江西卧龙谷花岗岩和铜厂花岗闪长斑岩的地球化学特征及成因——对赣东北地区铜矿成矿地质背景的制约

Petrology,Geochemistry and Petrogenesis of Wolonggu granites and Tongchang granodioritic porphyries:Constraints on copper metallogenic geological settings in northeastern Jiangxi Province

赣东北地区是江南造山带东北段重要的多金属成矿区。卧龙谷花岗岩体是典型的非铜矿成矿花岗岩体,由二长花岗岩组成,其LA-ICP-MS锆石U-Pb同位素分析揭示其岩浆结晶年龄为133 Ma±1Ma,形成于早白垩世。这些岩石表现出高的初始87Sr/86Sr比值(0.716079-0.719392)和较低的εNd(t)(-6.51--5.14)值,指示其岩浆起源于壳源变质沉积岩部分熔融。铜厂花岗闪长斑岩体是典型的铜矿成矿花岗岩体,主要由花岗闪长斑岩组成,形成于中侏罗世(171Ma±3Ma),表现出很低的初始87Sr/86Sr比值(0.704403-0.704475)、较高的εNd(t)(-1.14-+1.80)和高的Mg#值(28-53),指示铜厂花岗闪长斑岩体可能为俯冲板片和俯冲沉积物部分熔融的产物,并受到幔源物质污染。通过非铜矿成矿卧龙谷花岗岩和成矿的铜厂花岗闪长斑岩的对比,分析中生代花岗质岩浆作用对成矿地质背景的制约,为区域斑岩型铜矿找矿提供找矿标志和基础地质背景资料。

Northeastern Jiangxi Province is a major polymetaUic ore-forming area in northeastern segment of the Jiangnan orogenic belt. Wolonggu granitoid pluton is a typical nonmineralized granite pluton and consists chiefly of monzogranites. LA-ICP-MS zircon U-Pb isotopic dating yields a weighted mean 206pb/238U age of 133Ma±1Ma, which represents the age of magrnatic crystallization and reveals that the granitic pluton was emplaced in Early Cretaceous. Combined with their high initial 87Sr/66Sr values ranging from 0.716079 to 0.719392 and low εNd（t） values ranging from -6.51 to -5.14, the authors hold that the Wolonggu granites were probablyderived from partial melting of metamorphic pelitic rocks from the crustal source region. However, Tongchang granodioritic porphyric intrusion is a classic mineralized granitic pluton and consists mainly of granodioritic porphyries. Emplaced in Middle Jurassic （with crys- tallization age of 171Ma±3Ma）, the Tongchang granodioritic porphyries display low initialSTSr/86Sr values ranging from 0.704403 to 0.704475, high εNd （t） values ranging from -1.14 to ＋1.80 and higher Mg# values of 28-53, suggesting that the magma was possibly derived from partial melting of subducted oceanic slabs and relative sediments, and was polluted by mantle materials during its upward migration. The comparison of features between the nonmineralized granite pluton and the copper mineralized granitic phiton can de- tect the constraint of the Mesozoic granitoid magmatism on copper metallogenic geological settings, which may provide the essential geological data of the geodynamic setting for regional mineralization.