Constraints on Transport and Kinetics in Hydrothermal Systems from Zoned Garnet Crystals

Abstract

Zonation of oxygen isotope ratios, fluorine, and rare earth element abundances across garnet crystals from the Permian Oslo Rift reflect temporal variation of the hydrothermal system in which the garnets grew. A sharp rimward decrease in the (18)O/(16)O ratio (of 5 per mil) across the interface between aluminum-rich garnet cores and iron-rich rims indicates influx of meteoric fluids to a system initially dominated by magmatic fluids. This influx may record the transition from ductile to brittle deformation of the hydrothermally altered rocks. In contrast, fluorine and light rare earth element concentrations increase at the core-rim interface. These data may reflect enhanced advective transport and notable kinetic control on trace element uptake by the garnets during brittle deformation.

REE in skarn systems: A LA-ICP-MS study of garnets from the Crown Jewel gold deposit

“…The next questions are why does this relationship exist, and do these correlations have petrogenetic implications? The partitioning of trace elements, like REE, between a metasomatic fluid and a growing garnet is complex and strongly constrained by crystal chemistry, crystal-liquid equilibrium (e.g., P, T, fluid composition, complexation) as well as by kinetic effects such as growth rate and surface adsorption (e.g., Hickmott and Spear, 1992;Jamtveit and Hervig, 1994;Chernoff and Carlson, 1999;Smith et al, 2004).…”

“…Garnets are known to fractionate HREE from LREE and, in general, they have high Lu/Hf and Sm/Nd ratios, which make them very useful as geochemical tracers and in geochronological studies. Relevant studies include garnets from metamorphic rocks (e.g., Harris et al, 1992;Hickmott and Spear, 1992;Schwandt et al, 1993;Bea et al, 1994Bea et al, , 1997Skublov and Drugova, 2000), garnets from kimberlite rocks as an exploration tool for diamonds (e.g., Hoal et al, 1994;Shimizu and Sobolev, 1995;Zhang et al, 2000;Boyd et al, 2004), garnets in equilibrium with silicate magmas, critical to understanding mantle melting processes (van Westrenen et al, 1999(van Westrenen et al, , 2000(van Westrenen et al, , 2001, thermodynamic properties of REE garnets Pawlak et al, 1999), Lu-Hf and Sm-Nd geochronology (e.g., Mezger et al, 1992;Duchêne et al, 1997;Scherer et al, 1997Scherer et al, , 2000Blichert-Toft et al, 1999;Prince et al, 2000), and a few studies of garnets from skarn deposits (Jamtveit and Hervig, 1994;Nicolescu et al, 1998;Whitney and Olmsted, 1998;Smith et al, 2004). This paper presents in situ Laser Ablation-Inductively Coupled Plasma-Mass Spectroscopy (LA-ICP-MS) REE data for garnets from the Crown Jewel Au-skarn deposit, which will be interpreted, together with trace elements, major elements, and garnet textures, in terms of the factors that control incorporation of REE into garnets, and the petrogenetic implications.…”

Chemical compositions of garnet and clinopyroxene and their genetic significances in Yemaquan skarn iron–copper–zinc deposit, Qimantagh, eastern Kunlun

“…The development of a specific type of skarn depends on the local geological environment, such as the compositions of the sedimentary protolith and associated igneous rocks, depth of formation, and sulfur and oxygen fugacity (Cepedal et al, 2000;Ciobanu and Cook, 2004;Einaudi and Burt, 1982;Grammatikopoulos and Clark, 2006;Kamvong and Zaw, 2009;Lehrmann et al, 2009;Meinert, 1995;Meinert et al, 2005;Shimazaki, 1980). Although skarns cannot be solely characterized by their garnet or clinopyroxene compositions, consideration of both yields a relatively unique fingerprint, which serves as an additional aid in defining environments of formation (Gao et al, 2014a;Gaspar et al, 2008;Jamtveit and Hervig, 1994;Jamtveit et al, 1993Jamtveit et al, , 1995Liu et al, 2013;Smith et al, 2004;Somarin, 2004;Zhai et al, 2013;Zhao, 1997;Zhao et al, 1997Zhao et al, , 2002. Meinert (1992) and Meinert et al (1997aMeinert et al ( , 2005 have discussed the relationship between the ratios of garnet/clinopyroxene and oxidation state within different skarn zonations.…”

Quantification of mixing processes in ore-forming hydrothermal systems by combination of stable isotope and fluid inclusion analyses

“…Fluid mixing is a widely recognized process in upper crustal hydrothermal systems (e.g., Jamtveit and Hervig, 1994;Komninou and Yardley, 1997;Gleeson et al, 2000;Douglas et al, 2003;Gleeson et al, 2003;Upton et al, 2003). Mixing of fluids with different chemical composition and/or oxidation state commonly results in supersaturation of ore and gangue minerals and occurs under conditions far from equilibrium with the host rocks (e.g., Bethke, 1996).…”