硫同位素在岩浆Cu-Ni-PGE硫化物矿床成因研究中的应用  

The Application of Sulfur Isotope in the Genesis of Magmatic Cu-Ni-PGE Sulfide Deposits

作　　者：汤庆艳 鲍坚 赵瑛 TANG Qing-yan;BAO Jian;ZH AO Ying(School of Earth Sciences, Key Laboratory of Mineral Resources in Western China ( Gansu Province ),Lanzhou University Lanzhou 730000, China)

机构地区：[1]兰州大学地质科学与矿产资源学院甘肃省西部矿产资源重点实验室,兰州730000

出　　处：《矿物岩石地球化学通报》2019年第2期428-437,共10页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：国家自然科学基金资助项目(41872073;41472070);甘肃省科技计划项目(18JR3RA266);兰州大学中央高校基本科研业务费专项资金资助项目(lzujbky-2017-77)

摘　　要：岩浆Cu-Ni-PGE硫化物矿床形成的重要过程是硫化物熔体的熔离,而关键在于成矿岩浆中硫的过饱和。判断岩浆Cu-Ni-PGE硫化物矿床中硫来源最直接有效的方法就是研究其硫同位素特征。当矿床的硫同位素值超出了地幔硫同位素的组成范围,揭示了壳源硫的混入。如果矿床硫同位素值δ^(34)S落入地幔值的范围内,则需要结合围岩硫同位素组成、并考虑岩浆房中是否发生了硫同位素交换反应来进一步判断是否有围岩硫的加入。异常的Δ^(33)S值主要出现在太古宙沉积硫化物中,利用δ^(34)S与Δ^(33)S相结合可识别样品中是否存在太古宙岩石中来源的硫;然而,一些太古宙岩石中硫化物Δ^(33)S值也可以在0‰附近;在一些后太古宙岩石的硫化物中也发现了异常的Δ^(33)S值;因此在根据Δ^(33)S值来判断S是否来源于太古宙岩石时应谨慎。仔细测定围岩和潜在的混染源的硫同位素组成对于准确评价岩浆Cu-Ni-PGE硫化物矿床中S的来源是非常关键的。硫同位素和其他同位素如镍同位素、铜同位素、铁同位素相结合也许对于认识岩浆Cu-Ni-PGE硫化物矿床中成矿物质来源及成矿岩浆演化过程能够提供新的思路。Magmatic Cu-Ni-PGE(platinum group element)sulfide deposits are produced by segregation and concentration of immiscible sulfide liquid from mafic or ultramafic magmas,which depends on the sulfur saturation in the magma.Sulfur isotope is a powerful tracer of the source of sulfur in the genesis of magmatic Cu-Ni-PGE sulfide deposits.Addition crustal S would generally result in sulfur isotopic composition of deposits different from the mantle values.However,if δ34S values are similar to mantle-derived sulfur,the addition of crustal sulfur should be evaluated by sulfur isotope composition of the country rocks and sulfur isotope exchange reaction between magma and country rocks in the magma chamber. Anomalous Δ33S values are found primarily in sulfides in most Archean rocks,the Δ33S values in conjunction with δ34S values provides an effective means in evaluating the contribution of S from the Archean country rocks.However,Δ33S values of sulfides in some Archean rocks may also be near 0‰;and rare occurrences of nonzero Δ33S values have been identified in sulfides from younger rocks,and hence care should be taken in the evaluation of S derivation from Archean rocks based solely on Δ33S values.Systematic study of the S isotope composition of country rocks and potential contaminants are vital in deciphering the sources of sulfur for the formation of magmatic Cu-Ni-PGE sulfide deposits.The combination of multiple sulfur isotopes and other isotopes, such as Ni,Cu and Fe isotopes,may provide new knowledge for the understanding of the source of ore-forming materials and processes of magma evolution.

关 键 词：岩浆Cu-Ni-PGE硫化物矿床 太古宙 成矿物质来源 硫同位素 

分 类 号：P597[天文地球—地球化学]