Petrology and Crystallization History of Multiphase Sulfide Droplets in a Mafic Dike from Uruguay: Implications for the Origin of Cu-Ni-PGE Sulfide Deposits
Petrology and Crystallization History of Multiphase Sulfide Droplets in a Mafic Dike from Uruguay: Implications for the Origin of Cu-Ni-PGE Sulfide Deposits
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乌拉圭基性岩脉中多相硫化物液滴的岩石学和结晶历史：对 Cu-Ni-PGE 硫化物矿床起源的启示
DOI：
10.2113/gsecongeo.99.2.365
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发表时间：
2004
期刊：
影响因子：
5.8
通讯作者：
P. Fisher
中科院分区：
文献类型：
--
作者：
H. Prichard;D. Hutchinson;P. Fisher
乌拉圭岩墙群中的基性岩墙中的硫化物气泡在小尺度上复制了在较大的富含铂族元素的镍铜硫化物矿床（如萨德伯里和诺里尔斯克）中观察到的许多特征。这些气泡由不混溶硫化物液体的液滴结晶形成，形成约1 cm大小的卵圆形结晶结构，底部为磁黄铁矿和镍黄铁矿，顶部为黄铜矿和立方铜矿，边缘有含钛磁铁矿磁铁矿首先结晶，然后是富含镍和铁的单硫化物固溶体，它沉到液滴的底部，磁黄铁矿和镍黄铁矿随后从液滴中脱出。液滴上部剩余的富铜液体结晶形成中间固溶体，随后黄铜矿和立方铜矿从中析出。最后，富Cu、Fe、S、Pd、Sn、Pb、Mo、Ag、Bi、Te和Sb的液体结晶为10- 20 μ大小的细脉，填充磁铁矿和邻近硅酸盐矿物的裂隙。穿过磁铁矿的细脉通常在磁铁矿与周围硅酸盐矿物接触处终止于100 μ m大小的近圆形小球，表明细脉填充方向远离气泡中心。气泡中的纹理证据表明，随着结晶的进行和岩脉内不混溶的硫化物液滴下沉（相对于相邻硅酸盐的距离小于1 mm）到已经部分结晶的硅酸盐矿物上，硫化物液体包围并吸收已经固体的磁铁矿颗粒。在气泡的顶部，磁铁矿颗粒被隔离在硫化物液体上方，部分被石英、斜长石和角闪石包围，这是一种晚期岩浆的组合，当液滴下沉时，它被吸入液滴上方产生的空间，比周围的主岩脉更进化。岩脉内气泡的位置与岩脉外部的影响无关，这表明演化的不混溶富铜硫化物液体填充的裂缝与结晶过程有关，而不是与后期构造事件有关，并且铋、碲和锑具有晚期岩浆起源与不混溶硫化物液体的结晶有关。
Sulfide blebs in a mafic dike belonging to the Uruguayan dike swarm replicate, at a small scale, many features observed in larger platinum-group element–enriched nickel-copper sulfide deposits, such as in Sudbury and Noril’sk. These blebs, formed by the crystallization of droplets of immiscible sulfide liquid, form ~1-cm-sized ovoid geopetal structures with pyrrhotite and pentlandite at the base, chalcopyrite and cubanite at the top, and titaniferous magnetite at the margins. Magnetite crystallized first followed by nickel- and iron-rich monosulfide solid solution, which sank to the bottom of the droplets and from which pyrrhotite and pentlandite subsequently exsolved. The remaining copper-rich liquid in the upper part of the droplets crystallized to form an intermediate solid solution from which chalcopyrite and cubanite subsequently exsolved. The final extremely evolved Cu-, Fe-, S-rich, Pd-, Sn-, Pb-, Mo-,Ag-, Bi-, Te, and Sb-bearing liquid crystallized as 10- to 20- μ -sized veinlets filling fractures in the magnetite and adjacent silicate minerals. The veinlets crossing the magnetite often terminate in 100- μ m-sized subrounded globules at the contact of the magnetite and the surrounding silicate minerals, indicating a direction of veinlet filling away from the center of the blebs. Textural evidence in the blebs illustrates that as crystallization proceeded and the immiscible sulfide liquid droplets within the dike sank (a distance of less than 1 mm relative to the adjacent silicate) onto already partially crystallized silicate minerals, the sulfide liquid surrounded and resorbed the already-solid magnetite grains. At the top of the blebs magnetite grains were isolated above the sulfide liquid and partially surrounded by quartz, plagioclase, and amphibole, an assemblage representing a late-stage magma that had been drawn into the space created above the droplets as they sank and which is more evolved than that of the surrounding host dike. The location of the blebs within the dike, isolated from influences external to the dike, indicates both that the fracture filling by evolved immiscible Cu-rich sulfide liquid is related to crystallization processes rather than later tectonic events and that the bismuth, tellurium, and antimony have a late magmatic origin associated with crystallization of the immiscible sulfide liquid.