Late Granites Research Articles

Late Neoproterozoic P-T-t paths of syn- and post-collisional metamorphism in the Paranaguá Terrane, Ribeira Belt (Brazil): implications for West Gondwana assembly

ABSTRACT Phase diagram modelling and U-Pb monazite ages reveal a clockwise Pressure-Temperature-time metamorphic evolution in the Paranaguá Terrane (Ribeira Belt – SE Brazil) and characterized important tectonic events. Comparisons of our dataset with the Dom Feliciano and Kaoko belts indicate a contrasting metamorphic evolution of South American and African units during West Gondwana assembly. The Paranaguá Terrane is considered an arc-related unit formed during the western Gondwana accretion, comprising Paleoproterozoic basement inliers, metasedimentary rocks and late Neoproterozoic granites. Metapelites mineral assemblages and chemistry combined with isotopic data indicate three tectonometamorphic stages for the terrane. M1 (640–610 Ma) is associated with collisional processes that resulted in a greenschist to lower amphibolite facies regional metamorphism (540–580°C and ~6-8 kbar). The progression of the metamorphism followed a decompression path of c. 2–4 kbars and reached P-T conditions of ~725°C at ~5 kbars (M2 – 610-580 Ma). M2 is associated with post-collisional processes related to slab-break off and partial exhumation of deeply buried sequences. Metapelites low-temperature retrograde conditions define a late M3 (540–500 Ma) metamorphic event. Our results demonstrate the similarities and differences of the Paranaguá-Dom Feliciano-Kaoko orogenic system. The metamorphic evolution of the Paranaguá Terrane and Northern Dom Feliciano Belt exhibits a geothermal gradient controlled by broad magmatic activity and post-collisional processes. In contrast, their suggested African counterpart (Kaoko Belt) shows a Barrovian metamorphic trend. This dataset permitted a refined time-space evolution of these southwest Gondwana units.

Geological formations of the Mucuri river path in the State of Minas Gerais

In this work, the geological formations along the Mucuri River in the State of Minas Gerais were identified in order to contribute to multidisciplinary engineering projects, mainly for the consolidation of urban, rural and environmental planning. The Mucuri River is formed by the junction of the Mucuri do Norte and Mucuri do Sul rivers. The first appears in the municipality of Malacacheta at 720m height and the second in the municipality of Ladainha at 750m of height. The processes of metamorphism and later weathering, associated to erosion, along the geological time, modelled the landscape of the region, transforming its territory with different heights. Many places in the region have quaternary alluvial soil suitable for growing grasses adapted to the flooding of the river. In the source of the South Mucuri River, in the municipality of Malacacheta, appear the Serra Negra Formation, belonging to the Guanhães Group, which consists of banded biotite-gneiss. The geological formations that follow the waterway of the Mucuri River have characteristics of Neoproterozoic rocks (late-tectonic granites of the Galiléia Intrusive Suite, of the Rio Doce Group), and of the Eocambrian (post-tectonic late granites of the Aimorés Intrusive Suite), aged 585 to 630 Ma. The eighteen formations found are respectively: Serra Negra Formation, Concórdia do Mucuri Formation, Leucogranite Caraí, Tumiritinga Formation (Marble), Tumiritinga Formation, Tonalite São Vitor, Topazio Granodiorite, Leucogranite Faísca, Wolff Granite, Caladão Granite, Charnockite Padre Paraíso, Kinzigitic gneiss, Leucogranite Carlos Chagas, Ataléia Granite, alluvial soil, Nanuque Granite, Underbite Mangalô and Granite Rio Mucuri.

Rare and new compounds in the Ni-Cu-Sb-As system: first occurrence in the Gomati ophiolite, Greece

The Gomati ophiolite (Northern Greece) is located in the Serbo-Macedonian Massif, in the Hellenides orogenic belt. It consists of altered peridotites hosting scattered chromitite bodies. The ultramafics are enclosed in Silurian gneisses and schists, and are partially in contact with late Cenozoic granites. The present work focuses on accessory minerals in the Ni-Cu-Sb-As system, found in a chloritized clinopyroxenite in contact with chromitite. The electron microprobe analyses revealed the presence of known minerals such as orcelite (Ni 5 As 2 ) and breithauptite (NiSb) and other new phases that cluster around the following stoichiometries: (Ni,Cu) 7 (Sb,As) 3 , (Ni,Cu) 2 (Sb,As), (Ni,Cu) 11 (Sb,As) 8 , Ni 3 As, Ni 5 (As,Sb) 2 and Ni 7 (As,Sb) 3 . As orcelite is a non-stoichiometric mineral, (Ni,Cu) 7 (Sb,As) 3 , Ni 5 (As,Sb) 2 and Ni 7 (As,Sb) 3 may correspond to Cu and/or Sb-rich terms of this phase. A mineral phase corresponding to (Ni,Cu) 2 (Sb,As) was first described in the Tulameen complex of Canada. A phase with stoichiometry Ni 3 As was found in the Bon Accord oxide body of South Africa. The (Ni,Cu) 11 (Sb,As) 8 probably represents a Cu-rich Sb analogue of the mineral maucherite (Ni 11 As 8 ). Such mineral assemblage in the Gomati ophiolite is puzzling. While ultramafic rocks contain Ni and As of magmatic origin, the presence of Sb, Ag, Au and Cu minerals could be indicative of a metasomatic enrichment, probably linked to the presence of fluids emanating from the granite body in contact with the Gomati ophiolite.

Wandering continents of the Indian Ocean

Wandering continents of the Indian Ocean

Biotite chemistry and the role of halogens in Archaean greenstone hosted gold deposits: A case study from Geita Gold Mine, Tanzania

Geita Hill is one of the largest Tanzanian gold deposits, located southwest of Lake Victoria and ∼2 km along strike from the giant Nyankanga deposit. The deposit is hosted by metasedimentary rocks – dominated by ironstones and intruded by numerous diorite dykes. Textural, structural and geochronological observations indicate that the gold mineralisation overprints all the ductile fabrics and the late orogenic D6 reverse faulting event, suggesting that gold was introduced during later D7 and D8 events. The metamorphic background is characterized by biotite + K-feldspar + actinolite ± pyrhotite, which is overprinted by the gold related alteration consisting of sulfidation fronts, veins and micro-fractures dominated by quartz + biotite + K-feldpar + pyrite. The almost identical mineralogy of the mineralised assemblage and the metamorphic background makes it difficult to identify the source, the effect and the spatial extent of the mineralising fluid. As part of this study detailed analyses of biotite were conducted in order to identify the nature of the mineralising fluid and its spatial effect across the Geita Hill deposit. Results show that the mineralised assemblage is slightly more oxidized (pyrite + magnetite) compared to the metamorphic background (pyrrhotite + magnetite). The intense sulfidation within the ore zone resulted in the formation of Mg-rich biotite, which grades into more Fe-rich biotite away from the ore zone. This change in biotite chemistry causes a shift in the SWIR Fe-OH 2250 nm absorption feature to lower wavelengths, which is also correlated with an increase in gold grade within the mineralised zone. The abundance of F in biotite significantly increases within the ore zone indicating the presence of F-rich hydrothermal fluids during mineralisation. Late timing of mineralisation, synchronous with the emplacement of voluminous high-K granites, and the presence of K- and F-bearing fluids indicate a genetic connection between the mineralising fluids and the late granites. Biotite grains from different deposits types (porphyry, IOCG, lode-Au) appear to have distinct composition suggesting that the source of the fluids involved in the formation of each deposit type has a characteristic halogen chemistry.

Alteration and mineralization zoning, ore textures and ore-forming process of Yongping copper deposit, Jiangxi Province

Yongping copper deposit, associated with S-W-Pb-Zn mineralization, is located at the southern margin of the Jiangshan-Shaoxing suture and between the Yanshanian granite belt and the Hercynian-Indosinian depression in the northern Wuyi Mountains. Late Paleozoic stratigraphy, Yanshanian granite, and copper ore body is controlled by thrust napper structure, as the basement rocks of the Zhoutan Group thrusting on the Late Paleozoic strata, Early Yanshanian biotite granite-granodiorite, quartz porphyry, and granite porphyry intruding along weak planes of thrust, and stratiform ore bodies occurring within the skarnized Carboniferous Yejiawan Formation. The ore body occurred in garnet skarn, phyllitic shale and skarnized marble. This study deciphers the ore-forming episodes and metallogenic process of the deposit based on mineralization-alteration zonation and textures of the ores. Exploration and mining working faces indicate that the mineralization and alteration of the deposit is granite-centered. If taking one side into consideration, i. e., from the granite to the limestone wall rock, following zonation can be delineated : (1) skarn minerals vary from garnet, via diopside, to wollastonite ; (2) the garnet varies in color from red, via brown, to green; (3) economic mineralization mainly occurring as banded and stock veins in the brown garnet skarn zone, leading to the ore grade increasing firstly and then decreasing. Metal mineral association of banded and stock veins in skarns, metasandstone-shales, and large sulfide-quartz veins ( up to 10m wide) is identical, consisting mainly of pyrite, scheelite, galena, sphalerite and chalcopyrite, indicating that different types of ores in the Yongping copper deposit are products of the same hydrothermal mineralization system in diverse wall rocks and ore-controlling structures. According to mineral assemblages and ore textures, six metallogenic stages can be divided for the deposit, which are garnet, mag-hematite, scheelite, iron-copper sulfide, lead-zinc sulfide, and carbonate stages, respectively. Skarn zonation formed during garnet stage, and massive pyrrhotite-grunerite formed at late period of this stage; magnetite, hematite composed mag-hematite stage; scheelite stage dominate tungsten mineralization, occurring as quartz-scheelite stock and disseminated wolframite. Iron-copper sulfide stage is the main period of copper mineralization; lead-zinc and carbonate stage likely marks the late and end of the primary mineralization, respectively.

Zircon U–Pb geochronology and Hf isotopic constraints on the petrogenesis of the Late Silurian Shidonggou granite from the Wulonggou area in the Eastern Kunlun Orogen, Northwest China

ABSTRACTThe Wulonggou area in the Eastern Kunlun Orogen (EKO) in Northwest China is characterized by extensive granitic magmatism, ductile faulting, and orogenic gold mineralizations. The Shidonggou granite is located in the central part of the Wulonggou area. This study investigated the major as well as trace-element compositions, zircon U–Pb dates, and zircon Hf isotopic compositions of the Shidonggou granite. Three Shidonggou granite samples yielded an average U–Pb zircon age of 416 Ma (Late Silurian). The Late Silurian Shidonggou granite is peraluminous, with high alkali contents, high Ga/Al ratios, high (K2O + Na2O)/CaO ratios, and high Fe2O3T/MgO ratios, suggesting an A-type granite. The Shidonggou granite samples have zircon εHf(t) values ranging from −7.1 to +4.4. The Hf isotopic data suggest that the Late Silurian granite was derived from the partial melting of Palaeo- to Mesoproterozoic juvenile mantle-derived mafic lower crust. Detailed geochronological and geochemical data suggest that the Late Silurian granite was emplaced in a post-collisional environment following the closure of the Proto-Tethys Ocean. Combining data of other A-type granitic rocks with ages of Late Early Silurian to Middle Devonian, such post-collisional setting related to the Proto-Tethys Ocean commenced at least as early as ~430 Ma (Late Early Silurian), and sustained up to ~389 Ma (Middle Devonian) in the EKO.

The Late Silurian Age of the Reference Aralaul Granosyenites–Granite Massif (Northern Kazakhstan)

This work presents the results of U–Pb geochronological studies of alkaline granites of the Aralaul complex of Northern Kazakhstan, which allow one to substantiate their Late Silurian (420 ± 4 Ma) age. Taking into consideration the previously obtained data, we propose a new development scheme of Paleozoic granitoid magmatism in Northern Kazakhstan, which includes Late Ordovician granite–granodiorite (Zerenda and Krykkuduk), Early Silurian granite–leucogranite (Borovoe and Karabulak), Late Silurian granosyenites–granite (Aralaul), and Early Devonian (Balkashino and Orlinogorsk) complexes.

Timing, petrogenesis, and setting of granites from the southern Beishan late Palaeozoic granitic belt, Northwest China and implications for their tectonic evolution

Late Palaeozoic granites are widely distributed in the southeastern Beishan area, which is located in the central part of the southern Central Asian Orogenic Belt (CAOB). U–Pb zircon dates of five late Palaeozoic granitic plutons from the southeastern Beishan area yield Permian ages: 285 ± 2 Ma (Shuwojing and Western Shuwojing plutons), 269 ± 3 Ma (Jianquanzi and Jiuquandihongshan plutons), and 260 ± 1 Ma (Jiujing pluton). The early Permian Shuwojing pluton, an unfractionated calc-alkaline biotite monzogranite with slightly positive εNd(t) (+0.7 and +0.6) and low initial 87Sr/86Sr (0.70722 and 0.70712), and the early Permian Western Shuwojing pluton, a high-K calc-alkaline biotite granite with slightly negative εNd(t) (−0.2 and −0.1) and low initial 87Sr/86Sr (0.70390 and 0.70919), are likely derived from a mixture of depleted (juvenile) mantle and upper continental crustal (or sedimentary) material. The mid-Permian Jianquanzi and Jiuquandihongshan monzogranites have highly fractionated potassium-rich calc-alkaline characteristics with negative εNd(t) (−4.3) and very high initial 87Sr/86Sr (0.71949), reflecting a continental crustal component. The compositionally diverse Jiujing pluton and the granodiorite and high-Sr monzogranite phases display adakite-like compositions with relatively low εNd(t) (−0.1 and −2.2) and high initial 87Sr/86Sr (0.70822 and 0.70913). The Jiujing low-Sr monzogranite has higher initial 87Sr/86Sr (0.73464) and lower εNd(t) (−2.8), indicating a significant continental crustal component in its genesis. This work, combined with the regional geology and previous studies, suggest that the early to middle Permian southern Beishan plutons formed in a post-collisional environment, probably an intracontinental rift environment linked to asthenospheric upwelling in response to the break-off of a subducted slab. In the late Permian, the southern Beishan area was in a compressive tectonic regime and thickening of the continental crust resulted in the formation of the Jiujing adakite-like granite.

Multiphase melting, magma emplacement and P-T-time path in late-collisional context: the Velay example (Massif Central, France)

AbstractThe West European Variscan chain is a remarkable illustration of how partial melting marks out the geodynamic evolution of mountain belt through time. Here, we focus on the Late Carboniferous melting events reported in the southeastern French Massif Central (Velay dome), with emphasis on the modes of partial melting, relationships between partial melting and magma emplacement, transition between the melting episodes and related P-T-t path. Following nappe stacking events under medium pressure/temperature conditions (M1 and M2 events), three melting events are identified in the southern envelope of the Velay dome. A first melting episode (M3 event) occurred within the biotite stability field at 325–315 Ma (T ≈ 720°C and P = 0.5–0.6 GPa). It led to the complete disappearance of muscovite and to the formation of migmatites consisting of biotite ± sillimanite melanosome and of granitic/tonalitic leucosomes depending on protolith composition. It is interpreted as the result of internal heating mainly linked to decay of heat producing elements accumulated in a thickened crust. It resulted in the formation of a partially molten middle crust with decoupling between the lower and upper crust, late-collisional extension and crustal thinning.The second episode of melting (M4 event) occurred at ca. 304 Ma (T 800°C and P 0.4 GPa), synchronously with emplacement of the Velay granites and growth of the dome. It led to the breakdown of biotite and growth of cordierite (locally garnet or tourmaline), with formation of diatexites and heterogeneous granites. This high-T event synchronous with crustal extension is considered to result from intrusion of hot mantle-derived and lower crustal magmas triggering catastrophic melting in the middle crust. This event ends with local retrograde hydrous melting within the stability field of biotite close to the solidus in response to local input of water during temperature drop in the late stage of emplacement of the Velay dome.The last evidence of melting in this area (M5 event) corresponds to emplacement of late granites generated under conditions estimated at ≈850°C and 0.4–0.6 GPa. They may have been generated from melting of specific lithologies triggered by injection of mafic magmas. These granites emplaced in a partly cooled crust (medium-grade conditions). The emplacement age of these granites is not well constrained (305–295 Ma) though they clearly post-date the Velay granites.The melting episodes in the Velay area and generation of granites appear to correspond to the conjunction between (i) the effects of collision-related crust thickening and (ii) those related to slab break off and asthenospheric mantle decompression melting. The driving process is mainly the internal radiogenic heat in a first stage, relayed by the propagation of a thermal anomaly initially located in the lower crust (M3 event), but which subsequently rose to the middle and upper crustal levels through magma transfer (M4 event). Overall, the Velay example is a remarkable illustration of the progressive dehydration and sterilisation of a thickened crustal segment. It documents how large amounts of granitic magmas can be produced at shallow crustal levels in relation to the injection of mantle-derived magmas.

Geochronology, geochemistry and its tectonic significance of Chahe granites in Hainan Island

There are very few studies on the granites formed in Late Permian in Hainan (海南) Island. Petrology, geochronology and geochemistry research on Late Permian granites in Chahe (叉河) area, Hainan Island will be reported in this article. The results show that, Chahe granites formed in 251 Ma, are riched in SiO2, alkali, Fe2O3 while depleted in MgO and CaO, with low Sr and high Yb, and have all the features consistent with A-type granite. The forming of Chahe granites may suggest that Hainan Island was already in post-orogenic setting in Late Permian.

Study on Space-Time Relationship of Tungsten and Uranium Mineralization

The metal organic series in Southern Jiangxi is the series of W & U deposits closely related with the Late Yanshanian granite within the South China fold system and the uplift belt. The host rock of W mineralization is fine or medium-fine grained biotitic granite of Early Yanshanian period, subordinated with Late Yanshanian granite The time initial of uranium concentration span from 103-70Ma. Vertically the mineralization zone of tungsten is above that of uranium, however horizontally it is in the center and that of uranium outwards. To the west of Wuyi tectonic belt, distinctly the uranium mineralized posterior to the tungsten, however to the east of Wuyi tectonic belt, the W-Mo-bearing grease negation quartz vein let remarkably cut off the U-bearing silicified fractured zone.

RADIOGENIC ISOTOPE SYSTEMATICS OF THE TANCO AND SILVERLEAF GRANITIC PEGMATITES, WINNIPEG RIVER PEGMATITE DISTRICT, MANITOBA

Isotopic ages for minerals of the Archean lithium–cesium–tantalum (LCT)-family Tanco and Silverleaf granitic pegmatites in southeastern Manitoba range from about 2660 Ma to 2600 Ma. Etched tantalite yields U–Pb ages between ca. 2640 and 2620 Ma, and the six oldest ages form an array indicating 2641 ± 3 Ma, which is interpreted as a major period of crystallization. Fragments of zircon megacrysts give U–Pb ages ranging from ~2660 to 2606 Ma, which may reflect lead loss after crystallization associated with subsolidus fluids from the pegmatite. A Pb–Pb age on megacrystic apatite and associated feldspar gives 2657 ± 18 Ma. Rb–Sr ages on lepidolite from Silverleaf (2620 ± 13 Ma) and Tanco (2631 ± 12 Ma) overlap and agree with the Rb–Sr age of muscovite from Tanco (2620 ± 20 Ma), using a 87 Rb decay constant of 1.395 × 10 −11 yr −1 . Pb–Pb data from K-feldspar and albite show highly evolved unsupported Pb compositions that scatter along or between a single-stage isochron of about 2640 Ma and a mixing line between the composition of common Pb at about 2640 Ma on the Stacey and Kramers growth curve and the composition of radiogenic Pb generated at around 2640 Ma. This indicates that feldspars exchanged Pb with radioactive minerals like tantalite both early, during the period of pegmatite emplacement and cooling, and in geologically recent times. Early exchange is consistent with the observation of progressive structural modification of feldspars, whereas disturbed Rb–Sr systematics indicate late exchange of these elements between feldspar and its environment. The peraluminous composition of late granites and pegmatites in this suite and high initial 87 Sr/ 86 Sr ratio (> 0.8) of the Tanco pegmatite suggest an origin from melting of metasedimentary rocks beneath the Bird River greenstone belt. These rocks are most likely associated with the English River Subprovince exposed to the northeast.

The Sierra Norte-Ambargasta batholith: Late Ediacaran–Early Cambrian magmatism associated with Pampean transpressional tectonics

The Sierra Norte-Ambargasta batholith is one of the largest plutonic expressions of the Pampean orogeny in western Argentina. A thorough petrographic, geochemical, isotopic (Sr and Nd) and geochronological (UePb SHRIMP) study is reported. The batholith comprises granitoid rocks that may be subdivided into those affected by Pampean D2 dextral shearing and mylonization and those emplaced after deformation had ceased; representative samples gave UePb zircon ages of 537 ±4 Ma and 530 ±4 Ma respectively. The earlier, dominant, groupwere derived largely frommetaluminous calc-alkaline subduction-related magmas, whereas the late granites are peraluminous. However, all have relatively high initial 87Sr/86Sr ratios (0.706 to at least 0.710, strongly negative eNdt values (-1.7 to -5.9) and, in some cases inherited 600 Ma and 970 Ma zircon, similar to the isotopic and zircon provenance seen in the metamorphic host rocks. A high degree of contamination of the magmas, possibly anatexis in the case of the post-mylonite granite, is related to emplacement during the latestage transpressional docking of the Pampean terrane against the Rio de la Plata craton. The absence of detrital zircon derived from the craton in either the Pampean metasedimentary host rocks or the batholith supports this collisional model for the Pampean orogen.

MAJOR THRUSTING IN THE GRANITE AND THE ROLE OF LATE INTRUSIONS IN EXPOSING THE DEEPER PARTS OF THE CENTRAL BLOCK OF THE GALWAY GRANITE BATHOLITH

New geological mapping in the centre of the Galway Granite at Camus, Co. Galway, reveals a major north—south thrust zone, the Furnace Thrust, typically dipping east at 35°, which thrust up westward deeper-crystallised granite, including two minor late intrusions, on top of a higher-level granite footwall. Al-in-hornblende geobarometry of the footwall and the hanging wall confirms the thrusting. At 2km east of the thrust, both the footwall and the hanging wall of the thrust sheet were later substantially further uplifted by the steeper Shannawona Fault. At 6km east of this fault, the granite contains post-400—395Ma, pre-370—378Ma thrusts that moved south-eastward, so a major block of the deep ∼400—395Ma Megacrystic Granite has been squeezed upward. This granite still farther east was later uplifted more by the steep Shannapheasteen Fault, which is connected with the late (?380Ma) central intrusion of the Shannapheasteen Granite, which pushed its roof upward. The uplift of the Central Block with its deeply crystallised Megacrystic Granite was therefore the result of thrusts and faults connected in a complex way with the coeval intrusive pressures of the late emplacement of the Shannapheasteen Granite and six other late granites. All seven late granites are confined to the Central Block and, having low densities, exerted protracted buoyancy uplift forces. This modifies the previous partly correct, but mechanically difficult, explanation for the origin of the Central Block of the Galway Batholith.

Lead Isotopic Composition and Lead Source of the Huogeqi Cu-Pb-Zn Deposit, Inner Mongolia, China

The Huogeqi orefield located on the northern side of Mt. Langshan, Inner Mongolia occurs in the Middle Proterozoic Langshan Group metamorphic rocks, and the orebodies are stratiform. In the past twenty years, many Chinese geologists have conducted researches on the Huogeqi Cu-Pb-Zn deposit, but there has been still a controversy on its origin. Some advocate that the deposit is of sedimentary-metamorphic reworking origin, some hold that it is of sea-floor SEDEX origin, and others have a preference for magmatic superimposition origin. The crux of the controversy is that there is no common understanding about the source of ore-forming materials. In this paper, the Pb isotopic compositions of regional Achaean-Early Proterozoic basement rocks, various types of sedimentary-metamorphic rocks and volcanic rocks in the mining district, Late Proterozoic and Hercynian magmatic rocks are introduced and compared with the ore-lead composition, so as to constrain the source of the ore lead. The result indicates that (1) sulfides in the ores have homogeneous Pb isotopic compositions, showing a narrow variation range. Their 206Pb/204Pb ratios are within a range of 17.027–17.317; 207Pb/204Pb ratios, 15.451–15.786 and 208Pb/204Pb ratios, 36.747–37.669; (2) the Pb isotopic compositions of the regional Achaean-Early Proterozoic basement rocks are characteristic of the old Pb isotopic composition at the early-stage evolution of the Earth, which varies over a wider range, reflecting significant differences in Pb isotopic compositions of the ores. All this indicates that the source of ore lead has no bearing on the basement rocks; (3) the sedimentary-metamorphic rocks in the mining district are characterized by highly variable and more radiogenic Pb isotopic compositions and their Pb isotopic ratios are obviously higher than those of ores, demonstrating that ore lead did not result from metamorphic reworking of these rocks; (4) Pb isotopic compositions of Late Proterozoic diorite-gabbro and Hercynian granite are higher than those of ores. Meanwhile, the Pb isotopic compositions of sulfides in the small-sized strata-penetrating mineralized veinlets formed at later stages are completely consistent with that of sulfides in stratiform-banded ores, suggesting that these veinlets are the product of autochthonous reworking of the stratiform-banded ores during the period of metamorphism and the late magmatic superimposition-mineralization can be excluded; (5) amphibolite, whose protolith is basic volcanic rocks, has the same Pb isotopic compositions as ores, implying that ore lead was derived probably from basic volcanism. So, the source of ore-forming materials for the Huogeqi deposit is like that of the volcanic massive sulfide (VMS) deposits. However, the orebodies do not occur directly within the volcanic rocks, and instead they overlie the volcanic rocks, showing some differences from those typical VMS-type deposits.

LA-ICPMS Zircon U-Pb Dating for Three Indosinian Granitic Plutons from Central Hunan and Western Guangdong Provinces and Its Petrogenetic Implications

: The LA-ICPMS zircon U-Pb geochronology of three typically Indosinian granitic plutons yielded weighted mean 206Pb/238U ages of 214.1±5.9 Ma and 210.3±4.7 Ma for the biotite monzonitic granites from the Xiema and Xiangzikou plutons in Hunan Province, and 205.3±1.6 Ma for biotite granite from the Napeng pluton, western Guandong Province, respectively, showing a similar late Indosinian age of crystallization. In combination with other geochronological data from Indosinian granites within the South China Block (SCB), it is proposed that those late Indosinian granites with an age of −210 Ma and the early Indosinian granites (230–245 Ma) have the similar petrogenesis in identical tectonic setting. The Indosinian granites within the SCB might be the products of anatexis of the thickening crust in a compressive regime. These data provide a further understanding for the temporal and spatial distribution of the Indosinian granites and the dynamic evolution of the SCB.

Discussion on Dill et al. (2007) ‘Cu-Fe-U phosphate mineralization of the Hagendorf-Pleystein pegmatite province, Germany: with special reference to laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) of limonite-cored torbernite’, Mineralogical Magazine, 71, 371–387

Dill et al. (2007) present laser ablation inductively coupled plasma mass spectrometry U-Pb data for torbernite, columbite, and limonite of the Hagendorf and Pleystein pegmatites. These pegmatites, which are intruded into a late Carboniferous granite, have been dated by Glodny (1997) to 317±3 Ma (2σ; 3-point Rb-Sr mineral isochron). Dill et al. (2007) report a torbernite age of 4.55±0.02 Ma, which is in line with earlier geochronological work in the region, showing the young redistribution of U and the formation of secondary U minerals (e.g. Carl and Dill, 1983; Wendt and Carl, 1985). Dill et al. (2007) present ages of 299.2±1.9 Ma and 302±3 Ma for ferrocolumbite from Hagendorf and Pleystein, respectively, that broadly agree with the Rb-Sr age of the Hagendorf pegmatite (Glodny, 1997). In addition, they present age data of ~345 to 380 Ma for four spot analyses on ferrocolumbite from the Pleystein pegmatite and a 549 ± 12 Ma discordia intercept age for limonite and torbernite mantling this limonite from the Hagendorf pegmatite. These ages are older than the rock hosting the dated minerals. Referring to older (Lower Ordovician) pegmatites in the Tepla-Barrandian (Glodny et al. , 1998), Dill et al. (2007) argue that the ages ~345 to ~380 Ma reflect the Devonian resetting of the U-Pb systematics of columbite from Lower Ordovician pegmatites and represent inherited domains in columbite. Apparently, Dill et al. (2007) were not aware that the Hagendorf and Pleystein pegmatites had emplaced into rocks of the Moldanubian Zone, which had an entirely different evolution than the Tepla-Barrandian from where Lower Ordovician pegmatites are known (e.g. Franke, 2000; Finger et al. , 2007). Furthermore, none of the numerous U-Pb TIMS studies on columbite from pegmatites (e.g. Romer and Wright, 1992; Romer and Smeds, 1994, 1996, 1997; Mauthner …

Origin of Archean late potassic granites: Evidence from the Yilgarn and Pilbara Cratons

Origin of Archean late potassic granites: Evidence from the Yilgarn and Pilbara Cratons

Single zircon LA-ICPMS U-Pb dating of Weishan granite (Hunan, South China) and its petrogenetic significance

A detailed microstructure analysis and LA-ICPMS U-Pb dating have been done for zircons of Weishan granite from Hunan Province, South China. The results indicate that the Weishan granite is a multistage batholith formed during the late Indosinian-early Yanshanian time. The intruded time of the late Indosinian granite is 211.0±1.6Ma and 215.7±1.9Ma (two samples), whereas that of the early Yanshanian granite is 187.4±3.5Ma and 184.5±5.1Ma (two samples). In combination with other geochronological data for Indosinian rocks of South China and the adjacent region, it is inferred that the late Indosinian granites of South China (especially Hunan Province) are probably formed under extension regime as a consequence of post-collision stress relaxation, which is a spontaneous response to intracontinental thickening attributed to the collision and extrusion of two Indosinian seams, namely Qinling-Dabie and Song Ma. Moreover, it is also deduced that the early Yanshanian granites of Hunan Province could not be directly related with the subduction of Paleo-Pacific plate towards Eurasian continent, and they are most likely derivation of the mid-or lower-crustal materials because of decompressional melting under the continuous extension setting.