Nyiragongo volcanic eruptions of 1977 and 2002 emitted silica-undersaturated lavas named melilite-nephelinites with microlithic to sub-porphyritic textures, and consisted of olivine, clinopyroxene (augite), phlogopite...Nyiragongo volcanic eruptions of 1977 and 2002 emitted silica-undersaturated lavas named melilite-nephelinites with microlithic to sub-porphyritic textures, and consisted of olivine, clinopyroxene (augite), phlogopite, melilite, magnetite, and rare plagioclases. This melilite-nephelinite as an evolved rock, shows low SiO<sub>2</sub> (38.40 - 39.52 wt%) and MgO (3.10 - 4.01 wt%), and relatively high FeOt (13.76 - 14.10 wt%), Al<sub>2</sub>O<sub>3</sub> (15.01 - 16.48 wt%), CaO (11.00 - 12.29 wt%) and Na<sub>2</sub>O + K<sub>2</sub>O (10.34 - 11.85 wt%). Unlike LA-ICP-MS on silicate melt inclusions (SMIs) hosted in augite show a pristine melt of picrobasaltic (low Ti-picrite) rock poor in SiO<sub>2</sub> (31.14 - 32.26 wt%), FeOt (2.19 - 2.79 wt%), Al<sub>2</sub>O<sub>3</sub> (8.01 - 9.57 wt%), and Na<sub>2</sub>O + K<sub>2</sub>O (2.34 - 3.05 wt%), while enriched in MgO (20.27 - 28.63 wt%), and CaO (24.95 - 33.17 wt%). The sums (∑REEs) for lavas and SMIs are ranging 712 - 799 and 43 - 119 ppm respectively. REE contracted multi-element patterns showed a W-feature for most lavas except for SMIs. High Rb/Sr, and low Ba/Rb, Zr/Nb, and Sm/Hf ratios of lavas suggest a phlogopite-rich source of materials. .展开更多
The Mokama granites are located in the Kibara belt (KIB) and hosts tin oxide group minerals (TOGM: Sn-W), and sulfide group minerals (SGM: Cu-Zn-Fe-As). The essential of Cu mineralization (non-economic deposit) is dis...The Mokama granites are located in the Kibara belt (KIB) and hosts tin oxide group minerals (TOGM: Sn-W), and sulfide group minerals (SGM: Cu-Zn-Fe-As). The essential of Cu mineralization (non-economic deposit) is disseminated inside the rock and consists of minerals (Raman, EPMA and metallographic microscopy) including chalcopyrite and bornite that are replaced by chalcocite and covellite, and the last also replaced later by malachite. The chemistry (XRF, LA-ICP-MS) of these peraluminous S-type leucogranites show SiO<sub>2</sub> (71 wt% - 79 wt%), ASI (1.4 - 3.1 molar), and are enriched in Rb (681 - 1000 ppm), Ta (12–151 ppm), Sn (43 - 142 ppm), Cu (10 - 4300 ppm), Zn (60 - 740 ppm), U (2.2 - 20.7 ppm) while depleted in Zr (20 - 31 ppm), Sr (20 - 69 ppm), Hf (1.3 - 2.0 ppm), Th (2.2 - 18.9 ppm), W (9 - 113 ppm), Pb (5 - 50 ppm), Ge (5 - 10 ppm), Cs (21 - 53 ppm) and Bi (0.6 - 17.4 ppm) and low ratios of (La/Yb) N, (Gd/Yb) N, (La/Sm) N). Fluid inclusion assemblages (FIAs) hosted in quartz in the Mokama granites show ranges of salinities of 4 - 23 wt% (NaCl equivalent) and homogenization temperatures (Th) of 190°C - 550°C. A boiling assemblage in the granite suggests a fluid phase separation occurred at about 380 - 610 bars, and this corresponds to apparent paleodepths of approximately 1 - 2 km (lithostatic model) or 3 - 5 km (hydrostatic model). FIAs hosted in TOGM such as cassiterite (salinities of 2 wt% - 10 wt% and Th of 220°C - 340°C) helped set up the possible temperature limit of SGM (Cu sulfide) precipitations that are estimated below 200°C.展开更多
Burial dissolution of feldspar and carbonate minerals has been proposed to generate large volumes of secondary pores in subsurface reservoirs. Secondary porosity due to feldspar dissolution is ubiquitous in buried san...Burial dissolution of feldspar and carbonate minerals has been proposed to generate large volumes of secondary pores in subsurface reservoirs. Secondary porosity due to feldspar dissolution is ubiquitous in buried sandstones;however, extensive burial dissolution of carbonate minerals in subsurface sandstones is still debatable. In this paper, we first present four types of typical selective dissolution assemblages of feldspars and carbonate minerals developed in di erent sandstones. Under the constraints of porosity data, water–rock experiments, geochemical calculations of aggressive fluids, diagenetic mass transfer, and a review of publications on mineral dissolution in sandstone reservoirs, we argue that the hypothesis for the creation of significant volumes of secondary porosity by mesodiagenetic carbonate dissolution in subsurface sandstones is in conflict with the limited volume of aggressive fluids in rocks. In addition, no transfer mechanism supports removal of the dissolution products due to the small water volume in the subsurface reservoirs and the low mass concentration gradients in the pore water. Convincing petrographic evidence supports the view that the extensive dissolution of carbonate cements in sandstone rocks is usually associated with a high flux of deep hot fluids provided via fault systems or with meteoric freshwater during the eodiagenesis and telodiagenesis stages. The presumption of extensive mesogenetic dissolution of carbonate cements producing a significant net increase in secondary porosity should be used with careful consideration of the geological background in prediction of sandstone quality.展开更多
Petrographic and geochemical characteristics of the Upper Triassic sandstones in the western Ordos Basin were studied to provide insight into weathering characteristics,provenance,and tectonic implications.Petrographi...Petrographic and geochemical characteristics of the Upper Triassic sandstones in the western Ordos Basin were studied to provide insight into weathering characteristics,provenance,and tectonic implications.Petrographic features show that the sandstones are characterized by low-medium compositional maturity and textural maturity.The CIA and CIW values reveal weak and moderate weathering history in the source area.The geochemical characteristics together with palaeocurrent data show that the northwestern sediments were mainly derived from the Alxa Block with a typical recycled nature,while the provenance of the western and southwestern sediments were mainly from the Qinling-Qilian Orogenic Belt.The tectonic setting discrimination diagrams signify that the parent rocks of sandstones in the western and southern Ordos Basin were mainly developed from continental island arc,which is closely related to the evolution of the QinlingQilian Orogenic Belt.However,the sandstones in the northwestern Ordos Basin show complex features,which may be resulted from a typical recycling process.Overall evidence from petrography,geochemistry and sedimentology,together with previous researches suggest the Kongtongshan and Helanshan areas were the southwestern and northwestern boundary of the Ordos Basin,respectively,and there was no clear boundary between the Hexi Corridor Belt and Ordos Basin,where a large,uniform sediment dispersal system developed during the Late Triassic.展开更多
Fifteen basaltic rock samples were collected from central Jordan at the Atarous volcanism basaltic flow area. The samples cover about 8 km2 from the Atarous Basalt flow (AB). The AB flow was introduced in the Miocene ...Fifteen basaltic rock samples were collected from central Jordan at the Atarous volcanism basaltic flow area. The samples cover about 8 km2 from the Atarous Basalt flow (AB). The AB flow was introduced in the Miocene to Pleistocene periods. The samples analyze major and trace elements by using XRF. Petrography, Geochemistry and Petrogensis have investigation to carried out for the AB. The petrography analyses of the AB rocks show they are composed of plagioclase (labradorite and bytownite), pyroxene (augite), and olivine (forsterite);accessory minerals include apatite and secondary minerals magnetite, ilmenite, spinel and iddingsite. The AB is classified within alkaline to sub-alkaline and tholeiitic to Calc-Alkaline basalt. The Mg# range between 0.39 and 0.49 of basalt samples exhibits different degrees of fractionation with a low degree of melting < 15% as indicated from the varying concentration of incompatible trace elements Ba, Rb, Sr. Trace elements of primary magna show low variable abundances of compatible and incompatible elements, which reflecs a homogenous source. Geochemical parameters such as Mg# and high Ti contents indicate that the corresponding magmas are of primary origin. The tectonic setting of AB is explained by using discrimination diagrams, Ti-Zr-Sr and Nb-Zr-Y and Ti-Zr-Y, the AB plotted within the plate basalt, alkali basalt and Calk alkaline basalt field, respectively. The spider diagram shows the samples AB enrichment of the Ba, K, Nb and Ce, depletion of Nb and Y. The AB exhibited positive Nb, Ce and Ti anomalies, and negative anomalies of Ba, Sr, and P. It is attributed to the fractionation of feldspar for Ba and Sr and apatite for P depletion. The spider diagram showed a positive Nb peak, which conforms to the tertiary and to recent continental alkali basalt provinces and indicates that the AB is the product of lithosphere from upwelling asthenosphere mantle.展开更多
The Pachmarhi, Denwa and Bagra Formations comprise of terrigenous sediments predominantly constitute the Mesozoic Gondwana sequence in Satpura basin of Madhya Pradesh, central India. The Pachmarhi Formation sandstones...The Pachmarhi, Denwa and Bagra Formations comprise of terrigenous sediments predominantly constitute the Mesozoic Gondwana sequence in Satpura basin of Madhya Pradesh, central India. The Pachmarhi Formation sandstones were studied with a view to understand the nature of the Satpura basin in relation to provenance and tectonic setting. Twenty representative samples of sandstone from Pachmarhi were examined for detrital mineralogy, petrofacies and tectonic implications. These sandstones are medium to coarse grained, moderately to moderately well sorted, subangular to subrounded and of moderate sphericity and composed of several varieties of quartz, feldspar, rock fragments, mica and a suite of heavy minerals. Petrographically, the Pachmarhi sandstones are quartzarenite and subarkose. The petrofacies studies reflect derivation of the sediments from continental block provenance and stable cratonic to fault-bounded basement uplift tectonic setting. The study suggests that the Precambrian granitoids occurring in the southern margin of the Satpura basin contributed sediments during Pachmarhi sedimentation.展开更多
Objective The widely exposed granites in the Wulashan area of Inner Mongolia are an important component of intermediate-acidic magma belt at the northern margin of the North China Craton,and are also a natural laborat...Objective The widely exposed granites in the Wulashan area of Inner Mongolia are an important component of intermediate-acidic magma belt at the northern margin of the North China Craton,and are also a natural laboratory to research the origin of granite bodies.The Shadegai pluton,a representative intrusion,intruded into the Wulashan Group metamorphic rocks,occurring as stock,展开更多
The study area is located around Guider and belongs to the Northern Cameroon Pan-African fold belt.It is essentially made of three generations of granitoids.The first generation G1 comprises diorites,tonalites and gra...The study area is located around Guider and belongs to the Northern Cameroon Pan-African fold belt.It is essentially made of three generations of granitoids.The first generation G1 comprises diorites,tonalites and granodiorites.The second one G2 is constituted by biotite granites and biotite-muscovite granites deformed in the solid-state.The third generation G3 is constituted by biotite-syenites,monzosyenites,and leucogranites. All the granitoids are cross cut by aplite veins展开更多
The Miocene molassic Surma sandstones in parts of the Naga-Manipur hills,in and around Nungba,Northeast India have been studied for their tectonic provenance using petrography and heavy mineral contents.The poorly-to-...The Miocene molassic Surma sandstones in parts of the Naga-Manipur hills,in and around Nungba,Northeast India have been studied for their tectonic provenance using petrography and heavy mineral contents.The poorly-to-moderately-sorted sub-litharenite to lithicarkose type Surma sandstones display predominance of monocrystalline quartz(av.61%)and include undulose and non-undulose varieties and almost equal amounts of feldspars(av.22%)and rock fragments(av.17%).The heavy mineral suite of Surma sandstones is dominated by transparent varieties(96%)that include garnet,zircon,tourmaline,rutile,staurolite,scapolite,phlogopite,chondrodite,humite,wollastonite,hedenbergite,sphene,chlorite,sillimanite,glauconite,glaucophane,and chloritoid.These heavy minerals characterize the granitic and silicic metamorphic complexes(GM)as well as the basic metamorphic rocks(MT)like greenstones,green schist,and amphibolites relating to passive continental margin setup.The opaque grains constitute nearly 4%of the total heavy minerals.The presence of euhedral,as well as abraded heavy mineral grains,further supports a mixed provenance having substantial contribution from sedimentary and metamorphic rocks.A ZTR index of approximately 45%indicates mineralogically sub-mature nature of Surma sandstones.Based on the light and heavy mineral suites coupled with the type of terrain available in the vicinity of the study area,it may be visualized that the sediment supply was largely made by the Himalaya,the IMR,the Shillong plateau,and the Mikir Hills under the influence of semi-arid to semi-humid climatic conditions.An overall supply from a recycled orogen provenance has been envisaged.展开更多
The studied area is located in the south to east of the Qorveh city(Kurdistan Province)in the Sanandaj-Sirjan zone.Based on field observations,the dykes are mafic to dioritic in composition,and followed by granitic
This research was conducted to investigate the mineralogy, petrography, geochemistry and petrogensis of the basaltic flows in Jurf Ed Darawish (JDB) area of central Jordan. Sexton representative basalt rock samples we...This research was conducted to investigate the mineralogy, petrography, geochemistry and petrogensis of the basaltic flows in Jurf Ed Darawish (JDB) area of central Jordan. Sexton representative basalt rock samples were selected from the studied JDB outcrops. Modally, JDB consists of plagioclase, olivine, pyroxene (diopside), opaque’s, calcite and iddingsite minerals. Petrographically, basalt is holocrystalline, hypidiomorphic fine to medium grained and exhibited aphanitic to porphyritic texture. The common textures of the JDB rock samples were aphanitic, porphyritic, trachytic, glomeroporphyritic, sub ophitic, vesicular, and amygdaloidal. Geochemically, all of the inspected samples of JDB are located within Trachy basalt and plate alkaline basalt. The tectonic setting of JDB was plotted within the calcalkaline basalt and continental basaltic field. The rare-earth elements showed enrichment of the Ba and K, depletion of Ce relative to K, and enrichment of Nb and Pb with depletion of Y and positive Nb, Zr and Ti anomalies. Negative anomalies of Ba, Sr, Ti and P may be attributed to the fractionation of feldspar for Ba and Sr depletion apatite for P depletion. The positive Nb peak conforms to the tertiary as well as to recent continental alkali basalt provinces and acts as an indicator to the JDB product for the lithosphere from upwelling of the asthenosphere mantle.展开更多
Kerman region where Sarcheshmeh zone is located includes the end part of Uremia-Dokhtar Zone. Extrusive igneous group in Sarcheshmeh is as follows: 1) andesite and 2) rhyodacite. The group of intrusive igneous rocks i...Kerman region where Sarcheshmeh zone is located includes the end part of Uremia-Dokhtar Zone. Extrusive igneous group in Sarcheshmeh is as follows: 1) andesite and 2) rhyodacite. The group of intrusive igneous rocks includes 1) porphyry granite, 2) porphyry granodiorite, and 3) porphyry diorite. Nochoon mine is located at 4 km of southwest of Sarcheshmeh copper mine and it comprises of a group of extrusive igneous rocks as follows: 1) andesite, and 2) dacite. Based on results of microprobe analysis, pyroxene mineral’s composition in these rocks of diopside and augite indicates amphiboles of composite zone of magnesium hosting type and existing plagioclases in regional rock for labradorite and bitonit composition. The most common compounds are chlorite with formula among antigorite and amosite. Comparison of magnetite mineralization in Sarcheshmeh and Nochoon indicates vein mineralization in Nochoon and disseminated granulation in Sarcheshmeh and particularly concerning to chalcopyrite, Nochoon includes more veins than Sarcheshmeh.展开更多
The Ib-valley coalfield of Odisha, India contains five coal seams viz. Ib-seam at the bottom overlain successively by Rampur seam, Lajkura seam, Parkhani seam and Belpahar seam. Twenty one representative samples were ...The Ib-valley coalfield of Odisha, India contains five coal seams viz. Ib-seam at the bottom overlain successively by Rampur seam, Lajkura seam, Parkhani seam and Belpahar seam. Twenty one representative samples were collected from three major seams (Ib, Rampur and Lajkura) and their petrography and chemical studies were carried out. Samples were not collected from the Parkhani and Belpahar seams as these are very small seams exposed locally having no regional correlation. The macroscopic study shows the dominance of durain which imparts a dull appearance to these coals. The maceral analysis reveals that vitrinite percentage varies from 4.5% to 80.2%, the exinite from 3.30% to 22.2% and the inertinite from 12.5% to 92.2% in different samples of the Ib valley coalfield. The very high proportion of inertinite suggests a shallower water deposition of plant materials followed by prolonged period of exposure and repeated cycle of weathering. The proximate analysis results show that the top Lajkura seam is comparatively lower in rank than the underlying Ib and the Rampur seam. The ultimate analysis exhibites that the percentage of variation in C is found from 77.88 to 85.79, H from 4, 4 to 5.91 and O from 7.26 to 15.3. H/C and O/C ratio including C.V. in this coalfield showing distinct variations from the bottom to top seam. The analyses results indicate that the petrographic and chemical characters of the ib valley coals are stratigraphically controlled.展开更多
To study petrography, microfacies, sedimentary environments and sequence stratigraphy of Asmari formation in central Fars, 4 stratigraphic sections have benn chosen and studied (Estahban, Shams-Abad, Sarvestan and Akb...To study petrography, microfacies, sedimentary environments and sequence stratigraphy of Asmari formation in central Fars, 4 stratigraphic sections have benn chosen and studied (Estahban, Shams-Abad, Sarvestan and Akbar-Abad Sections). Field and laboratories study recognized 16?carbonate microfacies and 2 clastic-carbanate facies. Study of microfacies, relative sea level?change and sequence stratigraphy evidences show these microfacies are deposited in carbonate ramp sedimentary environment in 5 facies belt zones: Open marine (A), Restricted (B), Shoal (C), Lagoon (D) and Tidal flat (E) during Oligomiocene. Petrography, microfacies analysis and sedimentary environment of Asmari formation shows this formation in study area consist of 3 depositional sequences. Lower sequence boundary of DS1 with Jahrum formation is erosional (disconformity) SB1. Lower and upper sequence boundary of DS2 is SB2. The upper sequence boundary of DS3 is SB1 and ended under the Razak clastic formation. In central Fars only lower part of Asmari is deposited and upper part of this formation have been eroded and disappeared.展开更多
The Proterozoic Aravalli-Delhi orogenic complex hosts a large number of economically important stratabound base metal sulphide deposits. In the present work, rock samples taken from Outcrop and Underground Mine of Sin...The Proterozoic Aravalli-Delhi orogenic complex hosts a large number of economically important stratabound base metal sulphide deposits. In the present work, rock samples taken from Outcrop and Underground Mine of Sindeskar Kalan, Vedanta Group, Rajpura Dariba-Bethumni Belt which is located at a distance of 76 kms from Udaipur city, Rajasthan have been studied. The chief litho units of the group which contain sulfide-bearing calc-silicate and graphite mica schist, dolomite marble, calc-biotite schist and quartzite are identified. An attempt has also been made to study/or hydrothermal in origin in the different types of fluid inclusions, hosted predominately in Geothermometry viz. heating and freezing study of entrapped palaeo-fluids (such as sedimentary and quartz host grain and a few in sphalerites). The quartz hosts are identified with four types of fluid inclusions, such as 1) monophase (gas/vapour), 2) gas-rich biphase, 3) liquid-rich biphase and 4) polyphase types. The primary types of fluid inclusions show that melting temperature of ice or depression freezing point (DFP) (ranging from -2.5°C to -7.2°C)/(salinity ranging from 4.5 - 13.25 wt% NaCl eq.) and temperature of homogenization into liquid phase (ranging from +188°C to +218°C) have been measured. Data from the fluid inclusions and salinity calculation (low salinity) reveal that rate of cooling is the important mechanism of ore deposition in the study area.展开更多
The Tobène deposit forms, with those of NdomorDiop and KeurMor Fall, the large phosphate deposit of Ta?ba. The Tobène site has been the subject of lithostratigraphic, biostratigraphic, mineralogical, petrogr...The Tobène deposit forms, with those of NdomorDiop and KeurMor Fall, the large phosphate deposit of Ta?ba. The Tobène site has been the subject of lithostratigraphic, biostratigraphic, mineralogical, petrographic and geochemical studies. The lithostratigraphic and biostratigraphic studies dated the series from Lutetian to Bartonian composed of five lithological units, which are assembled by [1] in three formations. The mineralogical study shows three groups of minerals associated with the different phosphatic facies identified in the various sectors of Tobène: 1) characteristic minerals of sedimentological conditions;2) minerals of diagenetic origin;3) minerals of alteration. The petrographic study allowed an inventory of the constituting visible grains of the microfacies as well as the different phases of diagenetic and post-diagenetic transformations that may have affected them. It thus appears that the phosphatic ore of Tobène has undergone an extensive diagenesis (compaction, dissolution-recrystallization, epigenesis) to which a relatively intense ferruginization has been added.展开更多
Middle Triassic carbonate sequences of Shotori Formation have a thickness of 70 m and are deposited Robat-e-Kalmard region of Tabas city in Central Iran basin. Gradationally and conformably overlying Sorkh shale Forma...Middle Triassic carbonate sequences of Shotori Formation have a thickness of 70 m and are deposited Robat-e-Kalmard region of Tabas city in Central Iran basin. Gradationally and conformably overlying Sorkh shale Formation, Shotori Formation, mostly composed of medium to thick dolomites (50 m), interbeded with thin lime and sandstones, is disconformable by a laterite horizon at its upper boundary. This Formation mainly consists of fine-to-coarsely crystalline dolomites. According to petrographic (fabric and grain size) and geochemical (elemental analysis of Ca, Mg, Na, Sr, Fe, Mn) evidence, five various types of dolomites were recognized in Shotori Formation. This variety results from early and late diagenetic processes, triggering a change in dolomitizing fluids and thereby forming various dolomites. Geochemical studies have revealed that the dolomites of Shotori Formation have formed under meteoric diagenesis and reducing conditions. Various dolomitization mechanisms are proposed for various types of dolomites;that is to say, Sabkha model is considered for type 1 dolomite, mixing zone model for type 2 and 3 dolomites and burial model for type 4 and 5 dolomites.展开更多
Al Azraq Al Shamali (AZS) basaltic rocks were investigated aiming to understand their mineralogy, petrography and geochemistry features, and to achieve that a total of sixteen representative rock samples were selected...Al Azraq Al Shamali (AZS) basaltic rocks were investigated aiming to understand their mineralogy, petrography and geochemistry features, and to achieve that a total of sixteen representative rock samples were selected for both geochemical and petrographic analysis from several sites in the study area. Petrographic characteristics were analyzed by optical microscopy after preparation thin sections for representative rock samples, which show that all basalt samples have minerals comprising: olivine, plagioclase (labradorite), clinopyroxene (augite), opaque’s and some secondary minerals such as Iddingsite, however, the proportions of each mineral vary between samples. Normative mineralogy by using CIPW Norm showed that AZS basalt samples dominated by olivine, Diopside, and nepheline, and AZS basalt can be normatively classified as alkali olivine basalt. Some textures that may be evident on microscopic examination such as porphyritic, glomeroporphyritic, vesicular, intergranular, and ophitic to sub-ophitic texture. X-Ray Fluorescence was used for whole rock major elements analysis (SiO<sub>2</sub>, TiO<sub>2</sub>, Al<sub>2</sub>O<sub>3</sub>, Fe<sub>2</sub>O<sub>3</sub>, MnO, MgO, CaO, Na<sub>2</sub>O, K<sub>2</sub>O and P<sub>2</sub>O<sub>5</sub> in wt%) and trace element (V, Cr, Co, Ni, Rb, Sr, Y, Zr, Nb, Ce, Nd and Ba in ppm). Geochemical analysis reveal that the basalt is alkaline and includes into Sodic series. AZS basalt are produced under-saturated within intraplate continental environment. The normalized trace element diagrams suggest that the AZS product of the asthenosphere part of the mantle at >100 km depth. Furthermore, the data of studied samples suggest that these rocks evolved from a melt formed by low degrees of partial melting. Also the geochemical variation trends of (AZS) basaltic samples supposing that the composition of these basalt have been influenced by fractional crystallization, without clear evidences for crustal contamination.展开更多
The Baïbokoum-Touboro-Ngaoundaye area is located in the Adamoua-Yade domain of the Pan-African Fold Belt in Central Africa. The present work concerns the petrographic and geochemical study. The study area is ...The Baïbokoum-Touboro-Ngaoundaye area is located in the Adamoua-Yade domain of the Pan-African Fold Belt in Central Africa. The present work concerns the petrographic and geochemical study. The study area is made up of plutonic rocks including two amphibole granites, four biotite and muscovite granites, two syenites and one monzonite sample. These rocks have a granular porphyroid texture, with a mylonitic tendency. The primary paragenesis consists of Opx + Cpx + Amp + Bt + Pl + Or + Mic + Qtz + Ap + Sph + Zr and the secondary paragenesis consisting of Ch + Op. Plutonic rocks are shoshonitic to calc-alkaline with a strong potassic affinity. The REE profiles of these rocks show a negative anomaly of Eu in the granites and no Eu anomaly in syenites and monzonite (syeno-diorite). Multielement spectra of plutonic rocks present a negative anomaly in Nb-Ta and Ti. Fractional crystallization is the process that made these rocks of study area. These rocks are placed in a subduction to syn-collisional (VAG + Syn-COLG) and of intraplate granitoids (WPG) environment.展开更多
The syenite from Ina (Central region of Cameroon) constitutes a 1000 km<sup>2</sup> syntectonic batholith intruded in the Paleoproterozoic granitic basement. The aim of this work is to assess the potential...The syenite from Ina (Central region of Cameroon) constitutes a 1000 km<sup>2</sup> syntectonic batholith intruded in the Paleoproterozoic granitic basement. The aim of this work is to assess the potential of the Ina batholith syenite as a feldspar minerals resource for industrial use through petrographic and geochemical characterization. Most of the rocks are grey coloured and consist of shimmering feldspar phenocrysts in a fine-grained ferromagnesian matrix. Petrography reveals the presence of two major syenite facies: a widely distributed porphyritic syenite and a less-abundant massive syenite. These facies are dominated by phenocrysts of sub-automorphic perthitic orthoclase. Its malgachite face is due to the presence of numerous inclusions of opaque minerals observed by scanning electron microscopy (ESEM-EDX). Plagioclase phenocrysts have a zonal texture characterised microscopically by an oscillatory compositional zonation. Biotite, hornblende and augite, identified by X-ray powder diffraction, are finely disseminated in the feldspar matrix. Quartz appears as small automorphic crystals with maximum abundance of about 4 wt%. The XRF chemical composition reveals, alongside silica (59.29 wt% to 63.27 wt%), significant proportion of alumina (15.82 wt% to 19.80 wt%), potassium and sodium oxides considered as fluxing elements (K<sub>2</sub>O + Na<sub>2</sub>O ≥ 10 wt%). The K<sub>2</sub>O/Na<sub>2</sub>O ratio varies between 1.65 and 5.51 (average 2.58). Iron and titanium oxides (1 ≥ wt% Fe<sub>2</sub>O<sub>3</sub> + TiO<sub>2</sub> ≥ 5), harmful in ceramic industry, are high as in most other feldspathic sources. The characteristics of the Ina syenite are close to most of the syenite ores used worldwide for ceramics and glass raw materials and necessitates purification and beneficiation treatments. Others rock types have been identified at the study site (granite, monzonite, granodiorite) and are considered as inappropriate as a source of industrial feldspars.展开更多
文摘Nyiragongo volcanic eruptions of 1977 and 2002 emitted silica-undersaturated lavas named melilite-nephelinites with microlithic to sub-porphyritic textures, and consisted of olivine, clinopyroxene (augite), phlogopite, melilite, magnetite, and rare plagioclases. This melilite-nephelinite as an evolved rock, shows low SiO<sub>2</sub> (38.40 - 39.52 wt%) and MgO (3.10 - 4.01 wt%), and relatively high FeOt (13.76 - 14.10 wt%), Al<sub>2</sub>O<sub>3</sub> (15.01 - 16.48 wt%), CaO (11.00 - 12.29 wt%) and Na<sub>2</sub>O + K<sub>2</sub>O (10.34 - 11.85 wt%). Unlike LA-ICP-MS on silicate melt inclusions (SMIs) hosted in augite show a pristine melt of picrobasaltic (low Ti-picrite) rock poor in SiO<sub>2</sub> (31.14 - 32.26 wt%), FeOt (2.19 - 2.79 wt%), Al<sub>2</sub>O<sub>3</sub> (8.01 - 9.57 wt%), and Na<sub>2</sub>O + K<sub>2</sub>O (2.34 - 3.05 wt%), while enriched in MgO (20.27 - 28.63 wt%), and CaO (24.95 - 33.17 wt%). The sums (∑REEs) for lavas and SMIs are ranging 712 - 799 and 43 - 119 ppm respectively. REE contracted multi-element patterns showed a W-feature for most lavas except for SMIs. High Rb/Sr, and low Ba/Rb, Zr/Nb, and Sm/Hf ratios of lavas suggest a phlogopite-rich source of materials. .
文摘The Mokama granites are located in the Kibara belt (KIB) and hosts tin oxide group minerals (TOGM: Sn-W), and sulfide group minerals (SGM: Cu-Zn-Fe-As). The essential of Cu mineralization (non-economic deposit) is disseminated inside the rock and consists of minerals (Raman, EPMA and metallographic microscopy) including chalcopyrite and bornite that are replaced by chalcocite and covellite, and the last also replaced later by malachite. The chemistry (XRF, LA-ICP-MS) of these peraluminous S-type leucogranites show SiO<sub>2</sub> (71 wt% - 79 wt%), ASI (1.4 - 3.1 molar), and are enriched in Rb (681 - 1000 ppm), Ta (12–151 ppm), Sn (43 - 142 ppm), Cu (10 - 4300 ppm), Zn (60 - 740 ppm), U (2.2 - 20.7 ppm) while depleted in Zr (20 - 31 ppm), Sr (20 - 69 ppm), Hf (1.3 - 2.0 ppm), Th (2.2 - 18.9 ppm), W (9 - 113 ppm), Pb (5 - 50 ppm), Ge (5 - 10 ppm), Cs (21 - 53 ppm) and Bi (0.6 - 17.4 ppm) and low ratios of (La/Yb) N, (Gd/Yb) N, (La/Sm) N). Fluid inclusion assemblages (FIAs) hosted in quartz in the Mokama granites show ranges of salinities of 4 - 23 wt% (NaCl equivalent) and homogenization temperatures (Th) of 190°C - 550°C. A boiling assemblage in the granite suggests a fluid phase separation occurred at about 380 - 610 bars, and this corresponds to apparent paleodepths of approximately 1 - 2 km (lithostatic model) or 3 - 5 km (hydrostatic model). FIAs hosted in TOGM such as cassiterite (salinities of 2 wt% - 10 wt% and Th of 220°C - 340°C) helped set up the possible temperature limit of SGM (Cu sulfide) precipitations that are estimated below 200°C.
基金funded by the Natural Science Foundation of China Project(Nos.41602138,41872140,41911530189)the National Science and Technology Special Grant(No.2016ZX05006-007+2 种基金No.2016ZX05006-003)the Fundamental Research Funds for the Central Universities(18CX07007A)the State Key Laboratory of Organic Geochemistry,GIGCAS(No.SKLOG-201709)
文摘Burial dissolution of feldspar and carbonate minerals has been proposed to generate large volumes of secondary pores in subsurface reservoirs. Secondary porosity due to feldspar dissolution is ubiquitous in buried sandstones;however, extensive burial dissolution of carbonate minerals in subsurface sandstones is still debatable. In this paper, we first present four types of typical selective dissolution assemblages of feldspars and carbonate minerals developed in di erent sandstones. Under the constraints of porosity data, water–rock experiments, geochemical calculations of aggressive fluids, diagenetic mass transfer, and a review of publications on mineral dissolution in sandstone reservoirs, we argue that the hypothesis for the creation of significant volumes of secondary porosity by mesodiagenetic carbonate dissolution in subsurface sandstones is in conflict with the limited volume of aggressive fluids in rocks. In addition, no transfer mechanism supports removal of the dissolution products due to the small water volume in the subsurface reservoirs and the low mass concentration gradients in the pore water. Convincing petrographic evidence supports the view that the extensive dissolution of carbonate cements in sandstone rocks is usually associated with a high flux of deep hot fluids provided via fault systems or with meteoric freshwater during the eodiagenesis and telodiagenesis stages. The presumption of extensive mesogenetic dissolution of carbonate cements producing a significant net increase in secondary porosity should be used with careful consideration of the geological background in prediction of sandstone quality.
基金the National Natural Science Foundation of China [Grant No. 41802119 and 41602212]Natural Science Foundation of Shaanxi [Grant No. 2019JQ-088]+1 种基金Special Projects of China Geological Survey [Grant No. 12120113039900 and 12120114009201]Doctor’s fund of Xi’an University of Science and Technology [Grant No. 2017QDJ051]
文摘Petrographic and geochemical characteristics of the Upper Triassic sandstones in the western Ordos Basin were studied to provide insight into weathering characteristics,provenance,and tectonic implications.Petrographic features show that the sandstones are characterized by low-medium compositional maturity and textural maturity.The CIA and CIW values reveal weak and moderate weathering history in the source area.The geochemical characteristics together with palaeocurrent data show that the northwestern sediments were mainly derived from the Alxa Block with a typical recycled nature,while the provenance of the western and southwestern sediments were mainly from the Qinling-Qilian Orogenic Belt.The tectonic setting discrimination diagrams signify that the parent rocks of sandstones in the western and southern Ordos Basin were mainly developed from continental island arc,which is closely related to the evolution of the QinlingQilian Orogenic Belt.However,the sandstones in the northwestern Ordos Basin show complex features,which may be resulted from a typical recycling process.Overall evidence from petrography,geochemistry and sedimentology,together with previous researches suggest the Kongtongshan and Helanshan areas were the southwestern and northwestern boundary of the Ordos Basin,respectively,and there was no clear boundary between the Hexi Corridor Belt and Ordos Basin,where a large,uniform sediment dispersal system developed during the Late Triassic.
文摘Fifteen basaltic rock samples were collected from central Jordan at the Atarous volcanism basaltic flow area. The samples cover about 8 km2 from the Atarous Basalt flow (AB). The AB flow was introduced in the Miocene to Pleistocene periods. The samples analyze major and trace elements by using XRF. Petrography, Geochemistry and Petrogensis have investigation to carried out for the AB. The petrography analyses of the AB rocks show they are composed of plagioclase (labradorite and bytownite), pyroxene (augite), and olivine (forsterite);accessory minerals include apatite and secondary minerals magnetite, ilmenite, spinel and iddingsite. The AB is classified within alkaline to sub-alkaline and tholeiitic to Calc-Alkaline basalt. The Mg# range between 0.39 and 0.49 of basalt samples exhibits different degrees of fractionation with a low degree of melting < 15% as indicated from the varying concentration of incompatible trace elements Ba, Rb, Sr. Trace elements of primary magna show low variable abundances of compatible and incompatible elements, which reflecs a homogenous source. Geochemical parameters such as Mg# and high Ti contents indicate that the corresponding magmas are of primary origin. The tectonic setting of AB is explained by using discrimination diagrams, Ti-Zr-Sr and Nb-Zr-Y and Ti-Zr-Y, the AB plotted within the plate basalt, alkali basalt and Calk alkaline basalt field, respectively. The spider diagram shows the samples AB enrichment of the Ba, K, Nb and Ce, depletion of Nb and Y. The AB exhibited positive Nb, Ce and Ti anomalies, and negative anomalies of Ba, Sr, and P. It is attributed to the fractionation of feldspar for Ba and Sr and apatite for P depletion. The spider diagram showed a positive Nb peak, which conforms to the tertiary and to recent continental alkali basalt provinces and indicates that the AB is the product of lithosphere from upwelling asthenosphere mantle.
文摘The Pachmarhi, Denwa and Bagra Formations comprise of terrigenous sediments predominantly constitute the Mesozoic Gondwana sequence in Satpura basin of Madhya Pradesh, central India. The Pachmarhi Formation sandstones were studied with a view to understand the nature of the Satpura basin in relation to provenance and tectonic setting. Twenty representative samples of sandstone from Pachmarhi were examined for detrital mineralogy, petrofacies and tectonic implications. These sandstones are medium to coarse grained, moderately to moderately well sorted, subangular to subrounded and of moderate sphericity and composed of several varieties of quartz, feldspar, rock fragments, mica and a suite of heavy minerals. Petrographically, the Pachmarhi sandstones are quartzarenite and subarkose. The petrofacies studies reflect derivation of the sediments from continental block provenance and stable cratonic to fault-bounded basement uplift tectonic setting. The study suggests that the Precambrian granitoids occurring in the southern margin of the Satpura basin contributed sediments during Pachmarhi sedimentation.
基金funded by the National Natural Science Foundation of China(grant No.41302064)
文摘Objective The widely exposed granites in the Wulashan area of Inner Mongolia are an important component of intermediate-acidic magma belt at the northern margin of the North China Craton,and are also a natural laboratory to research the origin of granite bodies.The Shadegai pluton,a representative intrusion,intruded into the Wulashan Group metamorphic rocks,occurring as stock,
文摘The study area is located around Guider and belongs to the Northern Cameroon Pan-African fold belt.It is essentially made of three generations of granitoids.The first generation G1 comprises diorites,tonalites and granodiorites.The second one G2 is constituted by biotite granites and biotite-muscovite granites deformed in the solid-state.The third generation G3 is constituted by biotite-syenites,monzosyenites,and leucogranites. All the granitoids are cross cut by aplite veins
基金funding the research programme through Inspire Fellowship No. IF140996
文摘The Miocene molassic Surma sandstones in parts of the Naga-Manipur hills,in and around Nungba,Northeast India have been studied for their tectonic provenance using petrography and heavy mineral contents.The poorly-to-moderately-sorted sub-litharenite to lithicarkose type Surma sandstones display predominance of monocrystalline quartz(av.61%)and include undulose and non-undulose varieties and almost equal amounts of feldspars(av.22%)and rock fragments(av.17%).The heavy mineral suite of Surma sandstones is dominated by transparent varieties(96%)that include garnet,zircon,tourmaline,rutile,staurolite,scapolite,phlogopite,chondrodite,humite,wollastonite,hedenbergite,sphene,chlorite,sillimanite,glauconite,glaucophane,and chloritoid.These heavy minerals characterize the granitic and silicic metamorphic complexes(GM)as well as the basic metamorphic rocks(MT)like greenstones,green schist,and amphibolites relating to passive continental margin setup.The opaque grains constitute nearly 4%of the total heavy minerals.The presence of euhedral,as well as abraded heavy mineral grains,further supports a mixed provenance having substantial contribution from sedimentary and metamorphic rocks.A ZTR index of approximately 45%indicates mineralogically sub-mature nature of Surma sandstones.Based on the light and heavy mineral suites coupled with the type of terrain available in the vicinity of the study area,it may be visualized that the sediment supply was largely made by the Himalaya,the IMR,the Shillong plateau,and the Mikir Hills under the influence of semi-arid to semi-humid climatic conditions.An overall supply from a recycled orogen provenance has been envisaged.
文摘The studied area is located in the south to east of the Qorveh city(Kurdistan Province)in the Sanandaj-Sirjan zone.Based on field observations,the dykes are mafic to dioritic in composition,and followed by granitic
文摘This research was conducted to investigate the mineralogy, petrography, geochemistry and petrogensis of the basaltic flows in Jurf Ed Darawish (JDB) area of central Jordan. Sexton representative basalt rock samples were selected from the studied JDB outcrops. Modally, JDB consists of plagioclase, olivine, pyroxene (diopside), opaque’s, calcite and iddingsite minerals. Petrographically, basalt is holocrystalline, hypidiomorphic fine to medium grained and exhibited aphanitic to porphyritic texture. The common textures of the JDB rock samples were aphanitic, porphyritic, trachytic, glomeroporphyritic, sub ophitic, vesicular, and amygdaloidal. Geochemically, all of the inspected samples of JDB are located within Trachy basalt and plate alkaline basalt. The tectonic setting of JDB was plotted within the calcalkaline basalt and continental basaltic field. The rare-earth elements showed enrichment of the Ba and K, depletion of Ce relative to K, and enrichment of Nb and Pb with depletion of Y and positive Nb, Zr and Ti anomalies. Negative anomalies of Ba, Sr, Ti and P may be attributed to the fractionation of feldspar for Ba and Sr depletion apatite for P depletion. The positive Nb peak conforms to the tertiary as well as to recent continental alkali basalt provinces and acts as an indicator to the JDB product for the lithosphere from upwelling of the asthenosphere mantle.
文摘Kerman region where Sarcheshmeh zone is located includes the end part of Uremia-Dokhtar Zone. Extrusive igneous group in Sarcheshmeh is as follows: 1) andesite and 2) rhyodacite. The group of intrusive igneous rocks includes 1) porphyry granite, 2) porphyry granodiorite, and 3) porphyry diorite. Nochoon mine is located at 4 km of southwest of Sarcheshmeh copper mine and it comprises of a group of extrusive igneous rocks as follows: 1) andesite, and 2) dacite. Based on results of microprobe analysis, pyroxene mineral’s composition in these rocks of diopside and augite indicates amphiboles of composite zone of magnesium hosting type and existing plagioclases in regional rock for labradorite and bitonit composition. The most common compounds are chlorite with formula among antigorite and amosite. Comparison of magnetite mineralization in Sarcheshmeh and Nochoon indicates vein mineralization in Nochoon and disseminated granulation in Sarcheshmeh and particularly concerning to chalcopyrite, Nochoon includes more veins than Sarcheshmeh.
文摘The Ib-valley coalfield of Odisha, India contains five coal seams viz. Ib-seam at the bottom overlain successively by Rampur seam, Lajkura seam, Parkhani seam and Belpahar seam. Twenty one representative samples were collected from three major seams (Ib, Rampur and Lajkura) and their petrography and chemical studies were carried out. Samples were not collected from the Parkhani and Belpahar seams as these are very small seams exposed locally having no regional correlation. The macroscopic study shows the dominance of durain which imparts a dull appearance to these coals. The maceral analysis reveals that vitrinite percentage varies from 4.5% to 80.2%, the exinite from 3.30% to 22.2% and the inertinite from 12.5% to 92.2% in different samples of the Ib valley coalfield. The very high proportion of inertinite suggests a shallower water deposition of plant materials followed by prolonged period of exposure and repeated cycle of weathering. The proximate analysis results show that the top Lajkura seam is comparatively lower in rank than the underlying Ib and the Rampur seam. The ultimate analysis exhibites that the percentage of variation in C is found from 77.88 to 85.79, H from 4, 4 to 5.91 and O from 7.26 to 15.3. H/C and O/C ratio including C.V. in this coalfield showing distinct variations from the bottom to top seam. The analyses results indicate that the petrographic and chemical characters of the ib valley coals are stratigraphically controlled.
文摘To study petrography, microfacies, sedimentary environments and sequence stratigraphy of Asmari formation in central Fars, 4 stratigraphic sections have benn chosen and studied (Estahban, Shams-Abad, Sarvestan and Akbar-Abad Sections). Field and laboratories study recognized 16?carbonate microfacies and 2 clastic-carbanate facies. Study of microfacies, relative sea level?change and sequence stratigraphy evidences show these microfacies are deposited in carbonate ramp sedimentary environment in 5 facies belt zones: Open marine (A), Restricted (B), Shoal (C), Lagoon (D) and Tidal flat (E) during Oligomiocene. Petrography, microfacies analysis and sedimentary environment of Asmari formation shows this formation in study area consist of 3 depositional sequences. Lower sequence boundary of DS1 with Jahrum formation is erosional (disconformity) SB1. Lower and upper sequence boundary of DS2 is SB2. The upper sequence boundary of DS3 is SB1 and ended under the Razak clastic formation. In central Fars only lower part of Asmari is deposited and upper part of this formation have been eroded and disappeared.
文摘The Proterozoic Aravalli-Delhi orogenic complex hosts a large number of economically important stratabound base metal sulphide deposits. In the present work, rock samples taken from Outcrop and Underground Mine of Sindeskar Kalan, Vedanta Group, Rajpura Dariba-Bethumni Belt which is located at a distance of 76 kms from Udaipur city, Rajasthan have been studied. The chief litho units of the group which contain sulfide-bearing calc-silicate and graphite mica schist, dolomite marble, calc-biotite schist and quartzite are identified. An attempt has also been made to study/or hydrothermal in origin in the different types of fluid inclusions, hosted predominately in Geothermometry viz. heating and freezing study of entrapped palaeo-fluids (such as sedimentary and quartz host grain and a few in sphalerites). The quartz hosts are identified with four types of fluid inclusions, such as 1) monophase (gas/vapour), 2) gas-rich biphase, 3) liquid-rich biphase and 4) polyphase types. The primary types of fluid inclusions show that melting temperature of ice or depression freezing point (DFP) (ranging from -2.5°C to -7.2°C)/(salinity ranging from 4.5 - 13.25 wt% NaCl eq.) and temperature of homogenization into liquid phase (ranging from +188°C to +218°C) have been measured. Data from the fluid inclusions and salinity calculation (low salinity) reveal that rate of cooling is the important mechanism of ore deposition in the study area.
文摘The Tobène deposit forms, with those of NdomorDiop and KeurMor Fall, the large phosphate deposit of Ta?ba. The Tobène site has been the subject of lithostratigraphic, biostratigraphic, mineralogical, petrographic and geochemical studies. The lithostratigraphic and biostratigraphic studies dated the series from Lutetian to Bartonian composed of five lithological units, which are assembled by [1] in three formations. The mineralogical study shows three groups of minerals associated with the different phosphatic facies identified in the various sectors of Tobène: 1) characteristic minerals of sedimentological conditions;2) minerals of diagenetic origin;3) minerals of alteration. The petrographic study allowed an inventory of the constituting visible grains of the microfacies as well as the different phases of diagenetic and post-diagenetic transformations that may have affected them. It thus appears that the phosphatic ore of Tobène has undergone an extensive diagenesis (compaction, dissolution-recrystallization, epigenesis) to which a relatively intense ferruginization has been added.
文摘Middle Triassic carbonate sequences of Shotori Formation have a thickness of 70 m and are deposited Robat-e-Kalmard region of Tabas city in Central Iran basin. Gradationally and conformably overlying Sorkh shale Formation, Shotori Formation, mostly composed of medium to thick dolomites (50 m), interbeded with thin lime and sandstones, is disconformable by a laterite horizon at its upper boundary. This Formation mainly consists of fine-to-coarsely crystalline dolomites. According to petrographic (fabric and grain size) and geochemical (elemental analysis of Ca, Mg, Na, Sr, Fe, Mn) evidence, five various types of dolomites were recognized in Shotori Formation. This variety results from early and late diagenetic processes, triggering a change in dolomitizing fluids and thereby forming various dolomites. Geochemical studies have revealed that the dolomites of Shotori Formation have formed under meteoric diagenesis and reducing conditions. Various dolomitization mechanisms are proposed for various types of dolomites;that is to say, Sabkha model is considered for type 1 dolomite, mixing zone model for type 2 and 3 dolomites and burial model for type 4 and 5 dolomites.
文摘Al Azraq Al Shamali (AZS) basaltic rocks were investigated aiming to understand their mineralogy, petrography and geochemistry features, and to achieve that a total of sixteen representative rock samples were selected for both geochemical and petrographic analysis from several sites in the study area. Petrographic characteristics were analyzed by optical microscopy after preparation thin sections for representative rock samples, which show that all basalt samples have minerals comprising: olivine, plagioclase (labradorite), clinopyroxene (augite), opaque’s and some secondary minerals such as Iddingsite, however, the proportions of each mineral vary between samples. Normative mineralogy by using CIPW Norm showed that AZS basalt samples dominated by olivine, Diopside, and nepheline, and AZS basalt can be normatively classified as alkali olivine basalt. Some textures that may be evident on microscopic examination such as porphyritic, glomeroporphyritic, vesicular, intergranular, and ophitic to sub-ophitic texture. X-Ray Fluorescence was used for whole rock major elements analysis (SiO<sub>2</sub>, TiO<sub>2</sub>, Al<sub>2</sub>O<sub>3</sub>, Fe<sub>2</sub>O<sub>3</sub>, MnO, MgO, CaO, Na<sub>2</sub>O, K<sub>2</sub>O and P<sub>2</sub>O<sub>5</sub> in wt%) and trace element (V, Cr, Co, Ni, Rb, Sr, Y, Zr, Nb, Ce, Nd and Ba in ppm). Geochemical analysis reveal that the basalt is alkaline and includes into Sodic series. AZS basalt are produced under-saturated within intraplate continental environment. The normalized trace element diagrams suggest that the AZS product of the asthenosphere part of the mantle at >100 km depth. Furthermore, the data of studied samples suggest that these rocks evolved from a melt formed by low degrees of partial melting. Also the geochemical variation trends of (AZS) basaltic samples supposing that the composition of these basalt have been influenced by fractional crystallization, without clear evidences for crustal contamination.
文摘The Baïbokoum-Touboro-Ngaoundaye area is located in the Adamoua-Yade domain of the Pan-African Fold Belt in Central Africa. The present work concerns the petrographic and geochemical study. The study area is made up of plutonic rocks including two amphibole granites, four biotite and muscovite granites, two syenites and one monzonite sample. These rocks have a granular porphyroid texture, with a mylonitic tendency. The primary paragenesis consists of Opx + Cpx + Amp + Bt + Pl + Or + Mic + Qtz + Ap + Sph + Zr and the secondary paragenesis consisting of Ch + Op. Plutonic rocks are shoshonitic to calc-alkaline with a strong potassic affinity. The REE profiles of these rocks show a negative anomaly of Eu in the granites and no Eu anomaly in syenites and monzonite (syeno-diorite). Multielement spectra of plutonic rocks present a negative anomaly in Nb-Ta and Ti. Fractional crystallization is the process that made these rocks of study area. These rocks are placed in a subduction to syn-collisional (VAG + Syn-COLG) and of intraplate granitoids (WPG) environment.
文摘The syenite from Ina (Central region of Cameroon) constitutes a 1000 km<sup>2</sup> syntectonic batholith intruded in the Paleoproterozoic granitic basement. The aim of this work is to assess the potential of the Ina batholith syenite as a feldspar minerals resource for industrial use through petrographic and geochemical characterization. Most of the rocks are grey coloured and consist of shimmering feldspar phenocrysts in a fine-grained ferromagnesian matrix. Petrography reveals the presence of two major syenite facies: a widely distributed porphyritic syenite and a less-abundant massive syenite. These facies are dominated by phenocrysts of sub-automorphic perthitic orthoclase. Its malgachite face is due to the presence of numerous inclusions of opaque minerals observed by scanning electron microscopy (ESEM-EDX). Plagioclase phenocrysts have a zonal texture characterised microscopically by an oscillatory compositional zonation. Biotite, hornblende and augite, identified by X-ray powder diffraction, are finely disseminated in the feldspar matrix. Quartz appears as small automorphic crystals with maximum abundance of about 4 wt%. The XRF chemical composition reveals, alongside silica (59.29 wt% to 63.27 wt%), significant proportion of alumina (15.82 wt% to 19.80 wt%), potassium and sodium oxides considered as fluxing elements (K<sub>2</sub>O + Na<sub>2</sub>O ≥ 10 wt%). The K<sub>2</sub>O/Na<sub>2</sub>O ratio varies between 1.65 and 5.51 (average 2.58). Iron and titanium oxides (1 ≥ wt% Fe<sub>2</sub>O<sub>3</sub> + TiO<sub>2</sub> ≥ 5), harmful in ceramic industry, are high as in most other feldspathic sources. The characteristics of the Ina syenite are close to most of the syenite ores used worldwide for ceramics and glass raw materials and necessitates purification and beneficiation treatments. Others rock types have been identified at the study site (granite, monzonite, granodiorite) and are considered as inappropriate as a source of industrial feldspars.
