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The Rogart pluton is a typical example of high Ba–Sr granitic magmatism, emplaced in northern Scotland towards the end of the Caledonian Orogeny. It consists of three granitoid facies (tonalite, granodiorite, granite) that are locally associated with large enclaves of coeval mafic appinite. The overall range of compositions is therefore extreme, with MgO from 11.6 to <0.1 wt%, SiO 2 from 47.50 to >73.0 wt%, with relatively high Na 2 O+K 2 O especially for the mafic rocks (up to 8.4 wt%), associated with K 2 O/Na 2 O≈1.5. Trace element abundances vary extensively and coherently, and the typical high Ba–Sr elemental signature of the pluton is also carried by the appinites. This is consistent with a genetic relationship throughout the suite. Sr, Nd and O isotope ratios are sufficiently similar to support this contention, but vary systematically with magma evolution. The appinites were derived from an enriched mantle source ( 143 Nd/ 144 Nd 400 ≈0.51194, 87 Sr/ 86 Sr 400 ≈0.7061) with high δ 18 O (≈+8‰), probably related to active contemporaneous subduction. Quantitative elemental and isotopic modelling suggests that the granitoid magmas evolved from the appinites by crystal fractionation accompanied by minor crustal contamination. Early fractionation from appinite to tonalite was driven by crystallization of pyroxene plus biotite with minor plagioclase, replaced by a feldspar-dominated assemblage to produce granodiorite and granite. The total amount of crust assimilated was less than 25%, highlighting the juvenile nature of the high Ba–Sr granite class.

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(207 words) 11The paradigm for low-sulphidation (LS) volcanic-arc associated mineralization is the active 12 geothermal systems located along the Taupo Volcanic Zone (e.g. Broadlands). However, this 13 analogue is inapt where fluid salinities are consistently in excess of 3.5 wt % NaCl. 14 LS mineralization on Milos (Aegean arc) records high paleofluid-salinities. The δD and δ 18 O 15 data do not exemplify 18 O-shifted meteoric waters-typical of terrestrial geothermal systems. 16Nor is a submarine origin indicated-stable isotope data show mixing between meteoric, 17 seawater and volcanic-arc gases. Strontium isotope data are comparable to a nearby active 18 seawater-entrained geothermal system. These are features seen in hydrothermal systems 19 associated with emergent volcanoes. 20For the Milos LS mineralization, high-salinity fluids show it cannot be explained by a 21 Broadlands-type model. The absence of saliferous sequences and significant intrusive rocks 22 preclude these as salinity sources. The similarities between paleo and active systems in terms 23 of salinity, δD-δ 18 O and strontium isotope systematics strongly suggest that seawater is the 24 main source for Na and Cl. We suggest geothermal systems, containing seawater, associated 25 with emergent volcanoes are an alternative analogue for LS epithermal mineralization. 26 Furthermore, they bridge the gap between submarine, and large-scale terrestrial geothermal 27 systems-the modern analogues for VHMS and epithermal mineralisation in the scheme of 28 intrusion-centered hydrothermal mineralization. 29

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