Hydrothermal signatures and prospecting indicators in sediments along the Carlsberg Ridge

Abstract

As the most widespread hydrothermal products in the oceans, metalliferous sediments are particularly useful in prospecting for seafloor massive sulfide (SMS) deposits. A comparative study of metalliferous sediments from two types of hydrothermal fields and the background sediments along the Carlsberg Ridge has been performed to reveal their hydrothermal signatures and to determine the prospecting indicators for SMS deposits. Cu–Fe–Zn sulfides, sulfates, Fe-oxides, and Fe-oxyhydroxides are dominant in the near-vent sediments from the basalt-hosted hydrothermal fields. The near-vent sediments from the ultramafic-hosted field are abundant in detrital minerals of ultramafic source in addition to the minerals mentioned above in the basalt-hosted fields. Sulfide minerals with large grains are mainly deposited close to the vent, and as the distance from the vent increases, the grain size and abundance of the minerals rapidly decrease. Geochemically, the near-vent sediments in the basalt-hosted hydrothermal fields are abundant in Fe, Cu, Zn, Ag, Pb, Mo, Co, U, V, and P, whereas the sediments from the ultramafic-hosted system are enriched in Fe, Mn, Cu, Zn, Ag, Pb, Mo, Co, Mg, Ni, Cr, U, V, and P. The enrichment of these elements and element ratios, such as (Fe + Mn)/Al, Fe/Ti, Al/(Al + Fe + Mn), Cu/Fe, Zn/Fe, U/Fe, and V/Fe, can be indicators of the intensity of the hydrothermal inputs and the distance to the SMS deposits. Temporal and spatial variations of hydrothermally derived elements (e.g., Fe, Cu, Zn, and Pb) in sediment cores can serve as effective tools for reconstructing the hydrothermal history, evaluating the mineralization potential, and tracing inactive/buried SMS deposits. Finally, a prospecting model and method for SMS deposits is proposed based on the prospecting indicators revealed by the sediment study, combined with other prospecting indicators generally used during marine exploration. The results can provide guidance for the prospecting of hydrothermal fields and SMS deposits.