【摘要】 尕尔穷铜金矿位于班公湖—怒江缝合带西段南缘的措勤—申扎火山岩浆弧内,为与侵入岩有关的矽卡岩型-破碎带型铜金(铁)矿床。在已有石英闪长岩LA-ICP-MS锆石U-Pb测年的基础上,进一步对其进行锆石Hf同位素研究,同时对最新勘查成果显示具有一定成矿潜力的花岗斑岩进行LA-ICP-MS锆石U-Pb定年和Hf同位素研究,确定了两套侵入岩的形成顺序;结合前人总结的岩石地球化学特征,利用Hf同位素对其岩浆源区进行示踪。结果显示:花岗斑岩锆石206Pb/238U年龄加权平均值为(83.2±0.7)Ma,较石英闪长岩晚4 Ma左右,其初始176Hf/177Hf值为0.282 235～0.283 073,εHf(t)值为-17.2～12.5;石英闪长岩锆石初始176Hf/177Hf值为0.282 800～0.283 015,εHf(t)值为3.5～10.5。结合二者地球化学特征显示:石英闪长岩和花岗斑岩可能是同一岩浆系统不同分异阶段的产物,前者主要起源于具有幔源印记的初生地壳,而花岗斑岩具有和石英闪长岩相似的岩浆源区,但明显混入上地壳基底物质;暗示晚白垩世班怒带西段南缘内随着南羌塘—三江复合板片与冈底斯—念青唐古拉板片之间的弧-陆碰撞,先成的具有幔源印记的初生地壳重熔形成岩浆,随着碰撞的继续和岩浆的上涌分异,部分上地壳受挤压或热效应进一步重熔并参与岩浆系统中,由早至晚形成了由幔源特征向幔-壳混合源特征源区逐渐转变的花岗岩演化系列。尕尔穷铜金矿是起源于具有幔源印记的初生地壳的花岗岩的成矿专属性表现。更多还原

【Abstract】 Gaerqiong copper-gold deposit,located in the Cuoqin-Shenza volcanic-magmatic arc in the south edge of western Bangonghu-Nujiang sature zone of Tibet,is a skarn-and breccia type composite copper-gold(iron) deposit related to plutons.On the basis of known LA-ICP-MS zircon U-Pb dating for quartz diorite,we further studied its Hf isotope compositions.Furthermore,we carried out the analyses of zircon LA-ICP-MS U-Pb dating and Hf isotope compositions for a suite of granite porphyry which shows ore-forming potential according to the new exploration results,and based on the newly acquired data we determined the forming sequence as well as their sources of the two episodes of magmas.The results shows that the weight average zircon 206Pb/238U age for granite porphyry is(83.2±0.7)Ma,4 Ma later than quartz diorite.The(176Hf/177Hf)i and εHf(t) values for granite porphyry are 0.282 235-0.283 073 and —17.2-12.5 for granite porphyry,respectively,while the corresponding values are 0.282 800-0.283 015 and 3.5-10.5 for quartz diorite.Based on the Hf isotope and lithogeochemical characteristics,we infer that quartz diorite and granite porphyry are probably the results of different segregation stages within the same magma system.Quartz diorite originated from juvenile lower crust with mantle characteristics and granite porphyry originated from a similar magma source but with some upper crust materials mixed in.It is implied that,during the arc-continent collision between Gandise-Nianqingtanggula plate and southern Qiangtang-Sanjiang composite plate in the south part of western Bangonghu-Nujiang suture zone in Late Crataceous,the formed juvenile crust re-melted into magma.As the continuance of collision and upwelling and segregation of magma,partial upper crust also re-melted and participated into the magma system owing to the compression and heat effect,forming a series of granite with an evolving trend from mantle source to a mixed source of mantle and crust.Gaerqiong copper-gold deposit formed from granite which originated from juvenile crust with mantle signatures.更多还原