Sm-Nd dating of fluorites from the Vergenoeg, Buffalo and Morgenzon 533 KQ deposits, Bushveld Igneous Complex, South Africa: Evidence for late hydrothermal fluorite formation

We investigated three fluorite deposits associated with the Bushveld Igneous Complex in South Africa for their trace element characteristics (e.g., REE+Th+U): the two major and world-class Vergenoeg and Buffalo deposits, as well as the small Morgenzon deposit. Combined with published and unpublished data from the Vergenoeg deposit (host rock and mineral separates), which yield an age of 2050 ± 17 Ma (MSWD = 0.65), the new host rock and fluorite Sm-Nd isotope data confirms a primary magmatic origin for the Buffalo deposit as well. Whereas the host rock data for Morgenzon plot close to the 2050 Ma isochron, the Morgenzon fluorite data significantly diverge and plot along an errorchron corresponding to an age of 318 ± 59 Ma (MSWD = 7.4). The Morgenzon fluorites are also depleted in the abundances of REE+Th+U by almost a factor 100 compared to the Buffalo fluorites. Cathodoluminescence (CL) imaging reveals complex zoning patterns with a wide range in bluish CL colours for the Morgenzon fluorite. In contrast, fluorite from Buffalo is always very homogeneous (pale bluish CL colour), which indicates a single stage and likely primary magmatic formation process for the latter. Combined trace element and isotope data and CL evidence for the Morgenzon deposit suggest a late hydrothermal fluorite formation unrelated to the Bushveld igneous event.