Granitic Dikes Research Articles

Arc-shaped faults of the Golden Valley gold field of the Midlands greenstone belt in Zimbabwe and their role in localization of the ore mineralization

A detailed analysis of the geological and structural position of gold and tungsten deposits in the Golden Valley ore field of the Midlands greenstone belt has demonstrated that most of the gold deposits are controlled by arc-shaped faults that taken together form a semicircular structure with dimensions of 9×11 km. In addition, these arc-shaped faults apparently control the distribution of dikes of porphyry granites, that are associated with gold ore veins. Quartz-scheelite and gold-quartz-scheelite veins together form a second, less distinct, semicircular structure comparable in size to the first one. The highlighted structures were formed around isometric Late Archean granodiorite massifs, Lion Hill and Whitewaters, respectively, and are partially overlapped in space. The magnetic fi ld, also, reveals one additional arc-shaped fault and a series of linear faults. This arc-shaped fault, in conjunction with its associated branching veins of the Golden Valley and Patchway deposits, represents the so-called “horsetail” structure that is characteristic for gold deposits. This fault that is the most favorable structure for localization of gold ore veins, as well as the proposed junctions of arc-shaped and linear faults of radial and northwestern orientations, are considered as the most promising areas where geological prospecting is recommended.

Strain and kinematics within the Salmon River suture zone and western Idaho shear zone, Idaho, USA: Exploring the contribution of ductile stretching to mass transfer and exhumation in fold-thrust and transpressional systems

Measuring penetrative strain is critical for understanding the 3D strain field of structural systems. Here, we investigate ductile strain and kinematics in two Cordilleran structural systems in north-central Idaho: the Salmon River suture zone (SRSZ), which is a west-vergent ductile fold-thrust system that accommodated shortening associated with terrane collision between ∼144 and 105 Ma, and the north-striking, subvertical western Idaho shear zone (WISZ), which accommodated dextral-transpressional shearing between ∼105 and 86 Ma. We collected finite strain data from stretched clasts in three SRSZ thrust sheets, which define 56–87% average thrust-parallel stretching and 35–48% average thrust-normal thinning. Thrust-parallel stretching contributed >27 km of cumulative displacement to the up-dip portion of the fold-thrust system, comparable to the 34 km of total thrust displacement estimated at down-dip levels. In the WISZ, we documented dextral kinematics in lineation-normal planes, and we measured boudinaged and folded granitic dikes to estimate late-stage (∼91-86 Ma) strain, which yielded 65% minimum lineation-parallel stretching and 50% minimum east-west shortening. Subvertical stretching in the WISZ accommodated >9–10 km of exhumation relative to the Idaho batholith to the east. The SRSZ and WISZ both demonstrate the 1st-order importance of ductile stretching for accommodating the large-scale transfer of mass and exhumation in fold-thrust and transpressional systems.

Multi-stage leucogranite emplacement in the Yalashangbo dome in northern Himalaya: Trigger and consequence of faulting along the South Tibet Detachment System

Leucogranitic dikes emplaced at the lower-middle crust are particularly widespread in the Himalayas. How the magmatic activities evolved in relation to faulting along the Southern Tibetan Detachment system (STDS) remains debated. In this study, we investigate the multi-stage leucogranitic emplacement in relation to the structural evolution of the detachment fault in the Yalashangbo dome through detailed macro- and microscopic structural observations, LA-ICP-MS monazite U-Th-Pb dating, and whole-rock geochemical analysis of the leucogranitic dikes. We identified late syn- and post-kinematic granitic dikes from the dome. Timing of dominant STDS faulting is constrained from 27 to 17 Ma. Based on synthesis of geochronological and geochemical results of the present and previous studies, we suggest that two dominant stages of granitic emplacement occurred from Eocene to Miocene along the High Himalayas. An early stage of leucogranitic activity was probably ascribed to partial melting of mafic juvenile lower crust due to heating related to asthenosphere upwelling as the result of slab tearing or break-off during the Indian subduction. Emplacement of the leucogranitic melts subsequently softened the middle and lower crust and triggered the initiation of detachment faulting along the STDS as early as ca. 35 Ma. The large-scale detachment faulting likely led to intensive localized decompression melting of the lower crust. Contemporaneous detachment faulting in the lithospheric mantle allowed heat transfer from the asthenosphere to the lower crust, enhancing lower crustal melting and leading to generally higher crystallization temperatures in the late syn-kinematic granites than the post-kinematic ones.

Geochemical and petrological diversity of a transcrustal magmatic system driven by mushy magma mixing: Insights from the Triassic dike swarms in East Kunlun orogen, northern Tibetan Plateau

Geochemical and petrological diversity within transcrustal magmatic systems usually reflects the magma properties and magmatic processes and thus is critical to understanding the origin of magmatic complexes and the evolution of continental crust. Herein, we present an integrated study on the petrology, mineralogy, geochronology, geochemistry, and Sr-Nd-Hf isotopes of Triassic mafic-felsic dikes in the East Kunlun orogenic belt, northern Tibetan Plateau, to elucidate the nature and evolution of the transcrustal magmatic system. The studied dikes intruding into the granodiorite pluton (ca. 235−233 Ma) comprise coeval ca. 220−218 Ma gabbroic diorite porphyry, diorite porphyry, granodiorite porphyry, and alkali-feldspar granite, resembling composite dike swarms. The macrocrysts in these dikes show various zoning patterns, indicating episodic magma recharge and crystal resorption. The compositional gap between the intermediate-mafic dikes (SiO2 = 52.9−67.8 wt%) and the granitic dikes (SiO2 >75 wt%), as well as their homogeneous whole-rock Sr-Nd isotopes, with (87Sr/86Sr)i = 0.708387−0.710995 and εNd(t) = −5.83 to −4.34, but variable zircon Lu-Hf isotopes, i.e., εHf(t) = −7.67 to −0.36, demonstrates that magma mixing rather than cogenetic fractional crystallization accounts for their origin. In combination with thermobarometric insights, these results suggest that the mafic and felsic parental magmas originating from an enriched lithospheric mantle and ancient continental crust, respectively, were ultimately emplaced and stagnated at varying crustal depths (∼22−30 km and 8−17 km). Subsequently, the felsic magma mush was replenished and rejuvenated by the underplated mafic magma, leading to varying degrees of crystal-melt and/or melt-melt mixing. This mush-facilitated crust-mantle magma mixing is an important mechanism accounting for the compositional diversity of the transcrustal magmatic system.

The Val Biandino Intrusive Suite (central Southern Alps, N Italy): new geochronological and geochemical data on the Early Permian magmatic activity in the Southalpine Domain

The Early Permian in the present-day Europe area was a time when a major tectonic shift occurred, leading from the tectonic collapse of the Variscan orogeny to the crustal extension and thinning that characterized the Early Permian times. Crustal extension was associated with extensive magmatism at different crustal levels: from gabbro in the lower crust or at the mantle/crust transition to subaerial high-SiO2 volcanic activity. In the whole Southalpine Domain, the Early Permian intrusive bodies occur from the west (e.g. Ivrea-Verbano Complex and “Graniti dei Laghi”) to the east (Ifinger, Brixen and Cima d’Asta intrusive complexes). Among these, in the central Southern Alps (comprised between the Giudicarie Belt and the Lake Como), minor intrusive complexes also occur. The Val Biandino Intrusive Suite consists of two magmatic units: the Val Biandino Quartz-Diorite (VBQD) and the Valle di San Biagio Granite (VSBG). The first of them consists of gabbro-diorite to granodiorite bodies associated with leucocratic cordierite-bearing granitic dikes that intruded the pre-Permian basement. To the west, a W-dipping normal fault of Permian age represents the boundary between this unit and the Valle di San Biagio porphyric granite. All rock varieties of the Val Biandino Intrusive Suite display a high-K calc-alkaline affinity with metaluminous to peraluminous character. Field crosscutting relationships point to a late generation of the cordierite granites of the Val Biandino Quartz-Diorite unit with respect to the more mafic types. SHRIMP U–Pb zircon dating provided an age of 285.2 ± 1.9 Ma for a cordierite granite of the Val Biandino Quartz-Diorite unit and 283.2 ± 1.9 Ma for the porphyric Valle di San Biagio Granite. Geochemical data suggest that gabbro-diorite, quartz-diorite, granodiorite and leucogranite are not co-magmatic. The existing gaps in term of SiO2 wt% and the higher HREE contents in mafic and intermediate rocks with respect to granite coupled with similar LREE in all rocks support this hypothesis. The high Rb/Sr ratios (> 1) in leucogranite, together with the occurrence of white mica and cordierite point to a significant contribution of crustal partial melting in their genesis. The Val Biandino Intrusive Suite was likely formed through the interaction of magma genesis at the mantle/crust transition and partial melting of the heterogeneous pre-Permian basement of the Southalpine Domain. This scenario explains the strong heterogeneity displayed by the relatively small intrusive complex and the strong crustal signature exhibited by all the magmatic types of the Val Biandino Intrusive Suite.

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.

Eocene crustal thickening in the Tethyan Himalaya: Insights from Barrovian metamorphism and granite geochemistry from the Ramba area

Magmatism, structures, and metamorphism in the Ramba dome of the Tethyan Himalaya were investigated to shed light on orogenic processes during the early stages of the India-Asia collision. Deformed granite dikes in the dome envelope yield zircon U-Pb ages of ca. 45 Ma. These Eocene granites have adakitic, Na-rich compositions (K2O/Na2O = 0.20−0.61), weak to no Eu anomaly, enrichment in Sr, depletion in heavy rare earth elements and Y, and low MgO and Mg# contents. These characteristics contrast with the Miocene potassic granites in the core of the dome and suggest that the Eocene adakites were derived from the high-pressure melting of crustal amphibolites in a thick crust. The mica schists of the dome envelope have an early foliation (S1) that is overprinted by upright folds (F2). Phase-equilibria modeling of garnet and staurolite mica schists suggests a Barrovian-type, prograde P-T evolution in association with S1, with peak conditions of 6.7−7.2 kbar/590−605 °C and 7.3−7.8 kbar/650−670 °C, respectively, which are typical of crustal thickening metamorphism. Monazites from S1-dominated staurolite mica schists yield metamorphic ages of ca. 51−49 Ma, while those from the late foliation (S2) that transposed S1 give younger ages of ca. 10 Ma. The integration of geochemical, structural, metamorphic, and geochronological data suggests that peak Barrovian D1 metamorphism and adakitic magmatism occurred in the Eocene in response to crustal thickening. The results provide critical constraints for addressing the crustal shortening deficit of the region.

A Late Triassic gold metallogenic event within the extended tectonic evolution of the West Qinling Orogen, central China: Constraints from U-Pb and Ar-Ar geochronology in the Yangshan gold district

The West Qinling Orogen in central China resulted from Late Devonian to Triassic collisional orogenesis involving accreted terranes along the southwestern margin of the North China Block with subsequent ocean closure and collision of the South China Block with those terranes. The Yangshan gold district, with a pre-mining resource of more than 308 t gold, is situated along the Mianlue Suture Zone on the southern margin of the orogen. The gold orebodies are mainly controlled by the ENE-trending Anchanghe-Guanyinba Fault and its subparallel second-order faults. The relatively low pressure–temperature mineralization is dominated by disseminated pyrite, arsenopyrite, and stibnite hosted in phyllite and granite dikes, accompanied by intense muscovite-silica-carbonate alteration.Four major phases of deformation related to collisional tectonics are recorded in the Yangshan gold district. Early N-S-oriented compressional deformation (D1) is characterized by an alignment of muscovite, overgrowths on framboidal pyrite, and quartz veinlets. D2 is characterized by a series of continuous ENE-trending reverse faults and folds at multiple scales related to SSE-NNW-oriented compression. D3 is related to gold mineralization and is characterized by a series of ENE-trending, largely normal faults, formed during transtensional tectonics. D4 post-dates gold mineralization and is associated with the development of nearly N-S-trending, low-displacement normal faults.New high-precision SHRIMP zircon U-Pb dating of three types of granite dikes in the Yangshan gold district yields broadly coincident ages of 216 ± 3.0 Ma to 210 ± 9.7 Ma, which is a range identical to that of existing dates of 217–211 Ma for more regional granite magmatism in this district. New Ar-Ar dating of gold-related muscovite gives an age of 210.9 ± 1.6 Ma for the Yangshan gold deposit, indicating that hydrothermal activity overlapped or post-dated the final stages of granite intrusion. Pre-226 Ma peak metamorphism of the ore-hosting rocks occurred prior to extensional ductile shear deformation that is constrained by a published 40Ar/39Ar muscovite cooling age of 223 ± 2 Ma. In good agreement, U-Pb constrained ages of retrograde metamorphism and associated late magmatism of around 215 Ma are reported for rocks along the Mianlue Suture Zone.These geological and geochronological data suggest that relatively shallow-level gold mineralization was broadly coeval with Late Triassic transtensional, orogen-parallel deformation along the regional-scale fault system, late in the tectonic evolution of the West Qinling Orogen. This is consistent with its classification as epizonal orogenic gold mineralization.

THE Fe-Cu DISCONNECT: UNRAVELING A COMPOSITE IRON OXIDE COPPER-GOLD DEPOSIT IN THE OLYMPIC Fe-Cu-Au PROVINCE, GAWLER CRATON

Abstract The northern Olympic Cu-Au province, Gawler craton, Australia, includes a series of magnetite-dominated deposits/prospects associated with minor Cu-Au mineralization such as the 8.37 million tonne Cairn Hill deposit. Cairn Hill has long been considered a deep, magnetite end member of the iron oxide copper-gold (IOCG) family that is largely represented in the southern Olympic province by the 1590 Ma hematite-dominated Olympic Dam, Carrapeteena, and Prominent Hill deposits. In contrast to the southern district, the deposits in the northern Olympic Cu-Au province are hosted in rocks that experienced multiple phases of high-temperature metamorphism and deformation. New U-Pb zircon geochronology shows the magnetite-hornblende lodes at Cairn Hill were formed at ca. 1580 Ma at amphibolite facies conditions. The magnetite lodes are crosscut by ca. 1515 Ma granitic dikes. A second high-temperature event is recorded by U-Pb monazite geochronology at ca. 1490 Ma and involved deformation and metamorphism along the Cairn Hill shear zone at conditions of 4.6 to 5.3 kbar and 740° to 770°C. The 1490 Ma event reworked the iron lodes and 1515 Ma granitic dikes. However, Cu mineralization at Cairn Hill occurs in brittle fractures and quartz-biotite veins, overprinting the 1490 Ma deformation and metamorphism. Despite a spatial association between magnetite and Cu, the long thermal history that affected magnetite mineralization and the clear petrographic links between magnetite and high-temperature granulite facies minerals contrast with the late, low-temperature hydrothermal Cu mineralization and indicate the two are not paragenetically related. Therefore, the spatial but not temporal association between magnetite and Cu has effectively overlain two distinct episodes of mineralization to create the Fe-Cu deposit observed today. Although this fits within the broad IOCG deposit family, exploration strategies for Cairn Hill-style composite deposits should be distinct from IOCG deposits with cogenetic Fe and Cu.

The process of crustal thickening in the southern Lhasa terrane during India-Eurasia collision: Constraint from Eocene high Sr/Y rocks in the Quxu pluton

The crustal thickening process is the key to understanding global tectonic evolution and climatic patterns. The Sr/Y, (La/Yb)N ratios of granitoids can be used to quantitatively estimate crustal thickness and reconstruct the crustal thickening process. We present the geochemical characteristics, petrogenesis, and geodynamic implications of Eocene dioritic enclaves (monzodiorite), host granitoid rocks (monzonite), and granite dikes of southern Tibet to reveal the crustal thickening process underway during the collision of India and Asia. The Quxu dioritic enclaves were produced by magma mixing and represent mafic end member. The adakitic host rocks were generated by partial melting of lower crust with normal thickness. The high Sr/Y, (La/Yb)N ratios of the Quxu host rocks were inherited from their magma source region. The ∼40% fractional crystallization of amphibole from magma resembling Quxu host rocks formed the Quxu granite dikes. The continuous crustal thickening history determined by the locally weighted regression analysis shows that the crustal thickness of the Lhasa terrane during 50−45 Ma was no more than 36−46 km, and the crust thickened quickly during the syn-collisional period.

U–Pb and 40Ar/39Ar geochronology and tectonic setting of the peralkaline magmatism in the Borborema Province (NE Brazil)

Aegirine-augite granite and syenite plutons and dikes form a distinct magmatic pulse aligned in the NE-SW direction in the central and northern Borborema Province. We use SHRIMP zircon U–Pb and laser step-heating 40Ar/39Ar determinations to constrain the crystallization and cooling ages of syenites and alkali-feldspar granites and gabbros deformed by shear zones. Concordant zircon ages of the Triunfo and Cacimbas syenites vary between 596 ± 4 and 594 ± 4 Ma while sodic amphiboles from a granitic dike of Manaíra swarm yield 40Ar/39Ar plateau ages of 606 ± 5, 605 ± 6 and 599 ± 4 Ma. Muscovite from host mylonitic gneisses, in turn, yields plateau ages of 600 ± 3 Ma and 586 ± 2 Ma. Close to the Patos shear zone which limits the Central and Northern Borborema domains, foliated felsic dike of the Serra do Algodão suite yields a concordia age of 592 ± 2 Ma whereas the Catingueira granitic pluton records numerous inherited zircons. The Taperoá gabbro stock, situated next to the connection between E− and NE-trending shear zones, yields concordant ages of 592 ± 2 Ma. These results constrain the alkaline magmatism of the Central and Northern domains between 600 and 590 Ma, i.e., shortly after the continental collisions that amalgamated the province in the Ediacaran. Cooling was faster in the Triunfo-Manaíra suite and apparently slower close to the Patos shear zone. Host rock structures indicate that the Triunfo-Manaíra suite emplaced in the brittle upper crust, whereas the alkaline rocks of the Serra do Algodão suite emplaced in HT/LP ductile transtensional setting. A possible tectonic scenario includes slab break-off in a continental collision setting, partial melting of the sub-continental mantle and lower crust and magma transfer to the middle-upper crust. The distribution of these rocks next to the margins of volcanosedimentary belts suggests that their ascent and emplacement explored deep fault segments reactivated by crustal extension.

Dating Strike‐Slip Ductile Shear Through Combined Zircon‐, Titanite‐ and Apatite U–Pb Geochronology Along the Southern Tan‐Lu Fault Zone, East China

AbstractDating the timing of ductile shear deformation is critical to the understanding of complex, multi‐episode kinematics that commonly occur within the study of continental tectonics. The Tan‐Lu fault zone (TLFZ) in East China is a lithospheric discontinuity that records multistage sinistral strike‐slip shearing during Mesozoic time. Herein, based on field mapping, pressure‐temperature estimates via microstructures, quartz lattice preferred orientations, and geothermobarometer analysis, and U–Pb geochronology, we present a detailed examination of a portion of the southern TLFZ known as the Fucha Shan ductile shear zone. Two phases of sinistral ductile shear deformation in the shear zone are identified. The main phase occurred under amphibolite‐facies metamorphic conditions (500°C–650°C, 2.8–5.2 Kbar). U–Pb dating of synkinematic titanite indicate deformation occurred ca. 142–140 Ma. This age information is consistent with U–Pb dating of zircon from crosscutting granitic dikes that provide an upper limit of the shearing of ca. 134 Ma. A later, but less well‐developed phase of sinistral ductile shearing variably overprints older structures within the Fucha Shan shear zone at greenschist‐facies metamorphic conditions. U–Pb dating of apatite grains in rocks that record this later event are interpreted to indicate that shearing occurred ca. 118–108 Ma. These results provide new insight into Early Cretaceous shear deformation history within the southern TLFZ in the context of the late Mesozoic intracontinental deformation in East Asia.

Large-scale Permo-Triassic back-arc extensions of the Mongol- Okhotsk Ocean

The Late Paleozoic−Mesozoic Mongol-Okhotsk orogenic belt marks the final aggregation of East Asia. The geodynamics of the Mongol-Okhotsk oceanic plate subduction are still poorly understood due to its curved orogenic architecture, complex kinematics, and the protracted active continent margin that developed during oceanic subduction. Here, we report the discovery of an ophiolite within the southern paleo-active margin of the Mongol-Okhotsk orogenic belt. The ophiolitic slices are composed of serpentinites, metagabbros, and metabasalts, and interleaved with deformed volcaniclastic rocks. Using zircon U-Pb dating, we determined an age of 253 ± 2 Ma for the metagabbro, which suggests that the ophiolite formed during the Late Permian. Geochemical data and geologic relationships indicate that this ophiolite formed in a back-arc setting. The contemporaneous granitic dikes (ca. 255 Ma) intruding the basalts of the ophiolite were likely formed by crustal anatexis during the back-arc extension. Detrital zircon in sandstone associated with the ophiolite shows a prominent peak age of ca. 273 Ma that probably represents the sediments of the back-arc basin. Combining our discovery with the available data from the literature, we suggest that a >5000-km-long back-arc extension belt existed in the southwestern segment of the Mongol-Okhotsk belt, which indicates a probable Western Pacific-type active margin rather than the previously proposed Andean-type margin that formed during the Permo-Triassic period.

Characterization Of Dikes At Simpang Pulai Quarry, Perak

Due to dissolution, weathering and erosion, limestone and marble form karstic landscape with precipitous hills, rugged valleys, caves and sinkholes. In the event of an intrusion, the magma, which resides below the limestone bedrock will ascend toward the earth’s surface and fill up the fractures within the pre-existing rocks, forming dikes and sills. Dikes and veins can also be formed when minerals precipitate from hydrothermal fluids within a fracture. The objective of this study was to determine the texture and mineralogy of the dikes cutting the marble in the study area. The findings suggest that the mineral composition and physical structure of the dikes differ from the marble host rock based on its mineral, chemical and physical properties. Three samples were collected and analyzed using Scanning Electron Microscopy (SEM), X-ray diffraction analysis (XRD) and petrographic microscope. The results show that there are at least two types of dike, which are quartz and a coarse-grained granite dike at the study area. The presence of these dikes may affect the chemical and mechanical properties of aggregates produced from the quarry, and in turn affect the excavated rocks of its usage.

Petrogenesis of the Newly Discovered Early Cretaceous Peralkaline Granitic Dikes in Baerzhe Area of Jarud Banner, Inner Mongolia: Implications for Deciphering Magma Evolution

The super-large Baerzhe Be–Nb–Zr–REE deposit in NE China is hosted in the Early Cretaceous peralkaline granites. In this work, the newly discovered granitic dikes developed around the Baerzhe deposit were studied for the first time, focusing on their genesis and genetic relationships with the Baerzhe peralkaline granites. Zircon U-Pb dating of these granitic rocks (including the granite porphyry, rhyolite and miarolitic granite) yielded Early Cretaceous ages of 125–121 Ma. Their mineral assemblages and geochemical features suggest that they share similar features with the peralkaline A-type granites. Their geochemical data and zircon Hf isotopic compositions (εHf(t) = +3.4 to +10.5) indicate that the peralkaline granitic rocks were formed by the partial melting of dehydrated charnockite with extensive plagioclase crystal fractionation, which resulted in a peralkaline affinity. There are two types of distinct zircons in the studied samples: the type I zircon with a bright rim and dark core, which may represent a cumulate mineral phase captured together with aggregates during eruption, and the type II zircon with a higher evolution degree crystallized in the residual melts. Combined with the simulation results using whole-rock trace elements, we proposed that the peralkaline granitic dikes represent more evolved interstitial melts than the Baerzhe granitic magma. In the Early Cretaceous extensional tectonic settings, mantle-derived magma upwelled, which induced the melting of the lower crust and prolonged the evolutionary process of the magma crystal mush.

Deformational History of the Kanguer Subduction Complex in the Eastern Tianshan (NW China): Implications for Paleozoic‐Triassic Multiple Accretionary Tectonics of the Southern Altaids

AbstractThe Kanguer Subduction Complex in the Eastern Tianshan is critical to understanding the tectonic evolution of the southern Altaids as it marks the terminal suture along which the Paleo‐Asian Ocean was consumed. However, the nature and timing of this final collision, as well as the mechanism of shearing and related magmatism, remain enigmatic. The Kanguer Subduction Complex demonstrates obvious sinistral transtensional and dextral compressional deformation in different tectonic events along the Qiugemingtash Shear Zone in Huangshan area. Three sets of asymmetric plunging folds (e.g., basin‐like, S‐shaped and Z(W)‐shaped) were recognized in the sedimentary rocks. Locally, the folds are offset by dextral strike‐slip faults, indicating that they were formed by dextral shearing. The Huangshandong mafic‐ultramafic complex experienced brittle dextral shearing partitioned around the margins of the intrusion. Detrital zircon U‐Pb dates for deformed sedimentary rocks have maximum deposit ages (MDA) of 251 and 290 Ma, respectively, and syn‐compressional shearing conjugate granitic dikes that intruded into the deformed sedimentary rocks yield crystallization ages of 249 and 245 Ma, respectively. These ages reveal that the extensional and/or transtensional sedimentary basins formed between ca. 290–249 Ma, and dextral compressional shearing started ca. 249 Ma. Combining deformed units with transtensional basins and mantle‐derived magmatism, we suggest that ocean‐ridge subduction induced a sinistral transtensional regime in a forearc/intraarc setting related to the Tuva‐Mongol Orocline in the Permian. The oblique convergence between the Tarim Craton and southern Altaids triggered the Qiugemingtash dextral compressional shearing in the Early Triassic (ca. 249 Ma).

Granite Dike Swarm and U-Pb Ages in the Ueumdo, Hwaseong City, Korea

Granite Dike Swarm and U-Pb Ages in the Ueumdo, Hwaseong City, Korea

Multiple skarn generations related to composite leucogranites in the Cuonadong Sn-W-Be deposit, Himalaya

The newly discovered Cuonadong Sn-W-Be skarn deposit is related to fractionated leucogranitic intrusions hosted in the Cenozoic Himalayan gneiss dome, Tibet, however, temporal and genetic relationships between composite magmatism, skarn and mineralization remain unclear. Based on age and compositional features, three types of titanite were identified: Ttn1 and Ttn2 in the diopside-dominated skarn and adjacent greisenized granitic dike, and Ttn3 (subdivided into Ttn3a and 3b) in the Sn-mineralized garnet skarn. Ttn1 has a higher Ti content and yielded a U-Pb age of ∼35 Ma, consistent with the U-Pb ages of monazite from the pegmatitic granite (35.0 ± 0.6 Ma). Younger, recrystallized Ttn2 (∼28–27 Ma) is characterized by higher Al, F, Ta, Nb, Sn and Y contents and was likely formed by interaction between early Ttn1 and late fluids as indicated by the monazite U-Pb age of two-mica granite (28.8 ± 0.3 Ma). These two types of hydrothermal titanite are confined to the Oligocene unmineralized skarn and adjacent greisenized granitic dike.Titanite from the garnet-bearing Sn-mineralized skarn (Ttn3) provides the age of mineralization (16.8 ± 1.6 Ma), slightly younger than the emplacement age of the Miocene granite (monazite U-Pb age: 19.9 ± 0.3 Ma and columbite: 19.0 ± 0.4 Ma). The Sn-rich Ttn3b coexisting with garnet and interstitial cassiterite shows a deficit of Y and HREE and a high (Dy)N/(Yb)N ratio, implying that hydrothermal Sn metasomatism of Ttn3 occurred after garnet crystallization. Overall, our results shows that the Cuonadong multigenerational skarns were generated during three episodic magmatic-hydrothermal events, and mineralization occurred in the Miocene.

Deciphering deep-seated, highly fractionated, and reduced granitic magma systems associated with world-class scheelite skarn ores: A case study of the Zhuxi deposit, South China

The Zhuxi deposit, with 3.44 million tons (Mt) WO3 at 0.54%, is a world-class reduced scheelite skarn deposit and is spatially associated with highly fractionated and highly mineralized dikes, i.e., scheelite-bearing anorthite rock and albitite dikes. These scheelite-bearing dikes share similar rare earth element (REE) and Sr–Nd isotope compositions but display major element compositions distinct from those of the causative biotite monzogranite pluton associated with the Zhuxi deposit. The average compositions of apatite grains from anorthite rock, albitite, and the granitic pluton display roughly subparallel chondrite-normalized REE patterns. Additionally, subparallel chondrite-normalized REE patterns are displayed between the edges of scheelite grains from altered fine-grained granite and the cores of scheelite grains from albitite as well as between the edges of scheelite grains from albitite and scheelite grains from anorthite rock. Moreover, the in situ titanite (150.04 ± 0.39 Ma) and apatite (150.8 ± 1.7 Ma) U–Pb ages of the anorthite rock and the apatite U–Pb age (152.2 ± 2.6 Ma) of the albitite are consistent with the rock- and ore-forming ages (∼150 Ma) of the Zhuxi deposit. Furthermore, the water- and alkali-rich intergranular melt, which was extracted from the magma system, predated its solidification entirely and formed widespread intergranular albite rims surrounding plagioclase grains in the biotite monzogranite pluton where myrmekite is widespread.The scheelite-bearing anorthite rock and albitite dikes represent the products of highly fractionated melts that were saturated with volatiles and extracted from deep granitic magma reservoirs, which later crystallized to form the granitic pluton. Because W is highly incompatible and enriched in residual granitic magmas, large-tonnage W mineralization occurred above deep-seated causative granitic intrusions during the extraction of residual granitic melts if the parental magma exhibited metallogenic potential. Extensive W mineralization is directly associated with highly fractionated dikes rather than with granitic plutons, and these dikes could indicate pathways for W-bearing fluids.The exploration potential for reduced scheelite skarn deposits in deeply emplaced intrusions should not be confined to areas where granites are exposed at the surface but should include areas where granitic intrusions are possibly present at depth, particularly in regions with widespread, highly fractionated, highly mineralized discrete felsic dikes. If the causative granitic intrusions are exposed at the surface, most W orebodies and their spatially associated dikes could have been completely eroded. This is the reason for the disappearance of economic W orebodies adjacent to highly fractionated granitic plutons that share similar geochemical characteristics with granitic dikes surrounded by economic W orebodies. Thus, caution should be applied when assessing the W metallogenic potential of highly fractionated granitic rocks primarily according to their geochemical characteristics.

Distribution of Radionuclides and Radiological Health Assessment in Seih-Sidri Area, Southwestern Sinai.

The current contribution goal is to measure the distribution of the radionuclide within the exposed rock units of southwestern Sinai, Seih-Sidri area, and assess the radiological risk. Gneisses, older granites, younger gabbro, younger granites, and post granitic dikes (pegmatites) are the main rock units copout in the target area. Radioactivity, as well as radiological implications, were investigated for forty-three samples from gneisses (seven hornblende biotite gneiss and seven biotite gneiss), older granites (fourteen samples), and younger granites (fifteen samples of syenogranites) using NaI (Tl) scintillation detector. External and internal hazard index (Hex, Hin), internal and external level indices (Iα, Iγ), absorbed dose rates in the air (D), the annual effective dose equivalent (AED), radium equivalent activity (Raeq), annual gonadal dose (AGDE), excess lifetime cancer risk (ELCR), and the value of Upper Continental Core 232Th/238U mass fractions were determined from the obtained values of 238U, 232Th and 40K for the examined rocks of Seih-Sidri area. The average 238U mg/kg in hornblende biotite gneiss and biotite gneiss, older granites, and syenogranites is 2.3, 2.1, 2.7, and 8.4 mg/kg, respectively, reflecting a relatively higher concentration of uranium content in syenogranites. The results suggest that using these materials may pose risks to one’s radiological health.