Formation of the Vergenoeg F–Fe–REE Deposit (South Africa) by Accumulation from a Ferroan Silicic Magma
Formation of the Vergenoeg F–Fe–REE Deposit (South Africa) by Accumulation from a Ferroan Silicic Magma
复制标题
Vergenoeg FâFeâREE 矿床（南非）由硅铁岩浆堆积形成
DOI：
10.1093/petrology/egaa010
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发表时间：
2020
影响因子：
3.9
通讯作者：
M. L. Vennemann
中科院分区：
文献类型：
--
作者：
Brandt;Faßbender;M. L. Vennemann
vergeneg F-Fe-REE矿床位于南非古元古代Bushveld大火成岩省（LIP）的中心，是地球上最大的萤石矿床之一，同时也是最不寻常的萤石矿床。通过对富费雅石岩石中费雅石、磁铁矿、钛铁矿、氟磷灰石、萤石和allanite的主微量元素分析，结合费雅石、磁铁矿和钛铁矿的氧同位素数据，揭示了矿床的复杂演化。富铁矾岩的结构和成分特征支持岩浆形成的堆积和强烈的晚期热液叠印。铁矾石与少量富钛磁铁矿、钛铁矿、氟磷灰石和allanite一起在低氧逸度下由高度演化的贫水长英质熔体形成。用铁矾石-流纹岩分配系数重新计算的铁矾石和母熔体的球粒陨石归一化稀土元素（REE）模式显示正趋势，重REE （HREE）相对轻REE （LREE）强富集。除LREE耗竭外，其模式与高分馏高硅REE流纹岩相似，这些流纹岩常出现在硅质lip中。我们认为轻稀土元素的损耗是由副allanite的结晶引起的，而副allanite是堆积中轻稀土元素的主要寄主。根据allanite -流纹岩分配系数重新计算，在费雅石聚集之前，母体熔体的球粒陨石归一化稀土模式与Rooiberg组流纹岩的组成相似，因此记录了与Bushveld LIP的岩石成因联系。高δ 18o值（高达≈7·4‰）与其在流纹岩熔体中结晶一致，该熔体是由Bushveld LIP的基性成员Rustenburg层组的基性熔体广泛分馏形成的。原生萤石与稀有石英一起结晶，第二代铁矾石、磁铁矿和钛铁矿来自稀有的积云间，在堆积的铁矾石之间的空隙中熔化。构造和矿物组成数据以及磁铁矿的δ 18o值普遍为负（-2·9 ~ 0‰），表明vergeneg的主要磁铁矿-萤石矿床与热液叠印有关，热液叠印使岩石进一步富集F和Fe。富氟流体从Bushveld LIP （Lebowa Granite Suite）长英质花岗岩的结晶中释放出来，导致铁矾石广泛蚀变为鲍岭土，并被贫钛磁铁矿和石英所取代。热液叠印与次生萤石和少量氟磷灰石的广泛形成有关。我们对vergeneg矿床的新的岩石成因模型，从原始的法亚理岩堆积中得到约束，表明vergeneg矿床的形成与Bushveld LIP的演化直接相关。
Situated in the centre of the Paleoproterozoic Bushveld Large Igneous Province (LIP) of South Africa the Vergenoeg F–Fe–REE deposit is one of the largest, but at the same time most unusual, fluorite deposits on Earth.In situmajor and trace element analyses of fayalite, magnetite, ilmenite, fluorapatite, fluorite and allanite from fayalite-rich rocks are combined with oxygen isotope data for fayalite, magnetite and ilmenite to unravel the complex evolution of the deposit. Textural and compositional characterization of the fayalite-rich rocks supports a magmatic formation as cumulates and an intense late hydrothermal overprint. Fayalite accumulated together with minor Ti-rich magnetite, ilmenite, fluorapatite and allanite from a highly evolved, H2O-poor felsic melt at low oxygen fugacity. Chondrite-normalized rare earth element (REE) patterns of fayalite and the recalculated parental melts, using fayalite–rhyolite partition coefficients, exhibit positive trends with strong enrichment of the heavy REE (HREE) relative to the light REE (LREE). Apart from the LREE depletion the patterns are similar to those of highly fractionated high-silica REE rhyolites that often occur in siliceous LIPs. We attribute the LREE depletion to crystallization of accessory allanite, the main host of the LREE in the cumulates. Chondrite-normalized REE patterns of the parental melt prior to fayalite accumulation, recalculated using allanite–rhyolite partition coefficients, resemble the composition of the rhyolites of the Rooiberg Group and therefore document a petrogenetic link to the Bushveld LIP. Highδ18O values of fayalite (up to ≈7·4 ‰) are consistent with its crystallization in a rhyolitic melt that has formed by extensive fractionation from basic melts of the Rustenburg Layer Suite, the mafic member of the Bushveld LIP. Primary fluorite crystallized together with rare quartz, and a second generation of fayalite, magnetite and ilmenite from rare intercumulus melt in interstices between cumulate fayalite. Textural and mineral compositional data, as well as the generally negativeδ18O values of magnetite (–2·9 to 0 ‰), are in agreement with the main magnetite–fluorite ore formation in Vergenoeg being related to a hydrothermal overprint, which was responsible for further F and Fe enrichments of the rocks. Fluorine-rich fluids, released from the crystallizing granites of the felsic member of the Bushveld LIP (Lebowa Granite Suite), caused the extensive alteration of fayalite to bowlingite and its replacement by Ti-poor magnetite and quartz. The hydrothermal overprint was associated with the widespread formation of secondary fluorite and minor fluorapatite. Our new petrogenetic model for the Vergenoeg deposit, as constrained from the primary fayalite cumulates, implies that the formation of the Vergenoeg deposit was directly linked to the evolution of the Bushveld LIP.
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影响因子：
3.9
作者：
T. Günther;R. Klemd;X. Zhang;I. Horn;S. Weyer
通讯作者：
T. Günther;R. Klemd;X. Zhang;I. Horn;S. Weyer
南非布什维尔德大火成岩省 Rooiberg 熔岩的地幔来源和岩浆演化
影响因子：
3.5
作者：
Günther;Teschner
通讯作者：
Teschner
影响因子：
3.1
作者：
Whitney, Donna L.;Evans, Bernard W.
通讯作者：
Evans, Bernard W.
影响因子：
5
作者：
C. Bucholz;O. Jagoutz;J. VanTongeren;J. Setera;Zhengrong Wang
通讯作者：
C. Bucholz;O. Jagoutz;J. VanTongeren;J. Setera;Zhengrong Wang
埃及东部沙漠稀有金属和贫瘠花岗岩：地球化学特征和成矿方面
DOI：
--
发表时间：
1993
期刊：
影响因子：
--
作者：
F. H. Mohamed
通讯作者：
F. H. Mohamed