REE features of arsenian pyrite and vein quartz and their fluid inclusions in the Jinfeng (Lannigou) gold deposit, Guizhou province, China

The Jinfeng, previously known as the Lannigou, is the largest known Carlin-type gold deposit in the Yunnan-Guizhou-Guangxi triangle area, southwestern China. Arsenian pyrite is the most important An carrier mineral, and vein quartz is the product of the most marked hydrothermal alteration in the deposit. The two minerals and their fluid inclusions have the same REE features, showing a pronounced LREE/HREE fractionation with LREE/HREE = 7.95 similar to 31.77 and (La/Yb), = 8.97 similar to 40.49. The LREE shows a fairly pronounced fractionation with La/Sm)(N) = 3.20 similar to 5.29 and has greatly right- inclined patterns; the HREE fractionation is not pronounced, with (Gd/Yb)(N) = 1.41 similar to 3.35, and the patterns are flat. The negative Eu anomaly is pronounced with delta Eu = 0.59 similar to 0.71, and there is a weak negative Ce anomaly with delta Ce = 0.97 similar to 0.98. The REE distribution patterns and characteristic values of inclusions in vein quartz, which represent the characteristics of ore-forming fluids, are quite different from those of mantle-derived basic-ultrabasic rocks of regionally different ages but similar to those of country rocks, ores and arsenian pyrite and its inclusions, showing the characteristics of ordinary sedimentary rocks of the upper crust. This indicates that the ore-forming fluids were mainly derived from the crust rather than from the mantle. The negative Eu anomaly suggests a sub-acid (CO2-rich), reducing ore-forming environment. The weak Cc negative anomaly indicates that hydrothermal ore fluids may have stemmed from basin fluids dominated by sedimentary water and thermodehydration water.