Mineral exploration provides the commodities society requires, but continuing discovery and development of new critical mineral deposits is necessary to realize a sustainable, low-carbon future. Pegmatites in historic mining districts across North Carolina have been sites of mineral production for over a century, initially for mica and subsequently for spodumene. Most granitic pegmatites here are mineralogically simple feldspar, quartz, and muscovite pegmatites, with beryl, spodumene, and columbite-group minerals present in some chemically complex pegmatites. Analysis for Li, K, Zn, Ga, Rb, Sn and Cs content and K/Rb ratio by handheld LIBS has been undertaken for suites of muscovite samples from pegmatites in five historic mining districts across North Carolina—the Spruce Pine, Franklin-Sylva, and Cashiers districts in the Blue Ridge province and the Shelby district and Carolina Tin-Spodumene Belt (CTSB) in the Piedmont province, to assess their petrological character, degree of compositional evolution, and potential for rare element mineralization. Most pegmatites have only undergone moderate degrees of melt differentiation and compositional fractionation, and only rarely has melt evolution reached the extreme extent required for beryl or spodumene formation. The quartz-feldspar pegmatites of the Franklin-Sylva, Cashiers, and Shelby districts are poorly to moderately fractionated, whereas moderately to highly fractionated spodumene-bearing pegmatites are present in both the Spruce Pine district and Carolina Tin-Spodumene Belt. Muscovite from spodumene-bearing pegmatites is not unusually enriched in Li, but can be distinguished from its counterpart in common quartz-feldspar pegmatites by characteristically low K/Rb ratios of <40 and Li contents exceeding 0.05 wt. %.

The Carolina tin-spodumene belt, North Carolina, hosts one of the largest economic deposits of Li pegmatite ore in the United States, yet the petrogenesis of Carolina tin-spodumene belt pegmatites remains poorly understood. We use whole-rock and mineral trace element geochemistry to (1) evaluate the petrogenesis of Carolina tin-spodumene belt pegmatites, (2) compare their geochemistry to other Li-rich pegmatites worldwide, and (3) propose mineral chemistry indices for Li mineralization. Trace element modeling demonstrates that spodumene-bearing pegmatites are not related to the nearby Cherryville Granite through fractional crystallization, and rare earth element contents in plagioclase, garnet, and apatite indicate that spodumene-bearing pegmatites are also not derived from spodumene-free pegmatites. We prefer a petrogenesis in which both types of pegmatites and the Cherryville Granite are derived through similar, but individual, crustal anatectic events. Muscovite and K-feldspar K/Rb-Li systematics indicate that Carolina tin-spodumene belt pegmatites do not attain fractionation levels as high as those reached in the Oxford County pegmatite field in Maine or the Custer and Keystone pegmatite fields in South Dakota. Quartz and garnet Li abundances in Carolina tin-spodumene belt pegmatites are some of the highest in the world, and garnet rare earth element concentrations are the lowest. Contents of Ga, Mn, Ge, and Ti in spodumene allow for discrimination of pegmatites from the Carolina tin-spodumene belt, Maine, South Dakota, Canada, and Portugal. Based on this extensive trace element study, plagioclase, K-feldspar, quartz, muscovite, garnet, and apatite chemistry offer a comprehensive methodology to distinguish pegmatites with and without spodumene in the Carolina tin-spodumene belt, which may be useful in exploration for Li pegmatite ore worldwide.

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.

Laser-induced breakdown spectroscopy (LIBS) is a technology for compositional analysis that is particularly effective for light elements, particularly Li, which is a critical commodity for emerging green technologies. This study undertook analysis by handheld LIBS of muscovite from the drill core, outcrop, and soil on the Carolina Lithium Prospect (CLP) in Gaston County, North Carolina (USA), which lies within the Carolina Tin-Spodumene Belt (CTSB). Abundances of the alkali elements Li, K, and Rb were determined for more than 130 muscovites from the Li-rich pegmatites to track the degree of pegmatite fractionation as a pathfinder for spodumene mineralization. Across the CTSB and including the CLP, muscovite Li contents vary over an order of magnitude, ranging from 0.04 to 0.74 wt. %, with their K/Rb ratios varying between 63 and 8, features that together document the highly evolved character of pegmatites within the CTSB district. On average, muscovite Li contents are greater in spodumene-bearing pegmatites at 0.21 ± 0.12 wt. % than for common quartz-feldspar pegmatites at 0.14 ± 0.08 wt. %. Although overlapping substantially in the middle portions of their distributions, muscovite K/Rb ratios are biased toward low values for spodumene-bearing pegmatites (X- = 21 ± 6) compared to those for quartz-feldspar pegmatites (X- = 33 ± 9). This study provides a framework for the use of LIBS analysis of muscovite in outcrop, drill core, and soil samples as an analytical tool for in-field and on-site geochemical analysis during Li pegmatite exploration and prospect evaluation.

LIBS is a form of optical emission spectroscopy that has the expansive capability to undertake rapid and simultaneous multi-element analysis of geological materials and is particularly suited to the analysis of the light elements (Z<20). Quantitative analysis by LIBS is possible because the intensity of light emission for an element during its transition from an excited state in the LIBS plasma is proportional to its concentration in the material being analyzed. The calibration curve approach directly relates the measured intensity of an elemental peak in the LIBS emission spectrum to standards of known composition for a similar type of matrix measured under the same analytical conditions. Calibration curves have been developed for Li, K, Rb, and Cs in micas analyzed by handheld LIBS for a suite of muscovites and lepidolites of known composition. Analytical variability and different approaches to spectral normalization were assessed during our calibration work These calibrations were applied to LIBS analysis of muscovite separates from pegmatites at a Li prospect in the Carolina Tin-Spodumene Belt (CSTB) in Gaston County, NC where barren pegmatites are characterized by feldspar, mica, garnet, and sometimes tourmaline, whereas fertile Li-enriched pegmatites are dominated by assemblages of spodumene, quartz, and feldspar. Lithium can substitute in the octahedral site of the muscovite structure via couple substitutions involving Si, Al and vacancies. Evolved muscovite compositions in rare-element pegmatites generally have low K/Rb ratios and high Li contents, with pegmatite compositional fractionation trends typically characterized by decreasing K/Rb with increasing Li content. Thus, elevated values of Li in muscovite can be a pathfinder for the presence of Li-bearing assemblages in rare-element pegmatites, with a threshold value of approximately 0.05 wt. % serving as a prospecting guide for spodumene-bearing pegmatites. Fertile and barren pegmatites at the CTSB prospect can be distinguished on the basis of their K/Rb-Li systematics from LIBS analysis of muscovite using our calibration.

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.

ABSTRACT This study represents the precursor and complementary study for the new classification of granitic pegmatites by Wise et al. (this issue) and provides a detailed analysis of existing classifications of granitic pegmatites in terms of applied classification criteria and applicability. The analyses revealed that a new classification scheme for granitic pegmatites is required. In the second part measurable, inferred, and presumed classification criteria applicable for the classification of pegmatites are listed and discussed, including how they should be utilized in future classification schemes. This study records the process of how the new classification scheme for pegmatites was developed.

Earth is the primary source of some of man's most treasured gems and since antiquity, humans have used gem materials excavated from the Earth as decorative objects and for personal adornment. Diamond, ruby, sapphire, aquamarine, emerald, topaz, opal, and amethyst are well-known gem minerals, although theoretically any of the more than 5500 known mineral species may be fashioned into a gem provided certain physical and optical properties (e.g., adequate size, visually attractive, durable, and general rarity) that give them value are met. Gem materials, in this case naturally occurring minerals or rocks, form by igneous, sedimentary, and metamorphic processes at near-surface environments to deep within the Earth. Exceptional chemical, thermobarometric and physical conditions are required for the growth of gem-quality mineral crystals which can subsequently be shaped and polished to create a gemstone. A variety of treatment techniques are often applied to non-perfect gem materials to enhance their appearance and make them more economically desirable. The mining methods of gem minerals are as varied as the type of gem deposit (e.g., volcanogenic, pegmatite, skarns, placers) in which they are found. Surface and underground mining techniques are both used where the gem material is extracted by hand or by heavy machinery. Minerals that lack the physical and optical properties desirable for use as gem material may still find value as raw materials used for manufacturing consumer goods or as tools that aid in understanding the processes that shape our dynamic Earth.

Laser-induced breakdown spectroscopy (LIBS) is a simple and straightforward technique of atomic emission spectroscopy that can provide multi-element detection and quantification in any material, in-situ and in real time because all elements emit in the 200–900 nm spectral range of the LIBS optical emission. This study evaluated two practical applications of LIBS—validation of labels assigned to garnets in museum collections and discrimination of LCT (lithium-cesium-tantalum) and NYF (niobium, yttrium and fluorine) pegmatites based on garnet geochemical fingerprinting, both of which could be implemented on site in a museum or field setting with a handheld LIBS analyzer. Major element compositions were determined using electron microprobe analysis for a suite of 208 garnets from 24 countries to determine garnet type. Both commercial laboratory and handheld analyzers were then used to acquire LIBS broadband spectra that were chemometrically processed by partial least squares discriminant analysis (PLSDA) and linear support vector machine classification (SVM). High attribution success rates (>98%) were obtained using PLSDA and SVM for the handheld data suggesting that LIBS could be used in a museum setting to assign garnet type quickly and accurately. LIBS also identifies changes in garnet composition associated with increasing mineral and chemical complexity of LCT and NYF pegmatites.

PURPLE APATITE is a rare variety of fluorapatite that is widely distributed in many rock types. Although it is known to occur in some tin-silver veins (Wilson and Petrov 1999), tungsten-tin veins (Gaines and Thadeu 1971; Dunn 1977), mineralized granites (Romer et al. 2007), phosphatic iron formations (Robinson et al. 1992), and alpine clefts (Scalisi 2013), it is most prevalent in mineralogically and chemically evolved granitic pegmatites (e.g., Erongo Mountains, Namibia; Darai-Pech, Afghanistan; and the Foote mine, Kings Mountain, North Carolina [Rakovan 2013, 2015; Rakovan, Barnett, and White 2016]). The state of Maine has the distinction of producing some of the finest purple apatite crystals in the world, collected primarily from a small cluster of pegmatites in the Mount Apatite area near the town of Auburn. Purple apatite from Mount Apatite has attracted the attention of miners and collectors since its first documented discovery in the early 1900s to the bonanza find of Terry Szenics (Wilson 1977) in the late 1960s. Specimens from Mount Apatite range in color from light purple to dark royalMICHAEL A. WISE JEFFREY E. POST Department of Mineral Sciences National Museum of Natural History Smithsonian Institution Washington, DC 20013 wisem@si.edu postj@si.edu

Quartz from 254 pegmatites representing eight pegmatite fields and provinces worldwide was investigated by laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) to determine concentrations of trace elements Al, Ti, Li, Ge, B, Be, Rb, Na, K, Ca, P, Ga, Sb, Zn and U. A total of 271 new analyses combined with 535 published LA-ICP-MS quartz chemistry data were evaluated with binary and ternary trace element discrimination plots and principal component analysis (PCA). The classifications applied for discrimination of pegmatite types include the widely applied NYF(Nb-Y-F) - LCT(Li-Cs-Ta) classification and the new RMG (pegmatites derived from residual melts of granite magmatism) - DPA (pegmatites as direct products of anatexis) grouping. Pegmatites of both classifications can be well distinguished via Al-Ti, Al-Li and Al/Ti-Ge/Ti binary trace element plots and the Ti - Al/10 - 10*Ge ternary diagram. PCA applied to Al, Li, Ti, Be, B, Ge and Rb contents in quartz allowed to further distinguish between anatectic DPA-1 (Li-enriched DPA) and granite-pluton-derived RMG-1 (Li-enriched RMG) pegmatites. Some pegmatite fields and provinces (Hagendorf-Pleystein, Oxford County) are distinguishable by region-specific Li, Ge and Al contents. The results imply that the chemistry of pegmatite quartz is mainly controlled by the origin (source rock chemistry) of pegmatite melts and, to a much lesser extent, by the geodynamic setting of the pegmatite fields and provinces. Chemically primitive NYF and DPA-2 type pegmatites contain quartz with the lowest total trace-element contents and lowest internal-pegmatite trace-element variation, making it potentially suitable for high-tech application. Pegmatite quartz containing >30 μgg-1 Li and >100 μgg-1 Al is strongly indicative of economic spodumene/montebrasite mineralization and, thus, serves as a strong Li-mineralization pathfinder mineral. Quartz with >5 μgg-1 B may be a potential indicator for gem-quality tourmaline mineralization.

Research Article| September 30, 2019 Cathodoluminescence (CL) microscopy – a technique for understanding the dynamics of pegmatite crystallization Michael A. Wise; Michael A. Wise § Department of Mineral Sciences, Smithsonian Institution, Washington, D.C., 20013, USA § Corresponding author e-mail address: wisem@si.edu Search for other works by this author on: GSW Google Scholar Cathleen D. Brown Cathleen D. Brown Department of Mineral Sciences, Smithsonian Institution, Washington, D.C., 20013, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Michael A. Wise § Department of Mineral Sciences, Smithsonian Institution, Washington, D.C., 20013, USA Cathleen D. Brown Department of Mineral Sciences, Smithsonian Institution, Washington, D.C., 20013, USA § Corresponding author e-mail address: wisem@si.edu Publisher: Mineralogical Association of Canada First Online: 07 Oct 2019 Online Issn: 1499-1276 Print Issn: 0008-4476 © 2019 Mineralogical Association of Canada The Canadian Mineralogist (2019) 57 (5): 821–823. https://doi.org/10.3749/canmin.AB00030 Article history First Online: 07 Oct 2019 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Michael A. Wise, Cathleen D. Brown; Cathodoluminescence (CL) microscopy – a technique for understanding the dynamics of pegmatite crystallization. The Canadian Mineralogist 2019;; 57 (5): 821–823. doi: https://doi.org/10.3749/canmin.AB00030 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyThe Canadian Mineralogist Search Advanced Search Cathodoluminescence (CL) microscopy is a technique commonly applied to the study of sedimentary and metamorphic rocks, but over the past several decades, has also proven valuable in advancing the understanding of the dynamics of crystallization, cooling histories and post-magmatic alteration in igneous rocks (Finch & Walker 1991, Finch & Klein 1999, Müller et al. 2003). Cathodoluminescence microscopy allows for features to be seen that are invisible by optical microscopy and back-scattered electron imaging (Fig. 1). The technique aids in the identification of minerals and can reveal textures that result from mineral-fluid interaction. One... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Research Article| September 30, 2019 The petrologic significance of epidote in granitic pegmatites Michael A. Wise Michael A. Wise § Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D.C., 20013, USA § Corresponding author e-mail address: wisem@si.edu Search for other works by this author on: GSW Google Scholar The Canadian Mineralogist (2019) 57 (5): 817–819. https://doi.org/10.3749/canmin.AB00029 Article history first online: 07 Oct 2019 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Michael A. Wise; The petrologic significance of epidote in granitic pegmatites. The Canadian Mineralogist 2019;; 57 (5): 817–819. doi: https://doi.org/10.3749/canmin.AB00029 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyThe Canadian Mineralogist Search Advanced Search Epidote has been recognized as a major magmatic phase in granitic rocks of tonalitic and granodioritic compositions, less so in granites (Schmidt & Poli 2004 and references therein) and rarely as an accessory phase in granitic pegmatites (e.g., Andersen 1931, Lovering & Durrell 1959, Magloughlin 1987, Magloughlin & Merkel 2005, Sørensen 2006). Epidote from granitic pegmatites occurs sparingly in muscovite–rare-element and miarolitic pegmatites (Černý & Ercit 2005) and has been observed as aggregates of euhedral crystals in miarolitic cavities (Fig. 1A) and fractures, and as anhedral grains as... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

ABSTRACTBeusite-(Ca), ideally Ca${\rm Mn}_{\rm 2}^{2 +} $(PO4)2, is a new graftonite-group mineral from the Yellowknife pegmatite field, Northwest Territories, Canada. It occurs in a beryl–columbite–phosphate rare-element pegmatite where it is commonly intergrown with triphylite–lithiophilite or sarcopside, and may form by exsolution from a high-temperature (Li,Ca)-rich graftonite-like parent phase. It occurs as pale-brown lamellae 0.1–1.5 mm wide in triphylite, and is pale brown with a vitreous lustre and a very pale-brown streak. It is brittle, has a Mohs hardness of 5, and the calculated density is 3.610 g/cm3. Beusite-(Ca) is colourless in plane-polarized light, and is biaxial (+) with α = 1.685(2), β = 1.688(2), γ = 1.700(5), and the optic axial angle is 46.0(5)°. It is non-pleochroic with X || b; Y ˄ a = 40.3° in β obtuse; Z ˄ a = 49.7° in β acute. Beusite-(Ca) is monoclinic, has space group P21/c, a = 8.799(2), b = 11.724(2), c = 6.170(1) Å, β = 99.23(3)°, V = 628.3(1) Å3 and Z = 4. Chemical analysis by electron microprobe gave P2O5 41.63, FeO 19.43, MnO 23.63, CaO 15.45, sum 100.14 wt.%. The empirical formula was normalized on the basis of 8 anions pfu: (Ca0.94Fe0.92Mn1.13)Σ2.99(PO4)2.00. The crystal structure was refined to an R1 index of 1.55%. Beusite-(Ca) is a member of the graftonite group with Ca completely ordered at the [8]-coordinated M(1) site.