Trace Elements of Gangue Minerals from the Banbianjie Ge-Zn Deposit in Guizhou Province, SW China

Abstract

There are many dispersed element-rich Pb-Zn deposits hosted by Paleozoic carbonate rocks in the Middle-Upper Yangtze Block, China. The origin and nature of the ore-forming fluids that formed them are still much debated (syngenetic vs. epigenetic). The Banbianjie Ge-Zn deposit is located in the southeastern margin of the Yangtze Block, SW China. It is a newly discovered medium-sized Zn (Zn metal reserves > 0.39 Mt, @1.78%–9.5% Zn) and large-scale Ge deposit (Ge metal resources > 900 t, @100 × 10−6–110 × 10−6 Ge) in the Western Hunan–Eastern Guizhou Pb-Zn metallogenic belt, SW China. Gangue minerals in the Banbianjie deposit are very developed, including calcite, dolomite and barite, which are closely associated with sulfides. Hence, the trace elements of gangue minerals could be used to trace the nature, source and evolution of ore-forming fluids, and the ore genesis of this deposit can be discussed. These gangue minerals are nearly horizontally distributed in the plot of La/Ho-Y/Ho, suggesting that they are the products of the same hydrothermal fluids. The total rare earth element (∑REE) contents from calcite and dolomite to barite show an increasing trend, indicating that the REEs in the ore-forming fluids were mainly enriched in barite. Hence, the ∑REE of barite can approximately represent the ΣREE of the hydrothermal fluids, which are quite similar to those of the underlying strata, indicating that the ore-forming fluids were likely originated from and/or flowed through them. The Eu anomalies from dolomite (Eu/Eu* = 0.33–0.66) to calcite (Eu/Eu* = 0.29–1.13) and then to barite (Eu/Eu* = 1.64–7.71) show an increasing trend, suggesting that the ore-forming fluids experienced a shift in the ore-forming environment from reduced to oxidized. Hence, the source of the Banbianjie Ge-Zn deposit is the underlying strata, and the ore-forming physical–chemical condition has experienced a transition from reduction to oxidation during the Ge-Zn mineralization. The ore genesis of the Banbianjie Ge-Zn deposit is most likely a Mississippi Valley-type (MVT) deposit.