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Mobility of Au and related elements during the hydrothermal alteration of the oceanic crust: implications for the sources of metals in VMS deposits

Mobility of Au and related elements during the hydrothermal alteration of the oceanic crust: implications for the sources of metals in VMS deposits
Mobility of Au and related elements during the hydrothermal alteration of the oceanic crust: implications for the sources of metals in VMS deposits
Volcanogenic massive sulphide (VMS) deposits are commonly enriched in Cu, Zn and Pb and can also be variably enriched in Au, As, Sb, Se and Te. The behaviour of these elements during hydrothermal alteration of the oceanic crust is not well known. Ocean Drilling Program (ODP) Hole 1256D penetrates a complete in situ section of the upper oceanic crust, providing a unique sample suite to investigate the behaviour of metals during hydrothermal alteration. A representative suite of samples was analysed for Au, As, Sb, Se and Te using low detection limit methods, and a mass balance of metal mobility has been carried out through comparison with a fresh Mid-Oceanic Ridge Basalt (MORB) glass database. The mass balance shows that Au, As, Se, Sb, S, Cu, Zn and Pb are depleted in the sheeted dyke and plutonic complexes by ?46?±?12, ?27?±?5, ?2.5?±?0.5, ?27?±?6, ?8.4?±?0.7, ?9.6?±?1.6, ?7.9?±?0.5 and ?44?±?6 %, respectively. Arsenic and Sb are enriched in the volcanic section due to seawater-derived fluid circulation. Calculations suggest that large quantities of metal are mobilised from the oceanic crust but only a small proportion is eventually trapped as VMS mineralisation. The quantity of Au mobilised and the ratio of Au to base metals are similar to those of mafic VMS, and ten times enrichment of Au would be needed to form a Au-rich VMS. The Cu-rich affinity of mafic VMS deposits could be explained by base metal fractionation both in the upper sheeted dykes and during VMS deposit formation.
olcanic massive sulphide, Au-rich VMS, ODP Hole 1256D, Hydrothermal alteration, Oceanic crust
0026-4598
179-200
Patten, Clifford G.C.
338e47a8-92dd-47d8-8819-50e36c1b0591
Pitcairn, Iain K.
e6c79a72-1150-49fe-8b03-95db13e69c2e
Teagle, Damon A.H.
396539c5-acbe-4dfa-bb9b-94af878fe286
Harris, Michelle
2ea5985e-614c-4d8a-9cb0-82d9590d4ebc
Patten, Clifford G.C.
338e47a8-92dd-47d8-8819-50e36c1b0591
Pitcairn, Iain K.
e6c79a72-1150-49fe-8b03-95db13e69c2e
Teagle, Damon A.H.
396539c5-acbe-4dfa-bb9b-94af878fe286
Harris, Michelle
2ea5985e-614c-4d8a-9cb0-82d9590d4ebc

Patten, Clifford G.C., Pitcairn, Iain K., Teagle, Damon A.H. and Harris, Michelle (2016) Mobility of Au and related elements during the hydrothermal alteration of the oceanic crust: implications for the sources of metals in VMS deposits. Mineralium Deposita, 51 (2), 179-200. (doi:10.1007/s00126-015-0598-8).

Record type: Article

Abstract

Volcanogenic massive sulphide (VMS) deposits are commonly enriched in Cu, Zn and Pb and can also be variably enriched in Au, As, Sb, Se and Te. The behaviour of these elements during hydrothermal alteration of the oceanic crust is not well known. Ocean Drilling Program (ODP) Hole 1256D penetrates a complete in situ section of the upper oceanic crust, providing a unique sample suite to investigate the behaviour of metals during hydrothermal alteration. A representative suite of samples was analysed for Au, As, Sb, Se and Te using low detection limit methods, and a mass balance of metal mobility has been carried out through comparison with a fresh Mid-Oceanic Ridge Basalt (MORB) glass database. The mass balance shows that Au, As, Se, Sb, S, Cu, Zn and Pb are depleted in the sheeted dyke and plutonic complexes by ?46?±?12, ?27?±?5, ?2.5?±?0.5, ?27?±?6, ?8.4?±?0.7, ?9.6?±?1.6, ?7.9?±?0.5 and ?44?±?6 %, respectively. Arsenic and Sb are enriched in the volcanic section due to seawater-derived fluid circulation. Calculations suggest that large quantities of metal are mobilised from the oceanic crust but only a small proportion is eventually trapped as VMS mineralisation. The quantity of Au mobilised and the ratio of Au to base metals are similar to those of mafic VMS, and ten times enrichment of Au would be needed to form a Au-rich VMS. The Cu-rich affinity of mafic VMS deposits could be explained by base metal fractionation both in the upper sheeted dykes and during VMS deposit formation.

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Patten_etal_2016_Mineral_Deposita_Au_Mobility_IODP_1256D.pdf - Accepted Manuscript
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Accepted/In Press date: 27 June 2015
Published date: February 2016
Keywords: olcanic massive sulphide, Au-rich VMS, ODP Hole 1256D, Hydrothermal alteration, Oceanic crust
Organisations: Geochemistry

Identifiers

Local EPrints ID: 390075
URI: https://eprints.soton.ac.uk/id/eprint/390075
ISSN: 0026-4598
PURE UUID: 2479940b-c599-49d4-8ca3-eb16ab8e6a26
ORCID for Damon A.H. Teagle: ORCID iD orcid.org/0000-0002-4416-8409

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Date deposited: 17 Mar 2016 16:11
Last modified: 15 Aug 2019 05:34

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