| Title | Hybridized ultramafic rocks in the Black Label hybrid zone of the Black Thor intrusive complex, McFaulds Lake greenstone belt, Ontario |
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| Licence | Please note the adoption of the Open Government Licence - Canada
supersedes any previous licences. |
| Author | Spath, C S, III; Lesher, C M; Houlé, M G |
| Source | Targeted Geoscience Initiative 4: Canadian nickel-copper-platinum group elements-chromium ore systems -- fertility, pathfinders, new and revised models; by Ames, D E (ed.); Houlé, M G (ed.); Geological Survey of Canada, Open File 7856, 2015 p.
103-114, https://doi.org/10.4095/296682  Open Access |
| Image |  |
| Year | 2015 |
| Publisher | Natural Resources Canada |
| Document | open file |
| Lang. | English |
| Media | on-line; digital |
| Related | This publication is contained in Targeted Geoscience
Initiative 4: Canadian nickel-copper-platinum group elements-chromium ore systems -- fertility, pathfinders, new and revised models |
| File format | pdf |
| Province | Ontario |
| NTS | 43D/16 |
| Area | McFaulds Lake |
| Lat/Long WENS | -86.2278 -86.1783 52.7969 52.7722 |
| Subjects | metallic minerals; igneous and metamorphic petrology; geochemistry; nickel; platinum; chromium; ore mineral genesis; metallogeny; chromite; harzburgites; mineralization; whole rock geochemistry; whole
rock analyses; Superior Province; Black Thor intrusive complex; Precambrian |
| Program | Targeted Geoscience Initiative (TGI-4) Mafic-Ultramafic Ore Systems |
| Released | 2015 06 22; 2023 03 17 |
| Abstract | The ca. 2.7 Ga Black Thor intrusive complex (BTIC) is an ultramafic to mafic, layered intrusion composed primarily of dunite, peridotite, pyroxenite, and chromitite overlain by lesser gabbroic rocks and
rare anorthosite. After emplacement but before complete crystallization, a late websterite intrusion (LWI) reactivated the feeder conduit and transected the basal part of the BTIC, including the Black Label chromitite zone (BLCZ). All rocks have been
metamorphosed to lower greenschist facies, but igneous minerals are preserved in some parts (particularly in the LWI) and relict igneous textures are well preserved in most parts. Logging of selected parts of 39 drill cores shows that semi-concordant
intrusion of LWI magma and incorporation of inclusions produced a 1 to 10 m thick marginal zone of heterogeneous, interfingering brecciation defined as the Black Label hybrid zone (BLHZ). The BLHZ contains variably sized (1-50 cm) dunite/lherzolite/
chromitite inclusions with subangular to amoeboidal geometries, sharp to diffuse contacts, and locally significant amounts of patchy disseminated to patchy net-textured Fe-Ni-Cu-(PGE) sulphide mineralization. The core of the LWI is typically an
inclusion-free, medium-grained, orthopyroxene-rich adcumulate with accessory chromite or olivine; however, inclusion-rich intervals of the LWI contain more olivine and chromite produced by disaggregation and partial assimilation of BTIC ultramafic
rocks. There are two types of hybrid groundmass: one containing xenocrystic olivine and one containing xenocrystic chromite and olivine in varying proportions. Geochemical signatures of the hybrid rocks reflect the partial assimilation and
brecciation of chromitite/lherzolite/dunite sequences. Similar Th-U-Nb-Ta-light rare earth element LREE patterns suggest that the LWI is related to the BTIC, presumably representing a more fractionated magma from deeper in the system. Further
characterization of the hybrid rocks and inclusion variability is in progress and will help to establish the range and variability of processes within the BTIC, and their influence on the genesis of associated Fe-Ni-Cu-PGE sulphide mineralization in
the BLHZ. |
| Summary | (Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI-4) is a collaborative federal geoscience program that provides industry with the next generation of geoscience
knowledge and innovative techniques to better detect buried mineral deposits, thereby reducing some of the risks of exploration. This volume summarizes 22 research activities completed under the TGI-4 Ni-Cu-PGE-Cr ore systems project that focused on
revised and new geologic models for Ni-Cu-PGE, PGE-Cu and Cr deposits, innovative techniques for determining potential fertility of intrusion (Ni-Cu-PGE), and defining pathfinders for Ni-Cu-PGE mineralization. |
| GEOSCAN ID | 296682 |
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