Fine-grained Biotite Granite Research Articles

Litho-structural mapping and structural evolution of the Bocaranga pluton, northwest Adamawa-Yadé domain, Central African Republic

The Bocaranga pluton, in the northern domain of the Central African Orogenic Belt (CAOB) in the Central African Republic (CAR), is located in the Adamawa-Yadé domain, near the Mbéré Shear Zone (MBSZ). This study provides new results of the satellite image processing, the detailed structural and petrographic studies of Bocaranga pluton which helps to understand the emplacement mechanism of this pluton. Image processing of the satellite data and field showed the occurrence and spatial distribution of (1) amphibole-pyroxenites, (2) garnet-biotite rich amphibolite, (3) migmatite, (4) hornblende-biotite and hornblende-garnet gneiss, (5) hornblende-biotite granite (HBG), (6) two micas granite (TMG), (7) fine-grained biotite granite (FBG), and (8) coarse-grained biotite granite (CBG) rock types. The mapping of regional lineaments was carried out by automatic and manual lineament extraction methods. NE-SW direction corresponds to the direction of S2 and S3 foliations, faults, mineral lineation, quartz vein, dyke (aplitic granitic or pegmatitic). NW-SE direction also corresponds to the direction of S1 foliation, F1 folds, faults, quartz veins, dykes (aplitic granitic or pegmatitic). In the absence of absolute geochronological data in study area, it has been possible to propose a polyphase structural evolution, deduced from the relative chronology of the Bocaranga granitoid. Three phases of deformation can be defined in this study. D1 phase is represented by early NW-SE trending foliation (S1) that has been progressively rotated parallel to S2 overprinting foliation occurring in gneiss, amphibolites and hornblende-biotite granite (HBG) intrusion as well. D2 phase of ductile sinistral sense from NE-SW to ENE-WSW is responsible for an emplacement of Bocaranga granitic pluton. The scarcity of structure orientation in the TMG and FBG (except the contact zones), would imply that these granites would have been crystallized in the absence of any stress. D3 is a phase of brittle deformation with three main directions corresponding to the main direction of the shear zones in the Northern domain of the CAR Pan-African fold belt.The mylonitic deformation observed in study area illustrates the intensity of the deformation. The dominance of ellipsoidal structures observed in Bocaranga area suggests that the shear mechanism is the main controlling structure of Bocaranga granite emplacement, which can be correlated with the emplacement of Tamkoro-Bossangoa granitoid in CAR and the Adamawa-Yadé domain in Cameroon, Chad and NE Brazil.These results imply a syntectonic emplacement of Bocaranga pluton during sinistral simple shear regime related to deformation along the Central Cameroon Shear Zone (CCSZ).

Trace Elements and Pb-O Isotopes of Scheelite: Metallogenic Implications for the Shimensi W-Polymetallic Deposit in South China

The world-class Shimensi tungsten (W)-polymetallic deposit is located in Jiangnan Orogen, with an estimated reserve of 742.5 kt WO3 @ 0.195% W, 403.6 kt Cu and 28 kt Mo. In this paper, the trace elements and Pb-O isotopes of scheelite (the main ore mineral) are presented to study the ore-forming material source and ore-forming fluid evolution. The results show that the REE distribution in scheelite is mainly controlled by the substitution mechanism of 3Ca2+ = 2REE3+ + □Ca (where □Ca is the Ca-site vacancy). Oxygen isotope data indicate that the scheelite mineralization occurred under high-temperature oxygen isotope equilibrium conditions, and that the ore-forming fluid has a magmatic–hydrothermal origin. The variation in scheelite Eu anomalies and the wide range of scheelite Y/Ho ratio indicate that the ore-forming fluid evolves from reducing to oxidizing, and the early-stage and late-stage ore-forming fluid may have been relatively rich in F− and HCO3−, respectively. The significant Mo decrease in scheelite from the early to late stage that are opposite to the influence of fO2 variation may have resulted from the crystallization of molybdenite and Mo-rich scheelite. Lead isotopes of the ore minerals of scheelite, wolframite, molybdenite and chalcopyrite can be divided into three groups, similar to these of feldspars in different granites. Both the Mesozoic porphyritic and fine-grained biotite granites have Pb isotope ratios similar to the ores, which suggests that the former two are the main ore material source.

Zircon U-Pb Ages and Geochemistry of the Granite in the Xintianling Tungsten Deposit, SE China: Implications for Geodynamic Settings of the Regional Tungsten Mineralization

The Xintianling tungsten deposit is a super-large deposit in the Nanling tungsten–tin mineralization belt, which is genetically associated with the early-stage hornblende-biotite monzonitic granite of Qitianling pluton. The orebodies predominantly occur as veins and lenses within skarn rocks between Xintianling granite and limestone (Shidengzi group). In this work, whole-rock major and trace elements and zircon U–Pb ages of the Xintianling granite were studied in an attempt to investigate the geochronological framework, petrogenesis, tectonism, and metallogenesis with regard to the deposit. The petrographic and geochemical analyses indicated that the Xintianling granite consists of three intrusive units of medium- and coarse-grained biotite granite, fine-grained biotite granite, and granite porphyry, of which the biotite granite was strongly associated with mineralization. Biotite granite rocks are highly K-calc-alkaline and weakly peraluminous, with A/CNK ratios ranging from 0.99 to 1.05. Late-granite porphyry is aluminum-supersaturated with a high evolution degree, whose geochemical characteristics suggest that it is either an I- or S-type granite. LA-ICP-MS zircon U-Pb dating revealed that medium- and coarse-grained biotite granite (162.3 ± 1.2 Ma, MSWD = 1.3), fine-grained biotite granite (161.8 ± 1.3 Ma, MSWD = 1.8), and granite porphyry (154.3 ± 1.6 Ma, MSWD = 2.4) formed in the late Jurassic. The emplacement of the Qitianling A-type granite and associated tungsten-tin polymetallic mineralization is a continuous evolution process, and they are products of the large-scale mineralization of the Nanling in the middle–late Jurassic (150–160 Ma). Under the tectonic setting of the Mesozoic lithospheric extension, asthenosphere upwelling along deep-fault, intensive mantle–crust interaction processes probably provide not only the high heat flow, but also partly mantle-derived material for large-scale W-Sn-polymetallic mineralization in this area.

Late mesozoic magmatism in the Gucheng district: Implications for REE metallogenesis in South China

Regolith-hosted rare earth element (REE) deposits are common in South China. The newly-discovered Gucheng REE deposit in the western part of Guangdong Province, is characterized by HREE enrichment (with ∑HREE oxides of 55%). Three types of granites have been identified in the Gucheng ore district, a REE-fertile coarse-grained biotite granite (CGBG), a weakly REE-fertile fine-grained biotite granite (FGBG) and the barren medium-grained biotite granite (MGBG). New LA-ICP-MS zircon U-Pb dating reveals that the MGBG (107.7 ± 0.4 Ma), CGBG (103.2 ± 0.6 Ma) and the FGBG (98.9 ± 0.7 Ma) were all formed in the Late Cretaceous.Mineralogical and geochemical data indicate that the CGBG is an unfractionated I-type granite, whereas the FGBG and MGBG are fractionated I-type granites. The CGBG and FGBG have (87Sr/86Sr)i and εNd(t) ranging from 0.7121 to 0.7140 and −8.6 to −8.0, and 0.7125 to 0.7131 and −8.2, respectively. The source of these granites was mainly composed of two end-members: one having 90% Paleoproterozoic basement and another 10% enriched mantle metasomatized by subduction-related melts. The barren MGBG is also derived from partial melting of a Paleoproterozoic source with a minor contribution of enriched mantle. The involvement of enriched mantle can provide REE into the magmas, which plays an important role in REE enrichment. Geochemical data show that allanite have been crystallized during magma evolution process of all the three types of granites. However, no allanite has been discovered in the MGBG, and the FGBG contains lower abundance of allanite than that of the CGBG, which is due to different degrees of fractionation. The crystallization and separation of allanite has greatly affected the LREE of the three types of granites, which further influences their potential for LREE mineralization. Lower K/Rb and Nb/Ta ratios of the CGBG, FGBG and MGBG indicate that these three types of granites were affected by hydrothermal events after their crystallization. Zircon geochemical data show that the MGBG was formed in a lower oxygen fugacity environment than the CGBG and FGBG. Above all, involvement of enriched mantle, a relatively high oxygen fugacity, crystallization and separation of allanite as well as involvement of hydrothermal events after magmatic crystallization are important factors controlling REE mineralization at Gucheng, of which the hydrothermal events may play the most important role.

Petrogenesis of the Xingluokeng W-bearing granitic stock, western Fujian Province, SE China and its genetic link to W mineralization

The Xingluokeng deposit is the largest tungsten deposit discovered in the Wuyi metallogenic belt, with 30.43 Mt WO3 reserves averaging at 0.23%. The main orebody mainly occurs in an altered granitic stock, comprising veinlet-disseminated and vein-type scheelite and wolframite mineralization. A comprehensive study of field investigations with whole-rock and in-situ geochemical and isotopic compositions was conducted on different intrusive phases of the Xingluokeng ore-bearing granitic stock, aiming to constrain the petrogenesis and its genetic link to W mineralization. The Xingluokeng stock is mainly composed of the porphyritic biotite granite (G1) as the upper part of the stock, intruded by the medium- to fine-grained biotite granite (G2) in the deep. Petrographic observations suggest that the stock experienced intense fractional crystallization as well as assimilation of country rocks close to stock margins. Zircon U − Pb geochronology and trace element analyses indicate that G1 and G2 were emplaced coevally at ~152 Ma at a relatively lower oxygen fugacity condition (Ce4+/Ce3+ = 44 ± 18 for G1, and 104 ± 41 for G2). Ti-in-zircon thermometer and AlT-in-biotite geobarometer reveal average crystallization temperature and depth at 762 ℃−740 ℃ and 7.3–7.0 km, respectively. Geochemically, obvious negative correlation between SiO2 and P2O5 and low A/CNK values (mostly < 1.1) indicate that they belong to the weakly peraluminous I-type granite, rather than S-type granite as proposed previously. Whole-rock geochemical compositions from G1 to G2 display systematic variations, with a general decrease in major oxides (such as Al2O3, TiO2, FeOT, MgO, CaO) and Zr/Hf ratio, but a gradual increase in DI value, Rb/Sr ratio and δEu with increasing SiO2, suggesting fractional crystallization is the major factor that controls the compositional variations between G1 and G2. They have consistent initial 87Sr/86Sr ratios of 0.71170 to 0.71477 and εNd(t) values of −12.5 to −10.8, as well as zircon εHf(t) values of −17.4 to −9.2 with Paleoproterozoic Nd − Hf model ages (1783–2081 Ma), suggesting a mixed crustal source of about 88% Paleoproterozoic meta-basaltic rocks and about 22% Paleoproterozoic gneissic granites, with minor assimilation of country rocks. These results favor that the Xingluokeng granites were formed by co-magmatic evolution via K-feldspar-dominated fractionation. High degrees of fractional crystallization have immensely enriched W in reduced magma, then intensive fluid-rock interaction liberated Ca from the G1 to form the scheelite and some Fe might come from the country rocks (biotite hornfels) to precipitate the wolframite.

Two-stage magmatism and tungsten mineralization in the Nanling Range, South China: Evidence from the Jurassic Helukou deposit

Abstract The Helukou deposit, with proven reserves of 33 752 t WO3, is one of the newly exploited medium-scale tungsten (W) deposits in the Guposhan ore field, Nanling Range of South China. Skarn-type and less abundant altered granite-type tungsten orebodies were identified in this deposit. The ore mineralization in this district was a product of two-stage magmatism, as shown by LA-ICP-MS U-Pb dating of zircons and Re-Os dating of molybdenite. The former yielded U-Pb ages of 184.0 ± 3.6 Ma (MSWD = 0.15) and 163.8 ± 1.5 Ma (MSWD = 0.41) for fine-grained biotite granite and muscovite granite, respectively, as well as a U-Pb age of 181.5 ± 2.1 Ma (MSWD = 0.75) for zircon grains from altered granite-type tungsten ore. The latter yielded molybdenite Re-Os ages of 183.5 ± 2.8 Ma (without MSWD owing to a limited number of samples) and 163.4 ± 2.8 Ma (MSWD = 0.71) for altered granite-type and skarn-type tungsten deposits, respectively. Thus, two separate tungsten mineralization events occurred during the Early Jurassic and Middle Jurassic. Trace-element compositions suggest that scheelite I was controlled by the coupled substitution reactions of 2Ca2+ = Na+ + REE3+ and Ca2+ + W6+ = Nb5+ + REE3+, whereas scheelite II was controlled by the coupled reactions of 2Ca2+ = Na+ + REE3+ and 3Ca2+ = ☐Ca + 2REE3+ (where ☐ is a site vacancy). High Mo and low Ce contents suggest that both scheelite I and scheelite II were precipitated from oxidizing magmatic-hydrothermal fluids. Based on the mineral assemblage of the altered granite-type ores and geochemical characteristics of scheelite I [i.e., negative Eu anomalies (0.02–0.05; mean = 0.03 and STD = 0.01), and high 87Sr/86Sr ratios (0.70939–0.71932; mean = 0.71345 and STD = 0.00245)], we infer that fluid-rock interaction played an important role in modifying Early Jurassic ore-forming fluids. Scheelite II exhibits a geo-chemical composition [i.e., 87Sr/86Sr ratios (0.70277–0.71471; mean = 0.70940 and STD = 0.00190), Eu anomalies (0.14–0.55; mean = 0.26 and STD = 0.09), and Y/Ho ratios (16.1–33.7; mean = 27.9 and STD = 2.91)] similar to that of the Middle Jurassic Guposhan granites, suggesting inheritance of these features from granite-related magmatic-hydrothermal fluids. These results provide new insights into the two-stage magmatic and metallogenic history of the Nanling Range during the Jurassic Period.

Petrographical, petrochemical characteristics of Ta Kou massif granitoids, Ham Thuan Nam, Binh Thuan

Ta Kou is an isometric shape with an area of ​​about 15 km2. Petrographical composition is mainly biotite-hornblende granodiorite; minors are altered light-colored fine-grained biotite granite. Mineral composition is mainly plagioclase 45–50, quartz 25, potassium feldspar 15–20, biotite 5–10, hornblende (5–7); secondary is pyroxen; Accessory minerals include zircon, apatite, orthit, muscovite and rare ore. In some places, near fault or high arch of massif, rocks have been altered by other magma, especially near faults due to post-magma activity including fine-grained biotite granite which caused strongly by alkalization such as increasing the content of potassium felspar (35–50%) and quartz 30; reducing plagioclase content (30–25%); amphibole -colored minerals is rare, and pyroxene is absent. Chemical composition of medium acid granodiorite SiO2 61.08–62.14 (61.85); total alkalinity (K2O+Na2O) 5,99–6,04 (6.00); ratio of alkaline K2O/Na2O: 0.74-0.77 (0.75 &lt;1). Characterized trace elements content of granodiorite: Rb and Ba are low but Sr is quite high; ratios Rb/Sr: 0.24; Ba/Sr 1.40, Ba/Rb: 5.85; K/Rb: 245.39; La/Yb: 10.33; Ce/Yb: 22.11; normal Eu anomalies. When influencing the post-magmatic activity, some granite is more acidific, the chemical composition of altered granite SiO2 72.27–74.07 (73.17); total alkalinity (K2O+Na2O): 7.48–7.96 (7.72); the ratio of alkaline K2O/Na2O: 1.60–1.69 (1.64&gt;1). Characterized trace elements content of altered granite: Ba and Sr are low but high Rb; ratios of Rb/Sr: 1.43; Ba/Sr: 3.06, Ba/Rb: 2.79; K/Rb: 218.05; La/Yb: 8.60 and Ce/Yb: 15.74; strong Eu anomalies.Ta Kou granitoids belong to the medium to high aluminum series, medium to high potassium alkaline series, negative Eu anomalies are from normal to strong, type of I- granite. Granitoid characterized subduction-related formation and altered, which may be due to the effects of later phase magmatic activity. Compared with granitoid formations in South Vietnam, Ta Kou massif granitoids belong to phase 2 of Định Quán complex.&#x0D;

Petrogenesis of early Cretaceous granitoids in the southern Great Xing’an Range, NE China: Constraints from the Haliheiba pluton

Early Cretaceous granitoids are widespread in the southern Great Xing’an Range. However, the petrogenesis of these rocks is poorly understood. We therefore present field investigations, petrological observations, zircon U–Pb ages, whole-rock geochemistry and Hf isotope compositions for the Haliheiba pluton. The pluton comprises fine-grained biotite granite, medium- to coarse-grained biotite granite and porphyritic biotite granite, and mafic microgranular enclaves (MMEs) are unevenly distributed within the host granites. Zircon LA-ICP-MS U–Pb dating yields emplacement ages of ∼139 Ma for the three units. The host granites are characterized by high SiO2 contents (73.16–76.55 wt%) and alkali concentrations (7.92–8.62 wt%), enrichment in light rare earth elements (LREEs), Rb, U, Th, K, and Pb, depletion in heavy rare earth elements (HREEs), Sr, Ba, Ti, and P, and intensely negative Eu anomalies with δEu values from 0.14 to 0.47. The zircons in the host granites yield positive εHf(t) values of +5.0 to +11.2 and fairly young Hf model ages of 408 Ma to 731 Ma. These results indicate that the host granites have high-K calc-alkaline, metaluminous to weakly peraluminous A-type affinity and were mainly derived from partial melting of juvenile crustal materials originated from the depleted mantle, and fractional crystallization was involved in magma evolution. The MMEs have SiO2 contents of 63.45–64.14 wt% and have higher MgO, CaO, tFe2O3 and TiO2 contents than the host granites. The MMEs are enriched in LREEs relative to HREEs with slightly negative Eu anomalies (δEu values of 0.77–0.79) and are slightly enriched in Rb, U, Th, K, Sr, Pb and strongly to slightly depleted in Nb, Ta, Ti and P. These results, together with field investigations and petrological observations, indicate that crust-mantle magma mixing played an important role during the petrogenesis. Furthermore, the MMEs were intermediate members after magma mixing between mafic end-member magmas derived from lithospheric mantle and felsic end-member magmas derived from juvenile crustal materials. Combined with regional geology, our results suggest that a substantial crustal accretion in the southern Great Xing’an Range that occurred during the Neoproterozoic–Carboniferous, and the formation of the Early Cretaceous granitoids in this region was closely related to the lithospheric delamination triggered by the subduction of the Paleo-Pacific Ocean beneath Eurasia.

Emplacement of the Dschang granitic pluton (west-Cameroon): Constraints from microstructures and magnetic fabrics

Microstructures and Anisotropy of Magnetic Susceptibility (AMS) data were investigated in the Pan-African Dschang granitic pluton and its basement rocks in order to decipher its emplacement and time relationship within the Pan-African evolution of the Central Cameroon Shear Zone (CCSZ). The Dschang granitic pluton, emplaced in biotite-hornblende gneiss country rocks, is made of biotite megacrystic granite and fine-grained biotite granite. The pluton has mostly low susceptibility magnitude (Km ≤ 500 μSI) implying that AMS susceptibility is mostly controlled by biotite. The foliation of the pluton is underlined by platy alkali-feldspar megacrystals that strike ENE-WSW to E-W or WNW-ESE with moderate to high dips, associated with biotite schlieren and spindle-shaped xenoliths. The magnetic foliations also strike dominantly NE-SW to E-W or NNW-SSE to NNE-SSW directions with moderate to steep dips. Magnetic lineations have low to moderate plunges and show radiating pattern in the Schmidt projection diagram. The microstructures within the pluton point to continuous deformation from magmatic to sub-magmatic state. The Jelinek shape parameter Tj shows abundant triaxial and oblate shape AMS ellipsoids and uncommon negative values (42% of the stations). Low to very low values of Pj parameter associated to (i) mostly triaxial and oblate shape AMS ellipsoids and (ii) dominantly magmatic to submagmatic state microstructures suggest a syn-to post-kinematic emplacement of a high viscosity granitic magma by flow mechanism. Magnetic fabrics infer that the Dschang granitic pluton was emplaced in a ENE-WSW to E-W oriented fracture initiated during the transcurrent strike-slip CCSZ.

Petrogenesis and metallogenic significance of multistage granites in Shimensi tungsten polymetallic deposit, Dahutang giant ore field, South China

The Shimensi tungsten polymetallic deposit, situated in the Dahutang ore field, South China, is one of the largest tungsten deposits in the world, with an estimated WO3 reserve of 0.74 million tons. Coarse-grained porphyritic biotite granite (CPBG), fine-grained porphyritic biotite granite (FPBG), fine-grained biotite granite (FBG) and biotite granite porphyry (BGP) are all ore-related, but their diagenetic relationships and contributions to W-Cu-Mo mineralization are still in dispute. LA-ICP-MS monazite U-Pb dating of the CPBG, FPBG, FBG and BGP yield emplacement ages of 147.9 ± 1.1 Ma, 146.4 ± 1.1 Ma, 138.6 ± 0.98 Ma and 142.8 ± 1.7 Ma, respectively. Whole-rock geochemical results indicate that the four granites should be classified as S-type granites, but BGP has distinct features transitional between S- and I-type granites. They were possibly generated by partial melting of upper crustal pelites and basic volcanic rocks with different proportion from the Neoproterozoic Shuangqiaoshan Group in the source. Proportional variation in the magmatic source (clay and basic basalts) induces the change of geochemical compositions of the Shimensi granites. Geochemical characteristics suggest that they were derived from two magma chambers (the CPBG, FPBG and FBG vs. the BGP) and experienced different evolutionary processes and different degree of magmatic differentiation during magmatic evolution. Chondrite-normalized REE patterns for the four granites display low total REE contents, variable and strongly enriched LREE relative to HREE and medium-strong negative Eu anomalies. They are enriched in Rb, Th, U, Ta and depleted in Ba, Nb, Sr, P, Ti. Biotites are iron-rich and aluminum-poor, and can be classified as ferro-biotite (CPBG, FPBG and FBG) and siderophyllite (BGP). The partial melting of tungsten-rich metasediments of the Shuangqiaoshan Group and high degree of fractional crystallization led to enrichment in tungsten in the magma suites. Oxygen fugacities of the CPBG and FPBG declined from early (most above the NNO buffers) to late stages of fractional crystallization (between the NNO and QFM buffers) because of the higher degree of magmatic differentiation in the late stages. In the early stages of fractionation, tungsten accumulated in the residual melts rather than partitioning into accessory minerals. In the late stages, lower oxygen fugacities and high fluorine contents promoted the removal of tungsten from the residual magma into reduced hydrothermal fluids. On the other hand, the FBG and BGP remained constant (above the NNO buffers) over the entire process of crystallization owning to the stable degree of magmatic differentiation, promoting retention of tungsten in the melt and resulting in low grade tungsten mineralization. Tungsten mineralization in the Shimensi deposit is greatly controlled by the redox states of the associated magma. The two porphyritic granites (the CPBG and FPBG) are most likely the main contributors of tungsten, while the FBG and BGP are mainly responsible for copper and molybdenum in the Shimensi deposit. Prolonged multiphase magmatism and prolonged W-Cu-Mo mineralization play important roles in the formation of Shimensi large tungsten polymetallic deposit.

The role of hydrothermal alteration in tungsten mineralization at the Dahutang tungsten deposit, South China

The giant Dahutang tungsten deposit has total reserves of more than 1.31 Mt of WO3 with a scheelite/wolframite ratio of ∼1 and is mainly hosted by the Neoproterozoic Jiuling granodiorite batholith (∼820 Ma). The deposit is characterized by four types of alteration, including biotite alteration, phyllic alteration, greisenization and silicification. Whole-rock geochemical analyses showed that the elements Ti, Ni, V, Sc, and Lu exhibited immobility during the four alteration processes. The mobile element geochemistry effectively differentiated among four distinct hydrothermal alteration styles. During the biotite mineralization, there were mass gains in Al2O3, Fe2O3, MnO, MgO, K2O, P2O5, and W and depletions in SiO2, CaO, and Na2O. The phyllic alteration exhibited mass gains in SiO2, Fe2O3, MgO, and W and depletions in CaO, Na2O, and K2O, but Al2O3, MnO, and P2O5 were immobile. The weak greisenization exhibited mass gains in SiO2, Fe2O3, K2O, P2O5 and W and depletions in Na2O, MgO, and CaO, whereas Al2O3 and MnO remained immobile. The silicification exhibited mass gains in SiO2 and W and depletions in Al2O3, Fe2O3, MgO, CaO, Na2O, and K2O, but MnO exhibited immobility. These alterations were related to at least three major hydrothermal fluid systems. Firstly, a hydrothermal fluid caused biotitization zones and Fe + Mn ± W mineralization (mostly biotite) at temperatures ranging from 560 to 450 °C, and the magmatic hydrothermal fluids were derived from the Jurassic porphyritic biotite granite (∼150 Ma) and characterized by alkaline, oxidized, moderate-pressure, and low-salinity features. Secondly, a hydrothermal fluid was formed by the mixing of magmatic fluid with meteoric water and was responsible for the phyllic/weak greisenization alteration zones at temperatures ranging from 440 to 450 °C and characterized by alkaline, weakly oxidized, moderate-pressure, and low-salinity features. Thirdly, a hydrothermal fluid caused greisenization and silicification zones at temperatures ranging from 440 to 160 °C, which were characterized by acidic, reduced, high-pressure, and moderate- to low-salinity features, derived from the Cretaceous fine-grained biotite granite (∼144 Ma), and associated with the main W mineralization at Dahutang.The characteristics of Fe-enriched biotite in the biotitized and greisenized rock – decreasing temperature, high pressure, and high log(fH2O/fHCl) – could facilitate the formation of scheelite deposits, but the high F suppressed it. The decreasing temperature and f(O2) and the Fe-Mn released from biotite contributed to the formation and precipitation of wolframite. During alkaline alteration, biotite and apatite acted as storage places for Fe-Mn and Ca, which were subsequently released by acidic alteration to form scheelite and wolframite. There was no enough Ca was released from biotitized rock for the acidic alteration to provide the WO42− to form scheelite. Meanwhile, Fe was added, and Mn was released to form the scheelite + wolframite deposit. Based on all the results, we have developed a genetic model for tungsten mineralization including superimposed alteration processes (alkaline overprinted by acidic alteration), which led to the gain and loss of elements, and corresponding to two magmatic events, the Jurassic porphyritic biotite granite and the Cretaceous fine-grained biotite granite. The superposition of alterations played an important role in the mineralization of the Dahutang giant tungsten deposit.

Mineralogical and metasomatic evolution of the Jurassic Baoshan scheelite skarn deposit, Nanling, South China

The Baoshan scheelite deposit, located in the Nanling region, South China, is a skarn-type tungsten ore deposit. Orebodies occur in the contact zone between Carboniferous limestone and Baoshan granitic pluton. The pluton consists mostly of coarse-grained, porphyritic, and fine-grained biotite granites, which have zircon U-Pb ages of 172.4 ± 0.3 Ma, 166.6 ± 0.3 Ma, and 156.6 ± 1.4 Ma, respectively. These rocks have similar geochemical characteristics with high SiO2, total alkalis, high differentiation indexes and high Rb/Sr ratios of S-type granites formed by partial melting of upper continental crust. The porphyritic granites display the highest degree of fractionation, and are most closely associated with the formation of skarn ores.The skarns are zoned mineralogically outward from garnet, through clinopyroxene, to wollastonite, and overprinted by retrograde minerals. Three stages of skarnization are recognized: Early prograde, late prograde and retrograde. The early prograde stage is mainly composed of Al-rich garnet (Grs60–76) and Mg-rich clinopyroxene (Di41–62) with subordinate Mo-rich scheelite (Sch59–86), all of which are typically overgrown by late prograde assemblages of Fe-rich garnet (And67–95), Fe-rich clinopyroxene (Hd81–87), and Mo-depleted scheelite (Sch97–98). The retrograde stage is characterized by Al-rich garnet (Grs40–66) and pure scheelite (Sch100), accompanied by hydrous and sulfide minerals. Minor subcalcic garnet with magnetite sometimes occurs in the limited endoskarns. Fluid inclusions of the early prograde minerals homogenize at 390.5 to >550 °C, and one inclusion in wollastonite has a salinity of 13.0 equiv. wt% NaCl. Inclusions in minerals of the late prograde and retrograde stages have homogenization temperatures of 196.9–377.4 °C and 160.4–291.4 °C, respectively; their salinities 2.4–19.0 equiv. wt% NaCl and 1.4–11.6 equiv. wt% NaCl, respectively. Accordingly, the high-temperature and moderate- to high-salinity fluids in the early skarn stages are typical of magmatic fluids originating granites, whereas the lower temperature and variable salinity in the later stages suggest mixing with meteoric water.

Magmatic evolution and source of a Proterozoic rapakivi granite complex in the North China Craton: New evidence from zircon U−Pb ages, mineral compositions, and geochemistry

Typical Proterozoic rapakivi granite of the Northern Hemisphere occur in Precambrian shield areas, and are commonly associated with anorthosites, mangerites, and charnockites, thus belonging to the AMCG (anorthosite–mangerite–charnockite–granite) suite. A similar suite is represented in the North China Craton (NCC) by the Shachang rapakivi granite and Damiao anorthosite complexes. The Shachang complex consists of amphibole–biotite rapakivi granite, porphyritic biotite granite, coarse-grained biotite granite, medium- to fine-grained biotite granite, and two-mica granite (listed from the earliest to the latest phases). New zircon U–Pb dating shows that the complex was formed over the period 1700–1682 Ma. The mafic minerals of the complex are calcic amphibole (ferroedenite–ferrohastingsite) and biotite (annite–siderophyllite), and the compositions of the amphibole suggest that the matrix of the amphibole–biotite rapakivi granite crystallized at a pressure of ∼4 kbar. The temperatures of crystallization, obtained from the compositions of amphibole, biotite, and zircon, decreased from ∼780 °C for the amphibole–biotite rapakivi granite to ∼660 °C for the two-mica granite. Our study of the Shachang complex indicates an evolution from early potassium-rich magmas to late silicon-rich magmas. The early amphibole–biotite rapakivi granite crystallized under relatively high temperatures (760–780 °C) and low fO2, while the later rocks formed under lower temperatures (760–660 °C) and high fO2. The Shachang rapakivi granite and Damiao anorthosite complexes contain different mafic minerals and show diverse trace element ratios and disparate geochemical evolutionary trends, suggesting different sources. Zircon Lu–Hf and whole-rock Sm–Nd isotopic data for the Shachang complex are relatively homogeneous, with εHf(t) and εNd(t) values varying from −9.8 to −3.3 and −6.4 to −3.4, respectively. Corresponding two-stage Hf model ages and Nd depleted mantle model ages vary from 2650 to 2850 Ma and from 2480 to 2840 Ma, respectively. These model ages are similar to the ages of Neoarchean lower crustal metamorphic rocks in the NCC (2500–2800 Ma). In addition, the compositions of the amphiboles and biotites in the granite in the Shachang complex indicate derivation from the crust. All the evidence points to the Shachang rapakivi granite complex having been formed from magmas derived from the lower crust of the NCC, rather than from the fractionation of mantle-derived mafic magmas with minor crustal contamination. This paper provides a detailed case study of the Shachang complex that will further our understanding of the sources of Proterozoic rapakivi granite in the Northern Hemisphere that belong to the AMCG suite of rocks.

The Durulgui rare-metal granite‒pegmatite system in the eastern Transbaikal region: Petrological and geochronological aspects

The Durulgui granite‒pegmatite system unites the Dedova Gora granite massif and pegmatite field with the Chalotskoe beryl deposit. New geochronological data on micas from porphyric biotite granites, fine-grained biotite granites, two-mica granites, and Be-bearing pegmatites are discussed. The plateau age of 128.5(±1.5)–131.2(±1.5) should be considered as indicating the formation time of the granite‒pegmatite system as a whole. The age of the system implies the possibility of its formation owing to several magmatic pulses. This assumption concerns porphyric and fine-grained biotite granites and two-mica and muscovite granites, the contact between which is locally sharp. At the same time, the succession “two-mica granites → muscovite granites → granite‒pegmatites → microcline pegmatites → microcline‒albite pegmatites → albite pegmatites” demonstrates gradual facies transitions between rocks, which indicates their emplacement during a single magmatic pulse.

전암대자율을 이용한 여주 고달사지 원종대사탑비 비신의 복제용 석재 선정 연구

여주 고달사지 원종대사탑비는 과거 도괴되어 현재 귀부와 이수는 여주 고달사지에 남아있고 비신은 파손된 채 국립중앙박물관에 보관되어 있다. 탑비를 구성하는 암석은 두 종류로, 귀부와 이수는 조립질 흑운모화강암, 비신은 부분적으로 각섬석 집합체와 2~3 cm 크기의 장석반정이 특징적으로 관찰되는 세립질 흑운모화강암이다. 귀부와 이수의 조립질 흑운모화강암은 여주 일대에 분포하는 흑운모화강암과 전암대자율 및 암석기재적 특징이 매우 유사하다. 반면 비신의 암석은 이 지역 내에서 산출되는 암석과 다소 차이가 있어 국내 화강암의 전암대자율, 암석학적 특징, 탑비의 금석문과 고려시대 고문헌 기록을 토대로 유사한 암석의 산출지를 탐색하였다. 이 결과 북한 해주 지역의 화강암이 색상, 각섬석 집합체, 광물조성, 전암대자율 분포 등에 있어 비신의 세립질 흑운모화강암과 거의 동일하였다. 따라서 해주 화강암이 탑비 암석의 산지암석으로서 가능성이 가장 크며, 원종대사탑비 비신을 복제하기 위한 석재로 가장 적합한 것으로 판단된다. The Stele for Buddhist Monk Wonjong at Godalsa Temple Site was destroyed a long time ago. Only the tortoise-shaped pedestal and the ornamental capstone in the form of a hornless dragon remain at the site and the broken stele body is stored at the National Museum of Korea today. The stele is made of two kinds of rocks that are coarse-grained biotite granite for the pedestal and the capstone, and fine-grained biotite granite including hornblende assemblages and feldspar phenocrysts for the stele body. The coarse-grained biotite granite of the pedestal and capstone showed same magnetic susceptibility and lithological characteristics with biotite granite outcrops in Yeoju area, whereas the fine-grained granite of the stele body did not. To find a provenance of the stele body stone, we investigated Korean granites in terms of magnetic susceptibility, lithology and old recordings about construction process of the stele. As a result, Haeju granite is the most likely to be a cognate rock of the stele body stone as it has same texture and lithological characteristics like color, hornblende assemblages, mineral composition and magnetic susceptibility. It is imported from Haeju (North Korea) to South Korea via China commercially, and the most suitable for a replica stone of the stele body.

A study on the Dushiling tungsten-copper deposit in the Miao’ershan-Yuechengling area, Northern Guangxi, China: Implications for variations in the mineralization of multi-aged composite granite plutons

The polymetallic Dushiling W-Cu deposit is a large, altered, skarn-type deposit, located in the northeastern part of the Miao’ershan-Yuechengling pluton, China. Two types of granite have been identified in the deposit: a medium-grained porphyritic biotite granite, and a medium- to fine-grained biotite granite. Both are spatially and temporally related to ore bodies, suggesting they may be the source of mineralization in the deposit. A medium- to fine-grained porphyritic biotite granite is exposed at the surface in the region of mineralization. U-Pb dating of zircons yielded magmatic ages of 423 Ma for the medium-grained porphyritic biotite granite and 421 Ma for the medium- to fine-grained porphyritic biotite granite, while a younger age (217 Ma) obtained for surface samples indicates later diagenesis. Thus, magmatism occurred during the Caledonian and Indosinian, respectively. The petrological and geochemical characteristics of the two Caledonian granites show that both are calc-alkaline and peraluminous. They are moderately enriched in Cs, Rb, U, and REE, and strongly depleted in Sr,Ba,P,and Ti; they show similar REE behavior, including negative Eu anomalies. These geochemical similarities suggest that the two granites were derived from the same source, although they were emplaced during different stages of the evolution of the magma. Furthermore, the granites are associated with mineralization, suggesting they were the source of mineralization in the Dushiling W-Cu deposit. Sm-Nd ages of scheelite from the Dushiling W-Cu deposit indicate that metallogenesis occurred at 417±35 Ma, while the two types of titanite, intergrown with scheelite, yield U-Pb ages of 423–425 Ma (in altered granite sample) and 218 Ma (in skarn sample). These ages place the main mineralization event in the late Caledonian, and later magmatic-hydrothermal activity occurred in the Indosinian. The ages obtained for the Dushiling W-Cu deposit in the western Nanling Range, northern Yuechengling, together with the occurrence and ages of the Niutangjie W deposit in southern Yuechengling, provide insight into the process of ore concentration during the Caledonian and Indosinian.

Temporal consistency between granite evolution and tungsten mineralization in Huamei'ao, southern Jiangxi Province, China: Evidence from precise zircon U–Pb, molybdenite Re–Os, and muscovite 40Ar–39Ar isotope geochronology

The large Huamei'ao tungsten deposit, with total WO3 reserves of 67,400tons at an average grade of 1.334% WO3, is located in the convergent zone of the eastern Nanling E–W-trending tectono-magmatic belt and the western Wuyishan NNE–SSW-trending tectono-magmatic belt in southern Jiangxi Province, China. The tungsten mineralization in this deposit is mainly found in quartz–wolframite veins, with most orebodies distributed at the outer contact zone between concealed Late Jurassic granitic stocks and Sinian weakly metamorphosed sandstones and phyllites. Zircons collected from medium- to fine-grained biotite granite in a diamond drill hole at a sea level of ca. −10m yield a crystallization age of 159.9 (±1.2) Ma through laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA–MC–ICP–MS) U–Pb dating. Molybdenite and muscovite that were both separated from quartz–wolframite veins yield a Re–Os isochron age of 158.5 (±3.3) Ma and an 40Ar–39Ar weighted plateau age of 157.9 (±1.1) Ma, respectively. These dates, obtained via three independent geochronological techniques, constrain the ore-forming age of the Huamei'ao deposit and link the genesis of the ore and the underlying granite. Analyses of available high-precision zircon U–Pb, molybdenite Re–Os and muscovite 40Ar–39Ar radiometric ages of major W–Sn deposits in southern Jiangxi Province indicate that there is no significant time interval between W–Sn mineralization and its intimately associated parent granite emplacement (interval of 0–6Ma). These deposits formed over three intervals during the Mesozoic (240–210, 170–150, and 130–90Ma), with large-scale W–Sn mineralization occurring mainly between 160 and 150Ma. The majority of W–Sn deposits in this region are located in southern Jiangxi and southern Hunan provinces.

Hydro-geoelectric study of Ijare town, southwestern Nigeria

Geoelectric study involving fifty four (54) Vertical Electrical Soundings (VES) has been undertaken within Ijare, southwestern Nigeria with the aim of evolving the hydrogeologic setting of the town. Ijare is underlain by the Precambrian Crystalline Basement Complex rocks with inhabited parts of the town underlain by migmatite gneiss and fine-grained biotite granite while inselbergs of older granites suites adjoins the town on all sides. Based on the hydro-geoelectric characteristics obtained from geoelectric sections and maps, the study area is classified into low, moderate and high groundwater potential zones. Four geoelectric subsurface layers delineated from the study are the topsoil, weathered basement, fractured basement and the presumably fresh bedrock. The concealed ‘basement complex’ morphology is rugged in the town with concealed ridges underlying the central areas while the eastern and northwestern areas are underlain by irregular concealed depressions. The zones of concealed basement depressions with resultant significant overburden thickness constitute target areas for groundwater development in the town. Arising from the general classifications undertaken using the results of the geoelectric soundings, sustainable groundwater development schemes for Ijare is considered feasible on the eastern and northwestern flanks where groundwater potential rating varies from moderate to high. Key words: Geoelectric, groundwater, basement, ridge, depression, overburden, fracture.

Variscan granitoid plutonism in the Strzelin Massif (SW Poland): petrology and age of the composite Strzelin granite intrusion

Petrological data and recently published U/Pb zircon SHRIMP ages reveal a protracted Variscan magmatic evolution in the Strzelin Massif (SW Poland), with three main stages of granitoid plutonism: 1 – tonalitic I, 2 – granodioritic and 3 – tonalitic II/granitic. The granitoids of the second and third stages form the Strzelin intrusion that is composed of three varieties: medium-grained biotite granite, fine-grained biotite granite and fine-grained biotite-muscovite granite. New SHRIMP data show that the medium-grained and fine-grained biotite granites comprise different zircon populations that reflect complex and prolonged plutonic processes. Two distinct magmatic events seem to be represented by well-defined zircon populations with apparent 206 Pb/ 238 U ages of 303 ± 2 Ma in the medium-grained biotite granite, and 283 ± 8 Ma in the fine-grained biotite granite. These dates, however, do not necessarily reflect the true magmatic ages, possibly being “rejuvenated” by radiogenic lead loss in zircons (impossible to resolve based on routine SHRIMP data). Based on field evidence, the third variety, the biotite-muscovite granite, postdates both types of biotite granites. The petrographic and geochemical features, including Nd isotope signature, along with various zircon inheritance patterns and ages, suggest that the parental magmas of the three granites originated from different crustal sources and were emplaced during three successive magmatic pulses.

Sequential granite emplacement: a structural study of the late Variscan Strzelin intrusion, SW Poland

The Strzelin Massif in SW Poland (Central European Variscides) records a protracted igneous evolution, with three main magmatic stages: (1) tonalitic I, (2) granodioritic and (3) tonalitic II/granitic. In the northern part of this Massif, the Strzelin intrusion proper comprises three successively emplaced rock types: a medium-grained biotite granite (303 ± 2 Ma), a fine-grained biotite granite (283 ± 8 Ma) and a fine-grained biotite-muscovite granite; based on field evidence, the third variety postdates both types of the biotite granites. The structural data from the three granites, including their parallel, approximately E–W striking and steeply dipping lithological contacts and ENE–WSW trending subhorizontal magmatic lineations, suggest that the emplacement of all three successive granite varieties was controlled by an active, long-lived strike-slip fault, striking ESE–WNW, with a dextral sense of movement. After the emplacement of the youngest biotite-muscovite granite, the intrusion underwent brittle extension which produced “Q joints” striking NNW–SSE to N–S and dipping at 55–70° WSW to W, and showing evidence of broadly N–S directed sinistral displacements. The structural observations, supported by new geochronological data, indicate that the internal structure of the composite granitoid intrusion, including the faint magmatic foliation and lineation, formed in a long-lived strike-slip setting, different from the subsequent, post-emplacement extensional tectonics that controlled the development of brittle structures.