近日，喀麦隆巴门达大学Tufoin Samndong Cyril团队取得一项新突破。他们对Mbalam铁矿区（喀麦隆南部）的Metzimevin优质铁矿床进行了整体地球化学、Rb-Sr、Sm-Nd及稳定O-H同位素系统学研究。相关论文于2023年12月29日发表于国际顶尖学术期刊《地球化学学报》杂志上。

研究人员称Metzimevin铁矿位于喀麦隆南部Mbalam铁矿区，属赤铁矿-磁铁矿BIF体系，显示其几乎为纯的化学沉淀物，以SiO₂ +Fe₂O₃(97.1-99.84 wt%)为主，含低浓度的碎屑元素（如Al₂O₃, TiO₂和HFSE）。铁矿床的REE+Y特征显示出强的Eu正异常、强的Ce负异常、球粒—超球粒的Y/Ho比值，表明其在氧化环境下的海水—高温热液混合形成。BIF的⁸⁷Sr/⁸⁶Sr比值高于所有太古宙储层(块状硅酸盐土、太古宙地壳和太古宙海水)的⁸⁷Sr/⁸⁶Sr最大演化曲线，表明BIF的形成和蚀变过程中有陆源成分的参与。

Nd(t)(+ 2.26至+ 3.77)和Nd模式年龄表明，BIF的化学成分源于3.002- 2.88 Ga之间的无明显特征的地壳来源。O和H同位素数据的变化和多样性(1.9‰- 17.3‰；-57‰-136‰)，表明Metzimevin铁矿最初形成于岩浆柱，后来受到岩浆—变质—改造的大气流体的富集。质量平衡计算表明成矿作用为浸出和沉淀联合作用，平均铁富集因子大于2.67，SiO₂损耗系数为0.99。这与总体体积减少28.27%有关，反映了BIF原石的净浸出和体积崩塌。

附：英文原文

Title: Bulk geochemistry, Rb–Sr, Sm–Nd, and stable O–H isotope systematics of the Metzimevin high-grade iron ore deposit, Mbalam iron ore district, southern Cameroon

Author: Tufoin, Samndong Cyril, Suh, Cheo Emmanuel, Tabod, Tabod Charles, Ngiamte, George Lemewihbwen

Issue&Volume: 2023-12-29

Abstract: Bulk geochemistry, Sr, Nd, and O–H isotope systematics are reported for the first time on banded iron formation (BIF)-hosted high-grade iron ore at the north-western segment of Congo Craton (CC). Located in Mbalam iron ore district, Southern Cameroon, Metzimevin iron ore deposit is a hematite-magnetite BIF system, dominated by SiO₂+Fe₂O₃ (97.1 to 99.84 wt%), with low concentrations of clastic elements e.g., Al₂O₃, TiO₂, and HFSE, depicting a nearly pure chemical precipitate. The REE+Y signature of the iron deposit displays strong positive Eu anomaly, strong negative Ce anomaly, and chondritic to superchondritic Y/Ho ratios, suggestive of formation by mixed seawater-high temperature hydrothermal fluids in oxidising environment. The ⁸⁷Sr/⁸⁶Sr ratios of the BIF are higher than the maximum ⁸⁷Sr/⁸⁶Sr evolution curves for all Archean reservoirs (bulk silicate earth, Archean crust and Archean seawater), indicating involvement of continentally-derived components during BIF formation and alteration. The Nd(t) (+2.26 to+3.77) and Nd model age indicate that chemical constituents for the BIF were derived from undifferentiated crustal source, between 3.002 and 2.88 Ga. The variable and diverse O and H isotope data (1.9‰ to 17.3‰ and57‰ to 136‰ respectively) indicate that the Metzimevin iron ore formed initially from magmatic plumes and later enriched by magmatic-metamorphic-modified meteoric fluids. Mass balance calculations indicate mineralisation by combined leaching and precipitation, with an average iron enrichment factor of>2.67 and SiO₂ depletion factor of>0.99. This is associated with an overall volume reduction of 28.27%, reflecting net leaching and volume collapse of the BIF protholith.

DOI: 10.1007/s11631-023-00667-x

Source: https://link.springer.com/article/10.1007/s11631-023-00667-x