Low-Temperature Fluorocarbonate Mineralization in Lower Devonian Rhynie Chert, UK

Rare earth element (REE) fluorocarbonate mineralization occurs in lacustrine shales in the Lower Devonian Rhynie chert, Aberdeenshire, UK, preserved by hot spring silicification. Mineralization follows a combination of first-cycle erosion of granite to yield detrital monazite grains, bioweathering of the monazite to liberate REEs, and interaction with fluorine-rich hot spring fluids in an alkaline sedimentary environment. The mineral composition of most of the fluorocarbonates is referable to synchysite. Mineralization occurs at the surface, and the host shales subsequently experience maximum temperatures of about 110 degrees C. Most fluorocarbonate mineralization originates at much higher temperatures, but the Rhynie occurrence emphasizes that low-temperature deposits are possible when both fluorine and REEs are available from granite into the sedimentary environment.

Automated summary

Lacustrine shales in the Rhynie chert of Aberdeenshire, UK, contain rare earth element (REE) fluorocarbonate mineralization preserved by hot spring silicification. The mineralization results from erosion of granite, bioweathering of monazite, and interaction with fluorine-rich hot spring fluids. The low-temperature occurrence emphasizes the availability of fluorine and REEs from granite in the sedimentary environment.