A study on the substitution mechanism of trace elements of sphalerites and genesis of the Laodongzhai-Wuzuo Pb-Zn deposit in the Southeastern Guizhou

The Laodongzhai-Wuzuo Pb-Zn deposit is located in the southern section of the Xiangxi-Qiandong metallogenic belt. The Wushou II orebody is one of its main orebodies. The genesis of this deposit has not been clearly understood yet by previous researchers. This article systematically studied the mineral association of the Wushou II orebody and geochemical behaviors of trace elements within the sphalerite, in order to explore the genesis of the deposit. The sphalerites in the Wushou II orebody occurred in two hydrothermal stages. The early-stage sphalerite (Sp1) is mainly light yellow and grayish yellow sphalerite, which occurred commonly in brecciated ores. The late-stage sphalerite (Sp2) is brownish grey and light brownish yellow sphalerite with completed cleavages. The LA-ICP-MS analytical results of trace elements in sphalerites from the Wushou II orebody show that sphalerites of two stages are mainly enriched in Cu, Cd, Ge, and Ga, but relatively depleted in Mn, and In. Based on the binary relationships of main components in sphalerites, it is inferred that there is difference between the substitution mechanism of Cd in Sp1 and that of Cd in Sp2. The substitution mechanism of Cd in Sp1 may be Cd2++Fe2+↔Zn2+ and/or Cd2+↔Zn2+, while that of Cd in Sp2 may be Cd2++Fe2+↔2Zn2+. Ge in sphalerite could have different substitution mechanisms due to its different valence states. Ge occurred mainly as Ge4+ in Sp1 for substituting Zn2+, with the substitution mechanism of Ge4++2Cu+↔3Zn2+. A small amount of Ge occurred as Ge2+ in Sp1 for substituting Zn2+ with the substitution mechanism of Ge2++2Cu+↔2Zn2+. However, Ge occurred as Ge4+ in Sp2 for substituting Zn2+, with the substitution mechanisms of 2Fe2++Ge4++□↔4Zn2+ and/or 4(Cu++Sb3+)+(Ge4++2Ag+)+2□↔13Zn2+. Ga occurred as Ga3+ in both Sp1 and Sp2 for substituting Zn2+, with the substitution mechanism of Cu++Ga3+↔2Zn2+. The formation temperatures of sphalerites in the Wushou II orebody are relatively low. The formation temperatures of Sp1 crystals (129-252 ℃, average 177 ℃) are slightly higher than that of Sp2 crystals (120-228 ℃, average 149 ℃). By comparing previous research results, it is believed that the genetic type of the Wushou II orebody in the Laodongzhai-Wuzuo Pb-Zn deposit belongs to the MVT type of Pb-Zn deposit.