Alkali Feldspar Granite Research Articles

Petrogenesis of the early Jurassic Ora batholith in south‐western Cambodia

The Ora batholith in south-western Cambodia is situated in the western part of Indochina and east of the Inthanon–Bentong–Raub Palaeo-Tethys suture and thus bears significant constraints for the equivocal crustal generation of the Palaeo-Tethys orogenic belt in Mainland South-east Asia. The Ora batholith consists of monzonitic granite (Group 1), alkali-feldspar granite (Group 2), and biotite granite (Group 3), and they yield similar Early Jurassic ages of 186.0–199.7 Ma. Group 2 are high-silica (SiO2 > 75 wt%) rocks with lower TiO2, Al2O3, FeOtot, MgO, CaO, P2O5, Eu, Ba, Sr, P, and Ti contents compared to those of the other two groups. Group 2 and 3 are classified as fractionated-type granitoids, whereas Group 1 is unfractionated granite as the complementary residual of the fractionated rocks. All groups have positive εHf(t) values from +2.29 to +8.83, suggesting they were cogenetic and derived from partial melting of the lower crust with the addition of asthenospheric mantle material. Integrating with other granitoids in this region, we suggest the Ora granitoids belong to I-type granitoids. Our petrogenetic and zircon U–Pb age data suggest the Ora granitoids were related to the Early Jurassic post-collisional magmatism that resulted from crustal thickening and mantle lithospheric delamination due to a denser crustal root than the underlying mantle lithosphere after the Palaeo-Tethys Ocean closure and collision between the Sibumasu and Indochina terranes. Then the following upwelling of the asthenospheric mantle not only heated and caused partial melting of the lower crust and mantle wedge, but also supplied asthenospheric material to generate the high-εHf(t) magma.

Evolution of amphiboles of the Serra do Catu intrusive suite: Crystallization conditions of Ediacaran shoshonitic rocks in the sergipano orogenic system, NE Brazil

The Ediacaran shoshonitic Santa Maria, Monte Pedral, Bom Jardim, Niterói stocks, and the Curituba batholith, belonging to the Serra do Catu Intrusive Suite, occur in the Canindé and Poço Redondo domains, in the northern region of the Sergipano Orogenic System, located in the northeast of Brazil. These intrusions occur over a wide region, have different shapes and sizes, and consist of quartz-monzonite, monzogranite, quartz alkali feldspar syenite, alkali feldspar granite, and dioritic enclaves. Calcic amphibole is the dominant mafic mineral in these rocks. Magmatic amphibole corresponds to magnesio-hornblende, edenite, magnesio-hastingsite, hastingsite, and tschermakite, while post-magmatic amphibole consists of actinolite. The amphiboles in these intrusions have similar compositions as those crystals formed in alkaline and subalkaline magmas, a typical characteristic of shoshonitic series magmas. Geothermobarometers were tested and the most convenient, those that consider a greater number of chemical elements, one was selected for the type of magma/rock studied. It was inferred that the primary crystals were formed from mantle magmas and mixed magmas (mantle + crustal). These crystals were formed under high oxygen fugacity. The bodies of the studied suite were emplaced under different temperatures, pressures, and depth conditions: Santa Maria stock (808 °C; 470 MPa; 14.6 km), Niteroi stock (801 °C; 550 MPa; 17 km), Curituba batholith (879 °C; 740 MPa; 22.9 km), Bom Jardim enclaves stock (877 °C; 860 MPa; 26.6 km), and Curituba batholith enclaves (912 °C; 970 MPa; 30 km).

Nb-Zr enrichment in Jabal Al Bayda A-type granites, western Arabian Shield, Saudi Arabia: interplay of magmatic and hydrothermal processes

Al Bayda’s younger granitic pluton located within the western Arabian Shield, Al Madinah area, KSA, has been studied using collaborative techniques. The collected samples were studied petrographically using a polarizing microscope and geochemically using the XRF technique. Four suites of intrusions can be distinguished based on their mineralogical and geochemical characteristics. A muscovitized epidotize hornblende leucocratic altered granite is the earliest intrusion, followed by perthite alkali feldspar granite. Both are intruded by a chessboard-like texture, Arfvedsonite-aegirine nepheline peralkaline granite. These three types of younger granitoid rocks are intruded by pegmatite-aplite sheets. The metasomatically altered epidotized, muscovitized granite formed during a late magmatic phase that was probably followed by successive co-magmatic and hydrothermal alterations in a closed system. The metasomatic alteration produced enrichment in Zr (up to 699 ppm), Nb (up to 67 ppm), and REE (up to 261 ppm) contents. As a result, residual alkalis, fluoride complexes, and iron-rich mixing fluids contribute to these enrichments. The hypersolvus perthite alkali feldspar exhibited post-orogenic A-type geochemical characteristics, whereas the peralkaline exhibited an anorogenic affinity, and both have been generated within plate-related tectonic settings. An A-type signature is probably the result of melting in the lower crust, whereas tectonic mechanisms shifted from post-orogenic to anorogenic due to the Najd fault system. Utilizing Al Bayda granite placer deposit products in the ceramic industry requires removing zircon minerals. The recorded HFSE, Nb, and REE are also recommended for detailed exploration.

Cancer Risk Assessment and Geochemical Features of Granitoids at Nikeiba, Southeastern Desert, Egypt

Different rock types (syenogranite, alkali feldspar granite and quartz syenite intruded by microgranite dikes and quartz veins) were investigated in the Nikeiba region in Egypt. The main components of the studied intrusive rocks, comprised of granites and quartz syenite, are plagioclase, amphibole, biotite, quartz and K-feldspar in different proportions. Ground gamma ray measurements show that syenogranite, quartz syenite and microgranite dikes have the highest radioactivity (K, eU, eTh and their ratios) in comparison with alkali feldspar granite. Geochemically, syenogranite, alkali feldspar granite and quartz syenite are enriched with large-ion lithophile elements (LILE; Ba, Rb, Sr) and high field-strength elements (HFSE; Y, Zr and Nb), but have decreased Ce, reflecting their alkaline affinity. These rocks reveal calc–alkaline affinity, metaluminous characteristics, A-type granites and post-collision geochemical signatures, which indicates emplacement in within-plate environments under an extensional regime. U and Th are increased in syenogranite and quartz syenite, whereas alkali feldspar granite shows a marked decrease in U and Th. The highest average values of AU (131 ± 49 Bq·kg−1), ATh (164 ± 35) and AK (1402 ± 239) in the syenogranite samples are higher than the recommended worldwide average. The radioactivity levels found in the samples are the result of the alteration of radioactive carrying minerals found inside granite faults. The public’s radioactive risk from the radionuclides found in the investigated granitoid samples is estimated by calculating radiological risks. The excess lifetime cancer (ELCR) values exceed the permissible limit. Therefore, the granitoids are unsuitable for use as infrastructure materials.

Mid-Neoproterozoic tectonic evolution of the northern margin of the Yangtze Block, South China: New insights from high-temperature magma events

Numerous Neoproterozoic intrusive rocks are distributed along the northern margin of the Yangtze Block in South China, and their petrogenesis and tectonic setting remain the subject of debate. This study systematically compiled data from igneous rocks from the northern margin of the Yangtze Block, including abundant felsic plutons with formed temperatures of >800 °C. The data reveal two high-temperature rifting-related events at ~830–780 and 750–700 Ma. Significant changes in Hf-O isotopes appeared at ~790 Ma, with later rocks exhibiting positive εHf(t) and low δ18O. To clarify the nature and tectonic significance of these high-temperature events, we sampled plutonic rocks from the Lianghekou (LHK) and Dalanggou (DLG) areas of Hannan, on the northern margin of the Yangtze Block. The samples from LHK are ~785 Ma monzogranite emplaced towards the end of the first high-temperature event and derived from partial melting of thickened juvenile crust contaminated by older crustal material. These rocks have εHf (t) values between +4.6 and + 11.5, δ18O values between +6.2‰ and + 7.3‰, and contain residual combinations of garnet, clinopyroxene, rutile, and amphibole. The genesis of the monzogranite is interpreted as being emplaced in an initial rifting environment and related to a super mantle plume. The DLG samples are ~743 Ma alkali feldspar granite representing the second event; they have the geochemical characteristics of a reduced A-type granite enriched in Fe and poor in Mg, FeOT/(FeOT + MgO) values close to 1, and emplacement temperatures of 813 °C–848 °C. The alkali feldspar granite originated from partial melting of a tholeiitic source and was influenced by extensive fractionation. It has εHf(t) values of +2.5 to +10.9, δ18O values of +6.6‰ to +7.4‰, and contains residual plagioclase. The DLG alkali feldspar granite and nearby reduced A-type granite indicate that the northern margin of the Yangtze Block experienced a low oxygen fugacity environment at ~817–743 Ma. The second high-temperature event possibly reflected rifting that gradually matured after 790 Ma, at which point the mantle changed from a source of heat alone into a source of both heat and material.

Prognostic Exploration of U-F-Au-Mo-W Younger Granites for Geochemical Pathfinders, Genetic Affiliations, and Tectonic Setting in El-Erediya-El-Missikat Province, Eastern Desert, Egypt

Younger granite bodies form two arches, the western and the eastern (WA, EA), which extend from the south northwards from the Meatique, ophiolitic group-island arc rocks, to the large older granite outcrop to the north. This paper concerns the feasibility of exploration in the El-Erediya-Ria El-Garah-El-Gidami-El-Missikat Y Gr regions. Fieldwork and remote sensing, together with geochemical, petrochemical, and mineralogical studies, are used to show the controlling factors, routes, and the origins of the deposits. Remote sensing is used to delineate the different rock units. Normal and strike–slip NW, NNE faults, veins, fractured ENE shear zones, and alteration zones of magmatic-hydrothermal fluids are discussed. Granites are considered using petrochemical diagrams as resources. These rocks are categorized as syeno- and alkali feldspar granites. Geochemical binary relationships recognized the granites are highly fractionated calc-alkaline-altered Monzo-, syeno-, and alkali feldspar granites formed in the active continental margin. The observed positive Ga vs. Cu, Zn, and Ni correlations are used for epithermal-magmatic-hydrothermal polymetallic veins and mineralized greisen zones. Negative Cu vs. Mo correlation patterns show probable Mo-porphyry deposits in the deeper zones at the contact point between porphyritic perthite and perthite granitic El-Erediya mass. The Zr/Sr between 1.65 to 2.93 plus fluorites in El-Missikat and up to 5.48 plus fluorites in El-Erediya show both U-poor at El-Missikat and U-rich deposits at El-Erediya. The recorded U, Th, Cu, and Pb vertical zoning sequence of deposition differentiates U aureole and deposit zones. The estimated lateral zoning sequences of deposition of these elements define the centers of U deposits. Pathfinders for the deposit of the examined area include the positive Fe2O3 vs. Mg O and Fe2O3 vs. Ca O correlations, and also negative Rb/Sr vs. K/Na and Rb vs. Sr ones, can be applied to future prospecting for similar U-F-Au-W-Mo deposits in the Eastern Desert of Egypt.

Ridge subduction and episodes of crustal growth in accretionary belts: Evidence from late Paleozoic felsic igneous rocks in the southeastern Central Asian Orogenic Belt, Inner Mongolia, China

Abstract The Central Asian Orogenic Belt (CAOB) is one of the largest accretionary orogens on Earth and preserves evidence that more than 50% of this orogen represents juvenile crustal growth over an extended period of some 750 million years from ca. 1000 Ma to ca. 250 Ma. However, the mechanism of crustal growth is controversial, as implied by a variety of proposed models ranging from contributions of mantle-derived basaltic underplating in a post-collisional extensional setting to subduction-related processes in an island arc setting. To distinguish among these models, we report petrological, geochemical, whole-rock Sr-Nd isotope and zircon U-Pb and Hf isotope analyses of late Paleozoic felsic igneous rocks from the northern Inner Mongolia region, southeastern CAOB. New zircon U-Pb analyses of three plutonic and extrusive magmatic suites yield Late Carboniferous to Early Permian ages of 319–279 Ma. The Xi Ujimqin granodiorites have low-K tholeiitic to calc-alkaline, metaluminous to weakly peraluminous compositions, and are magnesian I-type granitoids. These granitoids are also characterized by relatively high MgO and Sr contents, high Mg# values, mid-ocean ridge basalt (MORB)-like Nd-Hf isotope compositions and young Nd-Hf model ages of 600–298 Ma. These features indicate that the parental magmas of the Xi Ujimqin I-type granitoids originated from a depleted lithospheric mantle that had been metasomatized by fluids released from a subducting slab. By contrast, the Xilinhot alkali-feldspar granites and Dashizhai rhyolites display geochemical signatures of ferroan granites. These, together with their moderately depleted Nd-Hf isotope compositions and young Nd-Hf model ages of 809–277 Ma, suggest that they were produced by re-melting of juvenile lower crust via underplating of mantle-derived magmas. The coexistence of an association of boninite-adakite-high-Mg andesite-Nb-enriched basalt, and MORB to ocean island basalt-type mafic rocks in the northern Inner Mongolia region implies a dramatic change in composition from fluid-related calc-alkaline arc magmatism to melt-related and mantle-derived magmatism initiated by upwelling asthenosphere. We infer that ridge subduction may have occurred in this region during Late Carboniferous to Early Permian. Combined with previous studies, there are two ridge subduction events during the early and late Paleozoic in Inner Mongolia within the southeastern CAOB, which coincide with two large-volume magmatic flare-ups (300 ± 20 and 450 ± 20 Ma). Furthermore, our model calculations suggest that most of the juvenile crust in the southeastern CAOB was generated in a relatively short interval (~20–40 m.y.) during each long-lived tectonic cycle (>140 m.y. spanning oceanic rifting, subduction, and collision) of magmatic activity. Ridge subduction may have played a significant role in the rhythmic growth of juvenile crust in the CAOB during the Phanerozoic. Repeated cycles of punctuated, rapid growth of juvenile crust associated with long-lived subduction systems represent a pattern that may be generalized to other Phanerozoic accretionary belts on Earth.

Natural Radioactivity and Radiological Implications of Stream Sediments at Wadi Aidib Area, South Eastern Desert, Egypt

Wadi Aidib lies at the extreme southern part of the Eastern Desert, Egypt, between 22o15'- 22o21' N and Longitudes 36o20'-36o30' E. Landsat ETM+ false color composite image (bands 3, 2, 1) was used for regional discrimination for different rock types and provide an excellent base map for the study area, morphological features of the stream deposits of the study area were known from Landsat ETM images, in addition to several field observations. The studied stream sediments accumulate in the form of alluvial fans. They are mainly composed of sands, gravels, boulders and contain some heavy valuable minerals which are derived from metavolcanics, metasediments, quartz diorite, biotite and alkali feldspar granites. Heavy liquid separation and magnetic separation techniques in addition to microscopic examination for the studied stream sediment samples were applied to identify the heavy minerals in these sediments. These minerals are represented by magnetite, ilmenite, rutile, garnet, zircon, monazite and Green silicates. The distribution of some elements in the study area is clear that they are concentrated near the outcrops of granites. The radionuclide concentrations were measured in different stations using a calibrated gamma-ray portable detector (RS 230) and the heavy minerals causing radioactivity were separated by heavy liquids and determined by binuclear and environmental scanning electron microscopes. Uranium ranges between 5.25 and 32.05 ppm with an average of 16.63 ppm, Th between 4.4 and 17 ppm with 11.34 ppm as an average and potassium fall between 1.8 and 5.15% with an average of 3.4 %. Correlation between soil radioactivity and its mineralogical content indicate that the high radionuclides contents are mainly attributed to the presence monazite which is the principal source of both uranium and thorium. Uranium high concentrations could be related to the metamict zircon. Absorbed Dose Rate (D), annual effective dose equivalent radium equivalent activity, external and internal hazard index, in addition to activity gamma index caused by gamma emitting natural radionuclide are determined from the obtained values of 238U, 232Th and 40K. Fairly, some of the studied stations do not satisfy the universal standards. 40K plays the main and most important role in dose rate contribution.

Statistical analysis on the radiological assessment and geochemical studies of granite rocks in the north of Um Taghir area, Eastern Desert, Egypt

Abstract Granite rocks are currently one of the foremost raw materials that can be used for various economic purposes such as ornamentation and building materials, because they do not possess radioactive concentrations and have good physical and mechanical properties. The granite rocks of north Um Taghir are connected to neoproterozoic rocks and integrated to the north Arabian-Nubian Shield (ANS), which lies in Northeast Africa. Inductively coupled plasma mass spectrometry (ICP-MS) and X-ray fluorescence analysis, concurrent to some statistical analysis, have been carried for major oxides and some trace elements to extract much fundamental information by following certain mathematical methods. The exposed granite rock units in north Um Taghir are classified into four rock units represented by tonalite, granodiorite, monzogranite, and alkali-feldspar granite which are cut by different types of dikes. The magma of tonalite and granodiorite is low-to-medium K calc-alkaline affinity, while the magma of monzogranite and alkali-feldspar granite is medium-to-high K calc-alkaline affinity, and of metaluminous to peraluminous nature. Granite rocks show a slightly depletion of fractionated patterns from light rare earth elements (LREEs) to heavy rare earth elements (HREEs) with slightly positive to negative Eu anomalies from tonalite to monzogranite and alkali-feldspar granites. The statistical criteria have been achieved to explore the significant differences of radiological hazard parameters among samples. It is obvious that there is no homogeneity among samples; furthermore, in Kruskal–Wallis test, Mann–Whitney test, and Pearson correlation coefficient, it can be noticed that there are significant differences between each pair of samples: tonalite, monzogranite; tonalite, alkali-feldspar granite; granodiorite, monzogranite; and granodiorite, alkali-feldspar granite. There is a strong direct relationship among granodiorite and both tonalite and alkali-feldspar granite, and among alkali-feldspar granite and tonalite and granodiorite. There is a strong inverse relationship among monzogranite and tonalite, granodiorite, and alkali-feldspar granite. As stated by all results, it can be mentioned that the granite rocks have a worthy result of mechanical and physical properties. So that they can be used for various economic purposes.

Carboniferous to Early Permian magmatism in the Uliastai continental margin (Inner Mongolia) and its correlation with the tectonic evolution of the Hegenshan Ocean

This study presents a comprehensive analysis of zircon U–Pb–Hf isotopic and whole-rock geochemical data of Carboniferous–Early Permian felsic igneous rocks from the Uliastai continental margin (UCM), southeastern Central Asian Orogenic Belt, to constrain the amalgamation of the Inner Mongolia–Daxing'an Orogenic Belt (IMDOB) in the late Paleozoic. Zircon laser ablation inductively coupled plasma mass spectrometry UPb ages of monzogranite, granite porphyry, felsic volcanic rock, and alkali feldspar granite reveal three stages of magmatism in the Early Carboniferous (ca. 336–320 Ma), Late Carboniferous (ca. 311–307 Ma), and Early Permian (ca. 298 Ma). The Early Carboniferous igneous rocks, including monzogranites and later granite porphyries, exhibit affinity with the high-K calc-alkaline highly fractionated I-type granite, and are depleted in high-field-strength elements and enriched in large-ion lithophile elements. Their zircon εHf(t) values of the Early Carboniferous rocks range from +4.6 to +9.1, indicating that they were generated by partial melting of the juvenile crustal materials in a north-dipping subduction-related environment along with the opening of the Hegenshan Ocean. The Late Carboniferous felsic volcanic rocks are highly fractionated high-K calc-alkaline to alkali-calcic I- and A-type granitoids, with relatively strong peraluminous affinities. Considering the zircon εHf(t) values (+6.2 to +10.6) and relatively low Rb/Ba (0.71–3.57) and Rb/Sr (4.18–8.12) ratios, they were likely derived from a juvenile crust and are comparable to partial melts of clay-poor but plagioclase-rich metaigneous rocks. Notably, the A-type granitoids are gradually increasing in the UCM after 311 Ma, and these magmatic rocks have markedly increased zircon saturation temperatures and (K2O + Na2O)/CaO ratios. These changes may result from the slab break-off of the Hegenshan Ocean, and the Late Carboniferous felsic volcanic rocks were formed in a post-collisional setting. The Early Permian alkali feldspar granites are characterized by typical A-type granite geochemistry, with high Ga/Al ratios; low MgO, Cr, Co, and Ni contents; and high zircon saturation temperatures. These rocks have positive εHf(t) values of +10.2 to +12.7 and record an intracontinental extension setting. In combination with the regional geology, the Late Carboniferous post-collisional magmatic rocks suggest that a change from a subduction-related continental margin to a post-collisional tectonic regime might have occurred in the UCM before 311 Ma.

Nb/Ta, Zr/Hf and REE fractionation in exotic pegmatite from the Keivy province, NW Russia, with implications for rare-metal mineralization in alkali feldspar granite systems

The White Tundra pegmatites are associated with the Keivy alkali feldspar granite complex in the Kola Peninsula, NW Russia. The host granites are aegirine-arfvedsonite, biotite-arfvedsonite and biotite-ferrohastingsite varieties, ranging compositionally from peralkaline through metaluminous to peraluminous. The pegmatites are remarkable for the diversity of the rare-metal mineralization. The inferred crystallization sequence of the main REE, HFSE and Ti minerals in the pegmatite is: zircon – fergusonite-(Y) – monazite-(Ce) – gadolinite-hingganite series – britholite-(Y) – astrophyllite – titanite – allanite-(Ce) –– chevkinite-(Ce) – ilmenite – kainosite-(Y) – REE carbonates. The pegmatites show unusual parageneses indicating a transition of the mineral associations from agpaitic to miaskitic in the same body (e.g. zirconosilicate → zircon; astrophyllite → titanite). A number of minerals have anomalous minor element contents. Astrophyllite and some titanites have low (even < 1) Nb/Ta and Zr/Hf ratios that contrast with the overall geochemical environment (ratios ≫ 1); titanite with very high Y and HREE contents; elevated Sn, W and V contents in some titanosilicates; allanite-(Ce) with very high Ti contents coupled with low (less than stoichiometric) values of Al, suggesting a Ti → Al substitution. Whole-rock compositions of the host granite show a steady decrease of Nb/Ta and Zr/Hf ratios in peralkaline through metaluminous to peraluminous types. Compositions of Ti minerals suggest that further fractionation of Nb-Ta, Zr-Hf and REE in the White Tundra exotic pegmatite and the crystallization of Ti minerals with anomalous compositions are due to a combination of several factors: assimilation by the primary magma (enriched in Zr, Nb, REE) of upper crustal lithologies enriched in Ta, Hf, LREE, W, Sn; consumption of significant amounts of Nb and Zr by early-crystallized pegmatitic fergusonite and zircon with Nb/Ta and Zr/Hf ≫ 1; transition of HFSE mineral assemblages in pegmatite from agpaitic to miaskitic with consequent lowering of Nb/Ta and Zr/Hf; crystallization of minerals in a low-temperature (hydrothermal) environment with changing F contents, that promoted a sporadic further decrease of Nb/Ta and Zr/Hf (to values < 1) and increase of Y + HREE. The implications of the fractionation mechanisms for ore-forming processes related to rare-metal granites are discussed.

Cassiterite U–Pb, mica 40Ar–39Ar dating and cassiterite trace-element composition of the Furong tin deposit in the Nanling Range, South China

The Furong tin deposit (530,000 t Sn @ 0.8% Sn) is located in the southern part of the Mid–Late Jurassic, multiphase, granitic Qitianling batholith in the Nanling Range, South China. The spectrum of tin mineralization comprises skarn, chloritized granite, greisen, and quartz vein types, of which the skarn type is the most important. Cassiterite U–Pb dating provided Tera-Wasserburg lower intercept ages of 157.1 ± 1.5 Ma and 156.3 ± 1.5 Ma for skarn-type mineralization, 158.1 ± 1.4 Ma and 158.7 ± 1.6 Ma for chloritized granite-type mineralization, 155.8 ± 3.4 Ma for greisen-type mineralization, and 160.1 ± 1.7 Ma for quartz vein-type mineralization. These ages overlap with each other and define a pooled weighted mean age of 157.9 ± 1.1 Ma (2σ) for the tin ore system. Hydrothermal phlogopite from tin skarn and muscovite from tin greisen yielded younger 40Ar–39Ar plateau ages of 154.3 ± 1.9 Ma and 150.0 ± 1.5 Ma, respectively, which may reflect resetting due to post-ore fluid circulation. Distinctive cathodoluminescence textures and trace-element patterns of various cassiterite types indicate that the four ore types resulted from pulsed ore-forming fluids and changes in temperature in a single magmatic-hydrothermal system. In combination with the geological characteristics, the geochronological and trace-elemental data of cassiterite indicate that the formation of different ore types at Furong was associated with the most fractionated and latest alkali-feldspar granite of the Qitianling batholith, and resulted from the specific interactions of the ore-forming fluids with their granite and limestone host rocks.

Role of uranium redistribution in radioactive heat production of granitic rocks, Northern Eastern Desert, Egypt

Granitoid intrusions traditionally form a focus for geothermal heat exploration, as granite is a major host for Heat-Producing Elements (HPE; U, Th & K). Airborne spectral gamma-ray data for the study area highlight variations in HPE abundances in granitic rock units, indicating variation in the Radioactive Heat Production (RHP) values of these rocks. The computed arithmetic means of RHP for granitic rocks range from 0.96 µWm−3 for tonalite-quartz diorite to 1.10 µWm−3 for granodiorite, followed by a gradual increase to 1.52 µWm−3 for monzogranite and 2.51 µWm−3 for alkali-feldspar granite. The major control on the distribution of U and Th elements in the granitoid rocks appears to have been primarily of magmatic differentiation and is reflected in the linear correlation between these elements. Besides, subsequent post-magmatic hydrothermal fluids play their important roles in remobilization of profitable secondary U-mineralizations to be trapped and enrichment in the alkali-feldspar granitic rocks.

Granitoids and trachytes of Um Shager-Hamadat area, Central Eastern Desert, Egypt: Remote sensing characterization and petrology

The late Neoproterozoic granitoids of Gebel Um Shager and Gebel Hamadat, Central Eastern Desert of Egypt, in addition to Paleozoic trachytes of both areas were discriminated using Landsat-8, and Sentinel-2 dataset. Band rationing and Principal Component Analysis techniques were applied. The studied granitoids represent the extreme end-members of the subduction-related I-type calc-alkaline granitic magmas (primitive to more evolved varieties) that developed over a long period of time. These granites were extruded by Paleozoic intra-plate trachytes. Petrography and petrogenesis of these rocks were dealt with and discussed. The Um Shager Older Granitoids (calcic tonalite to quartz monzodiorite) represent poorly differentiated metaluminous magma characterized by very low Rb/Sr ratio ∼0.07. Evolutionary, they follow the calc-alkaline subtype trend and most probably were originated from parent gabbroic magma by fractional crystallization in a volcanic arc setting. On contrary, the Hamadat Younger Granites represent alkali calcic magma which was developed in post-collision setting. They comprise evolved subsolvus metaluminous syenogranite and alkali feldspar granite. Evolutionary, they follow the subalkaline subtype trend. Crystallization courses of both syenogranite and alkali feldspar granite were started by alkali feldspar, followed by cotectic crystallization of alkali feldspar and quartz and ended by eutectic crystallization of all quartzofeldspathic minerals. The trachytes represent intra-plate continental alkaline magmatism. The Um Shager trachytes were developed at local extension zones, while the Hamadat trachytes were originated during global continental rifting system. Syenogranite, alkali feldspar granite and trachytes are important sources of alkali feldspar, which has wide spectrum applications in industry and agriculture.

Geologic Map of the Woodrock Quadrangle, Sheridan and Big Horn Counties, Wyoming

Here we present the results of detailed (1:24,000 scale) mapping of the Woodrock 7.5 Minute Quadrangle Wyoming, which mainly consists of Archean basement rocks of the Laramide Bighorn uplift. Our focus was on the Archean geology of the Laramide age Bighorn uplift. Isotopic age determinations (U-Pb on zircon) were conducted at the University of Arizona LaserChron Center. Our work revealed the presence of four different components of the batholith. The oldest unit is a ~2880 Ma foliated Lookout Mountain Granodiorite that occurs in the southern part of the quadrangle in the vicinity of Bruce and Lookout Mountains. The ~2775 Black Mountain Tonalite occurs in the northeastern part of the quadrangle. The age of the Black Mountain Tonalite and Lookout Mountain Granodiorite overlap but the units are distinct in terms of structure and lithology so they were mapped separately. The central part of the quadrangle is underlain by the massive, ~2860 Ma Taylor Mine Granite. This unit is poorly exposed and variable in texture. The youngest unit is the ~2850 Ma Owen Creek Alkali Feldspar Granite, which occurs in the western part of the quadrangle. Mafic dikes of variable geometry, texture and age cross-cut the quartzofeldspathic rocks. Less than 25 m of poorly exposed Cambrian Flathead Sandstone occurs along the extreme western margin of the quadrangle. We discovered as much as 30 m of Oligocene White River Formation strata occur as terrace deposits along the western side of the Tongue River in the central part of the quadrangle. The White River strata are poorly exposed and consist of thin bedded tuffaceous sandstone and massive conglomerate that are light colors and include as clasts Paleozoic carbonate and Archean basement rocks. Less than 50 m of Pinedale-age glacial tills occur along the upper Tongue River in the southern part of the Quadrangle, forming hummocky, poorly-drained topography. Quaternary alluvium occurs along some of the larger streams.

Petrology and kinematic vorticity constraints of the Al Amar region, Northern Ar-Rayn terrane, Eastern Arabian shield, Saudi Arabia

The Neoproterozoic basement rocks in Ar Rayn terrane set as parts in the Eastern Arabian Shield. It focus the petrological and kinematic vorticity for high deformed volcanic and granitoids rocks in the Al-Amar locality. The volcanic rocks divide into two main series, the eastern sequence cycle represents dacite, rhyodacite, rhyolite and ignimbrites, and the western sequence cycle characterizes andesite and pyroclastics. Furthermore, the granitoids rocks content monzodiorite, tonalite, granodiorite and alkali-feldspar granite. For assessing the proportions of pure and simple shear contributions in penetrative deformed rocks, the kinematic vorticity number (Wm) to the mean appreciation by applying porphyroclast, rotating in a flowing matrix is crucial. In the Ar Rayn terrane of Arabian shield, kinematic vorticity numbers for high deformed metavolcanics and granitoids gneisses vary from 0.4 to 0.6. The deformation in the studied area varied from simple shear, according to vorticity and strain studies. Nappe stacking getting ready during the thrusting activity only through the Al Amar –Idsas fault, according to the results, most likely due to brittle imbrication. A penetrative sub-horizontal foliation formed sub-parallel to the nappe contacts with the beneath laying nappes, showing that the ductile strain was superimposed on the construction of the nappe under high pressure. The Ar Rayn terranewas created sub-horizontal foliation by the buildup of ductile strain during under plating, which was induced by a vertical shortening component. This foliation was formed in the majority of cases during the thrusting nappes upon each other, implying that nappe stacking was related to vertical shortening due to a massive scale by the active Al Amar –Ideas fault.

Chronology and geochemical characteristics of the highly fractionated alkali feldspar granite from the Maodeng deposit in the southern Great Xing'an Range

毛登矿床位于内蒙古锡林浩特境内，是大兴安岭南段典型的钼铋锡铜矿床，产于阿鲁包格山杂岩体晚阶段侵位的碱长花岗岩和花岗斑岩以及下-中二叠统大石寨组火山角砾岩中。本文以碱长花岗岩为主要研究对象，开展了岩石地球化学、Sr-Nd-Hf同位素、锆石U-Pb定年和微量元素地球化学研究，以探讨成岩时代、岩浆结晶的物理化学条件及其对成矿的制约。研究显示，碱长花岗岩锆石结晶年龄为140.5±0.8Ma，侵位于早白垩世。岩体高硅，富碱，贫钙、镁、铝，富集Rb、F、Th、Nd、Sm、Zr和Hf等元素，亏损Eu、Ba、Sr、P、Nb、Ti和轻稀土等元素，轻、重稀土分馏较小，具稀土四分组效应。碱长花岗岩锆石Ti温度为654~817℃，Ce⁴⁺/Ce³⁺值为0.1~19，岩浆氧逸度lgf（O₂）为-25.7~-18.6，表明原生岩浆为高温、低氧逸度的熔体。岩体具较高的ε_Nd（t）值（-0.1~+2.9）和正的ε_Hf（t）值（+4.0~+9.3）以及年轻的二阶段模式年龄（t^Nd_DM2=699~940Ma；t_HfDM^C=600~936Ma），表明岩浆源区来自含大量幔源组分的新生地壳的部分熔融。碱长花岗岩经历了高度分异演化和熔体-流体作用，具高F、低氧逸度特征，是毛登矿区钼、铋、锡、铜金属矿化形成的重要先决条件。;Located in Xinlinhot of Inner Mongolia in the southern segment of Great Xing'an Range, the Maodeng deposit is a typical Mo-Bi-Sn-Cu deposit occurred in the alkali feldspar granite and granite porphyry in the late emplacement of Alubaogeshan complex, as well as the volcanic breccia of Lower-Middle Permian Dashizhai Formation. In this paper, whole-rock geochemistry, Sr-Nd-Hf isotope, zircon U-Pb age and trace element geochemistry of alkali feldspar granite have been studied, aiming to investigate the rock-forming age, the formation conditions, the significance for petrogenesis and metallogenesis. The zircon dating yields a weighted mean U-Pb age of 140±0.8Ma, which indicates the emplacement of the alkali feldspar granite took place during the Early Cretaceous. Geochemically, the alkali feldspar granite is characterized by high concentrations of SiO₂ and (Na₂O+K₂O), with low contents of CaO, MgO and Al₂O₃. The rock is enriched in Rb, F, Th, Nd, Sm, Zr and Hf, while depleted in Eu, Ba, Sr, P, Nb, Ti and LREE. It is especially characterised by a low LREE/HREE ratio, with a huge Eu depletion and a REE tetrad pattern. The zircon of the alkali feldspar granite shows high temperature (654~817℃) and low Ce⁴⁺/Ce³⁺ ratio (0.1~19), oxygen fugacity (lgf(O₂)=-19.6~-14.4) of the magma. The granite has relatively high ε_Nd(t) (-0.1~+2.9), positive ε_Hf(t) (+4.0~+9.3) and young two-stage Nd and Hf model ages (t^Nd_DM2=699~940Ma; t_HfDM^C=600~936Ma), suggesting that the rock is dominantly derived from the partial melting of a juvenile lower crust which was originated from source rocks or magma separated shortly from the upper mantle, followed by strong fractional crystallization during magma ascent. Based on the above reasearch, it is proposed that under the condition of relatively low oxygen fugacity and high temperature, the magma evolves by highly fractional crystallisation and melt-fluid interaction during the late stage. Therefore, it is believed that the alkali feldspar granite plays an important role in Mo-Bi-Sn-Cu mineralization in the Maodeng deposit.

Geochemical and geochronological constraints on the gold-sulfide mineralization and host granitoid rocks in the Bulghah and Al-Maham prospects, central Arabian Shield, Saudi Arabia

Among several gold-sulfide deposits and prospects scattered in the Afif terrane of the Arabian Shield, the Bulghah and Al-Maham prospects are investigated to assess the spatial and temporal relationships between gold mineralization and the host lithologies and regional structures. Both prospects are hosted by the sulfide-bearing Hulayfah Group metavolcano-sedimentary successions, and are confined to cross-cutting granitoid intrusions. Tonalite-granodiorite and monzogranite from the two areas have geochemical characteristics of metaluminous to weakly peraluminous calc-alkaline I-type granitoids. Younger alkali feldspar granite in the Bulghah area exhibits geochemical features of A-type granite, likely formed in a post-collisional or transitional setting. ID-TIMS dating of zircons from two granodiorite samples from the Al-Maham prospect yielded 206Pb/238U ages of ∼662 and 651 Ma. A tonalite sample from the Bulghah mine area gave a concordia age of 674.8 ± 0.8 Ma (2σ; MSWD = 0.42), whereas the alkali feldspar granite sample has an age of ∼ 631 ± 1 Ma. The newly defined ages can be considered as the upper age limit of the auriferous quartz veins, evidently attendant to the Nabitah orogeny (∼680–640 Ma). Gold-bearing quartz veins in the two prospects are identical in terms of ore mineralogy, textures and paragenesis. Gold-bearing quartz veins are associated with intersecting veinlets and stockwork of arsenopyrite, pyrite, and less common pyrrhotite, chalcopyrite, and sphalerite. Recrystallized pyrite and arsenopyrite are ubiquitous in quartz veins, whereas pyrrhotite-chalcopyrite intergrowths in-fills or replacements prevail in the deformed host metavolcanic rocks. Free gold typically occurs as fine inclusions in quartz veins, commonly in deformed pyrite and arsenopyrite crystals. The sulfides of Al-Maham prospect have significantly higher Re-Os concentrations (ppb level), compared with those in the Bulghah prospect, and define an isochron with a Model-1 age of 360 ± 2 Ma and an initial 187Os/188Os ratio of 1.962 ± 0.032. The obtained Re-Os age and the crustal initial Os isotope ratio do not necessarily define the primary age of gold mineralization since ore textures indicate that pyrrhotite was a paragenetically late sulfide phase in both prospects. Alternatively, this age may be interpreted as the time of remobilization and recrystallization of older sulfides in response to Hercynian uplift and deformation (370–290 Ma), manifested as intermittently rejuvenated reverse faults elsewhere in the Arabian Shield.

Petrogenesis and tectonic setting of the late Early Cretaceous Kong Co A-type granite in the northern margin of Central Lhasa Subterrane, Tibet

在中拉萨地块北部尼玛控错地区发育着一套碱性长石花岗岩，对该花岗岩体开展成因和形成背景的研究，能为探索班公湖-怒江洋的构造演化提供有价值的信息。用LA-ICP-MS方法测得该花岗岩的锆石²⁰⁶Pb/²³⁸U年龄加权平均值为104.9±1.4Ma （MSWD=1.5）和104.6±1.3Ma （MSWD=1.3），表明该岩体形成于早白垩世。花岗岩具有高硅（SiO₂=76.75%~77.51%，平均77.27%）、高钾（K₂O=4.61%~4.85%，平均4.77%）、高碱（K₂O+Na₂O=8.24%~8.57%，平均8.44%）、低钙（CaO=0.28%~0.48%，平均0.35%）、低镁（MgO=0.11%~0.16%，平均0.13%）和低铝（Al₂O₃=11.79%~12.22%，平均12.09%）等特征，里特曼指数（σ）为1.96~2.15（平均2.08），A/NK值为1.06~1.09，A/CNK值为1.01~1.04。这些特征表明控错花岗岩为弱过铝质的高钾钙碱性-钾玄岩系列岩石。控错花岗岩相对富集Zr、Nb、Ce、Y和Hf等微量元素，相对亏损Ti、Ba、Sr和P等微量元素，分异系数（DI）为95.5~96.9（平均：96.3），还具有较高的FeO^T/MgO值（5.61~10.22，平均7.26）、10000Ga/Al值（2.78~2.56，平均2.84）、Y/Nb值（2.29~4.97，平均3.57）、Rb/Nb值（11.6~18.2，平均15.2）；此外，该岩体还具有较高的全岩Zr饱和温度（875~910℃，平均890℃）和锆石Ti饱和温度（848~919℃，平均890℃），明显的Eu负异常（δEu=0.04~0.09，平均0.06），以及向右缓倾的Ⅴ型稀土元素配分曲线，这些特征表明控错花岗岩为产于碰撞后环境的A2型花岗岩。正的锆石ε_Hf（t）值（4.26~6.38，平均5.16）、相对年轻的锆石Hf地壳模式年龄（t_DM2=757~889Ma，平均833Ma）、下地壳与地幔混合特征的（⁸⁷Sr/⁸⁶Sr）_t（0.7194~0.7407，平均0.7313）、ε_Nd（t）（-3.39~-3.00，平均-3.24））和Pb同位素特征（（²⁰⁶Pb/²⁰⁴Pb）_t=18.792~18.845，（²⁰⁷Pb/²⁰⁴Pb）_t=15.708~15.718，（²⁰⁸Pb/²⁰⁴Pb）_t=38.870~38.037），指示控错花岗岩熔融于幔源物质加入的新生地壳。研究结果揭示，控错花岗岩形成于羌塘-拉萨地块碰撞作用下，俯冲板片的断离后，软流圈上涌诱发的地壳部分熔融，并经历了显著的以钾长石和角闪石为主的分离结晶作用。;A set of alkali feldspar granite develops well in the Kong Co of Nyima County in the northern margin of Central Lhasa Subterrane, Tibet, which can provide invaluable information to explore the geological evolution of the Bangong Co-Nujiang Ocean. The weighted averaged zircon ²⁰⁶Pb/²³⁸U ages of the granite measured by LA-ICP-MS are 104.9±1.4Ma (MSWD=1.5) and 104.6±1.3Ma (MSWD=1.3), respectively, indicating that it was formed in the late phase of Early Cretaceous magmatism. The rocks in Kong Co granite are grayish-white, with fine-grained equigranular structure and medium coarse-grained porphyritic-like texture. The rock-forming minerals mainly include quartz, potassium feldspar, plagioclase, and a small amount of transparent accessory minerals such as biotite and amphibole, as well as a few melanocratic mineral like magnetite. The granite is characterized by high contents of SiO₂ (6.75%~77.51%), K₂O (4.61%~4.85%), and K₂O+Na₂O (8.24%~8.57%), with low contents of CaO (0.28%~0.48%), MgO (0.11%~0.16%) and Al₂O₃ (11.79%~12.22%), and a Rittman index (σ₄₃) of 1.96~2.15 and A/CNK ratios of 1.01~1.04. These characteristics reveal that the Kong Co granite is weakly peraluminous high potassium calc-alkaline-potassium basalt series rock. The granite is relatively enriched in Zr, Nb, Ce, Y and Hf, and deficient in Ti, Ba, Sr and P. It shows a highly variation of index (DI:95.50~96.90), and also has high values of FeO^T/MgO (5.61~10.22), 10000Ga/Al (2.78~2.56), Y/Nb (2.29~4.97), Y/Nb (2.29~4.97), Rb/Nb (11.6~18.2), which is consistent with A2-type granites produced in post collision environment. In addition, the rock has high whole-rock Zr saturation temperatures (875~910℃) and zircon Ti saturation temperatures (848~919℃), with a significant negative Eu anomaly (δEu=0.04~0.09), and a Ⅴ-shaped rare earth element curve gently inclined to the right. These characteristics also prove the Kong Co granite is A2 type granite. They have relatively positive ε_Hf(t) values (4.26~6.38), and two-stage Hf model ages (t_DM2) ranging from 757Ma to 889Ma, with (⁸⁷Sr/⁸⁶Sr)_t=0.7194~0.7407 and ε_Nd(t)=-3.39~-3.00, and Pb isotopic ((²⁰⁶Pb/²⁰⁴Pb)_t=18.792~18.845, (²⁰⁷Pb/²⁰⁴Pb)_t=15.708~15.718, (²⁰⁸Pb/²⁰⁴Pb)_t=38.870~38.037) characteristics of lower crust-mantle mixture. These data indicate that the granite was sourced from interaction between mantle-derived and juvenile lower crust-derived melts. This occurred when the post collision extension of Qiangtang and Lhasa terranes the subduction plate split to create a slab window, and rising asthenosphere triggered re-melting of the lower crust basalt, resulting in the formation of the late Early Cretaceous A-type granite around Kong Co.

Mechanism of Nb and REE enrichment in the Tiemuli alkali-feldspar granite, Chongyi County, Jiangxi Province

华南是我国重要的战略性矿产资源基地，以花岗岩相关的稀有和稀土金属成矿作用而举世瞩目。其中，铌的成矿作用一般与过铝质高分异花岗岩有关，稀土元素则随岩浆演化程度增强而富集程度降低，而江西铁木里含黑云母碱长花岗岩体同时富集铌和稀土元素，矿化组合极具特色。本文在详细的矿物岩相学研究基础上，利用电子探针、飞秒激光电感耦合等离子质谱对铌和稀土矿物进行了矿物地球化学分析，借此对铁木里碱长花岗岩中铌和稀土元素的富集机制进行探讨。铁木里岩体由肉红色含黑云母碱长花岗岩（r-G）和灰白色含黑云母碱长花岗岩（g-G）组成，发育暗色包体。r-G中的铌矿物主要为岩浆期形成的铌铁金红石，稀土矿物包括岩浆期形成的硅钛铈矿、独居石、磷灰石和热液期形成的独居石和氟碳（钙）铈矿。g-G中的铌矿物包括岩浆期形成的铌铁金红石和热液期形成的铌铁金红石、易解石、铌铁矿，稀土矿物包括岩浆期磷灰石和热液期磷灰石、独居石、氟碳（钙）铈矿。暗色包体为岩浆混合成因，内含磷灰石、独居石和零星的硅钛铈矿、金红石。矿物组合特征显示，铁木里碱长花岗岩中的铌和稀土元素经过了岩浆和热液两个时期的富集。应用金红石、磷灰石、绿泥石等矿物成分特征约束了岩浆-热液演化过程中体系的物理化学状态，反演了铌和稀土元素的富集过程。在岩浆结晶阶段（688~500℃）铌形成铌铁金红石，稀土元素形成磷灰石、独居石、硅钛铈矿，部分稀土元素进入云母类矿物。在岩浆期后热液阶段，铌主要在高温阶段（500~486℃）形成热液金红石、易解石、铌铁矿，稀土元素发生活化、迁移，在中温热液阶段（~280℃）形成热液独居石、氟碳铈矿、氟碳钙铈矿等稀土矿物。岩浆体系处于高氧逸度状态，随着演化程度的增高，温度、氧逸度均呈下降趋势，热液体系处于低氧逸度的还原状态。流体温度和氧逸度的降低以及岩浆演化及岩浆与碳酸盐岩围岩反应导致的成分变化是造成稀土元素活化、迁移、沉淀的重要因素。铁木里碱长花岗岩体发育岩浆-热液型铌-稀土矿化，可作为该类资源综合评价的重要靶区。