内蒙古双尖子山银多金属矿床花岗斑岩年代学、地球化学特征及构造意义

本文对内蒙古双尖子山银多金属矿床花岗斑岩进行了锆石SHRIMP U-Pb定年,并对花岗斑岩的主量元素、微量元素组成进行了分析研究。结果显示,双尖子山花岗斑岩加权平均年龄为(133.4±1.2)Ma,为大兴安岭南段早白垩世岩浆活动集中期产物;花岗斑岩SiO_2含量为68.81%~70.05%,低MgO、TiO_2,K_2O/Na_2O为0.97~1.27,较为富钾;A/CNK在0.94~1.12之间,属准铝-弱过铝系列;富集Rb、Th、U、K等大离子亲石元素(LILE),亏损Sr、P、Ti等高场强元素(HFSE);稀土总量ΣREE中等,δEu为0.55~0.62,Eu中等负异常。本文认为双尖子山银多金属矿床为多期次叠加的岩浆热液型矿床,160Ma和133Ma可能分别是岩浆活动的两个高峰期。花岗斑岩形成于陆内晚造山期-造山期后的伸展环境,蒙古-鄂霍次克洋俯冲板片在深部断离,引发软流圈物质上涌,这是导致大兴安岭南段早白垩世岩石圈伸展环境的主要机制。

Zircon U-Pb dating and geochemistry of the granite porphyry from the Shuangjianzishan silver polymetallic deposit in Inner Mongolia and tectonic implications

This paper presents a series of studies on the granite porphyry from the Shuangjianzishan silver polymetallic deposit,including dating of zircon SHRIMP U-Pb,and analysis of major elements and trace elements.The results show that the granite porphyry,a product of active magmatic activity in the southern Dahinggan Mountains during the early Cretaceous,has an age of (133.4--± 1.2) Ma on average.It contains 68.81％ ～70.05％ of SiO2,and small amounts of MgO and TiO2.The K2O/Na2O value is between 0.97 to 1.27,indicating a feature of slight potassium-rich.The A/CNK is between 0.94 and 1.12,which belongs to metaluminous-weak peraluminous series.The lithophylic elements (LILE) such as Rb,Th,U and K are rich,while HFSE such as Sr,P,and Ti are deficit.The total amount of race earth content ΣREE is normal.δEu is between 0.55 to 0.62.Eu is medium negative anomalous.We conclude that the Shuangjianzishan silver polymetallic deposit belongs to the multi-period magmatic hydrothermal deposits.160Ma and 133 Ma are probably the two peak periods of magmatic activity,respectively.The granite porphyry formed under the condition of the intraplate environment of late orogenic and post-orogenic extension.The resulted asthenospheric material upwelling due to the deep break of the subducting plate of Mongolia-Okhotsk is the main mechanism of the intraplate extensional environment during the early Cretaceous in southern Dahinggan Mountains.