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Abstract. The trace metal iron (Fe) is an essential micronutrient that controls phytoplankton productivity, which subsequently affects organic matter cycling with feedback on the cycling of macronutrients. Along the continental margin of the US West Coast, high benthic Fe release has been documented, in particular from deep anoxic basins in the Southern California Borderland. However, the influence of this Fe release on surface primary production remains poorly understood. In the present study from the Santa Barbara Basin, in situ benthic Fe fluxes were determined along a transect from shallow to deep sites in the basin. Fluxes ranged between 0.23 and 4.9 mmol m−2 d−1, representing some of the highest benthic Fe fluxes reported to date. To investigate the influence of benthic Fe release from the oxygen-deficient deep basin on surface phytoplankton production, we combined benthic flux measurements with numerical simulations using the Regional Ocean Modeling System coupled to the Biogeochemical Elemental Cycling (ROMS-BEC) model. For this purpose, we updated the model Fe flux parameterization to include the new benthic flux measurements from the Santa Barbara Basin. Our simulations suggest that benthic Fe fluxes enhance surface primary production, supporting a positive feedback on benthic Fe release by decreasing oxygen in bottom waters. However, a reduction in phytoplankton Fe limitation by enhanced benthic fluxes near the coast may be partially compensated for by increased nitrogen limitation further offshore, limiting the efficacy of this positive feedback.
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The Shepherd Mountain iron ore deposit in Southeast Missouri, USA – An extension of the Pilot Knob magmatic-hydrothermal ore system: Evidence from iron oxide chemistry
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null (Ed.)Iron oxide-copper-gold (IOCG) deposits are major sources of Cu, contain abundant Fe-oxides and may contain Au, Ag, Co, rare earth elements (REE), U and other metals as economically important byproducts in some deposits. They form by hydrothermal processes, but the source of the metals and ore fluid(s) is still debated. We investigated the geochemistry of magnetite from the manto and breccia ore bodies at the Mina Justa IOCG deposit in Peru to assess the source of the iron oxides and their relationship with the economic Cu mineralization. We identified three magnetite types: Type Inclusion (I) is only found in the manto, is the richest in trace elements, and crystallized between 459 - 707 °C; Type Dark (D) has no visible inclusions and formed at around 543 °C; and Type Bright (B) has no inclusions, has the highest Fe content, and formed at around 443 °C. Magnetite samples from Mina Justa yielded an average δ56Fe ± 2σ value of 0.28 ± 0.05‰ (n=9), an average δ18O ± 2σ value 2.19 ± 0.45‰ (n=9), and Δ’17O values that range between -0.075‰ and -0.047‰. Sulfide separates yielded δ65Cu values that range from -0.32‰ to -0.09‰. The trace element compositions and textures of magnetite, along with temperature estimations for magnetite crystallization, are consistent with the manto magnetite belonging to an IOA style mineralization that was overprinted by a younger, structurally-controlled IOCG event that formed the breccia ore body. Altogether, the stable isotopic data fingerprint a magmatic-hydrothermal source for the ore fluids carrying the Fe and Cu at Mina Justa and preclude the input from meteoric water and basinal brines.more » « less
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null (Ed.)Iron oxide-copper-gold (IOCG) deposits are major sources of Cu, contain abundant Fe-oxides and may contain Au, Ag, Co, rare earth elements (REE), U and other metals as economically important byproducts in some deposits. They form by hydrothermal processes, but the source of the metals and ore fluid(s) is still debated. We investigated the geochemistry of magnetite from the manto and breccia ore bodies at the Mina Justa IOCG deposit in Peru to assess the source of the iron oxides and their relationship with the economic Cu mineralization. We identified three magnetite types: Type Inclusion (I) is only found in the manto, is the richest in trace elements, and crystallized between 459 - 707 °C; Type Dark (D) has no visible inclusions and formed at around 543 °C; and Type Bright (B) has no inclusions, has the highest Fe content, and formed at around 443 °C. Magnetite samples from Mina Justa yielded an average δ56Fe ± 2σ value of 0.28 ± 0.05‰ (n=9), an average δ18O ± 2σ value 2.19 ± 0.45‰ (n=9), and Δ’17O values that range between -0.075‰ and -0.047‰. Sulfide separates yielded δ65Cu values that range from -0.32‰ to -0.09‰. The trace element compositions and textures of magnetite, along with temperature estimations for magnetite crystallization, are consistent with the manto magnetite belonging to an IOA style mineralization that was overprinted by a younger, structurally-controlled IOCG event that formed the breccia ore body. Altogether, the stable isotopic data fingerprint a magmatic-hydrothermal source for the ore fluids carrying the Fe and Cu at Mina Justa and preclude the input from meteoric water and basinal brines.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.oregeorev.2021.104633
