滇西金宝山铂钯矿床S-Os同位素特征及其对成矿过程的制约  

Characteristics of S-Os isotopes and its constraints on the mineralization for the Jinbaoshan Pt-Pd deposit,western Yunnan,China

作　　者：卢宜冠 和文言[1] LU YiGuan;HE WenYan(State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China)

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083

出　　处：《岩石学报》2018年第5期1258-1270,共13页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划(2015CB452605;2009CB421008);北京市优秀博士学位论文指导老师科研项目(20111141501);中国地质调查局地质调查项目(12120114013501);高等学校学科创新引智计划(B07011)联合资助

摘　　要：金宝山铂钯矿床位于扬子板块西缘,毗邻哀牢山造山带北段,是三江成矿带唯一的大型岩浆型铂族元素矿床。以往的研究中,金宝山岩体是否经历地壳混染存在较大争议,制约了对硫饱和机制和矿床成因的认识。前人对矿石中硫化物的S同位素的研究发现绝大部分δ^(34)S值位于1‰~2‰,表现为幔源特征,显示少量或无明显地壳混染作用。本文对含非常规硫化物组合(紫硫镍矿-黄铁矿-黄铜矿)的矿石展开了同位素研究,结合最新研究数据,利用质量平衡原理定量建立了R值(硅酸盐岩浆/硫化物)、百分百硫化物PGE含量和δ^(34)S之间的关系。富PGE矿石具有较高的R值(2000~10000)和PGE含量(如Ir百分百硫化物:2429×10^(-9)~10738×10^(-9)),并具有地幔特征的δ^(34)S范围(1‰~2‰),而贫PGE(如Ir百分百硫化物:449×10^(-9)~2017×10^(-9))的矿石R值较低(500~2000),表现出显著的地壳S同位素的特征(4.4‰~6.7‰)。此外,Re-Os同位素研究表明金宝山铂钯矿床相比一些富硫化物铜镍矿床(如力马河和杨柳坪)具有较低的γOs(21.9~60.5)和较高R值,是大量岩浆与硫化物反应导致的结果,表明其矿石γOs的高低并不能直接反应岩体的地壳混染程度。因此我们在利用S-Os同位素在研究岩浆型铜镍铂族元素矿床时需特别注意,虽然δ^(34)S和γOs的大小通常作为研究地壳混染作用的指示剂,但它们却往往受到矿床类型(铂钯矿床、铜镍矿床)以及矿石类型(富PGE矿石、贫PGE矿石)的影响。特别是对于高R值的铂族元素矿床,矿石呈现出接近幔源特征的δ^(34)S和γOs同位素值并不能排除其在形成的过程中没有地壳物质的加入,而应综合SrNd同位素以及微量元素地球化学特征综合判断是否发生了明显的地壳混染作用。Jinbaoshan Pt-Pd deposit is located in the western margin of Yangtze block,adjacent to the northern part of Ailaoshan orogenic belt. It is the only large magmatic PGE deposit in the Sanjiang region. Previous studies show that whether there is a process of crustal contamination of Jinbaoshan intrusion is still an issue of debate,which constrain the understanding of sulfide saturation and ore genesis. It was suggested that most sulfides from the disseminated ores have δ^34 S values varying from 1‰ to 2‰（ mantle value）,indicating there is no obvious crustal contamination. Combined with published data,this paper reports the S isotopes of the ores with an unusual sulfide assemblage（ violarite-pyrite-chalcopyrite）,and establishes the relationship among R factor（ silicate magma/sulfide ratio）,PGE contents and δ^34 S values by mass balance calculation. Generally,the PGE-rich ores have relatively high R factor（2000 -10000） and PGE contents（ Ir100： 2429 × 10^-9- 10738 × 10^-9）,together with mantle-like δ^34 S values（1‰ - 2‰）,in contrast,PGEpoor ores（ Ir100： 449 × 10^-9- 2017 × 10^-9） have low R factors（500 - 2000） and show crustal S isotopic features（δ^34 S： 4. 4‰ -6. 7‰）. Besides,compared with sulfide-rich Ni-Cu deposits,Jinbaoshan Pt-Pd deposit has low γOs（21. 9 - 60. 5）,which is the result of the sulfide droplet mixed with large amounts of magma,consistent with high R factors. It is suggested that the γOs values of ores cannot reflect crustal contamination degree of the intrusion directly. Thus,it needs to be particularly careful when we apply S-Os isotopes to study magmatic Ni-Cu-PGE deposits. Although the δ^34 S and γOs values of ores are good indicators to evaluate crustal contamination degree,they are also affected by the deposit type（ PGE deposit or Ni-Cu deposit） and ore type（ PGE-rich ore or PGE-poor ore）. The ores have mantle-like S-Os isotopes cannot exclude that the magma did not experience massive crustal contamination. We also need

关 键 词：铂钯矿床 地壳混染 R值 S-Os同位素 金宝山 

分 类 号：P578.12[天文地球—矿物学] P597.2[天文地球—地质学]