| Title | Sulfide liquid entrainment by silicate magma: implications for the dynamics and petrogenesis of magmatic sulfide deposits |
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| Author | Saumur, B M ;
Cruden, A R; Boutelier, D |
| Source | Journal of Petrology vol. 56, 12, 2015 p. 2473-2490, https://doi.org/10.1093/petrology/egv080  Open Access |
| Image |  |
| Year | 2015 |
| Alt Series | Natural Resources Canada, Contribution Series 20200242 |
| Publisher | Oxford University Press |
| Meeting | International Platinum Conference; Ekaterinburg; RU; August 11-14, 2014 |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Subjects | igneous and metamorphic petrology; Science and Technology; magmas; petrogenesis; magmatic deposits; mafic rocks; nickel; copper |
| Illustrations | models; sketches; tables; images; plots |
| Released | 2015 12 01 |
| Abstract | Many intrusion-hosted Ni-Cu magmatic sulfide deposits, such as Voisey's Bay (Labrador, Canada) and Jinchuan (China), show evidence for late-stage mobilization of high-density, low-viscosity sulfide-
rich melts, which range from sulfide-rich silicate magma pulses to coherent pulses of pure sulfide liquid. Here we investigate the possibility that such sulfide-rich pulses can be generated by the upward entrainment of pooled sulfide liquid by
immiscible silicate magma within a two-phase, density-stratified staging chamber. The potential degree of entrainment is measured by the critical draw-up height d, defined as the height of the overlying silicate magma at which the lower sulfide
liquid will be mobilized and entrained during withdrawal of silicate magma from the chamber. Previous analytical solutions for axisymmetric withdrawal from a density-stratified reservoir have focused on the volcanology of bimodal, felsic-mafic
silicate magma systems. We present new laboratory experiments of axisymmetric withdrawal that are tuned to the physical properties of mafic-sulfide systems, and find that the draw-up scales previously applied to felsic-mafic systems can be applied to
both viscous and inertial entrainment of sulfide liquid into silicate magma. Within viscous (Reynolds number, Re< 10) to transitional regimes (Re similar to 10-1000) d is dependent on the viscosity of the mafic layer, but independent of the viscosity
of the sulfide layer; at a given volumetric magma flow rate (Q), higher viscosity mafic magmas will be more efficient sulfide entrainers than lower viscosity magmas. Entrainment is independent of viscosity within inertial regimes (Re> 1000). In all
dynamic regimes d is proportional to Q and inversely proportional to the density difference between the fluids. Significant mobilization and entrainment of sulfide liquid, as indicated by predicted draw-up cones with d between 1 and 10m, can occur
under inertial conditions at high (Q similar to 1-1000 m(3) s(-1)) magma volumetric flow rates that are plausible for mid-to upper-crustal magma chambers. Although entrainment can potentially generate sulfide-rich magma pulses, it probably represents
only an initial step in the mobilization of sulfide liquid and the genesis of magmatic sulfide deposits. Entrained sulfide liquids must be transported upwards and/or laterally from their site of mobilization towards their site of deposition, which
may occur as coherent masses or as droplets depending on the dynamics of the system. Although entrainment may be viable at the scale of sills, dykes, chonoliths and lava flows, it may not be significant in scenarios where significant (>100m)
thicknesses of molten mafic magma must be expelled prior to reaching 1-10m scale critical draw-up heights; in such scenarios gravitational backflow of sulfide may be a more viable mechanism for producing economic concentrations of Ni-Cu sulfide
mineralization. |
| GEOSCAN ID | 326654 |
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