Comparison of gold precipitation processes between disseminated and quartz vein ores of orogenic gold deposits: insights from the Linglong gold field, Jiaodong Peninsula, China

Abstract

The presence of disseminated ores and quartz vein ores in orogenic gold deposits, has given rise to an ongoing discourse surrounding the mechanisms of gold precipitation. This study employs trace element analysis and sulfur isotope analysis of pyrite in the orogenic Linglong gold field to comparatively assess the gold precipitation processes. Pyrite in disseminated ores (Pyd) is classified into Pyd1 and Pyd2, with gold primarily hosted in Pyd2, followed by Pyd1. In the context of quartz vein ores (Pyv), pyrite is subdivided into Pyv1, Pyv2, and Pyv3, with gold predominantly hosted in Pyv3. In the context of disseminated ores, the Au and As content is below the solid solubility limit of Au in pyrite, thereby suggesting that gold primarily exists as a solid solution (Au¹⁺). The lg (Co)/lg (Ni) ratios in Pyd are −0.11 ± 1.23, predominantly below 1, suggesting water–rock interactions. The significantly lower ratios observed in Pyd2 (−0.26 ± 1.21) suggest intense water–rock interaction. The Ag/Co ratios in Pyd1 and Pyd2 are 0.074 and 23.65, with relative standard deviations (RSD) of 31.57 and 25.91, respectively, indicating weak fluid boiling. Furthermore, the sulfur isotope values (medians of 5.51 ‰ ± 0.81 ‰) indicate stable oxygen fugacity in disseminated ores. The presence of visible gold in the quartz veins ores of Pyv2 and Pyv3, in contrast to the low gold content observed in the pyrite (median value of 0.03 ppm), further substantiates these observations. The lg (Co)/lg (Ni) ratio for Pyv is 0.98 ± 2.04, which is close to 1, indicating weak water–rock reactions. The Ag/Co ratios in Pyv1, Pyv2, and Pyv3 are 0.0008, 0.009, and 0.09, with RSD values of 10.5, 63.55, and 89.86, respectively. The values of Pyv2 and Pyv3 are significantly higher than those in Pyv, indicating fluid boiling. Furthermore, a decline in sulfur isotope values from 7.6 ‰ ± 0.2 ‰ in Pyv1 to 5.0 ‰ ± 1.2 ‰ in Pyv3 is indicative of an increase in oxygen fugacity. The analysis of pyrite indicates that gold precipitation in disseminated ore is predominantly attributable to water–rock reactions. In contrast, precipitation in quartz vein ores is primarily driven by fluid boiling, which is concomitant with elevated oxygen fugacity.