Humankind’s use of silica raw materials began at least 1.85 million years ago with production of flint tools and spans to today’s more than 1000 industrial applications, all relying on its chemistry and specific physical properties. Among the key achievements are the discovery of the piezoelectric effect of quartz for timekeeping, the critical importance of silicon-based semiconductor technologies for the digitalization of our society, and the production of renewable energy through photovoltaics. One of the greatest challenges regarding raw material supply and security lies in identifying new quartz deposits of sufficient purity, size, and properties to meet increasing demands. Although quartz is mined from a variety of deposits, economically viable sources remain difficult to locate for reasons that we explain.

This study aims to assess the transferability of unsupervised clustering with subsequent data-driven pegmatite prospectivity assignment to the under-explored south Leinster region, Ireland, where consistent genetic or targeting models for spodumene-bearing pegmatites are limited by very poor (< 1 %) outcrop. We apply self-organizing maps to simple, reproducible, and machine-readable features derived from airborne magnetic and radiometric data that capture lithological variability and tectonic stress pattern, deliberately excluding data sets potentially affected by displacement, anthropogenic activity or glacial overprint. The methodology segments the survey area by unsupervised clustering without using known pegmatite occurrences as training input. Probabilistic prospectivity maps are generated by aggregating multiple clustering realizations with known pegmatite occurrences. The results show that the approach reliably separates pegmatite-bearing from pegmatite-free boreholes and delineates a focused set of prospective zones, mainly along the eastern margin of the Leinster Granite, within the East Carlow Deformation Zone and along other major faults. Treating barren pegmatites separately further improves discrimination of targets. We conclude that airborne magnetic and radiometric data contain exploitable information on pegmatite emplacement, as they capture lithological variability and structural patterns in the near-surface ground, and that our approach provides a robust framework for early-stage exploration in data-poor regions.

Quartz and other silica minerals are amongst the most important constituents of the Earth’s crust, both as rock-forming mineral components and as tools for understanding Earth processes. Quartz and other forms of silica are essential parts of both the geological and biochemical cycles with the potential to help us understand the processes of our planet across disciplines. This article is a narrative of quartz, starting with its crystallization from fractionated, silica-rich magmas, transport, and deposition of silica by hydrothermal fluids, as well as physical, chemical, and biogenic processes resulting in silica weathering, transport, accumulation, and the formation of sedimentary silica deposits. Extraterrestrial quartz and silica occurrences are also discussed.

This study investigates the effectiveness of A- and C-horizon soil geochemical mapping and gamma-ray surveying as exploration tools for shallowly buried spodumene pegmatites at two localities: Moylisha, southeast Ireland, and Wolfsberg, southern Austria. In these areas, of contrasting topographic relief and bedrock geology, spodumene pegmatites occur beneath thin (<1 m), residual (i.e. non-transported) soils. In both areas, spodumene pegmatite-associated elements (e.g., Li, Sn and Cs) show positive anomalies in both A- and C-horizon soils overlying subcropping spodumene pegmatites. Transects with sample sites ~30–40 m apart are suitable to detect small swarms of 1–10 m thick spodumene pegmatites. However, the presence of elevated Li and Cs concentrations in C-horizon soils extending well beyond the underlying spodumene pegmatites at Moylisha, and high Cs in both A- and C-horizon soils on the slopes below known pegmatite subcrops at Wolfsberg, suggest hydromorphic transport of Li and Cs. Diagnostic radiometric signatures are generally weak at both sites due to low U and Th concentrations and the small size of pegmatite bodies. At Wolfsberg, however, spodumene pegmatites and their halos are slightly more U-rich than their amphibolite host, suggesting potential for radiometric survey detection of thicker pegmatites, or under thinner soils, in basic or metabasic host rocks. This study demonstrates that A- and C-horizon soil mapping effectively identifies geochemical anomalies linked to concealed spodumene pegmatites. Ground gamma-ray surveying is less effective but may succeed where host rocks show significant contrast in radioactivity and where pegmatites are spatially associated with lithological boundaries and geological structures.

We investigate the origin and evolution of quartz populations in tourmaline‑bearing rocks of the Cornubian Batholith, SW England, to constrain fluid sources and Sn‑mineralization processes. Our study focuses on massive quartz–tourmaline rocks (MQT) because of their spatial and genetic association with Sn mineralization. MQT occur as small stock‑ to dyke‑like bodies (typically < 300 m) exemplified by Roche Rock and Porth Ledden. Fifteen quartz samples from MQT and comparative quartz from biotite granite, tourmaline granite, pegmatite, tourmaline breccia and veins (Porth Ledden, Porthmeor Cove, Roche Rock, Tresayes, Wheal Remfry) were subject to SEM‑cathodoluminescence and oxygen‑isotope (δ18O) analysis. SEM‑CL reveals multiple quartz generations: primary magmatic quartz (granites, aplites, MQT), pegmatitic quartz, secondary fracture‑fill quartz, oscillatory hydrothermal overgrowths on magmatic cores (typical in MQT), and complexly zoned vein quartz. All δ18O values are relatively high (+ 11.5 to + 27.7‰), mostly clustering between + 12 and + 15‰. Magmatic quartz (granites, aplites) range from + 11.5 to + 14.8‰, overlapping pegmatite quartz, implying incorporation into the granitic melts of high‑δ18O metasedimentary material, consistent with local Devonian metasediments. Hydrothermal quartz spans + 12.7 to + 27.7‰; two anomalously high values (+ 25.6, + 27.7‰) in crystal rims suggest late addition of formation waters. We infer that MQT at Porth Ledden and Roche Rock formed by partial metasomatic replacement of tourmaline granite due to infiltration and entrapment of pneumatolytic, B‑rich fluids in the roof zone. Metasomatism dissolved K‑feldspar, mobilizing K, Rb, Ba, Sr, Cs, Pb and notably Sn, producing cavities later infilled by hydrothermal quartz and tourmaline. A progressive increase in δ18O from magmatic to late hydrothermal quartz suggests fluid cooling and possible mixing with oxidizing formation waters, rather than a component of meteoric-derived waters that contributed to the precipitation of cassiterite.

Alteration halos in wall rocks are potential indicators of rare element pegmatites; however, halos associated with niobium-yttrium-fluorine (NYF) pegmatites are poorly documented. It is also unclear whether such halos can survive subsequent orogenic overprinting. In this contribution, we examine the wall rocks of Paleoproterozoic rare element pegmatites that underwent amphibolite facies metamorphism during the Scandinavian Caledonian orogeny. These pegmatites represent the largest known intraplutonic NYF-type bodies globally. Radiometric and geochemical profiles of the surrounding granitic gneiss wall rocks reveal similar to 2- to 15-m-wide dispersion halos marked by radiometric anomalies and enrichment in rare and radioactive elements, including Cs, Li, F, Sn, Ta, U, Th, Nb, Rb, and Tl. These elements are carried by Caledonian metamorphic minerals but originated from the interaction between Paleoproterozoic pegmatite-derived fluids and the granitic protolith. Remarkably, the Caledonian profiles preserve the geochemical signatures of the original Paleoproterozoic pegmatite halos. Our findings demonstrate that the geochemistry of alteration halos of rare element pegmatites can persist through high-grade metamorphic overprinting. These halos can be traced using radiometry or bulk and mineral geochemistry, offering a promising vectoring tool for exploring ancient NYF-type pegmatites in younger orogenic belts.

In the Proterozoic Evje-Iveland pegmatite field of southern Norway, five pegmatites have been found to exhibit features of large-scale hydraulic brecciation that have been previously overlooked or misinterpreted. We provide the first detailed description and characterization of these breccias from a study of the Landsverk 1 pegmatite, with additional insights from Gudmundsgruve, Haugen 1 and Haugen 2 and Storsynken. This is based on studies of the breccia cement, specifically oxygen isotope, trace element and cathodoluminescence data for quartz, Ar-40/Ar-39 dating of K-feldspar and trace elements in fluorite. The clast-supported breccias in the Landsverk 1 pegmatite consist of millimetre- to meter-sized fragments of pegmatite (similar to 95 vol%) and wall rocks (similar to 5 vol%) incorporated due to sidewall collapse. Fluid flow through the breccias led to infilling and replacement mostly by milky white quartz and epidote, but also left a high percentage of open space, including cavities up to 1.5 m in size. The process responsible for breccia formation was fluid-assisted hydraulic fracturing caused by a single pulse of stress at pressures between 50 and 250 MPa. Ar-40/Ar-39 dating of K-feldspar crystals from cavities in the cement yielded an early Triassic age of 246.1 +/- 0.9 Ma, which is approximately 660 Ma younger than the emplacement of the pegmatite-forming melts. This indicates that, contrary to previous interpretations, brecciation was not part of the magmatic evolution of the pegmatite. From the delta O-18 values of breccia cement quartz (-8.38 +/- 0.28 parts per thousand), fluids involved in the initial stages of cementation had a temperature of 549 +/- 23 degrees C and were meteoric in origin. So far, five megabreccias have been identified within a 12 km long, NNW-SSE-striking corridor in the Evje-Iveland area, indicating that the brecciation event is a regional phenomenon. The orientation and timing indicate formation under E-W to ENE-WSW extensional stress, with dolerite dykes emplaced along associated faults during the South-Scandinavian Permian-Triassic rift (phase 1).

Despite their simple chemical composition, silica (silicon dioxide, SiO2) minerals comprise a complex system with diverse polymorphs of distinct crystal structures and different stabilities and properties. Quartz is arguably the most important mineral throughout human history, from early survival tools to critical materials for modern advanced technology. In addition, quartz and other silica polymorphs and varieties are excellent archivers and important tools for deciphering geological, environmental, and planetary processes and histories.

This contribution is a new multimethod toolset to explore for buried, small-scale (0.01-5 million m3) rare metal and high-purity quartz pegmatites, which was developed as part of the four-and-a-half-year European Union H2020 GREENPEG project. It is underpinned by a complementary suite of existing, revised, and new methodologies, the use of three GREENPEG-developed geophysical exploration devices (EASA-certified, helicoptercompatible nose stinger magnetometer, piezoelectric seismograph, and drone-borne hyperspectral system), and two new databases (spectral library and petrophysical database for pegmatite ores). The toolset is based on the latest understanding of how pegmatites form and become enriched in ore minerals. In this regard, the theoretical component of the toolset resembles that of a comprehensive review article. The toolset has been tested in four active pegmatite exploration areas in a representative range of European surface environments-from coastal Arctic to temperate forest, alpine, and Mediterranean settings. Individual tools or tool combinations can be used to vector toward buried pegmatite-related mineralization, such as for Li, high-purity quartz for silica and metallic Si, ceramic feldspar, rare earth elements, Ta, Be, and Cs, to maximize the success of subsequent more costly exploration such as drilling in ways that optimize environmental, social, and governance outcomes. The tools are optimized for the small size, variable surface environment, depth, geologic setting, mineralogy, chemistry, and often highly variable physicochemical properties of pegmatite ore deposits. They can be used at province, district, and/or prospect scale. This guide is for those who have exploration knowledge and/or experience but who may be new or need updating in the state of the art of pegmatite exploration.

The Scandinavian Caledonides are generally considered an orogenic region with low lithium (Li) abundance, thus explaining the general absence of spodumene-minerali zed pegmatites. However, in the Mel & oslash;y-Glomfjord area of northern Norway several Caledonian Li-enriched pegmatites have been identified. The most evolved among these is the & Aring;gskardet pegmatite, to date the only known spodumene-bearing pegmatite in the Scandinavian Caledonides. The & Aring;gskardet pegmatite was emplaced in the metasediments of the Caledonian R & ouml;dingsfj & auml;llet Nappe Complex, immediately above the Caledonian basal thrust, under high-grade amphibolite-facies conditions. The pegmatite exhibits complex mineralogical-chemical zoning, which is mapped as a wall zone at the contact with the host rocks, followed by intermediate and core zones. Spodumene crystals, ranging from 2 to 8 cm in size, are rare and restricted to randomly distributed quartz-rich domains within the core zone. Finegrained albite zones containing abundant colored tourmaline occur discordantly across the intermediate and core zones. We aim to understand the pegmatite-internal fractionation that caused Li enrichment in micas, tourmaline, and quartz and formation of spodumene. Major and trace elements in micas, feldspar, tourmaline, and quartz from the different zones of the pegmatite analyzed by electron microprobe and LA-ICP-MS reveal a strong chemical zoning of the pegmatite body. However, the original albite zone melt was likely much richer in Li, as evidenced by the high Li content in mica, which can reach up to 2 wt.% Li. Despite this, spodumene formation did not take place during the final stage of pegmatite development. It is suggested that the crystallization of spodumene was suppressed due to the significant Li consumption by mica and tourmaline, whose crystallization was favored by elevated levels of H2O, F, and B in the albite melt. Bulk rock analyses of pegmatite zones and wall rocks indicate that the local Li enrichment of metasediments facilitated the formation of spodumene-bearing pegmatites in the otherwise Li-poor Scandinavian Caledonides.

The Pan-African rare-element pegmatites of the Alto Ligonha Pegmatite District in northern Mozambique contain abundant Li-rich micas and primary Li aluminosilicates, such as spodumene. Given the rising global demand for Li in the manufacture of Li-ion batteries, these pegmatites are viewed as potential hard rock sources of Li. In this study, five pegmatites from the Alto Ligonha region were investigated to gain a better understanding of the fractionation processes of pegmatite melts that lead to Li enrichment and to assess the economic potential of the Li mineralization. Mica, quartz, and spodumene collected from various zones within these pegmatites were analyzed. Contents of Li, Rb, Cs, Ta, and Tl in mica and of Li and Al in quartz reveal a very strong internal fractionation of the pegmatite melt with progressing crystallization. Li2O contents in micas increase from 0.1 to 1.4 wt% in the wall zones, to 0.3-1.7 wt% in the intermediate zones, to 1.5-3.8 wt% in the core zones and up to 5.4 wt% in the core zone pockets. Using known mica/melt Li partition coefficients, the Li contents of the melt at the initial crystallization stage was calculated to be between 315 and 3910 ppm for the Li-rich pegmatites. The Li saturation of about 5000 ppm in respect to spodumene crystallization was exceeded for most pegmatites at the final core-zone crystallization. The theoretical calculations confirm field observations that spodumene occurs in pegmatite core zones only. The analyzed spodumene show low and variable bulk Li2O contents between 1.2 and 3.0 wt%. The low Li contents in spodumene are mainly the result of kaolinization due to tropical weathering. The final deposition of the released Li, however, could not be identified. Inferred resource calculations revealed that the investigated pegmatites contain low Li2O tonnages. However, spodumene as well as Li-rich mica might be mined selectively as a by-product of gemstone and columbite-tantalite mining.

Group 2/NYF pegmatites may be economically enriched in rare minerals. In this study we report testing of two exploration methods, gamma ray surveying and soil geochemical mapping, undertaken within the GREENPEG project. Palaeoproterozoic metapegmatites in the Tysfjord area, Nordland, Norway, include some which have been mined for pure quartz. Geologically, the ore zones are the quartz cores of metapegmatites whose other zones and metasomatic halos are enriched in U, Th, REE, Nb and other rare elements. The Jennyhaugen metapegmatite was the main test site because its subcrop beneath 0.1-1.0 m soil can be traced from an open pit mine, and aerial surveying is unobstructed by trees. Helicopter-borne radiometry at 60 m altitude and droneborne radiometry at 25-35 m altitude detect the metapegmatite, while walking (1.0 or 1.6 m height) and 15 m altitude drone-borne radiometry resolve the metapegmatite and metasomatic halo subcrop in detail. Total gamma ray count measurements provide as good an exploration tool as Th or U radiation; K radiation does not show useful anomalies. Both A- and C-horizon soil geochemical mapping also reveal U, Th, Nb and other geochemical anomalies above metapegmatite and halo subcrop. A-horizon soil samples appear to more accurately locate these targets, perhaps because they effectively sample larger surface areas of subcropping rock, whose grain size is very coarse (typically metre scale) within the metapegmatite. C-horizon samples collected from the soil-rock interface are less likely to be representative of the metapegmatite. Gamma ray surveying is recommended rather than soil chemical mapping for exploration, by helicopter at district scale and by drone or walking at prospect scale. It is quicker, requires less field workers, has higher resolution and is less expensive than soil geochemical mapping. Soil chemistry may be preferred for prospect-scale exploration, however, where the commodity sought does not spatially correlate with U and/or Th concentrations.

In situ Lu - Hf geochronology offers the potential for direct dating of garnet within petrographic context. However, the method requires matrix -matched standards to calibrate measured Lu/Hf ratios. In order to assess the accuracy of this calibration, as well as the reproducibility of the resulting Lu - Hf dates, two Lu-rich (up to 1 wt% Lu) garnet samples from the T & oslash; rdal pegmatite field in southern Norway were analysed over six analytical sessions. Multi -session isochron Lu - Hf dates of 930.3 +/- 1.4 Ma (MSWD = 1.0, 164 analyses) and 930.3 +/- 1.7 Ma (MSWD = 1.5; 125 analyses) were obtained, conform with previously published age constraints. The relative standard deviation of 0.1% between the analytical sessions indicates that the dates are highly reproducible. For each individual analytical session, age uncertainties of 0.3-0.6% were achieved by measuring high Lu count rates in analog detection mode. We further describe a calibration strategy that deals with Lu - Hf datasets where Lu is measured in both pulse and analog detector mode. Given the high analytical precision and reproducibility, we suggest that the T & oslash; rdal garnets are suitable reference materials for future LA-ICP-MS/MS Lu - Hf studies.

The Austroalpine Unit Pegmatite Province (AUPP) in the eastern European Alps hosts abundant Permian-aged, variably rare-metal-enriched pegmatite bodies. However, only a small number containing spodumene [LiAlSi2O6] have been discovered. Here, we characterize three drill cores from the AUPP’s largest spodumene pegmatite resource, the Wolfsberg deposit (Austria), to determine the extent of rare-metal halo formation within different host rock types generated by pegmatite-derived fluids and their applicability to spodumene pegmatite exploration. The halos in both mica schist and amphibolite host rocks, as quantified via whole-rock mass-balance calculations, are characterized by enrichments in Li, Cs, Sn, Rb and Tl, amongst others, elements which were highly mobile during initial interactions between pegmatite-derived fluids and host rocks. The concentrations of these elements within the halos can be several times that present in unaltered host rock. They are most enriched in altered host rock interbedded or at the contacts with pegmatite, and decrease with distance from pegmatite to a distance of at least 4 m in mica schist and <3 m in amphibolite. Lithium, and in mica schist, Cs, have the most consistent and furthest extending halos, with respective concentrations of >590 ppm and >40 ppm in mica schist, and >390 ppm Li in amphibolite indicating proximity to spodumene pegmatite. An ID-TIMS U-Pb titanite age of ca. 103 Ma derived from a rare-metal-enriched amphibolite within the alteration halo reflects recrystallization of the Permian protolith during the Cretaceous Alpine orogeny and indicates preservation of the original pegmatite signature through eclogite-facies metamorphism. Recognition of rare-metal halos surrounding pegmatite at Wolfsberg serves as a potential geochemical exploration tool for spodumene pegmatite within the AUPP and may be applicable to other regions.

Tourmaline is common in rare element pegmatites of the Nb -Y -F (NYF) type in the south -central part of the Proterozoic Sveconorwegian orogen in southern Norway. In the global context, however, tourmaline appears rare in this type of pegmatite. This study aims to explain the unusual tourmaline abundance in these pegmatites and the origin of boron (B) in the respective melts, and to raise awareness of tourmaline in NYF pegmatites generally. Tourmalines from six pegmatites in three Sveconorwegian lithotectonic units: Bamble, Kongsberg and Idefjorden, were investigated in terms of their mineral chemistry and delta 11 B values, in addition to bulk rock analyses of pegmatites and host rocks. Tourmalines in pegmatites from Bamble and Kongsberg record B isotopic compositions ( delta 11 B = -1.0 to + 9.9 %o) that are heavy relative to continental crust and mantle sources. In contrast, tourmaline in pegmatites and host rocks from Idefjorden have light B isotopic ratios ( delta 11B = -14.8 to -12.5 %o) that are typical crustal values. We suggest that the latter melts were sourced from orthogneisses at depth. We relate the heavy B isotopic composition of Bamble and Kongsberg pegmatites to regional Nametasomatism by fluids sourced from Mesoproterozoic shallow marine sediments. This is supported by previously published delta 11 B ratios from metasomatized Bamble host rocks. The spatial association of pegmatites with Na-metasomatism in the basement rocks suggests that metasomatism enhanced the fertility and B -concentration in the affected lithologies, favouring partial melting and the formation of tourmaline-bearing pegmatites. These findings contribute to understanding the petrogenesis of Sveconorwegian pegmatites but they also imply that B can play a greater role in the formation of NYF pegmatites than previously thought and that tourmaline has value as a petrogenetic tool in this type of pegmatites as well as in the Li -Cs -Ta (LCT) type to which is it is more commonly applied.

NASA-ESA are jointly preparing the Mars Sample Return (MSR) campaign and are planning to collect and transport a set of martian samples from Mars to Earth for the purpose of scientific investigation, based on the highest priority recommendations of the international science community. The samples are being collected by NASA’s Mars 2020 Perseverance Rover [1,2] and consist of a variety of rocks (e.g., sedimentary and volcanic), regolith, and atmospheric gas.Analogue samples, representing various properties of the Mars 2020 samples, are needed for engineering, science, curation, and planetary protection developments in the context of Mars Sample Return (MSR). Depending on the activity for which the analogue sample material will be used, different properties or groups of properties of the analogue sample may be important, including but not limited to geophysical, geochemical, geomechanical, or mineralogical properties.Analogues are selected for their representativity in attributes that are most relevant for e.g. (i) tests performed as part of research and development activities, (ii) validation and verification of sample processing or analysis, or (iii) for use in outreach or communications activities. Characteristics may range from basic physical or geological properties (e.g. density, grain size distribution, porosity) to mineralogical, bulk chemical or other higher order parameters that are defined to serve the needs of the above. An analogue sample may be a natural sample collected from the field or an existing collection or a synthetic sample.The collection of new natural samples from the field is carried out through dedicated field campaigns, which are supported by NASA and ESA. The characterization of analogue samples will be performed at the Norwegian Geotechnical Institute (NGI) in Oslo, Norway and will be supported by ESA. All MSR analogue samples are stored at and distributed from the Natural History Museum in Oslo in collaboration with the University of Oslo (UiO). This activity is supported by the Norwegian Space Agency (NOSA) and ESA. The UiO will be responsible for establishing an MSR analogue sample catalogue, sub-sectioning samples, and distributing analogue samples in response to allocation decisions taken on requests received. The sample allocation process will be managed by a NASA-ESA MSR Analogue Sample Allocation Panel (ASAP). Requests for analogue samples will be made via a web-interface and processed in a timely manner. References: [1] Farley K. & Stack K. (2022) Mars 2020 Initial Reports, Vol. 1 Crater Floor Campaign, Aug. 11, 2022. [2] Farley K. & Stack K. (2023) Mars 2020 Initial Reports, Vol. 2, Delta Front Campaign, Feb. 15, 2023

The diverse suite of trace elements incorporated into apatite in ore-forming systems has important applications in petrogenesis studies of mineral deposits. Trace element variations in apatite can be used to distinguish between different types of rocks as well as discriminating between deposit types, and thus have potential as mineral exploration tools. Such classification approaches commonly employ two-variable scatterplots of apatite trace element compositional data. While such diagrams offer easy and convenient visualization of compositional trends, they often struggle to effectively distinguish deposit types because they do not employ all the high-dimensional (i.e. multi-element) information accessible from high-quality apatite trace element analysis. To address this issue, we employ, for the first time, a supervised machine learning-based approach (eXtreme Gradient Boosting, XGBoost) to correlate apatite compositions with ore deposit type, utilizing high-dimensional information. We evaluated 8629 apatite trace element data from five deposit types (porphyry, skarn, orogenic Au, iron oxide copper gold, and iron oxide-apatite) along with unmineralized apatite to discriminate between apatite in mineralized vs unmineralized systems. We could show that the XGBoost classifier efficiently and accurately classifies high-dimensional apatite trace element data according to the ore deposit type (overall accuracy: 94% and F1 score: 89%). Interpretation of the model using the SHAPley Additive exPlanations tool (SHAP) shows that Th, U, Eu and Nd are the most indicative elements for classifying deposit types using apatite trace element chemistry. Our approach has broad implications for the understanding of the sources, chemistry and evolution of melts and hydrothermal fluids resulting in ore deposit formation.Keywords: Machine learning; apatite; Trace elements; Ore deposit type; XGBoost

This Special Issue of Minerals, section Mineral Deposits, on the topic of “Petrology and Mineralogy of Pegmatite Deposits”, was inspired by the currently growing scientific and economic interest in pegmatites [...]

Geochemical and mineralogical investigations of the Lower Permian Kemmlitz rhyolite within the NW-Saxonian Basin (Germany) and associated lithophysae (high-temperature crystallization domains) as well as agates were carried out to constrain the genesis and characteristics of these volcanic rocks and the origin of the agate-bearing lithophysae. The volcanic rocks of rhyolitic composition are dominated by quartz, sanidine, and orthoclase and most likely derive from lava flows. Agate-bearing lithophysae were exclusively formed in a glassy facies (pitchstone) of the rhyolites, which was afterwards altered to illite-smectite mixed-layer clays. The results of this study show that agate formation can be related to the alteration of the volcanic rocks accompanied by the infill of mobilized silica into cavities of lithophysae. Fluid inclusion studies point to temperatures of agate formation above 150 °C, indicating that the mobilization and accumulation of silica started already during a late phase of or soon after the volcanic activities. Remarkable high concentrations of B (29 ppm), Ge (> 18 ppm), and U (> 19 ppm) as well as chondrite-normalized rare earth element (REE) distribution patterns of the agates with pronounced negative Eu-anomalies, slightly positive Ce-anomalies and enriched heavy rare earth elements (HREE) indicate interactions of the host rocks and transport of SiO 2 with magmatic volatiles (F/Cl, CO 2 ) and heated meteoric water. Characteristic yellow cathodoluminescence (CL), heterogeneous internal textures as well as high defect density of micro- and macrocrystalline quartz detected by electron paramagnetic resonance (EPR) spectroscopy point to crystallization processes via an amorphous silica precursor under non-equilibrium conditions.

Trace element concentrations in quartz were determined from two major LCT pegmatite occurrences in Europe to test the applicability of quartz as a pathfinder mineral for Li mineralized pegmatites. The Wolfsberg spodumene pegmatite deposit and pegmatites throughout the wider Austroalpine Unit (Austria), and the Moylisha spodu-mene pegmatite deposit (SE Ireland), present two distinctly different geological histories. Spodumene pegmatites at Wolfsberg are associated with late Permian lithospheric extension that formed the Austroalpine Unit Pegmatite Province spanning the Eastern Alps. They were metamorphosed at up to eclogite-facies conditions during the Alpine orogeny. Contrastingly, the simple and spodumene pegmatites at Moylisha form a late Silurian to early Devonian NE-SW-striking pegmatite belt that intruded the East Carlow Deformation Zone along the SE margin of the late Caledonian S-type Leinster Batholith. All analyzed pegmatites contain assemblages including K-feldspar, albite, quartz, muscovite +/- spodumene. LA-ICP-MS analysis shows quartz from spodumene pegmatites in both regions is distinguishable from that in simple pegmatites by higher concentrations of Al, Li, Ge and B, whereas simple pegmatite quartz contains higher Ti. Increasing concentrations of Al, Li and Ge and decreasing Ti in quartz from simple pegmatites (to leucogranites in the Austroalpine Unit) to spodumene pegmatites reflects increasing degree of fractionation, resulting from either magmatic differentiation or separately generated but increasingly fractionated melts. Chemical profiles through individual spodumene pegmatite bodies show relatively little chemical variation, consistent with Li saturation through most of their crystallization history. Principal component analysis of quartz data shows that high Ge, Be and B concentrations characterize quartz in pegmatites from the Austroalpine Unit whereas high Al and Li concentrations characterize quartz in pegmatites from Moylisha. Concentrations of >100 mu gg(-1) Al and >30 mu gg(-1) Li in pegmatite quartz represent an important threshold for potential spodumene mineralization, which may also be indicated by host rocks (e.g., mica schist) metasomatized by fluids expelled by pegmatites during emplacement and/or crystallization and generating a chemical halo. Retention of pegmatite chemical signatures at Wolfsberg supports the robustness of quartz as an effective pathfinder tool for Li mineralized pegmatites in regions that have been affected by high-pressure metamorphism. LA-ICP-MS of quartz in soil and stream sediments may also be a useful pathfinder in pegma-tite provinces where Li-rich quartz is not too diluted by other quartz.