东天山圪塔山口镁铁-超镁铁质岩体地球化学、锆石U-Pb年代学及其对Ni-Cu成矿的指示

Geochemistry and zircon U-Pb geochronology of Getashankou mafic-ultramafic intrusions,eastern Tianshan,and its implication for Ni-Cu mineralization

摘要新疆新近发现的圪塔山口镍铜硫化物矿床位于东天山康古尔一黄山镍铜硫化物成矿带的东端。矿区包含4个镁铁．超镁铁质岩体，其中I、Ⅱ、Ⅲ号岩体均见镍铜硫化物矿化。本文利用SIMS锆石u-Pb法测得I号矿化岩体辉长岩年龄为282．6±1．9Ma。不仅与东天山地区其它含Ni-Cu矿化的镁铁-超镁铁质岩体形成时代一致，而且与塔里木玄武岩、镁铁质岩墙及北山地区的镁铁．超镁铁质岩体形成时限相一致。其形成可能与造山后伸展背景下的地幔柱叠加作用有关。地球化学数据表明圪塔山口岩体具有高Mg特征，除2个辉长岩样品m／f值较低外，其余14个样品集中于2．73—5．05之间，属铁质超基性岩。岩石稀土元素配分模式为右倾式，轻、重稀土比2．64—3．39；含长角闪辉橄岩及部分含长角闪橄辉岩和含长橄辉岩8Eu具正异常，可能与这3个岩相中存在斜长石的结晶有关。微量元素蛛网图表明岩石富集大离子亲石元素Cs、Rb、Ba、K、Sr。富集高场强元素U、Pb，亏损高场强元素n、Nb等特征。主量元素SiO2-（Na20＋K2O）与（FeO^T／MgO）-FeO^T图解、微量元素相关图及微量元素比值相关图说明圪塔山口岩体成岩物质为来源于亏损地幔的钙碱性玄武质岩浆，成岩作用以岩浆结晶分异为主导，并受到地壳的混染作用，具有较好的镍铜硫化物矿床成矿潜力。

The newly-discovered Getashankou Ni-Cu deposit is located in the eastern of the Kanggur-Huangshan ductile shear fracture zone, eastern Tianshan, NW-China. There are four mafie-uhramafic intrusions, of them the intrusion I , II and III are Ni-Cu sulfide bearing intrusions. By high-precision SIMS Zircon U-Pb dating, we obtained the concordant age of 282. 6 ± 1.9Ma （ MSWD = 0. 15） for gabbros of No. I ore-bearing intrusion. The age is not only consistent with the ages of other sulfide bearing marie and uhramafie intrusions in eastern Tianshan area, but also consistent with the age of malie-ultramafic intrusions in Beishan area and the Tarim basalt and marie dyke swarm. Therefore the formations of Getashankou intrusions may be related to the Permian mantle-plume activity add to the post-orogenic processes. The geochemical data shows that the Getashankou intrusions characterized by high MgO contents （ m/f values of 14 samples range from 2. 73 to 5.05, falling into the range of ferruginous uhramafic rocks ）, LREE-rich pattern with the ratio of LREE/HREE ranges from 2. 64 to 3.39, enriched LILE （ Cs, Rb, Ba, K, Sr） and HFSE （ U, Pb）, depleted HFSE （Th, Nb）. The diagrams of SiO2 -（ Na O ＋ K2 O） and （FeOT/MgO）- FeOT, trace elements correlation and its ratio correlation indicate that the magma of Getashankou is ealc-alkaline basaltic which derived from depleted mantle, the diagenesis is mainly controlled by the magmatic crystallization, and contaminated by the crust during upward of magma, and the intrusions have good potential for Ni-Cu sulfide exploration.