东疆天宇岩浆Cu-Ni矿床的铂族元素地球化学特征及其对岩浆演化、硫化物熔离的指示  

PGE Geochemical Characteristics of Tianyu Magmatic Cu-Ni Deposit:Implications for Magma Evolution and Sulfide Segregation

作　　者：唐冬梅[1,2] 秦克章[1] 孙赫[1,2] 漆亮[3] 肖庆华[1,2] 苏本勋[1,2] 

机构地区：[1]中国科学院矿产资源研究重点实验室,中国科学院地质与地球物理研究所,北京100029 [2]中国科学院研究生院,北京100049 [3]中国科学院地球化学研究所,贵阳550002

出　　处：《地质学报》2009年第5期680-697,共18页Acta Geologica Sinica

基　　金：中国科学院知识创新工程重要方向项目(编号KZCX2-YW-107);国家"十一五"科技支撑计划新疆305项目东天山铜镍矿专题(编号2006BAB07B03-01)资助。

摘　　要：新疆东部天宇镁铁-超镁铁杂岩体位于中天山地块的北部边缘,北侧为塔里木板块前缘活动带——沙泉子深大断裂。该杂岩体由辉长岩、辉石岩、橄辉岩、辉橄岩和橄榄岩组成,橄辉岩、辉橄岩和橄榄岩是主要的Cu、Ni矿赋矿岩相。同位素稀释法测得的铂族元素（PGE）结果显示天宇镁铁-超镁铁岩和铜镍矿石中∑PGE含量低（0.106×10-9~57.369×10-9）,为原始地幔的0.01~1倍。随岩石基性程度的升高,PGE含量略有增高。不同矿化程度的矿石大致表现出随硫化物含量的增多,∑PGE含量增高的趋势。岩石和矿石标准化曲线均表现出正斜率,Pt都为负异常或无异常。Pd/Ir,Cu/Ni投图显示原始岩浆主要为高Mg玄武岩。根据橄榄石和硫化物中Ni和S含量,计算得出天宇铜镍硫化物矿床R值为446~3845,该R值可以形成铜镍矿床,但无法形成铂族元素矿床。矿石中100%硫化物PGE含量仅相当于地幔5%部分熔融形成的岩浆（R=446~3845时）达到硫饱和,发生0.01%硫化物熔离时,剩余岩浆中PGE含量。与高Mg玄武岩的熔融程度不符。通过模拟计算得出,天宇矿区存在同源但R值不同的两种岩浆作用。Tianyu mafic-ultramafic intrusion is located in the northern margin of the Central Tianshan Massif in the eastern Xinjiang and to the south of the Shaquanzi deep-seated fracture, frofit active zone of the Tarim block. The intrusion consists of gabbro, pyroxenite, olivine pyroxenite, pyroxene peridotite and peridotite. The olivine pyroxenite, pyroxene peridotite and peridotite are the main host rocks for the Cu-Ni ores. Using isotope dilution ICP-MS to measure contents of platinum group element （PGE）, the results show that ∑PGE contents （about 0. 106 ×10-6 -57. 369 × 10-6） of mafic-ultramafic complex and Cu-Ni ores are both lower than primitive mantle＇s value. The contents of ∑PGE increased gently with increasing MgO contents. In Cu-Ni ores, PGE increased with the increasing of S contents. Moreover, PGE primitive mantle normalized patterns of rocks and ores are all positive slope and display Pt positive anormaly or no anormaly. Geochemical characteristics of Pd/Ir, Cu/Ni indicates that parental magma of Tianyu mafic ultramafic complex was high-magnesium basalt. Based on the contents of metal Ni and S in olivine and sulfide, the calculated R values of Tianyu deposit vary from 446 to 3845, suggested it was only able to form Cu-Ni deposit but unfavored to form PGE deposit. On the 100% sulfide basis, contents of PGE are equivalent to that of remnants magma formed by 5% partial melting of upper mantle （R=446- 3845） ,reaching sulfur saturation and losing its 0.01 %sulfide and metals, and degree of partial melting is inconsistent with high-magnesium basalt. PGE model calculations suggest that sulfide segregation from magmatic system resulted in depletion of PGE in remnant magma obviously, and there were two parental magmas with different R value from the same source.

关 键 词：天宇 岩浆型Cu-Ni矿 PGE 地球化学 硫化物熔离 东疆 

分 类 号：P595[天文地球—地球化学]