甘肃北山地区二叠纪含铜镍硫化物镁铁-超镁铁质岩体岩浆作用与成矿

In Gansu-Xinjiang Beishan Area, the previous research on the Permian magmatic Ni-Cu sulfide deposits were all focused on the Pobei-Hongshishan district of Xinjiang. This study is going to focus on the newly-discovered Permian Ni-Cu sulfide-bearing mafic-ultramafic intrusion in Liuyuan, Gansu Beishan area. On the basis of detailed field work, a comprehensive study is carried out, including apatite Sr-Nd and zircon Hf-O isotopes, and minerals and whole-rock major and trace elements, to constrain the nature of the mantle source and the progress of magma evolution. This, combined with the zircon U-Pb dating and geochemistry study, will be used to discuss the relationship between magmatism and regional tectonic evolution. The composition of sulfur isotope in sulfide minerals would be analyzed, combined with magma fractional crystallization and the constraint of degree of crustal contamination, to explore main controlling factors of sulfur saturation in sulfide-bearing mafic-ultramafic intrusion. The above results are used to compare with other sulfide-bearing mafic-ultramafic intrusion in Xinjiang Beishan area, and then reveal the Ni-Cu ore-forming potential evaluation in Gansu Beishan. After that, this study is expected to provide suggestion for regional exploration.

在甘-新北山地区，以往对二叠纪岩浆铜镍硫化物矿床的研究均集中在新疆的坡北-红石山地区。本项目针对甘肃柳园地区新发现的二叠纪含铜镍硫化物镁铁-超镁铁质岩体进行研究，在详细的野外和室内工作基础上，通过岩石和矿物的主微量元素和磷灰石Sr-Nd及锆石Hf-O同位素测试分析研究，约束岩体的岩浆源区性质，论证岩浆演化过程；结合锆石U-Pb定年和元素及同位素地球化学研究，探讨岩浆作用与区域构造演化的关系；通过硫化物微区S同位素的分析，结合岩浆分离结晶与地壳混染程度约束，探讨含矿岩体硫饱和的主要控制因素；结合甘-新北山地区含矿岩体地质地球化学综合对比研究，探讨甘肃北山地区二叠纪岩体铜镍矿成矿潜力，为区域矿产勘查提供理论依据。

以往对甘肃北山二叠纪含矿岩体研究薄弱，本项目对骆驼山和西南山镁铁-超镁铁质含矿岩体全岩、造岩矿物主微量元素组成，全岩Sr-Nd以及锆石O-Hf同位素组成，锆石U-Pb年龄进行了系统研究。骆驼山和西南山岩体年龄分别为283 Ma和277 Ma，与新疆北山二叠纪含矿岩体为同期；两岩体氧逸度范围为FMQ +1.0～+1.7，反演的母岩浆含水量分别为3.4%和3.6%，原始岩浆形成于富水源区；两岩体全岩初始87Sr/86Sr分别为0.703919～0.705272和0.704554～0.705329，εNd(t)分别为+0.42～+6.10和-0.14～+6.36，εHf(t)分别为+7.9～+14.1和+7.2～+12.1，且Pb同位素组成相对较低，TiO2/Yb、Nb/Yb等比值较低，表明岩浆源于亏损的地幔源区；轻稀土元素和大离子亲石元素（Ba、Sr、Rb等）的富集、明显的负Nb-Ta-Zr-Hf异常以及La/Nb、Ce/Pb和Th/Yb比值，表明地幔源区先前受到了俯冲相关的交代作用；岩石学特征和Sr-Nd-Hf同位素计算表明，母岩浆经受了中等程度的地壳混染（5～15%），随后经历了分离结晶过程。基于上述，约束了岩体的岩浆源区性质，论证岩浆演化过程，在中亚造山带二叠纪岩体研究中取得了新进展。研究区与新疆北山矿化岩体时代相近，具有相似的地球化学和母岩浆特征及硫化物饱和机制，表明研究区二叠纪镁铁-超镁铁质岩体具有与新疆北山类似的成矿潜力，从而为在北山中东部寻找铜镍硫化物矿床提供了重要信息。