Glacial diamictites of Serra Azul Formation (Ediacaran,Paraguay belt): Evidence of the Gaskiers glacial event in Brazil

Discontinuous outcrops of diamictites and siltstones are found above post-Marinoan carbonates from the Araras Formation and represent the record of a second glaciation in the northern Paraguay belt, Brazil. This new stratigraphic unit, named the Serra Azul Formation, varies in thickness between 250 and 300 m; it lies on top of dolomites of the Araras Group and is overlain by sandstones of the Raizama Formation. Massive diamictite, approximately 70 m thick, composes the basal unit (Unit A), followed by 200 m thick laminated siltstones (Unit B), which contain sparse intercalations of very fine-grained sandstone lenses. This new diamictite level is probably related to the Gaskiers Glaciation, with an age of approximately 580 Ma, and represents the youngest Neoproterozoic glacial event recorded in South America.     

The Xitieshan volcanic sediment-hosted massive sulfide deposit,North Qaidam,China: Geology,structural deformation and geochronology

The Xitieshan deposit (~ 64 Mt at 4.86% Zn, 4.16% Pb, 58 g/t Ag, and 0.68 g/t Au) is hosted by the Middle to Late Ordovician Tanjianshan Group of the North Qaidam tectonic metallogenic belt, NW China. This belt is characterized by island arc volcanic, ultra-high pressure (UHP) metamorphic and ophiolitic rocks. The Tanjianshan Group constitutes a succession of metamorphosed bimodal volcanic and sedimentary rocks, which are interpreted to have formed on the margin of a back-arc ocean basin between the Qaidam block and the Qilian block.Four stratigraphic units are identified within the Ordovician Tanjianshan Group. From northeast to southwest they are: 1) unit a, or the lower volcanic-sedimentary rocks, comprising bimodal volcanic rocks (unit a-1) and sedimentary rocks (unit a-2) ranging from carbonates to black carbonaceous schist; 2) unit b, or intermediate-mafic volcaniclastic rocks, characterized by intermediate to mafic volcaniclastic rocks intercalated with lamellar carbonaceous schist and minor marble lenses; 3) unit c, a purplish red sandy conglomerate that unconformably overlies unit b, representing the product of the foreland basin sedimentation during the Early Silurian; 4) unit d, or mafic volcanic rocks, from base to up, comprising the lower mafic volcaniclastic rocks (unit d-1), middle clastic sedimentary rocks (unit d-2), upper mafic volcaniclastic rocks (unit d-3), and uppermost mafic volcanic rocks (unit d-4). Unit a-2 hosts most of the massive sulfides whereas unit b contains subordinate amounts.The massive stratiform lenses constitute most of the Xitieshan deposit with significant amount of semi-massive and irregularly-shaped sulfides and minor amounts in stringer veins. Pyrite, galena and sphalerite are the dominant sulfide minerals, with subordinate pyrrhotite and chalcopyrite. Quartz is a dominant gangue mineral. Sericite, quartz, chlorite, and carbonate alteration of host rocks accompanies the mineralization.U-Pb zircon geochronology yields three ages of 454 Ma, 452 Ma and 451 Ma for the footwall felsic volcanic rocks in unit a-1, sedimentary host rocks in unit a-2 and hanging-wall unit b, respectively. The Xitieshan deposit is considered to be coeval with the sedimentation of unit a-2 and unit b of the Tanjianshan Group. The Xitieshan deposit has been intensely deformed during two phases (main ductile shear and minor ductile-brittle deformation). The main ductile shear deformation controls the general strike of the ore zones, whereas minor deformation controls the internal geometry of the ore bodies. ⁴⁰Ar-³⁹Ar age of muscovite from mylonitized granitic gneisses in the ductile shear zone is ~ 399 Ma, which is interpreted to date the Xitieshan ductile shear zone, suggesting that Early Devonian metamorphism and deformation post-dated the Tanjianshan Group.The Xitieshan deposit has many features similar to that of the Bathurst district of Canada, the Iberian Pyrite Belt of Spain, the Wolverine volcanogenic massive sulfide deposit in Canada. Based on its tectonic setting, host-rock types, local geologic setting, metal grades, geochronology, temperatures and salinities of mineralizing fluid and source of sulfur, the Xitieshan deposit has features similar to sedimentary exhalative (SEDEX) and VMS deposits and is similar to volcanic and sediment-hosted massive sulfide (VSHMS) deposits.     

Age,provenance and tectonic setting of the Canastra and Ibiá Groups (Brasília Belt,Brazil): Implications for the age of a Neoproterozoic glacial event in central Brazil

The Brasília Belt is one of the best preserved Neoproterozoic orogens in Brazil. It comprises a thick Meso–Neoproterozoic sedimentary/metasedimentary pile including the Canastra and Ibiá Groups, which are the object of this study. The Canastra Group constitutes a regressive sedimentary sequence made mainly of greenschist-facies metapelitic and metapsammitic rocks, including phyllite, sandy metarhythmite and quartzite, with minor intercalations of limestone, as well as carbonaceous and carbonatic phyllite. The Ibiá Group is formed of a basal diamictite followed upwards by phyllites and calc-schists. It rests on an erosional unconformity on top of the Canastra Group.A provenance study based on U–Pb zircon geochronology on a selection of seven samples helped to establish the various source areas and maximum depositional ages of the original sediments. In addition, seven new Sm–Nd analyses are presented and discussed together with previously published data.LAM-ICP-MS U–Pb dating of detrital zircon grains indicates a maximum depositional age of the Canastra and Ibiá Groups of ca. 1030 and 640 Ma, respectively. The provenance signature of the Canastra Group comprises a wide range of detrital zircon ages with a significant Paleoproterozoic component (～1.8 and ～2.1 Ga) and an important Mesoproterozoic source (1.1–1.2 Ga), especially for the Paracatu Formation, indicating the São Francisco–Congo Craton as main source. These provenance data, in particular the absence of Neoproterozoic zircon grains, typical of the active margin of the Brasília Belt, allied with the homogeneous Paleoproterozoic T_DM values are consistent with the previous interpretation that the Canastra Group represents a sedimentary sequence deposited on a passive margin setting.Zircon grains from the diamictite of the Ibiá Group yielded ages ranging from 936 to 2500 Ma. In contrast, the overlying calc-phyllite of the Rio Verde Formation reveals a dominant Neoproterozoic provenance pattern with important peaks at 665, 740 and 850 Ma. The São Francisco-Congo Craton and Goiás Magmatic Arc are, most probably, the two main source regions for the Ibiá Group which may represent, therefore, a former fore- or back-arc sedimentary sequence. Tectonically, therefore, the Ibiá Group is equivalent to the Araxá Group exposed in central Goiás and both represent syn-orogenic sedimentary sequences formed with important detrital contributions derived from the Neoproterozoic Goiás Arc.The provenance data presented here indicate that the Cubatão Formation is most possibly representative of a Marinoan or younger glacial event.     

Turmoil before the boring billion: Paleomagnetism of the 1880–1860 Ma Uatumã event in the Amazonian craton

The Uatumã silicic large igneous province (SLIP) has covered about 1,500,000 km² of the Amazonian craton at ca. 1880 Ma, when the Columbia/Nuna supercontinent has been assembled. Paleomagnetic and geochronological data for this unit were obtained for the Santa Rosa and Sobreiro Formations in the Carajás Province, southwestern Amazonian craton (Central-Brazil Shield). AF and thermal demagnetizations revealed northern (southern) directions with high upward (downward) inclinations (component SF1), which passes a ‘B’ reversal test, and is carried by magnetite and SD hematite with high-blocking temperature. This component is present on well-dated 1877.4 ± 4.3 Ma (U-Pb zrn - LA-ICPMS) rhyolitic lava flows, providing the SF1 key paleomagnetic pole (Q = 6) located at 319.7°E, 24.7°S (A₉₅ = 16.9°). A second southwestern (northeastern) direction with low inclination (Component SF2) was obtained for a well-dated 1853.7 ± 6.2 Ma (U-Pb zrn - LA-ICPMS) dike of the Velho Guilherme Suite. This component also appears as a secondary component in the host rhyolites of the Santa Rosa Fm and andesites of the Sobreiro Fm at the margins of the dike previously dated. Its primary origin is confirmed by a positive baked contact test, where a Velho Guilherme dike crosscuts the 1880 Ma andesite from the Sobreiro Formation. The corresponding SF2 key pole is located at 220.1°E, 31.1°S (A₉₅ = 5°) and is classified with a reliability criterion Q = 7. The large angular distance between the almost coeval (difference of ~ 25 Ma) SF1 and SF2 poles implies high plate velocities (~ 39.3 cm/yr) which are not consistent with modern plate tectonics. The similar significant discrepancy of paleomagnetic poles with ages between 1880 and 1860 Ma observed in several cratons could be explained by a true polar wander (TPW) event. This event is the consequence of the reorganization of the whole mantle convection, and is supported by paleomagnetic reconstructions at 1880 Ma and 1860 Ma and also by geological/geochronological evidence.     

Clockwise rotation of the Santa Marta massif and simultaneous Paleogene to Neogene deformation of the Plato-San Jorge and Cesar-Ranchería basins

A moderate amount of vertical-axis clockwise rotation of the Santa Marta massif (30°) explains as much as 115 km of extension (stretching of 1.75) along its trailing edge (Plato-San Jorge basin) and up to 56 km of simultaneous shortening with an angular shear of 0.57 along its leading edge (Perijá range). Extensional deformation is recorded in the 260 km-wide, fan-shaped Plato-San Jorge basin by a 2–8 km thick, shallowing-upward and almost entirely fine-grained, upper Eocene and younger sedimentary sequence. The simultaneous initiation of shortening in the Cesar-Ranchería basin is documented by Mesozoic strata placed on to lower Eocene syntectonic strata (Tabaco Formation and equivalents) along the northwest-verging, shallow dipping (9–12° to the southeast) and discrete Cerrejón thrust. First-order subsidence analysis in the Plato-San Jorge basin is consistent with crustal stretching values between 1.5 and 2, also predicted by the rigid-body rotation of the Santa Marta massif. The model predicts about 100 km of right-lateral displacement along the Oca fault and 45 km of left-lateral displacement along the Santa Marta–Bucaramanga fault. Clockwise rotation of a rigid Santa Marta massif, and simultaneous Paleogene opening of the Plato-San Jorge basin and emplacement of the Cerrejón thrust sheet would have resulted in the fragmentation of the Cordillera Central–Santa Marta massif province. New U/Pb ages (241 ± 3 Ma) on granitoid rocks from industry boreholes in the Plato-San Jorge basin confirm the presence of fragments of a now segmented, Late Permian to Early Triassic age, two-mica, granitic province that once spanned the Santa Marta massif to the northernmost Cordillera Central.     

New geochemical and mineralogical constraints on the genesis of the Vani hydrothermal manganese deposit at NW Milos island,Greece: Comparison with the Aspro Gialoudi deposit and implications for the formation of the Milos manganese mineralization

The Mn-Ba-Pb deposit at Aspro Gialoudi in NW Milos is shown to be a fossil inhalative-exhalative hydrothermal deposit that represents the deepest part of the Vani succession at the western extremity of the main Vani manganese deposit. The geology of the Vani-Aspro Gialoudi area is characterized by Upper Pliocene-Lower Pleistocene dacitic and rhyodacitic lava domes, which are overlain by the Vani volcaniclastic unit considered to be part of the 2.66–1.44 Ma magmatic event at Milos Island. The presence of in-situ and intrusive hyaloclastite breccias surrounding the coherent lava domes at Aspro Gialoudi and Vani areas indicates submarine emplacement for the domes. The dacitic-rhyodacitic domes are variously altered (mainly propylitic and/or argillic alteration, silicified and in some cases locally exhibiting adularia alteration). Both Aspro Gialoudi and main Vani deposit are located proximal to fault systems: the main Vani manganese deposit is adjacent to the NW-trending Kondaros-Katsimouti-Vani Dome fault, whereas the Aspro Gialoudi deposit is adjacent to the relatively minor NE-trending fault on the west coast of Milos. At Aspro Gialoudi, mineralization took place in a subseafloor and/or seafloor environment and is characterized by a stratabound Mn-barite-rich deposit mainly within a package of propylitized intrusive hyaloclastites and within the overlying sandstones. Banded epithermal veins trending NE-SW and composed of chalcedonic silica/quartz + barite + Mn-oxide ± sulfides crosscut the dacitic lavas, the hyaloclastites and the overlying volcaniclastic sequence at Aspro Gialoudi and are considered to represent the feeder zones of the manganese-barite mineralization. Within the veins, early sulfide (galena-sphalerite) barite and quartz deposition is followed by manganese oxides and aragonite, thus resembling the epithermal-style Pb-Zn-Ag-Mn mineralization across the NW-trending Katsimoutis-Kondaros-Vani fault. Mineralization in Aspro Gialoudi and Vani deposits seems to be controlled by alternating cycles of deposition of sulfides and hydrothermal manganese oxides within the faults. Manganese deposition in both deposits formed in a similar manner, namely by transport of hydrothermal fluids through the adjacent fault systems into a reservoir of volcanoclastic sandstone and hyaloclastites to produce a deposit initially consisting of principally of pyrolusite and occasionally ramsdellite, which were subsequently replaced by cryptomelane, hollandite, coronadite and hydrohaeterolite. Precipitation of hydrothermal manganese oxides took place very quick and under microbial Mn(II) oxidation. Compositional data show that metallic elements most enriched in the Aspro Gialoudi and Vani manganese deposits relative to the average continental crust, lie in the sequences Pb > Cd > Mn > As > Sb > Zn > W > Tl > Ba > Cu > Mo > Co > Bi and As > Sb > Pb > Mn > Tl > Cd > Zn > W > Cu > Ba > Mo > Co, respectively. Mineralogical and geochemical (e.g. REE) data from both Aspro Gialoudi and main Vani deposit are taken to indicate mainly a seawater source for the hydrothermal fluids. These two deposits are genetically and spatially related to base- and precious metal intermediate-sulfidation epithermal mineralization. They formed successively by similar processes and are considered to be integral parts of the same hydrothermal system.     

Glaciation and deglaciation of the Libyan Desert: The Late Ordovician record

Detailed outcrop studies at the flanks of Al Kufrah Basin, Libya, reveal the nature of glacially-related sedimentation and post-depositional deformation styles produced in association with the Late Ordovician glaciation, during which ice sheets expanded northward over North Africa to deposit the Mamuniyat Formation. At the SE basin flank (Jabal Azbah), the Mamuniyat Formation is sand-dominated, and incises interfingering braidplain and shallow marine deposits of the Hawaz Formation. The glacially-related sediments include intercalations of mud-chip bearing tabular sandstones and intraformational conglomerates, which are interpreted as turbidite and debrite facies respectively. These record aggradation of an extensive sediment wedge in front of a stable former ice margin. An increase in mudstone content northward is accompanied by the occurrence of more evolved turbidites. A widespread surface, bearing streamlined NW–SE striking ridges and grooves, punctuates this succession. The structures on the surface are interpreted to have formed during a regional north-westward ice advance. Above, siltstones bearing Arthrophycus burrows, and Orthocone-bearing sandstones beneath tidal bars testify to glaciomarine conditions for deposition of the underflow deposits beneath. By contrast, the northern basin margin (Jabal az-Zalmah) is appreciably different in recording shallower water/paralic sedimentation styles and major glaciotectonic deformation features, although facies analysis also reveals northward deepening. Here, a siltstone wedging from 8 to 50 m toward the north was deposited (lower delta plain), succeeded by climbing ripple cross-laminated sandstones up to 60 m in thickness (distal through proximal delta mouth bar deposits) with occasional diamictite interbeds. These rocks are deformed by thrusts and > 50 m amplitude fault-propagation folds, the deformation locally sealed by a diamictite then overlain by conglomeratic lag during ultimate deglaciation. Integrating observations from both basin margins, a model of fluvial-dominated delta systems feeding a pulsed debrite and turbidite fan system in a shallow proglacial shelf is proposed.     

Petrogenesis of ore-bearing porphyry from the Tangjiaping porphyry Mo deposit,Dabie orogen: Zircon U-Pb geochronology,geochemistry and Sr-Nd-Hf isotopic constraints

Extensive Early Cretaceous post-collisional igneous rocks, especially the large volume of granitoids developed in the Dabie orogen. Some of these granitic rocks are spatially, temporally, and genetically associated with economically important molybdenum deposits. The Tangjiaping large-scale (> 0.1 million ton) porphyry Mo deposit is located in the northwest of the Northern Dabie Complex unit. The Mo mineralization is mainly hosted in molybdenite-bearing quartz veinlets and stockworks in the Tangjiaping granite porphyry, which intruded into Proterozoic biotite-plagioclase gneiss and amphibole-plagioclase gneiss. Two alteration zones from the porphyry centre outwards and downwards can be recognized: (1) K-silicate alteration-silicification zone; (2) silicification-phyllic alteration zone. The Tangjiaping ore-bearing granite porphyry occurs as an individual stock with an outcrop of 0.4 km². LA-ICP-MS zircon U-Pb dating of the Tangjiaping granite porphyry yields crystallization age of 115 ± 1 Ma, which is consistent with the molybdenite Re-Os age of the deposit given by previous studies. The Tangjiaping granitic rocks are metaluminous and belong to high-K calc-alkaline and shoshonitic series. They are relatively enriched in light rare earth elements and have moderately negative Eu anomalies. Geochemical and mineralogical characteristics indicate that the Tangjiaping granite is an A-type granite and was generated by partial melting of intermediate-felsic rocks at pressures of ca. 0.4–0.8 GPa. There are high initial ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.707367 to 0.709410 and negative ε_Nd(t) values varying from − 15.0 to − 14.2 for the Tangjiaping granite. In situ zircon Hf isotopic analyses show that the ε_Hf(t) values of zircons from the Tangjiaping granite porphyry vary from − 17.0 to − 6.0. The geochemical data and Sr-Nd-Hf isotopes, coupled with the Neoproterozoic inherited zircon age (652 ± 21 Ma), indicate that the Tangjiaping granite porphyry was most likely derived from partial melting of the Northern Dabie gneiss with some relatively enriched mantle materials involved. The Tangjiaping Mo ore-forming granite porphyry was formed in an extensional setting. The Early Cretaceous asthenospheric upwelling might have played an important role in the formation of the approximately coeval Mo-bearing magmas in the Dabie orogen.     

Tectono-thermal events in East Kunlun,Northern Tibetan Plateau: Evidence from zircon U–Pb geochronology

The widely distributed high-grade gneisses in the East Kunlun Orogenic Belt (EKOB) are keys to understand the Precambrian tectonic evolution of the Northern Tibetan Plateau. In this study, new LA-ICP-MS zircon U–Pb ages from paragneiss and schist of the Proterozoic Jinshuikou Group and quartzite of the Proterozoic Binggou Group are reported in an attempt to evaluate the Neoproterozoic and Paleozoic tectono-thermal events of the EKOB. These geochronologic data can be classified into 4 groups: Group 1 ages ranging from 2243 Ma to 3701 Ma are represented by inherited zircons from protolith and confirm the existence of Eoarchean to Paleoproterozoic continental nucleus in the source region of the Jinshuikou Group. Group 2 ranging from 928 Ma to 1849 Ma yields lower intercept ages of 0.9–1.0 Ga which represent the Neoproterozoic tectono-thermal event. This event, similar to that of the northern margin of Qaidam, might be a response to the assembly of Rodinia. Group 3 ranges from Neoproterozoic to early Paleozoic with lower intercept ages which are identical to the weighted mean ages of Group 4. These two age groups confirm the tectono-thermal event related to Paleozoic oceanic subduction. Moreover, based on the youngest age of 2.2 Ga in Group 1 and the upper intercept age of 1.8 Ga in Group 2, the depositional timing of the Jinshuikou and Binggou groups can be defined as Paleoproterozoic and Mesoproterozoic, respectively.     

Neoproterozoic glacial deposits from the Araçuaí orogen,Brazil: Age,provenance and correlations with the São Francisco craton and West Congo belt

Glacigenic diamictite successions of the Macaúbas Group are widespread in the western domain of the Araçuaí orogen, east of the São Francisco craton (Brazil). Diamictites also occur on this craton and in the African counterpart of the Araçuaí orogen, the West Congo belt. Detrital zircon grains from the matrix of diamictites and sandstones from the Macaúbas Group were dated by the U–Pb SHRIMP technique. The geochronological study sets the maximum depositional age of the glacial diamictites at 900 Ma, and indicates multiple sources for the Macaúbas basin with ages ranging from 900 to 2800 Ma. Sm–Nd T_DM model ages, determined on whole rock samples, range from 1.8 Ga to 2.5 Ga and get older up-section. Comparison of our data with those from the cratonic area suggest that these glacial deposits can be correlated to the Jequitaí and Carrancas diamictites in the São Francisco craton, and to the Lower Mixtite Formation of the West Congolian Group, exposed in Africa. The 900–1000 Ma source is most probably represented by the Zadinian–Mayumbian volcanic rocks and related granites from the West Congo belt. However, one of the most voluminous sources, with ages in the 1.1–1.3 Ga interval, has not been detected in the São Francisco-Congo craton. Possible sources for these grains could occur elsewhere in Africa, or possibly from within the Brasília Belt in western central Brazil.     

Zircon U–Pb,molybdenite Re–Os and muscovite Ar–Ar isotopic dating of the Xitian W–Sn polymetallic deposit,eastern Hunan Province,South China and its geological significance

The Xitian tungsten–tin (W–Sn) polymetallic deposit, located in eastern Hunan Province, South China, is a recently explored region containing one of the largest W–Sn deposits in the Nanling W–Sn metallogenic province. The mineral zones in this deposit comprise skarn, greisen, structurally altered rock and quartz-vein types. The deposit is mainly hosted by Devonian dolomitic limestone at the contact with the Xitian granite complex. The Xitian granite complex consists of Indosinian (Late Triassic, 230–215 Ma) and Yanshanian (Late Jurassic–Early Cretaceous, 165–141 Ma) granites. Zircons from two samples of the Xitian granite dated using laser ablation-inductively coupled mass spectrometer (LA-ICPMS) U–Pb analysis yielded two ages of 225.6 ± 1.3 Ma and 151.8 ± 1.4 Ma, representing the emplacement ages of two episodic intrusions of the Xitian granite complex. Molybdenites separated from ore-bearing quartz-veins yielded a Re–Os isochron age of 149.7 ± 0.9 Ma, in excellent agreement with a weighted mean age of 150.3 ± 0.5 Ma. Two samples of muscovites from ore-bearing greisens yielded ⁴⁰Ar/³⁹Ar plateau ages of 149.5 ± 1.5 Ma and 149.4 ± 1.5 Ma, respectively. These isotopic ages obtained from hydrothermal minerals are slightly younger than the zircon U–Pb age of 151.8 ± 1.4 Ma of the Yanshanian granite in the Xitian area, indicating that the W–Sn mineralization is genetically related to the Late Jurassic magmatism. The Xitian deposit is a good example of the Early Yanshanian regional W–Sn ore-forming event (160–150 Ma) in the Nanling region. The relatively high Re contents (8.7 to 44.0 ppm, average of 30.5 ppm) in molybdenites suggest a mixture of mantle and crustal sources in the genesis of the ore-forming fluids and melts. Based upon previous geochemical studies of Early Yanshanian granite and regional geology, we argue that the Xitian W–Sn polymetallic deposit can be attributed to back-arc lithosphere extension in the region, which was probably triggered by the break-off of the flat-slab of the Palae-Pacific plate beneath the lithosphere.     

SHRIMP U–Pb (zircon), Ar–Ar (muscovite) and Re–Os (molybdenite) isotopic dating of the Taoxikeng tungsten deposit,South China Block

The Taoxikeng tungsten deposit is located in the Jiangxi Province in the southern part of China, and is one of the largest wolframite quartz-vein type tungsten deposits in the country. The deposit is situated in Sinian (Neoproterozoic) to Permian strata at the contact with the buried Taoxikeng Granite. Sensitive High Mass Resolution Ion Microprobe (SHRIMP) zircon U–Pb analysis of the granite has yielded dates of 158.7 ± 3.9 and 157.6 ± 3.5 Ma, which are interpreted as the emplacement age of the granite. Molybdenite separated from ore-bearing quartz-veins yields a Re–Os isochron age of 154.4 ± 3.8 Ma, and muscovite separated from greisen between the granite and country rocks yields ⁴⁰Ar/³⁹Ar plateau ages of 153.4 ± 1.3 and 152.7 ± 1.5 Ma. These dates obtained from three independent geochronological techniques constrain the ore-forming age of the Taoxikeng deposit and link the ore genesis to that of the underlying granite. The Taoxikeng deposit is an example of a Jurassic regional-scale tungsten–tin ore-forming event between 160 and 150 Ma in the Nanling region of the South China Block. The deposit's strikingly low rhenium contents (4.9 to 13.0 × 10^? 3 μg/g) in molybdenite suggests that the ore was derived from a crustal source. This conclusion is consistent with previously published constraints from S, D and O stable isotopes, Sr–Nd systematics, and petrogenetic interpretations of spatially related granites.     

U–Pb zircon,Re–Os molybdenite geochronology and Rb–Sr geochemistry from the Xiaobaishitou W (–Mo) deposit: Implications for Triassic tectonic setting in eastern Tianshan,NW China

The Xiaobaishitou W (–Mo) deposit is located in the eastern segment of the Central Tianshan, northwestern China. The deposit represents a skarn system distributed in the contact zones of biotite granite and crystalline limestone of the Mesoproterozoic Kawabulag Group. The Xiaobaishitou deposit is characterized by a typical calc-silicate mineralogy dominated by garnet, diopside and wollastonite, with minor epidote, tremolite, actinolite, chlorite, quartz, fluorite and calcite. The prograde and retrograde skarns are characterized by garnet–clinopyroxene–wollastonite and epidote–tremolite–actinolite–chlorite, respectively, intruded and replaced by mineral assemblages of scheelite–cassiterite–magnetite, quartz–sulfides and calcite–quartz–fluorite in younger order.Six molybdenite samples from the deposit yielded Re − Os isotope model ages ranging from 239.7 ± 3.6 Ma to 251.4 ± 3.6 Ma. The zircon crystals from biotite granite and Mo-mineralized granite yield weighted ²⁰⁶Pb/²³⁸U age of 242 ± 1.7 and 240.5 ± 2.1 Ma, respectively. Both the zircon U − Pb and the molybdenite Re − Os ages obtained in this study fall in a narrow span of 242–240 Ma, which suggest that the Xiaobaishitou W (–Mo) system was formed in the Triassic. The Re contents of the molybdenites range from 40.33 to 64.67 ppm, suggesting that the ore-forming materials were derived mainly from continental crust together with the involvement of minor mantle components. Combined with the ⁸⁷Sr/⁸⁶Sr ratios of tungsten-bearing quartz veins from other studies, which scatter between 0.707153 and 0.709877, demonstrating mixing between two end-member isotopic compositions of crust and mantle. It can be concluded that the Indosinian Xiaobaishitou deposit was formed in a tectonic transition from collisional crust shortening and thickening to post-collisional extension and thinning.     

Combined zircon and cassiterite U–Pb dating of the Piaotang granite-related tungsten–tin deposit,southern Jiangxi tungsten district,China

The large low-grade Piaotang W–Sn deposit in the southern Jiangxi tungsten district of the eastern Nanling Range, South China, is related to a hidden granite pluton of Jurassic age. The magmatic-hydrothermal system displays a zonation from an inner greisen zone to quartz veins and to peripheral veinlets/stringers (Five-floor zonation model). Most mineralization is in quartz veins with wolframite > cassiterite. The hidden granite pluton in underground exposures comprises three intrusive units, i.e. biotite granite, two-mica granite and muscovite granite. The latter unit is spatially associated with the W–Sn deposit.Combined LA-MC-ICP-MS U–Pb dating of igneous zircon and LA-ICP-MS U–Pb dating of hydrothermal cassiterite are used to constrain the timing of granitic magmatism and hydrothermal mineralization. Zircon from the three granite units has a weighted average ²⁰⁶Pb/²³⁸U age of 159.8 ± 0.3 Ma (2 σ, MSWD = 0.3). The cathodoluminescence (CL) textures indicate that some of the cassiterite crystals from the wolframite-cassiterite quartz vein system have growth zonations, i.e. zone I in the core and zone II in the rim. Dating on cassiterite (zone II) yields a weighted average ²⁰⁶Pb/²³⁸U age of 159.5 ± 1.5 Ma (2 σ, MSWD = 0.4), i.e. the magmatic and hydrothermal systems are synchronous. This confirms the classical model of granite-related tin–tungsten mineralization, and is against the view of a broader time gap of >6 Myr between granite magmatism and W–Sn mineralization which has been previously proposed for the southern Jiangxi tungsten district. The elevated trace element concentrations of Zr, U, Nb, Ta, W and Ti suggest that cassiterite (zone II) formed in a high-temperature quartz vein system related to the Piaotang granite pluton.     

In-situ LA-ICP-MS trace elemental analyses of magnetite and Re–Os dating of pyrite: The Tianhu hydrothermally remobilized sedimentary Fe deposit,NW China

The Tianhu Fe deposit (> 104 Mt at 42% TFe) in the Eastern Tianshan (NW China) is hosted in the schist, quartzite, marble, and amphibolite of the Neoproterozoic Tianhu Group. The deposit consists of disseminated, banded and massive ores. Metallic minerals are dominantly magnetite and pyrite, with minor titanite, pyrrhotite, chalcopyrite, and sphalerite. Gangue minerals include dolomite with minor forsterite, diopside, apatite, biotite, chlorite, tourmaline, tremolite, talc, calcite, and magnesite. Pyrite separates from ores have 10.7 to 54.7 ppb Re and 0.033 to 0.175 ppb common Os. Those from the massive ores have a model 1 isochron age of 535 ± 36 Ma (2σ), in agreement with the isochron age (528 ± 18 Ma) of pyrite from the banded ores by regression of seven Re–Os analyses. The Re–Os age of ~ 530 Ma reflects the timing of a hydrothermal event that remobilized the Tianhu deposit. Magnetite has Mg, Al, Ti, V, Mn, Zn, and Ga contents ranging from ~ 5 to 3500 ppm and Cr, Co, Ni, and Sn contents ranging from ~ 1 to 200 ppm. Most magnetite grains have Ca + Al + Mn and Ti + V contents similar to those of the banded iron formation (BIF). Some grains have elevated Ti and V contents, indicating that that magnetite was formed by sedimentary process and overprinted by hydrothermal activity. Pyrite has δ³⁴S_CDT values from − 9.23 to 10.96‰, indicating that the sulfur was reduced from the marine sulfates either by bacterial or thermochemical processes. Pyrite has relatively high Co (~ 346 to 3274 ppm) but low Ni (~ 5.6 to 35.4 ppm) with Co/Ni ratios ranging from ~ 10 to 270, indicating remobilization from a volcanic–hydrothermal fluid. Therefore, the Tianhu Fe deposit was originally a sedimentary type deposit but was overprinted by a hydrothermal event related to volcanic activity.     

Re–Os pyrite and U–Pb zircon geochronology from the Taldybulak Levoberezhny gold deposit: Insight for Cambrian metallogeny of the Kyrgyz northern Tien Shan

The Taldybulak Levoberezhny gold deposit, located in the eastern part of the Kyrgyz Northern Tien Shan, is hosted in highly deformed Precambrian schist and gneisses that have undergone intense quartz, carbonate, fuchsite and tourmaline alterations. Gold mineralization is ultimately subdivided into two stages based on the observation of alteration assemblages, orebody geometries, and the occurrences of Au-bearing minerals. Negative thermal ionization mass spectrometry Re–Os isotopic analyses of five Au-rich pyrite samples from the early stage yielded an isochron age of 511 ± 18 Ma. Zircon sensitive high-resolution ion microprobe U–Pb dating of a diorite dike sample postdating the late stage mineralization yielded a wide range of ages from 3055 to 291 Ma, while a weighted mean ²⁰⁶Pb/²³⁸U age of 414.6 ± 6.8 Ma is believed to represent the age of dike intrusion and the upper limit on the timing of the late stage quartz–tourmaline–gold formation. The pyrite ¹⁸⁷Os/¹⁸⁸Os_(initial) ratio of 0.132 ± 0.011, together with γ_Os values varying from 0 to + 14, indicate a major mantle component for the source of Os and by inference ore metals, which may be linked to the ophiolite suite of the Kopurelisai Complex in the Taldybulak Levoberezhny area. Considering the geodynamic setting of the Kyrgyz Northern Tien Shan during the early Paleozoic, we suggest that Cambrian mineralization of the Taldybulak Levoberezhny deposit can be attributed to a subduction-related setting, probably associated with the earliest accretion of the Northern Tien Shan.     

Zircon U–Pb and molybdenite Re–Os dating of the Chalukou porphyry Mo deposit in the northern Great Xing’an Range,China and its geological significance

The newly discovered Chalukou giant porphyry Mo deposit, located in the northern Great Xing’an Range, is the biggest Mo deposit in northeast China. The Chalukou Mo deposit occurs in an intermediate-acid complex and Jurassic volcano-sedimentary rocks, of which granite porphyry, quartz porphyry, and fine-grained granite are closely associated with Mo mineralization. However, the ages of the igneous rocks and Mo mineralization are poorly constrained. In this paper, we report precise in situ LA-ICP-MS zircon U–Pb dates for the monzogranite, granite porphyry, quartz porphyry, fine grained granite, rhyolite porphyry, diorite porphyry, and andesite porphyry in the Chalukou deposit, corresponding with ages of 162 ± 2 Ma, 149 ± 5 Ma, 148 ± 2 Ma, 148 ± 1 Ma, 137 ± 3 Ma, 133 ± 2 Ma, and 132 ± 2 Ma, respectively. Analyses of six molybdenite samples yielded a Re–Os isochron age of 148 ± 1 Ma. These data indicate that the sequence of the magmatic activity in the Chalukou deposit ranges from Jurassic volcano-sedimentary rocks and monzogranite, through late Jurassic granite porphyry, quartz porphyry, and fine-grained granite, to early Cretaceous rhyolite porphyry, diorite porphyry, and andesite porphyry. The Chalukou porphyry Mo deposit was formed in the late Jurassic, and occurred in a transitional tectonic setting from compression to extension caused by subduction of the Paleo-Pacific oceanic plate.     

3D geological modeling for prediction of subsurface Mo targets in the Luanchuan district,China

Three-dimensional (3D) district-scale geoscience information for the Luanchuan Mo district was integrated for understanding the development of its regional geology and ore-forming processes and for decision-making about potential targets for mineral exploration. The methodology and datasets used were: (1) construction of an initial geological model (25 km × 20 km × 2.5 km) using 1:10,000 scale geological map, nine geological cross-sections and gravity and magnetic data; (2) construction of three large-scale Mo deposits model (5 km × 4 km × 2.5 km) using 1:2000 scale geological and topographic maps, 288 boreholes (total core length of 158,700 m), and 32 1:2000 scale cross-sections; (3) 3D inversion of 1:25,000 scale gravity and magnetic data for identification metallogenic anomaly zones which are associated with Jurassic intrusions; (4) extraction of ore-controlling formation and sequence of the Luanchuan Group using the large-scale 3D models of Mo deposits and results of analysis of lithogeochemical samples from outcrops and borehole cores; (5) identification of ore-forming and ore-controlling faults using the large-scale 3D model of Mo deposits and mineralized Jurassic granite porphyry stocks; (6) boost weights-of-evidence and concentration–volume (C–V) fractal analyses to integrate metallogenic information and to identify and classify potential Mo targets. Four classes of exploration targets were identified using C–V modeling and 3D known orebodies model: the first and second class targets are mainly located in three large magma-skarn type deposit camps, occupying ~ 1.4 km³ with total estimated reserve of ~ 2.3 Mt; the third class targets, which are mainly located in Huangbeiling and Yuku deposit camps comprising concealed magma-skarn type deposits, occupy ~ 2.8 km³ and represent a new target exploration zone in the Luanchuan district; the fourth class targets, which are located in the Huoshenmiao, Majuan, and Daping zones, occupy ~ 15 km³ and represent potential mineral resources with likely similar orebody features as the Yuku deposit.     

Primary diagenetic copper carbonate at the Malbunka copper deposit,Amadeus Basin,Northern Territory,Australia

The Malbunka copper deposit, located about 220 km west of Alice Springs, in the Northern Territory of Australia, may be a rare example of primary formation of copper carbonate mineralization. This deposit consists of unusual azurite disks up to 25 cm diameter, and lesser amounts of secondary azurite crystals and malachite. Carbon isotope values of the copper carbonate minerals are consistent with formation from groundwater-dissolved inorganic carbon. Oxygen isotope thermometry formation temperature estimates are 5–16 °C above ambient temperatures, suggesting the copper carbonates formed at a depth between 0.3 and 1.6 km in the Amadeus Basin. Azurite fluid inclusion waters are rich in boron, chlorine, and other elements suggestive of dilute oil basin formation fluids. In addition, presence of euhedral tourmaline with strong chemical zonation suggest that this was a low temperature diagenetic setting. The strong correlation of structures associated with hydraulic fracturing and rich copper carbonate mineralization suggest a strongly compartmentalized overpressure environment. It is proposed that copper carbonates of the Malbunka deposit formed when deep, copper-rich formation fluids were released upward by overpressure-induced failure of basin sediments, permitting mixing with carbonate-rich fluids above. This work bears directly upon exploration for a new type of primary copper deposit, through understanding of the conditions of genesis.     

Tectonic evolution of the India–Asia suture zone since Middle Eocene time,Lopukangri area,south-central Tibet

Suture zones often archive complex geologic histories underscored by episodes of varying style of deformation associated with intercontinental collision. In the Lopukangri area of south-central Tibet (29°54′N, 84°24′E) field relationships between tectonic units juxtaposed by the India–Asia suture are well exposed, including Indian passive margin rocks (Tethyan Sedimentary Sequence), forearc deposits (Xigaze Group), magmatic arc rocks (Gangdese batholith and Linzizong Formation) and syncollision deposits (Eocene–Miocene conglomerates). To better understand the structural history of this area, we integrated geologic mapping with biotite ⁴⁰Ar/³⁹Ar thermochronology and zircon U–Pb geochronology. The first-order structure is a system of north-directed thrusts which are part of the Great Counter thrust (GCT) that places Indian passive margin rocks and forearc deposits on top of magmatic arc rocks and syn-tectonic conglomerates. We infer the south-directed Late Oligocene Gangdese Thrust (GT) exists at unexposed structural levels based on field mapping, cross sections, and regional correlations as it has been documented immediately to the east. A granite in the footwall has a U–Pb zircon age of 38.4 ± 0.4 Ma, interpreted to be the age of emplacement of the granite, and a younger ⁴⁰Ar/³⁹Ar biotite age of 19.7 ± 0.1 Ma. As the granite sample is situated immediately below a nonconformity with low grade greenschist facies rocks, we interpret the younger age to reflect Miocene resetting of the biotite Ar system. Syn-tectonic deposits in the Lopukangri area consist of three conglomerate units with a total thickness of ∼1.5 km. The lower two units consist of cobble gravel pebble conglomerates rich in volcanic and plutonic clasts, transitioning to conglomerates with only sedimentary clasts in the upper unit. We correlate the syncollision deposits to the Eocene–Oligocene Qiuwu Formation based on field relationships, stratigraphy and petrology. Petrology and clast composition suggest the lower two units of the Qiuwu Formation had a northern provenance (Lhasa block and magmatic arc) and the upper unit had a southern provenance (Tethyan Sedimentary Sequence). Our observations are consistent with paleocurrent data from other studies which suggest a predominant south-directed paleoflow for this formation. We propose a model in which: (1) granites intrude at 38.4 ± 0.4 Ma; (2) are exhumed by erosion; (3) and buried due to regional subsidence and initial deposition of a conglomerate unit; (4) exposed by the GT at ∼27–24 Ma to provide detritus; (5) buried a second time by hanging wall-derived sedimentary deposits and the GCT, then (6) exposed from a depth of ∼12–10 km by a blind thrust at ∼19 Ma. An alternate model describes: (1) intrusion of the granites at 38.4 ± 0.4 Ma, followed by (2) exhumation of the granites via normal faulting to provide detritus; (3) then burial by the GCT at ∼24 Ma, followed by (4) exhumation via regional erosional denudation at ∼19 Ma. Exposure of the GT west of Xigaze has not been confirmed. We suggest that shallower structural levels of the India-Asia suture zone are exposed to the west of the study area, compared to the east, where the GT has been previously documented. The GCT in the area is short-lived, as it is cut and offset by a Middle Miocene ∼N-striking W-dipping oblique normal fault system.