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TitleOn the emplacement of the Voisey's Bay intrusion (Labrador, Canada)
AuthorSaumur, B. M.; Cruden, A. R.
SourceGeological Society of America Bulletin vol. 128, (2016), no. 1/2, 2015 p. 147-168, https://doi.org/10.1130/B31240.1
Year2015
Alt SeriesEarth Sciences Sector, Contribution Series 20140590
PublisherGeological Society of America
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
ProvinceNewfoundland and Labrador
NTS14C; 14F
AreaVoisey's Bay
Lat/Long WENS -62.0000 -60.0000 58.0000 56.0000
Subjectseconomic geology; general geology; geochemistry; igneous and metamorphic petrology; metallic minerals; structural geology; dykes, mafic; plutons; magmatic deposits; magmatic rocks; sulphide deposits; nickel; copper; breccias; sills; xenoliths; shear zones; faulting; Mafic Intrusive Complex; Magma Chamber; Proterozoic
Illustrationsgeologic map; structural cross-section; sketch map; location maps; tables; photographs; photomicrographs; graphs; stereonets
ProgramWestern Arctic, High Arctic LIP, GEM2: Geo-mapping for Energy and Minerals
AbstractThe Mesoproterozoic Voisey's Bay Intrusion is a small (~10 km3) mafic intrusive complex forming part of the 20,000 km2 Nain Plutonic Suite of Labrador (Canada), and hosting a world class orthomagmatic Ni-Cu-Co sulfide deposit. An extensive database of drill core and down-hole televiewer data provides a wealth of sub-surface three-dimensional information on the intrusion. The intrusion consists of the upper Eastern Deeps Chamber and lower Western Deeps Chamber, connected via a complex network of dykes. The Eastern Deeps Chamber can be divided into six units that are distinguished based on geometrical styles, dominant lithologies and the occurrences of bodies of wall rock partly separating units. Unit I, occurring at the highest levels of the chamber, is tabular and consists dominantly of olivine gabbro with minor normal textured (orthocumulate) troctolite. Units at midlevels of the Eastern Deeps Chamber (IIA, IIB, IIC) are sill shaped bodies consisting of normal troctolite (i.e., orthocululate, locally with tiling of plagioclase laths) with local variably textured troctolite (i.e., mesocumulates, locally pegmatitic or dynamically recrystallized). Units from the lowermost level (IIIA, IIIB) are irregularly shaped and consist of variable troctolite, breccias containing cm-sized xenoliths of host-rock paragneiss and strongly sulfide-mineralized rocks. At least three different feeder dykes deliver magmas associated with unit IIIB. The overall dyke system has an upward curving geometry such that the dike dips shallow upwards and as they approach the Eastern Deeps Chamber. This is analogous to fault geometries produced during caldera collapse or cauldron subsidence. Evolving emplacement styles reflect internal igneous processes and intermittent normal movement along pre-syn-emplacement brittle wall rock structures. High-temperature normal sense shear zones are prominent near the basal contact of the chamber (<100 m), and are interpreted to have formed in response to late stage normal faulting of the chamber floor. The geometry and internal structure of the Eastern Deeps Chamber is indicative of top-down incremental emplacement associated with floor subsidence. Our findings are consistent and provide a kinematic and dynamic underpin to previously established petrogenetic models of Voisey¿s Bay and other intrusion-hosted Ni-Cu sulfide deposits.
Summary(Plain Language Summary, not published)
This structural study focuses on the geometry and formation of the ~1.3 billion year old Voisey¿s Bay magma intrusion (Labrador) and its associated world class (and currently mined) nickel-copper deposit. New information on the intrusion was obtained from fieldwork, drill core and an important database of subsurface information on the intrusion and surrounding rocks. The intrusion consists of an upper chamber (Eastern Deeps), for which most of the data is available, and a lower chamber (Western Deeps); these are connected by a network of tabular feeder intrusions (dykes). The Eastern Deeps can be divided into 6 units that show distinct geometries and styles of magma emplacement, and are temporally distinct. The Eastern Deeps was emplaced incrementally, from the top-down, by floor subsidence. The feeder dykes are only associated with the lowermost and latest units of the Eastern Deeps, and delivered most of the Ni-Cu sulphide-rich magmas that form the deposit today.
GEOSCAN ID296261