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Genesis of emerald at Lened, NWT

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LAKE DJ GROAT LA FALCK H CEMPÍREK Jan KONTAK D MARSHALL D MULJA T

Rok publikování 2017
Druh Článek ve sborníku
Konference MINERAL RESOURCES TO DISCOVER, VOLS 1-4
Fakulta / Pracoviště MU

Přírodovědecká fakulta

Citace
Popis The sources of emerald-forming fluids and chromophores at the Lened occurrence were assessed using field relationships, Ar-Ar dating, whole rock geochemistry, stable isotopes (O, C, S), and mineral chemistry; the results clearly show that the similar to 100 Ma (Ar-Ar muscovite) Lened emerald occurrence is a Type I (igneous) emerald deposit and relates to the proximal similar to 100 Ma (Ar-Ar biotite) Lened Pluton. Stable isotope analyses suggest the veins formed from a primarily granite-derived fluid with lesser components of meteoric and shale-equilibrated fluids. Beryllium and other incompatible elements (including W, Sn, and F) concentrated in evolved magmatic fluid that exsolved during the last stages of crystallization of the Lened pluton. Local overpressuring of vein-forming fluids under a brittle carapace of early pyroxene-garnet skarn led to fracture and emplacement of quartz-calcite-beryl-scheelite-tourmaline-pyrite veins. Less than 5% of the beryl can be considered pale bluish green emerald. Vanadium concentration in the emerald averages 1563 ppm; Cr averages 75 ppm, and Sc attains concentrations of 782 ppm. The key emerald chromophore vanadium was mobilized by metasomatic breakdown of V-rich black shales (averaging 2000 ppm V) that underlie the emerald occurrence.

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