Origin and composition of hydrothermal fluids related to the formation of granite-related Sn-W deposits in SW England.

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Cu-Sn-W deposits of SW England are related to Variscan granitic magmatism and accompanying greisen and hydrothermal veins. Tourmaline is a perfect recorder of this sequence of events as it is present during all these stages in abundant quantities and it incorporates (besides many other trace elements) Cu, Sn and W into its structure. During the first funding period, the major, minor and trace element composition of the various tourmaline generations was determined in relation to their textural context and the presence or absence of ore minerals (mainly cassiterite). To finish up this project we aim to characterize the nature of the involved fluid types in detail in order to understand, which fluid carried the ore-forming elements. It is therefore anticipated to complete the microthermometric studies (heating-freezing stage) and to determine the major, minor and trace element composition of selected fluid inclusions of the best-suited and well-characterized samples by means of LA-ICP-MS. To illuminate the origin of the important elements it will be of fundamental importance to identify the origin of the fluid types themselves, which will be accomplished by analyzing O- and H-isotopes for tourmaline and O isotopes of quartz. With this comprehensive dataset, we will be able to develop a detailed model for the genesis of the diverse magmatic to hydrothermal systems of the Cornubian batholith in SW England, with possible application to granite-related Sn-Wo deposits in general.