The Nova-Bollinger Ni-Cu sulfide ore deposit is the first economic Ni-Cu-Co sulfide deposit to have been discovered in the Albany-Fraser orogen in Western Australia. The host rocks are mafic-ultramafic intrusive cumulates subdivided into two connected intrusions, designated Upper and Lower. The Upper Intrusion is bowl-shaped and modally layered with alternating peridotite and norite mesocumulate layers, with a Basal Series of dominantly orthocumulate mafic lithologies. The Lower Intrusion is a much thinner, semiconformable chonolith (flattened tube-shaped intrusion) consisting of mostly unlayered mafic to ultramafic orthocumulates. The Lower Intrusion hosts all the high-grade mineralization and most of the disseminated ores. A distinctive plagioclase-bearing lherzolite containing both orthopyroxene and olivine as cumulus phases is a characteristic of the Lower Intrusion and the Basal Series of the Upper. The intrusions differ slightly in olivine and spinel chemistry, the differences being largely attributable to the more orthocumulate character of the Lower Intrusion. Sector zoning in Cr content of pyroxenes is observed in the Lower Intrusion and in the lower marginal zone of the Upper and is attributed to crystallization under supercooled conditions. Symplectite pyroxene-spinel-amphibole coronas at olivine-plagioclase contacts are ubiquitous and are attributed to near-solidus peritectic reaction between olivine, plagioclase, and liquid during and after high-pressure emplacement, consistent with high Al contents in igneous pyroxenes and estimates of the peak regional metamorphism. Original cumulus olivines had compositions around Fo₈₆ and were variably Ni depleted, interpreted as the result of preintrusion equilibration with sulfide liquid. The Upper and Lower Intrusion rocks represent cumulates from a similar parental magma, a high-Al tholeiite with MgO between 10 and 12%, low TiO₂ (0.5–0.6%), and high Al₂O₃ (14–17%). Modeling using alphaMELTS indicates a primary water content of around 2 wt %. The cumulates of both intrusions were derived via multiple magma pulses of liquid-olivine-sulfide slurries with variable amounts of orthopyroxene emplaced into the deep crust at pressures of around 0.7 GPa during the peak of regional metamorphism. The intrusions developed initially as a bifurcating sill, the lower arm developing into the ore-bearing Lower Intrusion chonolith and the upper arm inflating into the cyclically layered Upper Intrusion.

中文翻译：

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西澳大利亚弗雷泽区 Nova-Bollinger Ni-Cu 硫化物矿床：主体侵入体的岩石成因

Nova-Bollinger Ni-Cu 硫化物矿床是在西澳大利亚的 Albany-Fraser 造山带中发现的第一个经济的 Ni-Cu-Co 硫化物矿床。主岩是镁铁质-超镁铁质侵入堆积体，细分为两个相连的侵入体，分别称为上部和下部。上部侵入体呈碗状，呈模态层状，交替出现橄榄岩和诺长岩细晶层，具有以正积层镁铁质岩性为主的基底系列。下部侵入体是一种更薄、半整合的 chonolith（扁平管状侵入体），主要由未分层的镁铁质至超镁铁质正积岩组成。下侵入体拥有所有高品位矿化和大部分浸染性矿石。含有斜方辉石和橄榄石作为积云相的独特的带有斜长石的斜长石是下部侵入体和上部基底系列的特征。侵入体在橄榄石和尖晶石化学中略有不同，差异主要归因于下侵入体的更正累积特征。在下部侵入体和上部下部边缘区观察到辉石 Cr 含量的扇区分区，这归因于过冷条件下的结晶。橄榄石-斜长石接触处的正辉石-尖晶石-闪石日冕无处不在，归因于高压就位期间和之后橄榄石、斜长石和液体之间的近固相包晶反应，与火成辉石中的高铝含量和峰值区域变质作用的估计一致。原始的积云橄榄石在 Fo 周围有成分₈₆和可变镍耗尽，解释为预侵入与硫化物液体平衡的结果。上侵入体和下侵入体岩石代表类似母岩浆的堆积物，即 MgO 含量在 10% 和 12% 之间的高 Al 拉斑沸石、低 TiO ₂ (0.5-0.6%) 和高 Al ₂ O ₃（14-17%）。使用 alphaMELTS 建模表明主要含水量约为 2 wt%。在区域变质作用的高峰期，两次侵入体的累积是通过多次岩浆脉冲的液态橄榄石硫化物浆液产生的，其中不同数量的斜方辉石在约 0.7 GPa 的压力下进入地壳深处。侵入体最初发展为一个分叉的基台，下臂发展为含矿的下侵入体球岩，上臂膨胀为循环层状的上侵入体。