The origin of most major sulfide Ni-Cu deposits is attributed to the segregation of immiscible sulfide liquids from intraplate silicate melts, in response to assimilation of siliceous or sulfur-bearing rocks. The Älgliden gabbroic dike in the Skellefte district (Sweden) contains Ni-Cu sulfide mineralization that is atypical because it formed in an arc setting and has a high Au content and low Ni/Cu ratio. This association led previously to a model in which the mineralization was linked to the assimilation of Cu-Au porphyry wall rocks. Based on new petrological, geochemical, and S isotope analyses of the dike and its wall rocks, we propose that assimilation of mineralized wall rocks was not instrumental in the formation of the deposit. Instead, we propose that the sulfides segregated during olivine crystallization from an evolved arc basalt and were injected into the dike in an olivine-rich crystal mush. This scenario explains the uniform dissemination of sulfide ores within norites, together with the high Au content and low Ni/Cu ratio of the ores. We propose that sulfide segregation from oxidized arc basalt was triggered by a decrease in the oxidation state of the melt, likely due to the cooling of the silicate melt or to the interaction with meta-sediments rich in organic matter, as proposed for other arc-related Cu-Ni sulfide deposits in Fennoscandia and elsewhere. At Älgliden, melt reduction would have occurred relatively late during magma evolution, leading to the formation of an uneconomic deposit consisting of low Ni ores and lacking massive sulfides.

中文翻译：

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Älgliden Ni-Cu-Au 矿床：俯冲环境中的岩浆硫化物

大多数主要硫化物镍铜矿床的起源归因于不混溶的硫化物液体从板内硅酸盐熔体中分离，以响应硅质或含硫岩石的同化作用。Skellefte 区（瑞典）的 Älgliden 辉长岩脉包含非典型的 Ni-Cu 硫化物矿化，因为它在弧形环境中形成并且具有高 Au 含量和低 Ni/Cu 比。这种关联以前导致了一个模型，其中矿化与 Cu-Au 斑岩围岩的同化有关。根据对堤坝及其围岩的新岩石学、地球化学和 S 同位素分析，我们提出矿化围岩的同化作用对矿床的形成没有帮助。反而，我们提出硫化物在橄榄石结晶过程中从演化的弧形玄武岩中分离出来，并以富含橄榄石的结晶糊注入岩脉。这种情况解释了硫化矿在褐铁矿中的均匀分布，以及矿石的高 Au 含量和低 Ni/Cu 比。我们认为氧化弧玄武岩的硫化物分离是由熔体氧化态的降低引发的，这可能是由于硅酸盐熔体的冷却或与富含有机物的变质沉积物的相互作用，正如其他弧形玄武岩所提出的那样。 Fennoscandia 和其他地方的相关铜镍硫化物矿床。在阿格利登，熔体还原在岩浆演化过程中发生的相对较晚，导致形成由低镍矿石和缺乏块状硫化物组成的不经济矿床。