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Durham University

Department of Earth Sciences

Academic Staff

Publication details for Prof. Dave Selby

Zeng, Z., Ma, Y., Yin, X., Selby, D., Kong, F. & Chen, S. (2015). Factors affecting the rare earth element compositions in massive sulfides from deep-sea hydrothermal systems. Geochemistry, geophysics, geosystems 16(8): 2679-2693.

Author(s) from Durham

Abstract

To reconstruct the evolution of ore-forming fluids and determine the physicochemical conditions of deposition associated with seafloor massive sulfides, we must better understand the sources of rare earth elements (REEs), the factors that affect the REE abundance in the sulfides, and the REE flux from hydrothermal fluids to the sulfides. Here, we examine the REE profiles of 46 massive sulfide samples collected from seven seafloor hydrothermal systems. These profiles feature variable total REE concentrations (37.2–4,092 ppb) and REE distribution patterns (LaCN/LuCN ratios = 2.00–73.8; (Eu/Eu*)CN ratios = 0.34–7.60). The majority of the REE distribution patterns in the sulfides are similar to those of vent fluids, with the sulfides also exhibiting light REE enrichment. We demonstrate that the variable REE concentrations, Eu anomalies, and fractionation between light REEs and heavy REEs in the sulfides exhibit a relationship with the REE properties of the sulfide-forming fluids and the massive sulfide chemistry. Based on the sulfide REE data, we estimate that modern seafloor sulfide deposits contain approximately 280 tons of REEs. According to the flux of hydrothermal fluids at mid-ocean ridges (MORs) and an average REE concentration of 3 ng/g in these fluids, hydrothermal vents at MORs alone transport more REEs (>360 tons) to the oceans over the course of just two years than the total quantity of REEs in seafloor sulfides. The excess REEs (i.e., the quantity not captured by massive sulfides) may be transported away from the systems and become bound in sulfate deposits and metalliferous sediments. This article is protected by copyright. All rights reserved.