Geological and rock geochemical characteristics and U-Pb age of the Ullan lead-zinc deposit in Mongolia

The Ullan lead-zinc deposit in Mongolia, together with Tsav, Jiawula, Chaganbulagen lead-zinc deposits, forms a leadzinc ore concentration area in the Kerulen-Manchuria metallogenic belt. Geological characteristics of the Ullan deposit were described in the aspects of ore-bearing strata, ore-controlling structure, ore-bearing dike, wall rock alteration and orebody characteristics. Rock geochemical studies show that ore-bearing rocks are calc-alkaline volcanic rocks with medium-high Si, medium-Al and high K. The rocks are enriched in large-ion lithophile elements (Ba, Rb, Ce), high field-strength elements (Nb, Ta, Th), Zr and depleted in Li, Sr, Y, with the data ΣREE=412.25×10^-6-999.06×10^-6, (La/Yb)_N=4.41-43.10 and strong Eu anomalies (δ Eu=0.56-0.88). Zircon LA-ICPMS U-Pb isotope ages indicate that wall rocks formed in Late Jurassic (from (150.8±4.4) Ma to (164.7 ±3.1) Ma). The authors also determined that Ullan lead-zinc deposit was formed in a rift setting after the formation of Transbaikal-Da Hinggan Mountains transpressional arc in the period of 140-155 Ma and hence belongs to the hypabyssal hydrothermal vein-type deposit controlled by explosion breccia.