Sm‐Nd isochron age and Sr‐Nd isotopes of the calcite from the Nibao gold deposit in the Youjiang Basin, SW China

Abstract

The Youjiang Basin in SW China is the second‐largest Carlin‐like goldfield in the world after Nevada, USA. However, the age and the hydrothermal origin of the gold mineralization are still in controversy, which leads to ambiguities in understanding the geodynamic setting and genetic mechanism of the gold deposition. Nibao is a large, stratabound, and fault‐controlled Carlin‐type gold deposit in the north of the Youjiang Basin. Three ore stages have been recognized in the evolution of the mineralizing hydrothermal fluid, with the stages being characterized by assemblages of the early quartz–porous pyrite, the main quartz–calcite‐apatite–sericite–pyrite–arsenopyrite‐gold, and the late quartz–calcite–fluorite–realgar–orpiment–stibnite. Calcite veins from the main and late ore stage at Nibao are enriched in middle rare earth elements, which is a distinctive characteristic of hydrothermal calcite veins associated with low‐temperature hydrothermal Au‐Sb deposits in the Youjiang Basin, and yield a Sm‐Nd isochron age of 138 ± 1 Ma. The vast majority of the ore stage calcite samples have narrow 87Sr/86Sr ratios and εNd(t) values ranging from 0.708119 to 0.708423 and − 1.1–−3.3, respectively, indicating that the gold‐bearing hydrothermal fluid could be derived from the mixing of mantle and crustal materials. Therefore, we proposed that the gold mineralization during the Early Cretaceous in the Youjiang Basin was triggered by the large‐scale lithosphere extension following the retreat of the subducted Paleo‐Pacific oceanic crust, and the hydrothermal fluid could be originated from the mantle and underwent the contamination of Yangtze upper continental crust.