Abstract
AbstractRutile from a wide range of orogenic gold deposits and districts, including representative world-class deposits, was investigated for its texture and trace element composition using scanning electron microscopy, electron probe microanalysis, and laser ablation-inductively coupled plasma-mass spectrometry. Deposits are hosted in various country rocks including felsic to ultramafic igneous rocks and sedimentary rocks, which were metamorphosed from lower greenschist to middle amphibolite facies and with ages of mineralization that range from Archean to Phanerozoic. Rutile presents a wide range of size, texture, and chemical zoning. Rutile is the dominant TiO2 polymorph in orogenic gold mineralization. Elemental plots and partial least square-discriminant analysis suggest that the composition of the country rocks exerts a strong control on concentrations of V, Nb, Ta, and Cr in rutile, whereas the metamorphic facies of the country rocks controls concentrations of V, Zr, Sc, U, rare earth elements, Y, Ca, Th, and Ba in rutile. The trace element composition of rutile in orogenic gold deposits can be distinguished from rutile in other deposit types and geologic settings. Elemental ratios Nb/V, Nb/Sb, and Sn/V differentiate the rutile trace element composition of orogenic gold deposits compared with those from other geologic settings and environments. A binary plot of Nb/V vs. W enables distinction of rutile in metamorphic-hydrothermal and hydrothermal deposits from rutile in magmatic-hydrothermal deposits and magmatic environments. The binary plot Nb/Sb vs. Sn/V distinguishes rutile in orogenic gold deposits from other geologic settings and environments. Results are used to establish geochemical criteria to constrain the source of rutile for indicator mineral surveys and potentially guide mineral exploration.
Highlights
Rutile occurs in a wide range of rock types including igneous, sedimentary, and high-grade metamorphic rocks as well as in mineral deposits (Force, 1980; Deer et al, 2013)
Rutile from deposits hosted in felsic rocks commonly has higher V concentrations than those from deposits hosted in intermediate rocks
Our study shows that rutile trace element composition changes between middle and upper greenschist facies such that rutile in deposits formed at lower to middle greenschist facies has high rare earth element (REE), Y, Ca, Th, and Ba concentrations and low Zr, Sc, U, and V concentrations compared with deposits formed at upper greenschist to middle amphibolite facies that have low REE, Y, Ca, Th, and Ba concentrations and high Zr, Sc, U, and V concentrations (Figs. 8, 9, 13)
Summary
Rutile occurs in a wide range of rock types including igneous, sedimentary, and high-grade metamorphic rocks as well as in mineral deposits (Force, 1980; Deer et al, 2013). Rutile occurs as a primary magmatic mineral in evolved felsic rocks, alkaline rare-metal granites, and pegmatites (Černý et al, 1999, 2007; Force, 1980; Carruzzo et al, 2006). Rutile commonly occurs in mineralized zones of mineral deposits and in alteration zones proximal to distal of the mineralization (Clark and Williams-Jones, 2004).
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