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Cracking the Metallogenetic Code for Fijian Epithermal Gold Mineralisation

机译：破解斐济膜状金矿化的成矿码

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摘要

Shoshonite suite (absarokite-shoshonite-banakite) and adakite-hosted epithermal Au deposits are a feature of circum-Pacific magmatism. Fijian examples include Tavua (Emperor) and Tuvatu on Viti Levu. New discoveries of shoshonite suite and adakite-hosted epithermal Au mineralisation have been made in the southern Yasawa Islands and in central-northern and central-western Viti Levu. The Fijian shoshonites define four NE-SW trending suites. The oldest is the northern 7.9-5.0 Ma Yasawa suite, followed by the 4.7-3.5 Ma Sabeto-Tavua-Rakiraki suite in northern Viti Levu, the 4.7-4.2 Ma Yanuca-Vatulele suite approximately 20 km south of Viti Levu and the 3.4 Ma Astrolabe suite approximately 75 km further south. Shoshonite suite lithologies with 3.8-3.0 Ma ages also occur in the Lomaiviti islands between Vatu-Cake and Moala, to the east of Viti Levu, defining a trend oblique to the NE-SW shoshonite belts. Seatura, a 3.3-2.8 Ma ocean island basalt (OIB) volcano, sits at the northern end of the Lomaiviti trend shoshonites. Trace element/isotopic chemistries indicate that shoshonite arc magma genesis involved the melting of a hydrated supra-subduction zone mantle wedge and also a lower mantle-derived plume (OIB) component. The upwelling plume provided heat for melting and possibly Au enrichment. Accessing the melt generation zone associated with the plume required a slab conduit or window. Such slab windows form by tearing during subduction or occur at slab edges. Adakites form by plume-induced slab melting. The four NE-SW Fijian shoshonite suites are interpreted to occur in back-arc extensional zones above a slab window (tear) that migrated southward during rollback of the New Hebrides-Vanuatu subduction zone. The plume (Seatura OIB) that is interpreted to have caused mantle wedge melting and formation of the Lomaviti trend shoshonites was focused along the interface between the north-dipping Vanuatu-New Hebrides subduction zone and the west-dipping Tonga subduction zone, which we have seismically imaged at approximately 400 km depth. Our model 'cracks the metallogenetic code' for shoshonites and adakites and has regional and global implications for Au exploration.
机译：湿山岩套房（Absarokite-Shoshonite-Bakakite）和Adakite托管的膜质AU矿床是循环岩浆广告的一种特色。斐济的例子包括Tavua（皇帝）和Tuvatu在Viti Levu。南亚华群岛南部和中西部的Viti Levu，已经在南部和中西部和中西部地区进行了新发现的舒逊岩套件和Adakite主持的膜状卵形AU矿化。 Fijian Shoshonites定义了四个Ne-SW趋势套房。最古老的是北部7.9-5.0 ma Yasawa套房，其次是4.7-3.5 ma Sabeto-tavua-rakiraki套房位于北方Viti Levu，4.7-4.2 ma Yanuca-Vatulele套房约20公里的Viti Levu和3.4 ma Astrolabe套房套房约75公里。 Shoshonite Suite Lithologies含有3.8-3.0 mA岁的血管群岛，在Vatu-Cake和Moala之间的Lomaiviti岛屿到Viti Levu以东，定义了对Ne-SW Shoshonite皮带的趋势。 Seatura，A 3.3-2.8 Ma海岛玄武岩（OIB）火山，坐落在洛马力潮流潮流岩的北端。痕量元素/同位素化学表明，湿岩弧岩浆成因涉及水合的上俯冲区搭式垫片的熔化以及较低的披露羽流（OIB）组分。升温羽流提供熔化和可能是富含富集的热量。进入与羽流相关的熔融产生区域需要板条导管或窗口。通过在俯冲期间撕裂或在板坯边缘发生这种板坯形式。通过羽流诱导的板坯熔化形式的Adakites形式。四个NE-SW Fijian Shoshonite套件被解释为在板坯窗口（撕裂）之上的后弧延伸区域，在新的Hebrides-Vanuatu俯冲区回滚期间迁移到南方。被解释为导致地幔楔形熔化和Lomaviti趋势舒蒙特的羽毛（座椅Oib）沿着北杜瓦图鲁 - 新赫布里省俯冲区和西浸汤加俯冲区之间的界面集中了在大约400公里深度上遭受地造成地映像。我们的型号“破解了斯库什蒂岩和Adakites的成分”，并对AU勘探具有区域和全球影响。

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    《PACRIM Congress》|2015年||共8页
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    S Lai; Q Williams;

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