Letteratura scientifica selezionata sul tema "LCT pegmatites"

AbstractThe evolution of the trace-element patterns of quartz during crystallization of pegmatite melt was investigated using laser ablation inductively coupled plasma mass spectrometry. The contents of Al, B, Ba, Be, Cr, Fe, Ge, Li, Mn, P, Rb, Sn, Sr and Ti were analysed in quartz from the border, intermediate and core zones of four granitic pegmatites differing in degree of fractionation and origin. The material investigated originates from the pegmatite district of the Strážek Unit, Moldanubian Zone, Bohemian Massif, Czech Republic and includes: lepidolite LCT (Li-Cs-Ta) pegmatite from Rožná; berylcolumbite LCT pegmatite from Věžná; anatectic pegmatite from Znětínek; and intragranitic NYF (Nb-Y-F) pegmatite Vladislav from the Třebíč Pluton. The abundances of the elements analysed varied over wide intervals: <1 to 32 ppm Li, 0.5 to 6 ppm B, <1 to 10 ppm Ge, 1 to 10 ppm P, 10 to 450 ppm Al, 1 to 45 ppm Ti and <1 to 40 ppm Fe (average sample contents). Concentrations of Be, Rb, Sr, Sn, Ba, Cr and Mn are usually <1 ppm. Quartz from LCT pegmatites exhibits a distinct evolutionary trend with a decrease in Ti and an increase in Al, Li and Ge from the pegmatite border to the core. In comparison with the most fractionated rare-metal granites, pegmatitic quartz is relatively depleted in Al and Li, but strongly enriched in Ge. Quartz from simple anatectic and NYF pegmatites is poor in all trace elements with their evolution marked by a decrease in Ti and a small increase in Ge. There is little Al or Li and neither shows any systematic change with pegmatite evolution. Using the Ti-in-quartz thermobarometer, the outer zones of the Znětínek and Vladislav pegmatites crystallized at ∼670°C, whereas the border zone in the Rožná pegmatite yields a temperature near 610°C.

Abstract. The in situ Lu–Hf geochronology of garnet, apatite, fluorite, and carbonate minerals is a fast-developing novel analytical method. It provides an alternative technique for age dating of accessory minerals in lithium–caesium–tantalum (LCT) rare-element (RE) pegmatites where zircon is often metamict due to alteration or radiation damage. Currently most dates from Finnish LCT pegmatites are based on columbite-group minerals (CGMs), but their occurrence is restricted to mineralised zones within the pegmatites. Accessory minerals such as garnet and apatite are widespread in both mineralised and unmineralised LCT pegmatites. Lu–Hf dating of garnet and apatite provides an exceptional opportunity to better understand the geological history of these highly sought-after sources for battery and rare elements (Li, Nb, Ta, Be) that are critical for the green transition and its technology. In this paper we present the first successful in situ Lu–Hf garnet date of 1801 ± 53 Ma for an LCT pegmatite from the Kietyönmäki deposit in the Somero–Tammela pegmatite region, SW Finland. This age is consistent with previous zircon dates obtained for the region, ranging from 1815 to 1740 Ma with a weighted mean 207Pb / 206Pb age of 1786 ± 7 Ma.

The pegmatitic rocks located in the south-east of Côte d'Ivoire between the Comoé basin and the Sefwi belt are the subject of this study. The geology of this region consists of gneisses, granites, microgranites, amphibolites, mylonites and metasediments. All these rocks are generally crosscut by quartz and pegmatite lodes. The petrographic studies allow us to discriminate four groups of pegmatites on the basis of mineralogy: (i) beryl-muscovite bearing pegmatite (Aboisso-Comoé), (ii) albite-tourmaline bearing pegmatite (Aboisso-Comoé), (iii) micas-tourmaline bearing pegmatite (Alosso) and (iv) muscovite-garnet bearing pegmatite (Songan forest). XRD analyzes on 4 samples revealed the presence of lepidolite (lithium ore) in the muscovite-garnet bearing pegmatite (Songan forest) and phengite in beryl-muscovite bearing pegmatite (Aboisso-Comoé). The pegmatite diffractograms of Aboisso-Comoé (beryl-muscovite bearing pegmatite) and Songan forest (muscovite-garnet bearing pegmatite) show almost same signatures and would suggest that those pegmatites come from the same source. Geochemical analyzes by portable XRF carried out on muscovite and feldspar minerals indicate that the samples from Aboisso-Comoé and Songan forest have the characteristics of Lithium-Cesium-Tantale type (LCT) pegmatites. The geochemical diagrams indicated the probable presence of beryl and spodumene type mineralization in the muscovite-garnet bearing pegmatite.

The Giraúl granitic pegmatite field in Angola is composed of five pegmatite types, the most evolved belong to the beryl-columbite, beryl-columbite-phosphate and spodumene types. Pegmatites are concentrically zoned with increased grain size toward a quartz core; the most evolved pegmatites have well-developed replacement units. These pegmatites are rich in Nb-Ta oxide minerals and the field has a moderate interest for critical elements such as Ta and Hf. Tourmaline, garnet and micas occur as accessory minerals. The abundance of Zr and Nb-Ta minerals increases with the evolution of the pegmatites, as well as the proportions of beryl and Li-rich minerals. The Ta/(Ta + Nb) ratio in Nb-Ta oxide minerals and the Hf/(Hf + Zr) ratio in zircon also increase with the evolution of the pegmatites and within each pegmatite body from border to inner zones, and especially in the late veins and subsolidus replacements. Textural patterns and occurrence of late veins with Ta-rich minerals suggest that Nb and especially Ta can be enriched in late hydrothermal fluids exsolved from the magma, along with Hf and other incompatible elements as Sn, U, Pb, Sb and Bi.

The increasing demand for green technology and battery metals necessitates a review of geological exploration techniques for Li–Cs–Ta (LCT) pegmatites, which is applicable to the work of mining companies. This paper reviews the main controls of LCT pegmatite genesis relevant to mineral exploration programs and presents a workflow of grassroots exploration techniques, supported by examples from central Europe and Africa. Geological exploration commonly begins with information gathering, desktop studies and Geographic Information System (GIS) data reviews. Following the identification of prospective regional areas, initial targets are verified in the field by geological mapping and geochemical sampling. Detailed mineralogical analysis and geochemical sampling of rock, soil and stream sediments represent the most important tools for providing vectors to LCT pegmatites, since the interpretation of mineralogical phases, deportment and liberation characteristics along with geochemical K/Rb, Nb/Ta and Zr/Hf metallogenic markers can detect highly evolved rocks enriched in incompatible elements of economic interest. The importance of JORC (Joint Ore Reserves Committee) 2012 guidelines with regards to obtaining geological, mineralogical and drilling data is discussed and contextualised, with the requirement of treating LCT pegmatites as industrial mineral deposits.

The Kangxiwa–Dahongliutan pegmatite field in the Western Kunlun Orogen, China contains numerous granitic pegmatites around a large granitic pluton (the Dahongliutan Granite with an age of ca. 220 to 217 Ma), mainly including barren garnet-, tourmaline-bearing pegmatites, Be-rich beryl-muscovite pegmatites, and Li-, P-rich albite-spodumene pegmatites. The textures, major element contents, and trace element concentrations of columbite-group minerals (CGM) and cassiterite from three albite-spodumene pegmatites in the region were investigated using a combination of optical microscopy, SEM, EPMA and LA-ICP-MS. The CGM can be broadly classified into four types: (1) inclusions in cassiterite; (2) euhedral to subhedral crystals (commonly exhibiting oscillatory and/or sector zoning and coexisting with magmatic cassiterite); (3) anhedral aggregates; (4) tantalite-(Fe)-ferrowodginite (FeSnTa2O8) intergrowths. The compositional variations of CGM and cassiterite are investigated on the mineral scale, in individual pegmatites and within the pegmatite group. The evolution of the pegmatites is also discussed. The variation of Nb/Ta and Zr/Hf ratios of the cassiterite mimics the Nb-Ta and Zr-Hf fractionation trends in many LCT pegmatites, indicating that these two ratios of cassiterite may bear meanings regarding the pegmatite evolution.

Lithium is rare in the cosmos, but the formation of continental crust has concentrated lithium into economic deposits. The 124 recognized Li mineral species occur largely in four geologic environments: (1) lithium–cesium–tantalum (LCT) granitic pegmatites and associated metasomatic rocks; (2) highly peralkaline pegmatites; (3) metasomatic rocks not directly associated with pegmatites; (4) manganese deposits. The geologically oldest Li minerals are reported from LCT pegmatites and date to 3,000–3,100 Ma, a critical period in the evolution of the continental crust and the rate of its generation. This suggests a link between the earliest appearance of LCT-family pegmatites and the onset of plate tectonics, consistent with the correlation between the observed abundance of LCT-family pegmatites and supercontinent assembly.

Laser-induced breakdown spectroscopy (LIBS), which has recently emerged as tool for geochemical analysis outside the traditional laboratory setting, is an ideal tool for Li exploration because it is the only technique that can measure Li in minerals, rocks, soils, and brines in-situ in the field. In addition to being used in many products essential to modern life, Li is a necessary element for a reduced carbon future and Li–Cs–Ta (LCT) granitic pegmatites are an important source of Li. Such pegmatites can have varying degrees of enrichment in Li, Rb, Cs, Be, Sn, Ga, Ta>Nb, B, P, and F. We focus here on the LCT pegmatites of the Carolina Tin-Spodumene Belt (CTSB) situated in the Kings Mountain Shear Zone, which extends from South Carolina into North Carolina. The CTSB hosts both barren and fertile pegmatites, with Li-enriched pegmatites containing spodumene, K-feldspar, albite, quartz, muscovite, and beryl. We illustrate how handheld LIBS analysis can be used for real-time Li analysis in the field at a historically important CTSB pegmatite locality in Gaston County, N.C. in four contexts: (i) elemental detection and identification; (ii) microchemical mapping; (iii) depth profiling; and (iv) elemental quantitative analysis. Finally, as an example of a practical exploration application, we describe how handheld LIBS can be used to measure K/Rb ratios and Li contents of muscovite and rapidly determine the degree of pegmatite fractionation. This study demonstrates the potential of handheld LIBS to drastically reduce the time necessary to acquire geochemical data relevant to acquiring compositional information for pegmatites during a Li pegmatite exploration program.

The Reflejos de Mar Li-pegmatite, located in northwestern Argentina, is part of the Villismán pegmatite group, Ancasti District, Pampean Pegmatite Province. Four garnet crystals from the outermost part of the pegmatite were analyzed by major and minor elements (SiO2, TiO2, Al2O3, Cr2O3, MgO, CaO, MnO, FeO) using electron microprobe. The pegmatite belongs to the rare-element class, spodumene type, LCT (Li-Cs-Ta) petrogenetic family. Based on their Mn and Fe contents, the analyzed garnet can be assigned to the spessartine-almandine serie. The cores and rims of the analyzed garnets show significant differences for the divalent components in VIII-coordination, especially, Mn and Fe. The average MnO and FeO contents in the cores of the grains is 34.6 and 8.29 wt%, respectively, while in the rims is 29.31 and 12.95 wt%, respectively. The Fe/Mn ratio at the core of the grains is 0.24 while at the rims it is 0.44. Cr2O3 and TiO2 contents are very low (˂0.17 wt%) and the values of SiO2 and Al2O3 are ~36 and ~21 wt%, respectively. The mean chemical and molecular formulas of the core can be expressed: [(Mn2.40 Fe0.57 Ca0.02 Mg0.02)3.01 (Al1.99 Cr0.002)2.00 (Si2.99 Ti0.01)3.00 O12]; {Sps79.8 Alm18.9 Grs0.7 Prp0.5}; and the rim as: [(Mn2.04 Fe0.89 Ca0.05 Mg0.04)3.02 (Al2.00 Cr0.002)2.00 (Si2.98 Ti0.005)3.00 O12]; {Sps67.6 Alm29.5 Grs1.6 Prp1.3}. The chemical composition of garnet from the Reflejos de Mar pegmatite is similar to other worldwide examples in similar rocks, especially LCT pegmatites, which are highly evolved and associated with Li mineralization. Therefore, its composition could be used as an additional tool in the exploration of Li-bearing pegmatites in the Pampean Pegmatite Province. The differences in Fe-Mn contents between core and rim of the crystals would be controlled by variations in composition of the pegmatitic melt and, in addition, by the simultaneous precipitation of other mineral phases, for example, schorl and Mn-Fe-bearing phosphates.

A dataset of >1190 published compositional analyses of muscovite from granitic pegmatites of varying mineralogical types was compiled to reevaluate the usefulness of K-Rb-Li systematics of muscovite as a tool for distinguishing mineralogically simple pegmatites from pegmatites with potential Li mineralization. Muscovite from (i) common, (ii) (Be-Nb-Ta-P)-enriched, (iii) Li-enriched, and (iv) REE- to F-enriched pegmatites contain Li contents that vary between 10 and 20,000 ppm depending on the degree of pegmatite fractionation. Common pegmatites are characterized by low degrees of fractionation as exhibited by K/Rb ratios ranging from 618 and 25 and Li contents generally being <200 ppm but infrequently as high as 743 ppm in muscovite. Moderately fractionated pegmatites with Be, Nb, Ta, and P enrichment contain muscovite having K/Rb ratios mostly between 45 and 7 plus Li contents between 5 to >1700 ppm. Muscovite from moderately to highly fractionated Li-rich pegmatites exhibit a wide range of K/Rb ratios and Li values: (i) K/Rb = 84 to 1.4 and Li = 35 to >18,100 ppm for spodumene pegmatites, (ii) K/Rb = 139 to 2 and Li = 139 to >18,500 ppm for petalite pegmatites, and (iii) K/Rb = 55 to 1.5 and Li = 743 to >17,800 ppm for lepidolite pegmatites. Pegmatites that host substantial REE- and F-rich minerals may carry muscovite with K/Rb ratios between 691 to 4 that has Li contents between 19 to 15,690 ppm. The K/Rb-Li behavior of muscovite can be useful in assessing the potential for Li mineralization in certain granitic pegmatite types. The proposed limits of K/Rb values and Li concentrations for identifying spodumene- or petalite-bearing pegmatites as part of an exploration program is reliable for Group 1 (LCT) pegmatite populations derived from S-type parental granites or anatectic melting of peraluminous metasedimentary rocks. However, it is not recommended for application to Group 2 (NYF) pegmatites affiliated with anorogenic to post-orogenic granitoids with A-type geochemical signatures or that derived by the anatexis of mafic rocks that generated REE- and F-rich melts.

Les pegmatites à éléments rares de type LCT sont depuis longtemps étudiées et exploitées pour leurs gemmes et les métaux rares qu’elles contiennent. Malgré de nombreuses études réalisées sur les processus d’enrichissement en éléments rares, ou les mécanismes à l’origine de leurs textures, très peu d’études ont été dédiées aux mécanismes de mise en place des pegmatites et à leur répartition spatiale à l’échelle du champ. Afin de déterminer les mécanismes moteurs à l’origine de l’ascension de ces magmas, une étude multidisciplinaire a été menée sur 3 champs de pegmatites à éléments rares, répartis à l’échelle de la chaîne Varisque. Les résultats démontrent la proximité entre la localisation des pegmatites minéralisées et l’intensité de la déformation encaissante. De plus, la mise en place de ces magmas semble facilitée par un certain mode de fracturation. La modélisation numérique de la mise en place des magmas dans ces zones crustales fragilisées indique que l’ascension est facilitée par leurs faibles viscosité et densité, mais aussi par des perméabilités crustales très élevées (> 10⁻¹² m²), à des profondeurs de l’ordre de 10 km. Enfin, d’après les signatures isotopiques du Li mesurées sur des micas pegmatitiques, le lithium ne fractionne pas depuis le granite voisin, jusqu’aux pegmatites les plus différenciées, puisque les valeurs δ⁷Li (‰) sont toutes comprises dans une gamme de - 2 à + 2 ‰, similaire à celle rencontrée dans les granites orogéniques. Nous suggérons donc que la genèse des magmas pegmatitiques est commune à celle des granites hyperalumineux. Les mécanismes de fracturation et d’attraction (« magma-pumping ») sont envisagés pour avoir favorisé l’ascension de ces magmas résiduels, enrichis en éléments rares, de faibles volumes, au cours de transitions brutales et de courtes durées (~ 10³ ans), de la perméabilité. L’ensemble de ces résultats permet de remettre en question le modèle du granite parent classiquement utilisé pour la prospection de ces gisements, et de proposer un modèle revisité couplant la genèse et la mise en place de ces magmas
LCT-type rare-element pegmatites have long been studied and exploited for their gems and rare metals they contain. Despite many studies about the rare-element enrichment, or about the mechanisms leading their exotic textures, very few studies have been dedicated to the mechanisms controlling their emplacement and their spatial distribution at the scale of the pegmatite field. To better investigate the origin of ascent-driving mechanisms of these magmas, a multidisciplinary study was conducted on 3 rare-element pegmatite fields across the Variscan belt. The results demonstrate the spatial proximity of the rare-metals-rich pegmatites with the intensity of deformation of the hosting rocks. In addition, spatial statistical analyses suggest that the emplacement of such magmas has been facilitated by fracture-controlled model. According to numerical models, the rise of these pegmatite-forming melts along weakened crustal zones would be facilitated by their peculiar physico-chemical properties (low viscosity and density), but also by very high crustal permeability (> 10⁻¹² m²) at depths around 10 km. Finally, accordingly to Li isotope signatures measured on pegmatitic micas, lithium does not fractionate from neighbouring granite up to the more differentiated pegmatites, since all δ⁷Li (‰) fall within a range of - 2 to + 2 ‰, as for orogenic granites. Therefore, we suggest that the genesis these pegmatite-forming melts is common to that of peraluminous granites. Mechanisms of fracturation and magma-pumping may have favoured the rise of these low volumes of residual melts, enriched in rare-elements, during short periods (~ 10³ yrs) of strong permeability increase. These results question the granitic model commonly used for the exploration of this type of mineral deposits. We suggest a revisited model accounting for both genesis and emplacement controlling mechanisms of the pegmatite-forming melts

Lithium Cesium Tantalum (LCT) pegmatites are important resources for rare metals like Cesium, Lithium or Tantalum, whose demand increased markedly during the past decade. At present, Cs is known to occur in economic quantities only from the two LCT pegmatite deposits at Bikita located in Zimbabwe and Tanco in Canada. Host for this Cs mineralisation is the extreme rare zeolite group mineral pollucite. However, at Bikita and Tanco, pollucite forms huge massive, lensoid shaped and almost monomineralic pollucite mineralisations that occur within the upper portions of the pegmatite. In addition, both pegmatite deposits have a comparable regional geological background as they are hosted within greenstone belts and yield a Neoarchean age of about 2,600 Ma. Furthermore, at present the genesis of these massive pollucite mineralisations was not yet investigated in detail. Major portions of Western Australia consist of Meso- to Neoarchean crustal units (e.g., Yilgarn Craton, Pilbara Craton) that are known to host a large number of LCT pegmatite systems. Among them are the LCT pegmatite deposits Greenbushes (Li, Ta) and Wodgina (Ta, Sn). In addition, small amounts of pollucite were recovered from one single diamond drill core at the Londonderry pegmatite field. Despite that, no systematic investigations and/or exploration studies were conducted for the mode of occurrence of Cs and especially that of pollucite in Western Australia. In the course of the present study nineteen individual pegmatites and pegmatite fields located on the Yilgarn Craton, Pilbara Craton and Kimberley province have been visited and inspected for the occurrence of the Cs mineral pollucite. However, no pollucite could be detected in any of the investigated pegmatites. Four of the inspected LCT-pegmatite systems, namely the Londonderry pegmatite field, the Mount Deans pegmatite field, the Cattlin Creek LCT pegmatite deposit (Yilgarn Craton) and the Wodgina LCT pegmatite deposit (Pilbara Craton) was sampled and investigated in detail. In addition, samples from the Bikita pegmatite field (Zimbabwe Craton) were included into the present study in order to compare the Western Australian pegmatites with a massive pollucite mineralisation bearing LCT pegmatite system. This thesis presents new petrographical, mineralogical, mineralchemical, geochemical, geochronological, fluid inclusion and stable and radiogenic isotope data. The careful interpretation of this data enhances the understanding of the LCT pegmatite systems in Western Australia and Zimbabwe. All of the four investigated LCT pegmatite systems in Western Australia, crop out in similar geological settings, exhibit comparable internal structures, geochemistry and mineralogy to that of the Bikita pegmatite field in Zimbabwe. Furthermore, in all LCT pegmatite systems evidences for late stage hydrothermal processes (e.g., replacement of feldspars) and associated Cs enrichment (e.g., Cs enriched rims on mica, beryl and tourmaline) is documented. With the exception of the Wodgina LCT pegmatite deposit, that yield a Mesoarchean crystallisation age (approx. 2,850 Ma), all other LCT pegmatite systems gave comparable Neoarchean ages of 2,630 Ma to 2,600 Ma. The almost identical ages of the LCT pegmatite systems of the Yilgarn and Zimbabwe cratons suggests, that the process of LCT pegmatite formation at the end of the Neoarchean was active worldwide. Nevertheless, essential distinguishing feature of the Bikita pegmatite field is the presence of massive pollucite mineralisations that resulted from a process that is not part of the general development of LCT pegmatites and is associated with the extreme enrichment of Cs. The new findings of the present study obtained from the Bikita pegmatite field and the Western Australian LCT pegmatite systems significantly improve the knowledge of Cs behaviour in LCT pegmatite systems. Therefore, it is now possible to suggest a genetical model for the formation of massive pollucite mineralisations within LCT pegmatite systems. LCT pegmatites are generally granitic in composition and are interpreted to represent highly fractionated and geochemically specialised derivates from granitic melts. Massive pollucite mineralisation bearing LCT pegmatites evolve from large and voluminous pegmatite melts that intrude as single body along structures within an extensional tectonic setting. After emplacement, initial crystallisation will develop the border and wall zone of the pegmatites, while due to fractionated crystallisation immobile elements (i.e., Cs, Rb) become enriched within the remaining melt and associated hydrothermal fluids. Following this initial crystallisation, a relatively small portion (0.5–1 vol.%) of immiscible melt or fluid will separate during cooling. This immiscible partial melt/fluid is enriched in Al2O3 and Na2O, as well as depleted in SiO2 and will crystallise as analcime. In addition, this melt might allready contains up to 1–2 wt.% Cs2O. However, due to the effects of fluxing components (e.g., H2O, F, B) this analcime melt becomes undercooled which prevents crystallisation of the analcime as intergranular grains. Since this analcime melt exhibits a lower relative gravity when compared to the remaining pegmatite melt the less dense analcime melt will start to ascent gravitationally and accumulate within the upper portion of the pegmatite sheet. At the same time, the remaining melt will start to crystallise separately and form the inner portions of the pegmatite. This crystallisation is characterised by still ongoing fractionation and enrichment of incompatible elements (i.e., Cs, Rb) within the last crystallising minerals (e.g., lepidolite) or concentration of these incompatible elements within exsolving hydrothermal fluids. As analcime and pollucite form a continuous solid solution series, the analcime melt is able to incorporate any available Cs from the melt and/or associated hydrothermal fluids and crystallise as Cs-analcime in the upper portion of the pegmatite sheet. Continuing hydrothermal activity and ongoing substitution of Cs will then start to shift the composition from Cs-analcime composition towards Na-pollucite composition. In addition, if analcime is cooled below 400 °C it is subjected to a negative thermal expansion of about 1 vol.%. This contraction results in the formation of a prominent network of cracks that is filled by late stage minerals (e.g., lepidolite, quartz, feldspar and petalite). Certainly, prior to filling, this network of cracks enhances the available conduits for late stage hydrothermal fluids and the Cs substitution mechanism within the massive pollucite mineralisation. Furthermore, during cooling of the pegmatite, prominent late stage mineral replacement reactions (e.g., replacement of K-feldspar by lepidolite, cleavelandite, and quartz) as well as subsolidus self organisation processes in feldspars take place. These processes are suggested to release additional incompatible elements (e.g., Cs, Rb) into late stage hydrothermal fluids. As feldspar forms large portions of pegmatite a considerable amount of Cs is released and transported via the hydrothermal fluids towards the massive pollucite mineralisation in the upper portion of the pegmatite. Consequently, the initial analcime can accumulate enough Cs in order to shift its composition from the Cs-analcime member (>2 wt.% Cs2O) towards the Na-pollucite member (23–43 wt.% Cs2O) of the solid solution series. The timing of this late stage Cs enrichment is interpreted to be quasi contemporaneous or immediately after the complete crystallisation of the pegmatite melt. However, much younger hydrothermal events that overprint the pegmatite are also interpreted to cause similar results. Hence, it has been demonstrated that the combination of this magmatic and hydrothermal processes is capable to generate an extreme enrichment in Cs in order to explain the formation of massive pollucite mineralisations within LCT pegmatite systems. This genetic model can now be applied to evaluate the potential for occurrences of massive pollucite mineralisations within LCT pegmatite systems in Western Australia and worldwide
Lithium-Caesium-Tantal-(LCT) Pegmatite repräsentieren eine bedeutende Quelle für seltene Metalle, deren Bedarf im letzten Jahrzehnt beträchtlich angestiegen ist. Im Falle von Caesium sind zurzeit weltweit nur zwei LCT-Pegmatitlagerstätten bekannt, die abbauwürdige Vorräte an Cs enthalten. Dies sind die LCT-Pegmatitlagerstätten Bikita in Simbabwe und Tanco in Kanada. Das Wirtsmineral für diese Cs-Mineralisation ist das extrem selten auftretende Zeolith-Gruppen-Mineral Pollucit. In den Lagerstätten Bikita und Tanco bildet Pollucit dagegen massive, linsenförmige und fast monomineralische Pollucitmineralisationen, die in den oberen Bereichen der Pegmatitkörper anstehen. Zusätzlich befinden sich beide Lagerstätten in geologisch vergleichbaren Einheiten. Die Nebengesteine sind Grünsteingürtel die ein neoarchaisches Alter von ca. 2,600 Ma aufweisen. Die Bildung derartiger massiver Pollucitmineralisationen ist bis jetzt noch nicht detailliert untersucht worden. Große Bereiche von Westaustralien werden von meso- bis neoarchaischen Krusteneinheiten (z.B. Yilgarn Kraton, Pilbara Kraton) aufgebaut, von denen auch eine große Anzahl an LCT-Pegmatitsystemen bekannt sind. Darunter befinden sich unter anderem die LCT-Pegmatitlagerstätten Greenbushes (Li, Ta) und Wodgina (Ta, Sn). Zusätzlich wurden kleine Mengen an Pollucit in einer einzigen Kernbohrung im Londonderry Pegmatitfeld angetroffen. Ungeachtet dessen, wurden in Westaustralien bis jetzt keine systematischen Untersuchungen und/oder Explorationskampagnen auf Vorkommen von Cs und speziell der von Pollucit durchgeführt. Im Verlauf dieser Studie wurden insgesamt neunzehn verschiedene Pegmatitvorkommen und Pegmatitfelder des Yilgarn Kratons, Pilbara Kratons und der Kimberley Provinz auf das Vorkommen des Minerals Pollucit untersucht. Allerdings konnte in keinem der untersuchten LCT-Pegmatitsystemen Pollucit nachgewiesen werden. Von vier der untersuchten LCT-Pegmatitsystemen, dem Londonderry Pegmatitfeld, dem Mount Deans Pegmatitfeld, der Cattlin Creek LCT-Pegmatitlagerstätte (Yilgarn Kraton) und der Wodgina LCT-Pegmatitlagerstätte (Pilbara Kraton) wurden detailliert Proben entnommen und weitergehend untersucht. Zusätzlich wurden die massiven Pollucitmineralisationen im Bikita Pegmatitfeld beprobt und in die detailierten Untersuchungen einbezogen. Der Probensatz aus dem Bikita Pegmatitfeld dient als Referenzmaterial mit dem die Pegmatitproben aus Westaustralien verglichen werden. Die vorliegende Arbeit fasst die wesentlichen Ergebnisse der petrographischen, mineralogischen, mineralchemischen, geochemischen und geochronologischen Untersuchungen sowie der Flüssigkeitseinschlussuntersuchungen und stabilen und radiogenen Isotopenzusammensetzungen zusammen. Alle vier der in Westaustralien untersuchten LCT-Pegmatitsysteme kommen in geologisch ähnlichen Rahmengesteinen vor, weisen einen vergleichbaren internen Aufbau, geochemische Zusammensetzung und Mineralogie zu dem des Bikita Pegmatitfeldes in Simbabwe auf. Weiterhin konnten in allen LCT-Pegmatitsystemen Hinweise für späte hydrothermale Prozesse (z.B. Verdrängung von Feldspat) nachgewiesen werden, die einhergehend mit einer Anreicherung von Cs verbunden sind (z.B. Cs-angereicherte Säume um Glimmer, Beryll und Turmalin). Mit der Ausnahme der Wodgina LCT-Pegmatitlagerstätte, in der ein mesoarchaisches Kristallisationsalter (ca. 2,850 Ma) nachgewiesen wurde, lieferten die Altersdatierungen in den anderen LCT-Pegmatitsystemen übereinstimmende neoarchaische Alter von 2,630 Ma bis 2,600 Ma. Diese fast identischen Alter der LCT-Pegmatitsysteme des Yilgarn und Zimbabwe Kratons suggerieren, dass die Prozesse, die zur LCT-Pegmatitbildung am Ende des Neoarchaikums führten, weltweit aktiv waren. Ungeachtet dessen stellt das Vorhandensein von massiver Pollucitmineralisation das Alleinstellungsmerkmal des Bikita Pegmatitfeldes dar, welche sich infolge eines Prozesses gebildet haben der nicht Bestandteil der üblichen LCT-Pegmatitentwicklung ist und sich durch eine extreme Anreicherung an Cs unterscheidet. Die neuen Ergebnisse die in dieser Studie von den Bikita Pegmatitfeld und den Westaustralischen LCT-Pegmatitsystemen gewonnen wurden, verbessern das Verständnis des Verhaltens von Cs in LCT-Pegmatitsystemen deutlich. Somit ist es nun möglich, ein genetisches Modell für die Bildung von massiven Pollucitmineralisationen in LCT-Pegmatitsystemen vorzustellen. LCT-Pegmatite weisen im Allgemeinen eine granitische Zusammensetzung auf und werden als Kristallisat von hoch fraktionierten und geochemisch spezialisierten granitischen Restschmelzen interpretiert. Die Bildung von massiven Pollucitmineralisationen ist nur aus großen und voluminösen Pegmatitschmelzen, die als einzelner Körper entlang von Störungen in extensionalen Stressregimen intrudieren möglich. Nach Platznahme der Schmelze bildet die beginnende Kristallisation zunächst die Kontakt- und Randzone des Pegmatits, wobei infolge von fraktionierter Kristallisation die immobilen Elemente (v.a. Cs, Rb) in der verbleibenden Restschmelze angereichert werden. Im Anschluss an diese erste Kristallisation entmischt sich nach Abkühlung eine sehr kleine Menge (0.5–1 vol.%) Schmelze und/oder Fluid von der Restschmelze. Diese nicht mischbare Teilschmelze/-fluid ist angereichert an Al2O3 und Na2O sowie verarmt an SiO2 und kristallisiert als Analcim. Zusätzlich kann diese Schmelze bereits mit 1–2 wt.% Cs2O angereichert sein. Aufgrund der Auswirkung von Flussmitteln (z.B. H2O, F, B) wird allerdings der Schmelzpunkt dieser Analcimschmelze herabgesetzt und so die Kristallisation des Analcims als intergranulare Körner verhindert. Da diese Analcimschmelze im Vergleich zu der restlichen Schmelze eine geringere relative Dichte besitzt, beginnt sie gravitativ aufzusteigen und sich in den oberen Bereichen des Pegmatitkörpers zu akkumulieren. Währenddessen beginnt die restliche Schmelze separat zu kristallisieren und die inneren Bereiche des Pegmatits zu bilden. Diese Kristallisation ist einhergehend mit fortschreitender Fraktionierung und der Anreicherung von inkompatiblen Elementen (v.a. Cs, Rb) in den sich als letztes bildenden Mineralphasen (z.B. Lepidolit) oder der Konzentration der inkompatiblen Element in die sich entmischenden hydrothermalen Fluiden. Da Analcim und Pollucit eine lückenlose Mischungsreihe bilden, ist die Analcimschmelze in der Lage, alles verfügbare Cs von der Restschmelze und/oder assoziierten hydrothermalen Fluiden an sich zu binden und als Cs-Analcim im oberen Bereich des Pegmatitkörpers zu kristallisieren. Fortschreitende hydrothermale Aktivität und Substitution von Cs verschiebt dann die Zusammensetzung des Analcims von der Cs-Analcim- zu Na-Pollucitzusammensetzung. Zusätzlich erfährt der Analcim bei Abkühlung unter 400 °C eine negative thermische Expansion von ca. 1 vol.%. Diese Kontraktion führt zu der Bildung des markanten Rissnetzwerkes das durch späte Mineralphasen (z.B. Lepidolit, Quarz, Feldspat und Petalit) gefüllt wird. Vor der Mineralisation allerdings, erhöht dieses Netzwerk an Rissen die verfügbaren Wegsamkeiten für die späten hydrothermalen Fluide und begünstigt somit den Cs-Substitutionsmechanismus in der massiven Pollucitmineralisation. Weiterhin kommt es bei der Abkühlung des Pegmatits zu späten Mineralverdrängungsreaktionen (z.B. Verdrängung von K-Feldspat durch Lepidolit, Cleavelandit und Quarz), sowie zu Subsolidus-Selbstordnungsprozessen in Feldspäten. Diese Prozesse werden weiterhin interpretiert inkompatible Elemente (z.B. Cs, Rb) in die späten hydrothermalen Fluide freizusetzen. Da Feldspäte große Teile der Pegmatite bilden, kann somit eine beträchtliche Menge an Cs freigeben werden und durch die späten hydrothermalen Fluide in die massive Pollucitmineralisation in den oberen Bereichen des Pegmatitkörpers transportiert werden. Infolgedessen ist es möglich, dass genügend Cs frei gesetzt werden kann, um die Zusammensetzung innerhalb der Mischkristallreihe von Cs-Analcim (>2 wt.% Cs2O) zu Na-Pollucit (23–43 wt.% Cs2O) zu verschieben. Die zeitliche Einordnung dieser späten Cs-Anreicherung wird als quasi zeitgleich oder im direkten Anschluss an die vollständige Kristallisation der Pegmatitschmelze interpretiert. Es kann allerdings nicht vernachlässigt werden, dass auch jüngere hydrothermale Ereignisse, die den Pegmatitkörper nachträglich überprägen, ähnliche hydrothermale Prozesse hervorrufen können. Somit konnte gezeigt werden, dass es durch Kombination dieser magmatischen und hydrothermalen Prozessen möglich ist, genügend Cs anzureichern, um die Bildung von massiven Pollucitmineralisationen in LCT-Pegmatitsystemen zu ermöglichen. Dieses genetische Modell kann nun dazu genutzt werden, um das Potential von Vorkommen von massiven Pollucitmineralisationen in LCT-Pegmatitsystemen in Westaustralien und weltweit besser einzuschätzen

The study concerns pegmatites ourcropping in the Central Alps where geochemical, structural, petrological and mineralogical analysis were performed
Lo studio riguarda le pegmatiti delle Alpi centrali caratterizzate da un punto di vista geologico, petrologico, geochimico e mineralogico

La région de Bougouni a pour spécificité la présence de pegmatites et d'aplites porteuses de lithium. Le lithium est actuellement un élément stratégique au regard des besoins croissants en cette matière première. Les pegmatites lithinifères font ainsi partie des gisements les plus recherchés pour le lithium.La zone d'étude, située au SE de Bamako (Mali), appartient à la partie sud du craton ouest africain. Les différentes roches de cette zone se sont formées au cours des événements de croissance crustale du Birimien, lors de l'orogenèse éburnéenne, entre ca. 2200 et 1800 Ma. Les formations rencontrées sont des roches métavolcanosédimentaires et plutoniques majoritairement de nature granitoïdique (tonalite à monzogranite à deux micas), structurées dans une direction NNE-SSW par l'existence de grandes zones de cisaillement. Les dykes sont intrusifs dans ces roches encaissantes sous forme de filons d'épaisseur décimétrique à décamétrique depuis des faciès aplitiques à des faciès pegmatitiques. La mise ne place dans un domaine cassant couplé au bas grade métamorphique des métasédiments encaissants indiquent une mise en place des dykes au niveau de la croûte continentale supérieure.La province de Bougouni compte une centaine de dykes riches en lithium (Li2O > 1.00 wt% de la roche totale). Le spodumène, principal phase minérale porteuse de lithium (Li2O = 8 wt%), représente entre 5 et 30 vol.% de la roche, accompagné de feldspath alcalin, plagioclase, quartz et d'une faible quantité de muscovite et de biotite. Sont également présents une centaine de dykes pauvres en lithium (Li2O < 0.05 wt%) caractérisés par le même assemblage minéralogique que les dykes riches en lithium à l'exception du spodumène remplacé par le grenat.Concernant la géochronologie, les âges U-Pb sur zircons pour l'ensemble des granitoïdes (faciès granodioritiques à granitiques à deux micas) s'étendent entre 2100 ± 14 et 2136 ± 19 Ma. Ces âges sont en accord avec les âges d'autres formations plutoniques s'étalant entre 2080 et 2120 Ma à l'échelle du Birimien. Les âges U-Pb sur apatites magmatiques des dykes sont compris entre 2070 - 2000 Ma. La comparaison des données géochronologique à d'autres pegmatites du Birimien permettent de définir la période ca. 2070 - 2000 Ma comme la période de mise en place des dykes pegmatitiques (notamment les pegmatites de la famille LCT) du Birimien. Cette période tardi- à post orogénique représenterait l'étape finale du magmatisme paléoprotérozoïque dans le domaine du Baoulé-Mossi.Concernant la géochimie en éléments majeurs et traces, l'absence d'une évolution géochimique continue depuis les granitoïdes aux dykes ne permettent pas d'expliquer les liquides pegmatitiques comme étant les termes les plus évolués des granitoïdes. Cette conclusion est en accord avec les données géochronologiques qui témoignent d'une différence d'âge beaucoup trop importantes entre ces formations pour qu'elles puissent avoir un lien génétique. Concernant les dykes, bien qu'ils soient contemporains, les différences en termes de signature géochimique ne permettent pas d'expliquer qu'ils puissent avoir évolués depuis un seul et même liquide parent. Cependant, il est fort probable que les liquides à l'origine des deux types de dykes puissent provenir de la fusion du même type de protolithe de nature métapélitique.En somme, les données de terrain, pétrographiques, géochronologiques et géochimiques ne donnent pas de lien génétique entre les dykes et les granitoïdes de Bougouni. Les deux faciès de dykes sont formés à partir de deux liquides distincts issus d'un seul et même protolithe. La différence de composition minéralogique et géochimique, notamment en Li, entre les dykes riches en lithium et ceux pauvres en lithium pourrait être expliquée par le rôle de fluides d'origine sédimentaire ayant pu percoler et interagir avec les roches mères et/ou les liquides pegmatitiques permettant d'enrichir certains liquides en éléments mobiles, tel que le lithium
The Bougouni region in southern Mali is well known for the ore body lithium-bearing pegmatites and aplites. Lithium is currently a strategic element in view of the growing need for this raw material. The lithiniferous pegmatites are thus among the most sought-after deposits for lithium.The study area, located SE of Bamako (Mali), belongs to the southern part of the West African Craton. The various rocks in this area were formed during the Birimian crustal growth events, during the Eburnean oOrogeny, between ca. 2200 and 1800 Ma. The formations encountered are metavolcano sedimentary and plutonic rocks, mostly granitoid (tonalite to two-mica monzogranite), structured in a NNE-SSW direction by the existence of large shear zones. The dykes are intrusive in these host rocks, which occur in the form of decimeter to decameter thick dykes ranging from aplitic to pegmatitic facies. The emplacement in a brittle domain coupled with the low metamorphic grade of the enclosing metasediments indicate a dyke emplacement in the upper continental crust.The Bougouni province has about 100 Li-rich dykes (Li2O > 1.00 wt% of total rock). Spodumene, the main lithium-bearing mineral phase (Li2O = 8 wt%), represents between 5 and 30 vol.% of the rock, accompanied by alkali feldspar, plagioclase, quartz and a small quantity of muscovite and biotite. In addition to, 100 Li-poor dykes (Li2O < 0.05 wt%) that are characterized by the same mineralogical assemblage as the lithium-rich dykes except for spodumene, which is replaced by garnet.Concerning geochronology, U-Pb ages on zircons for all granitoids (granodioritic to granitic facies with two micas) range between 2100 ± 14 and 2136 ± 19 Ma. These ages are in agreement with the ages of other plutonic formations ranging between 2080 and 2120 Ma on the Birimian scale. The U-Pb ages on magmatic apatites of the dykes are between 2070 - 2000 Ma. Comparison of the geochronological data with other pegmatites of the Birimian allow us to define the period ca. 2070 - 2000 Ma as the period of establishment of the pegmatitic dykes (notably the LCT family pegmatites) of the Birimian. This late- to post-Orogenic period would represent the final stage of paleoproterozoic magmatism in the Boulé-Mossi domain.Concerning major and trace elements geochemistry, the absence of a continuous geochemical evolution from granitoids to dykes does not allow to explain the pegmatitic fluids as the most evolved terms of the granitoids. This conclusion is in agreement with the geochronological data that show a much too large age difference between these formations to be genetically related. Concerning the dykes, although they are contemporaneous, the differences in geochemical signature do not allow to explain that they could have evolved from a single parent melt. However, it is very likely that the melts that gave rise to both types of dykes may have been derived from the melting of the same type of metapelitic protolith.In sum, the field, petrographic, geochronological and geochemical data do not provide a genetic link between the Bougouni dykes and granitoids. The two dyke facies are formed from two distinct melts derived from a single protolith. The difference in mineralogical and geochemical composition, particularly in Li, between the Li-rich and Li-poor dykes could be explained by the role of fluids of sedimentary origin that may have percolated and interacted with the source? host rocks and/or the pegmatitic melts, allowing the enrichment of certain fluids in mobile elements such as lithium

The Dumper Dew is a newly discovered pegmatite located on the eastfacing slope of Uncle Tom Mountain in Oxford County, Maine. It is a geochemically evolved LCT-type pegmatite petrogenetically linked to the middle Paleozoic Sebago batholith. Shallow emplacement of the Dumper Dew is evidenced by abundant miarolitic cavities found in the pegmatite. The sheet-like structure of the pegmatite coupled with its intrusion in lowmetamorphic grade country rock suggests rapid crystallization. Northern portions of the wall zone and intermediate zones have undergone hydrothermal alteration by the migration of late-stage fluids. The pegmatite hosts a diverse assemblage of rare-element mineral phases due to its high degree of geochemical fractionation. Trends of geochemical fractionation of individual mineral phases such as K-feldspar, muscovite, garnet, apatite, beryl, spodumene, triphylite-lithiophilite, tourmaline, cassiterite, and columbite-tantalite were attained via instrumentation assay. These trends illustrate an enhanced degree of magmatic differentiation relative to other pegmatites in the area.

Lithium Cesium Tantalum (LCT) pegmatites are important resources for rare metals like Cesium, Lithium or Tantalum, whose demand increased markedly during the past decade. At present, Cs is known to occur in economic quantities only from the two LCT pegmatite deposits at Bikita located in Zimbabwe and Tanco in Canada. Host for this Cs mineralisation is the extreme rare zeolite group mineral pollucite. However, at Bikita and Tanco, pollucite forms huge massive, lensoid shaped and almost monomineralic pollucite mineralisations that occur within the upper portions of the pegmatite. In addition, both pegmatite deposits have a comparable regional geological background as they are hosted within greenstone belts and yield a Neoarchean age of about 2,600 Ma. Furthermore, at present the genesis of these massive pollucite mineralisations was not yet investigated in detail. Major portions of Western Australia consist of Meso- to Neoarchean crustal units (e.g., Yilgarn Craton, Pilbara Craton) that are known to host a large number of LCT pegmatite systems. Among them are the LCT pegmatite deposits Greenbushes (Li, Ta) and Wodgina (Ta, Sn). In addition, small amounts of pollucite were recovered from one single diamond drill core at the Londonderry pegmatite field. Despite that, no systematic investigations and/or exploration studies were conducted for the mode of occurrence of Cs and especially that of pollucite in Western Australia. In the course of the present study nineteen individual pegmatites and pegmatite fields located on the Yilgarn Craton, Pilbara Craton and Kimberley province have been visited and inspected for the occurrence of the Cs mineral pollucite. However, no pollucite could be detected in any of the investigated pegmatites. Four of the inspected LCT-pegmatite systems, namely the Londonderry pegmatite field, the Mount Deans pegmatite field, the Cattlin Creek LCT pegmatite deposit (Yilgarn Craton) and the Wodgina LCT pegmatite deposit (Pilbara Craton) was sampled and investigated in detail. In addition, samples from the Bikita pegmatite field (Zimbabwe Craton) were included into the present study in order to compare the Western Australian pegmatites with a massive pollucite mineralisation bearing LCT pegmatite system. This thesis presents new petrographical, mineralogical, mineralchemical, geochemical, geochronological, fluid inclusion and stable and radiogenic isotope data. The careful interpretation of this data enhances the understanding of the LCT pegmatite systems in Western Australia and Zimbabwe. All of the four investigated LCT pegmatite systems in Western Australia, crop out in similar geological settings, exhibit comparable internal structures, geochemistry and mineralogy to that of the Bikita pegmatite field in Zimbabwe. Furthermore, in all LCT pegmatite systems evidences for late stage hydrothermal processes (e.g., replacement of feldspars) and associated Cs enrichment (e.g., Cs enriched rims on mica, beryl and tourmaline) is documented. With the exception of the Wodgina LCT pegmatite deposit, that yield a Mesoarchean crystallisation age (approx. 2,850 Ma), all other LCT pegmatite systems gave comparable Neoarchean ages of 2,630 Ma to 2,600 Ma. The almost identical ages of the LCT pegmatite systems of the Yilgarn and Zimbabwe cratons suggests, that the process of LCT pegmatite formation at the end of the Neoarchean was active worldwide. Nevertheless, essential distinguishing feature of the Bikita pegmatite field is the presence of massive pollucite mineralisations that resulted from a process that is not part of the general development of LCT pegmatites and is associated with the extreme enrichment of Cs. The new findings of the present study obtained from the Bikita pegmatite field and the Western Australian LCT pegmatite systems significantly improve the knowledge of Cs behaviour in LCT pegmatite systems. Therefore, it is now possible to suggest a genetical model for the formation of massive pollucite mineralisations within LCT pegmatite systems. LCT pegmatites are generally granitic in composition and are interpreted to represent highly fractionated and geochemically specialised derivates from granitic melts. Massive pollucite mineralisation bearing LCT pegmatites evolve from large and voluminous pegmatite melts that intrude as single body along structures within an extensional tectonic setting. After emplacement, initial crystallisation will develop the border and wall zone of the pegmatites, while due to fractionated crystallisation immobile elements (i.e., Cs, Rb) become enriched within the remaining melt and associated hydrothermal fluids. Following this initial crystallisation, a relatively small portion (0.5–1 vol.%) of immiscible melt or fluid will separate during cooling. This immiscible partial melt/fluid is enriched in Al2O3 and Na2O, as well as depleted in SiO2 and will crystallise as analcime. In addition, this melt might allready contains up to 1–2 wt.% Cs2O. However, due to the effects of fluxing components (e.g., H2O, F, B) this analcime melt becomes undercooled which prevents crystallisation of the analcime as intergranular grains. Since this analcime melt exhibits a lower relative gravity when compared to the remaining pegmatite melt the less dense analcime melt will start to ascent gravitationally and accumulate within the upper portion of the pegmatite sheet. At the same time, the remaining melt will start to crystallise separately and form the inner portions of the pegmatite. This crystallisation is characterised by still ongoing fractionation and enrichment of incompatible elements (i.e., Cs, Rb) within the last crystallising minerals (e.g., lepidolite) or concentration of these incompatible elements within exsolving hydrothermal fluids. As analcime and pollucite form a continuous solid solution series, the analcime melt is able to incorporate any available Cs from the melt and/or associated hydrothermal fluids and crystallise as Cs-analcime in the upper portion of the pegmatite sheet. Continuing hydrothermal activity and ongoing substitution of Cs will then start to shift the composition from Cs-analcime composition towards Na-pollucite composition. In addition, if analcime is cooled below 400 °C it is subjected to a negative thermal expansion of about 1 vol.%. This contraction results in the formation of a prominent network of cracks that is filled by late stage minerals (e.g., lepidolite, quartz, feldspar and petalite). Certainly, prior to filling, this network of cracks enhances the available conduits for late stage hydrothermal fluids and the Cs substitution mechanism within the massive pollucite mineralisation. Furthermore, during cooling of the pegmatite, prominent late stage mineral replacement reactions (e.g., replacement of K-feldspar by lepidolite, cleavelandite, and quartz) as well as subsolidus self organisation processes in feldspars take place. These processes are suggested to release additional incompatible elements (e.g., Cs, Rb) into late stage hydrothermal fluids. As feldspar forms large portions of pegmatite a considerable amount of Cs is released and transported via the hydrothermal fluids towards the massive pollucite mineralisation in the upper portion of the pegmatite. Consequently, the initial analcime can accumulate enough Cs in order to shift its composition from the Cs-analcime member (>2 wt.% Cs2O) towards the Na-pollucite member (23–43 wt.% Cs2O) of the solid solution series. The timing of this late stage Cs enrichment is interpreted to be quasi contemporaneous or immediately after the complete crystallisation of the pegmatite melt. However, much younger hydrothermal events that overprint the pegmatite are also interpreted to cause similar results. Hence, it has been demonstrated that the combination of this magmatic and hydrothermal processes is capable to generate an extreme enrichment in Cs in order to explain the formation of massive pollucite mineralisations within LCT pegmatite systems. This genetic model can now be applied to evaluate the potential for occurrences of massive pollucite mineralisations within LCT pegmatite systems in Western Australia and worldwide.:Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii Zusammenfassung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v Versicherung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi 1. Introduction 1 1.1. Motivation and Scope of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2. Structure of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Fundamentals 7 2.1. The Alkali Metal Cesium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1.1. Distribution of Cesium . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1.2. Mineralogy of Cesium . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.1.3. Geochemical Behaviour of Cesium . . . . . . . . . . . . . . . . . . . . 13 2.1.4. Economy of Cesium . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.2. Pollucite – (Cs,Na)2Al2Si4O12×H2O . . . . . . . . . . . . . . . . . . . . . . . . 16 2.2.1. Crystal Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.2.2. Analcime–Pollucite–Series . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.2.3. Formation of Pollucite . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.2.4. Pollucite Occurences . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.3. Pegmatites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 2.3.1. General Characteristics of Pegmatites . . . . . . . . . . . . . . . . . . 34 2.3.2. Controls on Pegmatite Formation and Evolution . . . . . . . . . . . . . 40 2.3.3. Pegmatite Age Distribution and Continental Crust Formation . . . . . . 43 3. Geological Settings of Archean Cratons 47 3.1. Zimbabwe Craton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 3.1.1. Tectonostratigraphic Subdivision . . . . . . . . . . . . . . . . . . . . . 48 3.1.2. Tectonometamorphic Evolution of the Northern Limpopo Thrust Zone . 49 3.1.3. Pegmatites within the Zimbabwe Craton . . . . . . . . . . . . . . . . . 52 3.1.4. Masvingo Greenstone Belt . . . . . . . . . . . . . . . . . . . . . . . . . 53 3.1.5. Geological Setting of the Bikita Pegmatite District . . . . . . . . . . . . 58 3.2. Yilgarn Craton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 3.2.1. Tectonostratigraphic Framework and Geological Development . . . . . 62 3.2.2. Tectonic Models for the Development . . . . . . . . . . . . . . . . . . . 70 3.2.3. Pegmatites within the Yilgarn Craton . . . . . . . . . . . . . . . . . . . 76 3.2.4. Geological setting of the Londonderry Pegmatite Field . . . . . . . . . . 76 3.2.5. Geological Setting of the Mount Deans Pegmatite Field . . . . . . . . . 85 3.2.6. Geological Setting of the Cattlin Creek Pegmatite Deposit . . . . . . . . 91 3.3. Pilbara Craton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 3.3.1. Tectonostratigraphic Framework and Geological Development . . . . . 99 3.3.2. Tectonic Model for the Development . . . . . . . . . . . . . . . . . . . 101 3.3.3. Pegmatites within the Pilbara Craton . . . . . . . . . . . . . . . . . . . 105 3.3.4. Geological Setting of the Wodgina Pegmatite District . . . . . . . . . . 106 4. Fieldwork and Sampling of Selected Pegmatites and Pegmatite Fields 115 4.1. Bikita Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 4.2. Londonderry Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 4.2.1. Londonderry Feldspar Quarry Pegmatite . . . . . . . . . . . . . . . . . 115 4.2.2. Lepidolite Hill Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . . 117 4.2.3. Tantalite Hill Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 4.3. Mount Deans Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 4.3.1. Type I – Flat Lying Pegmatites . . . . . . . . . . . . . . . . . . . . . . . 118 4.3.2. Type II – Steeply Dipping Pegmatites . . . . . . . . . . . . . . . . . . . 120 4.4. Cattlin Creek Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 4.5. Wodgina LCT-Pegmatite Deposit . . . . . . . . . . . . . . . . . . . . . . . . . . 121 4.5.1. Mount Tinstone Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . 123 4.5.2. Mount Cassiterite Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . 123 5. Petrography and Mineralogy 139 5.1. Quantitative Mineralogy by Means of Mineral Liberation Analysis . . . . . . . . 141 5.2. Mineralogical and Petrographical Characteristics of Individual Mineral Groups . 141 5.2.1. Feldspar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 5.2.2. Quartz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 5.2.3. Mica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 5.2.4. Pollucite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 5.2.5. Petalite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 5.2.6. Spodumene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 5.2.7. Beryl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 5.2.8. Tourmaline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 5.2.9. Apatite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 5.2.10. Ta-, Nb- and Sn-oxides . . . . . . . . . . . . . . . . . . . . . . . . . . 157 5.3. Reconstruction of the General Crystallisation Sequence . . . . . . . . . . . . . 162 6. Geochemistry 165 6.1. Major Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 6.2. Selected Minor and Trace Elements . . . . . . . . . . . . . . . . . . . . . . . . 174 6.3. Fractionation Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 6.4. Rare Earth Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 7. Geochronology 193 7.1. 40Ar/39Ar-Method on Mica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 7.1.1. Bikita Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 7.1.2. Mount Deans Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . 195 7.1.3. Londonderry Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . 195 7.1.4. Cattlin Creek Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . . 195 7.1.5. Wodgina Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 7.2. Th-U-Total Pb Monazite Dating . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 7.2.1. Monazite Ages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 7.3. U/Pb Dating of Selected Ta-, Nb- and Sn-Oxide Minerals . . . . . . . . . . . . 203 7.3.1. Bikita Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 7.3.2. Londonderry Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . 203 7.3.3. Mount Deans Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . 206 7.3.4. Cattlin Creek Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . . 206 7.3.5. Wodgina Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 8. Fluid Inclusion Study 211 8.1. Bikita Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 8.2. Wodgina Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 8.3. Carbon Isotope Analysis on Fluid Inclusion Gas of Selected Mineral Phases . . 212 9. Stable and Radiogenic Isotopes 217 9.1. Whole Rock Sm/Nd-Isotopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 9.1.1. New Whole Rock Sm/Nd Data . . . . . . . . . . . . . . . . . . . . . . 217 9.2. Lithium Isotope Analysis on Selected Mineral Phases . . . . . . . . . . . . . . . 220 9.2.1. New Lithium Isotope Data . . . . . . . . . . . . . . . . . . . . . . . . . 220 10.Discussion 227 10.1. Regional Geological and Tectonomagmatic Development . . . . . . . . . . . . 227 10.1.1. Constraints from Field Evidence . . . . . . . . . . . . . . . . . . . . . . 227 10.1.2. Petrographical and Mineralogical Constraints . . . . . . . . . . . . . . 229 10.1.3. Geochemical Constraints . . . . . . . . . . . . . . . . . . . . . . . . . 230 10.1.4. Isotopic Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232 10.1.5. Constraints from Fluid Inclusion Data . . . . . . . . . . . . . . . . . . . 233 10.1.6. Geochronological Constrains . . . . . . . . . . . . . . . . . . . . . . . 233 10.2. Massive Pollucite Mineralisations . . . . . . . . . . . . . . . . . . . . . . . . . . 243 10.2.1. Unique Characteristics of Massive Pollucite Mineralisations . . . . . . . 243 10.2.2. New Concepts for the Formation of Massive Pollucite Mineralisations . . 252 10.3. Genetic Model for the Formation of Massive Pollucite Mineralisations within LCT Pegmatite Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264 11.Summary and Conclusions 267 References 273 Lists of Abbreviations 309 General Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 Mineral Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 List of Figures 311 List of Tables 315 Appendix 317 A. Legend for Topographic Maps 319 B. Sample List 323 C. Methodology 331 C.1. Quantitative Mineralogy by Means of Mineral Liberation Analysis . . . . . . . . 331 C.2. Geochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 C.3. 40Ar/39Ar-Method on Mica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335 C.4. Th-U-Total Pb Monazite Dating . . . . . . . . . . . . . . . . . . . . . . . . . . . 335 C.5. U/Pb Dating of Selected Ta-, Nb- and Sn-Oxide Minerals . . . . . . . . . . . . 336 C.6. Fluid Inclusion Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337 C.7. Whole Rock Sm/Nd-Isotopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338 C.8. Lithium Isotope Analysis on Selected Mineral Phases . . . . . . . . . . . . . . . 338 D. Data – Mineral Liberation Analysis 341 E. Data – Geochemistry 345 F. Data – Geochronology 349 G. Data – Stable and Radiogenic Isotopes 353
Lithium-Caesium-Tantal-(LCT) Pegmatite repräsentieren eine bedeutende Quelle für seltene Metalle, deren Bedarf im letzten Jahrzehnt beträchtlich angestiegen ist. Im Falle von Caesium sind zurzeit weltweit nur zwei LCT-Pegmatitlagerstätten bekannt, die abbauwürdige Vorräte an Cs enthalten. Dies sind die LCT-Pegmatitlagerstätten Bikita in Simbabwe und Tanco in Kanada. Das Wirtsmineral für diese Cs-Mineralisation ist das extrem selten auftretende Zeolith-Gruppen-Mineral Pollucit. In den Lagerstätten Bikita und Tanco bildet Pollucit dagegen massive, linsenförmige und fast monomineralische Pollucitmineralisationen, die in den oberen Bereichen der Pegmatitkörper anstehen. Zusätzlich befinden sich beide Lagerstätten in geologisch vergleichbaren Einheiten. Die Nebengesteine sind Grünsteingürtel die ein neoarchaisches Alter von ca. 2,600 Ma aufweisen. Die Bildung derartiger massiver Pollucitmineralisationen ist bis jetzt noch nicht detailliert untersucht worden. Große Bereiche von Westaustralien werden von meso- bis neoarchaischen Krusteneinheiten (z.B. Yilgarn Kraton, Pilbara Kraton) aufgebaut, von denen auch eine große Anzahl an LCT-Pegmatitsystemen bekannt sind. Darunter befinden sich unter anderem die LCT-Pegmatitlagerstätten Greenbushes (Li, Ta) und Wodgina (Ta, Sn). Zusätzlich wurden kleine Mengen an Pollucit in einer einzigen Kernbohrung im Londonderry Pegmatitfeld angetroffen. Ungeachtet dessen, wurden in Westaustralien bis jetzt keine systematischen Untersuchungen und/oder Explorationskampagnen auf Vorkommen von Cs und speziell der von Pollucit durchgeführt. Im Verlauf dieser Studie wurden insgesamt neunzehn verschiedene Pegmatitvorkommen und Pegmatitfelder des Yilgarn Kratons, Pilbara Kratons und der Kimberley Provinz auf das Vorkommen des Minerals Pollucit untersucht. Allerdings konnte in keinem der untersuchten LCT-Pegmatitsystemen Pollucit nachgewiesen werden. Von vier der untersuchten LCT-Pegmatitsystemen, dem Londonderry Pegmatitfeld, dem Mount Deans Pegmatitfeld, der Cattlin Creek LCT-Pegmatitlagerstätte (Yilgarn Kraton) und der Wodgina LCT-Pegmatitlagerstätte (Pilbara Kraton) wurden detailliert Proben entnommen und weitergehend untersucht. Zusätzlich wurden die massiven Pollucitmineralisationen im Bikita Pegmatitfeld beprobt und in die detailierten Untersuchungen einbezogen. Der Probensatz aus dem Bikita Pegmatitfeld dient als Referenzmaterial mit dem die Pegmatitproben aus Westaustralien verglichen werden. Die vorliegende Arbeit fasst die wesentlichen Ergebnisse der petrographischen, mineralogischen, mineralchemischen, geochemischen und geochronologischen Untersuchungen sowie der Flüssigkeitseinschlussuntersuchungen und stabilen und radiogenen Isotopenzusammensetzungen zusammen. Alle vier der in Westaustralien untersuchten LCT-Pegmatitsysteme kommen in geologisch ähnlichen Rahmengesteinen vor, weisen einen vergleichbaren internen Aufbau, geochemische Zusammensetzung und Mineralogie zu dem des Bikita Pegmatitfeldes in Simbabwe auf. Weiterhin konnten in allen LCT-Pegmatitsystemen Hinweise für späte hydrothermale Prozesse (z.B. Verdrängung von Feldspat) nachgewiesen werden, die einhergehend mit einer Anreicherung von Cs verbunden sind (z.B. Cs-angereicherte Säume um Glimmer, Beryll und Turmalin). Mit der Ausnahme der Wodgina LCT-Pegmatitlagerstätte, in der ein mesoarchaisches Kristallisationsalter (ca. 2,850 Ma) nachgewiesen wurde, lieferten die Altersdatierungen in den anderen LCT-Pegmatitsystemen übereinstimmende neoarchaische Alter von 2,630 Ma bis 2,600 Ma. Diese fast identischen Alter der LCT-Pegmatitsysteme des Yilgarn und Zimbabwe Kratons suggerieren, dass die Prozesse, die zur LCT-Pegmatitbildung am Ende des Neoarchaikums führten, weltweit aktiv waren. Ungeachtet dessen stellt das Vorhandensein von massiver Pollucitmineralisation das Alleinstellungsmerkmal des Bikita Pegmatitfeldes dar, welche sich infolge eines Prozesses gebildet haben der nicht Bestandteil der üblichen LCT-Pegmatitentwicklung ist und sich durch eine extreme Anreicherung an Cs unterscheidet. Die neuen Ergebnisse die in dieser Studie von den Bikita Pegmatitfeld und den Westaustralischen LCT-Pegmatitsystemen gewonnen wurden, verbessern das Verständnis des Verhaltens von Cs in LCT-Pegmatitsystemen deutlich. Somit ist es nun möglich, ein genetisches Modell für die Bildung von massiven Pollucitmineralisationen in LCT-Pegmatitsystemen vorzustellen. LCT-Pegmatite weisen im Allgemeinen eine granitische Zusammensetzung auf und werden als Kristallisat von hoch fraktionierten und geochemisch spezialisierten granitischen Restschmelzen interpretiert. Die Bildung von massiven Pollucitmineralisationen ist nur aus großen und voluminösen Pegmatitschmelzen, die als einzelner Körper entlang von Störungen in extensionalen Stressregimen intrudieren möglich. Nach Platznahme der Schmelze bildet die beginnende Kristallisation zunächst die Kontakt- und Randzone des Pegmatits, wobei infolge von fraktionierter Kristallisation die immobilen Elemente (v.a. Cs, Rb) in der verbleibenden Restschmelze angereichert werden. Im Anschluss an diese erste Kristallisation entmischt sich nach Abkühlung eine sehr kleine Menge (0.5–1 vol.%) Schmelze und/oder Fluid von der Restschmelze. Diese nicht mischbare Teilschmelze/-fluid ist angereichert an Al2O3 und Na2O sowie verarmt an SiO2 und kristallisiert als Analcim. Zusätzlich kann diese Schmelze bereits mit 1–2 wt.% Cs2O angereichert sein. Aufgrund der Auswirkung von Flussmitteln (z.B. H2O, F, B) wird allerdings der Schmelzpunkt dieser Analcimschmelze herabgesetzt und so die Kristallisation des Analcims als intergranulare Körner verhindert. Da diese Analcimschmelze im Vergleich zu der restlichen Schmelze eine geringere relative Dichte besitzt, beginnt sie gravitativ aufzusteigen und sich in den oberen Bereichen des Pegmatitkörpers zu akkumulieren. Währenddessen beginnt die restliche Schmelze separat zu kristallisieren und die inneren Bereiche des Pegmatits zu bilden. Diese Kristallisation ist einhergehend mit fortschreitender Fraktionierung und der Anreicherung von inkompatiblen Elementen (v.a. Cs, Rb) in den sich als letztes bildenden Mineralphasen (z.B. Lepidolit) oder der Konzentration der inkompatiblen Element in die sich entmischenden hydrothermalen Fluiden. Da Analcim und Pollucit eine lückenlose Mischungsreihe bilden, ist die Analcimschmelze in der Lage, alles verfügbare Cs von der Restschmelze und/oder assoziierten hydrothermalen Fluiden an sich zu binden und als Cs-Analcim im oberen Bereich des Pegmatitkörpers zu kristallisieren. Fortschreitende hydrothermale Aktivität und Substitution von Cs verschiebt dann die Zusammensetzung des Analcims von der Cs-Analcim- zu Na-Pollucitzusammensetzung. Zusätzlich erfährt der Analcim bei Abkühlung unter 400 °C eine negative thermische Expansion von ca. 1 vol.%. Diese Kontraktion führt zu der Bildung des markanten Rissnetzwerkes das durch späte Mineralphasen (z.B. Lepidolit, Quarz, Feldspat und Petalit) gefüllt wird. Vor der Mineralisation allerdings, erhöht dieses Netzwerk an Rissen die verfügbaren Wegsamkeiten für die späten hydrothermalen Fluide und begünstigt somit den Cs-Substitutionsmechanismus in der massiven Pollucitmineralisation. Weiterhin kommt es bei der Abkühlung des Pegmatits zu späten Mineralverdrängungsreaktionen (z.B. Verdrängung von K-Feldspat durch Lepidolit, Cleavelandit und Quarz), sowie zu Subsolidus-Selbstordnungsprozessen in Feldspäten. Diese Prozesse werden weiterhin interpretiert inkompatible Elemente (z.B. Cs, Rb) in die späten hydrothermalen Fluide freizusetzen. Da Feldspäte große Teile der Pegmatite bilden, kann somit eine beträchtliche Menge an Cs freigeben werden und durch die späten hydrothermalen Fluide in die massive Pollucitmineralisation in den oberen Bereichen des Pegmatitkörpers transportiert werden. Infolgedessen ist es möglich, dass genügend Cs frei gesetzt werden kann, um die Zusammensetzung innerhalb der Mischkristallreihe von Cs-Analcim (>2 wt.% Cs2O) zu Na-Pollucit (23–43 wt.% Cs2O) zu verschieben. Die zeitliche Einordnung dieser späten Cs-Anreicherung wird als quasi zeitgleich oder im direkten Anschluss an die vollständige Kristallisation der Pegmatitschmelze interpretiert. Es kann allerdings nicht vernachlässigt werden, dass auch jüngere hydrothermale Ereignisse, die den Pegmatitkörper nachträglich überprägen, ähnliche hydrothermale Prozesse hervorrufen können. Somit konnte gezeigt werden, dass es durch Kombination dieser magmatischen und hydrothermalen Prozessen möglich ist, genügend Cs anzureichern, um die Bildung von massiven Pollucitmineralisationen in LCT-Pegmatitsystemen zu ermöglichen. Dieses genetische Modell kann nun dazu genutzt werden, um das Potential von Vorkommen von massiven Pollucitmineralisationen in LCT-Pegmatitsystemen in Westaustralien und weltweit besser einzuschätzen.:Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii Zusammenfassung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v Versicherung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi 1. Introduction 1 1.1. Motivation and Scope of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2. Structure of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Fundamentals 7 2.1. The Alkali Metal Cesium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1.1. Distribution of Cesium . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1.2. Mineralogy of Cesium . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.1.3. Geochemical Behaviour of Cesium . . . . . . . . . . . . . . . . . . . . 13 2.1.4. Economy of Cesium . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.2. Pollucite – (Cs,Na)2Al2Si4O12×H2O . . . . . . . . . . . . . . . . . . . . . . . . 16 2.2.1. Crystal Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.2.2. Analcime–Pollucite–Series . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.2.3. Formation of Pollucite . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.2.4. Pollucite Occurences . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.3. Pegmatites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 2.3.1. General Characteristics of Pegmatites . . . . . . . . . . . . . . . . . . 34 2.3.2. Controls on Pegmatite Formation and Evolution . . . . . . . . . . . . . 40 2.3.3. Pegmatite Age Distribution and Continental Crust Formation . . . . . . 43 3. Geological Settings of Archean Cratons 47 3.1. Zimbabwe Craton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 3.1.1. Tectonostratigraphic Subdivision . . . . . . . . . . . . . . . . . . . . . 48 3.1.2. Tectonometamorphic Evolution of the Northern Limpopo Thrust Zone . 49 3.1.3. Pegmatites within the Zimbabwe Craton . . . . . . . . . . . . . . . . . 52 3.1.4. Masvingo Greenstone Belt . . . . . . . . . . . . . . . . . . . . . . . . . 53 3.1.5. Geological Setting of the Bikita Pegmatite District . . . . . . . . . . . . 58 3.2. Yilgarn Craton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 3.2.1. Tectonostratigraphic Framework and Geological Development . . . . . 62 3.2.2. Tectonic Models for the Development . . . . . . . . . . . . . . . . . . . 70 3.2.3. Pegmatites within the Yilgarn Craton . . . . . . . . . . . . . . . . . . . 76 3.2.4. Geological setting of the Londonderry Pegmatite Field . . . . . . . . . . 76 3.2.5. Geological Setting of the Mount Deans Pegmatite Field . . . . . . . . . 85 3.2.6. Geological Setting of the Cattlin Creek Pegmatite Deposit . . . . . . . . 91 3.3. Pilbara Craton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 3.3.1. Tectonostratigraphic Framework and Geological Development . . . . . 99 3.3.2. Tectonic Model for the Development . . . . . . . . . . . . . . . . . . . 101 3.3.3. Pegmatites within the Pilbara Craton . . . . . . . . . . . . . . . . . . . 105 3.3.4. Geological Setting of the Wodgina Pegmatite District . . . . . . . . . . 106 4. Fieldwork and Sampling of Selected Pegmatites and Pegmatite Fields 115 4.1. Bikita Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 4.2. Londonderry Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 4.2.1. Londonderry Feldspar Quarry Pegmatite . . . . . . . . . . . . . . . . . 115 4.2.2. Lepidolite Hill Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . . 117 4.2.3. Tantalite Hill Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 4.3. Mount Deans Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 4.3.1. Type I – Flat Lying Pegmatites . . . . . . . . . . . . . . . . . . . . . . . 118 4.3.2. Type II – Steeply Dipping Pegmatites . . . . . . . . . . . . . . . . . . . 120 4.4. Cattlin Creek Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 4.5. Wodgina LCT-Pegmatite Deposit . . . . . . . . . . . . . . . . . . . . . . . . . . 121 4.5.1. Mount Tinstone Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . 123 4.5.2. Mount Cassiterite Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . 123 5. Petrography and Mineralogy 139 5.1. Quantitative Mineralogy by Means of Mineral Liberation Analysis . . . . . . . . 141 5.2. Mineralogical and Petrographical Characteristics of Individual Mineral Groups . 141 5.2.1. Feldspar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 5.2.2. Quartz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 5.2.3. Mica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 5.2.4. Pollucite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 5.2.5. Petalite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 5.2.6. Spodumene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 5.2.7. Beryl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 5.2.8. Tourmaline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 5.2.9. Apatite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 5.2.10. Ta-, Nb- and Sn-oxides . . . . . . . . . . . . . . . . . . . . . . . . . . 157 5.3. Reconstruction of the General Crystallisation Sequence . . . . . . . . . . . . . 162 6. Geochemistry 165 6.1. Major Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 6.2. Selected Minor and Trace Elements . . . . . . . . . . . . . . . . . . . . . . . . 174 6.3. Fractionation Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 6.4. Rare Earth Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 7. Geochronology 193 7.1. 40Ar/39Ar-Method on Mica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 7.1.1. Bikita Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 7.1.2. Mount Deans Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . 195 7.1.3. Londonderry Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . 195 7.1.4. Cattlin Creek Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . . 195 7.1.5. Wodgina Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 7.2. Th-U-Total Pb Monazite Dating . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 7.2.1. Monazite Ages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 7.3. U/Pb Dating of Selected Ta-, Nb- and Sn-Oxide Minerals . . . . . . . . . . . . 203 7.3.1. Bikita Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 7.3.2. Londonderry Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . 203 7.3.3. Mount Deans Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . 206 7.3.4. Cattlin Creek Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . . 206 7.3.5. Wodgina Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 8. Fluid Inclusion Study 211 8.1. Bikita Pegmatite Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 8.2. Wodgina Pegmatite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 8.3. Carbon Isotope Analysis on Fluid Inclusion Gas of Selected Mineral Phases . . 212 9. Stable and Radiogenic Isotopes 217 9.1. Whole Rock Sm/Nd-Isotopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 9.1.1. New Whole Rock Sm/Nd Data . . . . . . . . . . . . . . . . . . . . . . 217 9.2. Lithium Isotope Analysis on Selected Mineral Phases . . . . . . . . . . . . . . . 220 9.2.1. New Lithium Isotope Data . . . . . . . . . . . . . . . . . . . . . . . . . 220 10.Discussion 227 10.1. Regional Geological and Tectonomagmatic Development . . . . . . . . . . . . 227 10.1.1. Constraints from Field Evidence . . . . . . . . . . . . . . . . . . . . . . 227 10.1.2. Petrographical and Mineralogical Constraints . . . . . . . . . . . . . . 229 10.1.3. Geochemical Constraints . . . . . . . . . . . . . . . . . . . . . . . . . 230 10.1.4. Isotopic Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232 10.1.5. Constraints from Fluid Inclusion Data . . . . . . . . . . . . . . . . . . . 233 10.1.6. Geochronological Constrains . . . . . . . . . . . . . . . . . . . . . . . 233 10.2. Massive Pollucite Mineralisations . . . . . . . . . . . . . . . . . . . . . . . . . . 243 10.2.1. Unique Characteristics of Massive Pollucite Mineralisations . . . . . . . 243 10.2.2. New Concepts for the Formation of Massive Pollucite Mineralisations . . 252 10.3. Genetic Model for the Formation of Massive Pollucite Mineralisations within LCT Pegmatite Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264 11.Summary and Conclusions 267 References 273 Lists of Abbreviations 309 General Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 Mineral Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 List of Figures 311 List of Tables 315 Appendix 317 A. Legend for Topographic Maps 319 B. Sample List 323 C. Methodology 331 C.1. Quantitative Mineralogy by Means of Mineral Liberation Analysis . . . . . . . . 331 C.2. Geochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 C.3. 40Ar/39Ar-Method on Mica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335 C.4. Th-U-Total Pb Monazite Dating . . . . . . . . . . . . . . . . . . . . . . . . . . . 335 C.5. U/Pb Dating of Selected Ta-, Nb- and Sn-Oxide Minerals . . . . . . . . . . . . 336 C.6. Fluid Inclusion Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337 C.7. Whole Rock Sm/Nd-Isotopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338 C.8. Lithium Isotope Analysis on Selected Mineral Phases . . . . . . . . . . . . . . . 338 D. Data – Mineral Liberation Analysis 341 E. Data – Geochemistry 345 F. Data – Geochronology 349 G. Data – Stable and Radiogenic Isotopes 353

A área de estudo desta dissertação localiza-se no concelho de Montalegre (norte de Portugal) e, geologicamente, situa-se no Domínio Parautóctone Superior da Zona de Galiza-Trás-os-Montes. Foram estudadas amostras de pegmatitos duma zona de concessão para eventual exploração de lítio, bem como de litologias associadas (metassedimentos e granitos). Os metassedimentos estudados pertencem à Formação Pelito-Grauváquica (à qual tem sido atribuída idade de deposição do Silúrico Inferior), têm composição pelítica e, no clímax térmico das condições metamórficas, atingiram condições em que se formaram granada e andaluzite. Quanto à sua composição isotópica, os valores calculados para uma idade próxima da formação dos granitos variscos variam entre 0,7227 e 0,7314, no caso da razão 87Sr/86Sr, e entre -11,4 e -10,7, no que respeita ao εNd. Os granitos instalaram-se em relação com a D3 varisca, incluem sienogranitos e monzogranitos, e todos eles têm características peraluminosas (A/CNK entre 1,21 e 1,28), magnesianas e alcali-cálcicas, revelando claramente serem do tipo S. Os valores iniciais de 87Sr/86Sr nestas rochas variam de 0,7164 a 0,7198, e os de εNd vão de -5,4 a -8,4, o que está de acordo com a assinatura de tipo S. A ausência de sobreposição com as composições isotópicas dos metassedimentos pode dever-se ou ao pequeno número de amostras de metapelitos analisadas, ou ao facto de a fonte dos magmas graníticos pertencer a outra unidade litoestratigráfica. O esclarecimento desta dúvida requer o prosseguimento de análises isotópicas em rochas desta região. Os pegmatitos estudados pertencem à família LCT e são essencialmente constituídos por plagioclase (albite), quartzo, petalite, feldspato potássico (ortoclase) e, em menores proporções, moscovite. Acessoriamente, encontram-se biotite, apatite, montebrasite, cassiterite e esfalerite. Os pegmatitos LCT são habitualmente considerados como diferenciados extremos de magmas graníticos peraluminosos, do tipo S, instalados nas últimas etapas de orogenias. Apesar das dificuldades analíticas impostas por valores extremamente baixos das concentrações de Sr, Sm e Nd, verificou-se que: os dados isotópicos Rb-Sr apontam para uma idade de 300 ± 14 Ma (modelo 3 de Ludwig) do corpo pegmatítico que é o objeto principal de prospeção na área de Montalegre; a assinatura isotópica Sr-Nd inicial deste corpo tem valores em torno de 87Sr/86Sr = 0.718 e de εNd = -8.4. Assim, é de supor que o magma granítico parental deste corpo pegmatítico tivesse grande semelhança geoquímica com os granitos amostrados, e que ele se tivesse formado e evoluído durante episódios finais da orogenia varisca.
The study area of this dissertation is located in the municipality of Montalegre (northern Portugal), and geologically it belongs to the Upper Parauthocthonous Domain of the Galicia-Trás-os-Montes Zone. Samples of pegmatites from a lithium prospect area, as well as samples of spatially related lithologies (metasediments and granites), were studied in the scope of this dissertation. The studied metasediments belong to the Pelite-Greywacke Formation (which is considered to have a Lower Silurian deposition age), have pelitic compositions and display evidence that, during the thermal maximum of the Variscan metamorphism, blastesis of garnet and andalusite took place. Sr-Nd isotope compositions, calculated to an age compatible with the generation of Variscan granitic magmas, show variations of 87Sr/86Sr from 0.7227 to 0.7314, and of εNd from -11.4 to -10.7. The sampled granites were emplaced in relation with the Variscan D3. They are syenogranites and monzogranites and display peraluminous (A/CNK between 1.21 and 1.28), magnesian and alkali-calcic compositions, revealing that they are S-type granites. Initial 87Sr/86Sr and εNd values range from 0,7164 to 0,7198, and from -5.4 to -8.4, respectively, which are in agreement with the S-type fingerprint. However, there is no overlap with the isotopic signature of the metasediments, which may be due either to the small number of analysed metasediment samples, or to the occurrence of the anatectic processes in a different lithostratigraphic unit. Additional isotopic analyses in future works will be necessary to solve this uncertainty. Pegmatite samples are clearly of the LCT family, being formed of plagioclase (albite), quartz, petalite, K-feldspar (orthoclase) and minor amounts of muscovite. Accessory minerals include biotite, apatite, montebrasite, cassiterite and sphalerite. LCT pegmatites are usually considered as extreme differentiates from peraluminous S-type granitic magmas, emplaced during late stages of orogenies. Despite the analytical difficulties resulting from extremely low concentrations of Sr, Sm and Nd, some conclusions based on isotopic information are: Rb-Sr data point to an age of 300 ± 14 Ma (Ludwig’s age model 3) to the emplacement of the pegmatite body which is the main target of the exploration campaign in the Montalegre area; the initial Sr-Nd isotopic signature of this body has values around 87Sr/86Sr = 0.718 and εNd = -8.4. Therefore, the available evidence suggests that this pegmatite had a parental granitic magma with a strong geochemical resemblance to the sampled granites, and that this magma formed and evolved during late stages of the Variscan orogeny.
Mestrado em Engenharia Geológica

Dissertação de mestrado Ordenamento e Valorização de Recursos Geológicos
O campo aplito-pegmatítico da Serra d’ Arga apresenta uma grande diversidade paragenética de corpos pegmatíticos, maioritariamente incluídos na classe de elementos raros, onde se distinguem linhagens mais precoces, com filiação NYF e linhagens mais evoluídas, típicas de uma filiação LCT. No presente estudo, é feita uma síntese dessa diversidade, sistematizada num conjunto de paragéneses paradigmáticas, estabelecidas de acordo com critérios paragenéticos (minerais essenciais e acessórios) e estruturais. Este conjunto foi alvo de uma análise petrogenética, que permitiu a construção de quadros de modos de contacto e, consequentemente, de quadros paragenéticos contrastantes. Foi ainda suportada por um conjunto de intercrescimentos, hábito e agregados tipomórficos. A evolução paragenética foi caracterizada através de diferentes grelhas petrogenéticas (ASH, BASH, LASH e óxidos de Ti-Sn-Nb-Ta) e outros agrupamentos mineroquímicos com importância tipomórfica e tipológica. Proporcionam indicações sobre as condições de equilíbrio que influenciaram os processos de cristalização e de subsequentes trajectórias evolutivas (em subsolvus e subsolidus). Como consequência desta investigação, deduziu-se o conjunto de estados paragenéticos evolutivos, bem como das sequências gerais de cristalização, e sua relação com cronologias de instalação ao nível do campo.
The Arga aplite-pegmatite field includes a wide paragenetic variety of pegmatite bodies, classified in the rare element class, with earlier NYF filiations, and LCT later evolutions. In the present study a paragenetic diversity summary is proposed, resulting in several types of paradigmatic paragenesis, established according to paragenetic and structural criteria. This set of paragenesis, were target of later petrogenetic analysis, which allowed the construction of contact mode frames and paragenetic contrasting frames. This section was also supported with a group of intergrowths, habits and tipomorfic aggregates. Different petrogenetic grids (BASH, LASH and Ti-Sn-Nb-Ta oxides) and other mineral and chemical groups, with typomorphic and typological significance, were used to explain the paragenetic evolution, providing information about the equilibrium conditions that influenced the crystallization process, and the subsequent evolutionary trends (subsolvus and subsolidus). As final result of the investigation, were deduced the assembly of evolutionary paragenetic states, as well as the general sequences of crystallization, and its relationship with installation chronologies over the pegmatitic field.

Indicator mineral research is currently being undertaken in partnership with the Nova Scotia Department of Natural Resources and Renewables at the Brazil Lake lithium-cesium-tantalum (LCT) pegmatites in southwest Nova Scotia as part of the Geological Survey of Canada's Targeted Geoscience Initiative(TGI) program. The pegmatites, discovered in 1960, are well known from previous detailed bedrock mapping and surficial studies, and are informally named based on their relative geographic positions as the South and North pegmatites. The South pegmatite naturally outcrops, and both pegmatites are surrounded by spodumene-rich boulders on the surface of the thin-till covered (&amp;lt;4 m) drumlinized glacial landscape. For these reasons, the pegmatites are excellent sites to test indicator mineral exploration methods for Li and associated critical elements (e.g. Ce, Ta). Five pegmatite samples were collected for detailed study and analysis of potential indicator minerals. Close to the pegmatite and up to 13 km down ice (south-southeast), 87 bulk (10-14 kg), till sediment samples were collected for indicator mineral analysis. A total of 105 till samples were collected around the pegmatite and across the region for matrix geochemistry. A preliminary list of indicator minerals includes mid-density (e.g., spodumene, tourmaline, blue apatite) and high-density mineral species (e.g., columbite-tantalite, cassiterite) and this list is expected to expand as the detailed studies progress. Trenches dug in the Fall 2022 to collect till samples on the proximal down ice (south) sides of both pegmatites revealed abundant spodumene pebbles and small cobbles in the till, indicating that the local till should display strong indicator mineral and matrix geochemical signatures derived from the pegmatites.

The Tl isotopic and trace element composition of K-feldspar, mica, pollucite and pyrite from 13 niobium-yttrium-fluorine (NYF)-type and 14 lithium-cesium-tantalum (LCT)-type rare-element pegmatites was investigated. In general, the epsilon-205Tl values for K-feldspar in NYF- and LCT-type pegmatites increases with increasing magmatic fractionation. Both NYF and LCT pegmatites display a wide range in epsilon-205Tl (-4.25 to 9.41), which complicates attempts to characterize source reservoirs. We suggest 205Tl-enrichment during pegmatite crystallization occurs as Tl partitions between the residual melt and a coexisting aqueous fluid or flux-rich silicate liquid. Preferential association of 205Tl with Cl in the immiscible aqueous fluid may influence the isotopic character of the growing pegmatite minerals. Subsolidus alteration of K-feldspar by aqueous fluids, as indicated by the redistribution of Cs in K-feldspar, resulted in epsilon-205Tl values below the crustal average (-2.0 epsilon-205Tl). Such low epsilon-205Tl values in K-feldspar is attributed to preferential removal and transport of 205Tl by Cl-bearing fluids during dissolution and reprecipitation. The combination of thallium isotope and trace element data may be used to examine late-stage processes related to rare-element mineralization in some pegmatites. High epsilon-205Tl and Ga in late-stage muscovite appears to be a favorable indicator of rare-element enrichment LCT pegmatites and may be a useful exploration vector.

This open file reports geochemical data for till samples collected as a part of a till geochemical and surficial mapping project around the Brazil Lake lithium-cesium-tantalum (LCT-type) pegmatite in southwestern Nova Scotia (NTS map sheets 21A/04, 20O/16 and 20P/13). The global rise in lithium demand has motivated the Geological Survey of Canada's (GSC) recent investigations of the Brazil Lake pegmatites to study surficial geochemistry methods that can be used to explore for lithium and associated critical minerals (i.e., Cs, Ta, Be, In, Sn, W). These types of deposits are important sources of lithium, tin, and rubidium and the primary source of tantalum. This research at Brazil Lake is being undertaken as part of the GSC's Targeted Geoscience Initiative Program and has been carried out in partnership with the Nova Scotia Department of Natural Resources and Renewables (NSDNRR). The goals of the research are to increase exploration success in regions covered by glacial sediments by documenting how critical minerals and associated elements are glacially dispersed in till from pegmatites at the Brazil Lake property. Newly available LiDAR data assisted in deciphering ice flow trajectories, which in turn, allowed for targeted till sampling. A total of 184 till samples were collected for till geochemistry in 2020, 2021 and 2022 and the data reported here include widely spaced regional samples collected across southwest Nova Scotia, proximal samples collected up-ice, overlying, and down-ice of the Brazil Lake pegmatites. The widely spaced till samples provide the regional context for the interpretation of the case study samples and assess the potential for additional pegmatites buried by extensive till cover. Data reported in this Open File include sample descriptions, location, site photos, and geochemical analyses of the coarse sand (1.0 - 2.0 mm) and silt + clay (&amp;lt;0.063 mm) fractions. For the 2020 samples only, the &amp;lt;0.002 mm (clay) fraction was also analyzed. Analyses over the 3 years (2020-2021-2022) include various combinations of different digestions or fusions to test and compare their efficacy for the various pathfinder elements for LCT pegmatites: aqua regia (partial) digestion, 2) Na peroxide fusion (total), 3) 4-acid (near total) digestion, 4) Li-meta/tetraborate fusion, 5) loss on ignition, and 6) portable X-ray fluorescence (XRF).

This report describes field work carried out as part of the Geological Survey of Canada's Targeted Geoscience Initiative indicator mineral research activities at the Brazil Lake Li-Cs-Ta pegmatites in southwest Nova Scotia. This research is being undertaken in partnership with the Nova Scotia Department of Natural Resources and Renewables (NSDNRR). In the fall of 2022, 44 till samples were collected around and down-ice of the Brazil Lake Li-Cs-Ta pegmatites to document the geochemical and indicator mineral signatures of the pegmatites in the till. In 2020, 2021, and earlier in the summer of 2022, 105 till samples were collected across southwest Nova Scotia by the NSDNRR to provide regional context for the interpretation of the 44 case study samples. Till samples were also collected at the Salmon River beach section ~25 km north of Yarmouth where a thick coastal exposure (&amp;gt; 20 m) contains multiple till units that reflect several phases of glacial deposition and shifting ice-flow directions across southwest Nova Scotia. These section samples will provide insight and additional details on the regional glacial context.