Metal-organic complex as a Pb/Zn carrier in the formation of Mississippi Valley-Type (MVT) Pb-Zn deposits: A case study of the Mayuan Pb-Zn ore district, the northern margin of the Yangtze Block, Central China

Abstract

The temporal and spatial association of Mississippi Valley-Type (MVT) Pb-Zn deposits and oil/gas reservoirs in foreland basins has been widely recognized worldwide. The genetic relationship between organic matter related to oil/gas and Pb-Zn metals clarifying the formation of MVT Pb-Zn deposits has been documented in literatures. It is well known that organic matter can play an important role in the transportation and accumulation of Pb and/or Zn to form MVT Pb-Zn deposits. However, mechanisms underlying the relationship between organic matter and these metals are still poorly understood. In this study, we employed Soxhlet extraction experiments to compare the organic matter extracted from potential source rocks and bitumen-rich Pb-Zn ores. Our findings show that source rocks contain relatively high hydrocarbon contents, while bitumen-rich Pb-Zn ores are characterized by high non-hydrocarbon components. Among these non-hydrocarbon components, a large amount of oxygen-bearing organic matter is detected and it has the potential to form metal–organic complexes. Through theoretical calculations on metal–organic complexes, we confirmed that oxygen-bearing organic matter was more conducive to complexing metal ions than other kinds organic matters, while ester-type oxygen-bearing organic matter had the highest tendency to form complexes with and release metal ions. Based on these results, we propose a mineralizing model in which organic matter can act as a transport agent for Pb and Zn in a form of the metal–organic complex. This study provides novel insights about the importance of organic matter in formation of MVT Pb-Zn deposits, contributing to a better understanding of the complex processes involved in ore genesis.