Time Scales of Porphyry Cu Deposit Formation: Insights from Titanium Diffusion in Quartz

Mercer, Celestine N.; Reed, Mark H.; Mercer, Carolyn R.

doi:10.2113/econgeo.110.3.587

Cited by 81 publications

(43 citation statements)

References 55 publications

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“…This does not mean that Cu is continuously precipitated at this rate. Rather, as pointed out by several geochronological studies91039, this suggests that larger deposits are formed by a higher number of short-lived (few tens of ka) pulses distributed over a longer timescale than in smaller deposits, with the long-term average rate of Cu deposition being similar in both cases. The overall longer lifetime of magmatic-hydrothermal activity in the larger deposits could be due either to a larger availability of hybrid melt in the deep reservoir of the larger deposits or to earlier tectonic interruption of the hybrid melt transfer from depth for the smaller deposits.…”

Section: Resultsmentioning

confidence: 67%

Stochastic modelling of deep magmatic controls on porphyry copper deposit endowment

Chiaradia

Caricchi

2017

Sci Rep

140

133

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Porphyry deposits, our main source of copper and of significant amounts of Mo, Re and Au, form at convergent margins in association with intermediate-felsic magmas. Although it is accepted that copper is transported and precipitated by fluids released by these magmas, the magmatic processes leading to the formation of economic deposits remain elusive. Here we perform Monte Carlo petrological and geochemical modelling to quantitatively link crustal magmatic processes and the geochemical signatures of magmas (i.e., Sr/Y) to the formation of porphyry Cu deposits of different sizes. Our analysis shows that economic deposits (particularly the largest ones) may only form in association with magma accumulated in the lower-middle crust (P > ~0.5 GPa) during ≥2–3 Ma, and subsequently transferred to and degassed in the upper crust over periods of up to ~2.0 Ma. Magma accumulation and evolution at shallower depths (<~0.4 GPa) dramatically reduces the potential of magmatic systems to produce economic deposits. Our modelling also predicts the association of the largest porphyry deposits with a specific Sr/Y interval (~100 ± 50) of the associated magmatic rocks, which is virtually identical to the range measured in giant porphyry copper deposits.

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Section: Resultsmentioning

confidence: 67%

Stochastic modelling of deep magmatic controls on porphyry copper deposit endowment

Chiaradia

Caricchi

2017

Sci Rep

140

133

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“…Based on the pulsed hydrothermal process suggested here, together with cyclic mineralization processes constrained by recent high-precision U-Pb and Re-Os dating, titanium diffusion modeling, and concentric excess aluminum in plagioclase (Mercer et al, 2015;Spencer et al, 2015;Tapster et al, 2016;Williamson et al, 2016;Li et al, 2017a), we propose that a pulsed magmatic-hydrothermal process is common in the formation of porphyry deposits. Such a process is most likely controlled by periodic fluid release during gradual cooling of the source pluton at depth (Chelle-Michou et al, 2017), although a decline in the amount of melt and fluid associated with multiple recharging events is a competitive alternative mechanism.…”

Section: Pulsed Magmatic-hydrothermal Processmentioning

confidence: 71%

“…Such a process is most likely controlled by periodic fluid release during gradual cooling of the source pluton at depth (Chelle-Michou et al, 2017), although a decline in the amount of melt and fluid associated with multiple recharging events is a competitive alternative mechanism. By inference, the lifetime of the source pluton is estimated to be hundreds of thousands of years, with much shorter durations (tens of thousands of years) for the fluid release events (Mercer et al, 2015;Buret et al, 2016;Tapster et al, 2016;Chelle-Michou et al, 2017;Li et al, 2017a).…”

Section: Pulsed Magmatic-hydrothermal Processmentioning

confidence: 99%

“…Traditionally, this is done via the relative time frame defined by vein types, and in a single mineralization event/pulse, an A-type vein is earlier than a B-type vein, with a D-type vein being the latest (Sillitoe, 2010). However, the relative chronology of veining cannot be correlated at a deposit scale confidently, especially with the presence of multiple mineralization pulses (Stein, 2014;Mercer et al, 2015;Spencer et al, 2015;Li et al, 2017a).…”

Section: Introductionmentioning

confidence: 99%

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Pulsed magmatic fluid release for the formation of porphyry deposits: Tracing fluid evolution in absolute time from the Tibetan Qulong Cu-Mo deposit

Yang

Selby

et al. 2017

Geology

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The magmatic-hydrothermal evolution of porphyry-style mineralization in the shallow crust that is linked to magmatic processes at depth has been extensively studied using bulksample isotopic analysis combined with relative timing constraints. However, a lack of evaluation of the fluid evolution process against an absolute time frame limits further understanding of the ore-forming process. Here, we quantify the fluid evolution process within an absolute time frame for the first time by integrating new in situ oxygen isotope data from the Qulong porphyry Cu-Mo deposit (Tibet) with existing fluid inclusion data and high-precision Re-Os dates of co-precipitated hydrothermal quartz and molybdenite, respectively. We demonstrate that vein quartz records primary oxygen isotopic compositions and reached oxygen isotope equilibrium with ore-forming fluids, and therefore is an archive of the isotopic composition and source of the ore-forming fluids. The δ

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“…More recent studies of porphyry Mo systems suggest that a persistent magma conduit may not be required for focusing fractionated fluids into the upper crust. Instead, they suggest that mineralization is accomplished through multiple discrete events during protracted assembly of intrusions (e.g., Chiaradia et al, 2014;Chelle-Michou et al, 2015;Mercer et al, 2015b). Thus, an alternate explanation is that the feeder conduits are short-lived features that act to pass magma and volatiles from deeper parts of the system; convection within the conduit might be an unnecessary component.…”

Section: Introductionmentioning

confidence: 99%

Intrusive history of the Oligocene Questa porphyry molybdenum deposit, New Mexico

2019

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Subsurface mapping and core analyses of upper crustal intrusions and mineralization at the Questa porphyry molybdenum deposit, New Mexico, reveal that Mo-mineralization occurred through episodic emplacement of at least six intrusive units. The structure of intrusions associated with the Questa deposit is documented in a series of detailed cross sections and visualized with a 3D animation. Mineralizing intrusions are underlain by two post-mineralization intrusions and cut by late-stage barren dikes. The plutonic complex was structurally focused along a system of preexisting flat-lying faults and their associated fractures. Mineralization is spatially associated with specific intrusive units in the subsurface, and the highest Mo ore grades within established ore blocks are structurally associated with the smallest intrusions. Existing U/Pb thermal ionization mass spectrometry (TIMS) zircon geochronology in conjunction with new relative chronology presented herein indicate that mineralization began before 24.91 Ma. We present three new chemical abrasion U/Pb TIMS zircon ages-one from an amphibole-bearing intrusion associated with high-grade mineralization (dark-matrix porphyry, 24.74 ± 0.37 Ma), a rhyolite dike that cuts ore-grade rocks (24.50 ± 0.02 Ma), and an equigranular granite discovered during deep drilling (23.67 ± 0.02 Ma). The dark-matrix porphyry contains clasts of an earlier amphibole-free intrusion that is spatially associated with low-grade mineralization. Thus, mineralizing intrusions were, in part, intruded into slightly older porphyries, confirming that episodic mineralization continued after 24.91 Ma. The age of the barren dike (24.50 ± 0.02 Ma) is indistinguishable from that of a previously dated granite porphyry that is associated with low-grade mineralization (<0.05 wt% MoS 2 ; Questa granite porphyry). These data suggest that mineralization waned by 24.5 Ma and that ore deposition occurred over ~500 ka. The new 23.67 Ma age of the deep equigranular granite, which underlies the Questa granite porphyry, further suggests that intrusions underlying the deposit were not related to mineralization. Detailed subsurface mapping and exploratory drilling indicate that intrusions associated with mineralization were small in volume and cooled rapidly, as evidenced by multiple internal contacts within sheets and rebrecciation textures. On the basis of observed cross-section reconstructions, petrology, alteration, and mineralization, the porphyritic rhyolite intrusions associated with mineralization in one of the largest orebodies in the deposit (the deep northeast) are less than 20-m-thick sheets that are separated by andesite wall rock. Thus, there is no evidence that this orebody formed above a cylindrical magma conduit that facilitated rapid convection, as is often modeled in these systems. We hypothesize that a set of similarly small-volume intrusions were responsible for the bulk of the ore in the southwest ore zone. Our interpretation that the mineralizing intrusions are small, thin, and subhorizontal ...

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Time Scales of Porphyry Cu Deposit Formation: Insights from Titanium Diffusion in Quartz

Cited by 81 publications

References 55 publications

Stochastic modelling of deep magmatic controls on porphyry copper deposit endowment

Stochastic modelling of deep magmatic controls on porphyry copper deposit endowment

Pulsed magmatic fluid release for the formation of porphyry deposits: Tracing fluid evolution in absolute time from the Tibetan Qulong Cu-Mo deposit

Intrusive history of the Oligocene Questa porphyry molybdenum deposit, New Mexico

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