Mica Granite Research Articles

Indosinian isotope ages of plutons and deposits in southwestern Miaoershan-Yuechengling, northeastern Guangxi and implications on Indosinian mineralization in South China

The Miaoershan-Yuechengling complex pluton is the largest granitoid complex in the western Nanling metallogenic belt with a surface exposure of >3000 km2. The complex pluton is composed of an early stage granitoid batholith and late stage small intrusions. The early stage batholith contains mainly medium-grained porphyritic mica granite and porphyritic monzonite granite, whereas the late stage intrusions are composed of muscovite granite porphyry and muscovite monzonitic granite. There are many W-Sn-Mo-Pb-Zn-Cu ores in the contact zone between the batholith and strata, forming an ore-rich belt around the batholith. Based on zircon LA-ICP-MS U-Pb ages, the southwestern part of the early stage batholith formed at 228.7 ± 4.1 Ma (MSWD = 2.49), with slightly earlier magmatic activity at 243.0 ± 5.8 Ma (MSWD = 2.62). The Yuntoujie muscovite granite was associated with W-Mo mineralization and has a zircon LA-ICP-MS U-Pb age of 216.8 ± 4.9 Ma (MSWD = 1.44). The Re-Os isochron age of molybdenite from the Yuntoujie W-Mo ore was 216.8 ± 7.5 Ma (MSWD = 11.3). Our new isotope data suggest that the late stage intrusive stocks from the southwestern Miaoershan-Yuechengling batholith were closely associated with W-Mo mineralization from the Indosinian period. These new results together with previous isotope data, suggest that South China underwent not only the well-known Yanshanian mineralization event, but also a widespread Indosinian metallogenic event during the Mesozoic period. Therefore, South China has a greater potential for Indosinian mineralization than previously thought such that more attention should be given to the Indosinian ore prospecting in South China.

Structural control of El Sela granites and associated uranium deposits, Southern Eastern Desert, Egypt

The El Sela area is a part of the basement complex of the Eastern Desert of Egypt and the Pan-African Shield. The area comprises outcrops of dismembered ophiolites thrust over arc volcano-sedimentary sequence and intruded by different syn- to post-tectonic granitoids. Structural analysis of the area enabled the separation and definition of four structural episodes: (E1) folding–thrusting episode associated with the cratonization of the arc/inter-arc rock association and the intrusion of the syntectonic (Older) granites. (E2) Upright folding episode associated with the compression and shortening to the ENE–WSW direction which is different from the NNW–SSE shortening direction during E1; at the end of E2, late tectonic granites were intruded. (E3) Post-tectonic granitic intrusion episode: two mica granite and granitic dikes were intruded during this episode. (E4) Fracturing, faulting, and post-granitic dike extrusion episodes caused different faults that took place after cratonization until the present. There are three generations of folds during ductile deformation (E1 and E2). The F2 folds are nearly coaxial (along ENE–WSW trend) with the F1 folds. The F3 folding is displayed by folds generally trending NNW–SSE. Therefore, the ENE–WSW and NNW–SSE trends can considered as preexisting discontinuities and mechanical anisotropy of the crust in the following structure episodes. Brittle deformation (E3 and E4) reveals the importance of those trends which control the multi-injections and many alteration features in the study area. During reactivation, a simple shear parallel to the inherited ductile fabrics was responsible for the development of mineralized structures along the ENE–WSW and NNW–SSE trends. So they can be considered as paleochannel trends for deep-seated structures and can act as a good trap for uranium and/or other mineral resources. Most of the uranium anomalies are delineated along ENE–WSW and NNW–SSE shear zones where quartz-bearing veins bounded the lamprophyre dike and microgranites and dissected them in relation to the successive fracturation and brecciation corresponding to the repeated rejuvenation of the structures. Therefore, the structural controls of the uranium mineralizations in the El Sela area appear to be related to the interaction between inherited ductile fabrics and overprinting brittle structures.

MINERAL - PETROGRAPHICAL, PETROCHEMICAL CHARACTERISTICS OF XUAN THU GRANITOID MASSIF, QUANG NGAI PROVINCE

The first time, Xuanthu granitoid massif was researched and arranged into component of Bana complex in project of 1/50,000 scale geological mapping and minerals prediction of Quangngai sheets (Than Duc Duyen et al, 1999). The investigations carried out within area of Nuocnhieu stream, SE corner of Xuanthu massif which has displayed mainly plutonic formations, such as biotite granite, medium - coarse granular 2 mica granite, fine granular granite and fine granular 2 mica granite. Vein phases are commonly aplite, pegmatoid, porphyry granite.... This paper is mainly to research on mineral - petrography and petro - geochemical characteristics as well as to make more clearly about material component, mineral forming order, forming original explaining and related mineralizations of Xuanthu granitoid massif.

GRANITOID PETROLOGY OF HAI VAN MASSIF

The granitoid formations of Hai Van massif with petrographical components consist of biotite granite, two mica granite. Chemical components of rocks are: SiO2: 69,34=73,92%, Na2O+KO: 6,11-8,11%, K2O/Na20>1. Content of Ba, Sr is low but Rb is higher. From results of Nd-Sm isotopic analysic shows that they are nearly same with stable crust material. Age of source region formation is 1,33 billion years (model of homogeneous chondrite source region), or 1,95 billion years (model of poor mantle source region). U-Pb isotopic age: 241,9+ 2 and 241,4+2.1 million years.

Radiogenic Isotope Fractionation as an Indication for Uranium Mobility in the Granites of El Shallal Area, West Central Sinai, Egypt

The granitic rocks at Wadi El Shallal area are categorized into metaluminous hornblende-biotite granites and peraluminous two- mica granites. The chemical analyses indicate that the two-mica granites are slightly altered and characterized by high uranium and thorium contents (averages 20.27 and 27.12 ppm, respectively). Compared to the hornblende-biotite granites, the 230 Th/ 234 U and 234 U/ 238 U activity ratios of the two-mica granites display values that depart significantly from equilibrium. The sample plots of the two granitic types are distributed in a trend reflecting more 234 U loss from the two-mica granites. Leaching experiments confirmed that the area around mineral grain boundaries are more enriched in 234 U relative to its parent 238 U as a result of α-recoil process that displaces the daughter nuclei outside the grain surface. This daughter ( 234 U) is ejected from the grain into the open spaces and therefore, subjected to leaching by fluids. The observed uranium series disequilibrium in the granitic rocks from El Shallal area reflects isotopic fractionation and a recent migration of uranium in the two-mica granites. The high uranium contents and U-Th isotopic composition of the two-mica granites fairly suggest that these rocks are probably the source for uranyl mineralization of the nearby Um Bogma Formation reflecting a history of leaching, mobilization and precipitation by meteoric and groundwater. However, more intensive investigations for uranium *Dept. Geology, Fac. Science, Ain Shams Univ., Cairo, Egypt.

시험방법에 따른 국내 골재의 알칼리-실리카 반응성 평가

The purpose of this study was to evaluate the alkali-silica reactivity for aggregates in Korea according to test methods: accelerated mortar bar test (AMBT) by ASTM C 1260; chemical test by KS F 2545 (ASTM C 289). The results are as follows: The AMBT (ASTM C 1260) results showed that two (2) igneous rocks (two mica granite and felsite), three (3) sedimentary rocks (arkose, red sandstone and shale), two (2) metamorphic rock (slate and vitric tuff), one (1) mineral (quartz) showed more expansion than 0.1% at 14 days. But, some sedimentary rocks and metamorphic rocks expanded more than 0.1% at 28 days even though they were less than 0.1% at 14 days. Therefore, it is necessary to extend the experimental dates more than 14 days to evaluate the possibility of alkali-aggregate reactivity. The chemical test (KS F 2545) results showed that five (5) igneous rocks (andesite, diabase, granite porphyry, muscovite granite and diorite) were indicative of potentially deleterious expansion, while two (2) igneous rocks (diorite porphyry and quartz porphyry) were possible indicative of expansion, and three (3) igneous rocks (biotite granite, two mica granite and felsite) were indicative of innocuous reactivity. The above results showed that the results from chemical method (KS F 2545) and AMBT (ASTM C 1260) had little relationship.

ASTM C 1260 실험에 의한 국내 골재의 알칼리-실리카 반응 팽창 특성

The concrete pavement at Seohae Expressway in Korea has suffered from serious distress, only after four to seven years of construction. The deterioration of ASR has seldom been reported per se in Korea, because the aggregate used for the cement concrete has been considered safe against alkali-silica reaction so far. The purpose of this study is to examine the expansion behavior of aggregates of Korea due to alkali-silica reaction by ASTM C 1260 standard method of the accelerated mortar bar test (AMBT), stereo microscopic analysis, scanning electronic microscope (SEM) analysis, and electron dispersive X-ray spectrometer (EDX) analysis. The results are presented as it follows. The accelerated mortar bar test (AMBT) showed that mica granite and felsite of igneous rocks, aroke, red sandstone and shale of sedimentary rocks, slate of metamorphic rock, and dendrite and quartz of mineral rock showed more expansion than 0.1% at 14 days. But, some sedimentary rocks and metamorphic rocks expanded more than 0.1% at 28 days even though they were less than 0.1% at 14 days. The mortar bars, which showed more than occurred 0.1% expansion, resulted in cracking on surface. SEM and EDX analysis confirmed that the white gel was a typical reaction product of ASR. The ASR gel in Korea mainly consisted of Silicate (Si) and Potassium (K) from the cement. The crack in the concrete pavement was caused by ASR. It seems that Korea is no longer safe zone against alkali-silica reaction.

Rb-Sr isotopic study of the Hwacheon granite in northern Gyeonggi massif, Korea: A case of spurious Rb-Sr whole rock age

The Yonghwasan pluton of the Hwacheon granite intruding the Precambrian metamorphic rocks of the northern Gyeonggi massif gives two apparent Rb-Sr whole rock isochrons depending on lithology: 177±11 Ma with an initial87Sr/86Sr of 0.71538±0.00031 for mica granite and 134±10 Ma with an initial87Sr/86Sr of 0.72183±0.00096 for garnet two-mica granite. However, the whole rock age for the garnet two-mica granite is much younger than mineral ages: Rb-Sr biotite (146.2±2.2 Ma) and muscovite (160.2±1.6 Ma), and reported CHIME monazite and K−Ar muscovite. Circumstantial evidences suggest that the young whole rock isochron may be the result from fortuitous alignment of data due to assimilation of country rocks, and thus meaningless, rather than resetting of whole rock Sr isotope ratios by later events such as post-emplacement heating and fluid infiltration. Considering the above, the best Rb-Sr whole rock age of the Yonghwasan pluton is estimated to be 172.0±6.8 Ma. The isotopic ages of this and previous studies for the garnet two-mica granite form a near linear cooling curve with a cooling rate of about 14.5°C/Ma.

Timing of Early Proterozoic magmatism along the Southern margin of the Siberian Craton (Kitoy area)

ABSTRACTSeveral granites and basement gneisses along the southern margin of the Siberian Craton were sampled to obtain precise age constrains and compositional isotopic data. The analysed granite plutons are interpreted to have been emplaced between 1880 and 1850 Ma, and are related to Palaeoproterozoic collisional and post-collisional events. Pb-Pb whole data of a granulite (1884 ± 26 Ma) and a two mica granite (1821 ± 29 Ma) constrain these U-Pb single zircon ages. Sr, Nd and Pb-Pb isotope data reveal the crustal origin of the investigated rocks and the reworking of Archaean material. Nevertheless, a minor influence of a mantle component is still visible in the Pb isotopes. Geodynamically, the magmatic and metamorphic ages in the Kitoy area are linked to several Early Proterozoic events along the southern margin of the Siberian Craton. Since these events are all older than the assembly of Rodinia (about 1·4 Ga ago) the collisional processes are linked to the consolidation of the Siberian Craton itself in Early Proterozoic times.

Air pollution load of forest stands in Vojířov and the impact on soil and run-off water chemistry

Research plots in Vojířov were established in a spruce stand and in a mixed stand. They are situated south of Jindřichův Hradec, near the border with Austria, on the ridge sloping to the Třeboň basin, exposed to western winds. The soils (Haplic Podzols) have developed on deep overlaps of eolian sands, between boulders of mica granite. Since summer 1991, the chemistry of precipitation water and run-off water from the O-humus horizon has been studied. Bulk deposition has been measured in the open area by the hunter’s cottage Dubovice, where the chemistry of water in a local spring has also been studied. During the investigation the deposition of air pollutants in throughfall water was higher in the spruce stand than under beech trees in the mixed stand. In 1996, an increased deposition of pollutants was observed due to long-term winter period and high precipitation. This load of the ecosystem influenced soil water chemistry, mainly the chemistry of water in the spring, expressed by decreased pH, increase in SO<sub>4</sub><sup>–2</sup>, F<sup>–</sup>, Al, Mn, only slowly disappearing in the subsequent years. At the end of the nineties the emissions of H<sup>+ </sup>, S/ SO<sub>4</sub><sup>–2</sup>, F<sup>–</sup>, N(NO<sub>3</sub><sup>–</sup>+ NH<sub>4</sub><sup>+</sup>) decreased more significantly under the spruce stand than under beech. On the contrary, pH of precipitation water decreased in the open area. Soil analyses, carried out in 1991 and 1999, confirmed certain improvement of bio-genous supply in the humus horizons and decrease in sorbed basic cations in the surface horizons of mineral soil, and increase in the supply in deeper horizons, but it still remains at a low level.

Geology and Geochemistry of Granites Around Jaswantpura, Jalore District, Southwestern Rajasthan, India

The Neoproterozoic granite plutons around Jaswantpura, western India, form a large complex of granitic rocks and, at least, four distinct granite types, based on cross-cutting relationships, have been found: coarse- to medium-grained biotite granites; medium- to fine-grained two- mica granites; coarse- to medium-grained porphyritic hornblende granites and fine-grained biotite granites with accessory hornblende. Younger acidic and basic dykes cut these granites. The Jaswantpura granites show a narrow range of variation in terms of their chemistry. The hornblende granites are hypersolvus with mild peralkaline character as reflected by the enrichment in incompatible trace elements including Zr, Nb, La and REE but are characterized by relatively low Sr and Al 2O 3. The biotite granites are subsolvus, mildly to moderately peraluminous and are characterized by relatively high SiO 2, Al 2O 3, Rb and low Zr, Nb and REE contents compared to the hornblende granites. The mineralogical and chemical characteristics of the different granite types exposed in the Jaswantpura area point to a continental crust source.

Postcollisional granites in the South Tien Shan Variscan Collisional Belt, Kyrgyzstan

Two major types of the potassium-rich postcollisional granites of Permian age were studied in the South Tien Shan Variscan Collisional Belt. The first type, metaluminous granites of the Jangart complex, are located along the southeastern boundary of this belt with the Precambrian Tarim Block. The plagioclase rims on K-feldspar megacrysts (rapakivi texture), extremely high FeOt/(FeOt+MgO) ratio, indications of the low H2O and O2 fugacities, high concentrations of the incompatible elements especially light rare earth elements (LREE), Ba, Nb along with heightened contents of the compatible elements especially Ni, Cr and moderately initial 87Sr/86Sr ratio (Sr0=0.7075) make those granites similar to other rapakivi granites. The second type, peraluminous granites of the Inylchek complex, is located along the northwestern boundary of the belt with the Caledonian Kazakh Microcontinent. Those granites are rich in F, B, Li, Rb, Cs, Sn, Ta and heavy rare earth elements (HREE), but are poor in Ba, Sr, Ni and Cr and are characterized by the relatively high initial 87Sr/86Sr ratio (Sr0=0.7098). Li–mica granites are distributed widely among them. The granites of a transitional type (Uchkoshkon complex) occupy an intermediate geographic position between major granite types. The initial Sr isotopic composition of the transitional granites varies widely (Sr0 from 0.7080 to 0.7256). The variation in chemical composition of the coeval postcollisional granites across the Collisional belt, together with the variability of initial Sr isotopic ratios of the transitional granites, are thought to indicate basement heterogeneity. This heterogeneity, in turn, is probably related to thrusting of the Tarim Block under South Tien Shan during the collision.

Uranium mineralization in the two mica granite of Gabal Ribdab area, South Eastern Desert, Egypt

Among the different rock units in the Gabal Ribdab area, the two-mica leucogranite and muscovite pegmatitic granite are the most favourable host rocks for uranium and thorium mineralization. The muscovite pegmatitic granite shows evidence of post-magmatic alteration, e.g. Na- and K-metasomatism, whereas the two-mica leucogranite could be regarded as being fresh. The spectrometric survey revealed the presence of three enriched zones with a maximum eU content of 140 ppm and the maximum eTh is 36 ppm. Uranophane, zippeite and becquerelite are the most abundant uranium minerals. The origin of these secondary minerals is mainly related to alteration of primary minerals by the action of oxidizing fluids, mobilization of uranium and then redeposition in other forms. Redistribution by circulating meteoric waters might have taken place.

Geochemical evolution of peraluminous paleoproterozoic bandal orthogneiss NW, Himalaya, Himachal Pradesh, India: implications for the ancient crustal growth in the Himalaya

Paleoproterozoic (1900±100 Ma) granites along a 2000 km linear belt in the Lesser Himalaya are significant in terms of their tectonic setting and emplacement as they form the basement for younger sedimentary cover rocks. The geochemistry and petrogenesis of one granitic body (Bandal Orthogneiss, 1904±70 Ma) from the Lesser Himalayan belt has been studied and correlated with the other plutons in the belt. The Paleoproterozoic Bandal orthogneiss, covering ∼500 sq. km surface area, occupies the core of the Kulu-Rampur window, Himachal Pradesh, NW Lesser Himalaya. The orthogneiss is S-type, peraluminous and can be subdivided into two suites: a muscovite-biotite granite [Suite I, coarse grained porphyritic gneiss (CPG) and fine grained gneiss (FG)] and a tourmaline-muscovite granite [Suite II, leucogranite, (LG)]. The two mica granites (Suite I) form the bulk of the Bandal orthogneiss whereas the tourmaline-bearing granite, which cuts across suite I, occurs in the central part of the main pluton. Comparison of their bulk composition with melt experimental data suggest formation of LG from a water-undersaturated magma of minimum-melt composition at pressures around 3–4 kbar whereas the tourmaline-free granites may have been derived by melting due to biotite dehydration at pressures >5 kbar. High concentrations of MgO+FeO, Ba/Sr, Rb/Sr and Ti of the two-mica granites reflect higher extents of melting derived from biotite dehydration melting of a metasedimentary source. Tourmaline leucogranites with higher Rb/Sr and low Ba/Sr ratios represent low-fraction melts extracted from their protoliths under conditions of low water activity. The striking similarities in terms of the geological setting, geochemical characteristics and the age data between Bandal orthogneisses and the adjoining Wangtu Gneisses suggest that they were formed under similar tectono-magmatic environment during Paleoproterozic period. The wide spread occurrence of Paleoproterozoic gneisses in the Lesser Himalayan belt strongly suggest that they represent the granitic basement on which the younger sedimentary rocks were deposited. The geochemical studies on the overlying sedimentary rocks (Chail and Jutogh formations) in the Lesser Himalaya suggest that the huge volumes of granitic magmatism played a significant role in changing the crustal composition of the Himalayan rocks from mafic to felsic during the post-Archean.

CHIME monazite age of granitic rocks in the Sunchang shear zone, Korea: timing of dextral ductile shear

A CHIME (chemical U-Th-total Pb isochron method) age determination was carried out for the first time for monazite grains from the Sunchang, Taegang, and Namwon granites in the northeastern part of the Sunchang dextral ductile shear zone (Imsil-Namwon area), Korea. The results show that (1) the Sunchang granite is of 179±2 Ma, (2) the Taegang granite, 178±2 Ma, and (3) the Namwon granite 180±10 Ma (two mica granite), 181±6 Ma (porphyritic granite), 180±3 Ma (biotite granite), and 178±5 Ma (pegmatitic granite). These ages and closure temperature of monazite (650–700°C) suggest that the emplacement of these granites was contemporaneous in Early Jurassic. Based on the cooling curve of granitic rocks and deformation condition (ca. 300–550°C) estimated by feldspar microstructures of mylonites, the Sunchang shear zone was mylonitized during the period between 180 and 160 Ma. It indicates that the dextral ductile shear of the Sunchang shear zone occurred in early Middle Jurassic.

Geologic and geochemical characteristics of the Yichun Ta-Nb-Li deposit, Jiangxi Province, South China

The Yichun Ta-Nb-Li mine is situated within a small, sheetlike body of topaz-lepidolite granite which is the most fractionated phase of the Yashan batholith. Volumetrically, the most important phase in the batholith is a coarse-grained, protolithionite-muscovite granite which has a finer grained, muscovite granite margin. The protolithionite-muscovite granite is intruded by small bodies of muscovite granite which form the locus of a tungsten vein system at the Xin Fang tungsten mine. Two sheetlike bodies, a lower Li mica granite and an upper topaz-lepidolite granite intrude the upper contact between the protolithionite-muscovite granite and the host metasediments. The granites are crosscut by unmineralized porphyry dikes that are exploited as a source of kaolin. The topaz-lepidolite granite is a major, low-grade Ta-Nb-Li deposit which is exploited via open-pit mining. The topaz-lepidolite granite is composed dominantly of albite, lepidolite. and quartz, with topaz. K feldspar, amblygonite, and accessory zircon, monazite, pollucite, columbite-tantalite, microlite, and Ta-rich cassiterite. Phenocrysts of quartz, topaz, and K feldspar contain abundant inclusions of albite laths and occasional lepidolite crystals along growth zones (snowball texture), indicating simultaneous crystallization of these minerals from a subsolvus, residual magma. The topaz-lepidolite granite is characterized by high F, Li, P, Al 2 O 3 , and Na 2 O contents (with Na 2 O > K 2 O), and by very low SiO 2 , TiO 2 , MgO, CaO, and K 2 O contents. It is strongly enriched in Rb, Nb, and Ta, and strongly depleted in Sr and Zr compared with the earlier granite phases. Chemical trends are consistent with an origin via fractionation involving especially the removal of plagioclase, K feldspar, quartz, Fe-Mg silicates, and zircon. Most of this fractionation appears to have taken place within a deeper level magma chamber, with successive magma batches emplaced into the present level of exposure. Mineralization at Yichun consists of columbite-tantalite, microlite, and Ta-rich cassiterite which occur throughout the topaz-lepidolite granite closely associated with, and as inclusions, in lepidolite. The ore minerals also occur as interstitial crystals between the major silicate phases. Crystallization of the Nb-Ta-Sn minerals is an integral part of the cystallization of the topaz-lepidolite granite, and the effects of postmagmatic alteration in the formation of mineralization are absent or minor.

Geochemistry of Dadeldhura granite and its mineral potential

Dadeldhura granite is a cordierite bearing two mica granite. It is S-type, leucocratic and rich in silica, alumina and potash and slightly low in soda. In this granite a remarkable evolutionary trend is marked by the general increase in SiO2, Al2O3 , K2O , Na2O , P2O5, Rb, Nb and depletion of CaO, MgO, Fe2O3, TiO2, Ba, Sr, Zr, Zn and V etc. towards later phase. Mineral chemistry of biotite and feldspar and plot of chemical data on variation diagrams and triangular diagrams show a moderate to fairly strong differentiation trend from (i) granite gneiss (GGN), (ii) biotite granite (BGR) to (iii) muscovite granite (MGR) and (iv) aplitic tourmaline granite (TGR). Many physical, mineralogical and chemical characteristics of Dadeldhura granite resemble with world's average tin granite.

Intrusion sequences within ore‐bearing granitoid plutons

AbstractA new database of some 200 granitic bodies throughout the world associated with Sn, W and Mo deposits is analysed with respect to size and petrological characteristics. Most Sn, W and Mo deposits relate to small stocks not exceeding 25 km2. Biotite granites are the most common type of ore‐bearing plutons, while two mica granites are subordinate. There seems to be an upward grading in grain size such that the later, higher members of a suite are the finest grained. Ore‐bearing processes relate to deep evolving differentiation of specialized magmas modified by mantle fluids.

Geología y geoquímica del granito de Montánchez (Cáceres)

The granite of Montanchez (Caceres, Spain) is located to the S.E. of the Albala granite and is separated from it by a strongly tectonized zone. According to the mica content, three perografic facies have been distinguished in the Montanchez granite. Facies 1, is made up of medium to coarse grained, two mica granites richer in muscovite, which occupy the northern half of the granite and have been extremely deformed. Facies II, consiting of coarse to very coarse grained, sometimes porphyrblastic, two-mica granites, richer in biotite, has not been deformed, or very little. Facies III is made up of aplitic muscovite granties which are poor in biotite and rich in tourmaline. The Montanchez granite frecuently contains tonalitic xenolith, sometimes quitee large. Regarding the geochemistry of the Montanchez granite the major and some trace elements have been analyzed on 22 samples belonging to the three different facies and the tonalitic xenoliths. As for the major elements, the chemical-mineralogical parameters of la Roche, the binary diagrams of Harker, Larsen, la Roche and Deban and Le Fort, and the ternary diagrams Na 2 O, K 2 O, CaO, Na 2 O+K 2 O, Al 2 O 3 , CaO and AFM have been calculted. They indicate that these granties are made up alkaline rocks richer in Na than K, poor in Ca, and with a markedly peraluminous character. Concerning the distribution of the trace elements in the Montanchez granite the average conten in Rb, Ba, Sr, Zr and Nb lower and those in Sn and Zn higher, than the values reported by different autors for several world granites considered to be standard.

Geochemistry of the granitic rocks and their minerals from Serra da Estrela, Central Portugal

Several types of Hercynian peraluminous granitic rocks ranging from biotite-muscovite granodiorite to muscovite granite occur in the horst of Serra da Estrela. Variation diagrams of most major and trace elements of the rocks and biotites and Cr and V of muscovites show fractionation trends. However, Nb, Li, Rb, K Rb , Li Mg variation diagrams of the rocks and muscovites and also of Sn, Cs, Cs K of the muscovites indicate that the muscovite granite probably originated by another mechanism. Least squares analysis of major elements and modelling of trace elements indicate that the coarse grained porphyritic biotite-muscovite granite, granite porphyry and fine to medium grained muscovite-biotite granite were derived from the granodiorite magma by fractional crystallization of plagioclase, quartz and biotite. Emplacement of granodiorite magma took place at 3.5–3 Kb and 720°C: granites and granite porphyry probably originated about 690°C, but were completely crystallized about 520°C. ƒ O2 was about 10 −17 for the granodiorite and <10 −18 for the two mica granites and granite porphyry. Log ( ƒ HCl ƒ HF ) was higher, whereas log ( ƒ h2o ƒ hcl ) was lower in the granodiorite than in the other granitic rocks of the fractionated series. The coarse-grained porphyritic biotite-muscovite granite was hydrothermally altered between 400–350°C and 260–230°C at about 1.5–1 Kb. The hydrothermal fluids were probably mainly meteoric in origin, but some fluids released during the late stage of granite solidification might also have been involved.