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Department of Mines, Industry Regulation and Safety

Granitic pegmatites are coarse-grained igneous rocks that contain abundant crystals with skeletal, graphic or other strongly directional growth-habits, or anisotropic layered mineral fabrics (London, 1992, 2018). Giant or megacrystic crystals may also be present.

Several classification schemes exist for granitic pegmatites (Cerný and Ercit, 2005; London, 2008; Simmons and Webber, 2008) — the simplest scheme divides them into common pegmatites and rare-element pegmatites. More complex schemes are based upon the presence of different rare-metal mineral assemblages. The rare-element pegmatites have anomalous contents of Be, Li, Ta, Sn and Cs. Beryllium is most commonly present as beryl, Li occurs as spodumene or lepidolite, Ta as columbite–tantalite, Sn as cassiterite and Cs as pollucite (Bradley et al., 2017). Pegmatites are also often mined for high-purity quartz, potassium feldspar, albite, kaolinite, white mica, gem beryl, gem tourmaline and museum-quality specimens of many rare minerals.

Rare-element pegmatites are divided into two end-member petrogenetic/compositional families (Cerný, 1991; Cerný and Ercit, 2005) as a simple chemical division to emphasise key differences in the geological processes responsible for rare-element mineralization:

  • Lithium–caesium–tantalum (LCT) pegmatites are enriched in Li, Cs, Ta, Be, B, F, P, Mn, Ga, Rb, Nb, Sn and Hf. Examples of major LCT pegmatite deposits include the Tin Mountain pegmatite in the United States; Tanco pegmatite in Canada, Altai Number 3 pegmatite in China; the Greenbushes, Wodgina and Pilgangoora pegmatites in Western Australia; Bikita pegmatite in Zimbabwe; and the Kenticha pegmatite district in Ethiopia (e.g. see summaries of Cerný et al., 2005; Bradley et al., 2017).
  • Niobium–yttrium–fluorine (NYF) pegmatites are enriched in Be, Sn, B, Nb > Ta, Ti, Y, rare earth elements (REE), Zr, Th, U, Sc and F, but are depleted in Li, Cs and Rb. Biotite is more common in NYF pegmatites, whereas muscovite is dominant in LCT pegmatites. Notable NYF pegmatite deposits, as summarized by Ercit (2005), include the South Platte granite and pegmatite system in Colorado (Simmons et al. 1987), the Grötingen granite and Abborselet and other associated pegmatites in Sweden (Kjellman et al., 1999), the Lac du Bonnet biotite granite and Shatford Lake pegmatite group in Canada (Buck et al., 1999), and the Stockholm granite and Ytterby pegmatite group, Sweden (Kjellman et al., 1999).
  • Mixed or ‘hybrid’ rare-element pegmatites have blended rare-element signatures and are considered to be products of contamination of NYF pegmatites at the magmatic or postmagmatic stage. For example, they have been suggested to result from remelting of newly formed NYF pegmatites by metasomatic fluids rich in Li, B, Ca and Mg (Cerný and Ercit, 2005; Martin and De Vito, 2005). Some examples of mixed pegmatites include those at Kimito in Finland (Pehrman, 1945 ), the Tørdal district of Norway (Bergstøl and Juve, 1988; Cerný, 1991) and the O'Grady batholith in Canada (Ercit et al., 2003).

Lithium–caesium–tantalum pegmatites are present in all continents and span three billion years of Earth history. Their global age distribution mirrors those of orogenic granites and detrital zircons, corresponding to times of supercontinent assembly and major collisional orogenic events (Tkachev, 2016; Bradley et al., 2017). In Proterozoic–Phanerozoic settings, where collisional tectonic processes are well documented, LCT pegmatites most likely formed in orogenic hinterlands related to plate convergence (Bradley et al., 2017). Arc-related processes that control pegmatite generation include: i) overthickening of continental crust, ii) slab breakoff, iii) slab delamination, iv) extensional collapse occurring late in the collisional event and involving decompression melting. Lithium–caesium–tantalum pegmatites are consequently hosted in metamorphosed supracrustal rocks (e.g. greenstone belts). Intrusions are emplaced at midcrustal levels late during orogeny and are controlled by existing faults, fractures, foliation and bedding in country rocks. Pegmatites exposed to these conditions are tabular, whereas at lower levels of the crust, ductile hydrostatic conditions promote lensoid to irregular pegmatites (Brisbin, 1986). In the Proterozoic and Phanerozoic, LCT pegmatites are products of extreme fractional crystallization of S-type granites, derived from melting of metasedimentary rocks in continental collision zones (Cerný and Ercit, 2005). Specific examples include pegmatite fields in South Norway (Müller et al. 2015), Namibia (Fuchsloch et al., 2018), Maine (Webber et al., 2019) and in the Italian Alps (Konzett et al., 2018). An alternate process proposed for pegmatite generation is by direct melting of rocks with the appropriate composition (e.g. metasedimentary rocks with evaporite sequences: Simmons and Webber, 2008; London, 2008, 2018).

In Archean settings such as the Pilbara and Yilgarn Cratons, S-type granites are scarce and the largest known deposits hosted by LCT pegmatites (e.g. the Wodgina, Pilgangoora and Greenbushes deposits) are associated with highly fractionated I-type granites (Sweetapple and Collins, 2002; Sweetapple, 2017). Although contentious, some form of plate tectonics is generally agreed upon for the Archean (e.g. Cawood et al., 2013). In this context, progressive partial melting of trondhjemite–tonalite–granodiorite precursors is one possible method for the enrichment of rare-elements in melts that act as the parental sources of mineralized pegmatites (Sweetapple, 2017). These pegmatites are most commonly emplaced into mafic or ultramafic host rocks within greenstone belts (e.g. the Pilbara Craton, Sweetapple and Collins, 2002; Yilgarn Craton, Witt, 1992). In these Archean settings, regional-scale structures control the distribution of pegmatites, being responsible for focusing and transporting fluids and magmas (e.g. Sweetapple and Collins, 2002; Demartis et al., 2011; Deveaud et al., 2013).

Most LCT pegmatite melts are enriched in fluxing components (H2O, F, P and B) that depress the solidus temperature, lower the magma density and increase rates of ionic diffusion. Hence, LCT pegmatites form relatively thin dykes with large crystals at lower temperatures (350–550°C) compared to common granitic melts (London, 2008, 2018). Rates of crystallization modelled experimentally are remarkably short (days to years; Webber et al., 1997; London, 2008, 2018).

Pegmatites are located within 10 km of cogenetic peraluminous granites and leucogranites (as modelled experimentally by Baker, 1998). The roof zones of large plutons are the most favourable positions (London, 2018). Proximal pegmatites are the least evolved and are poorly mineralized, containing only the general rock-forming minerals (Fig. 1). More distal and evolved pegmatites may include beryl, beryl and columbite, tantalite and Li aluminosilicates, and pollucite in the most evolved pegmatites. The spatial zonation of pegmatites around a common granitic source is a fundamental starting point for exploration models (London, 2018).

Niobium–yttrium–fluorine pegmatites are identified in most continents and their crystallization ages correspond to major intervals of global continent assembly from the Archean to the Neogene, with a peak at ~1000 Ma corresponding to the Grenville orogeny in Laurentia (McCauley and Bradley, 2014).

Niobium–yttrium–fluorine pegmatites are products of pronounced differentiation of anorogenic, A-type granites, which are a common product of bimodal gabbro-granite magmatism in rift zones. Geological processes controlling the genesis of A-type granites include: i) fractionation of direct partial melts from the upper mantle, ii) remelting of basalts that accumulate beneath the thinned lithosphere, iii) partial melting of lower crustal gneisses (Eby, 1990; Christiansen and McCurry, 2008). In the advanced rift setting where A-type granites are commonly generated, the mafic and felsic melts are mostly metaluminous. The melts are near or above silica saturation, with the granites notably depleted in Ca and P, and possessing heavy rare earth element (HREE) enrichment (London, 2018).

Like the LCT pegmatites, NYF pegmatites are often controlled by structures, fabrics and bedding in country rocks. However, regional zonation patterns around parental granites do not appear to occur in NYF pegmatite fields (Simmons and Webber, 2008). Rather, the NYF pegmatites are commonly hosted within granites (e.g. in the Pilbara Craton; Sweetapple and Collins, 2002).

Figure1 Schematic model in profile that shows regional zoning patterns in a pegmatite field (from Bradley et al., 2017 and references therein). Characteristic rare-element suites of the most enriched pegmatites in each zone are indicated.

Derived layers are grouped based on their critical features:

SOURCE – Formation of fertile magmas

PATHWAY – Structures, foliation and bedding in country rocks

TRAP – Cooling and chemical diffusion in fractionating melts

PRESERVATION – Erosion and uplift of rare-element pegmatites

The Mineral System Tree is the graphical display of a mineral systems analysis showing the link between critical/constituent processes and their recommended targeting features and GIS layers.

 Mineral System Tree: Rare-element pegmatite

Baker, R 1998, The escape of pegmatite dikes from granitic plutons: constraints from new models of viscosity and dike propagation: The Canadian Mineralogist, v. 36, no. 2, p. 255–263.

Bergstøl, S and Juve, G 1988, Scandian ixiolite, pyrochlore and bazzite in granite pegmatite in Tørdal, Telemark, Norway. A contribution to the mineralogy and geochemistry of scandium and tin: Mineralogy and Petrology, v. 38, no. 4, p. 229–243, doi:10.1007/BF01167090.

Bradley, DC, McCauley, AD and Stillings, LL 2017, Mineral-deposit model for lithium-cesium-tantalum pegmatites: United States Geological Survey, Reston, VA, Scientific Investigations Report 2010-5070, 58p.

Brisbin, WC 1986, Pegmatite emplacement mechanics: American Mineralogist, v. 71, no. 4, p. 644–651.

Buck, HM, Cerný, P and Hawthorne, FC 1999, The Shatford Lake pegmatite group, southeastern Manitoba: NYF or not? The Eugene E. Foord Memorial Symposium on NYF-type Pegmatites, v. 37, p. 830–831.

Cawood, PA, Hawkesworth, CJ and Dhuime, B 2013, The continental record and the generation of continental crust: Journal of the Geological Society, v. 125, no. 1-2, p. 14–32, doi:10.1130/B30722.1.

Cerný, P 1989, Exploration strategy and methods for pegmatite deposits of tantalum, in Lanthanides, Tantalum and Niobium edited by P Möller, P Cerný and F Saupé: Springer-Verlag, p. 274–302.

Cerný, P 1991, Rare-element granitic pegmatites. Part I: Anatomy and internal evolution of pegmatite deposits: Geoscience Canada, v. 18, p. 49–67.

Cerný, P, Blevin, PL, Cuney, M and London, D 2005, Granite-related ore deposits: Economic Geology 100th Anniversary Volume, p. 337–370.

Cerný, P and Ercit, TS 2005, The classification of pegmatites revisited: The Canadian Mineralogist, v. 43, no. 6, p. 2005–2026, doi:10.2113/gscanmin.43.6.2005.

Christiansen, EH and McCurry, M 2008, Contrasting origins of Cenozoic silicic volcanic rocks from the western Cordillera of the United States: Bulletin of Volcanology, v. 70, no. 3, p. 251–267, doi:10.1007/s00445-007-0138-1.

Demartis, M, Pinotti, LP, Coniglio, JE, D’Eramo, FJ, Tubía, JM, Aragón, E and Agulleiro Insúa, LA 2011, Ascent and emplacement of pegmatitic melts in a major reverse shear zone (Sierras de Córdoba, Argentina): Journal of Structural Geology, v. 33, no. 9, p. 1334–1346, doi:10.1016/j.jsg.2011.06.008.

Deveaud, S, Gumiaux, C, Gloaguen, E and Branquet, Y 2013, Spatial statistical analysis applied to rare-element LCT-type pegmatite fields: an original approach to constrain faults-pegmatites-granites relationships: Journal of Geosciences, v. 58, no. 2, p. 163–182, doi:10.3190/jgeosci.141.

Eby, GN 1990, The A-type granitoids: A review of their occurrence and chemical characteristics and speculations on their petrogenesis: Lithos, v. 26, no. 1, p. 115–134, doi:10.1016/0024-4937(90)90043-Z.

Ercit, TS 2005, REE-enriched granitic pegmatites in Rare-element geochemistry and mineral deposits edited by RL Linnen and IM Samson: Geological Association of Canada Short Course Notes 17, p. 175–199.

Ercit, TS, Groat, LA and Gault, RA 2003, Granitic pegmatites of the O'Grady batholith, N.W.T., Canada: A case study of the evolution of the elbaite subtype of rare-element granitic pegmatite: The Canadian Mineralogist, v. 41, no. 1, p. 117–137, doi:10.2113/gscanmin.41.1.117.

Fuchsloch, WC, Nex, PAM and Kinnaird, JA 2018, Classification, mineralogical and geochemical variations in pegmatites of the Cape Cross-Uis pegmatite belt, Namibia: Lithos, v. 296-299, p. 79–95, doi:10.1016/j.lithos.2017.09.030.

Galeschuk, CR and Vanstone, PJ 2005, Exploration for buried rare element pegmatites in the Bernic Lake region of southeastern Manitoba, in Rare-element geochemistry and mineral deposits edited by RL Linnen and IM Samson: Geological Association of Canada, Short Course Notes 17, p. 159–173.

Kjellman, J, Cerný, P and Smeds, S-A 1999, Diversified NYF pegmatite populations of the Swedish Proterozoic: outline of a comparative study: The Eugene E. Foord Memorial Symposium on NYF-type Pegmatites, v. 37, p. 832–833.

Konzett, J, Schneider, T, Nedyalkova, L, Hauzenberger, C, Melcher, F, Gerdes, A and Whitehouse, M 2018, Anatectic granitic pegmatites from the eastern alps: A case of variable rare-metal enrichment during high-grade regional metamorphism - i: Mineral assemblages, geochemical characteristics, and emplacement ages: The Canadian Mineralogist, v. 56, no. 4, p. 555–602, doi:10.3749/canmin.1800008.

London, D 1992, The application of experimental petrology to the genesis and crystallization of granitic pegmatites: Canadian Mineralogist, v. 30, p. 499–540, 42p.

London, D 2008, Pegmatites: Mineralogical Association of Canada, The Canadian Mineralogist Special Publication 10, 347p.

London, D 2018, Ore-forming processes within granitic pegmatites: Ore Geology Reviews, v. 101, p. 349–383, doi:10.1016/j.oregeorev.2018.04.020.

Martin, RH and De Vito, C 2005, The patterns of enrichment in felsic pegmatites ultimately depend on tectonic setting: The Canadian Mineralogist, v. 43, no. 6, p. 2027–2048, doi:10.2113/gscanmin.43.6.2027.

McCauley, A and Bradley, DC 2014, The global distribution of granitic pegmatites: The Canadian Mineralogist, v. 52, no. 2, p. 183–190, doi:10.3749/canmin.52.2.183.

Müller, A, Ihlen, PM, Snook, B, Larsen, RB, Flem, B, Bingen, B and Williamson, BJ 2015, The chemistry of quartz in granitic pegmatites of southern Norway: Petrogenetic and economic implications: Economic Geology, v. 110, no. 7, p. 1737–1757, doi:10.2113/econgeo.110.7.1737.

Pehrman, G 1945, Die Granitpegmatite von Kimito (S.W. Finnland) und ihre Minerale: Acta Academiae Aboensis: Mathematica et physica, v. 26, 84p.

Simmons, WB, Lee, MT and Brewster, RH 1987, Geochemistry and evolution of the South Platte granite-pegmatite system, Jefferson County, Colorado: Geochimica et Cosmochimica Acta, v. 51, no. 3, p. 455–471, doi:10.1016/0016-7037(87)90061-5.

Simmons, WS and Webber, KL 2008, Pegmatite genesis: state of the art: European Journal of Mineralogy, v. 20, no. 4, p. 421–438, doi:10.1127/0935-1221/2008/0020-1833.

Sweetapple, MT 2017, Granitic pegmatites as mineral systems: examples from the Archaean, in PEG2017 8th International Symposium on Granitic Pegmatites: NGF Abstracts and Proceedings edited by A Müller and N Rosing-Schow: Geological Society of Norway, Kristiansand, Norway, p. 139–142.

Sweetapple, MT and Collins, PLF 2002, Genetic framework for the classification and distribution of Archean rare metal pegmatites in the North Pilbara Craton, Western Australia: Economic Geology, v. 97, p. 873–895.

Tkachev, AV 2016, Evolution of metallogeny of granitic pegmatites associated with orogens throughout geological time: Geological Society, London, Special Publications, v. 350, p. 7–23, doi:10.6084/M9.FIGSHARE.3454913.V1.

Trueman, DL and Cerný, P 1982, Exploration for rare-element granitic pegmatites, in Granitic Pegmatites in Science and Industry edited by P Cerný: Mineralogical Association of Canada, Short Couse Handbook 8, p. 463–494.

Webber, KL, Falster, AU, Simmons, WB and Foord, EE 1997, The role of diffusion-controlled oscillatory nucleation in the formation of Line Rock in pegmatite–aplite dikes: Journal of Petrology, v. 38, no. 12, p. 1777–1791, doi:10.1093/petroj/38.12.1777.

Webber, KL, Simmons, WB, Falster, AU and Hanson, SL 2019, Anatectic pegmatites of the Oxford County pegmatite field, Maine, USA: The Canadian Mineralogist, v. 57, no. 5, p. 811–815, doi:10.3749/canmin.AB00028.

Witt, WK 1992, Heavy-mineral characteristics, structural settings, and parental granites of pegmatites in Archaean rocks of the eastern Yilgarn Craton: Geological Survey of Western Australia, Record 1992/10, 54p.

See the included reference list.

Subject matter experts:

  • Marcus Sweetapple (consultant)

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