西藏多不杂铜矿床锶、钕、铪同位素特征及其地质意义

摘要

探讨西藏自治区改则县多不杂铜矿床的成矿物质来源及成矿动力学原理.选择矿区内花岗闪长斑岩全岩、黄铁矿以及锆石样品,测试锶、钕、铪同位素组成.结果显示,多不杂铜矿床样品中的Sr初始值介于幔源镁铁质岩石 Sr 同位素的平均值和壳源硅铝质岩石 Sr 同位素的平均值之间,靠近幔源镁铁质岩石,暗示花岗闪长斑岩的原始岩浆起源于地幔,在上升侵位时与硅铝质地壳物质发生交换,使其具有壳幔混染特征;花岗闪长斑岩具有相对高(87Sr/86Sr)i、低143Nd/144Nd的特征是交代富集地幔的反映,锶同位素的迁移行为与成矿元素相似,携带含矿物质的流体由斑岩体向围岩进行了迁移,并与围岩之间发生充填交代,导致变质砂岩含矿;锆石εHf(t)值基本为正值,且变化范围较大,是有较多幔源组分参与成岩的标志,指示幔源岩浆作用过程中伴有地壳流体的混染.矿床成因综合研究初步揭示多不杂铜矿床是由地幔流体作用引发壳幔物质混染叠加成矿.%The Sr,Nd and Hf isotopic compositions from the granodiorite porphyry rocks,pyrite and zircon samples in Duobuza copper deposit of Tibet are studied so as to discuss the sources of ore-forming materials and dynamic principle of the Duobuza copper deposit.It shows that the initial Sr values of the Duobuza copper deposit is in the average value range of mantle derived mafic rock and values of crust derived siliceous and aluminous rocks,and close to the parameter of mantle derived mafic rocks,suggesting that the primitive magma of granodiorite porphyry is originated from the mantle.In the process of magmatic emplacement,the mantle derived magma is exchange with crustal material of silica alumina and lead to the appearance of mantle crust mixation characteristics.The features of relatively high (87Sr／86Sr)iand low 143Nd／144Nd in the granodiorite porphyry is resulted from the metasomatic enrichment in the mantle.The migration of strontium isotope is similar to that of ore-forming elements,and the metal ore-forming elements in the solution are moved from porphyry body to the wallrocks.In the migration process filling and metasomatism occur and the metamorphic sandstone becomes ore-bearing rock.TheεHf(t)values of zircon is basically positive and varied in a large range,as result of the addition of mantle material in the formation of rock,and from fluid contamination of mantle and crust.The comprehensive study of the ore deposit genesis reveals that the mantle fluid effect leads to crust-mantle hybridism and to the formation of superimposed mineralization.