德兴含铜埃达克质斑岩的地球化学特征、成因及地质意义

Geochemical characteristics,petrogenesis and its geological significance of adakitic porphyries from the Dexing copper deposit,Jiangxi Prvince

德兴斑岩铜矿位于扬子地块江南隆起带东缘,含矿斑岩类型为花岗闪长斑岩。岩石主矿物组合为斜长石(中长石、更长石)+石英+钾长石+角闪石+黑云母,常见副矿物为磁铁矿、磷灰石、榍石、钛铁矿和锆石。斑岩主量元素具有高硅(SiO2=63.59%)、高铝(Al2O3=15.54%)、低镁(MgO=2.2%)的特征,岩石富钾贫钠(K2O=3.06%;Na2O=3.67%),高K2O/Na2O(0.89)比;ALK=6.66%,A/CNK=1.086,σ=2.18,A.R=2.07,显示岩石为弱过铝质高钾钙碱性系列;稀土元素特征表现为轻稀土富集(121.81×10-6),重稀土亏损(8.8×10-6),具有较大的LREE/HREE比值(13.93);微量元素表现为富集大离子亲石元素LILE(Rb、Ba、La、Sr)和亏损高场强元素HFSE(Nb、Ta、Y),具低Y(11.21×10-6)和Yb(1.23×10-6)含量特征,有较高Sr/Y(57.29)、La/Yb(28.93)比值,具较高的87Sr/86Sr比值(>0.7040),弱的负Eu异常(δEu=0.91),以及负εNd值等特征,表明德兴花岗闪长斑岩为"C"型高钾钙碱性埃达克岩,埃达克岩浆来源于活动陆缘加厚下地壳的部分熔融。

The Dexing porphyry copper deposit is located to the eastern part of Jiangnan paleouplift in the Yangtze landmass,and the rock type of copper-bearing porphyries is granodiorite porphyry with the major mineral assemblage consisted of plagioclase（andesine,oligoclase）＋ quartz＋ potassium feldspar＋hornblende＋ biotite and some accessory minerals consisted of magnetite,apatite,titanite,ilmenite and zircon.The granodiorite porphyries are geochemically characteristic of higher silicon（SiO2=63.59%）,higher aluminum（Al2O3=15.54%）,lower magnesium（MgO=2.2%）,and are rich in potassium and poor in sodium（K2O=3.06%;Na2O=3.67%）with higher K2O/Na2 O ratio（0.89）,rocks belong to weak peraluminous high-K calc-alkaline series,ALK=6.66%,A/CNK=1.086,σ=2.18,A.R=2.07,showing that the rocks belong to weak peraluminous high-k calc-alkaline series.The granodiorite porphyries are obviously rich in LREE（LREE=121.81×10-6）and LILE（Rb,La,Ba,Sr）,and depleted in HREE（HREE=8.8×10^-6）and HFSE（Nb,Ta,Y）,with higher LREE/HREE ratio（13.93）.The geochemical characteristics of trace elements are show by lower Y（11.21×10^-6）and Yb（1.23×10^-6）,and with higher Sr/Y（57.29）and La/Yb（28.93）,higher 87Sr/86 Sr（0.7040）and weakly negative Eu anomaly（δEu：=0.91）negativeεNd.Through the analysis of petrological and geochemical characteristics,it is considered that the Dexing granodiorite porphyries belong to the＂C＂type high-K calc-alkaline adakites,which were formed from partial melting of the thickened lower crust at active continental margin.