The Study of Gold Mineralization at the Polymetallic Dapingzhang VMS-Type Copper–Gold Deposit, Yunnan Province, China

The Dapingzhang Cu-polymetallic deposit in Yunnan is a volcanic massive sulfide (VMS) deposit, located on the western edge of the Lanping&ndash:Simao block. Recently, gold-rich polymetallic orebodies with significant economic value have been discovered. However, the occurrence and enrichment mechanisms of the gold remain unclear. This study investigates the massive sulfide orebodies (V1) through detailed geological surveys. Techniques such as optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and electron probe microanalysis (EPMA) were used to clarify the occurrence of gold, and to reveal the enrichment mechanisms. The genesis of the orebodies consists of three stages: (I) pyrite&ndash:quartz, (II) pyrite&ndash:chalcopyrite&ndash:sphalerite&ndash:galena&ndash:quartz, and (III) pyrite&ndash:chalcopyrite&ndash:sphalerite&ndash:galena&ndash:quartz&ndash:calcite. Gold precipitated during each of these mineralization stages, and it may be described as multiphase mineralization. Gold predominantly exists as invisible gold (&le:0.1 &mu:m), with minor visible gold as native gold and independent minerals (k&uuml:stelite, electrum, calaverite). Invisible gold mainly occurs as gold microinclusions (Au+) in pyrite, chalcopyrite, and sphalerite. Combined with the previous research, comprehensive analysis determined that deep-circulating seawater, driven by a magmatic hydrothermal system, leaches and dissolves mineralizing materials from underlying volcanic rocks. The mineralizing fluid, mixed with magmatic fluid, migrates upward through volcanic conduits or is expelled to the seafloor. Changes in physicochemical conditions lead to the co-precipitation of gold and sulfides, forming a mineralization structure with lower channel facies and upper eruptive facies.