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 northwestern segment of Congo Craton(CC).Located in Mbalam iron ore d...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 northwestern 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 SiO_(2)+Fe_(2)O_(3)(97.1 to 99.84 wt%),with low concentrations of clastic elements e.g.,Al_(2)O_(3),TiO_(2),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^(87)Sr/^(86)Sr ratios of the BIF are higher than the maximum^(87)Sr/^(86)Sr 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.TheƐ_(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‰and−57‰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 SiO_(2)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.展开更多
文摘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 northwestern 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 SiO_(2)+Fe_(2)O_(3)(97.1 to 99.84 wt%),with low concentrations of clastic elements e.g.,Al_(2)O_(3),TiO_(2),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^(87)Sr/^(86)Sr ratios of the BIF are higher than the maximum^(87)Sr/^(86)Sr 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.TheƐ_(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‰and−57‰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 SiO_(2)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.
