内蒙古曹四夭钼矿区花岗斑岩地球化学特征及地质意义

曹四夭钼矿床位于华北克拉通北缘凉城断隆东侧,其矿化与多期次侵位的花岗质杂岩体具有密切的时间和空间联系。杂岩体的岩石类型包括:少斑状花岗斑岩、多斑状花岗斑岩、中细粒花岗岩、二长花岗斑岩和正长花岗斑岩等;前人的锆石U-Pb法测年数据表明,矿区岩浆活动可以分为155 Ma、149~140 Ma、134~131 Ma三个期次。本次研究获得矿区少斑状花岗斑岩的锆石LA-ICP-MS U-Pb法测年加权平均年龄为167Ma±1.2Ma,反映矿区可能还存在较早期的岩浆活动(中-晚侏罗世),其可与155 Ma岩浆岩划分为矿区早期的岩浆活动。花岗斑岩体具有高酸度、高钾和高铝质含量特征,总体属于酸性富钾钙碱性系列;花岗斑岩体含铝指数(A/CNK)介于1.20~2.49之间,Tb、Nd、Ga和LREE(Eu除外)富集,Eu、Ti、Sr、P亏损,属于高度分异的A型花岗岩系列。曹四夭花岗斑岩体形成于中-晚侏罗世构造机制转化时期,可能与蒙古-鄂霍次克洋闭合后的后造山伸展有关,为晚侏罗世钼多金属矿化的母岩。

The geochemistry feature and geological significance of granitic porphyry in Caosiyao molybdenum deposit, central Inner Mongolia, China

Caosiyao molybdenum deposit is located in the east side of Liangcheng faulted uplift at the north margin of the North China craton. The Mo mineralization is spatially and temporally closely related to the multi-emplacement of granitic complex. The complex includes less porphyric granitic porphyry and more porphyric granite, fine-to medium-grained granite, monzotic granoporphyry and orthoclase granoporphyry. Previous zircon U-Pb dating shows that magmatic activity can be divided into multiple magmatic episodes:155 Ma, 149~140 Ma and 134~131 Ma. During this study the less porphyric granoporphyry was dated with Zircon LA-ICPMS U-Pb method at weighted age of 167 Ma±1.2 Ma, suggesting that earlier magmatism(middle-late Jurassic) occurred. Together with magmatism of 155 Ma they belong to the earlier magmatism of the study area. The granoporphyry is characteristic of high acidity, K and Al belonging to calci-alkli series. The aluminium-containing index (A/CNK) of the granoporphyry is in range of 1.20~2.49 with concentration of Tb, Nd, Ga and LREE (except Eu) and depletion of Eu, Ti, Sr and P belonging to highly differentiated A type granite. Caosiyao granoporphyry was formed at Middle-Late Jurassic structural transformation period, possibly related to the post orogenic extension related to the post Mongolian Okhotsk ocean closure and is the mother rock of Late Juraddic Mo polymetallic mineralization