Rare-earth-element enrichment in post-Variscan polymetallic vein systems of the Harz Mountains, Germany
Rare-earth-element enrichment in post-Variscan polymetallic vein systems of the Harz Mountains, Germany
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DOI：
10.1007/s00126-018-0847-8
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发表时间：
2018-10
影响因子：
4.8
通讯作者：
Jonas Alles;A. Ploch;T. Schirmer;Nicole Nolte;Wilfried Liessmann;B. Lehmann
中科院分区：
文献类型：
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作者：
Jonas Alles;A. Ploch;T. Schirmer;Nicole Nolte;Wilfried Liessmann;B. Lehmann
上哈茨山华力西期后重要的Pb-Zn-Cu-Ag多金属脉系中碳酸盐脉石的稀土元素含量（REE+Y，1500 ± 340 ppm;n= 16）明显升高。这种富集是由于方解石中存在丰富的微米级的正长岩包裹体，通过拉曼光谱鉴定。方解石整体分析具有屋顶形PAAS标准化REE模式，具有Eu峰，但没有Ce或Y异常，并具有陡峭的HREE模式。微束分析（电子探针和LA-ICPMS）确定这些模式为占主导地位的synchysite-（Ce-Nd），具有较强的Eu富集的重量百分比范围和LREE/HREE分馏（La/Lu ~ 100，PAAS标准化）。在哈尔茨山多金属矿脉中均发现方解石脉石中的同晶岩成分，这似乎是该地区的一个特征，表明存在一个大规模的中生代流体系统。然而，上（西部）哈尔茨系统没有萤石有更多的稀土元素含量升高，与较低（东部）哈尔茨萤石丰富的系统，稀土元素含量较少。上哈茨系统的碳酸盐脉石的87 Sr/86 Sri约为0.714，εNdiof ~ − 9，而下哈茨系统的碳酸盐脉石的87 Sr/86 Sri约为0.716，εNdiof − 2至− 5。下哈茨山萤石具有较强的正Y异常和可变Eu异常，稀土元素丰度普遍较低，没有稀土矿物包裹体。萤石中的Sr和Nd同位素组成变化很大，表明是一个开放系统（87 Sr/86 Sri，0.710-0.718; εNdi，− 3-− 17）。上哈尔茨山方解石脉石中的同晶矿MREE富集与中国和其他地方的碳酸盐岩相关的轻稀土元素为主的氟碳铈矿相比毫不逊色，并允许一个有趣的视角作为铅锌矿开采的副产品。
Carbonate gangue in historically important post-Variscan polymetallic Pb-Zn-Cu-Ag vein systems in the Upper Harz Mountains has elevated rare earth element contents (ΣREE+Y, 1500 ± 340 ppm;n= 16) in bulk samples. This enrichment is due to the occurrence of abundant micrometer-sized synchysite inclusions in calcite, identified via Raman spectroscopy. Calcite bulk analyses have roof-shaped PAAS-normalized REE patterns with a Eu peak but without Ce or Y anomalies and with a steeply dipping HREE pattern. Microbeam analysis (electron microprobe and LA-ICPMS) identifies these patterns as dominated by synchysite-(Ce–Nd) with strong Eu enrichment in the weight percent range and LREE/HREE fractionation (La/Lu ~ 100, PAAS-normalized). The synchysite component in calcite gangue is detected in polymetallic veins all over the Harz Mountains, which seems to be a diagnostic feature of the region and suggests a large-scale Mesozoic fluid system. However, the Upper (western) Harz systems with no fluorite have more elevated REE content, compared with the Lower (eastern) Harz fluorite-rich systems with less REE content. Carbonate gangue in the Upper Harz systems has homogeneous87Sr/86Sriaround 0.714 and εNdiof ~ − 9, while carbonate gangue in the Lower Harz systems has87Sr/86Sriaround 0.716 and εNdiof − 2 to − 5. Fluorite in the Lower Harz Mountains has strong positive Y anomalies and variable Eu anomalies at generally low REE abundances and no REE-mineral inclusions. Both Sr and Nd isotope compositions in the fluorite are very variable and indicate an open system (87Sr/86Sri, 0.710–0.718; εNdi, − 3 to − 17). The synchysite MREE enrichment in calcite gangue in the Upper Harz Mountains compares favorably with carbonatite-related LREE-dominated bastnäsite from China and elsewhere and allows an interesting perspective as a by-product of Pb–Zn mining.