南秦岭宁陕地区新铺钼矿地质特征、辉钼矿Re-Os年龄及地质意义

Geological characteristics,Re-Os geochronology of Xinpu molybdenum deposit in Ningshan,southern Qinling and its implications

要新铺钼矿是南秦岭地区近年来发现的一个石英脉型钼矿，矿体主要呈脉状、透镜状分布产于东江口花岗质岩体内的NE向断裂中。矿石类型以石英脉型和碎裂岩型为主，少量钾长石．石英脉型。赋矿花岗闪长岩、石英闪长岩主元素地球化学显示了贫硅（56．85％-65．45％）、富铝（14．59％-15．59％）、高铁（4．81％-6．41％）、高镁（51．3％～60．2％）、高钙（3．63％～5．78％）、低钾高钠（K，OINa，O=0．45—0．71），属于高钾钙碱性和钙碱性系列，A／CNK比值为0．73—0．96，属于准铝质；稀土配分模式显示轻稀土富集，弱负Eu异常；微量元素具有高Sr、低Y、高Ba、高Sr／Y和La／Yb比值。辉钼矿Re-Os等时线年龄为197．0±1．6Ma，表明成矿作用发生于早侏罗世，明显滞后于成岩年龄10～30Ma。综合分析岩石Sr、Nd、Hf同位素、矿区地质特征和区域构造演化，我们认为新铺钼矿的形成可能与赋矿围岩没有直接的成岩联系，赋矿围岩主要形成于晚三叠世洋陆俯冲环境向陆陆碰撞体制转变阶段，由残余洋壳熔融和上覆地幔楔及古老陆壳混染而成的埃达克质岩浆形成，属于同熔型花岗岩；成矿作用发生于晚三叠一早白垩世的陆陆碰撞造山转换到碰撞后伸展阶段，受控于区域NE向构造。

The Xinpu Mo deposit is situated in Ningshan County of southern Qinling and the mineralization hosted in granodiorite. The orebody generally occurs as veins and lenses in faults and cracks inner granodiorite. The ore types are divided into quartz vein type, tectonite-type and K-feldspar quartz vein type. The former two are the major ore type. Main elements analysis of the host granodiorite shows that they are high potassic calc-alkaline and calc-alkaline series, with depleted in SiO2 （56. 85% - 65.45% ）, rich in Al2O3 （ 14. 59% - 15.59% ）, Fe2O3^T（4. 81% -6.41% ）, Mg^#（51.3 - 60. 2）, CaO （3.63% -5.78% ）, low K2O/Na2O （0. 45 -0. 71 ） and metaluminous rock （A/CNK = 0. 73 - 0. 96 ）. The chondrite-normalized REE patterns are characterized by LREE enrichment with middle negative Eu anomalous （δEu = 0. 7 - 0. 83 ）. The trace elements of the host rocks show high content of Sr, Ba and low content of Y, with high in Sr/Y, La/Yb. The Re-Os geochronological dating of five molybdenite separates from the major Mo mineralized bodies gives an isochron age of 197.0 - 1.6Ma and represents the ore-forming time of Mo mineralization belong to Early Jurassic. This age lag behind 10Ma to 30Ma of the emplacement of Late Triassic granitoids in southern Qinling. Base on St, Nd, Hf isotopic compositions of granites and regional tectonic evolution in southern Qinling, we conclude that the host rocks were emplaced during the transition regime from oceanic slab subduction to intercontinental collision. The granitoids belongs to the syntectie granite series and formed by adakitie melts which produced from magma mixing of partial melting of subdueted oceanic crust, overling mantle wedge and Early-Proterozoic upper crust. The Mo mineralization occurred in the intercontinental collision to post-collisional regime. We should pay more attention to Late Triassic to Early Jurassic intermediate-acid pluton for Mo exploration on the future.