Multi-stage arc magma evolution recorded by apatite in volcanic rocks

Nathwani, Chetan; Loader, Matthew; Wilkinson, Jamie J.; Buret, Yannick; Sievwright, Robert; Hollings, Pete

doi:10.1130/g46998.1

Cited by 84 publications

(27 citation statements)

References 35 publications

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“…The apparent change in geochemistry (whole-rock and zircon) as the Yerington system began to produce porphyry deposits is consistent with observations across a wide range of global localities where precursor magmatism and syn-mineralisation intrusions have been examined e.g. 19,20,22,25,66 . Typically these changes have been interpreted as being due to long-term, arc-scale, transitional "ramp-ups" towards ore-formation over millions of years e.g.…”

Section: Genetic Implications For Porphyry Deposit-forming Magmatic Systemssupporting

confidence: 83%

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An abrupt switch in magmatic plumbing taps porphyry copper deposit-forming magmas

Carter

Tapster

Williamson

et al. 2021

Preprint

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Porphyry-type deposits are a vital source of green technology metals such as copper and molybdenum. They typically form in subduction-related settings from large, long-lived magmatic systems. The most widely accepted model for their formation requires that mantle-derived magmas undergo a multi-million year timescale ramp-up in volatiles and ore-forming constituents in mid- to lower-crustal reservoirs, however this does not explain why porphyry deposits are absent from the vast majority of arc magmatic systems. To address this, we have carried out geochemical and geochronological studies on the tilted, ~8 km depth equivalent, cross-section through the classic Yerington magmatic system, Nevada. Here we show that the magmas underwent a major and abrupt change in chemistry over a period of 100 kyrs which is coincident with the initiation of ore formation. This is attributed to a wholesale switch in the magmatic plumbing system whereby volatile-rich granitic melts were extracted from an estimated ~30 km depth and transported to shallow levels (~3-8 km) where exsolving fluids were focussed through highly permeable pathways to form porphyry deposits. The change in magma chemistry is documented across the entire plutonic to volcanic record. Its rapidity suggests that the increase in a magma’s ore-forming potential is not solely driven by tectonic factors, that occur over multi-million year scales, but through internal processes within the melt evolution zone, operating at more than an order of magnitude faster than previously envisaged. This short timescale narrows the temporal-geochemical footprint of magmas associated with porphyry mineralisation which will aid in targeting the next generation of ore deposits.

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Section: Genetic Implications For Porphyry Deposit-forming Magmatic Systemssupporting

confidence: 83%

“…Most indicators reflect the geochemical signatures of amphibole fractionation and plagioclase suppression due to the hydrous nature of the magmas from which porphyry-type deposits form e.g. 7,[11][12][13][14][15][16][17][18][19][20] .…”

Section: Introductionmentioning

confidence: 99%

An abrupt switch in magmatic plumbing taps porphyry copper deposit-forming magmas

Carter

Tapster

Williamson

et al. 2021

Preprint

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“…The ability of Eu/Eu* zircon to record a deep-crustal fractionation history is dependent on it reflecting the bulk magma Eu/Eu* (cf., Nathwani et al 2020). Although Eu/Eu* zircon appears to reflect changes in the inferred bulk magma Eu/ Eu* based on the correlation between Eu/Eu* zircon and whole-rock Eu/Eu*, modification of the melt composition (largely prior crystallisation of plagioclase in the uppercrust) prior to zircon saturation would be expected.…”

Section: The Decoupling Of Zircon Chemistry From Bulk Magma Compositionsmentioning

confidence: 95%

From long-lived batholith construction to giant porphyry copper deposit formation: petrological and zircon chemical evolution of the Quellaveco District, Southern Peru

Nathwani

Simmons

Large

et al. 2021

Contrib Mineral Petrol

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Porphyry Cu ore deposits are a rare product of arc magmatism that often form spatiotemporal clusters in magmatic arcs. The petrogenetic evolution of igneous rocks that cover the temporal window prior to and during porphyry Cu deposit formation may provide critical insights into magmatic processes that are key in generating these systems. This study documents the magmatic evolution of the Palaeocene–Eocene Yarabamba Batholith, Southern Peru, that was incrementally assembled between ~ 67 and ~ 59 Ma and hosts three, nearly contemporaneous, giant porphyry Cu–Mo deposits that formed at 57–54 Ma (Quellaveco, Toquepala and Cuajone). Whole-rock geochemistry, U–Pb geochronology and zircon trace element chemistry are reported from Yarabamba rocks that span the duration of plutonic activity, and from six porphyry intrusions at Quellaveco that bracket mineralisation. A change in whole-rock chemistry in Yarabamba intrusive rocks to high Sr/Y, high La/Yb and high Eu/Eu* is observed at ~ 60 Ma which is broadly coincident with a change in vector of the converging Nazca plate and the onset of regional compression and crustal thickening during the first stage of the Incaic orogeny. The geochemical changes are interpreted to reflect a deepening of the locus of lower crustal magma evolution in which amphibole ± garnet are stabilised as early and abundant fractionating phases and plagioclase is suppressed. Zircons in these rocks show a marked change towards higher Eu/Eu* (> 0.3) and lower Ti (< 9 ppm) compositions after ~ 60 Ma. Numerical modelling of melt Eu systematics and zircon-melt partitioning indicates that the time series of zircon Eu/Eu* in these rocks can be explained by a transition from shallower, plagioclase-dominated fractionation to high-pressure amphibole-dominated fractionation at deep crustal levels from ~ 60 Ma. Our modelling suggests that any redox effects on zircon Eu/Eu* are subordinate compared to changes in melt composition controlled by the fractionating mineral assemblage. We suggest that growth and intermittent recharge of the lower crustal magma reservoir from ~ 60 Ma produced a significant volume of hydrous and metallogenically fertile residual melt which ascended to the upper crust and eventually generated the three giant porphyry Cu–Mo deposits at Quellaveco, Toquepala and Cuajone from ~ 57 Ma. Our study highlights the importance of high-pressure magma differentiation fostered by strongly compressive tectonic regimes in generating world-class porphyry Cu deposits.

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“…Porphyry Cu(-Au-Mo) deposits are amongst the most significant mineralizing systems on Earth, comprising around 75% of global Cu resources 37 . They are considered to be a product of a complex series of processes related to volcanic arc activity 1 , 4 – 7 , 38 . These include (1) generation of hydrous basaltic melts from metasomatized mantle wedge above the subducting slab; (2) accumulation of these mafic magmas in lower crustal MASH zones to produce amphibole-rich cumulates; (3) ascent of buoyant, hydrous magmas to upper crustal depths where they pond, differentiate and release magmatic volatile phases leading to (4) porphyry ore formation by precipitation of Cu- and other metal-enriched sulfides from the volatile flux triggered by cooling, phase separation, mixing, and/or reaction with wall rocks.…”

Section: Discussionmentioning

confidence: 99%

Mobilisation of deep crustal sulfide melts as a first order control on upper lithospheric metallogeny

et al. 2022

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Magmatic arcs are terrestrial environments where lithospheric cycling and recycling of metals and volatiles is enhanced. However, the first-order mechanism permitting the episodic fluxing of these elements from the mantle through to the outer Earth’s spheres has been elusive. To address this knowledge gap, we focus on the textural and minero-chemical characteristics of metal-rich magmatic sulfides hosted in amphibole-olivine-pyroxene cumulates in the lowermost crust. We show that in cumulates that were subject to increasing temperature due to prolonged mafic magmatism, which only occurs episodically during the complex evolution of any magmatic arc, Cu-Au-rich sulfide can exist as liquid while Ni-Fe rich sulfide occurs as a solid phase. This scenario occurs within a ‘Goldilocks’ temperature zone at ~1100–1200 °C, typical of the base of the crust in arcs, which permits episodic fractionation and mobilisation of Cu-Au-rich sulfide liquid into permeable melt networks that may ascend through the lithosphere providing metals for porphyry and epithermal ore deposits.

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Multi-stage arc magma evolution recorded by apatite in volcanic rocks

Cited by 84 publications

References 35 publications

An abrupt switch in magmatic plumbing taps porphyry copper deposit-forming magmas

An abrupt switch in magmatic plumbing taps porphyry copper deposit-forming magmas

From long-lived batholith construction to giant porphyry copper deposit formation: petrological and zircon chemical evolution of the Quellaveco District, Southern Peru

Mobilisation of deep crustal sulfide melts as a first order control on upper lithospheric metallogeny

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