东秦岭东沟超大型斑岩钼矿SHRIMP锆石U-Pb和辉钼矿Re-Os年龄及其地质意义

SHRIMP Zircon U-Pb and Molybdenite Re-Os Dating for the Superlarge Donggou Porphyry Mo Deposit in East Qinling,China,and Its Geological Implication

东沟钼矿是在东秦岭钼矿带中于近年新发现的超大型斑岩钼矿床。对其含矿斑岩和矿石进行了成岩成矿年龄精测。采用SHRIMP锆石u—Pb测年技术，对东沟含矿铝质A型花岗斑岩体进行了年代学研究，获得成岩年龄为112±1Ma；采用ICP—MS法测定东沟钼矿中辉钼矿Re-Os同位素年龄，获得模式年龄为116．5±1．7～115．5±1．7Ma；两种方法获得的年龄相近，表明成岩与成矿大致同时形成。东沟斑岩钼矿与东秦岭金堆城、南泥湖、上房沟、雷门沟等斑岩钼矿具有20Ma以上的时差，反映它们形成于不同的地球动力学背景。

Located in the eastern Qinling Molybdenum Belt, the Donggou deposit is a superlarge porphyry Mo deposit discovered in recent years. This study provides the first highly precise dating of the mineralization and rock- forming in the Donggou Mo deposit. The dating of zircon from Donggou aluminous A-type granitic porphyry determined by SHRIMP yields an age of 112±1 Ma. The ^187Re and ^187Os contents of molybdenite from the molybdenum deposit are determined by the Inductively Coupled Plasma Mass Spectrometry （ICP-MS）, with analytical errors of Re and Os between 0.2%-0.3% （20）. The results obtained show that the Re-Os model ages of the deposit are between 116. 5±1. 7- 115. 5±1. 7 Ma, with average age of 116 ±1. 7 Ma. The SHRIMP zircon U-Pb and molybdenite Re-Os isotopic ages are quite close. The results suggest that the Donggou Mo deposit was formed at least 20 Ma later than the Jinduicheng, Nannihu, Shangfanggou and Leimengou porphyry molybdenum deposits in the same molybdenum belt. On the basis of the accurately confirmed ages of the mineralization and rock-forming, their relationships, the ore-forming mechanism and the geodynamic evolution are further discussed. They formed in different tectonic settings. The Donggou Mo deposit formed during the rapid lithospheric thinning of eastern China at ca. 120 Ma, while the other Mo deposits formed when the tectonic transformation predominated at ca. 140 Ma.