Chemical variation and significance of tourmaline from Southwest England

University of Oklahoma, School of Geology and Geophysics, Norman, OK, United States
University of Manchester, United Kingdom

Tourmaline is a common and locally abundant mineral in all products of the granite magmatism and associated hydrothermal activity in southwest England, particularly in the county of Cornwall. Tourmaline of magmatic origin is homogeneous and is marked by high Fe/Mg, high F, and high Al in the place of divalent cations (R2 site). The substitution of Al for divalent cations such as Mg and Fe (super 2+) is charge-compensated by a deficit of alkalies and protons in other structural sites. Tourmaline compositions from the granites clearly reflect the sequence of increased differentiation among the magma types, with biotite granites as the least evolved, and topaz granites as the most evolved. In contrast, tourmaline of hydrothermal origin within granites displays fine-scale compositional zonation with a general tendency toward more magnesian compositions nearer the schorl-dravite solid solution (i.e., little or no Al in the R2 site). Metasomatic tourmaline precipitated in the surrounding pelitic and mafic rocks also possesses fine-scale zonation, and generally reflects the compositions of the host rocks. In addition, tourmaline formed in the country rocks has a higher proportion of Fe (super 3+) to Fe (super 2+) , which presumably indicates a higher oxidation state of fluids in the metamorphic rocks than in the granites. This variation may correlate with the mobilization of tin from the granites and its consequent deposition as cassiterite in the host rocks. The abundance of magmatic tourmaline is limited by the initial Fe-Mg content of the magmas to not more than a few modal or weight percent. Although they contain tourmaline, the biotite granites are not the most likely sources of boron for voluminous, late-stage tourmalinization. Magmas that contained only tourmaline or no Fe-Mg minerals at all, such as the those that formed the topaz granites, may have been sources of large quantities of boron. The most intense areas of tourmalinization do surround the small stocks and sheets of topaz microgranite. High concentrations of tourmaline, for example in hydrothermal veins and breccias, appear to require mixing of two different chemical reservoirs: one a source of boron (the magmas or fluids..

This record provided courtesy of AGI/GeoRef.

This article has been cited by other articles:

				A. C. Zhang, R. C. Wang, S. Y. Jiang, H. Hu, and H. Zhang CHEMICAL AND TEXTURAL FEATURES OF TOURMALINE FROM THE SPODUMENE-SUBTYPE KOKTOKAY No. 3 PEGMATITE, ALTAI, NORTHWESTERN CHINA: A RECORD OF MAGMATIC TO HYDROTHERMAL EVOLUTION Can Mineral, February 1, 2008; 46(1): 41 - 58. [Abstract] [Full Text] [PDF]

				T. Oyman and M. D. Dyar CHEMICAL SUBSTITUTIONS IN OXIDIZED TOURMALINE IN GRANITE-RELATED MINERALIZED HYDROTHERMAL SYSTEMS, WESTERN TURKEY Can Mineral, December 1, 2007; 45(6): 1397 - 1413. [Abstract] [Full Text] [PDF]

				S. Roberts, M. R. Palmer, and L. Waller Sm-Nd and REE Characteristics of Tourmaline and Scheelite from the Bjorkdal Gold Deposit, Northern Sweden: Evidence of an Intrusion-Related Gold Deposit? Economic Geology, November 1, 2006; 101(7): 1415 - 1425. [Abstract] [Full Text] [PDF]

				A. ERTL, U. KOLITSCH, S. PROWATKE, M. D. DYAR, and D. J. HENRY The F-analogue of schorl from Grasstein, Trentino - South Tyrol, Italy: crystal structure and chemistry European Journal of Mineralogy, October 1, 2006; 18(5): 583 - 588. [Abstract] [Full Text] [PDF]

				M. S.J. Mlynarczyk and A. E. Williams-Jones ZONED TOURMALINE ASSOCIATED WITH CASSITERITE: IMPLICATIONS FOR FLUID EVOLUTION AND TIN MINERALIZATION IN THE SAN RAFAEL SN CU DEPOSIT, SOUTHEASTERN PERU Can Mineral, April 1, 2006; 44(2): 347 - 365. [Abstract] [Full Text] [PDF]

				D. London, A. Ertl, J. M. Hughes, G. B. Morgan VI, E. A. Fritz, and B. S. Harms Synthetic Ag-rich tourmaline: Structure and chemistry American Mineralogist, April 1, 2006; 91(4): 680 - 684. [Abstract] [Full Text] [PDF]

				E. Roda, A. Pesquera, P. P. Gil-Crespo, J. Torres-Ruiz, and F. Fontan Origin and internal evolution of the Li-F-Be-B-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian Zone, Zamora, Spain) American Mineralogist, November 1, 2005; 90(11-12): 1887 - 1899. [Abstract] [Full Text] [PDF]

				A. Muller, B. J. Williamson, and M. Smith Origin of quartz cores in tourmaline from Roche Rock, SW England Mineralogical Magazine, August 1, 2005; 69(4): 381 - 401. [Abstract] [Full Text] [PDF]

				N. Sengupta, D. Mukhopadhyay, P. Sengupta, and R. Hoffbauer Tourmaline-bearing rocks in the Singhbhum shear zone, eastern India: Evidence of boron infiltration during regional metamorphism American Mineralogist, August 1, 2005; 90(8-9): 1241 - 1255. [Abstract] [Full Text] [PDF]

				I. A. Baksheev and O. E. Kudryavtseva NICKELOAN TOURMALINE FROM THE BEREZOVSKOE GOLD DEPOSIT, MIDDLE URALS, RUSSIA Can Mineral, August 1, 2004; 42(4): 1065 - 1078. [Abstract] [Full Text] [PDF]

				A. Ertl, A. Ertl, J. M. Hughes, S. Prowatke, G. R. Rossman, D. London, and E. A. Fritz Mn-rich tourmaline from Austria: structure, chemistry, optical spectra, and relations to synthetic solid solutions American Mineralogist, August 1, 2003; 88(8-9): 1369 - 1376. [Abstract] [Full Text] [PDF]

				D. J. Kontak, J. Dostal, T. K. Kyser, and D. A. Archibald A PETROLOGICAL, GEOCHEMICAL, ISOTOPIC AND FLUID-INCLUSION STUDY OF 370 Ma PEGMATITE-APLITE SHEETS, PEGGYS COVE, NOVA SCOTIA, CANADA Can Mineral, October 1, 2002; 40(5): 1249 - 1286. [Abstract] [Full Text] [PDF]

				M. Wilke, P. I. Nabelek, and M. D. Glascock B and Li in Proterozoic metapelites from the Black Hills, U.S.A.: Implications for the origin of leucogranitic magmas American Mineralogist, April 1, 2002; 87(4): 491 - 500. [Abstract] [Full Text] [PDF]

				A. KALT, W. SCHREYER, T. LUDWIG, S. PROWATKE, H.-J. BERNHARDT, and A. ERTL Complete solid solution between magnesian schorl and lithian excess-boron olenite in a pegmatite from the Koralpe (eastern Alps, Austria) European Journal of Mineralogy, December 1, 2001; 13(6): 1191 - 1205. [Abstract] [Full Text] [PDF]

				B. J. WILLIAMSON, J. SPRATT, J. T. ADAMS, A. G. TINDLE, and C. J. STANLEY Geochemical Constraints from Zoned Hydrothermal Tourmalines on Fluid Evolution and Sn Mineralization: an Example from Fault Breccias at Roche, SW England J. Petrology, September 1, 2000; 41(9): 1439 - 1453. [Abstract] [Full Text] [PDF]

				P. Garofalo, A. Audetat, D. Gunther, C. A. Heinrich, and J. Ridley Estimation and testing of standard molar thermodynamic properties of tourmaline end-members using data of natural samples American Mineralogist, January 1, 2000; 85(1): 78 - 88. [Abstract] [Full Text] [PDF]

				C. E. Lazareth and J.-C. C. Mercier Geochemistry of ballast granites from Brouage and La Rochelle, France: evidence for medieval to post-medieval trade with Falmouth, Cornwall, and Donegal, Ireland Geological Society, London, Special Publications, January 1, 1999; 165(1): 123 - 137. [Abstract] [PDF]

				D. A. C. MANNING, P. I. HILL, and J. H. HOWE Primary lithological variation in the kaolinized St Austell Granite, Cornwall, England Journal of the Geological Society, December 1, 1996; 153(6): 827 - 838. [Abstract] [PDF]