萨北锡矿的SHRIMP 锆石U-Pb定年及其地质意义

新疆东准噶尔萨北锡矿矿体可于黑云母花岗岩中呈锡石石英脉产出，也可于富碱花岗岩中呈锡石碱性角闪石石英脉出现，其分布受NNE和NE走向的断裂构造控制。卡拉麦里成矿带中石英脉及其含矿性变化与花岗岩岩性变化关系密切：沿(N)NW－(S)SE方向，岩性由钙碱性→偏碱性花岗岩→碱性花岗岩演化，矿化（体）由以石英脉型（为主）→锡石石英脉型（为主）→锡石碱性角闪石石英脉型（为主）转变。SHRIMP锆石U-Pb测年表明：黑云母花岗岩中锡石石英脉的锆石年龄为（329.2±1.5） Ma，与老鸦泉－红土井子及苏吉泉黑云母花岗岩基成岩期相近；富碱花岗岩中的锆石年龄为（313±2）～（314±5） Ma，与东准噶尔后碰撞深成岩浆活动期（330～310 Ma）吻合。因此，萨北锡矿成矿成岩时代可分别与新疆北部后碰撞成矿三个高峰期的第一、第二（340～330 Ma、300～285 Ma）高峰期相对应，该成矿作用具多期性，矿化不仅与碱性花岗岩有关，还与黑云母花岗岩成矿关系密切。

Zircon U-Pb Dating of Sabei Tin Deposits and Its Geological Implications

Sabei tin deposits in the eastern Zunghar in Xinjiang occur in the quartz veins of biotite granites and also alkali amphibole-bearing quartz veins of alkali-enriched granites，whose distribution is generally controlled by the NNE- and NE- trending faults in the area.The quartz veins and their mineralization are closely related with the lithological variations in granites in Kalamaili ore deposits zone.The lithology evolves from calc-alkaline，via near-alkali granites，to alkali granites from (N)NW to (S)SE，along with the quartz veins varying from quartz-dominated，via cassiterite-bearing quartz-dominated，to cassiterite-bearing amphibole quartz-dominated.SHRIMP U-Pb zircon dating indicates that the age of the zircon in cassiterite-quartz is （329.2±1.5） Ma，close to the formation time of the Laoyaquan-Hongtujing-Sujiquan biotite granitic batholith; and the age of the zircon in alkaline-enriched granites is （313±2） Ma~（314±5） Ma，in conformity with the active period of post-collisional plutonic rocks (330~310 Ma) in the eastern Junggar.Therefore，the ages of diagenesis and mineralization of Sabei tin deposits correspond respectively to the first (340~330 Ma) and second (300~285 Ma) of the three peak phases of the post-collisional mineralization in the northern Xinjiang Province.This ore formation is of multi-phase type and is not only related to alkali granites but also to biotite granites.