Samarium neodymium direct dating of fluorite mineralization

Posted by / 13-Dec-2020 19:48

Samarium neodymium direct dating of fluorite mineralization

Experimental data of REE-carbonate and -hydroxide complexation at elevated temperatures is particularly scarce, although recent simulations predict abundant transportation of REE carbonates in solutions with high CO and low salinity [12].

Fluid-rock and fluid-fluid interactions add further complexity to REE fractionation in natural systems, yet the applicability of experimentally determined partitioning has been implemented in geochemical, physical, and thermal evolution models of magmatic-hydrothermal systems at Strange Lake granitic pluton, Canada [3, 13] and in carbonatites such as those at Bayan Obo, China [14] and Songwe Hill, Malawi [15].

Fluid-rock interactions may affect REE distribution along the fluid pathway, where the availability of REE-complexing agents and the solubility of REE precipitation products will control REE fractionation through retention and precipitation [10].

REE fluorides, carbonates, and hydroxides are strong complexes that can under certain conditions become unstable and thus act as depositional complexes with limited capability to carry REE [5].

This is explained by efficient REE retention in the granite via incorporation in accessory phosphates, zircon, and fluorite and unfavorable conditions for REE partitioning in fluids at the magmatic and early hydrothermal stages.

A noteworthy feature is substantial heavy REE (HREE) enrichment of calcite in the vein system, in contrast to the relatively flat patterns of greisen calcite.

REE-fractionation patterns and fluid-inclusion data suggest that chloride complexation dominated REE transport during greisenization, whereas carbonate complexation contributed to the HREE enrichment in vein calcite.The REE fractionation of the vein calcite is explained mainly by fractional crystallization, where the initially precipitated epidote in the veins preferentially incorporates most of the light REE (LREE) pool, leaving a residual fluid enriched in the HREE from which calcite precipitated.Fluorite occurs throughout the system and displays decreasing REE concentrations from granite towards greisen and veins and different fractionation patterns among all these three materials.The temporal relationship between the intrusion and veins is investigated by a newly developed high spatial resolution Rb-Sr dating technique [16], applied for the first time on hydrothermal veins and greisen mineralization.At the study site (Laxemar, SE Sweden), the country rock is part of the Transscandinavian Igneous Belt (TIB) and is composed of a suite of approximately 1.80 Ga intrusive rocks dominated by granodiorite and quartz-monzodiorite with close temporal and genetic relationships (Figure 1).

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