Tourmaline-rich features in the Heemskirk and Pieman Heads granites from western Tasmania, Australia: Characteristics, origins, and implications for tin mineralization

Abstract

Distinctive magmatic-hydrothermal tourmaline-rich features have developed in the Heemskirk and Pieman Heads granites from western Tasmania, Australia. They are categorized as tourmaline-rich patches, orbicules, cavities, and veins, based on their distinctive morphologies, sizes, mineral assemblages, and contact relationships with host granites. These textural features occur in discrete layers in the roof zone of granitic sills within the Heemskirk and Pieman Heads granites.Tourmaline patches commonly occur below a tourmaline orbicule-rich granitic sill. Tourmaline-filled cavities have typically developed above the tourmaline-quartz orbicules in the upper layer of the white phase of the Heemskirk Granite. Tourmaline-quartz veins penetrate all exposed levels of the granites, locally cutting tourmaline orbicules and cavities.The tourmalines are mostly schorl (Fe-rich) and foitite, with an average end-member component of schorl45 dravite6 tsilaisite1 uvite0 Fe-uvite3 foitite31 Mg-foitite4 olenite10. Element substitutions of the tourmalines are controlled by FeMg-1, Y Al X □(R 2+ Na)-1, and minor Y AlO(R 2+ OH)-1 (where R 2+ = Fe 2+ + Mg 2+ + Mn 2+ ) exchange vectors. A number of trace elements in tourmaline have consistent chemical evolutions grouped from tourmaline patches, through orbicules and cavities, to veins. There is a progressive decrease of most transition and large ion lithophile elements, and a gradual increase of most high field strength elements. These compositional variations in the different tourmaline-rich features probably relate to element partitioning occurring in these phases due to volatile exsolution and fluxing of aqueous boron-rich fluids that separated from the granitic melts during the emplacement of S-type magmas into the shallow crust (4 to 5.5 km).

Evaluating the Changes from Endogranitic Magmatic to Magmatic-Hydrothermal Mineralization: The Zaaiplaats Tin Granites, Bushveld Igneous Complex, South Africa

“…The solubility of metals improves with increasing volatile concentration and acidity, facilitating their transportation within these magmatic-hydrothermal fluids [81,[86][87][88][89]. Thus, internally derived magmatic fluid, produced by the crystallizing Bobbejaankop granite, would have become enriched in various metals, such as Fe, Al, and Sn.…”

Cathodoluminescence features, trace elements and oxygen isotopes of quartz in unidirectional solidification textures from the Sn-mineralized Heemski rk Granite, western Tasmania

“…American Mineralogist, in press. DOI: https://doi.org/10.2138/am-2019-6534 pegmatites, discontinuous vein dykes, and/or tourmaline-quartz orbicules in the roof zones of the Heemskirk Granite (Hong et al 2017b). The CL textures, trace element and O-isotopic compositions of quartz (e.g., Figs.5-7 ), as well as the textures and compositions of magnetite within USTs, are all consistent with the comb-layered USTs, and quartz-filled miarolitic cavities in the Heemskirk Granite precipitating from volatile-rich, silica-saturated fluid pockets trapped in the carapace of the crystallizing felsic melts during the magmatic-hydrothermal transition (cf.…”

“…The CL textures, trace element and O-isotopic compositions of quartz (e.g., Figs.5-7 ), as well as the textures and compositions of magnetite within USTs, are all consistent with the comb-layered USTs, and quartz-filled miarolitic cavities in the Heemskirk Granite precipitating from volatile-rich, silica-saturated fluid pockets trapped in the carapace of the crystallizing felsic melts during the magmatic-hydrothermal transition (cf. Kirkham and Sinclair 1988;Carten et al, 1988;Candela and Blevin 1995;Lowenstern and Sinclair 1996;Harris et al 2004;Hong et al 2017b).…”

“…Unidirectional solidification textures are commonly associated with miarolitic cavities, vein dykes, saccharoidal quartz, and/or pegmatite pods within granitic stocks (Kirkham and Sinclair 1988;Candela and Blevin 1995;Lowenstern and Sinclair 1996;Lickfold et al 2003;Harris et al 2004;Breiter et al 2005;Hong et al 2017b). These distinctive textures typically occur in the apices of shallow-level granitoids, and can be associated with porphyry Cu, Au, Mo, and W deposits or granite-related Sn deposits (Shannon et al 1982;Carten et al, 1988;Kirkham and This is a preprint, the final version is subject to change, of the American Mineralogist (MSA) Cite as Authors (Year) Title.…”

“…Sinclair 1988; Lowenstern and Sinclair 1996;Kirwin and Seltmann 2002;Lickfold et al 2003;Wilson et al 2003;Harris et al 2004;Cannell et al 2005;Lickfold et al 2007;Hong et al 2017b). In porphyry deposits, zones of comb-layered quartz generally underlie the mineralized stockwork, and form during the transitional stage prior to main-stage mineralization (Carten et al, 1988;Harris et al 2004;Cannell et al 2005).…”