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We use a set of analytical techniques for fluid inclusion analysis to determine the bulk properties of the ore fluids from five orogenic gold deposits. The most common ore fluid is a low salinity (0.4–6.5 wt% NaCl) two- to three-phase aqueous-carbonic fluid. Its Th(total) range is 200–400 °C, and total homogenization occurs by bubble or liquid disappearance. A less common aqueous fluid of similar bulk salinity and Th(total) is also documented. Microchemical data show that the ore fluid in the five deposits is chemically uniform and made of Na, subordinate K and B and minor to trace amounts of Cu, As, Li, Sr, Rb, Ba, Cs, Sb and Au (range 0.5–5 µg/g). Thermodynamic modelling carried out for one of the studied deposits indicates that the ore fluid was in equilibrium with vein minerals at the time of gold deposition, and that its vapour phase was distinctly enriched in Au, B, As and Sb. The proposed mechanism of gold precipitation is a combination of fluid decompression and boiling. Combining these results with 3D geometrical reconstructions of one of the studied deposits (Sigma), we estimate that a minimum ore fluid volume of c. 0.1–1.0 km3 is sufficient to generate a world-class orogenic deposit.

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A method was developed for the precise and accurate determination of ovalbumin labelled with p-hydroxy-mercuribenzoic acid (pHMB) using polyacrylamide gel electrophoresis with ns-laser ablation-inductively coupled plasma mass spectrometry. Following systematic optimisation of the ablation process in terms of detection sensitivity, two different quantification strategies were applied: external calibration using standards of the derivatized protein after (13)C(+) normalization and, as a proof of concept, label-specific isotope dilution analysis (IDA) using pHMB enriched in the isotope (199)Hg. Due to the inhomogeneous distribution of the protein within the gel bands, it could be demonstrated that the IDA approach was superior in terms of precision and accuracy. Furthermore, it permits a reliable quantification, if more complex separation protocols are applied, as typically occurring analyte loss and degradation can be compensated for as soon as complete mixture of spike and sample is achieved. The estimated limit of detection was 160 fmol in the case of ovalbumin. In contrast to earlier studies using metals naturally present in proteins, no loss of mercury was observed during separation under denaturing conditions and other sample preparation steps. Using label-specific IDA, the measured isotope ratios in the gel corresponded to recoveries between 95% and 103%.