Pegmatitic Rocks Research Articles

Structural control and Sn-Ta-Nb mineralization potential of pegmatitic bodies in Numbi, South Kivu Eastern D.R Congo

The Numbi pegmatites of South Kivu Province (D.R.C) in the Kibaran belt which intruded the Mesoproterozoic Formation (1.6-0.9 Ga) was investigated to elucidate the structural imprints and geochemical characteristics related to the pegmatitic rocks associated with Sn - Nb - Ta mineralization, source(s) of the mineralisation, processes responsible for its formation and the economic viability of Tin-Niobium-Tantalum mineralisation. The structural features include: the pegmatitic veins with orientation from N150°E to N160°E characterized with direction and dip values averages of N84°E/13°SSE for horizontal veins and N138°E/73°WSW for subvertical veins. From the different stresses, the pegmatite and quartz veins occurred during the same tectonic phase. The characteristic high SiO2, Al2O3, Fe2O3 and Na2O, indicates peraluminous and S-type pegmatite, ferroan and medium to high K, characteristics of a collisional tectonic environment. The pegmatite showed an enrichment of Rb (114.70 – 1000 ppm), Ta (27.50 – 370.90 ppm), Cs (28.90 – 682.80 ppm), Sn (238 – 2451 ppm) and Nb (31.80 – 139.20 ppm) trace element, consistent with indices for mineralisation. The La/Yb vs. La and Sm/Yb vs. La/Sm diagrams established magmatic compositional heterogeneities and/or mixing in the lava suits that formed the pegmatites. Variation plots of Ta vs Ga, Ta vs Cs, Ta vs Cs + Rb and Ta vs K/Cs showed consistent trend of mineralization using their position relative to the Beus and Gordiyenkos line. These ratios - K/Ba, K/Rb, Ba/Rb, Rb/Sr and geochemical models- Y vs. Nb, (Y+Nb) vs. Rb, Zr vs. Ta/Zr, B (=Fe+Mg+Ti) vs A(=Al-(K+Na+2Ca), R1(=4Si+11(Na+K)-2(Fe+Ti)) vs R2(=6Ca+2Mg+Al) with observed tectonic markers like lineation/foliation, joints and veins suggests a structurally controlled mineralisation. The Numbi pegmatites are of partial melting of lithospheric mantle sources, relatively rich in Sn, Ta and Nb of economic value that are structurally controlled.

Melt-rock interaction between granitic pegmatites and hosting amphibolites from the Chiavenna Ophiolitic Unit (Tanno Pegmatitic Field, Central Alps, North Italy)

The Tanno pegmatitic field, placed southward of Chiavenna (Central Alps, Sondrio, Italy), develops a large number of subplanar dykes that crosscut the Chiavenna Unit, an ophiolitic complex mainly composed, in the study area, of amphibolite rocks. This study focuses on the contact between a pegmatitic dyke and the amphibolitic country rock. We distinguished four zones across the contact: I) inner amphibolite, II) contact amphibolite, III) contact pegmatite, IV) inner pegmatite. The inner amphibolite, not affected by melt-rock interaction, is composed of amphibole, phlogopite, ilmenite, titanite and rutile. Two amphibole generations occur, both of them showing a patchy compositional zoning. Amphibole I are Mg-hornblende, whereas Amphibole II have a pargasitic composition. The contact amphibolite shows an enrichment of mica belonging to the phlogopite-biotite series, titanite and the presence of fluorapatite and plagioclase (Ab45-60), that is absent in the inner amphibolite. Close to the contact, amphiboles display no zoning and gain an Mg-horneblenditic composition. The contact pegmatite has quartz, albitic plagioclase, garnet (almandine-spessartine series), muscovite, K-feldspar and fluorapatite. It shows a comb texture, with elongation of plagioclase crystals normal to the contact itself. Far from the contact, the inner pegmatite has an increasing grain-size and a less organized texture. In this zone several accessory phases occur, including gahnite, columbite-(Fe), monazite-(Ce), xenotime-(Y), uraninite and betafite. Whole rock analyses suggest that a chemical exchange, concerning both major elements and trace elements, occurred between the pegmatitic melt and the hosting amphibolite. A considerable increase of SiO2, Na2O and, to a lesser extent, of Al2O3 is observed from the amphibolite towards the pegmatite; K2O and CaO show a decrease at the same extent. The REE pattern in the pegmatite highlights an enrichment in HREE at the contact. Mineral chemistry confirms this trend with variations observable in plagioclase, gradually more albitic from the amphibolite to the pegmatite. Mineralogical characters and geochemical features allow to classify the Tanno pegmatite in the LCT (Lithium, Cesium, Tantalium) family. Based on the metamorphic peak conditions reported from the Lepontine Dome the ambient conditions during pegmatite intrusion were ca. 550°C and 5 kbar. The reduced thermal difference between pegmatite and wall rock explains the diffuse contact observed by X-ray micro-computed tomography. The collected data suggest a chemical interaction between melt and wall rock, according to the following reaction taking place in the amphibolite Amphibole I + Amphibole II + Ilmenite + Pegmatitic melt → Amphibole III + Plagioclase + Phlogopite + Titanite + Fluorapatite

Sustainable geopolymer using lithium concentrate residues

Australia is a key player in the global supply of lithium products given its large resources of spodumene. This mineral occurs in pegmatite rocks and can be processed to extract lithium salts used to make valuable products such as lithium ion batteries, ceramics, lubricants along with specific by-products such as lithium aluminosilicate residue (LASR). This paper investigates, for the first time, the use of LASR as a geopolymer precursor. A total of ten mixes have been synthesised, comparing the performance of LASR, fly ash, ground granulated blust-furnace slag (GGBS), kaolin and metakaolin. Ranges of mechanical and chemical tests have been carried out to examine the hardening of the mixes. Our experimental results reveal that LASR has a good thermal stability up to 1000 °C. While it has a low reactivity in alkaline solutions, its presence significantly improves the efficiency of other binder materials. LASR particles bridge the gaps between the larger sand grains, resulting in reduced micro-cracking. Based on the hardening trends, pH measurements and XRD analysis, we noticed that LASR could effectively retard the setting of geopolymer mixtures. A high 28-day compressive strength of 84.8 MPa has been obtained in the mix with 50% LASR and 50% GGBS; this mix produces three times higher strength than conventional concrete. With the delayed reactions and lower extent of micro-cracks, our hardening tests suggest that the strength can continue to develop past 28 days.

Coupling restites and mobilizates – Geological and litho-chemical investigations of paired belts of calcsilicate fels and quartzite (SE German Basement) – Quo vadis David London’s pegmatology?

In some areas of the Variscan orogen felsic mobilizates (pegmatitic and aplitic rocks) are closely associated with stratiform and stockwork-like bodies enriched in Ca minerals (e.g. wollastonite, diopside-hedenbergite s.s.s., grossular-spessartine s.s.s., siderite..) and bodies aligned to them similar in structure but abundant in quartz, plagioclase and mica. Geological mapping and lithochemical studies are the tools to decipher the nature of these crystalline rocks which are common to the Hagendorf-Pleystein Pegmatite Province, SE Germany, and present in many ensialic orogens elsewhere. Geological and chemical data suggest paired belts of a restite-mobilization system. The Ca and Si metasomatites are different from calcareous metasediments and quartzites elsewhere in the SE German basement devoid of mobilizates (parent rocks: limestones and cherts). Mobilization conducive to this paired belt of metasomatites involved silica mobilized from a deep level of the crust as a result of metamorphic-metasomatic alteration of Precambrian to Early Paleozoic metagreywackes during retrograde metamorphism from HP to LP metamorphism around 680–600 °C. The arrangement of mobilizates and restites in the field has been denominated as metamorphic differentiation sensu lato. The zone of silica mobilization is transitional into a zone of pegmatoids and aploids that overlaps with another one characterized by rocks derived from Ca metasomatism the footwall facies of which developed in the range 750–400 °C while in the hanging wall metamorphic rocks of rare-element pegmatites 570–430 °C occurred. The intensity of Ca metasomatism diminishes from the footwall to the hanging wall rocks and reflects a subcrustal impact. These investigations call attention among exploration geologists and petrologists to an alternative origin of “metasilica” and “metacarbonate” rocks being encountered in a zoned arrangement with felsic mobilizates (pegmatitic and aplitic rocks). The current study also raises the question “Quo vadis” pegmatology? It is an amendment to the mainstream geoscientific handling of pegmatitic rocks as “..texturally complex igneous rocks” genetically linked to granitic plutons (see review of London (2018) in Ore Geology Reviews). Taking a holistic approach can give us a reality check and prevent pegmatology from converting into a one-way street (granites-only) that eventually ends up in a dead-end street. The field evidence is the litmus test for all our models created in the laboratory and on the PC. There is no ore geology without field geology.

PGE-Enrichment in Magnetite-Bearing Olivine Gabbro: New Observations from the Midcontinent Rift-Related Echo Lake Intrusion in Northern Michigan, USA

The Echo Lake intrusion in the Upper Peninsula (UP) of Michigan, USA, was formed during the 1.1 Ga Midcontinent Rift event in North America. Troctolite is the predominant rock unit in the intrusion, with interlayered bands of peridotite, mafic pegmatitic rock, olivine gabbro, magnetite-bearing gabbro, and anorthosite. Exploratory drilling has revealed a platinum group element (PGE)-enriched zone within a 45 m thick magnetite-ilmenite-bearing olivine gabbro unit with grades up to 1.2 g/t Pt + Pd and 0.3 wt. % Cu. Fine, disseminated grains of sulfide minerals such as pyrrhotite and chalcopyrite occur in the mineralized interval. Formation of Cu-PGE-rich sulfide minerals might have been caused by sulfide melt saturation in a crystallizing magma, which was triggered by a sudden decrease in fO2 upon the crystallization and separation of titaniferous magnetite. This PGE-enriched zone is comparable to other well-known reef-like PGE deposits, such as the Sonju Lake deposit in northern Minnesota.

Classification of Granitic Pegmatites and Pegmatite-Bearing Granitic Systems

The paper discusses the concepts of pegmatitic rocks, pegmatite and pegmatoid bodies, and classification of granitic pegmatites and their relationships with various types of granite. Six types of pegmatitebearing granitic systems (PGS) are proposed: (I–PGS) granitic series with normal alkalinity in the form of central-type plutons with crystal-bearing chamber pegmatites; rare-metal Li–F granite and related pegmatoids, which are hosted in sequences of virtually unmetamorphosed rocks and formed at low pressure with no evidence of high alkalinity of granites (e.g., Zhanchivlan, Zuun-Bayan, and Gorikho in Mongolia; Adun- Chelon and Sokhondo-Ugdyri in the Transbaikal region); (II–PGS) granitic series with elevated alkalinity in the form of central-type plutons with crystal-bearing chamber pegmatites occasionally with indications of Y–REE mineralization; rare-metal, including REE, alkali granites and related pegmatoids hosted in almost unmetamorphosed sequences, where they formed under low pressure (e.g., Aqzhailau, Zerenda, Bayan-Aul, and Kent in Kazakhstan; Korosten in Ukraine; Pikes Peak and Mount Princeton in the United States; Ulkan and Ingur in Russia; Strange Lake in Canada; and Khalzaan-Buregte and Khan-Bogdo in Mongolia); (III–PGS) granitic series with lower alkalinity expressed in fields of dikes, layers, and stocks with rare-metal-bearing pegmatites; rare-metal albite and spodumene–albite granites, related pegmatoids, and complex raremetal pegmatites hosted in sequences of rocks metamorphosed under greenschist and amphibolite facies conditions, which correspond to pegmatite formation under medium pressure (e.g., Koktogai in China; Bernick Lake in Canada; Bikita in Zimbabwe; Karibib in Namibia; and Vishnyakovsky in Russia); (IV–PGS) granite series with elevated alkalinity represented by dike fields, layers, stocks with rare-metal, including REE pegmatites, which form under medium pressure in host rocks metamorphosed under epidote-amphibolite facies conditions (e.g., the Ilmeny Mountains in the Urals; the Western Keivy on the Kola Peninsula; and Sludyanka- 2 and Abchad in the Olkhon region); (V–PGS) low-alkaline granitic series expressed in fields of dikes, layers, stocks of mica-bearing and muscovite–rare-metal pegmatites formed under high pressure in zones of the kyanite–sillimanite-type amphibolite-facies metamorphism (e.g., in northern Karelia, Eastern Siberia, etc.); (VI–PGS) synorogenic granites and migmatites of potassium series with elevated alkalinity are expressed as dike fields, layers, stocks with high-pressure ceramic and uranium–REE pegmatites hosted in rock sequences metamorphosed under amphibolite- and granulite-facies conditions (e.g., northern Ladoga region, Bug River Basin, etc.).

Evaluation of the petrogenetic significance of melt inclusions in pegmatitic schorl-dravite from graphic tourmaline-quartz assemblages: Application of LA-ICP-QMS analyses and volume ratio calculations

The composition of melt inclusions in tourmaline was studied from graphic quartz-tourmaline intergrowth assemblages of common, muscovite – rare-element class pegmatites belonging to the lithium-caesium-tantalum family. This study applied laser ablation inductively coupled quadrupole mass spectrometry in combination with 2D and 3D microscopic volume calculation to analyse these unhomogenised melt inclusions. The determination of the analytical precision of the method is performed by repeated microscope-scanning and laser ablation analyses of tourmaline mineral inclusions in muscovite hosts for which the compositions have been independently measured by electron microprobe.The analysed melt inclusions are hosted in schorl-dravite series tourmaline from the early-Neoproterozoic pegmatite dykes of the Gatumba-Gitarama field in Rwanda. Multiple dykes have been studied, representing three regional pegmatite zones showing an increasing bulk regional degree of differentiation. The sampled graphic quartz-tourmaline assemblages are the only manifestation of an internal mineralogical zonation within these pegmatite dykes.The melt inclusions dominantly contain muscovite, quartz, dickite, feldspars, jeremejevite and childrenite minerals and variable amounts of Cs-rich, interstitial fluid. The major element composition of the ablated melt inclusions is variable but mainly plot on the low Ca-granitic compositional trend. The inclusions show, moreover, a significantly higher normative quartz content compared to bulk pegmatitic rock counterparts. The melt inclusions demonstrate a near-constant Rb concentration (100 up to 160 ppm) whereas Cs concentrations vary between 10 and 1000 ppm. Although Rb and Cs enrichment trends are accurate proxies to deduce pegmatite melt differentiation in general, both the Rb and Cs concentrations of the melt inclusions are remarkably unrelated to the regional degree of differentiation deduced from the constituent bulk rock and rock-forming minerals of the Gatumba-Gitarama pegmatites. A comparison of the alkali metal content of melt inclusions and cogenetic fluid inclusions with previously modelled bulk melt concentration indicates that this deviating Rb and Cs behaviour is caused by heterogeneous trapping of variable portions of the Cs-enriched aqueous fluid phase together with the residual melt and this during melt inclusion formation.The melt inclusions in tourmaline represent local and residual, hydrous boro-aluminosilicate melt compositions. The formation of graphic intergrowths inside the pegmatite dykes indicates rapid tourmaline growth rates causing in turn quartz saturation and nucleation in the surrounding residual melt. Fast tourmaline crystallisation contributed directly to the formation of these “melt pools” with distinct residual compositions. Our study shows that already for less-differentiated common pegmatites, melt inclusions from internal mineralogical zones represent closed melt subsystems that cannot be directly linked to the bulk system. These findings imply, moreover, that the use of tourmaline trace element compositions as an indirect geochemical proxy for the bulk melt composition of pegmatites and evolved granites, has to be considered with caution.

The crystal-chemistry of riebeckite, ideally Na2Fe32+ Fe23+Si8O22(OH)2: a multi-technique study

AbstractIn this work we report on a complete crystal-chemical characterization of a near end-member riebeckite from Malawi, and use the available data to critically compare information obtained from different analytical methods. The sample occurs as well-formed and very large single crystals in pegmatitic rocks. Accurate site-populations were determined by combining single-crystal structure refinement and electron microprobe analysis (EMPA). The Fe3+/Fe2+ ratio was obtained from Mössbauer spectroscopy. Lithium was quantified by Laser Ablation Inductively Coupled Plasma Mass Spectroscopy (LA-ICP-MS).Fourier-Transform Infrared (FTIR) spectra, collected both on powders and single crystals, are presented and discussed. FTIR spectra in the NIR region are also presented for the first time for this amphibole. The FTIR data are compatible with complete local ordering of A cations close to F, and complete Fe2+/Mg disorder at M(1,3). Polarized Raman-scattering data collected from single crystals confirm this conclusion. In addition, it was found that FTIR data collected on powders provide the best agreement with the site occupancies derived from chemical (EMPA and LA-ICP-MS) and crystal-chemical data, possibly because they do not depend on experimental issues such as orientation and polarization.

Petrogenesis of syn-orogenic rare metal pegmatites in the Chinese Altai: Evidences from geology, mineralogy, zircon U-Pb age and Hf isotope

Recently, an increasing number of anatetic pegmatites have been confirmed. In contrast to the granitic pegmatite, the anatetic pegmatite has no relation to granite. It is therefore necessary to reacquaint the origin and classification of pegmatitic rocks. As one of the largest pegmatite provinces, the Chinese Altai provides a natural laboratory for pegmatite study. To date, the type, age, source and tectonic setting of the syn-orogenic pegmatites in the Chinese Altai remain unclear. In this work, the CMS (Chemical composition-Mineral assemblage-Structural geology) classification is primarily applied on the pegmatitic rocks in the Chinese Altai. Five types’ pegmatitic rocks, including metapegmatite, pegmatoid, pegmatite, pseudopegmatite and granite pegmatite, are identified by their CMS features. In addition, the geology, mineralogy, zircon U-Pb ages and Hf isotopes of six pegmatites are presented in this work. The pegmatites, numbered JMHB02, QBL02, TLT01, ALJK01, AMLG01 and TMLT01, are dated at 394.8 ± 4.0 Ma, 402.6 ± 5.5 Ma, 385.9 ± 3.5 Ma, 368.0 ± 4.0 Ma, 358.3 ± 4.6 Ma and 333.0 ± 6.0 Ma, respectively, indicating that they were formed during the syn-orogenic stage of the Altai orogenic process. They are exposed in the Qiongkuer domain in the southern Chinese Altai, juxtaposed with the late- and/or post-orogenic pegmatites in the same pegmatite field. No parental granite can be confirmed for all these pegmatites. Comparatively, the synorogenic pegmatites are scarce, and have lower mineralization grades than the late- and postorogenic pegmatites. Zircon Hf isotopic compositions of the syn-orogenic pegmatites have positive ɛHf(t) values of +2.06–+8.28 and old TDM2 ages of 1,234–860 Ma and are consistent with those of most of the syn-orogenic I- and S-granites, which indicates that the pegmatites and granites have a common immature crustal source from the early Paleozoic metasedimentary rocks. Compared to the post-orogenic pegmatites in the Central Altai domain, the syn-orogenic pegmatites in this work have larger positive ɛHf(t) values and younger TDM2 ages, indicating that more juvenile components were involved in their magma sources. Combining this study with previous works, we suggest that the anatexis of metasediments induced by decompression and injection of heat energy and mantle-derived materials under a forearc extensional setting led to the formation of the syn-orogenic pegmatites in the Chinese Altai.

Single crystal elasticity of natural topaz at high-temperatures

Topaz is an aluminosilicate mineral phase stable in the hydrothermally altered pegmatitic rocks and also in subducted sedimentary lithologies. In nature, topaz often exhibits solid solution between fluorine and hydrous end members. We investigated elasticity of naturally occurring single crystal topaz (Al2SiO4F1.42(OH)0.58) using Resonant Ultrasound Spectroscopy. We also explored the temperature dependence of the full elastic constant tensor. We find that among the various minerals stable in the Al2O3-SiO2-H2O ternary system, topaz exhibits moderate elastic anisotropy. As a function of temperature, the sound velocity of topaz decreases with frac{{boldsymbol{d}}{{boldsymbol{V}}}_{{boldsymbol{P}}}}{{boldsymbol{d}}{boldsymbol{T}}} and frac{{boldsymbol{d}}{{boldsymbol{V}}}_{{boldsymbol{S}}}}{{boldsymbol{d}}{boldsymbol{T}}} being −3.10 and −2.30 × 10−4 km/s/K. The elasticity and sound velocity of topaz also vary as a function of OH and F content. The effect of composition ({{boldsymbol{x}}}_{{boldsymbol{O}}{boldsymbol{H}}}) on the velocity is equally important as that of the effect of temperature. We also note that the Debye temperature ({{boldsymbol{Theta }}}_{{boldsymbol{D}}}) of topaz at room temperature condition is 910 K and decreases at higher temperature. The Debye temperature shows positive correlation with density of the mineral phases in the Al2O3-SiO2-H2O ternary system.

A Model for the High-temperature Origin and Paradoxical Distribution of Pegmatites in Mafic Plutons, Smartville Complex, California

The distribution of pegmatitic rocks in the zoned gabbro–diorite plutons of the late Jurassic Smartville Complex is counter-intuitive. Whereas pegmatitic gabbros are common in mafic cumulate olivine gabbros within the zoned plutons, they appear to be absent from the more evolved gabbros and diorites. We argue that this paradox is resolved by examining the crystallization and temperature history of the rocks in question. The evolved rocks in the plutons consist of two-pyroxene hornblende biotite gabbro and diorite. The amphibole in these rocks occurs as a partial replacement of pyroxene that forms as a consequence of the incongruent crystallization reaction generalized as amphibole ± quartz ± plag1 = pyroxene + hydrous melt ± plag2 [reaction (1)]. This is a vapor-absent reaction that can buffer melt water content during crystallization and conceivably preclude water saturation altogether. Experimental evidence places the onset of the incongruent formation of amphibole at c. 900°C. In contrast, amphibole and other hydrous phases occur only in trace amounts in the cumulate olivine gabbros. The water-buffering reaction is not encountered during crystallization, the intercumulus melt proceeds to water saturation, and high-temperature plagioclase–pyroxene pegmatites form. We argue that the primary role for undercooling favored for the formation of granitic pegmatites is not likely to be applicable to the Smartville gabbro pegmatites. As crystallization of the gabbro pegmatite proceeds, the amphibole-in boundary is eventually reached and incongruent crystallization of amphibole occurs. Nevertheless, once water saturation occurs, it is irreversible, and is eventually manifested by the low-temperature deuteric alteration associated with the pegmatites. In short, we argue that pegmatite formation in the Smartville gabbros, and probably many other gabbroic plutons, reflects water saturation of a magma at high temperature, estimated here at >900°C. In systems where reaction (1) is attained prior to water saturation, pegmatite formation may be delayed until late in the crystallization history or precluded altogether. MELTS modeling of basalt crystallization suggests a solution to the paradox, indicating that the difference between the two systems can reflect equilibrium versus fractional crystallization. Equilibrium crystallization of trapped, intercumulus melt favors high-temperature crystallization and water saturation and, hence, pegmatite formation. Fractional crystallization, for example in an open-system magma chamber, favors lower-temperature crystallization and permits reaction (1) to proceed, inhibiting water saturation and preventing pegmatite formation. The open-system nature of the fractionating magma chamber might also allow escape of volatiles at its margins, with the lower volatile content then communicated to the magma as a whole as the system convects or otherwise mixes.

Creation of Hyper spectral library and Lithological discrimination of Granite rocks using SVCHR -1024: Lab based approach

The advances of worldwide research for identification of rocks and minerals in remote sensing data with a help of spectral pattern of different rocks and minerals now a days we all are referring only for USGS or JHU spectral library and these libraries were constructed mostly based on the lithological discrimination of rocks present outside of our country. There is no spectral library available for Rocks and Minerals present in Tamil Nadu. Hence the present study was under taken to construct the hyper spectral library using Spectroradiometer (SVC HR-1024) which covers 340nm to 2500nm wavelength and this study only carried out in the room environment. In the present study, for creation of the hyperspectral library 21 rocks of Igneous, Metamorphic and Sedimentary rocks were selected from the lab and spectral library was created using spectro radiometer. Different variety of granite rocks were selected based on their physical and chemical properties of rocks such as Granite (coarse and fine grain), Granodiorite, Granite porphyry, Graphic granite and Pegmatite rocks and their spectral reflectance were compare with both hyper spectral library which was created and universal spectral libraries. Spectral behaviour of selected granite rocks shows similar pattern of different rocks and minerals and some variations also observed because of different physical and chemical properties of minerals and environment of collection of spectral behaviour of rocks.

On the composition of gastroliths from broiler breeders.

The purpose of this study was to ascertain the composition and origin of certain gastroliths or gizzard stones from broiler breeders (Gallus gallus domesticus). Fourier transform infrared spectroscopy (FTIR) and X-ray powder diffraction techniques were used as analysis tools. The main components resulted to be organic fibre and minerals referred to a pegmatite rock (quartz, feldspar albite and haematite) used as grit. Although the generally accepted purpose of gastroliths in chicken is the crushing and grinding of foodstuff in the ventriculus, the importance of mineral uptake from grit of iron and other essential elements such as Al, Ca, K, Cl, P, Ti, Mn, Mg, Cu, Zn and Zr (in ppm) as a secondary effect of the abrasion and dissolution of gastroliths should not be disregarded.

Provenance, tectonic setting and source of Archean metasedimentary rocks of the Browns Range Metamorphics, Tanami Region, Western Australia

ABSTRACTThis study combines U–Pb age and Lu–Hf isotope data for magmatic and detrital zircons, with whole-rock geochemistry of the Browns Range Metamorphics (BRM), Western Australia. The BRM are medium- to coarse-grained metasandstones that consist of angular to sub-rounded detrital quartz and feldspars with minor granitic lithic fragments. The sequence has undergone partial to extensive quartz–muscovite alteration and rare-earth-element mineralisation and has been intruded by mafic/ultramafic, syenitic and pegmatitic intrusive rock units. Uranium–Pb and Lu–Hf isotopic data on detrital zircons from the metasandstones and intruding granitic rocks yield a well-defined age of ca 3.2 to ca 3.0 Ga for all samples, with relatively radiogenic ϵHf values (ϵHf = –1.7 to 5.1) indicating derivation from Mesoarchean granite basement of juvenile origin. This is consistent with geochemical and petrological data that support deposition from a granitic source in a continental rift basin setting. The timing of sediment deposition is constrained between the ca 3.0 Ga age of the source rocks and ca 2.5 Ga age of the granitic intrusive bodies that cross-cut the metasedimentary rocks. The ca 2.5 Ga zircons from the intrusive rocks have ϵHf model ages of ca 3.4 to ca 3.1 Ga, which is consistent with formation via partial melting of the BRM, or the Mesoarchean granite basement. Zircons of the Gardiner Sandstone that unconformably overlies the BRM return detrital ages of ca 2.6 to ca 1.8 Ga with no trace of ca 3.1 Ga zircons, which discounts a significant contribution from the underlying BRM. The Mesoarchean age and isotopic signatures of the BRM zircons are shared by some zircon records from the Pine Creek Orogen, and the Pilbara, Yilgarn and Gawler cratons. Collectively, these records indicate that juvenile Mesoarchean crust is a more significant component of Australian cratons than is currently recognised. This work also further demonstrates that detrital minerals in Paleoproterozoic/Archean sedimentary rocks are archives to study the early crustal record of Earth.

MINERALOGICAL AND RADIOACTIVE CHARACTERIZATION OF GABAL EL-URF PEGMATITES, CENTRAL EASTERN DESERT, EGYPT

The present study deals with the mineralogical and radioactive characteristics of the pegmatitic rocks at Gabal El-Urf area, Central Eastern Desert of Egypt.The zoned pegmatites of El-Urf area are composed of three enriched mineral zones; extremely milky quartz core, intermediate mica zone and feldspars wall zone.The identified separated heavy minerals in the studied pegmatite can be grouped into three mineral groups; the primary minerals (pyrite, molybdenite, rutile, magnetite, thorianite, zircon, columbite and garnet), the secondary minerals (uranophane, kasolite, uranothorite, samarskite, uranopolycrase, dravite, ilmenorutile, allanite and titanite.) and the gangue minerals (lanarkite, barite, hematite, ilmenite, goethite, apatite, monazite and kamitugaite).The studied zoned pegmatites hosting or acting as a source for uranium and rare metals (Zr, Y, Nb and Th) mineralizations. Multistage deformation, magmatic and hydrothermal processes accompanied by events of uranium mineralization with the associated rare metals mineralizations in different episodes affected Gabal El-Urf zoned pegmatites.The rare metals can be originated through magmatic and hydrothermal fluids under the restrictive sets of conditions that commonly prevail in these zoned pegmatites. The magmatic and hydrothermal processes enriched with rare metals mineralization accompanied by event of an intensive tectonic structure affected Gabal El-Urf pegmatites.

Can cathodoluminescence of feldspar be used as provenance indicator?

We have studied feldspar from crystalline rocks for its textural and spectral cathodoluminescence (CL) characteristics with the aim to reveal their provenance potential. We analyzed ca. 60 rock samples of plutonic, volcanic, metamorphic, and pegmatitic origin from different continents and of 16Ma to 2Ga age for their feldspar CL textures and ca. 1200 feldspar crystals from these rocks for their CL color spectra. Among the analyzed rocks, igneous feldspar is most commonly zoned, whereby oscillatory zoning can be confirmed to be typical for volcanic plagioclase. The volcanic plagioclase also less commonly contains twin lamellae that are visible in CL light than crystals from other rock types. Alkali feldspar, particularly from igneous and pegmatitic rocks, was noted to be most affected by alteration features, visible as dark spots, lines and irregular areas. The size of all textural features of up to ca. 150μm, in combination with possible alteration in both the source area and the sedimentary system, makes the CL textures of feldspar possible to use for qualitative provenance research only. We observed alkali feldspar mostly to luminesce in a bluish color and sometimes in red, and plagioclase in green to yellow. The corresponding CL spectra are dominated by three apparent intensity peaks at 440–520nm (mainly blue), 540–620nm (mainly green) and 680–740nm (red to infrared). A dominance of the peak in the green wavelength interval over the blue one for plagioclase makes CL particularly useful for the differentiation of plagioclase from alkali feldspar. An apparent peak position in red to infrared at <710nm for plagioclase mainly is present in mafic rocks. Present-day coastal sand from Peru containing feldspar with the red to infrared peak position mainly exceeding 725nm for northern Peruvian sand and a larger variety for sand from southern Peru illustrates a discriminative effect of different source areas. We conclude that the provenance application particularly can reveal first-cycle input from mafic rocks and source variations for detritus from arid areas that has been affected by little feldspar alteration.

An Evaluation of the Permittivity of Two Different Rock Types Using Microwave Resonator and Waveguide Cutoff Principles

Abstract Methods of measuring the complex permittivity of different rock types are demonstrated in the frequency range from 6 GHz to 17 GHz. The used methods are based on the cylindrical resonator and waveguide cutoff frequency principles. This study is part of a larger research project that aims to characterize the electrical properties of asphalt for road surveying purposes. The studied rock types are metavolcanic rock with intermediate composition and pegmatite. The permittivity values gained with the resonator method are 6.2 for the metavolcanic rock and 4.5 for the pegmatite rock type, whereas the imaginary parts are 0.04 and 0.02. The permittivity values gained with the cutoff frequency method are 6.17 and 4.76 respectively. A reference measurement was made only for the metavolcanic rock in a transmission configuration with two antennas and the permittivity result was 6.21. The three different methods provide consistent permittivity values and are suitable for reliable permittivity evaluation.

Petrography and Petrochemical Characteristics of Rare Metal Pegmatites around Oro, Southwestern Nigeria

Petrographic and geochemical evaluation of pegmatite bodies occurring as discontinuous dykes have been studied in Oro area of southwestern Nigeria, with a view to determine the compositional characteristics that may be related to Ta-Nb mineralization potentials. They are found intruding semi discordantly, the older assemblages of quartz mica schist and granite gneiss.&#x0D; A total of twenty-eight samples comprising whole rock pegmatites and eluvial soils were analyzed for major, trace and rare earth elements using (ICP-AES) geochemical method which show the pegmatite samples to be generally highly siliceous with SiO2 values ranging from (71.49-97.77%) with an average of 86.43% in the whole rock samples, and it also ranges from (41.88-57.99%) with an average of 48.43% in the eluvial soil samples, while Al2O3 content is as high as 25.87% in the eluvial soil samples and 6.86% in the whole rock samples depicting the complexity of the pegmatite rock.&#x0D; Variation plots of K/Rb versus Rb, Ta versus Rb, Ta versus Nb, Ta versus K/Cs, Ta versus Cs+Rb and Ta versus Cs discriminant plot indicate the potentials of rare metal mineralization.

Petrography and Petrochemical Characteristics of Rare Metal Pegmatites around Oro, Southwestern Nigeria

Petrographic and geochemical evaluation of pegmatite bodies occurring as discontinuous dykes have been studied in Oro area of southwestern Nigeria, with a view to determine the compositional characteristics that may be related to Ta-Nb mineralization potentials. They are found intruding semi discordantly, the older assemblages of quartz mica schist and granite gneiss. A total of twenty-eight samples comprising whole rock pegmatites and eluvial soils were analyzed for major, trace and rare earth elements using (ICP-AES) geochemical method which show the pegmatite samples to be generally highly siliceous with SiO2 values ranging from (71.49-97.77%) with an average of 86.43% in the whole rock samples, and it also ranges from (41.88-57.99%) with an average of 48.43% in the eluvial soil samples, while Al2O3 content is as high as 25.87% in the eluvial soil samples and 6.86% in the whole rock samples depicting the complexity of the pegmatite rock. Variation plots of K/Rb versus Rb, Ta versus Rb, Ta versus Nb, Ta versus K/Cs, Ta versus Cs+Rb and Ta versus Cs discriminant plot indicate the potentials of rare metal mineralization.

The pegmatitic rocks of El-Hudi and Um Hibal areas, Southeastern Desert, Egypt: genesis and petrological characteristics

In an effort to understand the genesis of the pegmatitic rocks of El-Hudi and Um Hibal areas, detailed field, petrographic, and geochemical investigations were conducted. These investigations revealed evidence of two distinct modes of emplacement of these rocks. El-Hudi pegmatites are emplaced concordantly in a belt of folded gneisses and migmatites that mostly fit well with a metasedimentary protolith, which are later cataclased or even mylonitized. El-Hudi pegmatites can be classified into (1) plagioclase or sodic and (2) k-feldspar or potassic pegmatites. Their mineral assemblage, the variable forms of albite bodies in perthitized k-feldspars, and the myrmekite and graphic intergrowths are conclusive evidence indicating metasomatic and later stages of replacement. Geochemically, the peraluminous character of these pegmatites, compressional setting, partial melting parentage, and S-type affinity confirm their metasedimentary source and support a linkage with their host gneisses. The following stages explained the most accepted scenario for the development of these pegmatites “partial melting from metasedimentary protoliths, minimal fractionation and differentiation, injection into foliation, fractures and/or tectonic planes of the host gneisses, and invading the gneiss and migmatite hosts reflecting metasomatic exchanges, segregated earlier or contemporaneous with the genesis of garnet-bearing granites.” In Um Hibal pegmatites, their vein- and miarolitic-type emplacements with the characteristic chilled margin of the later, the recorded hydrothermal nature of the well-preserved silica gels, and the well-crystallized accessory zircons revealed their magmatogenic origin. The similar behavior in depletion or enrichment of the rare earth element contents of Um Hibal pegmatites and their host granites indicate that they are genetically related. They have a mild to peralkaline affinity, emplaced in an extensional regime and shallow depth environment, of within plate and A1-type granite characters. However, the pegmatites seem to be fractionally crystallized from the residual melt of the host granites.