云南中甸地苏嘎印支期斑岩地球化学特征及其成矿标识

Geochemistry and Their Implications for Mineralization of Disuga Indosinian Porphyry in Zhongdian,Yunnan,China

地苏嘎印支期斑岩体位于中甸岛弧东斑岩带的北端,岩性为石英闪长玢岩,与普朗超大型斑岩铜矿的成矿岩体同属于甘孜—理塘洋壳俯冲作用晚期岩浆活动的产物。全岩地球化学特征显示,地苏嘎石英闪长玢岩具有中等的SiO2含量,较高的Al2 O3及全碱(K2O+Na2O)含量。全岩亏损高场强元素,富集大离子亲石元素,稀土元素配分曲线呈典型的右倾状,显示出轻稀土富集、重稀土相对亏损的特点。主量元素和微量元素成矿指示方面的研究结果表明:与普朗38个与成矿有关的石英闪长玢岩的全岩数据相比,地苏嘎石英闪长玢岩具有相对较低的SiO2和Y含量、较高的ΣREE和(La/Yb)N比值,但二者的Al2 O3/(CaO+Na2O+K2O)比值及MnO含量差别不大。在成矿与非成矿斑岩的SiO2-Al2 O3/(CaO+Na2O+K2O)和Y-MnO图解中,地苏嘎石英闪长玢岩与普朗石英闪长玢岩数据投图结果类似。此外,地苏嘎斑岩体在物探异常、化探异常及遥感影像特征上具有明显的矿化标志,同时岩体的剥蚀深度小于侵位深度,有利于矿床的保存。以上研究结果表明地苏嘎斑岩体具有成为斑岩型铜矿床的潜力。

Disuga Indosinian porphyry,proved as quartz diorite porphyry,is located at the north of the easternporphyry belt in Zhongdian island arc.Influenced by subduction of the Ganzi-Litang Ocean,both porphyries from Disuga and Pulang super-large porphyry copper deposit,are products of the same magmatic activity in the late subduction.Studies on major element compositions show that Disuga quartz diorite porphyries contain normal SiO2 but high Al2 O3 and alkali(K2 O+Na2 O)contents.The porphyries are also enriched in large ion lithophile elements(LILEs)and depleted in high field strength elements(HFSEs).Light and heavy rare earth elements are highly fractionated in these porphyries,and they are enriched in LREEs but depleted in HREEs.Compared with 38 chemical data of Pulang ore-bearing quartz diorite porphyries,Disuga quartz diorite porphyries have lower SiO2 and Y,higher∑REE and(La/Yb)Nratio,but similar MnO and Al2 O3/(CaO+Na2 O+K2 O)ratio.In diagrams of SiO2-Al2 O3/(CaO+Na2 O+K2 O)and Y-MnO for ore-bearing and baron porphyries,Disuga porphyries data were ploted in the same area as Pulang.In addition,Disuga porphyries have obvious anomalies of geophysical survey,geochemical prospecting and remote sensing images,which can serve as mineralized indicators.The local denudation predicted was less than the porphyry emplacement in depth,which was more favorable to the ore preservation.The above results indicate that Disuga porphyry intrusion has the potential to hold a certain large scale porphyry copper deposit.