A metasomatized lithospheric mantle control on the metallogenic signature of post-subduction magmatism

David A Holwell,Manuel Keith,Marco Fiorentini,Andrea Giuliani,Iain Mcdonald,Marek Locmelis,Yongjun Lu,Daniel J Smith

doi:10.1038/s41467-019-11065-4

Abstract

Ore deposits are loci on Earth where energy and mass flux are greatly enhanced and focussed, acting as magnifying lenses into metal transport, fractionation and concentration mechanisms through the lithosphere. Here we show that the metallogenic architecture of the lithosphere is illuminated by the geochemical signatures of metasomatised mantle rocks and post-subduction magmatic-hydrothermal mineral systems. Our data reveal that anomalously gold and tellurium rich magmatic sulfides in mantle-derived magmas emplaced in the lower crust share a common metallogenic signature with upper crustal porphyry-epithermal ore systems. We propose that a trans-lithospheric continuum exists whereby post-subduction magmas transporting metal-rich sulfide cargoes play a fundamental role in fluxing metals into the crust from metasomatised lithospheric mantle. Therefore, ore deposits are not merely associated with isolated zones where serendipitous happenstance has produced mineralisation. Rather, they are depositional points along the mantle-to-upper crust pathway of magmas and hydrothermal fluids, synthesising the concentrated metallogenic budget available.

Highlights

Ore deposits are loci on Earth where energy and mass flux are greatly enhanced and focussed, acting as magnifying lenses into metal transport, fractionation and concentration mechanisms through the lithosphere
A thread of mineral systems with a common alkali-enriched signature can be traced through the continental crust: from lower (>15 km) and mid-crustal hydrous alkaline intrusions, which locally contain magmatic Ni–Cu–Au–Te and platinum-group element (PGE) sulfide mineralisation[3,4,9], all the way to upper crustal (
Whereas these are from a range of selected global localities, they all share a common association with post-subduction magmatism

Summary

Introduction

Ore deposits are loci on Earth where energy and mass flux are greatly enhanced and focussed, acting as magnifying lenses into metal transport, fractionation and concentration mechanisms through the lithosphere. The Sub Continental Lithospheric Mantle (SCLM) that was metasomatised during subduction may undergo localised partial melting[3,4] This post-subduction process forms relatively small volume, hydrous magmas that range from high-K-calc-alkaline, through silicasaturated to silica-undersaturated alkaline compositions[1], and are referred to as alkali-enriched. Whereas the Au–Terich nature of these deposits is well documented[6,7,8], the causes of this metal enrichment, and the crustal architecture in which the deposits sit, remain poorly understood In this framework, a thread of mineral systems with a common alkali-enriched signature can be traced through the continental crust: from lower (>15 km) and mid-crustal hydrous alkaline intrusions, which locally contain magmatic Ni–Cu–Au–Te and platinum-group element (PGE) sulfide mineralisation[3,4,9], all the way to upper crustal (

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Results

Conclusion