3 ± 6.7 Ma, respectively, which correspond to the age of magmatic early stage (Nb–Ta)-mineralization within uncertainty in northeastern Hunan. The Sr isotopic composition of apatite provides evidence for the provenance of the MFSC batholith in the rare-metal metallogenesis of the Lengjiaxi Group. Therefore, we hypothesize that apatite in granitic rare-metal deposits within metasedimentary–magmatic–pegmatite systems might be employed as a viable proxy to explore the textures and geochemical fingerprints of fluid exsolution and hydrothermal alteration. Supplementary material: Analytical techniques and the results for apatite grains in this investigation are available at https://doi.org/10.6084/m9.figshare.c.7038699

Microstructural and isotopic analysis of shocked monazite from the Hiawatha impact structure: development of porosity and its utility in dating impact craters

U–Pb geochronology of shocked monazite can be used to date hypervelocity impact events. Impact-induced recrystallisation and formation of mechanical twins in monazite have been shown to result in radiogenic Pb loss and thus constrain impact ages. However, little is known about the effect of porosity on the U–Pb system in shocked monazite. Here we investigate monazite in two impact melt rocks from the Hiawatha impact structure, Greenland by means of nano- and micrometre-scale techniques. Microstructural characterisation by scanning electron and transmission electron microscopy imaging and electron backscatter diffraction reveals shock recrystallisation, microtwins and the development of widespread micrometre- to nanometre-scale porosity. For the first time in shocked monazite, nanophases identified as cubic Pb, Pb3O4, and cerussite (PbCO3) were observed. We also find evidence for interaction with impact melt and fluids, with the formation of micrometre-scale melt-bearing channels, and the precipitation of the Pb-rich nanophases by dissolution–precipitation reactions involving pre-existing Pb-rich high-density clusters. To shed light on the response of monazite to shock metamorphism, high-spatial-resolution U–Pb dating by secondary ion mass spectrometry was completed. Recrystallised grains show the most advanced Pb loss, and together with porous grains yield concordia intercept ages within uncertainty of the previously established zircon U–Pb impact age attributed to the Hiawatha impact structure. Although porous grains alone yielded a less precise age, they are demonstrably useful in constraining impact ages. Observed relatively old apparent ages can be explained by significant retention of radiogenic lead in the form of widespread Pb nanophases. Lastly, we demonstrate that porous monazite is a valuable microtexture to search for when attempting to date poorly constrained impact structures, especially when shocked zircon or recrystallised monazite grains are not present.

Correlations on the southern Kaapvaal Craton Margin, 1: Ventersdorp lavas transgressed the Doornberg lineament

Abstract Two small exposures of quartz-porphyritic rocks occur on the farm Zoutpekel 98 in the Marydale Terrane between the Doornberg Fault and Brakbos Shear Zone, apparently overlying Kaapvaal basement granite but lacking clear field relationships due to sand and Dwyka tillite cover. They are lavas and tuffs, metamorphosed in lower amphibolite facies. They contain quartz phenocrysts with a distinctive blue colour, due to metamorphic exsolution of rutile. Microbeam U-Pb zircon dating gives a combined 207Pb/206Pb age of 2 722 ± 3 Ma (seven determinations on four samples), interpreted as the age of extrusion. Three of these samples give the same discordia upper intercept age, but one sample gives discordia intercepts of 2 688 ± 15 and 1 223 ± 120 Ma, thought to reflect metamorphic lead loss related to the ~1 210 Ma Namaqua terrane assembly collisions. The Zoutpekel exposures are coeval with the 2 720 ± 2 Ma Makwassie Formation of the Platberg Group, Ventersdorp Supergroup. They also correspond geochemically to the Makwassie Formation and no other unit of the supergroup. A sample from the T’kuip Formation of the nearest Ventersdorp Supergroup inlier on the Kaapvaal Craton (east of the Doornberg Fault), gives an age of 2 716 ± 8 Ma, also confirming its lithostratigraphic and geochemical correlation with the Makwassie Formation. The Zoutpekel exposures show that not only the Kaapvaal basement granites, but also the supracrustal cover rocks of the Ventersdorp Supergroup, extend southwards across the Doornberg Fault, The Marydale Terrane is thus not an exotic terrane, but probably represents a passive continental margin developed at the beginning of the 1 300 to 1 000 Ma Namaqua-Natal Wilson cycle. The age range of the Ventersdorp Supergroup and the age and stratigraphic correlation of the Marydale Group thrust complex, which straddles the Zoutpekel exposures, will be investigated in two companion papers.

Gemological and Chemical Characterization of Gem-Quality Titanite from Morocco

Titanite is a widespread accessory mineral in igneous, metamorphic, and hydrothermal rocks, but few comply with gem-grade requirements. Previous studies on Moroccan titanite focused on elementary composition and U-Pb dating. In this study, two gem-grade titanites (MA-1 and MA-2) from the Moroccan Central High Atlas were investigated through gemological and chemical studies, including infrared spectrum, Raman spectrum, SEM-EDS, and LA-ICP-MS. Two titanite samples are yellow, transparent–translucent with a greasy luster, 3.5 and 2.5 mm long. MA-1 and MA-2 have similar gemological properties, the refractive index (RI) is beyond the range of the refractometer (&gt;1.78), the specific gravity (SG) values fall in the range of 3.52~3.54 and both are inert to short-wave and long-wave UV radiation. The spectral characteristics have high consistency with the RRUFF database. The major elements’ composition shows a negative correlation between Al, Fe, V, and Ti, suggesting the titanites underwent substitutions such as (Al, Fe3+) + (F, OH) ↔ Ti + O. The titanite samples, characterized by a low abundance of REE (802~4088 ppm) and enriched in LREE, exhibit positive Eu (δEu: 1.53~7.79) and Ce (δCe: 1.08~1.33) anomalies, indicating their formation in a hydrothermal environment with low oxygen fugacity. The 238U/206Pb and 207Pb/206Pb ratios of the titanites yield lower intercept ages of 152.6 ± 2.2 and 151.4 ± 5.3 Ma (1s), consistent with their weighted average 206Pb/238U ages of 152.3 ± 2.0 and 150.7 ± 3.2 Ma (1s) respectively. The results of U-Pb dating are matched with the second main magmatic activities in the High Atlas intracontinental belt of Morocco during the Mesozoic to Cenozoic period. Moreover, the two titanite samples have almost no radiational damage. All the results show that the titanite from High Atlas, Morocco, has the potential to be a reference material for LA-ICP-MS U–Pb dating, but further experiments are needed to be sure.

U–Pb Dating, Gemology, and Chemical Composition of Apatite from Dara-e-Pech, Afghanistan

Minerals of the apatite group commonly occur in granite pegmatites, and their ability to incorporate a wide range of trace elements makes them a good indicator of magma composition and magmatic–hydrothermal processes. Gem-quality purple apatite crystals from the Dara-e-Pech pegmatite field in Afghanistan have rarely been reported. Here, we investigated apatite crystals originated from this locality, using gemological testing, chemical analysis, and in situ U–Pb dating, with the purpose of identifying their origin, the constraints on the magma source in which the apatite crystals were formed, and the timing of the magmatic–hydrothermal activity. Our findings demonstrate that the purple apatite crystals were impure fluorapatite, characterized by heavy rare-earth element (HREE) enrichment, intermediate Eu anomalies, and non-CHARAC Y/Ho ratios. The results showed that these apatite crystals yielded a lower intercept age of 135.8 ± 6.9 Ma. We proposed that the pegmatitic apatite samples formed in a transitional magmatic–hydrothermal pegmatitic system with moderate fO2 in the Early Cretaceous (~135 Ma). Our study helps to constrain the magmatic–hydrothermal activities of the little-known Dara-e-Pech pegmatite field.

Miocene Volcanism in the Slovenský Raj Mountains: Magmatic, Space, and Time Relationships in the Western Carpathians

The Miocene volcanic-intrusive complex in the Slovenský Raj Mountains, middle Slovakia, comprises a swarm of subalkaline basalts and basaltic andesites with alkaline basalts, trachybasalts and basaltic trachyandesites. Basaltic to doleritic feeder dykes and sporadic hyaloclastite lavas are exposed in contact with the Triassic Bódvaszilas Formation of the Silica Nappe. The primary clinopyroxene, plagioclase, and Fe-Ti oxide assemblage also contains calcite spheroids inferred to represent carbonatitic melt. These spheroids are associated with subsolidus chlorite, actinolite, magnetite, titanite, calcite, and epidote. Micropoikilitic clinopyroxene, albite, and Ti-magnetite formed due to rapid quenching. There was an incorporation of host rock carbonate during the eruption. The erupted products are the result of magmatic differentiation of the parental basaltic tholeiitic magma with a redox of ∆QFM = +1 to +3, affected by varying degrees of 0%–50% fractionation and the assimilation of carbonate material in a shallow magmatic reservoir. REE geochemistry shows N-MORB-like type patterns with both LaN/YbN and LaN/SmN &lt; 1 at near constant Eu/Eu* (~0.9). This is supported by εNd(t=13 Ma) values of +8.0 to +7.4 determined from the basaltic rocks. The REE values can be modeled by 1% fractional melting of garnet peridotite mixed with 7% melting of spinel peridotite of PM composition (1:9 proportions). SIMS and LA-ICP-MS U/Pb analysis of zircons yields a concordant age of 12.69 ± 0.24 Ma and a 13.3 ± 0.16 Ma intercept (Serravallian) age. The Middle Miocene volcanic activity was related to subduction-collision processes along the boundary of the Cenozoic ALCAPA (Alps–Carpathians–Pannonia) microplate and the southern margin of the European plate.

Microtexture, geochemistry and geochronology of monazite and zircon from the Jialu deposit in the Lesser Qinling: Implications for multi-stage magmatic and metamorphic events in the southern margin of the North China Craton

The Lesser Qinling area is the largest outcrop of the Precambrian basement in the southern margin of the North China Craton (S-NCC). Notably, many carbonatite-related polymetallic deposits are distributed in this area, including the Jialu deposit with light and heavy REE mineralization. Carbonatite and granite from the Jialu deposit contain diverse monazite and zircon grains, and deciphering the age distributions and chemical compositions of these monazites and zircons is crucial for comprehending the multi-stage magmatic and metamorphic events in the S-NCC. Type I monazite from banded REE ore veins yields a U-Pb age of 217.0 ± 5.0 Ma, representing the formation age of carbonatite. Type II monazite from granite yields consistent U-Pb and Sm-Nd ages of ∼1.95 Ga, representing the emplacement age of granite. Type III monazite is hydrothermal in origin, and yields two dominant age peaks at ∼550 Ma and ∼525 Ma. Types I, II and III zircons are xenocrysts from the Taihua Group and yield two main age peaks at ∼2.35 and ∼2.17 Ga. Of note, type III zircon also records an early Paleozoic tectonothermal event by a lower intercept age of 532 ± 59 Ma, which overlaps the ages recorded by hydrothermal monazite. The early Paleozoic tectonothermal events discovered may be a manifestation of the global Pan-African Orogeny in the S-NCC. This new finding further implies that the S-NCC was significantly affected by the assembly of the Gondwana supercontinent during the early Paleozoic.