加拿大萨德伯里奈恩地区镁铁-超镁铁岩体特征及其成矿机制

The Characteristics of Mafic-ultramafic Intrusion and Metallogenic Mechanism in the Nairn Area,Sudbury,Canada

加拿大萨德伯里(Sudbury)地区分布一种成因上与萨德伯里陨石撞击事件无关的岩浆铜镍硫化物矿床。该类矿床的形成受古元古代尼帕辛(Nipissing)镁铁-超镁铁侵入岩套控制,其中以莎士比亚(Shakespeare)矿床和奈恩(Nairn)矿床为典型。奈恩岩体在地表出露Ⅰ号和Ⅱ号两个岩体,呈北东走向岩墙式分布,在深部二者合并为一个整体。奈恩岩体的岩浆分异性良好,从岩体底部至顶部具有明显的岩相分带,下部辉石岩相和中部苏长辉长岩相为主要含矿岩相。辉石岩中发育块状-半块状铜镍硫化物;苏长辉长岩中发育浸染状-星散状铜镍硫化物。奈恩岩体中各岩石单元属于钙碱性系列。根据(Mg/<Fe>)对(Mg+<Fe>)/Si变异图、(Mg+Fe)/Ti-Si/Ti图解、(Na_2O+K_2O)对SiO_2变异图、Al_2O_3对SiO_2变异图、FMC图解,奈恩岩体属于镁铁-铁镁质、低铝、弱碱质和低钙(贫钙)岩体。奈恩地区成矿机制概括为四个岩浆演化阶段,第一、第二阶段中的含硫围岩混染作用、双扩散对流作用,对岩浆分异和含硫岩浆的熔离起了重要作用,铜镍硫化物的最终形成主要是在第三和第四阶段完成。

There is a kind of Cu-Ni sulfides deposits in the Sudbury region,Canada,the Shakespear deposit and Nairn deposit as a typical,which are controlled by the Nipissing mafic-ultramafic intrusive suite and unrelated to the Sudbury meteorite impact. The Nairn intrusion exposed I and II blocks,as dikes in NE toward,on the surface,which combined into a whole in deep. Magma differentiation was good in Nairn property,which exhibits clear lithofacies belts from the bottom to the top. Massive-semi massive sulfides distributed in the lower of pyroxenite;disseminated sulfides distributed in the middle part of norite-gabbro. Most of the rock units in the Nairn intrusion belong to the calc-alkaline series. According to the（ Mg / Fe ） on（ Mg ＋ Fe ） / Si variation diagram,（ Mg ＋ Fe） /Ti-Si/Ti diagram,（ Na_2O ＋ K_2O） on SiO_2 variation diagram,Al_2O_3 on SiO_2 variation diagram,FMC diagram,the Nairn intrusion exhibited mafic-femic,low aluminum,weak-alkalic and low calcium（ poor in calcium）. Metallogenic mechanism in the Nairn area can be summarized into four magma evolution phases. Contamination of sulfur wall-rock and development of a double-diffusive interface（ DDI） play an important role in the first and second phase for magmatic differentiation and isolating of sulfur-magma. Cu-Ni sulfides deposition was completed in the third and fourth phase.