Extended Method

Laboratory Processing
Calcite samples were selected and cut (in ~1cm3 blocks) to reveal internal sections that cross-cut the veins. Subsequently, the calcite pieces were mounted in 1-inch (2.5cm) round epoxy mounts using epoxy cure resin (5g epoxy resin and 1.15g epoxy hardener) and ground (using 800 and 2000 grit sandpaper) and polished (using a 3μm polishing cloth with diamond suspension fluid) to reveal a smooth surface.
Sample imaging was conducted at the British Geological Survey, Nottingham, UK. Cathodoluminescence imaging was conducted with a Technosyn 8200 MKII cold-cathode luminoscope stage attached to a Nikon optical microscope with a Nikon long working distance lens, and equipped with a Zeiss AxioCam MRc5 digital camera; vacuum and electron beam voltage and current were adjusted as required to generate optimum luminescence. Back-scattered electron and charge-contrast imaging were conducted using a FEI QUANTA 600 environmental scanning electron microscope (ESEM) with a working distance of 10 mm. BSE images were recorded using a solid-state (dual-diode) electron detector, with a 20 kV electron beam accelerating voltage, and beam currents between 0.1 and 0.6 nA,. Charge Contrast Images were recorded using a FEI large-field gaseous secondary electron (electron cascade) detector, with 20 kV electron beam accelerating voltage, and beam currents of 1.2 to 4.5 nA.
LA-ICP-MS U-Pb spot-analysis
LA-ICP-MS analysis was conducted at the University of Adelaide using an ASI resolution LR Laser Ablation System coupled to an Agilent 7900 mass spectrometer in order to determine U and Pb concentrations. Large spot sizes (110 microns) were selected in order to maximise the signals from elements that were expected to have low concentrations. Only isotopes necessary for U-Pb dating (43Ca,202Hg 204Pb,206Pb, 207Pb,208Pb, 232Th and238U) were measured during spot analysis in order to maximise the dwell time on masses expected to have low abundance, such as the isotopes of Pb. Standard-sample bracketing was used, with the NIST614 glass reference material used for fractionation correction of the Pb-Pb ratios, and the WC-1 calcite reference material (Age: 254.4 ± 6.4) for correction of the U-Pb ratios [Li et al. , 2014;Roberts and Walker , 2016; Roberts et al. , 2017]. An in house calcite sample labelled ‘Prague’ of known stratigraphic age (~424 Ma) was used as an accuracy check [Farkaš et al. , 2016]. In more detail, a correction factor was calculated based on the offset between the measured age and the known age of WC-1. This factor was then used to correct both the ‘Prague’ secondary standard and the unknowns.
LA-ICP-MS Elemental Mapping:
LAIPCMS elemental mapping was conducted to identify alteration and different growth zones. Before elemental mapping, the surface of samples was gently re-ground (using 2000 grit sandpaper) to just below the laser ablation pits. Following this the surface was re-polished (using a 3μm polishing cloth as before). Maps were created at the University of Adelaide using an ASI resolution LR Laser Ablation System coupled to an Agilent 7900 mass spectrometer (i.e. the same as U-Pb analysis). A square laser beam of 91x91μm was used to create line rasters on selected areas of calcite samples. Data reduction was conducted using Iolite software [Paton et al. , 2011]. Elemental map data was produced using the Monocle plugin for Iolite [Petrus et al. , 2017]. In more detail, polygons, termed regions of interest (ROI) [Petrus et al. , 2017] surrounding to ablation spots were used to query elemental concentrations. Some spot analyses were removed based on anomalous chemistry, particularly high Al and U.