混合稀释剂法测定岩石样品中Sr-Nd同位素组成——以新疆松喀尔苏铜(金)矿区含矿花岗斑岩为例

Using the Method of Mixing Diluents to Identify the Sr-Nd Isotopic Composition in Rock Samples:Taking Ore-bearing Granite Porphyry in the Songkaersu Copper-Gold Mining Area in Eastern Junggar of Xinjiang as an Example

混合稀释剂法是测定地质样品中放射性同位素组成的重要手段,具有样品用量少、测试精度和灵敏度高等优点。应用混合稀释剂法获取了新疆东准噶尔松喀尔苏铜(金)矿区含矿花岗斑岩的Sr-Nd同位素数据,其中,含矿斑岩样品初始87Sr/86Sr值(ISr)较低且比较分散,变化范围为0.70268~0.71004,均低于大陆地壳ISr平均值(0.719);εNd值较高且为正值,变化范围为+3.8^+8.3,并具有非常年轻二阶段Nd模式年龄,t2DM值在0.4~0.8 Ga之间。Sr、Nd同位素组成与新疆北部富碱侵入岩相似,其源区很有可能是由于幔源岩浆的底侵作用添加到下地壳中,地壳停留时间较短的新生年轻地壳与幔源岩浆发生了源区混合。东准噶尔卡拉麦里成矿带晚石炭世加厚岩石圈的拆沉导致大规模的幔源岩浆底侵作用,碰撞后的伸展环境为成矿物质的向上运移提供了通道,形成了以多金属矿为主的成矿带。

Mixing diluents method was an extremely important way in identifying the composition of radioactive isotopes in rock samples,and it had the advantage of less samples,higher test precision and sensitivity.Therefore, mixing diluents method was applied to obtain date about the Sr-Nd isotopic composition of ore-bearing porphyry in the Songkaersu copper （gold） deposit mining area in eastern Junggar.The 87Sr/86Sr （ISr） initial value was relatively low and decentralized with the range of 0.70268 to 0.71004,which was lower than the average ISr value （0.719） in crust.Additionally,theεNd value was high and positive with the range of＋3.8~＋8.3 as well very young two-stage Nd model ages,and the t2DM value was between 0.4~0.8 Ga.Sr-Nd isotopic composition was similar to the alkali rich intrusive rock in northern Xinjiang.Its source area was likely to be due to the effect of bottom of invasion of the mantle-derived magma adding to the lower crust,and the newborn and young crust with shorter crustal residence time mixed with mantle-derived magma.The delamination of upset the late carboniferous to the lithosphere in east Carboniferous resulted in large bottom of invasion mantle-derived magma.The stretching environment after collision provided the ore-forming materials of upward migration channel,and formed metallogenic belt which was mainly with polymetallic ore.