Abstract
This paper reviews data from numerous publications focused on the physicochemical parameters and chemical composition of ore-forming fluids from orogenic gold deposits formed during various geological epochs. The paper presents analysis of the distribution of the principal parameters of mineralizing fluids depending on the age of the mineralization. Some parameters of the fluids (their salinity and pressure) at orogenic gold deposits are demonstrated to systematically vary from older (median salinity 6.1 wt.%, median pressure 1680 bar) to younger (median salinity 3.6 wt.%, median pressure 1305 bar) deposits. The detected statistically significant differences between some parameters of mineralizing fluids at orogenic gold deposits are principally new information. The parameters at which mineralization of various age was formed are demonstrated to pertain to different depth levels of similar mineralization-forming systems. The fluid parameters of the most ancient deposits (which are mostly deeply eroded) correspond to the deepest levels of orogenic fluid systems. Hence, the detected differences in the salinity and pressure of the mineralizing fluids at orogenic deposits of different age reflect the vertical zoning of the mineralizing fluid systems.
Highlights
Orogenic gold deposits are one of the world’s main groups of gold deposits that provide a source of gold ([1], etc.)
For each group of deposits, we report the state of the fluids, brief characteristics of their phases (H2 O–salt solution, dense gas), and the principal parameters of the fluid inclusions
Notes: * salinity of fluid expressed in wt% NaCl equiv.; ** composition of gas phase of fluid inclusions; Number of determinations is shown in parentheses
Summary
Orogenic gold deposits are one of the world’s main groups of gold deposits that provide a source of gold ([1], etc.). Data on mineral-hosted fluid inclusions from gold deposits have been reported extensively in the economic geology literature during the past four to five decades. This information includes estimates of the composition and P–T parameters of the mineral-forming fluids, and the age of the ore-forming processes. Some publications on multiphase fluid inclusions containing saturated chloride brines quote homogenization temperatures as those when the gas bubble dissolved in the inclusion, despite the halite phase dissolving at a higher temperature Because salinities in these inclusions were calculated from the NaCl solubility relationships, in the publications lacking reported halite dissolution temperatures, these data fall behind the saturation curve of aqueous solution with sodium chloride. To transform information on such inclusions into a reasonably accurate form, we quote their homogenization temperatures as the calculated homogenization temperatures of a saturated NaCl solution whose concentration is as specified in the paper
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