The mobility of copper, zinc, molybdenum, and tungsten in subduction zone fluids

Title data

Liu, Siqi ; Keppler, Hans:
The mobility of copper, zinc, molybdenum, and tungsten in subduction zone fluids.
In: Geochimica et Cosmochimica Acta. Vol. 365 (2024) . - pp. 174-185.
ISSN 0016-7037
DOI: https://doi.org/10.1016/j.gca.2023.11.009

Official URL:

Abstract in another language

Porphyry-type ore deposits are closely associated with subduction zones, but the ultimate source of the metals in these deposits is still uncertain. To test whether aqueous fluids from the subducted slab may contribute to the metal enrichment, we investigated the partitioning of Cu, Zn, Mo, and W between saline aqueous fluids and the subducted basaltic crust at 2.5–3.0 GPa and 650–670 °C by experiments in piston cylinder presses. The bulk fluid/solid partition coefficients (Dfluid/solid) of Cu and Zn increase significantly with fluid salinity. For Cu, Dfluid/solid is less than 1 in a salt-free aqueous fluid, but at a salinity of 10 wt NaCl, Dfluid/solid approaches 10. On the other hand, the Dfluid/solid of Zn is still below 0.4 even at the same salinity. Dfluid/solid of Mo is always relatively high (>4), with only a very slight enhancement by salinity at 2.5 GPa. The fluid/solid partition coefficient of W is close to 1 for a chloride-free fluid, but slightly decrease with increasing salinity. Overall, these experimental data show that saline aqueous fluids released from the basaltic layer of the subducted oceanic slab can effectively transport Cu and Mo and therefore enrich these two metals in the mantle wedge. This enrichment does not contradict the observation that Cu concentrations in primitive arc magmas and MORB are similar, since these concentrations may be controlled by a buffering sulfide phase. The enrichment of copper in the source then does not necessarily increase Cu concentrations in the melt, but it ensures that the copper-bearing sulfide phase is not exhausted during repeated melting events. For molybdenum, our data suggest that aqueous fluids from the slab are the major source of Mo in arc magmas. Due to the high pre-enrichment of Mo in some sediments, there may be a direct link between the types of subducted sediment and the location of porphyry Mo deposits. On the other hand, the contribution of slab fluids to the Zn budget of these magmas is likely negligible. The W partitioning data are consistent with isotopic evidence for the mobility of W in subduction fluids. Moreover, the behavior of Mo and W is strongly affected by the abundance of rutile in the solid residue. In a rutile-free lithology, not only Mo, but also W would strongly partition into the fluid. As some sediments may be highly enriched in W relative to the average mantle, fluids from such sediments may also produce a significant W enrichment in the mantle wedge, provided that the sedimentary residue is free of rutile.

Further data

Item Type:	Article in a journal
Refereed:	Yes
Keywords:	Subduction zones; Aqueous fluids; Partitioning; Salinity; Ore-forming metals; Porphyry deposits
Institutions of the University:	Research Institutions > Central research institutes > Bavarian Research Institute of Experimental Geochemistry and Geophysics - BGI
Result of work at the UBT:	Yes
DDC Subjects:	500 Science > 550 Earth sciences, geology
Date Deposited:	12 Nov 2024 06:48
Last Modified:	12 Nov 2024 06:48
URI:	https://eref.uni-bayreuth.de/id/eprint/91013