A record made of microthermometric data, Raman spectra determinations, spindle stage measurements of volume fractions, and Laser Ablation-ICP-Mass Spectrometric analyses gathered on >800 fluid inclusions from five orogenic Au deposits of various tectonic settings and age show relatively uniform physical-chemical properties of the ore fluid. In most cases, this fluid is represented by a two- to three-phase (aqueous liquid, carbonic liquid, vapour) H2O-CO2-NaCl model fluid with a relatively low bulk salinity, φ=13-50 vol%, and a quite uniform vapour composition (CO2±CH4-N2). Its Th(total) range from values as low as 200 °C (Wattle Gully deposit) to 400 °C (Sigma deposit), and total homogenisation occurs by bubble and liquid disappearance. In one case (Sigma deposit), a H2O-NaCl fluid of similar salinity and Th(total) is documented. LA-ICP-MS data show that the most abundant analyte in these ore fluid is invariably Na, with subordinate K and B, and minor to trace amounts of As, Cu, Sr, Rb, Mg, Mn, Li, Ba, Cs, Sb, and Pb. These trace components are not systematically determined in all the studied deposits or samples. Au has been determined in four high-Th(total) assemblages from Sigma to be in the 0.5-5 μg/g range. By combining a previous quantitative estimation of mineral abundance in the Sigma deposit with the range of B concentrations determined from the Sigma fluid inclusions, we estimate that a total ore fluid volume of 0.1-0.3 km3 was necessary to form that orogenic deposit. This small volume of hydrothermal fluid represents a fundamental constraint on genetic models for this class of deposits.

Physical-chemical properties of Au-bearing hydrothermal fluids from orogenic deposits of distinct age and tectonic settings

GAROFALO, PAOLO;
2011

Abstract

A record made of microthermometric data, Raman spectra determinations, spindle stage measurements of volume fractions, and Laser Ablation-ICP-Mass Spectrometric analyses gathered on >800 fluid inclusions from five orogenic Au deposits of various tectonic settings and age show relatively uniform physical-chemical properties of the ore fluid. In most cases, this fluid is represented by a two- to three-phase (aqueous liquid, carbonic liquid, vapour) H2O-CO2-NaCl model fluid with a relatively low bulk salinity, φ=13-50 vol%, and a quite uniform vapour composition (CO2±CH4-N2). Its Th(total) range from values as low as 200 °C (Wattle Gully deposit) to 400 °C (Sigma deposit), and total homogenisation occurs by bubble and liquid disappearance. In one case (Sigma deposit), a H2O-NaCl fluid of similar salinity and Th(total) is documented. LA-ICP-MS data show that the most abundant analyte in these ore fluid is invariably Na, with subordinate K and B, and minor to trace amounts of As, Cu, Sr, Rb, Mg, Mn, Li, Ba, Cs, Sb, and Pb. These trace components are not systematically determined in all the studied deposits or samples. Au has been determined in four high-Th(total) assemblages from Sigma to be in the 0.5-5 μg/g range. By combining a previous quantitative estimation of mineral abundance in the Sigma deposit with the range of B concentrations determined from the Sigma fluid inclusions, we estimate that a total ore fluid volume of 0.1-0.3 km3 was necessary to form that orogenic deposit. This small volume of hydrothermal fluid represents a fundamental constraint on genetic models for this class of deposits.
2011
“Let’s Talk Ore Deposits”
562
564
P.S. Garofalo; D. Guenther; M. Fricker; D. Bersani
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/109948
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