Phosphate mineral associations of the Aldehuela de la Boveda Li-Sn-Nb+-Ta-bearing pegmatite (Salamanca, Spain)

摘要

In the Aldehuela de la Boveda Li-Sn-Nb+-Ta-bearing pegmatite, partly intruding into a gabbroic body, three different associations of phosphates have been distinguished. In these associations the primary phosphates, the secondary and the coexisting minerals (mainly silicates and oxides), are different in paragenesis, texture and chemistry. Thus, the most evolved association, which exhibits the lowest contents in Mg, consists of Li-bearing tryphilite, montebrasite, as well as cassiterite and columbo-tantalite among other minerals. In the less evolved one, the Li-bearing phosphates are not found, whereas the Mg-bearing magniotriplite and johnsomervilleite are common, together with garnet. Moreover, the Mg contents in all the phases are high, presumably due to the influence of the gabbro in the marginal zones of the pegmatite. The third association shows intermediate characteristics. All this let us establish a trend of crystallisation, with a higher degree of evolution inwards the pegmatite body.