The 1.34 Gyr-old Voisey’s Bay Complex is a troctolite-anorthosite-diorite suite located at the western margin of the Archaean Nain Province, Labrador, norther Canada. Magmatic sulfide deposits occur in the two tabular magma chambers (Eastern Deeps and Western Deeps) as well as in the magma conduits (Ovoid, Mini-Ovoid conduits, Eastern Deeps feeder, etc.; Li and Naldrett 1999). Nickel-copper sulfides have disseminated to semi-massive textures at the base of the Eastern Deeps chamber, whereas sulfides are only disseminated in the Western Deeps chamber. In the conduits, sulfide textures range from disseminated to massive and develop sulfide-matrix breccia textures along the footwall contacts. Fragment in the sulfide-matrix breccias comprise endogenously-derived troctolite, olivine gabbro and peridotite as well as paragneiss and orthogneiss xenoliths. These sulfide-rich clast-supported breccias are interpreted to have formed through the downward percolation of sulfide melt, which displaced the interstitial silicate melt between the endogenous fragments and the xenoliths (Barnes et al., 2017). At the interface between the silicate clasts and the sulfide matrix are often present continuous biotite-hornblende reaction rims. Detailed textural analysis suggests that these hydrous silicates formed through reactions between the breccia fragments and volatile component derived from the sulfide liquid. Experimental and field evidence support this hypothesis, as the sulfide melt is able to host minor amounts of water and halogens (Mungall and Brenan, 2003; Wykes and Mavrogenes, 2005). However, the origin of K required for the formation of biotite is yet to be fully understood. Furthermore, the occurrence of accessory minerals such as apatite and ilmenite, which are commonly regarded as residual, within the sulfide-matrix breccias is at odds with conventional genetic models of magmatic Ni-Cu-Co sulfide deposits. In this study we characterise the trace element composition of apatite, biotite and Fe-oxides in barren troctolite, sulfide-rich and sulfide-poor breccia samples to trace the origin of the volatile component in the Ni-Cu-Co Ovoid deposit. Furthermore, we explore the ability of these accessory phases to record the effects of ore-forming processes and their potential as vectors toward mineralisation.

Reference(s)

Barnes, S.J., Le Vaillant, M., and Lightfoot, P.C., 2017, Textural development in sulfide-matrix ore breccias in the Voisey’s Bay Ni-Cu-Co deposit, Labrador, Canada: Ore Geology Reviews, v. 90, p. 414–438.

Li, C., and Naldrett, A.J., 1999, Geology and petrology of the Voisey’s Bay intrusion: reaction of olivine with sulfide and silicate liquids: Lithos, v. 47, p. 1–31.
 
Mungall, J.E., and Brenan, J.M., 2003, Experimental evidence for the chalcophile behavior of the halogens: The Canadian Mineralogist, v. 41, p. 207–220.

Wykes, J.L., and Mavrogenes, J.A., 2005, Hydrous sulfide melting: Experimental evidence for the solubility of H2O in sulfide melts: Economic Geology, v. 100, p. 157–164.