The older layers of thick ferromanganese (FeMn) crusts from the central Pacific Ocean have undergone diagenetic phosphatization, during which carbonate fluorapatite (CFA) filled fractures and pore space and replaced carbonates. The effects of phosphatization on individual trace metal concentrations, speciation, and phase associations in FeMn crusts remain poorly understood yet may be important to metal enrichment mechanisms, paleoceanography, and extractive metallurgy. This study examines the concentrations, speciation, and mineral phase associations of Pb in phosphatized and nonphosphatized layers within three Pacific Ocean crusts using standard chemical and mineralogical techniques, in addition to bulk X-ray absorption spectroscopy (XAS) and microfocused X-ray fluorescence (μ-XRF) mapping. Our findings challenge the conclusions of previous works, which reported that most Pb in phosphatized crusts was associated with the CFA-dominated residual phase after sequential leaching experiments. These results were interpreted as an indication of Pb transfer from the oxide phases to diagenetic CFA during phosphatization. However, our results reveal an inverse correlation of Pb with Ca and P in the μ-XRF mapping of in situ FeMn crust sections and bulk chemistry. Furthermore, XAS measurements reveal that Pb speciation in bulk phosphatized FeMn crust layers is very similar to nonphosphatized layers, indicating only minor, if any, change in speciation during diagenetic phosphatization. Small differences in the EXAFS spectra for one highly phosphatized layer indicate that minor amounts of Pb may have been altered during phosphatization, but the new Pb-bearing phase was not unequivocally identified. Taken together, our results demonstrate that Pb speciation is not significantly affected by phosphatization.

中文翻译：

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磷化对锰铁结壳中矿物缔合和铅形态的影响

来自太平洋中部的较厚的厚锰铁壳（FeMn）壳经历了成岩作用的磷化作用，在此期间碳酸盐氟磷灰石（CFA）填充了裂缝和孔隙，并置换了碳酸盐。磷化对铁锰结壳中单个痕量金属浓度，形态和相缔合的影响仍然知之甚少，但对金属富集机制，古海洋学和萃取冶金学可能很重要。本研究使用标准化学和矿物学技术，除了大量X射线吸收光谱法（XAS）和微聚焦X射线荧光光谱法（XAS）之外，还使用标准化学和矿物学技术检查了三个太平洋洋壳中磷化层和非磷化层中Pb的浓度，形态和矿物相的缔合（ μ-XRF）映射。我们的发现挑战了以前的工作结论，据报道，经过连续浸出实验后，磷化皮中的大多数铅与CFA为主的残留相有关。这些结果被解释为在磷化过程中Pb从氧化物相转移到成岩CFA的迹象。然而，我们的结果显示在原位FeMn壳层切片和整体化学的μ-XRF图谱中，Pb与Ca和P成反比。此外，XAS测量表明，整体磷化FeMn壳层中的Pb形态与非磷化层非常相似，这表明在成岩性磷化过程中，形态只有很小的变化（如果有的话）。一层高度磷化的层的EXAFS光谱之间的细微差异表明，在磷化过程中可能已改变了少量的Pb，但并未明确鉴定出新的Pb轴承相。