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Maria Florencia Marquezzavalia - One of the best experts on this subject based on the ideXlab platform.
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la icp ms upb columbite ages and trace element signature from rare element granitic Pegmatites of the pampean Pegmatite province argentina
Lithos, 2021Co-Authors: Miguel Angel Galliski, Albrecht Von Quadt, Maria Florencia MarquezzavaliaAbstract:Abstract Crystals of the columbite-group minerals (CGM) from 23 rare-element granitic Pegmatites of the Pampean Pegmatite Province (PPP) were analyzed by LA-ICP-MS technique. The resulting database shows weighted mean 206Pb/238U ages between 530 and 335 Ma defining two time windows, T1 and T2. T1, from 490 to 440 Ma, spans 75% of the ages of LCT rare-element Pegmatites formed during the Famatinian collisional orogeny of peri-Gondwana location. T2, from 370 to 340 Ma, comprises postorogenic Pegmatites with lithium-caesium‑tantalum (LCT) and niobium‑yttrium‑fluorine (NYF) or mixed NYF-LCT signatures. The CGM ages of the PPP orogenic Pegmatites show a shifting from older in the north to younger in the south. The major elements composition of the CGM shows preference for high #Mn at variable but usually moderate to high #Ta. The normalized, with the Global CGM median, trace elements composition of the CGM of most orogenic LCT (Li-Cs-Ta) Pegmatites shows an enrichment in Bi, Pb and U, a remarkable depletion in Sn and sometimes a slight decrease in W (Y ± Yb). The postorogenic Pegmatites show CGM with a general enrichment in Y (±Yb), W, Pb, U, and occasionally in Sn. The REEN diagrams of CGM from the northern districts of the PPP show patterns with LREEN HREEN and strong negative Eu anomalies. In the southern districts, there is a bimodal behavior in the total content and distribution of the normalized patterns of REE. The CGM from some Pegmatites of the Conlara Pegmatite district have similar features to the ones from the northern districts. It seems that the kind of Pegmatite has no definitive control in the type of pattern. The other group shows low contents of REEN mostly comprised between 0.01 and 10 times the chondrite values, flattened patterns, weak to moderate negative anomalies of Eu, and occasionally a weak Ce anomaly. In the southern Totoral district, the CGM of the different kinds of Pegmatites also have approximately similar, though relatively lower, total REEN contents and patterns with LRREN
Michel Pichavant - One of the best experts on this subject based on the ideXlab platform.
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Mica-liquid trace elements partitioning and the granite-Pegmatite connection: The St-Sylvestre complex (Western French Massif Central)
Chemical Geology, 2019Co-Authors: Arnaud Villaros, Michel PichavantAbstract:We constrain the genetic relation between granite and Pegmatite parental melts from the Variscan Saint Sylvestre leucogranite complex and associated Pegmatite bodies (Massif Central, France) through compositions of micas. Using mica trace element concentrations and available partition coefficients for Li, Rb, Ba, Cs and F, we calculated the trace element contents of granitic and pegmatitic melts at equilibrium with micas. Biotite in leucogranites and Pegmatites ranges mostly from Fe-biotite to siderophyllite. More evolved facies contain protolithionite and zinnwaldite and lepidolite occurs in the most fractionated Pegmatite. White micas have homogeneous compositions, from muscovite to Li-phengite. In granites, biotite and muscovite trace element distributions are clustered. In Pegmatites, mica trace element contents globally follow differentiation from the least to the most evolved body. The reconstructed pegmatitic and granitic melts present strong compositional similarities such as enrichments in Li, Rb, Cs and depletion in Ba that suggest a similar origin. However, micas are shown to have selectively equilibrated with the last melt (or fluid) in contact and so trace element concentrations of early magmatic liquids are rarely preserved. Inversion of the mica data constrains the composition of parental melts and the trace element evolutions during crystallization. Leucogranite and Pegmatite melts show mutual incompatible element evolutions inconsistent with a parent-daughter genetic relation. The data and the modelling suggest that they represent non-cogenetic melts generated by discrete episodes of partial melting. Differentiation is thus inherited from source processes rather than being the consequence of fractional crystallization of a common parental melt/magma. We suggest that both the leucogranites and the Pegmatites originate from partial melting of a heterogeneous source rather than Pegmatites being the product of granite crystallization.
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Innovative and multi-disciplinary approach for discussing the emplacement of Variscan LCT-Pegmatite fields
2015Co-Authors: Sarah Deveaud, Eric Gloaguen, Romain Millot, Yannick Branquet, Arnaud Villaros, Laurent Guillou-frottier, Michel Pichavant, David SilvaAbstract:In order to define new metallogenic guides for Li, Nb and Ta supply, three Variscan LCT Pegmatite fields are investigated. A multidisciplinary approach is favoured to discuss both the genetic and emplacement models for LCT-type deposits. The spatial statistical analyses demonstrate the high clustering rate of Li-rich Pegmatites and the spatial relationships between Li-Pegmatites location and surrounding damage fractured zone. The Li-isotopes analyses on micas suggest the absence of genetic continuum between surrounding granites and Pegmatites since δ 7 Li values (‰) are similar through Pegmatite field and inside granite samples. To refine these previous results, preliminary numerical models are developed to constrain the ascent of these low viscosity Pegmatite-forming melts and determine key criterion of their uncoupling from parental magma source. According to these results, the high permeability seems to play a crucial role in the Pegmatite melts collection and during their ascent. The combination of geostatistical, geochemical and numerical tools allows suggesting an alternative model of direct crustal anatexis to the common parental granite model. These high permeability damage shear zones are considered to favour the low volume of Pegmatite-forming melt pumping and their escape from their deeper crustal magma source.
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Characterization of rare- element Variscan Pegmatite fields: multi- approaches study for new metallogenic guides
2014Co-Authors: Sarah Deveaud, Eric Gloaguen, Charles Gumiaux, Romain Millot, Yannick Branquet, Arnaud Villaros, Laurent Guillou-frottier, Michel PichavantAbstract:Rare- element Pegmatite fields mainly enriched in Li-Nb and Ta are subject to increasing mining exploration in the last few years. Indeed, Nb and Ta are more and more employed in design of high-tech applications whereas Li from Pegmatite deposits is recognized to be less sensitive to supply disruptions than Li from brine deposits. Thus, new metallogenic guides need to be defined/ to meet growing demand for Li, Nb and Ta metals and to ensure supply of strategic metals at European scale. Two Variscan rare-element Pegmatite fields have been selected to apply a multi-approaches study in order to understand their distribution and their genesis. Firstly, three methods have been developed on the Monts d'Ambazac Pegmatite field (Haute-Vienne, French Massif Central):i) spatial statistical analysis to constrain the spatial distribution of these deposits, ii) Li-isotopic analysis in micas to constrain the genesis relationships between different Pegmatite types and iii) U/Pb geochronological approach to discriminate temporal relationships between Pegmatites and surrounding granites. Secondly, the Forcarei-Lalin Pegmatite field (Galice, Spain) has been selected to constrain spatial and temporal relationships between Pegmatites and hosting- rocks with a structural field study and U/Pb geochronology on Colombo-tantalite crystals. The results demonstrate the main role of tectonic context during Pegmatite emplacement and secondly, the role of chemistry and rheology of hosting-rocks on Pegmatite differentiation type and on their morphology based on field observations. On the other hand, these two Pegmatite fields seem to result from direct crustal anatexis and not from a classical granitic differentiation. To refine this hypothesis, preliminary numerical models have been developed to first, constrain the ascent of pegmatitic melt from a deeper crustal source with respect to their physico-chemical properties and second, to investigate the role of tectonic constraints during their emplacement on the Pegmatite field 2D- distribution.
Hui Zhang - One of the best experts on this subject based on the ideXlab platform.
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k feldspar composition as an exploration tool for Pegmatite type rare metal deposits in altay nw china
Journal of Geochemical Exploration, 2018Co-Authors: Yong Tang, Hong Wang, Hui ZhangAbstract:Abstract Trace elements of potassium feldspar (Kfs) from Pegmatite veins in the Keketuohai Pegmatite district were determined in situ by LA-ICP-MS. As the K/Rb ratio decreases, the contents of compatible Ba and Sr decrease, while the contents of incompatible Li, Cs and Ga increase. The K/Rb ratios and above mentioned trace element contents of Kfs from the Be-Nb-Ta mineralized Pegmatite veins match those of Kfs from barren Pegmatite veins. In contrast, the mineralized Pegmatites are characterized by having K-feldspars with high phosphorus contents, mostly above 0.1 wt% P2O5, which is the boundary separating mineralized Pegmatites and barren Pegmatites. The high P2O5 content in Kfs indicates high concentration of this element in the melt from which these Pegmatites crystallized. The P2O5 content in K-feldspar can be used as an exploration tool for LCT type Be-Nb-Ta deposit.
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A new model for the granite-Pegmatite genetic relationships in the Kaluan-Azubai-Qiongkuer Pegmatite-related ore fields, the Chinese Altay
Journal of Asian Earth Sciences, 2016Co-Authors: Xin Zhang, Yong Tang, Hui Zhang, Jingyu Zhao, Yun-long LiuAbstract:Pegmatites commonly form in the waning stage of magma evolution by fractional crystallization of volatile-rich magmas and may be important host rocks of strategic metals (e.g., Li, Be, Cs, Ta, and Nb) and high-quality gem minerals. This study reports new zircon U-Pb dating results and Hf isotopic compositions of the KLA803 Pegmatite, the AZB-01 Pegmatite, the JMK-09 Pegmatite (abbreviated as the K-A-J Pegmatites) and the Halong granite from the Chinese Altay to determine the potential petrogenetic relationships between them. The geochronological data document that the K-A-J Pegmatites were emplaced at 224.6 +/- 2.3 Ma, 191.6 +/- 2.0 Ma and 192.0 +/- 2.3 Ma, respectively, and they are characterized by negative to low positive epsilon Hf(t) values (from -1.0 to +63) and old model ages (T-DM) (with the T-DM1 from 874 to 597 Ma and T-DM2 from 1298 to 833 Ma). In contrast, the Halong granite has an emplacement age of 398.3 +/- 2.4 Ma and is characterized by higher positive epsilon Hf(t) values (from +9.9 to +15.2) and younger model ages (T-DM) (with the T-DM1 from 626 to 414 Ma and T-DM2 from 760 to 423 Ma). They all have intruded into the Kulumuti group stratum, which has negative initial epsilon Nd(t) values (from -4.3 to -0.2) and old T-DM model ages (between 1.22 and 1.56 Ga). Based on the calculated results of the mixing ratios (f) of the initial magmas and the prevailing Paleozoic tectonic framework of the Chinese Altay, we establish two petrogenetic models for the K-A-J Pegmatites: Model 1 refers to that these Pegmatites originated from a mixed magma that was composed of 72-91 wt.% depleted mantle components and 9-28 wt.% lower crust components; and Model 2 refers to that they were derived from the partial melting of 38-83 wt.% Halong granite and 17-62 wt.% sedimentary rocks from the Kulumuti group. We also suggest that the initial magma of the Halong granite was significantly contributed by juvenile materials with a slight involvement of crustal materials. In Model 1, because LCT-type Pegmatites (classified as Li-Cs-Ta enriched Pegmatites associated with S-type granite that was produced by the partial melting of preexisting sedimentary rocks) have close geochemical affinities with crustal materials, the excessively high weight percentages (72-91 wt.%) of the depleted mantle components in the initial magma of the K-A J Pegmatites indicate that this model is unrealistic. Therefore, we consider that Model 2 is more reasonable at present for interpreting the petrogenesis of the K-A-J Pegmatites, and it needs to be verified in other Pegmatite fields of the Chinese Altay. (C) 2016 Elsevier Ltd. All rights reserved.
Judith A. Kinnaird - One of the best experts on this subject based on the ideXlab platform.
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Classification, mineralogical and geochemical variations in Pegmatites of the Cape Cross-Uis Pegmatite belt, Namibia
Lithos, 2017Co-Authors: Warrick C. Fuchsloch, Paul A. M. Nex, Judith A. KinnairdAbstract:Abstract The Pan African aged Damara Orogen in Namibia is host to the Cape Cross-Uis Pegmatite belt, one of several NE-trending Pegmatite belts which host Li, Nb, Ta and Sn mineralisation. Field mapping and structural analysis of thirty seven Pegmatite bodies has shown that the Pegmatites intrude along crustal weaknesses such as fold axes and bedding planes, predominantly following the approximate NE orientated regional structural fabric. The lack of deformation together with cross-cutting relationships mapped, suggest that Pegmatites were emplaced during post-tectonic extension that resulted from end-orogeny crustal relaxation. Based on mineralogy, geochemistry and ore mineralogy, three groups of Pegmatites are distinguished within the Cape Cross-Uis belt. (1) The most common are the unzoned Nb-Ta-Sn type with mineralised alteration areas in the form of greisenised and albitised zones that occur sporadically in the Pegmatites in various morphologies. (2) The garnet-tourmaline, crudely zoned Pegmatites are slightly less common. They are granite-hosted and differ from other Pegmatite types in terms of their low Rb, Sr, Nb, Ta, Sn, Cs (
Patrick Asamoah Sakyi - One of the best experts on this subject based on the ideXlab platform.
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la icp ms u pb zircon columbite tantalite and 40ar 39ar muscovite age constraints for the rare element Pegmatite dykes in the altai orogenic belt nw china
Geological Magazine, 2016Co-Authors: Qifeng Zhou, Kezhang Qin, Dongmei Tang, Chunlong Wang, Patrick Asamoah SakyiAbstract:The Chinese Altai is renowned for its rich rare-element resources. Nine representative rare-element (REL) Pegmatites were dated using LA-ICP-MS and 40Ar–39Ar methods. The columbite grains yield a weighted mean 206Pb/238U age of 239.6±3.8 Ma for the Dakalasu (Be-Nb-Ta) Pegmatite and concordia U–Pb ages of 258.1±3.1 Ma and 262.3±2.5 Ma for the Xiaokalasu (Li-Nb-Ta) Pegmatite. The zircons display a weighted mean 206Pb/238U age of 198.5±2.5 Ma for the Husite (Be) Pegmatite and concordia U–Pb ages of 194.3±1.6 Ma and 248.2±2.2 Ma for the Qunkuer (Be) and Taerlang (barren) Pegmatites. The muscovite 40Ar–39Ar dating gives plateau ages of 286.4±1.6 Ma, 297.0±2.6 Ma, 265.2±1.5 Ma, 178.8±1.0 Ma, 162.2±0.9 Ma, 237.7±1.3 Ma, 237.4±1.2 Ma and 231.9±1.2 Ma for the Talate (Li-Be-Nb-Ta), Baicheng (Nb-Ta), Kangmunagong (barren), Husite (Be), Qunkuer (Be-Nb-Ta), Xiaokalasu (Li-Nb-Ta), Weizigou (Be) and Taerlang (barren) Pegmatites, respectively. These new ages coupled with previous geochronological work suggest that the REL Pegmatites in the Chinese Altai formed during early Permain – Late Jurassic time. The REL Pegmatites located in the Central Altaishan terrane are younger than those in the Qiongkuer–Abagong terrane, showing a correlation with the coeval and adjacent granites. The formation of the REL Pegmatites and these granites indicates frequent and strong magmatic activity in the post-orogenic and anorogenic setting. The spatial and temporal distribution of Pegmatites and granites reveals a magmatism path from the SE (of age early–middle Permian), to the NW (middle Permian – Middle Triassic) and finally to the central part (Middle Triassic – Jurassic) of the Chinese Altai.