A LA-ICP-MS U-Pb chronological study of zircons from meta-acidic volcanics in Baiyin orefield, Gansu Province: new evidence for metallogenic age of Baiyin-type massive sulphide deposits.

The Baiyin orefield has Cu-polymetallic ore bodies which are controlled by meta-acid volcanic rocks. Zircons from meta-acid volcanic rocks show features of magmatic zircon. Two main populations of zircons from meta-quartz keratophyre showed average 206Pb/238U ages of 467.3 +/- 2.9 Ma and 414.2 +/-2.7 Ma, respectively. Three main populations of zircons from mylonitised quartz keratophyre showed average ages of 467.1 +/- 2.2, 435.9 +/- 3.6 Ma and 412.6 +/- 2. 1 Ma, respectively. The 467.3 +/-2. 9 - 467.1 +/- 2.2 Ma age represents the time of formation of the meta-acid volcanic rocks, and therefore the metallogenic epoch is Middle Ordovician. The 435.9 +/- 3.6 Ma and 414.2 +/- 2.7 - 412.6 +/- 2.1 Ma ages probably represent the ages of two geological events, mylonisation related to ductile shearing and collision orogeny.
The Baiyin orefield has Cu-polymetallic ore bodies which are controlled by meta-acid volcanic rocks. Zircons from meta-acid volcanic rocks show features of magmatic zircon. Two main populations of zircons from meta-quartz keratophyre showed average 206Pb/238U ages of 467.3 +/- 2.9 Ma and 414.2 +/-2.7 Ma, respectively. Three main populations of zircons from mylonitised quartz keratophyre showed average ages of 467.1 +/- 2.2, 435.9 +/- 3.6 Ma and 412.6 +/- 2. 1 Ma, respectively. The 467.3 +/-2. 9 - 467.1 +/- 2.2 Ma age represents the time of formation of the meta-acid volcanic rocks, and therefore the metallogenic epoch is Middle Ordovician. The 435.9 +/- 3.6 Ma and 414.2 +/- 2.7 - 412.6 +/- 2.1 Ma ages probably represent the ages of two geological events, mylonisation related to ductile shearing and collision orogeny.