新疆坡北铜镍矿床铂族元素特征及其对成矿过程的约束

Geochemical Characters of Platinum-group Elements and Its Significances on the Mineralization Process of the Pobei Cu-Ni Sulfide Depositin Xinjiang

坡北铜镍矿床位于塔里木克拉通东北缘,矿石类型主要为星点状和稀疏浸染状,二者之间呈渐变过渡关系。矿石∑PGE含量较低,变化范围为2.47×10^(-9)～404.17×10^(-9);S与Ni之间相关性较差,与Cu、Ir、Ru、Rh、Pt、Pd之间除个别样品外均呈较好的正相关性,表明铂族元素主要赋存于硫化物中。在铂族元素相关性图解上,Ir与Ru、Rh之间呈明显的正相关性,与Pd之间相关性较差,Pd与Ru、Rh、Pt之间均呈很好的正相关性,表明硫化物熔离后未发生明显的单硫化物固溶体(MSS)的分离结晶。100%硫化物计算后,矿石∑PGE平均含量为2806.9×10^(-9),原始地幔标准化图解呈Pd、Pt略富集的左倾型,相对于Ni、Cu明显亏损铂族元素。模拟计算表明坡北矿床多数样品硫化物熔离时"R"因子变化范围为50~500,母岩浆中Ru含量约为0.56×10^(-9),Pd含量为3.6×10^(-9)。研究表明导致铂族元素亏损的主要原因是岩浆源区残留有少量硫化物,成矿过程中深部携带硫化物珠滴的岩浆进入现存空间时岩浆流动速度较慢,硫化物聚集过程中流动分异作用微弱,限制了硫化物的聚集,使硫化物较为分散,可能是导致该矿床金属品位较低的主要原因。

The Pobei Cu-Ni deposit is located in the northeastern margin of Tarimcraton. The main ore types of this deposit contain speckled ore and sparse disseminated ore, which show grad-ual transition relationship. Sulfide ores show low ΣPGE content, which range from 2. 47× 10^-9 to 404. 17× 10^-9. The S has poor correlation with Ni, but has good positive correlation with Ir ,Ru, Rh , Pt and Pd except few samples, which suggest that PGE were mainly occurred in the sufides. The Irshows significant positive correlation with Ru and Rh, but poor relationship with Pd. The Pd shows good positive correlation with Ru, Rh and Pt, which indicate that no obvious-fractional crystallization of monosulfide solid solution （MSS） was occurred after the sulfide liqua-tion. After normalizing to 100% sulfide,the average content of ΣPGE is 2 806. 9 × 10^-9, the primitive mantle standardization diagram show left-oblique type of rich Pd and P t, which are ob-viously depleted in PGE when compared with Ni and Cu. The simulated calculation shows that the “ R” factors of the Pobei deposit are mainly range from 50 to 500, the content of Ru and Pd in parent magma are 0. 36× 10^-9 and 3. 6× 10^-9 , respectively. A small amount of sulfide residual in the magma source is the main cause for the deficit of PGE. The silicate magma contained sulfide would consolidated into the rock and ore at stability dynamic environment, which were unfavour-able for the effective accumulation sulfide, resulting the metal grade is low.