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Open File OF2018-4: Geology of the Tower Cu-Zn-Ag-Au Deposit, Sub Open File OF2018-4 Geology of the Tower Cu-Zn-Ag-Au deposit, sub-Phanerozoic Superior boundary zone, central Manitoba (part of NTS 63G14) by C.G. Couëslan Manitoba Geological Survey Winnipeg, 2018 ©Queen’s Printer for Manitoba, 2018 Every possible effort is made to ensure the accuracy of the information contained in this report, but Manitoba Growth, Enterprise and Trade does not assume any liability for errors that may occur. Source references are included in the report and users should verify critical information. Any third party digital data and software accompanying this publication are supplied on the understanding that they are for the sole use of the licensee, and will not be redistributed in any form, in whole or in part. Any references to proprietary software in the documentation and/or any use of proprietary data formats in this release do not constitute endorsement by Manitoba Growth, Enterprise and Trade of any manufacturer’s product. When using information from this publication in other publications or presentations, due acknowledgment should be given to the Manitoba Geological Survey. The following reference format is recommended: Couëslan C.G. 2018: Geology of the Tower Cu-Zn-Ag-Au deposit, sub-Phanerozoic Superior boundary zone, central Manitoba (part of NTS 63G14); Manitoba Growth, Enterprise and Trade, Manitoba Geological Survey, Open File OF2018-4, 38 p. NTS grid: 63G14 Keywords: juvenile volcanic arc; klippe; Manitoba; Superior boundary zone; Superior margin; Thompson nickel belt; Tower deposit; Trans-Hudson orogen; volcanogenic massive-sulphide Published by: Manitoba Growth, Enterprise and Trade Manitoba Geological Survey 360–1395 Ellice Avenue Winnipeg, Manitoba R3G 3P2 Canada Telephone: 1-800-223-5215 (General Enquiry) 204-945-6569 (Publication Sales) Fax: 204-945-8427 E-mail: [email protected] Website: manitoba.ca/minerals ISBN No.: 978-0-7711-1592-9 This publication is available to download free of charge at manitoba.ca/minerals Cover illustrations: Left: The author logging Tower deposit drillcore at Rockcliff Metals Corporation’s storage facility. Right: Chlorite schist representing intense hydrothermal alteration associated with the T2 zone of the Tower deposit. ii Manitoba Geological Survey Abstract from mobilization along a late (D3–D4) structure. The biotite- The Tower Cu-Zn-Ag-Au deposit is a bimodal, likely muscovite schist may represent an intense sericitic footwall mafic-dominated volcanogenic massive-sulphide (VMS) sys- alteration zone to the T1 mineralization. The T2 zone mineral- tem located along the sub-Phanerozoic Superior craton margin. ization is hosted near the structural base of the chlorite schist The deposit is hosted in a sequence of variably altered metavol- unit, which likely represents a zone of intense chloritic altera- canic rocks now represented by hornblende, biotite-garnet, and tion in the stratigraphic footwall of the deposit. The geometry grunerite-magnetite gneisses, and biotite-muscovite, garnet- of the T2 zone and host footwall alteration suggests the Tower biotite, cummingtonite, and heterogeneous chlorite schists. The stratigraphy may be overturned. various hornblende gneisses represent the least altered mafic Lithogeochemistry and Sm-Nd isotope geochemistry sug- volcanic rocks, whereas the biotite-garnet and grunerite-mag- gest the Tower stratigraphy consists of juvenile volcanic arc netite gneisses represent the least altered felsic to intermediate rocks. The arc rocks are distinct from those in the adjacent volcanic rocks. The schists represent zones of more intensely East Kisseynew domain based on trace-element profiles and altered volcanic rocks. The biotite-muscovite, and garnet-bio- εNd values of +0.1 to +3.2, compared to +3.0 to +3.7 for the tite and cummingtonite schists correspond to zones of intense East Kisseynew domain. The presence of felsic volcanic rocks sericite-paragonite alteration of felsic and mafic rocks, whereas with FII–FIIIa rhyolite geochemistry, local mafic rocks with the chlorite schist represents zones of intense chlorite alteration boninitic affinity, and ultramafic intrusions are suggestive of of dominantly mafic rocks. The Tower stratigraphy is intruded a rifted arc environment. Extensional arc environments are by gabbroic and ultramafic intrusions now represented by characterized by high heat-flow and localized structural perme- plagioclase amphibolite and ultramafic schist, respectively. A ability, features conducive to the formation of VMS mineraliza- granodiorite intrusion is present in the structural hangingwall to tion. The rocks hosting the Tower deposit likely formed in an the deposit. The rocks of the Tower deposit are characterized by island-arc environment, within the Manikewan ocean basin, at middle amphibolite-facies mineral assemblages. an unknown distance from the Superior craton margin. These The T1 zone mineralization is discordant to stratigraphy juvenile arc rocks were likely thrust onto the Superior craton and is hosted within biotite-muscovite schist in the north and margin during the Trans-Hudson orogeny and preserved as a hornblende gneiss in the south. The T1 zone varies from a sul- klippe, or erosional remnant. Additional thrust slices with simi- phidic schist to a sulphide breccia, the latter consisting of frag- lar VMS potential could exist elsewhere along the sub-Phanero- ments of wall-rock hosted in solid sulphide, interpreted to result zoic portion of the Superior craton margin. Open File OF2018-4 iii iv Manitoba Geological Survey TABLE OF CONTENTS Page Abstract ...........................................................................................................................................................................................iii Introduction ......................................................................................................................................................................................1 Regional setting ...............................................................................................................................................................................2 Ospwagan group stratigraphy .....................................................................................................................................................3 Winnipegosis komatiite belt ........................................................................................................................................................4 East Kisseynew domain ..............................................................................................................................................................5 Geology of the Tower deposit ..........................................................................................................................................................5 Stratigraphy of the Tower deposit ...............................................................................................................................................5 Methodology ..........................................................................................................................................................................5 Footwall to the T1 zone mineralization .................................................................................................................................8 The T1 zone mineralization ...................................................................................................................................................9 Stratigraphy between the T1 and T2 zones ............................................................................................................................9 The T2 zone mineralization .................................................................................................................................................12 Hangingwall to the Tower deposit .......................................................................................................................................12 Comments on the Tower stratigraphy ..................................................................................................................................12 Intrusions..............................................................................................................................................................................13 Lithogeochemistry and Sm-Nd isotope geochemistry ...................................................................................................................13 Sampling and analytical methods .............................................................................................................................................14 Tower chemostratigraphy ..........................................................................................................................................................14 Intrusions...................................................................................................................................................................................16 Metamorphism ...............................................................................................................................................................................16 Methods.....................................................................................................................................................................................16 Mineral assemblages .................................................................................................................................................................18
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