Abstract:Stromatolitic carbonate in moat-fill of a 1.48 Ga caldera was converted to mineralized calc-silicate skarn by interaction with magma-derived brine at Ketcherside Gap in southeastern Missouri. The skarnrecords early low fO2 conditions similar to those of reduced W and Au skarns. Initial skarn-forming conditions were: PL ≤ 221 bar (22.1 MPa), XCO2 ≤ 0.10, T = 450–;400°C, log fO2 ≈ –30, and log fS2 ≤ –13. Late skarn records combined effects of T↓, fO2↑,fS2↑, XCO2↓, and appearance of an immiscible CO2-rich vapour.… Show more
“…Coexistence of albite and non-perthitic K-feldspar is common in distal skarn and reflects low miscibility of alkali feldspar end-members under skarn-forming conditions (Lowell and Noll, 2001). The variability of the amphibole chemistry was limited in general to the concentration of calcium, magnesium and iron with only minor variations in other elements.…”
“…Coexistence of albite and non-perthitic K-feldspar is common in distal skarn and reflects low miscibility of alkali feldspar end-members under skarn-forming conditions (Lowell and Noll, 2001). The variability of the amphibole chemistry was limited in general to the concentration of calcium, magnesium and iron with only minor variations in other elements.…”
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