super(40)Ar super(39)Ar dating of hydrothermal activity, biota and gold mineralization in the Rhynie hot-spring system, Aberdeenshire, Scotland

This study presents a new high-precision super(40)Ar super(39)Ar age for the Devonian hot-spring system at Rhynie. Hydrothermal K-feldspar sampled from two veins that represent feeder conduits and a hydrothermally altered andesite wall rock, date the hydrothermal activity, the fossilised biota, and syn - K-feldspar gold mineralization at 403.9 +/- 2.1 Ma (2 sigma ). Oxygen isotope data for the parent fluid (-4ppt to 2ppt) show that the K-feldspar was precipitated from a dominantly meteoric fluid, which mixed with magmatic fluids from a degassing magma chamber. The super(40)Ar super(39)Ar age (403.9 +/- 2.1 Ma [2 sigma ]) when recalculated (407.1 +/- 2.2 Ma [2 sigma ]) with respect to the astronomically tuned age for Fish Canyon sanidine (28.201 +/- 0.023 Ma [1 sigma ]), also provides a robust marker for the polygonalis-emsiensis Spore Assemblage Biozone within the Pragian-?earliest Emsian. Furthermore, the age identifies the Devonian pull-apart volcano-sedimentary basins of the British and Irish Caledonides (and their root zones), as specific targets for future gold exploration.