Spodumene, lithium pegmatite, Maine, U.S.A.

Spodumene

a Lithium Ore Mineral from the Plumbago North Pegmatite, Maine, U.S.A.

Figs. 1-2: Here are two images of samples of apparently pure spodumene, with traces of what seem to be thin films of dark Mn and Fe oxides. The mineral forms elongate columnar prisms, as much as 10 or 11 metres in maximum length at this site! Samples are 9x5x4 cm and 17x9x(3-4.5) cm, respectively. Spodumene is found in highly evolved siliceous granitic pegmatites, and the largest examples are candidates for the largest crystals on Earth. A 13-metre crystal was unearthed at the Etta mine in South Dakota. No microscope required!

The crystals are striated parallel to length. Some edges display the typical pyroxene cleavage at 87°. Spodumene is brittle but also hard and tough. When struck with sufficient force, the resultant breakage generates sharp splinters. It is difficult to get a clean break across a prism, given the perfect pyroxene-type cleavage parallel to prism length, and numerous sharp chips and shards result. A rock saw would be a better bet.

Samples collected at Plumbago North on 11 September 2022. Weights (Figs 1-3) are 442, 1460 and 1971 grams, respectively. Measurements on five pieces from this deposit, 74 to 718 grams in size, yield a tight estimate of specific gravity (SG), 3.16±0.02 (2 s.d.), range 3.151 to 3.174. within the reported range of 3.03-3.23. In terms of other physical characteristics: a pale pinkish to orangey wash was observed in SW/LW ultraviolet light, and the sample in Fig. 2 contains a few 1-mm angular inclusions with electric-blue SW fluorescence (tiny crystals of calcite?). The fluorescence, though rather weak in two low-powered UV units, is enough to differentiate the spodumene from associated quartz and feldspar. The gemstone variant kunzite (typically lilac in colour) may fluoresce pink or violet in SW UV light (Schneider, 2006, pp.130,145). A silicate such as spodumene would be expected to have very low magnetic susceptibility, and indeed, observed values are <0.001x10^-3 SI units.

"Rock of the Month # 257, posted for November 2022" ---

Spodumene is a monoclinic lithium aluminosilicate, the type locality being the famous Varutrask pegmatite in Sweden. The formula is LiAlSi₂O₆. It is an inosilicate (a silicate with a structure based on chains of SiO₄ tetrahedra) related to more familar pyroxenes such as diopside, CaMgSi₂O₆. Spodumene is usually close to the ideal formula, often with a slight excess of Si, and some replacement of Li by Na. In the gemmy variants, the green colour of hiddenite is attributed to traces of Cr, the lilac kunzite is coloured by elevated Mn and a low Fe/Mn ratio (Deer et al., 1966, p.136). There is also a colourless to pale yellow variant, triphane. Spodumene, then, should have a composition near 8 wt.% Li₂O (lithia), 27 wt.% Al₂O₃ and 65 wt.% SiO₂. However, the substitution of Na for Li can be substantial (e.g., Ahlfeld and Angelelli, 1948, pp.251-252).

The samples from the Plumbago North pegmatite are snow white to yellowish-white with a vitreous lustre, the external faces variably sprinkled with black and orangey-brown spots that appear to be 2-dimensional films of secondary oxides of manganese and iron, which most probably have a negligible effect on bulk Mn + Fe contents and the SG.

The Plumbago North pegmatite is a lithium deposit in evolved leucogranitic rocks, located north of the villages of Bethel and Newry in western Maine. There is a tremendous concentration of pegmatites in southern Maine (Maine Geological Survey, 1957). The Plumbago Mountain area in Newry township has long been noted for beryl and spodumene, amongst the many unusual and/or gemmy mineral species to be found in the state. This Rock of the Month reflects the recent discovery of a new spodumene pegmatite occurrence on the north side of Plumbago Mountain, some 1.5 km northwest of the famed Dunton gem tourmaline pegmatite. This area of Oxford county is known as Spodumene Brook. The new find (Simmons et al., 2020) is an albite- quartz- spodumene pegmatite with huge crystals of spodumene and montebrasite. The upper parts of the pegmatite contain up to 50% spodumene, thus this is a potentially significant Li deposit. Some spodumene laths exceed 11 m in length (and are thus some of the biggest crystals of any mineral, found anywhere). An initial consideration of geometry and grade suggests the metric resource is some 10 MT grading an average 4.68% Li₂O, which is a very high grade of lithium. Plumbago North is hosted by Devonian-Silurian biotite schist. Pegmatites in Oxford county have been dated to roughly 270-250 Ma: these may be anatectic pegmatites formed by decompressional melting, associated with the early stages of rifting of Pangea (see Simmons et al., 2022, pp. 238-254 for a detailed discussion of this). The most abundant minerals are quartz, albite, muscovite and spodumene, with sparse microcline K-feldspar and local pods of the Li phosphates montebrasite and triphylite, plus other minerals, including secondary phosphates.

Figs. 3-4: Another hand specimen, 16x8x6 cm, and (right) part of the quarry face showing metre-scale laths of pale spodumene.

Lithium is becoming more and more important as an economic commodity, as the global move toward electrical vehicles gathers speed, and demand for lithium batteries rises. Lithium is used also in some small domestic batteries of AA and AAA size. Though more expensive, the Li cells have the twin advantages over alkaline cells of their longer life, and of being relatively impervious to low temperatures. As such, they are very useful for critical uses in outdoor equipment such as thermometers / weather stations and camping / mountaineering gear. While battery concerns dominate the market today, Li compounds have long been used in a range of other applications, such as ceramics, speciality alloys with magnesium and other metals, lubricants (as LiOH in grease formulations) and pharmaceuticals (such as anti-depression drugs).

Lithium is a highly reactive metal, and so does not occur naturally as a native element. It is also the lightest (least dense) metal. It is the lightest (smallest) alkali metal, its chemical "cousins" being sodium, potassium, rubidium and caesium. Lithium was discovered by Arfvedson in Stockholm in 1818, while examining the Li silicate petalite (LiAlSi₄O₁₀ from another Swedish locality) at the laboratory of Berzelius (Newton Friend, 1961, pp.145-146).

The lithium market operates on two basic forms (snapshot of prices in late 2022 --- a banner year! --- through early 2024):

Lithium carbonate (Li₂CO₃), 99% pure (China): US$75,435/tonne on 31 October 2022. The price was pretty volatile in 2022, rising to $81,687 by 10 November, falling back below $75,000 the week before Christmas! Indeed, by 17 March 2023, lithium carbonate had fallen to US$38,173/tonne, and to US$22,762 on 28 April. Price on 27 October 2023: US$21,250/tonne, a slight recovery from a month earlier, but then on downwards to $12,225 on 23 February 2024.
Spodumene (China, minimum Li₂O 5% **, CIF) at US6,000/tonne on 31 October 2022, a very valuable concentrate today (US$6,110 on 10 November, drifting down to US$5,040 on 17 March 2023, and to US$4,090 on 28 April 2023. ** 5% changed to 6% in mid-May 2023. Price on 15 December 2023: US$1,380/tonne. On 19 January and on to 23 February 2024: exactly US$1,000/tonne. This dismal trajectory finally broke in March 2024, with prices on 21 March 2024 rebounding to $1,210 and (99% carbonate) $15,071 ($15,600 for battery-grade carbonate). In this case, CIF is in the context of an international shipping agreement: "cost, insurance and freight", meaning the seller is responsible for transporting the goods to the customer's port of choice.

The price volatility and prolonged slump in lithium prices, late 2022 to early 2024, demands some explanation, especially given the contemporaneous market hype concerning electric vehicles and lithium ion batteries, that should logically boost interest in the lithium market. The prices must reflect a complex mix of market, geopolitical and source (brine vs. pegmatite [and spodumene vs. lepidolite] vs. clay) factors. Lithium chemistry is a lot simpler than that of the rare earth elements, but even within pegmatites there are different ore minerals with different processing costs: lepidolite mica is the main alternative to spodumene. Australia is the largest lithium producer, followed by Chile and China. The bulk of Australian production is exported to China, who dominate the lithium battery industry. Possibly supply has outstripped demand right now, but - as long as lithium-based batteries remain the prime choice for electric vehicles - demand should soar and thus price eventually rise again.

Fig. 5: A view of spodumene that clearly illustrates the 87-degree pyroxene cleavage traces.

The major sources of lithium are brines and pegmatites (the latter dominating hard rock sources). The Plumbago North deposit is a promising future source of this latter form of "hard rock" lithium. The largest producer has long been Australia, largely from pegmatites such as Greenbushes in Western Australia. To enlarge a little on this...

Brines, saline fluids rich in alkalies, lithium included, are found largely in arid regions (e.g., Chile, Argentina and Bolivia), though geothermal fluids circulating in highly evolved granites (as in the granite masses and associated tin mines of Cornwall, S.W.England) may also be Li-rich.
Hard rock - generally speaking, pegmatites. The traditional source of Li, Cs, Ta and other uncommon to rare elements. Depending on market conditions, a mine may switch focus back and forth to the commodity that is most in demand in a given year, e.g., Li vs Ta. An example would be the Tanco mine in Manitoba, that over time has focused on either Ta or Li (in spodumene), though the ores are also enriched in other elements such as Cs and Rb. Pegmatites with rare-element mineralization are, if not abundant, then certainly widespread in leucogranitic rocks in both Archean shields and Phanerozoic terranes. Thus, just east from Tanco in northwest Ontario, there are a variety of pegmatites containing spodumene, holmquistite (a Li-rich amphibole) and other Li minerals (Milne, 1962; Kissin and Zayachkivsky, 1986; Breaks, 1993; Breaks et al., 1999a,b, 2005,2006; Selway et al., 2002). Also in the Superior craton, in the Abitibi greenstone belt in Quebec, spodumene pegmatite dykes may occur associated with late phases of bodies such as the Preissac-Lacorne batholith near Val d'Or (Flanagan, 1979; Mulja et al., 1995). The largest example of a spodumene-rich pegmatite, with the longest continuous mining history, is surely the Greenbushes pegmatite in Western Australia (Hatcher and Clynick 1990; also Suttill, 1987; Saywell, 2012). The deposit has been variously worked for Sn, Ta and Li. The weathering of feldspar and spodumene has been intense, such that one product is a Li-rich clay valuable in ceramics production. At the Varutrask pegmatite in Sweden, alteration of spodumene was recognized early (Quensel, 1938), and even rubellite tourmaline may be altered to cookeite and lepidolite (Quensel and Gabrielson, 1939).

Lithium assay in both brines and pegmatite ores requires care in sample preparation and choice of analytical method (see de Souza et al., 2022). A quantitative balance of Li deportment between the various minerals in a rock requires all minerals to be dissolved in acid or flux, and some (e.g., tourmaline, spodumene) are hard to decompose. Minerals may contain parts per million to low percent levels of lithium, incorporated in their crystal structures (e.g., quartz, tourmaline). A surprising number have Li as an essential component of their mineral formula. Well-known examples include: silicates (e.g., spodumene and petalite, and the mauve mica, lepidolite), as well as phosphates such as montebrasite (see London, 2008; Simmons et al., 2022).

In recent years it has become possible to analyse for Li in the field using a handheld device utilizing LIBS. Laser ionization breakdown specroscopy works by firing a tightly collimated laser beam at a small (mm scale) area of a rock sample. The immediate target material is ionized to some degree, and the photon emission from the resultant plasma is analysed in an optical spectrometer. Thanks to a helpful staff member of the SciAps booth at the annual Prospectors and Developers Association meeting in Toronto, 07 March 2023, two samples from the Oxford pegmatite field were analysed with a Z-901 unit, yielding values on pairs of 2x2 mm areas (a 100-micron-wide laser beam is rastered over a wider area to obtain a more representative result). A small piece of the spodumene averaged 0.939% Li (2.01 wt.% Li₂O) while the graphic granite from the Havey quarry ** returned 115 ppm Li. Note that the latter, a first possible value for a granitic background level in that region, is still several times the clarke (mean concentration in the continental crust) which is 16 ppm lithium. The patchy nature of UV fluorescence in the analysed spodumene suggests there may be intergrown quartz and/or feldspar in the sample, which may explain the Li value which is lower than for theoretically pure spodumene. Given calibration with samples analysed in a conventional lab, this technology has great potential to characterize suites of rocks prospective for lithium in a given area.

Acknowledgements: The opportunity to visit this and other localities, and to learn about the geology and history of pegmatites and pegmatite research, arose through my participation in the Pegmatite Workshop held on 8-11 September 2022 at the recently-opened Maine Mineral & Gem Museum in Bethel, Maine. The course was organized by Skip Simmons, Karen Webber, Alexander Falster, Encar Roda-Robles and Donald Dallaire, the authors of the manual "Pegmatology" (2nd edition released in 2022: Visit Rubellite HERE). Thanks to them, Larry Stifler and Mary McFadden and the staff of MMGM, Mary and Gary Freeman of Freeman Resources, LLC, and especially to Richard Bedell, who suggested and facilitated my participation, at a time when I otherwise might have stayed at home!

References

Ahlfeld,F and Angelelli,F (1948) Las Especies Minerales de la Republica Argentina. Instituto de Geologia y Mineria, Universidad Nacional de Tucuman, Jujuy, Argentina, 304pp. (in Sp.).

Breaks,FW (1993) Granite-related mineralization in northwestern Ontario: I. Raleigh Lake and Separation Rapids (English River) rare-element pegmatite fields. In Summary of Field Work and Other Activities 1993 (Baker,CL, Dressler,BO, de Souza,HAF, Fenwick,KG, Newsome,JW and Owsiacki,L, editors), OGS Misc.Pap. 162, 318pp., 104-110.

Breaks,FW, Selway,JB and Tindle,AG (2005) Fertile peraluminous granites and related rare-element pegmatites, Superior province of Ontario. In Rare-Element Geochemistry and Mineral Deposits (Linnen,RL and Samson,IM editors). GAC Short Course Notes 17, 341pp., 87-125.

Breaks,FW, Selway,JB and Tindle,AG (2006) Fertile and peraluminous granites and related rare-earth mineralization in pegmatites, north-central and northeastern Superior province, Ontario. OGS OFR 6195, 143pp. plus 3 maps.

Breaks,FW, Tindle,AG and Smith,SR (1999a) Rare-metal mineralization associated with the Berens River-Sachigo subprovincial boundary, northwest Ontario: discovery of a new zone of complex-type, petalite subtype pegmatite and implications for future exploration. OGS Misc.Pap. 169, 168-182.

Breaks,FW, Tindle,AG and Smith,SR (1999b) Geology, mineralogy and exploration potential of the Big Mack pegmatite system: a newly discovered western extension of the Separation Rapids pegmatite group, NW Ontario. OGS OFR 6000, 25.1-22.

Deer,WA, Howie,RA and Zussman,J (1966) An Introduction to the Rock-Forming Minerals. Longmans, 528pp.

de Souza,H, Seyfarth,A, Turner,N and Woods,J (2022) Lithium analysis of brines and minerals for exploration and resource definition. Explore 194, 1,5-13, March.

Flanagan,JT (1978) Lithium deposits and potential of Quebec and Atlantic Provinces, Canada. In Lithium Needs and Resources (Penner,SS, editor), Pergamon Press, pp. 391-398.

Hatcher,MI and Clynick,G (1990) Greenbushes tin-tantalum-lithium deposit. In `Geology of the Mineral Deposits of Australia and Papua New Guinea' (Hughes,FE editor), Australasian Institute of Mining and Metallurgy Monograph 14, 1828pp., 599-603.

Kissin,SA and Zayachkivsky,B (1986) Staringite confirmed in the Georgia Lake pegmatite field, northwestern Ontario. GAC/MAC Prog.w.Abs. 11, 90.

London,D (2008) Pegmatites. Canadian Mineralogist Spec.Publ. 10, 347pp. + CD-ROM.

Maine Geological Survey (1957) Maine Pegmatite Mines and Prospects and Associated Minerals. Maine Geol.Surv. Mineral Resources Index No.1, 43pp.

Milne,VG (1962) The Petrography and Alteration of Some Spodumene Pegmatites near Beardmore, Ontario. PhD Thesis, University of Toronto, 242pp. plus map folder.

Mulja,T, Williams-Jones,AE, Wood,SA and Boily,M (1995) The rare-element-enriched monzogranite- pegmatite- quartz vein systems in the Preissac-Lacorne batholith, Quebec. II. Geochemistry and petrogenesis. Can.Mineral. 33, 817-833.

Newton Friend,J (1961) Man and the Chemical Elements. Charles Scribner's Sons, New York, 2nd edition, 354pp.

Quensel,P (1938) Minerals of the Varutrask Pegmatite 10: spodumene and its alteration products. GFF 60, 201-215.

Quensel,P and Gabrielson,O (1939) Minerals of the Varutrask Pegmatite 14: the tourmaline group. GFF 61, 63-90.

Saywell,T (2012) Greenbushes bears fruit for Talison. Northern Miner 98 no.15, 1-2, 28 May.

Schneider,S (2006) The World of Fluorescent Minerals. Schiffer Publishing Limited, Atglen, PA, 192pp.

Selway,JB, Tindle,AG and Breaks,FW (2002) Extreme tantalum-enrichment in the North Aubry rare-element granitic pegmatite, near Armstrong, northwestern Ontario. GAC/MAC Abs. 27, 107, Saskatoon.

Simmons,WB, Falster,AU and Freeman,G (2020) The Plumbago North pegmatite, Maine, USA: a new potential lithium resource. Mineralium Deposita 55 no.7, 1505-1510.

Simmons,WB, Webber,KL, Falster,AU, Roda-Robles,E and Dallaire,DA (2022) Pegmatology. Pegmatite Mineralogy, Petrology and Petrogenesis. 2nd edition. Rubellite Press, Cana, VA, 287pp. [Visit Rubellite HERE].

Suttill,KR (1987) Greenbushes: lithium generates a new source of income. Eng.Min.J. 188 no.11, 40-43, November.

Graham Wilson, posted 13-18 October 2022, last update (market prices mostly) to 21 March 2024,
revising Fig.1 and adding Fig. 5, 13 February 2024.

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** Graphic granite of the Havey quarry, Maine