藏南甲玛铜多金属矿床构造变形及其对成矿的制约  

Structural deformation and its constrains of mineralization of the Jiama copper-polymetallic deposit,southern Tibet

作　　者：马士委 许志琴[1,2] 张忠坤 马元[1,2] 赵中宝[1] 庞雪[4] 赵孝武 王慧[5] 

机构地区：[1]中国地质科学院地质研究所,中国地质调查局大陆构造与动力学创新研究中心,北京100037 [2]中国地质大学地球科学与资源学院,北京100083 [3]西藏华泰龙矿业开发有限公司,拉萨850200 [4]天津市地质调查研究院,天津300191 [5]河北区域地质矿产调查研究所,廊坊065000

出　　处：《岩石学报》2016年第12期3781-3799,共19页Acta Petrologica Sinica

基　　金：国家自然科学基金委创新群体项目(40921001);国土资源部公益性行业基金项目(201511022;201211093);中国地质调查局项目(121201102000150005;12120115026861;1212010818094)联合资助

摘　　要：甲玛铜多金属矿位于冈底斯成矿带的中东段，南拉萨地体之上，是一个典型的大型“碰撞型”矿床，矿体类型以矽卡岩型为主伴生角岩型和斑岩型。矽卡岩型铜多金属主矿体呈似层状、厚板状产于早白垩世林布宗组与晚侏罗世多底沟组的层间构造带。通过详细的野外地质调查和钻孔构造的研究发现，新生代以来，甲玛矿区及邻区主要经历了两次区域变形事件。第一次构造变形（D2）与印度一欧亚板块俯冲一碰撞有关，形成了一系列同斜倒转褶皱和逆断层，早白垩世林布宗组与晚侏罗世多底沟组之间形成层间滑脱构造带，为甲玛成矿提供了一定的容矿空间。第二次构造变形（D2）形成了一系列轴面直立或斜歪褶皱，叠加改造D2期褶皱。林布宗组砂板岩和多底沟组灰岩两者接触部位发生由北向南的逆冲剪切，逆冲断层伴随D2褶皱构成了甲玛褶皱一冲断带（JMD，Jiama decollement）。甲玛褶皱一冲断带中糜棱岩的石英、方解石的EBSD组构分析表明，甲玛剪切带形成于中低温（约400℃）环境。与第二次构造变形（D2）密切相关的矿化分为4类：1）产于面理S1层间裂隙和变质砂岩夹层中，随S1面理一起褶皱变形；2）产于平行于面理S1或者切面理S1的石英脉中，均发生褶皱变形；3）产于层间构造带中的矽卡岩，发育条带状构造铅锌矿石和斑铜矿矿石；4）产于陡倾石英脉和碳酸盐脉中，基本来变形。通过对甲玛矿区变形花岗岩脉进行LA—ICP—MS锆石U—Pb测年获得16．4Ma两个年龄，结合前人辉钼矿Re—Os同位素年龄（14．5～15．7Ma）和未变形含矿斑岩脉锆石U—Pb年龄（14．1Ma和14．2Ma），认为第二次构造变形事件可能发生于14～17Ma之间。因此，第二次构造变形应该为甲玛铜多金属矿床的控矿构造，综上初步建立了甲玛矿区的构造一成矿过程，对甲玛进一步找�Jiama copper polymetallic deposit locates in the middle-east part of the Gangdese metallogenic belt and is a typical large ＂collision＂ type deposit. The Jiama porphyry deposit is mainly skarn-type ore bodies associated hornfels-type and porphyry-type ore bodies. The mainly skarn-type ore bodies as a layered thick plate are distributed in the interlayer tectonic belt between Late Jurassic Duodigou Formation and Early Cretaceous Linbuzong Formation. Through detailed filed and core geological observation on the structural deformation features associated with the mineralization, since the Cenozoic, Jiama and its adjacent area have experienced two main regional deformation evens. The first deformation （ D1 ） associated with the subduction-collision of India-Eurasian plates developed a series of isoclinal folds and an interlayer tectonic belt between Late Jurassic Duodigou Formation and Early Cretaceous Linbuzong Formation, which probably provided important space for the development of Jiama deposit. The second deformation （ D2 ） formed a series of vertical or inclined slanting folds and reconstruction the Dt folds. The contact part between Duodigou Formation and Linbuzong Formation existed thrust shearing action. The thrust fault and folds compose Jiama fold-thrust belt （Jiama decollement）. The EBSD fabric result of quartz and calcite in mylonite showed that the Jiama decollement formed in the low temperature （ about 400~C ）. Four types of mineralization were founded spatially associated with the D2 deformation. 1 ） The type 1 exists in the interlayer fracture of S1 foliation and the metasandstone, which is folded with St foliation together. 2） The type 2 is quartz sulfide veins that are parallel or cut across St foliation were folded. 3 ） The type 3 is skarn-type ore bodies distributed in the interlayer tectonic belt. Banded skarn and copper mineralization had developed. 4） The type 4 is mainly quartz sulfide veins or carbonate sulfide veins with no deformation. We report new zircon U-Pb a

关 键 词：变形 EBSD 锆石U—Pb年龄 构造与成矿 西藏甲玛 

分 类 号：P542[天文地球—构造地质学] P597.3[天文地球—地质学]