Genesis of the Tuokesai Zn-Pb deposit in the Sayram Massif, Xinjiang, NW China: Constraints from geology, jasperite geochemistry and Si-S-Pb isotopes

Abstract

The Zn-Pb potential of the Sayram Massif has drawn significant attention since the discovery of the large Tekeli SEDEX Zn-Pb deposit, which is located 15 km from the Kazakhstan and Chinese border in Xinjiang. The Tuokesai Zn-Pb deposit was discovered in 2009 in the northern margin of the Sayram Massif, a major Precambrian terrane of the Kazakhstan-Yili Block. The geological characteristics of the ore-bearing strata at Tuokesai are similar to those of the nearby large Tekeli SEDEX mineral system. Tuokesai’s lens-shaped Zn-Pb orebodies are stratiform and conformable with marble of the Neoproterozoic Wenquan Group. The ore-bearing marbles are commonly interbedded with jasperite that is mainly composed of fine-microcrystalline quartz. The ore minerals include sphalerite, galena and pyrite with minor pyrrhotite, and they are mainly fine-grained with a laminate texture. The gangue minerals are mainly calcite and quartz. Both the jasperite’s relatively high δ30SiV-NBS-28 values (1.3 ~ 2.2‰) and it’s REE patterns show a seawater signature, whereas both its Y/Ho ratios (concentrated at 30.48 ~ 48.57) and its weakly positive Eu anomalies imply a minor hydrothermal influx. The jasperite’s Fe-Al-Ti compositions and La/Ce ratios, combined with the lithology of the host Wenquan Group, suggest that the ore-bearing strata were formed in a passive margin basin. The S isotopic compositions of Tuokesai’s Zn-Pb ores (8.1 ~ 20.4‰) suggest that the sulfur was derived from contemporaneous seawater sulfate. The Pb isotopic compositions of the metallic ore minerals (206Pb/204Pb = 17.227 ~ 17.549, 207Pb/204Pb = 15.447 ~ 15.547, 208Pb/204Pb = 36.912 ~ 37.097) indicate that they came from a mixed crustal-mantle source. In summary, Tuokesai is a SEDEX-type Zn-Pb deposit that was formed in a passive margin basin during Neoproterozoic. The Tuokesai deposit’s discovery suggests that the Sayram Massif may represent the eastern extension of the Tekeli metallogenic belt and has a high potential for successful Zn-Pb prospecting.