The relationship between magmatism and borate mineralisation in Western Turkey
2014-12-15T10:39:13Z (GMT) by
A limited number of lacustrine basins in western Turkey contain world class borate reserves, with mineralisation present as strata bound deposits in Neogene volcano-sedimentary successions. This study examined in detail the relationship between magmatism and borate mineralisation in two of these basins (Ernet and Kirka).;The magmatism comprised an Early Miocene K-rich acid phase, represented by granite, ignimbrite, rhyolite and dacite, and a more mafic K-rich, Middle - Late Miocene phase, represented by shoshonite and latite. Information from field observations, mineralogy, isotopic dates, immobile element concentrations and biotite compositions indicate that acid magmatism in Ernet and Kirka Basins was closely related in both space and time to the deposition of the borate-host sediments, whilst mafic volcanism occurred later.;The mineralogical and geochemical composition of the borate-host sediments was strongly influenced by the post-depositional modification of rhyolitic, ignimbritic and granitic-derived material in a saline, alkaline environment. The result of the interaction between saline, alkaline waters and dominantly acid igneous products, was the generation of an authigenic mineral assemblage comprising mainly calcite, dolomite, borate, trioctahedral smectite and K-feldspar. Trioctahedral smectite, dolomite and K-feldspar, together with elevated concentrations of As, Sr and Li, correlate particularly well with borate mineralisation.;The geochemistry of the Early Miocene acid igneous rocks suggests that acid magmatism represented a likely source for B and Li, and probably also for As and Sr. Possible mechanisms for the transfer of B and other elements from an igneous source to the basin sediments include; transfer by igneous-driven geothermal fluids, rich in B as a result of hydrothermal leaching and contributions from magmatic waters and gases, and the breakdown of igneous material in saline, alkaline lakes. Trace element and Nd and Sr isotropic data indicate that the ultimate source of the B was assimilated upper continental crust, perhaps with some component of melted lithospheric mantle. Comparison with other borate provinces shows a common tectonic setting, characterised by former convergence with associated subduction and crustal thickening.