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Ultramafic intrusions hosting Ni–Cu sulfide mineralization along a suture zone in the southwestern margin of the Amazonian craton, Brazil: Examples from Morro Sem Boné, Morro do Leme and their satellite intrusions
Journal of South American Earth Sciences ( IF 1.704 ) Pub Date : 2021-02-22 , DOI: 10.1016/j.jsames.2021.103240
Jomar Stabili de Farias; Cesar Fonseca Ferreira Filho

This research paper describes several medium-to small-sized ultramafic intrusions located along the Mesoproterozoic Guaporé Suture Zone in the southwestern margin of the Amazonian craton. Apart from minor sheared zones, ultramafic rocks have igneous minerals and textures largely preserved. Metamorphic parageneses of metapelites and amphibolites of country rocks, as well as those from sheared zones of the ultramafic intrusions, are indicative of the amphibolite facies of regional metamorphism. Intersections of disseminated to massive sulfides consisting mainly of pyrrhotite and pyrite are common in the metamorphosed volcanic and sedimentary country rocks. The ultramafic intrusions consist mainly of olivine cumulates with high MgO contents (up to 45.9 wt%) and Mg# (up to 0.84), consistent with the composition of their most primitive olivine (Fo93). The crystallization sequence, dominated by olivine, orthopyroxene and chromite, together with ratios and patterns of incompatible trace elements of ultramafic cumulates, support the interpretation that they originated from a high-MgO magma partially contaminated with crustal rocks. Sulfide mineralization in the ultramafic intrusions comprises different styles of magmatic sulfides associated with cumulate rocks, including contact-type, stratabound-type and conduit hosted mineralization. Significant intersections of interstitial to net-textured sulfides consisting of pyrrhotite, pentlandite and chalcopyrire have variable but generally low Ni–Cu-PGE contents (e.g., ~20 m at 0.5 wt% Ni, 0.1 wt% Cu, and 0.5 ppm Pt+ Pd). The range of tenors of Ni, Cu, Pt and Pd, from moderate to very low, is interpreted as resulting from varying efficiency of equilibration of sulfide xenomelts incorporated from the sulfide-bearing country rocks. The Ni–Cu-PGE mineralized ultramafic intrusions are interpreted to belong to a network of magma conduits and staging magma chambers intruding the sulfide-bearing volcanic-sedimentary sequence. Our results indicate an additional prospective belt of high-MgO Ni–Cu-PGE sulfide mineralized intrusions located in a cratonic margin in Brazil.



中文翻译:

巴西亚马孙克拉通西南缘缝合带沿镍铁硫化物矿化的超镁铁质侵入体:Morro SemBoné,Morro do Leme及其卫星侵入体的例子

这篇研究论文描述了沿亚马逊克拉通西南缘的中元古界瓜珀雷缝合线带分布的几个中小型超镁铁质侵入体。除了较小的剪切带,超镁铁质岩石还保留了火成岩矿物和质地。乡村岩石的变质岩和闪石的变质同生,以及超镁铁质侵入岩的剪切带中的变质同生,指示了区域变质的闪石相。在变质的火山岩和沉积岩中,常见的是散布到块状硫化物的相交点,主要由黄铁矿和黄铁矿组成。超镁铁质侵入岩主要由MgO含量最高(至多45.9 wt%)和Mg#(最高至0.84)的橄榄石堆积物组成,与其最原始的橄榄石(Fo93)组成一致。由橄榄石,邻苯二茂铁和铬铁矿为主的结晶序列,以及超镁铁质堆积物的不相容微量元素的比率和模式,支持了这样的解释:它们源自部分被地壳岩石污染的高MgO岩浆。超镁铁质侵入体中的硫化物矿化包括与堆积岩石相关的不同类型的岩浆硫化物,包括接触型,地层约束型和导管主控型矿化。由黄铁矿,方铁矿和黄铜矿组成的间隙到净织构硫化物的重要交点具有可变但通常较低的Ni – Cu-PGE含量(例如,在0.5 wt%Ni,0.1 wt%Cu和0.5 ppm Pt + Pd时约为20 m )。Ni,Cu,Pt和Pd的期限范围从中等到非常低,认为这是由于从含硫化物的乡村岩石中掺入的硫化物异种熔体的平衡效率不同而产生的。Ni-Cu-PGE矿化的超镁铁质侵入体被解释为属于岩浆管道和侵入含硫化物火山沉积序列的分段岩浆室的网络。我们的结果表明,位于巴西克拉通边缘的另一条高MgO Ni-Cu-PGE硫化物矿化侵入带。

更新日期:2021-02-25
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