Figure - available from: Mineralium Deposita
This content is subject to copyright. Terms and conditions apply.
Photomicrographs of Etoile Suite samples. a Leucogabbro with cumulus crystals of euhedral and subhedral tabular plagioclase, with some intercumulus clinopyroxene (RM32; Zone B; 2752 m). b Relatively deformed plagioclase in leucogabbro. Deformation manifests itself in the form of bent twin lamellae, undulose extinction and subgrain formation. (RM31; Zone B; 2237 m). c Cumulus olivine in leuco-olivine gabbro (RM16; Zone A; 439 m). d Anhedral mass of olivine in mela-olivine gabbro. Olivine grain forms extensions into interstitial space and contains inclusions of clinopyroxene and oxide (RM26C; Zone B; 1806 m). e Cumulus clinopyroxene forming equant grains in oxide-rich wehrlite (RM6; Zone B; 922 m). f Cumulus grain of orthopyroxene in leuco-olivine norite, some of which is altered (RM33; Zone C; 4304 m). Abbreviations: pl, plagioclase; ol, olivine; cpx, clinopyroxene; opx, orthopyroxene; ox, oxide
Source publication
Iron-titanium-vanadium (Fe-Ti-V) oxide mineralisation is commonly associated with Proterozoic massif-type anorthosites, but the conditions required for their formation remain poorly understood. The Etoile Suite Mafic Intrusion (1149 ± 11 Ma), in the Grenville Province, Quebec (Canada), comprises a layered mafic intrusion that is coeval with nearby...
Similar publications
The Kangan anticline in the Folded Zagros Zone contains phosphate deposits enriched in trace metals. Field observations, petrography, X-Ray Diffraction, Scanning Electron Microscopy, and whole-rock geochemistry are used to determine the petrogenesis of this phosphate deposit, evaluate the mechanisms of deposition, and assess the implications for tr...
Citations
... The PGE budget inherited from the accretion of the Earth is thought to have been largely stripped from the silicate mantle and crust during the formation of the metallic core (Holzheid et al. 2000). Hence, most of the PGE now concentrated in layered intrusions were originally introduced to their mantle sources by a late veneer following the core formation (Maier et al. 2009). This extraterrestrial input was spatially erratic and imposed a first-order control on the PGE contents of magmas prior to the mantle-wide homogenization of this newly inherited material, which was possibly complete by 2.9 Ga (Maier et al. 2009). ...
... Hence, most of the PGE now concentrated in layered intrusions were originally introduced to their mantle sources by a late veneer following the core formation (Maier et al. 2009). This extraterrestrial input was spatially erratic and imposed a first-order control on the PGE contents of magmas prior to the mantle-wide homogenization of this newly inherited material, which was possibly complete by 2.9 Ga (Maier et al. 2009). Therefore, it is possible that the oldest layered intrusions in the geological record could have originated from mantle sources that were either strongly depleted or enriched in the PGE compared to the mantle that existed from the Neoarchean onward. ...
Layered intrusions are plutonic bodies of cumulates that form by the crystallization of mantle-derived melts. These intrusions are characterized by igneous layering distinguishable by shifts in mineralogy, texture, or composition. Layered intrusions have been fundamental to our understanding of igneous petrology; however, it is their status as important repositories of critical metals-such as platinum-group elements, chromium, and va-nadium-that has predominantly driven associated research in recent decades. Many layered intrusions were emplaced during the Precambrian, predominantly at the margins of ancient cratons during intervals of super-continent accretion and destruction. It appears that large, layered intrusions require rigid crust to ensure their preservation, and their geometry and layering is primarily controlled by the nature of melt emplacement. Layered intrusions are best investigated by integrating observations from various length-scales. At the macroscale, intrusion geometries can be discerned, and their presence understood in the context of the regional geology. At the mesoscale, the layering of an intrusion may be characterized, intrusion-host rock contact relationships studied, and the nature of stratiform mineral occurrences described. At the microscale, the mineralogy and texture of cumulate rocks and any mineralization are elucidated, particularly when novel microtextural and mineral chemical datasets are integrated. For example, here we demonstrate how mesoscale observations and microscale datasets can be combined to understand the petrogenesis of the perplexing snowball oiks outcrop located in the Upper Banded Series of the Stillwater Complex. Our data suggest that the ortho-pyroxene oikocrysts did not form in their present location, but rather formed in a dynamic magma chamber where crystals were transported either by convective currents or within crystal-rich slurries. Critical metals may be transported to the level of a nascent intrusion as dissolved components in the melt. Alternatively, ore minerals are entrained from elsewhere in a plumbing system, potentially facilitated by volatile-rich phases. There are many ore-forming processes propounded by researchers to occur at the level of emplacement; however, each must address the arrival of the ore mineral, its concentration of metals, and its accumulation into orebodies. In this contribution, several of these processes are described as well as our perspectives on the future of layered intrusion research.
