Granitic Bodies Research Articles

Yingde–Guangning Granitic Plutons Record Complex Tectonic Evolution During Paleozoic-Mesozoic: Implications for Gold Exploration in Western Guangdong, South China

Western Guangdong, a part of the South China Block, has a complex geological history characterized by significant magmatic, metamorphic, and tectonic activities. This dynamic geological past, particularly during the Mesozoic era, created favorable conditions for the formation of various mineral deposits, including Au, Ag, Cu, and Pb. This makes the region a key area for precious metal resources in China. Despite extensive metallogenic studies, detailed structural information for western Guangdong remains insufficient, highlighting the need for further investigation. Thus, effective delineation of deformation periods is crucial for revealing geodynamic history and understanding regional tectonic activities, which are extremely important for guiding mineral exploration. This work focuses on the outcrops of granitic plutons in the Yingde–Guangning area of western Guangdong to establish the structure–tectonic setting. The tectonic events likely shaped the widespread Paleozoic–Mesozoic granitic bodies, which record extensive information on regional tectonic evolution. To achieve the primary objective, systematic identification and kinematic analysis of the various stages of structural traces, such as foliations and joints, have been conducted. This research proposes, for the first time, that the western Guangdong area underwent four distinct tectonic stages: (1) Early Paleozoic NW-SE compression phase; (2) Triassic NE-SW compressional stress; (3) Jurassic NW-SE compressional force; and (4) Cretaceous NW-SE extension stage. In metallogenic terms, the NW-SE trending auriferous veins of the Yingde–Guangning region were mostly formed during the Triassic NE-SW compression stage, whereas the NE-SW trending vein-type gold mineralization developed during the tectonic regime transformation from Jurassic NW-SE compression to Cretaceous NW-SE extension. This research emphasizes that systematic tectonic geological studies of regional granites can effectively guide mineral prospecting.

Formation of giant copper deposits driven by rapid uplift and sudden depressurization

Abstract Porphyry Cu deposits (PCDs) in collisional orogens are new targets for modern mineral exploration. A series of post-collisional (Miocene; 22-12Ma) porphyry copper deposit (PCDs) with Cu reserve over 45 Mt have been discovered in the Gangdese magmatic belt, southern Tibet. These magmas derived from partial melting of sulfide-bearing Tibetan juvenile lower crust are fertile for porphyry Cu in many aspects, such as high oxidation state, and rich volatiles such as water, S, and Cl, but some of individual plutons ended up with economic concentrations. The fundamental question remains what accounts for the significant Cu endowments. We measured the igneous zircon water contents of ore-related and barren high Sr/Y magmas in the Gangdese belt, southern Tibet and found that magmas that produce giant PCDs have lower zircon water contents than barren and small-deposit related magmas. Combined with previous fluid inclusions, magmatic breccias, apatite geochemistry, and thermal histories, which demonstrated higher initial water content in causative porphyries such as giant deposits of Qulong and Jiama, we believe that the lower zircon water content may be attributed to these magmas experiencing of faster cooling and sudden depressurization of a large, primed, volatile-saturated or supersaturated mid-upper crustal magma chamber, which could lead to rapid and voluminous volatile exsolution and fluid discharge. These processes caused intense hydrothermal alteration and large ore deposition. In contrast, magmas that experienced slow cooling and deep emplacement would undergo steady state degassing and weak alteration. The variable intrusive and thermal histories across Gangdese reflects interplay between surface and lithospheric dynamics within the Himalaya—Tibet orogen. Our findings suggest the difference of zircon water content reflects the emplacement rate and depth of granitic body, and therefore may serve as an indicator for tectonics and potential for mineralization.

Formation and degradation of a porphyry occurrence: The oligocene Khatoon-Abad porphyry Mo-Cu system, NW Iran

This study investigates the temporal relationships between mineralization and magmatism in the Khatoon-Abad porphyry Mo-Cu prospect (Urumieh-Dokhtar Magmatic Arc, NW Iran). Integrated zircon U-Pb and molybdenite Re-Os dating document a prolonged stationary magmatism, spanning ∼ 45 Myr (from ∼ 66 to ∼ 21 Ma; Paleocene-Early Miocene). Three main Oligocene ore-bearing granitic intrusions and an early Miocene barren dyke swarm are documented, with the main mineralization formed at ∼ 27 Ma, as attested by the molybdenite Re-Os age of 26.75 ± 0.14 Ma and the zircon U-Pb age 26.93 ± 0.30 Ma from the host granodiorite porphyry. Despite having similar geochemical fingerprints, including an adakitic signature and having REE patterns similar to productive magmas, the subsequent Oligocene granite bodies (∼26.0–25.7 Ma) yielded lower Mo-Cu enrichments and the early Miocene rhyodacite dykes (∼21 Ma) are barren. This evidence demonstrates that the efficiency of mineralization has been reduced by changes in the physiochemical conditions of magmatic-hydrothermal systems over time. We suggest that a perturbed geothermal gradient during later Oligocene granite (at ∼ 26 Ma) caused slow cooling/degassing of the melts, and hence determined an inefficient mineralization environment. We also infer that during the latest granite porphyry pulse (∼25.7 Ma), the structurally-controlled emplacement at shallower levels resulted in rapid melt cooling along with more meteoric water mixing, eventually minor potassic but vast phyllic alterations, and hence, causing a dispersed mineralization rather than a focused fluid flow. Therefore, the later Oligocene and early Miocene magmatic pulses degraded the early mineralization. The results of this study emphasize that a consistent magma supply into the chamber followed by a rapid magma-fluid flux to the mineralization site are needed for efficient mineralization in collisional settings. Otherwise, multiple mineralization pathways and sites would result in low-grade ore bodies.

The subaqueous felsic volcanism from the Upper Member of the Cordón de Lila Complex, Antofagasta region, northern Chile

This contribution presents the study of an Ordovician subaqueous felsic succession, formed by the ~400 m-thick Upper Member of the Cordón de Lila Complex (CISL), northern Chile. From bottom to top, the succession starts with two dacitic sills that intruded into the sediments of the lowermost part of the Upper Member. Then, it is followed by a thick sedimentary deposit, two rhyolitic lavas, a volcanoclastic felsic breccia with pyroclastic clasts, and ends with a red rhyolitic lava. The first rhyolitic lava shows centimetric to metric folds with a north-northwestern vergence, evidence of flow in that direction. In the volcanoclastic breccia, an abundant pumice-and-fiamme-rich green matrix wraps around lithic clasts, giving the rock an eutaxitic texture at the outcrop scale. This matrix and texture evidence is characteristic of hot pyroclastic flows deposited under subaqueous conditions. The described section of the breccia is formed by four coarsening-up sequences, reflecting respectively four pulses of building up energy. The lack of internal erosional features points to a single and continuous explosive eruption. An accidental granite clast in the upper part of the breccia suggests a connection with a granitic body, possibly the Pingo-Pingo monzogranite. The geochemical character of the felsic succession is calc-alkaline. The tectonic setting diagram shows a within-plate setting for the succession. This suggests a shift from the arc position inferred for the Lower Member of the CISL to a forearc continental setting for the Upper Member of the CISL.

3-D spatial distribution of concealed ore-forming granitoid intrusion and structures determined by the CSAMT survey of Wuxu Sb-Zn-polymetallic ore district, South China

Wuxu ore district is an important lead-zinc-antimony polymetallic ore field within the Danchi metallogenic belt of South China. Although previous geochemical studies have indicated that the deposit type is medium to low-temperature magmatic-hydrothermal, the existing metallogenic models remain controversial due to the thick covering layer and lack of exposure of granitic bodies. To address this issue, this study utilised four CSAMT parallel profiles across the Wuxu anticline to perform two-dimensional inversion, yielding high-resolution subsurface resistivity models. By comparing the resistivity anomalies along the regional strike shown by the profiles and integrating geochemical and ore deposit structural analyses, a detailed geological interpretation was conducted. A significant high-resistivity body beneath the core region of the Wuxu anticline is interpreted to be the Yanshanian period granitic intrusion. There are westward- and eastward-dipping high-conductivity belts existing within the western and eastern wings and appear to sandwich the inferred high-resistivity code of the Wuxu anticline, respectively. They may represent the deep faults extending underground and are the result of decoupling of lithological interface within the anticline and thereby rock fracturing. The high-conductivity feature may be the result of filling with high-conductivity saline fluids, and possible hydrothermal alteration. The regional compression stress during the Caledonian period and the early Yanshanian period promoted the formation of the anticline and rock fracturing of both wings of the anticline. After that, the regional extension background of the late Yanshanian period made the fault zones reactivated, becoming the site and channels for magmatic intrusion, upward transporting of hydrothermal fluid and alteration, causing lead-zinc-antimony polymetallic ore formation. The exposed ore deposits above may also corroborate this view point. In summary, our resistivity model visually depicts the spatial distribution of the granitic intrusion controlling ore formation and major structures such as anticlines, fault zones, and hydrothermal alteration zones in the 3-D space, providing new geophysical constraints for solving the controversy over the metallogenic model for Wuxu ore district.

Low resistivity anomalies in the upper crust of the Midlands of Tasmania from combined magnetotelluric datasets

Heat flow data obtained in connection with geothermal resource exploration suggests anomalous upper crustal structure and processes in parts of central east Tasmania. The regional scale crustal geology of the Midlands of Tasmania is, however, mostly obscured at the surface by the Permo-Triassic sedimentary sequences of the Tasmania Basin together with extensive exposures of Jurassic dolerite. We investigate controls on undercover crustal processes in this region by combining long period and broadband magnetotelluric (MT) datasets in 3D inversions for the geoelectric structure; followed by an interpretation that is informed by aspects of the pre-existing 3D regional geological and geophysical model. The new 3D model allows improved resolution of low resistivity anomalies together with a qualitative appraisal of spatially variable model sensitivity. The most robust features ( < 1 Ω m ) in the 2–3 km depth interval occur where N–S and E–W faults intersect with a high point in the topography of the upper surface of a deep seated granite body. Enhancement of conductivity in this zone by clay, graphite or mineralisation, or a combination thereof, is likely. Other low resistivity features suggest that conductive pathways exist where major or multiple faults are present. These interpretations provide support for continued exploration in the Midlands of Tasmania for a variety of resources related to crustal fluids and fracturing.

Constraining provenance and age of the siliciclastic rocks from the south-western Bundelkhand Craton, Central India

The lithology of the Bundelkhand craton, central India, includes highly deformed tonalite, trondhjemite and granodiorite (TTG) gneisses (3.55–2.7 Ga), followed by volcano-sedimentary greenstone belts and a suite of undeformed granitoids ranging in age from 2.52 to 2.49 Ga. The granitoids, which are by far the most dominant lithology of the craton, have intruded into the TTG gneiss-greenstone assemblage. In addition to huge granitic bodies, rhyolitic rocks of 2.54 Ga have also been observed in the Bundelkhand craton. In this study, we report the first occurrence of a small isolated outcrop of siliciclastic sedimentary rocks within the Bundelkhand granitoid suites in and around the Panchwara village, in the southwestern part of the craton. These siliciclastic sedimentary rocks are intruded by the youngest granitic phase of the Bundelkhand granitoid suite, dated as 2.49 Ga old. Thus, their age is determined to be older than 2.49 Ga. Petrographic studies suggest that these rocks are arkose in nature and geochemical composition indicates that they were derived from the older gneiss-greenstone successions and the older granitic phase (2.52 Ga) of the Bundelkhand granitoid suite. The REE modelling suggests that the sediment contribution from different sources is: 50% greenstone belt (15% basalt + 35% sedimentary rocks), 35% gneisses and 15% older granitoids. Detrital zircons from these sedimentary rocks reveal two age populations: one group of zircons is clustering around 2.52 Ga and the other group is ranging from 3.0 to 3.3 Ga indicating at least two protoliths for these sediments. Our field, petrographical and geochemical data, coupled with previously studied zircon geochronological data, is best explained by a model involving deposition of sediments derived from TTG gneiss, greenstone belt and also from the older phase of the granitoid suite. It is interesting to note that the basin received sediments from the older granitic phase of 2.52 Ga age and was closed before the emplacement of the youngest granitic phase at 2.49 Ga. This study, thus, provides for the first time, conclusive evidence for the presence of a late Archean sedimentary basin within the Bundelkhand craton. It is proposed that the sediments were deposited penecontemporaneously with the pulses of the granitoid magmatism in the Bundelkhand Craton that took place ~2.5 Ga.

Geochemical Study of the Osumi Granodiorite, Southwestern Japan

The Osumi Granodiorite, located on the Osumi Peninsula in southwest Japan, is an example of outer zone granites that were formed during a limited period (13–15 Ma) in response to the subduction of the Philippine Sea Plate. This event, which is linked to the separation of southwest Japan from continental Asia, resulted in unique igneous activity. The Osumi Granodiorite is the largest Miocene granite body in the region. It intrudes into the Mesozoic to Paleogene accretionary complex of the Shimanto Belt and affects contact metamorphism. Despite considerable research on the Osumi Granodiorite, limited geochemical studies, especially on trace and rare earth element (REE) analyses, have been conducted. Furthermore, there are insufficient data on the Rb–Sr isotopic system, leaving the formation process unclear. This study presents whole-rock geochemical and Rb-Sr isotopic data to investigate the petrogenesis of the Osumi Granodiorite. The results suggest a common magma origin for this pluton, as indicated by linear trends on the Harker diagrams and similar REE patterns. The presence of a relatively large Eu anomaly implies formation under a reducing environment. The AKF diagram indicates predominant contamination by pelitic rocks of the Shimanto Belt during magma formation. The Rb–Sr whole-rock isochron diagram and SrI–1000/Sr diagram suggest that the Osumi Granodiorite body was formed by heterogeneous assimilation of magma into the Shimanto Belt. Furthermore, the whole-rock isochron age is 64.3 Ma, which differs by approximately 50 My from the previously reported biotite K–Ar age (14–22 Ma). This age is considered to be a pseudo-isochron age, rather than the consolidation age. During the middle Miocene, the compressive stress field in the outer zone south of the Butsuzo Tectonic Line made it difficult for magma to rise. As a result, it reacted with the sedimentary rocks of the Shimanto Belt to various degrees. The Osumi Granodiorite underwent magma differentiation upon intrusion into the Shimanto Belt. It subsequently ascended, cooled, and interacted with pelitic rocks under stable geological conditions.

Geology, geochronology and tectonic context of the Carreira Comprida Anorthosite in the evolution of the Goiás Massif, Porto Nacional Domain – Tocantins Province

The Carreira Comprida Anorthosite (CCA) is exposed in the Paleoproterozoic Porto Nacional High-Grade Metamorphic Terrene, in the north of the Goiás Massif, central Brazil, represented by an ancient pluton affected by late Neoproterozoic tectonics, with protoliths predominantly of anorthosite consisting of more than 85% labradorite (An60-65), with subordinate presence of clinopyroxene, quartz, hornblende and garnet. There is evidence of intrusive relationships in paragneisses country rocks of the Morro do Aquiles Formation, due to the effects of high-temperature contact metamorphism (∼750 °C) that reached the hornblende hornfels facies. Features of a magmatic nature are present as a cumulate texture formed by the accumulation of tabular plagioclase megacrystals by flotation associated with gravitational action due to the difference in magma density and magmatic flow, with clinopyroxene and interstitial (intercumulated) quartz, during the emplacement of the pluton and crystallization of magma. At the end of the Neoproterozoic, the body was affected by the tectonics of the transcontinental strike-slip system of the Transbrasiliano Lineament (Porto Nacional Transcurrent Shear Zone). U–Pb dating on igneous zircon crystals indicated an age of 2084 ± 4 Ma, which represents the age of emplacement of the Carreira Comprida Anorthosite in the Rhyacian, characterizing an event of gabbroic-anorthosite magmatism not known in the Goiano Massif. Lu–Hf isotopic data show variable εHf (2.08 Ga) values ranging from −1.3 to +4.5 and Hf-TDMC model ages with two crust formation episodes, one from the Siderian (2.46 - 2.38 Ga) and another in Neoarchean (2.74 - 2.59 Ga) which indicates that their parental magmas were derived from a depleted mantle source and range in composition from uncontaminated to variably contaminated by pre-existing older crust in the formation of the CCA. Considering that the ages of the Hf-TDMC model are similar to those of the orthogranulites from the Porto Nacional Complex, its indication as a possible source of the CCA is suggestive. Field relationships, primary structural features, petrographic and compositional data, geochronological and literature data suggest that the emplacement of the CCA is late-tectonic in relation to the evolution of the high-grade terrain of Porto Nacional, in the Rhyacian. After its crystallization, the CCA was affected by the tectonics of the dextral transcurrent system of the Transbrasiliano Lineament that implemented the Porto Nacional Shear Zone at the end of the Neoproterozoic, imposing strong deformation on the anorthosite and surrounding rocks, generating a variety of mylonites. These transformations generated a diversity of microstructures (stretch lineation, mylonitic foliation, tectonic banding, ribbon quartz, lentiform porphyroclasts, microshear, undulatory extinction, thinning of mechanical twinning, wedge twinning, deformation bands, mantle-core, subgrains, symplectites of garnet), which are suggestive of ductile tectono-metamorphic transformations that reached amphibolite facies conditions. Finally, the CCA is a rare example in Brazil of a massif-type anorthosite developed in the Paleoproterozoic (2.08 Ga). On the other hand, the Rhyacian granite bodies of the Ipueiras Suite (2.08 - 2.07 Ga) located very close to the anorthosite pluton are contemporary with the CCA, allowing them to be considered an association of the Anorthosite-Mangerite-Charnockite (AMC) type.

Reconstructing a Super-Eruption From the Upper Ordovician Period in the Eastern Pyrenees, Spain

Abstract The Pyrenean basement rocks, NE of the Iberian Peninsula, southwestern Europe, include evidence of several pre-Variscan magmatic episodes which indicate the complex geodynamic history of this segment of the northern Gondwana margin from late Neoproterozoic to Early-Palaeozoic times. One of the most significant magmatic episodes was late Mid-early Upper Ordovician (Darriwilian-Katian) age that produced several granitic bodies and volcanic rocks interbedded with Sandbian-Katian sediments. This magmatism is well represented in the Ribes de Freser area (Freser valley, Bruguera and Campelles localities, eastern Pyrenees), where these Ordovician magmatic rocks were affected by an irregularly distributed Variscan deformation and mainly by severe Alpine tectonics, which originated the superposition of several structural units. We present a palinspatic reconstruction of this Alpine deformation (80-20 Ma), that permitted us to infer the geometry, facies distribution, original position, thickness, and significance of these volcanic rocks. This reconstruction allows us to interpret the volcanic rocks cropping out at the Freser valley, Bruguera, and Campelles areas as intra-caldera deposits representing a minimum preserved volume of the order of 100 km3. This may confirm the existence of super-eruptions of Upper-Ordovician age in that sector of the eastern Pyrenees and emphasizes the extent of the Upper-Ordovician felsic volcanism in this sector of the northern Gondwana margin, probably developed in an extensional scenario linked to the development of the Rheic Ocean during Gondwana margin breakup.

Lithologic Relationship and Structural Features of Crystalline Rocks in Ekiti, Southwestern Nigeria: A Geological Report on the Basement Complex

This paper investigates and report field relationship and structural features of the basement rocks in Ekiti, southwestern Nigeria. Systematic geological mapping reveals that Ekiti is underlain by migmatite-gneiss, quartz schist, quartzite, granite, and charnockite. These lithologies were intruded by series of aplite, dolerite, and pegmatite dykes. Structural deformations attributable to polycyclic orogenic activities manifested in all the basement rocks. Migmatite and its gneissic subunits form the country rock and exhibits complex folds, abundant quartz veins and haphazardly emplaced dykes. Foliation and lineament are oriented N-S, strike values range between N5oE -N18oE with westerly dip of 72º to 84º. Quartzite and quartz schist exhibits distinctive joint and fracture system which runs parallel to one another while minor ones are oblique. The polymetamorphic terrain has older tectonic fabrics massively overprinted by younger ones. The gneiss units are porphyroblastic to granoblastic, xenoliths of varying sizes are embedded within the granite bodies indicating the magmatic liquid was forcefully injected into the country rock. The presence of parallel fractures in fine-grained granite indicate Ekiti area is a shear zone. The occurrence of dykes of heterogenous lithologies on single granite outcrop suggests pluton assemblage occur as discrete pulses during the intrusive phases. Contact relationship indicate age decreases from migmatite to granite-charnockite to microgranite while dykes are the youngest. Deformation, metamorphism, and intrusive phases are the dominant geodynamic features of Ekiti area while the regional and local changes in rocks resulted from environmental constraints of pressure, temperature, and fluid activity. The plutonic activities which accompanied orogenic events resulted in deformation which is genetically related to evolution and geodynamic setting of Ekiti area.

Radiogenic geothermal systems of Bangka Island, Indonesia: Implications of high heat production and tectonic framework

The presence of geothermal manifestation in Bangka Island (Southeast Sumatra, Indonesia) with the absence of Quaternary volcanic activity and also relatively low seismicity events has raised intriguing questions on the control of the geothermal system in this area. As the regional tectonic setting of Indonesia volcanic geothermal systems has been known, that of non-volcanic geothermal systems such as radiogenic system become an issue to be investigated. This study reports the geochemistry and petrography analysis of Triassic granite related to radiogenic production at the vicinity of hot springs in Bangka Island. Surface temperatures of the Bangka hot springs range from 37 to 70.7 °C and pH values vary between 5.6 and 7.5. These hot springs are discharging either in close to massive granite bodies or occur in between two major NE-SW striking faults zones, i.e., Pemali fault and Payung fault. Our results indicate the average radiogenic heat production of Late Triassic Klabat granite in the northern area ranges from 28.5 to 38.34 μWm−3 and the southern area ranges from 28.3 to 49.5 μWm−3. In comparison to similar granite belt located in Malaysia, heat production of granitoid in Bangka hot springs is four times higher, possibly due to their different granite origins.

Tectonic pozition and metamorphism of rocks in the Chara-Tokko iron ore region

The article provides the material on the geological structure, structures, tectonic position and metamorphism of rocks developed within the Chara-Tokko iron ore region, identified in the western part of the Aldan-Stanovoy shield. Most researchers agree that the Chara-Tokko iron ore region is confined to a trough that formed on the site of one of the long-lived deep fault zones of meridional strike. This zone received various names (Derbegelakhskaya, Charo-Imalykskaya, Tarynakhskaya, etc.). Currently, the fault zone and the trough trough are called Chara-Tokko after the name of the iron ore region. It is assumed that to the south, the iron ore deposits of the Chara group (Sulumatskoye, Nizhne-Sakukanskoye) are confined to the continuation of this trough trough. The nature and conditions of metamorphism can be judged by the mineral associations of some rocks of the sedimentary productive complex, such as metapelites or ferruginous quartzites. It is noted that metapelites, now represented by gneisses and mica schists with high-alumina minerals, are especially important for this. Based on their characteristic mineral associations, three temperature facies were identified in the Chara-Tokko iron ore region: staurolite, biotite-muscovite gneiss and orthoclase-biotite-sillimanite. The internal structure of the Chara-Tokko iron ore field were not sufficiently studied and is extremely controversial. The boundaries of metamorphic zones are mainly parallel to the general strike of the structures and only in rare cases intersect the stripes of productive sedimentary units. After the temperature maximum of progressive metamorphism and past granitization, a significant period of cooling began, which was heated and in some places impregnated with layer-by-layer injections of migmatites and bodies of granites of the Borsala sequence. Gradual cooling was accompanied by regressive metamorphism with the formation of low-temperature minerals at the expense of higher-temperature ones. It is believed that ferruginous quartzites of the western part of the Aldan-Stanovoi shield are part of sedimentary-volcanogenic rock complexes that fill suture troughs or troughs confined to long-lived deep fault zones. The processes of regressive metamorphism manifested themselves most intensively in tectonic zones. The nature of the processes depends on the composition of the host rocks. The regressive phenomena of continuous chloritization and epidotization are associated with the local movement of components, mainly calcium.

Late Ediacaran post–collisional granite in Babouri–Figuil (Northwest Cameroon): Implication for crustal–mantle contributions in an extensional setting

The Babouri–Figuil Magmatic Complex (BFMC, adjacent to the central-south Chad domain) is located on the southern flank of the Saharan Metacraton. It is amongst the least geologically studied regions in Cameroon; only a few key research papers on geochronology and isotopes have been completed. The emplacement of granitic bodies is poorly constrained between the early and late–Neoproterozoic with inherited zircons of older Paleoproterozoic–Neoproterozoic ages. In this study, undeformed biotite granite massifs (Lombel and Badesi) were studied, and their geochronologic, geochemical and mineral chemical data, including Nd–Sr–Hf isotopes, are presented. The massifs are enriched in pink K-feldspar (orthoclase and microcline; 60–65 wt%) and plagioclase (8–10 wt%) anastomosing to intergranular quartz (18–20 wt%) and biotite (3–5 wt%) crystals. The Lombel massif yielded a Concordia age of 566 ± 2.5 Ma (MSWD = 1.6, zircon U–Pb), slightly older than the Concordia age of 556 ± 2.7 Ma (MSWD = 2.1, zircon U–Pb) obtained for the Badesi massif. These are interpreted as emplacement ages, which post–date arc magmatism by ∼ 45 Ma. The geochemistry of the massifs showed sub- to mid–alkaline, high–K alkali–calcic, and weakly peraluminous compositional characteristics. The calculated biotite temperatures ranged from 613 to 647 °C, pressures from 100 to 300 MPa, and H2O from 3.0 to 3.5 wt%. Whole–rock composition geothermobarometry revealed low pressure of 100–500 MPa, depths of 3.5–18 km and low oxygen fugacity (ΔQFM = −0.6), indicating reducing crystallization conditions. The estimated radiogenic isotopic values are similar for both massifs, falling in the range from initial εHf(t) = +2.6 to +8.4 and initial εNd(t) = +1.3 to +2.1, with a corresponding average initial Sr of 0.70212–0.70458. These radiogenic isotope values suggest a mantle–derived origin for this granite or the melting of a juvenile mafic crustal protolith, as confirmed by the two–stage model age obtained (TDM2 = ∼ 1.2 Ga). Given that biotite is interstitial in alkali feldspar and plagioclase in both massifs, this suggests that biotite chemistry records conditions of magma evolution. Overall, these results confirm that the studied massifs are post–collisional products emplaced at shallow crustal levels under evolved magmatic conditions. They are coeval with a few post–magmatic intrusions in the central–south Chad and emplaced after the Sao–Francisco Congo Craton collided with the Saharan Metacraton. The ages obtained enabled a possible correlation with several Neoproterozoic post–collisional granites in Cameroon, south-central Chad, Central African Republic and Borborema Province of Brazil. The ages also revealed that continental assembly coupled with regional late–magmatism occurred during the Proterozoic.

Magmatic-hydrothermal fluid evolution of the tin-polymetallic metallogenic systems from the Weilasituo ore district, Northeast China

The large Weilasituo Sn-polymetallic deposit is a recent exploration discovery in the southern Great Xing’an Range, northeast China. The ore cluster area shows horizontal mineralization zoning, from the inner granite body outward, consisting of high-T Sn–W–Li mineralization, middle-T Cu–Zn mineralization and peripheral low-T Pb–Zn–Ag mineralization. However, the intrinsic genetic relationship between Sn-W-Li mineralization and peripheral vein-type Pb–Zn–Ag–Cu mineralization, the formation mechanism and the deep geological background are still insufficiently understood. Here, we use fluid inclusions, trace elements concentrations in quartz and sphalerite, and H–O isotope studies to determine the genetic mechanism and establish a metallogenic model. Fluid inclusion microthermometry and Laser Raman spectroscopic analysis results demonstrates that the aqueous ore-forming fluids evolved from low-medium salinity, medium–high temperature to low salinity, low-medium temperature fluids. Laser Raman spectroscopic analysis shows that CH4 is ubiquitous in fluid inclusions of all ore stages. Early ore fluids have δ18OH2O (v–SMOW) values from + 5.5 to + 6.2‰ and δD values of approximately − 67‰, concordant with a magmatic origin. However, the late ore fluids shifted toward lower δ18OH2O (v–SMOW) (as low as 0.3‰) and δD values (~ − 136‰), suggesting mixing between external fluids derived from the wall rocks and a contribution from meteoric water. Ti-in-quartz thermometry indicates a magmatic crystallization temperature of around 700 °C at a pressure of 1.5 kbar for the magmatic ore stage. Cathodoluminescence (CL) imaging and trace element analysis of quartz from a hydrothermal vug highlight at least three growth episodes that relate to different fluid pulses; each episode begins with CL-bright, Al-Li-rich quartz, and ends with CL-dark quartz with low Al and Li contents. Quartz from Episode 1 formed from early Sn-(Zn)-rich fluids which were likely derived from the quartz porphyry. Quartz from episodes 2 and 3 formed from Zn-(Sn)-Cu-rich fluid. The early magmatic fluid is characterized by low fS2. The SO2 produced by magma degassing reacted with heated water to form SO42−, causing the shift from low fS2 to high fS2. The SO42− generated was converted to S2– by mixing with CH4-rich, Fe and Zn-bearing external fluid which led to late-stage alteration and dissolution of micas in vein walls, thus promoting crystallization of pyrrhotite, Fe-rich sphalerite and chalcopyrite and inhibiting the precipitation of anhydrite. This study shows that ore formation encompassed multiple episodes involving steadily evolved fluids, and that the addition of external fluids plays an important role in the formation of the later Cu–Zn and Ag–Pb–Zn mineralization in the Weilasituo ore district.

Heflikite, ideally Ca2(Al2Sc)(Si2O7)(SiO4)O(OH), the first scandium epidote-supergroup mineral from Jordanów Śląski, Lower Silesia, Poland and from Heftetjern, Tørdal, Norway

Abstract Heflikite, the first Sc-dominant epidote-supergroup mineral, was discovered in two occurrences. The holotype was found in a granitic pegmatite associated with rodingite-like calc-silicate rocks and metasomatised granitic bodies exposed in a serpentinite quarry at Jordanów Śląski near Sobótka, Lower Silesia, SW Poland. The cotype comes from the Heftetjern pegmatite, Tørdal region, Norway. The holotype is composed of (in wt.%): 35.69 SiO2, 0.22 TiO2, 21.98 Al2O3, 6.12 Sc2O3, 0.07 V2O3, 1.10 Fe2O3, 0.11 Y2O3, 1.55 La2O3, 4.05 Ce2O3, 0.31 Pr2O3, 1.53 Nd2O3, 0.40 Sm2O3, 0.11 EuO, 0.56 Gd2O3, 0.14 MnO, 3.56 FeO, 0.16 MgO, 19.16 CaO and 1.78 H2O(+)calc.; total 98.60. The cotype contains: 34.92 SiO2, 0.44 TiO2, 0.82 SnO2, 19.13 Al2O3, 4.79 Sc2O3, 1.96 Fe2O3, 2.55 La2O3, 7.39 Ce2O3, 0.48 Pr2O3, 0.67 Nd2O3, 0.12 EuO, 0.61 Gd2O3, 0.13 MnO, 5.97 FeO, 17.66 CaO and 1.73 H2O(+)calc.; total 99.37. The compositions correspond to the following empirical formulae: (Ca1.729Ce0.125La0.048Nd0.046Gd0.016Sm0.012Pr0.010Y0.005Eu2+0.003)Σ1.994[(Al2.182Sc0.449Fe3+0.070V3+0.005)Σ2.706(Fe2+0.251Mg0.020Mn0.010)Σ0.281Ti0.014]Σ3.001(Si3.006O11)O(OH) and (Ca1.644Ce0.235La0.082Nd0.021Gd0.018Pr0.015Eu2+0.004)Σ1.019[(Al1.958Sc0.362Fe3+0.128)Σ2.448(Fe2+0.434Mn0.009)Σ0.443(Ti0.029Sn0.029)Σ0.058]Σ2.949(Si3.033O11)O(OH), respectively, and to the ideal formula Ca2(Al2Sc)(Si2O7)(SiO4)O(OH). The crystal structure of the holotype was refined in the monoclinic system with an R1 index of 8.62%. The crystal-structure refinement indicates exclusively Si occupied T sites, Al occupied M1 and M2 sites, and a Ca occupied A1 site. The M3 site is filled predominantly by trivalent cations, mainly Sc3+, with divalent cations (mainly Fe2+) as minor occupants. The A2 site is filled mostly by Ca with minor amounts of rare earth elements (REE). The holotype heflikite crystallised from metasomatic fluids that infiltrated a contact between the granitic pegmatite and the surrounding rodingite-type calc-silicate rocks and serpentinites. The fluids that introduced Sc into the pegmatite could have been either hydrothermal or related to low-grade regional metamorphism that postdated the formation of the pegmatite. The cotype heflikite formed during the late-stage hydrothermal crystallisation of the Sc-enriched granitic pegmatite.

Transport of Magma in Granitic Mush Systems; an Example From the Götemar Pluton, Sweden

AbstractGranitic magma bodies form in the ephemeral part of magma mush systems and are emplaced by a variety of mechanisms in different tectonic settings. This study investigates how granitic magma emplacement processes and tectonomagmatic interactions assert control over the architecture of mush state pluton‐scale magma transport pathways. The 1.45 Ga shallow‐crustal Götemar pluton is a 4.5 km diameter circular pluton that consists of three granite units: a coarse‐grained red granite, a medium‐grained pale to red granite, and fine‐grained pale microgranite sheets. We employed geological mapping supported by Anisotropy of Magnetic Susceptibility (AMS) to examine the magmatic and regional tectonic controls on late‐stage magma transport in the Götemar granitic magma mush system. Multiple parallel arcuate subhorizontal microgranite and medium‐grained granite sheets (from 0.1 to 10s of meters thick) were mapped within the pluton. The arcuate sheets pinch out from the northern part of the pluton toward the SE inferring magma propagation direction. A dominant set of vertical granitic sheets within the granite body strikes NW‐SE. The AMS fabrics are contact‐parallel in the main medium‐grained granite body and indicate inflation. Within the microgranite sheets, the AMS fabrics are parallel to the sheet strike and support a sheet propagation direction to the SE. The Götemar pluton displays a clear link between arcuate (concentric) magma‐transporting sheets and concentric strain‐partitioning related to the intrusion of medium‐grained granite magma. The vertical magma sheet orientations are consistent with an NE‐SW extensional stress field that is associated with the extensional back‐arc stress regime of the contemporary Hallandian Orogen.

Mechanisms for concentrating critical metals in granitic complexes: insights from the Mourne Mountains, Northern Ireland

The Tellus stream sediment and deep soil geochemistry data sets for Northern Ireland were used to locate four types of critical metals anomalies in granite bedrocks of the Mourne Mountains. A curvi-linear array of Nb, REE, Th and U soil anomalies across the eastern Mourne Mountains correlated with late-stage and eutectic temperature minerals in the roof zone of the most peralkaline F- and volatile-rich granite body, remobilized on micron to millimetre scales. Li, Be, B, As, Sn, Mn 3+ and Ce 4+ partitioned into pockets of late-stage heterogeneously distributed F-rich silicic residual melts and relatively oxidizing halide-rich magmatic fluids, resulting in drusy mineral and hydrothermal assemblages. Isolated soil anomalies correlated with amorphous Mn 3+ - and Ce 4+ -rich masses infilling drusy cavities, which resulted from short-distance percolation of small volumes of late-stage magmatic fluids. A significant As plume in stream sediments emanated from a greisen that hosted multiple critical and base metals including Sn, from reactions between large volumes of magmatic As + halide-rich fluids and mafic silicate + diverse accessory minerals on the metre- to kilometre-scale along geological structures. Diverse, small-scale REE anomalies in the soil data along structural features in the western Mournes correlate with vein mineralization resulting from episodic migration of hydrous fluids of variable composition, probably with a much smaller magmatic component than elsewhere. The regional geochemical dataset proved useful to develop a multi-stage model for enrichment of critical metals in the Mourne Mountains granites, which is analogous to the petrogenesis of some of the igneous-hosted economic deposits of critical metals. Thematic collection: This article is part of the energy-critical metals for a low carbon transition collection available at: https://www.lyellcollection.org/topic/collections/critical-metals

Uncovering the Distribution Zones of Uranium and Thorium in Bangka Island

Radioactive minerals, especially containing uranium and thorium, can be used as a core element of nuclear fuel. Bangka Island is located in The Southeast Asian Tin Belt where it has a large uranium and thorium potential. The purpose of this study is to delineate distribution zone of uranium and thorium in Bangka Island. The study methods consist of radiometric measurement and mapping, petrographic analysis, and mineralogical analysis of pan concentrate samples. Based on radiometric measurement, positive anomaly value of equivalent uranium (eU) is ranging from 5-15 ppm while of equivalent thorium (eTh) is ranging from 45-75 ppm. The result of petrographic analysis from several outcrops of Klabat Granite indicated that there are monazites found in several samples of Mangkol Granite and of Bebuluh Granite. Radioactive mineral indication also can be identified as pleochroic halo within biotite in samples of Pelangas Granite and Menumbing Granite. Based on the result of mineralogical analysis of pan concentrate samples, it was identified that monazites can be found in all samples. Monazites constitute the percentages ranging from 2.82-10.66 %. Zircon also can be identified with percentages ranging from 9.13-76.75 % while ilmenite and magnetite minerals have average percentages of 24.09 % and 5.97 %, respectively. Favorable zones can be delineated in outcrops of Klabat Granite, Ranggam Formation and alluvial deposits in northern, northwestern, northeastern, central, and southeastern parts of Bangka Island. The occurrences of monazites in those lithological units are the main factors of high radioactivity in Bangka Island. Based on petrographic and mineralogical composition, those granite bodies which are correlated with Klabat Granite are mostly associated with ilmenite series with S-Type granitic rocks.

Three-Dimensional Inversion Algorithm with A Footprint Computational Domain for Underground Engineering

Granite bodies pose a common geohazard in urban underground engineering. The GEM-2 system, employing small coils as transmitter and receiver (Tx-Rx), has gained widespread adoption for efficiently and non-invasively delineating low resistivity targets with 1D results in the near-surface. In this paper, we propose a 3D inversion algorithm based on the footprint-guided compact finite element method and Gauss-Newton optimization to accurately delineate the 3D structure of granite boulders. To demonstrate the effectiveness of our 3D inversion method, we conducted a GEM-2 test survey in a scenario featuring a granite boulder. The inversion results exhibit superior horizontal resolution compared to the current 1D inversion methods. The three-dimensional contour of the boulder is clearly depicted by areas of relatively high resistance, showcasing the capability of our inversion algorithm.