沙溪斑岩铜矿地球化学特征及地质意义

Geochemical Features and Geological Application of Shaxi Porphyry Copper Deposit

沙溪斑岩铜矿是我国长江中下游成矿带的一个典型的陆内斑岩型矿床,文章在前人研究的基础上,对矿区岩石地球化学、矿体微量元素等进行了进一步测试分析,研究表明:石英闪长斑岩地球化学特征如下:w(SiO_2)为56.44%~62.69%,w(Al_2O_3)为13.98%~17.29%.岩石样品在K_2O-SiO_2图中落于钙碱性系列及高钾钙碱性系列范围内.样品A/CNK值为0.82~0.99,A/NK值为1.37~1.69,在A/CNK-A/NK图解中属于准铝质范围.沙溪斑岩Sr含量介于242×10^(-6)~1305×10^(-6),Y含量介于4.4×10^(-6)~27.8×10^(-6),Sr/Y比值为10.9~159.1.微量元素蛛网图显示,沙溪斑岩大离子亲石元素K、Rb、Ba、Sr表现出明显富集,高场强元素Zr,Ta,Nb、Ti亏损程度明显.稀土分配曲线显示轻稀土富集,重稀土亏损,稀土总量为31.2×10^(-6)~284.94×10^(-6),δEu=0.7~1.04,Eu弱异常.根据上述岩石地球化学初步认为,沙溪斑岩矿床属于壳幔型陆内斑岩矿床.石英闪长斑岩的形成与岩浆底侵作用和镁铁质下地壳的部分熔融有关.

The Shaxi Copper Deposit, a typical intracontinental porphyry deposit, is located in the middle-lower Yangtze River valley metallogenic belt. This paper focuses on the petrographic geochemistry and the further tests of trace elements and analyses based on the previous studies. The results show that the geochemical features of quartz diorite porphyry are as follows： with SiO2 content of 56. 44% -62. 69%, AlzO3 content of 13.98% - 17.29%. The chemical features of the rocks indicate that they belong to calc-alkaline series and high-K calc-alkaline series. A/CNK = 0. 82 ~ 0. 99, A/NK = 1.37 1.69, the results indicate that they belong to quasi-aluminous series. The Sr content of the Shaxi porphyry ranges from 242 ×10^-6 to 1305×10^-6, the Y content ranges from 4.4 ×10^-6 to 27.8 ×10^-6, and the Sr/Y ratio is 10.9 to 159.1. The trace elements normalized spider diagram shows that the Shaxi porphyry is enriched in LILE Rb and Sr, and depleted in K, Ba, and HFSE （Zr, Hf, Nb and Ti）. Chondrite-normalized REE patterns reveals the enrichment in LREE, heavy losses in HREE, and ∑REE=67.28×10^-6 to 284.94×10^-6, δEu=0. 7-1.04,with small negative anomaly. Based on the above petrological geochemistry research, the Shaxi Porphyry Deposit belongs to crust-mantle intracontinental porphyry deposit. The quartz diorite porphyry possibly derived from partial melting of lowermost crust and replacement of lower crust.