东准噶尔萨北锡矿SHRIMP锆石U-Pb测年及地质意义

Zircon SHRIMP U-Pb dating and geological implication of the Sabei Tin ore-deposit from Eastern Junggar of Xinjiang,China

萨北锡矿偏碱性黑云母花岗岩中锡石石英脉的SHRIMP锆石U-Pb测年表明,该矿床的锡成矿年龄为(324.2±3.4)Ma,与老鸦泉—红土井子和苏吉泉黑云母花岗岩体的成岩年龄(358.6Ma～304±2Ma)相当;明显早于萨北富碱花岗岩的成岩年龄(306±3Ma～314±5Ma)和富碱花岗岩体中的锡石(碱性角闪石)石英脉成矿年龄(263.6±3Ma～307±11Ma)。因此,萨北矿区至少存在两期锡矿化,而且这两期锡矿成矿时代与东准噶尔后碰撞深成岩浆活动的两个时段年龄(330～310Ma和305～280Ma)和新疆北部后碰撞3个成矿高峰期年龄(340～330Ma,300～285Ma,270～260Ma)相吻合。由此可见,萨北锡矿具成矿多期性,并且与偏碱性黑云母花岗岩-富碱花岗岩岩浆演化关系密切,萨北锡矿区两类锡矿及其赋矿的碱性花岗岩都是新疆北部晚古生代后碰撞岩浆-成矿活动的产物;卡拉麦里地区可能存在与晚古生代后碰撞碱性花岗岩质岩浆有关的锡矿成矿系统。

The Sabei tin ore deposits in the eastern Junggar are mainly developed in the quartz veins of the biotite granites and alkali amphibole-bearing quartz veins of the alkali-enriched granites. Zircons were selected from the cassiterite-bearing quartz veins of the biotite granites for SHRIMP U-Pb zircon dating, and yielded an age of 324.2 ±3.4Ma, implying the tin mineralization age. This age approximates to the formation time of the Laoyaquan-Hongtujing and Sujiquan biotite granitic batholith with 358.6 Ma-304±2 Ma, and obviously is earlier than those of the Sabei alkali-enriched granites （306±3 Ma-314±5 Ma） and alkali amphibole-bearing quartz veins （263.6±3 Ma-307±11 Ma） . We propose the existence of at least two periods of tin-mineralization, which is consistent with the post-collisional plutonic rocks （330 Ma-310 Ma and 305 Ma-280 Ma） in the eastern Junggar and correspond to the first two phases of the three post-collisional mineralization （340 Ma-330 Ma, 300 Ma-285 Ma,270 Ma-260 Ma） in the northern Xinjiang Province. Accordingly, we conclude that, the formation of the Sabei tin ore deposits has a multi-phase feature and is related not only to the alkali granites, but also to the biotite granites; the above two types of tin deposits and related alkali-enriched granites were resulted from the late paleozoic post-collisional magmatic and metallogenic events in the northern Xinjiang Province, a tin metallogenic system associated with late paleozoic post-collsional alkalic granites may be well developed in the Kalamaili ore deposits zone.