College of Earth Sciences，Jilin University，Changchun 130061，China

Erdaohezi lead- zinc deposit belongs to the Derbugan metallogenic belt lying on the northwestern Hailaer- Genhe Mesozoic volcanic basin， located on the western slope of the Da Hinggan Mountains． The deposit is considered as one of the hypabyssal low- temprature hydrothermal lead- zinc deposits associated with volca- nism． In order to lay the foundation on studying its diagenesis and mineralization ages， the detailed studies were carried out by dating the host rocks (i.e. rhyolitic lithic- crystal tuffs) using zircon LA- ICP- MS U- Pb method． The dating results show three groups of ages． The first group is the captured zircons (the weighted mean 206 Pb/ 238 U age as 175.6 ± 2.3 Ma，MSWD = 0.70，n = 3)． The second group can be regarded as the rock- forming age (the weighted mean 206 Pb/ 238 U age as 165.3 ±1.9 Ma，MSWD =2.40，n =14)． The third group should represent the late stage of the magmatic evolution (the weighted mean 206 Pb/ 238 U age as 161． 0 ± 3.1 Ma，MSWD =0.86，n =4)． According to the ages and the crystal form or CL image characteristics of zircons， it is determined that the diagenesis occurred in the late Middle Jurassic． Based on the regional geology and geo- chronological research，the acidic pyroclastic rocks are space accompaniment and time connection with the Tamu- langou Formation intermediate- mafic volcanic rocks． Both of them constitute the host rocks of the deposit togeth- er． The rock combination also provides favorable conditions for large- scale silver，lead and zinc mineralization in this area．