Tourmaline Granites Research Articles

The magmatic evolution of the Land's End pluton, Cornwall, and associated pre-enrichment of metals

The peraluminous Land's End granite is one of the composite plutons forming the late-Variscan Cornubian batholith. The western part of the pluton hosts the Sn–Cu mineralisation of the St. Just mining district. The pluton consists of early megacrystic biotite (Mg-siderophyllite) granites and albite microgranites and younger Li-siderophyllite granites, and tourmaline granites together with fine-grained massive quartz–tourmaline rocks (MQT). Most of the granite varieties evolved by fractional crystallisation from a common crustal magmatic reservoir, apart from the albite microgranite, which has a different source. Trace element analyses of K-feldspar megacrysts in the older biotite granites made using laser ablation ICP-MS reveal that the megacrysts were derived from moderately evolved sources and now reside in separate granite sub-stages with variable degrees of fractionation, so that equilibrium between phenocrysts and host no longer persists. The younger granites show a strong in situ fractionation at the cm- to 100-m-scale, whereby boron-rich melts are concentrated in the apical parts of the individual intrusive units. Geological, textural and mineralogical data suggest that the tourmaline granites and MQT evolved mainly from fractionated Li-siderophyllite granites. Cathodoluminescence, trace element and melt inclusion studies of quartz from the MQT reveal that the MQT was formed during the transition from the magmatic to hydrothermal states from a mixture of immiscible phases. The Li-siderophyllite granites, tourmaline granites and MQT appear to be the immediate magmatic precursors from which the hydrothermal fluids responsible for the mineralisation in the St Just district originated.

Late-stage alteration and tin–tungsten mineralization in the Khuntan Batholith, northern Thailand

The Khuntan Batholith is part of the Triassic–Jurassic eastern marginal belt of the Northern Thailand Granite Province. Most of the batholith consists of coarse-grained, porphyritic to megacrystic biotite–muscovite granite (Huai Mae San unit). However, the southeastern part, called the Muang Yao unit, consists of coarse- to medium-grained muscovite and muscovite–tourmaline granite and is associated with Sn–W mineralization. The Huai Mae San granite has S-type petrological features typical of batholiths in the eastern marginal belt, which formed in a syn-collisional setting. The more silicic Muang Yao granite differs chemically from felsic S-type granite, for example in extreme Rb–Y–Nb enrichment and Ba–Sr–Zr depletion, probably as a result of late-stage fluid alteration. Vein-hosted deposits of cassiterite, scheelite, and wolframite associated with minor sulfides occur in both the Muang Yao granite and adjacent metamorphic rocks. Fluid-inclusion studies indicate that both aqueous and aqueous-carbonic fluids of low salinity (0–8 wt% equiv. NaCl) were involved in vein formation, and were subject to pressure fluctuation between essentially lithostatic and hydrostatic conditions. Dilution of magmatic hydrous fluid by influx of meteoric water may explain the anomalously low salinity. Oxygen isotope data support a primary magmatic origin for the fluid, and indicate temperatures of ca. 400 °C for ore deposition. The three vein-type Sn–W deposits of this study represent a spectrum from an endogranite vein system to proximal-intermediate vein systems of magmatic-hydrothermal origin.

Boron determination in tourmaline by neutron induced radiography

The technique of neutron induced radiography has been applied to determine the boron concentration and its spatial distribution in mineral tourmaline collected from Swat Tourmaline Granite, Northern Pakistan. The technique involves the simultaneous irradiation of sample and a standard fixed on a track detector with thermal neutrons and the counting of alpha and 7 Li tracks produced in the detector from the nuclear reaction 10 B( n,α) 7 Li . Boron concentration is determined by comparing the 7 Li and alpha particle tracks density with that of a standard of known boron concentration. Boron concentration in tourmaline has been found to be (3.40±0.01)% in this study which is on the upper side within the normal range (2.5–3.8)% reported in the world. The presence of somewhat higher concentration of boron in tourmaline indicates that the Swat Tourmaline Granite was generated as a late stage hydrothermal activity during the Himalayan Orogeny.

Fluid-Absent Melting Behavior of a Two-Mica Metapelite: Experimental Constraints on the Origin of Black Hills Granite

We have studied experimentally the vapor-absent melting behavior INTRODUCTION of a Proterozoic metapelite (HP-60-1) from the Black Hills, South Peraluminous leucogranites such as the Miocene granites Dakota, to assess whether the high-dO, tourmaline-bearing granites of the Himalaya and tourmaline granites of the Harney of the Harney Peak suite resulted from muscovite-dominated dePeak suite in South Dakota are widely considered to be hydration-melting at 10 kbar. Samples were sealed with no added the product of muscovite dehydration-melting; yet few H2O in gold capsules, then run in a 0·5 inch (1·27 cm) pistonexperimental studies of muscovite dehydration-melting cylinder apparatus over the temperature interval 812–975°C. reactions have been performed, because the low temExperiments were conducted at 10 kbar to allow comparison with peratures of the reactions hinder the approach to equiother metapelite melting studies. Mass balance calculations imply librium. In addition, melt fractions generated are typically the melting reaction muscovite + biotite + plagioclase + quartz low, resulting in small melt pockets which are very difficult → melt + alkali feldspar + aluminosilicate + garnet until to analyze with the electron microprobe. In this study, muscovite is exhausted (<812°C), then the reaction biotite + we assess the possible genetic relationship between the plagioclase + quartz + alkali feldspar ± aluminosilicate → tourmaline-bearing granites of the Harney Peak suite melt + garnet. The inferred muscovite reaction is completed below and the aluminous metasediments these granites intrude. 812°C and produces 1–2 wt % melt. Melt production of the Although the attempt to investigate the muscovite decontinuous biotite reaction increases steadily with rising temperature, hydration-melting reaction was hindered by the surto 32 wt % in our highest temperature run. The low melt prisingly low melt productivity, we were able to infer a productivity of the muscovite reaction at 10 kbar suggests that balanced reaction, illuminating the dominantly peritectic melting at lower pressures may be necessary to generate mobile melt nature of fluid-absent muscovite breakdown under the fractions by muscovite-dominated reactions in our starting material. conditions investigated. In addition, melts of HP-60-1 are considerably more mafic than Isotopic and trace element studies indicate a genetic the tourmaline-bearing granites, with average combined TiO2 + relationship between S-type granites and aluminous metaMgO+ FeO contents of 1·85 wt % and 0·84 wt %, respectively. sediments in the Black Hills of South Dakota, where the In particular, melts of HP-60-1 are enriched in Ti, and would Harney Peak Granite (HPG) intruded Proterozoic and probably stabilize biotite rather than tourmaline upon cooling, Archean schists and metagreywackes undergoing regional arguing against HP-60-1 as a potential source rock for the metamorphism. The timing and mode of emplacement of tourmaline granites. the HPG, and the deformation and regional metamorphic

PADRÕES DE ETR EM GRANITOS CRUSTAIS, CÁLCIO-ALCALINOS E RAPAKIVI: INFLUÊNCIA DOS MINERAIS ACESSÓRIOS

One hundred and twenty three analyses for rocks, matrixes of porphyritic rocks and accessory minerals (sphene, zircon, tourmaline) from crustal (including tourmaline granites), calc-alkaline and rapakivi granites from the State of Sao Paulo, SE Brazil, are presented, compared and discussed. By zircon typology, these granites belong to the lineages 3,4a, 4b, and 5 in Pupin's (1980) classification. The data show large influence of sphene, zircon, and tourmaline in the shape of the whole rock REE pattern of the, respectively, crustal/calc-alkaline, rapakivi and tourmaline granites. The matrixes of porphyritic rocks show higher REE contents than the whole rocks; the zircons from different granitoids lineages have REE contents proportional to those of the host rocks, and in the tourmaline granites the REE contents reflect clearly the modal percentage of this accessory mineral. The mean REE contents in these rocks increase progressively along the lineage sequence 3, 4a, 4b and 5. The data also show the active participation of accessory minerals in the fractional crystallization of granitic magmas and that the interpretation of the REE pattern of granitoids is a complex task which requires not only whole rock data but also those of REE concentration in accessory minerals or chemical data which allow to trace their behaviour during magma evolution.

Primary lithological variation in the kaolinized St Austell Granite, Cornwall, England

Geological mapping of existing and redundant kaolin workings within the St Austell Granite has identified a suite of granitic rocks which show evidence of complex late-stage magmatic and hydrothermal processes. Coarse porphyritic biotite granites, like those which predominate in southwest England, occur much more widely than previously acknowledged, and are intruded by an apparently cogenetic suite of lithium-mica granites and tourmaline granites. The tourmaline granites characteristically exhibit very variable textures, with coarse quartz grains set within a fine grained, tourmaline-rich matrix. A highly evolved fine-grained tourmaline granite represents the most evolved of this suite. Topaz granites intrude the earlier granite varieties, and all are intruded by rhyolite porphyry dykes (elvans). Major and trace element chemical data suggest that the biotite granite–lithium-mica granite–tourmaline granite suite represents the product of crystallization of a granitic magma within which B (but not F) became progressively enriched until water saturation was achieved. Water exsolution effectively quenched any remaining granitic melt, resulting in the very variable textures shown by the tourmaline granites. The topaz granites are chemically distinct from their predecessors, showing marked enrichment in F, Li and P 2 O 5 (but not B). Instead of being products of differentiation of biotite granite magma, the topaz granite melts may have been derived separately in a later episode of partial melting of the same source. Kaolinization is widespread throughout the western part of the St Austell Granite, and deposits worked at present tend to be located in granite varieties other than biotite granite. The geochemical parameters used to distinguish the primary granite types (particularly Nb v. Zr and Ga–Nb–Zr plots) are sufficiently robust to permit the parent granitic rock type to be identified for heavily kaolinized material.

Rare metal mineralization related to granites and pegmatites, Phuket, Thailand

Rare metal mineralization on Phuket Island, southern Thailand, comprises deposits of Sn, Nb-Ta, and W. Mineralization is related to Cretaceous granites of the Khao Tosae Suite and their pegmatite derivatives. The Khao Tosae Suite granites and the pegmatites intrude other granite suites and the Carboniferous-Permian metasedimentary rocks of the Phuket Group. The Khao Tosae Suite consists of fine- to medium-grained, porphyritic biotite-muscovite + or - tourmaline granites. The pegmatites are grouped into three types according to their main mineral assemblages: K feldspar-muscovite-tourmaline, K feldspar-albite-muscovite, and albite- K feldspar-lepidolite dikes. Petrogenetic studies indicate that Sn and Nb-Ta mineralization is extended from the late-magmatic stage to the pegmatite and postmagmatic, hydrothermal stages of the Khao Tosae Suite. Besides its occurrence in the pegmatites, cassiterite precipitated during at least three periods in the Khao Tosae Suite granites, each of which has distinct petrochemical characteristics. Nb-Ta minerals occur in both the Khao Tosae Suite granites and the pegmatites as wolframoixiolite, niobian-tantalian rutile, and columbite- tantalite exsolutions in cassiterite. In addition, discrete grains of columbite-tantalite and microlite locally occur in the pegmatites. Wolframite is represented by huebnerite and is associated with the last stage of cassiterite deposition, occurring in late vugs and/or quartz veins in the Khao Tosae Suite granites. The Phuket deposits represent a rather rare example of a granite-related (Sn,Nb-Ta,W)-bearing system with substantial evolution of pegmatites as well as postmagmatic greisen and vein mineralization. The pegmatites are notable for their largely greenschist facies environment, lack of Be and P minerals, tourmaline sharply decreasing in abundance from early to late generations of pegmatite dikes, and a distinct accumulation of Sr and Ba in the otherwise most fractionated lepidolite-rich dikes. The pegmatites also provide the first example of Fe-Mn and Nb-Ta fractionation in successive generations of primary granitic to pegmatitic cassiterite (as reflected in its exsolved columbite-tantalite), which perfectly mimics fractionation trends established for primary columbite-tantalite in corresponding categories of pegmatites.

Pressure, temperature and time constraints on Himalayan metamorphism from eastern Kashmir and western Zanskar

Himalayan metamorphism in the Kashmir and Zanskar sector of the High Himalaya resulted from thrust- and fold-related crustal thickening within the Indian plate following the collision of India and Asia at c. 50 Ma. Interbanded metapelites, marbles, calcareous schists, amphibolites and quartzites represent metamorphosed equivalents of the Palaeozoic-Lower Mesozoic continental margin rocks. Granitic rocks include pre-collision K-feldspar megacrystic and biotite granites and post-collision two-mica ± garnet ± tourmaline granites. Average pressure-temperature conditions of equilibration using the self-consistent thermodynamic data-set of Holland &amp; Powell (1990) are presented across a 45 km traverse of the eastern Kashmir-western Zanskar High Himalaya. Kyanite is the stable aluminosilicate phase across 35 km outcrop width in the middle of the slab. Complex microstructures indicate that prograde metamorphism up to kyanite grade and fabric development in the upper structural nappes is early and unrelated to the Main Central thrust. Diachronous metamorphism propagated southwards with the overall structural evolution. Early isograds and thrust-fold structures were carried passively in the hanging-wall of the Main Central thrust. Peak metamorphism, based on 40 Ar/ 39 Ar hornblende ages, occurred pre–30.7 ± 2.0 Ma at the top of the slab, and in the middle of the slab was pre-22 ± 1.0 Ma, probably 25-28 Ma. The lower structural levels in Zanskar record peak metamorphic conditions around 700–750 °C and 8 kbar, reflecting depths of burial of 28–30 km. A new younger schistosity, which is not present in the higher structural levels, was developed under kyanite grade conditions. The regional distribution of high temperatures recorded by thermo-barometry does not support the concept of additional heat being supplied by frictional heating along the Main Central thrust or magmatic heat resulting from anatexis. Exhumation of the Himalayan metamorphic rocks was achieved by three major processes: erosion as a result of crustal thickening, uplift of the rocks along the hangingwall of the Main Central thrust above a major frontal ramp in the Kishtwar Window area, and extensional unroofing along the footwall of a large-scale, NE-dipping normal fault at upper crustal levels, probably synchronous with compression at depth.

The evolution of perpendicular linear fabrics in synkinematically emplaced tourmaline granite (central moravia-bohemian massif)

Sheets of leucocratic peraluminous tourmaline granite were synkinematically emplaced into metasediments of the Svratka Crystalline Unit during the Variscan orogeny. The granite was deformed under hightemperature conditions close to the solidus, as indicated by quartz microstructures and the presence of prism ( c) glide in quartz. Decrease in the temperature of deformation causing orthogneissification of the granite is documented by transition from prism ( c) to prism ( a) and basal ( a) glide operating in quartz grains. Two mutually perpendicular stretching lineations originated during high-temperature deformation of the granite. Detailed three-dimensional analysis of tourmaline preferred orientations underlining both lineations has been performed and the distributions have been compared with theoretical predictions of Jeffery and March for rotation of rigid linear markers. The origin of mutually perpendicular linear fabrics is discussed on the basis of numerical models. Transpression, considered as a combination of northwestward shearing accompanied by shortening across and lengthening along the shear plane, is proposed to explain the perpendicular linear fabrics observed.

The generation and crystallization conditions of the Proterozoic Harney Peak Leucogranite, Black Hills, South Dakota, USA: Petrologic and geochemical constraints

The mineralogy, petrology and geochemistry of the Proterozoic Harney Peak Granite, Black Hills, South Dakota, were examined in view of experimentally determined phase equilibria applicable to granitic systems in order to place constraints on the progenesis of peraluminous leucogranites and commonly associated rare-element pegmatites. The granite was emplaced at 3–4 kbar as multiple sills and dikes into quartz-mica schists at the culmination of a regional high-temperature, low-pressure metamorphic event. Principally along the periphery of the main pluton and in satellite intrusions, the sills segregated into granite-pegmatite couplets. The major minerals include quartz, K-feldspar, sodic plagioclase and muscovite. Biotite-{Mg No. [Molar MgO/(MgO+FeO)]=0.32-0.38} is the predominant ferromagnesian mineral in the granite's core, whereas at the periphery of the main pluton and in the satellite intrusions tourmaline (Mg No.=0.18–0.48) is the dominant ferromagnesian phase. Almandine-spessartine garnet is also found in the outer intrusions. There is virtually a complete overlap in the wide concentration ranges of SiO2, CaO, MgO, FeO, Sr, Zr, W of the biotite- and tourmaline-bearing granite suites with no discernable differentiation trends on Harker diagrams, precluding the derivation of one suite from the other by differentiation following emplacement. This is consistent with the oxygen isotope compositions which are 11.5 ± 0.6‰ for the biotite granites and 13.2 ± 0.8‰ for the tourmaline granites, suggesting derivation from different sources. The concentrations of TiO2 and possibly Ba are higher and of MnO and B are lower in the biotite granites. The normative Orthoclase/Albite ratio is extremely variable ranging from 0.26 to 1.65 in the biotite granites to 0.01–1.75 in the tourmaline granites. Very few sample compositions fall near the high-pressure, watersaturated haplogranite minima-eutectic trend, indicating that the granites for the most part are not minimum melts generated under conditions with \(a_{{\text{H}}_{\text{2}} {\text{O}}}\)=1. Instead, most biotite granites are more potassic than the water-saturated minima and eutectics and in analogy with experimentally produced granitic melts, they are best explained by melting at ∼6 kbar, \(a_{{\text{H}}_{\text{2}} {\text{O}}}\)<1 and temperatures ∼800°C. Such high temperatures are also indicated by oxygen isotope equilibration among the constituent minerals (Nabelek et al. 1992). Several of the tourmaline granite samples contain virtually no K-feldspar and have oxygen isotope equilibration temperatures 716–775°C. Therefore, they must represent high-temperature accumulations of liquidus minerals crystallized under equilibrium conditions from melts more sodic than the water-saturated haplogranite minima or during fractionation of intruded melts into granite-pegmatite couplets accompanied by volatile-aided differentiation of the alkali elements. The indicated high temperatures, \(a_{{\text{H}}_{\text{2}} {\text{O}}}\)<1, the relatively high TiO2 and Ba concentrations and the relatively low \(\partial ^{18} {\text{O}}\) values of the biotite granites suggest that they were generated by high-extent, biotite-dehydration melting of an immature Archean metasedimentary source. The ascent of the hot melts may have triggered low-extent, muscovite-dehydration melting of schists higher in the crust producing the high-B, low-Ti melts comprising the periphery of the main pluton and the satellite intrusions. Alternatively, the different granite types may be the result of melting of a vertical section of the crust in response to the ascent of a thermal pulse, with the low-\(\partial ^{18} {\text{O}}\) biotite granites generated at a deeper, hotter region and the high-\(\partial ^{18} {\text{O}}\) tourmaline granites at a higher, cooler region of the crust. The low-Ti and high-B concentrations in the high-\(\partial ^{18} {\text{O}}\) melts resulted in the crystallization of tourmaline rather than biotite, which promoted the observed differentiation of the melts into the granitic and pegmatitic layers found along the periphery of the main pluton and the satellite intrusions.

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.

Collision tectonics of the Ladakh-Zanskar Himalaya

The collision of the Indian Plate with the Karakoram-Lhasa Blocks and the closing of Neo-Tethys along the Indus Suture Zone (ISZ) is well constrained by sedimentologic, structural and palaeomagnetic data at ca. 50 Ma. Pre-collision high P— low T blueschist facies metamorphism in the ISZ is related to subduction of Tethyan oceanic crust northwards beneath the Jurassic-early Cretaceous Dras island arc. The Spontang ophiolite was obducted south westwards onto the Zanskar shelf before the Eocene closure (Dl). The youngest marine sediments on the Zanskar shelf and along the ISZ are Lower Eocene, after which continental molasse deposition occurred. After ocean closure, thrusting followed a SW-directed piggy-back sequence (D2). This has been modified by late-stage breakback thrusts, overturned thrusts and extensional normal faulting associated with culmination collapse and underplating. The ISZ and northern Zanskar shelf sequence are affected by late Tertiary redirected backthrusting (D3), which also affects the Indus molasse. A 50 km wide ‘pop-up’ zone with divergent thrust vergence was developed across the Zanskar Range. Balanced and restored cross sections indicate a minimum of 150 km of shortening across the Zanskar shelf and ISZ. Post-collision crustal thickening by thrust stacking resulted in widespread Barrovian metamorphism in the High Himalaya that reached a thermal climax during Oligocene-Miocene times. Garnet-biotite-muscovite + tourmaline granites were generated by intracrustal partial melting during the Miocene within the Central Crystalline Complex. Their emplacement on the hangingwall of localized ductile shear zones was associated with SW-directed thrusting along the Main Central Thrust (MCT) zone and concomitant culmination collapse normal faulting along the Zanskar Shear Zone (ZSZ) at the top of the slab. Metamorphic isograds have become inverted by post-metamorphic SW-verging recumbent folding and thrusting along the base of the High Himalayan slab. Along the top of the slab, isograds are the right way up but are structurally and thermally telescoped by normal faulting along the ZSZ. 1

Petrogenesis of tourmaline granites and topaz granites; the contribution of experimental data

Fluorine and boron are generally only minor components of granitic rocks, but may be found highly concentrated in certain tourmaline granites and topaz granites (up to 1 wt.% B 2O 3 and 3.2 wt.% F, respectively). Studies of various examples of these granite types, which occur as small bodies emplaced at shallow levels (P lithostatic < 3 kbar), suggest that both represent residual melts produced in late stages of high level fractionation of crustal granitic magmas. Textural and petrographic data indicate that the tourmaline and topaz granite magmas crystallized at low to moderate temperatures (below ∼ 700°C) and that a fluid phase may have been present during the crystallization interval. Both granites varieties are peraluminous (Co up to 5%), characterized by the presence of white micas (lithium micas or muscovite), aluminium silicates and other Al-rich minerals (garnet, cordierite). Boron and fluorine are hosted by tourmaline (schörl-rich member of the schörl-dravite series), topaz and mica, respectively. These granites have low Ca, Fe, Mg and Ti contents (each < 1% oxide) and characteristically have over 95% normative Qz + Ab + Or. Trace element data and the high volatile content is also consistent with an origin by crystallization of highly differentiated residual melts. Post-magmatic hydrothermal processes may redistribute both F and B as well as other elements and often involve SnW mineralization. The crystallization of tourmaline granite and topaz granite magmas is discussed using experimental data derived from studies of granitic systems with added boron and fluorine. Both elements act as a flux, enabling boron and fluorine enriched melts to persist to temperatures as low as 650°C at 1 kbar. In addition the effect of increasing fluorine content displaces the minimum in QAbOr at P H 2 O = 1 kbar toward the albite apex. Plots of fluorine-rich topaz granites coincide with this trend, suggesting that the role of fluorine in magmatic processes may have affected the rock composition as well as crystallization temperatures. Boron-rich granites plot near the low P H 2 O minima in QzAbOr, suggesting that boron has less of an influence on minimum melt compositions. The low temperatures of crystallization permits phases such as muscovite or andalusite, topaz, and two alkali feldspars to crystallize directly from F and B enriched melts at low pressures. In addition, the limited available experimental data are used to compare the effects of fluorine and boron on major and trace element distribution during melt-vapour interaction.

Mineralogy and Geochemistry of Palung Granite Massif

Palung massif which has a sharp contact with the country rocks, is one of those six granitic bodies that are situated in the Mahabharat Range of Central Nepal. This massif is a multiphase intrusive containing a number of facies rock varieties. The most widely distributed facies are coarse grained inequigranular porphyritic tourmaline granites in the central part and inequigranular tourmaline granites with portions of micropegmatitic texture in the apical part. Mineralogical and geochemical studies reveal that these granites are probably leucocratic differentiate of palingenetic granitic magma.

Experimental study of granitic rocks of Darjeeling (West Bengal, India) and its application to the origin of himalayan granites

The area around Darjeeling consists of low-to-high grade metamorphic rocks with the development of typical index minerals, viz. chlorite, biotite, almandine, kyanite and sillimanite. At the highest stage of regional metamorphism (sillimanite—orthoclase subfacies), rocks are intimately associated with the migmatites and granites. The high-grade gneisses contain inclusions of isolated, round, oval or thin lenticular masses of quartz + calcic plagioclase + garnet + clinopyroxene ± hornblende ± biotite ± sphene +- graphite +- zoisite rocks typical of hornblende/pyroxene granulite facies. Low-grade rocks are devoid of these inclusions.Phase relationships of a granite and a gneiss from Darjeeling have been determined at 4 and 7 kbar pressure in the presence of excess water. The beginning of melting and the disappearance of the phases, viz. sodic-plagioclase, K-feldspar, muscovite, biotite, and quartz have been noted. Plagioclase is the first phase melted out in the granite. In the gneissic rock, plagioclase melts out at a slightly higher temperature than muscovite. Both quartz and biotite are the silicate liquidus phases in the granite and gneiss. Complete fusion of both the rocks was achieved at temperatures below 800°C.The new data demonstrate that crystal—liquid equilibria played a dominant role in the formation of magmas of granodiorite → granite → pegmatite, the sequence of which is also established in the field. The anatectic magma left behind a more dessicated refractory rock now occurring as hornblende or pyroxene granulites.The granites of the Lower Himalaya are formed relatively at a lower temperature and pressure than the younger leucocratic tourmaline granites of the Higher Himalaya.

Minerais uraníferos de Perus, SP

This paper describes the secondary uranium minerals of the Perus district in Sao Paulo State, Brazil. The minera's may be genetically related to the igneous intrusions of the area. The uranium minerals are found in fractures and cracks of pegmatites and tourmaline bearing granites, which have been derived from a granitic magma, responsible also for the formation of the Pirituba granite. However, metamorphic rocks such as micaschists, amphibolites and hornfelses may be also found in the area. Several research methods have been utilized for the study of the uranium minerals, not only for identifying the various mineral species, but also for finding new physical and chemical data for the minerals themselves. The following methods have been used: optical microscopy and X-ray crystallography as the main techniques, and UV fluorescence, radioctivity detection, infra-red spectroscopy, thermal behaviour and chemical procedures as additional methods. Twelve different species of uranium minerals have been described in this paper: autunite, meta-autunite I, meta-autwrte II, hydrogen autunite, phosphuranylite, mineral X, torbenite, meta-torbenite I, meta-torbenite II, uranophane, beta-uranophane, and uranium opal. A few of those minerals, meta-autunite II and meta-torbenite II, are artificial species, obtained by meating of autunite and torbernite respectively. Unfortunately, not all the mentioned minerals have been studied thoroughly bythe use of all described methods of research, due to occurrence of small amounts. Such are the cases with phos phuranylite, mineral and hydrogen-autunite. The mineral X, thus provisionally designated, is probably a new mineral species. Its physical properties were thoroughly investigated. However, the small quantity available has not allowed trustoworthy chemical analysis. Nevertheless, the physical properties and some spectrographical analysis indicate the mineral as an uranyl phosphate, isostructural with phosphurany ite. Besides the description of the uranium, the primary minerals of pegmatites and tourmaline granites have been investigated, for field evidences have indicated these rocks as the probable source for uranuim. Albite, microcline, tourmalines, lepidolite, quartz and apatite were throughly investigated as far as their physical and chemical properties are concerned. Apatite seems to be the primary source of uranium. This type of genesis has been reported in several other areas of the globe, where U+4 ions replaces Ca+² in the apatite crystal structure. The very sensitive method of radioactivation analysis has revealed a rate of 56 ppm U for apatite of Perus, which represents a high percentage, when one compares this figure with the amount of U, found in the other pegmatite minerals (3 ppm). The underground water carrying CO2 and O2 in solution, have attacked, oxidized, and dissolved the apatite, forming acid mineralizing solutions containing UO2+², Ca+², HC0(3)-1 and PO4-3 ions. Through a neutralizing action, in contact with alkaline solutions, such mineralizing liquids have precipitated autunite and torbernite. Phosphuranylite has been formed by autunite alteration through pH modification, and the mineral X originated by precipitation of Mg-bearing solutions. Uranophane and beta-uranophane resulted from the interaction of coroidall silica and mineralizing fluids, whose ions have provoked collold fluculation. This mechanism explains the colloform and radiated habit of such minerals. The uranium-bearing opal had probably a similar origin, that is, by f oculation of colloidal silica solutions in contact with electrolites.

Geology of the Wisconsin Range batholith, Transantarctic Mountains

Abstract The Wisconsin Range consists mainly of a composite batholith of Late Precambrian and Early Paleozoic age. It is one of several batholiths that constitute the core of the Transantarctic Mountains. The batholithic rocks are flanked by the metamorphosed greywackes and argillites of the La Gorce Formation and the metavolcanic rocks of the Wyatt Formation that were deposited in the Ross geosyncline in Precambrian time. The metasedimentary and metavolcanic rocks were metamorphosed and partially reconstituted into granitic rocks during the Late Precambrian Mawson Orogeny. The resultant polygenetic batholithic complex ranges in composition from granite to quartz diorite, and has both foliated and massive facies. Some facies are characterised by abundant porphyroblasts of rapakivi feldspars. Tourmaline granite and porphyritic quartz monzonite make up other facies of the complex. The various facies have both gradational and intrusive relations with each other. Andesite dikes and plugs of hornblendite were intruded after consolidation of the batholith, probably in Early Paleozoic time. Aplitic quartz monzonite and pegmatites were intruded throughout the batholith in Early Ordovician time. This period of intrusion occurred during or after the Ross Orogeny. Foliation in the gneisses, and bedding and cleavage in the rocks of the La Gorce Formation, trend north-east, parallel to the axis of the Transantarctic Mountains. The present topography of the Wisconsin Range is controlled by block-type faults with total vertical displacement of more than half a mile.

METASOMATISM OF THE MAYKHURA GRANITES

Post-magmatic metasomatism of Maykhura granites has produced two distinctive zonal sequences (in increasing degree of alteration) as follows: Sequence (A) of 1) unaltered granodiorite, 2) muscovite granodiorite, 3) tourmaline granite, 4) muscovite granite, 5) orthoclase granite, 6) quartzalbite granite, and 7) monomineralic quartz rock. Sequence (B) differs in that one of the external zones contains chlorite instead of tourmaline. Both zonal rock-type alteration sequences produce the same end product of a quartz-feldspar (albite) metasomite at the end of the sequence immediately before the final formation of monornineralic quartz rock. R.M. Hutchinson

Disability Evaluation Following Hand and Wrist Injuries

Because of their low grades in critical metals such as Light Rare Earth Elements (LREE) or Sn, rare-metal granites are not considered as economic for metal recovery but, when altered, they are often exploited for their industrial minerals. The St Austell rare-metal granite is well known for its world-class kaolin deposits which formed as a result of the extensive weathering and alteration of the underlying granite. The St Austell granite body is composed of several granite components, each having its own accessory minerals assemblage. As a result of the kaolinisation process, some metal-bearing accessory minerals of the granite, such as monazite (LREE) or cassiterite (Sn), are partially liberated from the gangue which allow their pre-concentration in the micaceous residue which is considered as a potential source for critical metals recovery. Similarities with other similar rare-metal granites suggest that topaz granite is the most prospective for disseminated magmatic Sn-Nb-Ta-REE mineralization. However, comparison of the potentiality of 3 granite types i.e., biotite, topaz and tourmaline granites suggest that biotite granites is actually the most prospective due to higher degree of kaolinisation of the biotite granite which favour pre-concentration of its accessory mineral in the micaceous residue. In order to develop a geometallurgical framework for extraction of kaolin and metals from the selected granite component, a field sampling campaign is performed. Core samples are processed in the laboratory using a characterisation program that mimics the full-scale kaolin refining route. Two main products are recovered through this program, viz. MR180 (−180 +53 µm) and P5 (−5 µm), which correspond to a fine micaceous residue and a fine kaolin product respectively. These products are both analysed routinely for major and minor trace elements by XRF and yields are recorded to indicate process performance. A selected number of MR180 samples are also being characterised in terms of particle size by laser light scattering, geochemistry by ICP-MS, and mineralogy by QEMSCAN®. Comparison of characterisation results of MR180 samples and corresponding industrial residue samples shows a good correlation, suggesting that sample analyses are representative for the in-situ deposit and the processing behaviour. Monazite is found to be either fully liberated or fully locked from one sample to the other. Next, pilot-scale gravity concentration tests are performed on micaceous residue samples. Characterisation of the processing products shows that monazite lost in the tailings is mostly locked within tourmaline or micas and is fine grained. Then, predictive regression models for spiral separation performance in terms of recovery, product grade and enrichment as a function of the feed grade are developed for MR180 LREE grade data. Finally, kaolin resources can be classified using quantitative indicators such as yield of the P5 product and the iron oxides content which provides insight into the kaolin quality in terms of whiteness. This geometallurgical classification can be used to delineate zones of interest within the deposit. Although kaolin quality and recovery primarily inform extraction planning, zones which are also of interest for metal recovery can be identified. The proposed model predicts whether the expected LREE grade and recovery satisfy the by-product requirements.

The erratics of the English Chalk

A description is given of the Th. Wiltshire and G.E. Dibley Collections of erratics from the Chalk comprising 388 stones. Most of the specimens are small, from ½ to 5 cm. in length, only twenty are more than 9 cm. in length. The rock types represented include quartzitic sandstone, quartzite, quartzschist, vein-quartz, chert, rhyolite, quartz-porphyry, granite, gneiss, tourmaline granite of luxulyan type, tourmalinised sandstone, phosphatic sandstone and limestone. The vein-quartzes are notable for strain and partial recrystallisation. The fossiliferous cherts have been examined by Dr. K.P. Oakley and Mr. C.D. Ovey who determine one as Carboniferous and others as probably Carboniferous. The few larger stones more than 9 cm. in length may have been transported in the roots of trees or attached to seaweed, but many, and perhaps the majority, of the others are considered to be gastroliths picked up from pebbly beaches by marine reptiles (? plesiosaurs) and dropped from their drifting carcases. The 150 stones found within a few feet of one another at Rochester are probably the gastroliths of one reptile. The erratics have been obtained from many and distant shores. The more specialised types among them indicate that the south-west of England and the Oslo Fjord-south-west Sweden region have contributed material.