西秦岭早子沟金矿含矿岩体地球化学特征及成因机制探讨

Geochemistry and discussion of the genetic mechanism of the ore-bearing intrusions in the Zaozigou Gold Deposit,Gansu Province

早子沟金矿是西秦岭地区勘查发现的特大型金矿床之一。在成因上与闪长玢岩、石英闪长玢岩及黑云闪长玢岩密切相关。通过岩相学和岩石地球化学研究,它们属高钾钙碱性岩浆系列,具较高的SiO2(>56%)、Al2O3(>13%)和较低的MgO(<3%)含量,K2O>Na2O;且具低的Sr(<300×10-6)、Yb(<2×10-6)含量;岩石富集LREE和大离子亲石元素(Rb、Ba、Th、K等),而亏损HREE和高场强元素(Nb、Ta、Ti、Yb等),Eu异常不明显或具弱的Eu负异常(δEu=0.75~0.99),微量、稀土元素分配模式具有碰撞型花岗岩元素组合特征,且其曲线具有较好的相似性,表明它们具同源原生岩浆分异演化的特点。元素地球化学特征反映岩石构造环境为岛弧系统的碰撞造山环境,同时也具喜马拉雅型花岗岩的地球化学特征(如贫MgO、Sr和Yb)。依据上述特征并结合区域地质构造特征,认为早子沟金矿含矿岩体是在区域碰撞构造域中,由基性岩浆底侵到加厚的下地壳并诱使下地壳底部发生部分熔融的产物。

Abstract:The Zaozigou gold deposit is one of super-large size gold deposits discovered in the western Qinling area.The origin related to diorite porphyry、quartz diorite porphyry、biotite diorite porphyry。The intrusions belongs to high potassium Ca-alkaline series,high SiO2(>56%)、Al2O3(>13%),low MgO(<3%),K2O>Na2O;low Sr(<300×10-6)、Yb(<2×10-6);The rocks are enriched in LREE and LILE(Rb、Ba、Th、K),depleted in HREE and HFSE(Nb、Ta、Ti、Yb),has weak negative Eu anomalies or lack(δEu=0.75~0.99).The REE and trace elements patterns reveal collision-type granites of the element combination characteristics of collision-type granites in REE and trace elements patterns,and the similitude propert in the curves.It shows they have the homologous primary magma differentiation.The tectonic settings of rocks is collisional orogen setting and Himalaya granite(low MgO、Sr、Yb)in the geochemical characteristics.Based on the above characteristics and the regional geological structure characters,the ore-bearing intrusions were formed by the lower crust partial melting within the mafic magma intruded thickened lower crust,when regional collision tectonics,in the Zaozigou Gold Deposit.