Re-Os dating for ore-forming event in the late of Yanshan Epoch and research of ore-forming regularity in Zhongdian Arc.

The Zhongdian arc,which is the southward extension of the Yidun island arc,is an important Cu-Pb-Zn-Mo polymetallic metallogenic province in China.In this region,compared with the Indosinian metallogenic event,the late Yanshanian metallogenic event and ore deposits such as the Xiuwacu Wu-Mo deposit,Relin polymetallic occurrence and Hongshan polymetallic deposit formed in the area in this period are less studied.By using the molybdenite Re-Os dating technique,it was accurately determined that the Xiuwacu ore deposit and Relin ore occurrence formed at 83±1Ma and 81.2±2.3Ma respectively.According to the molyhdenite Re-Os age(77±2Ma)for altered granite and quartz vein type orebodies and the pyrite Re-Os age(75±18Ma)for the skarn type orebodies, it may be inferred that the Hongshan deposit formed mainly in the late Yanshanian.Based on the above-mentioned dating results,the metallogenic characteristics shown by mineralization of the Zhongdian arc may be summarized as follows:the Xiuwacu,Relin and Hongshan deposits(occurrences)are characterized by close mineralization ages,equal spacing,change of metallic minerals from the high-temperature to moderate-temperature mineral assemblages,similar mineralization types and progressive increase of the emplacement depth of their host rocks.These metallogenic characteristics are the result of the continuous evolution of the same tectono- magmato-mineralization.The aforesaid metallogenic characteristics show that the northern part of the Zhongdian arc has relatively good ore prospects.