Chemical and morphological variation in tourmalines from the Hub Kapong batholith of peninsular Thailand

Abstract

Electron probe microanalysis of tourmaline from late-stage aplites and mineralized (Sn-W) pegmatites from the Hub Kapong batholith of peninsular Thailand has revealed considerable chemical variation, and has shown that skeletal tourmaline crystals predominate within the pegmatites. The tourmalines show substitution towards the schorl end-member of the schorl-dravite series, as well as substitution towards alkali-free or proton deficient tourmaline. The extent of both substitutions increases (a) from aplites to pegmatites and (b) from core to rim within a single grain and so is believed to become greater with increasing degrees of differentiation of the aplite-pegmatite system. The development of skeletal crystals within the pegmatites and non-skeletal crystals within the aplites is believed to be due to the different kinetics of crystal growth obtaining within a hydrous, pegmatitic, fluid (viz. heterogeneous nucleation and comparatively rapid crystal growth rates) which in turn arise from differences in the structure of the aplitic magma and pegmatitic fluid. The observed chemical and morphological variation shown by the tourmalines is used to discuss the petrogenesis of the aplites and pegmatites, and associated ore deposits. During differentiation, the volatile content of the aplite magmas increased, leading to water saturation and the separation of a hydrous pegmatitic fluid. After a period of coexistence, possibly in chemical equilibrium, the crystallization of the pegmatites continued once the aplite magma had completely consolidated.

Chemical and mineralogical characterization of elbaites from the Alto Quixaba pegmatite, Seridó province, NE Brazil

“…Another possibility is that this diagram can not be applied for tourmalines of the schorl-elbaite series. On the other hand, this diagram shows that the compositions are rather homogeneous, which can be related to the decreasing temperature and large degree of evolution as suggested by Manning (1982).…”

Developpement des aureoles de contact d oulmes et de ment (Maroc central)

“…Manning, 1982;Henry et Guidotti, 1985). Dans les zones II et III, la tourmaline est souvent juxtaposée à la biotite.…”

Coupled Substitutions in Schorl-Dravite Tourmaline: New Evidence from SE Ireland

“…Both substitutions improve local charge balance but proton loss does so more effectively and alkali-defect tourmalines are inherently unstable (Foit and Rosenberg, 1977). The degree of replacement of divalent cations by A13+ was found to increase with decreasing temperature (Rosenberg and Foit, 1979;Manning, 1982). Alkali-defect and proton-loss substitution in SE Ireland tourmalines are illustrated in Figs.…”

“…1 and 7), the material in relatively Al-rich schist (mean 22.4% A1203, n=32) showing a high degree of substitution compared to tourmaline in granite which has a relatively low A1203 content (mean 16.5% A1203, n = 20) (see Scoon, 1978, for whole rock analyses). No evidence is available for the temperature of formation of these tourmalines and hence the I I I I T1C T2 T3 T4 T5 T6 T7 T8 T9 T10 Tll T12R AG4 question of whether bulk chemistry or temperature (as suggested by Foit, 1979, andby Manning, 1982) is more important in controlling the degree of trivalent-for-divalent substitution cannot be resolved for SE Ireland.…”