Issue 54 October 1996 Tectonostratigraphic And Depositional Setting Of Paleoproterozoic Volcanogenic Massive Sulphide Deposits, Flin Flon, Manitoba MDD - 1996 Julian Boldy Award Winner Eric C. Syme1, Alan H. Bailes1, Stephen B. 2 2 (~30%), and minor (<10% total) ocean pla- abundances in the estimated mantle source of Lucas and Richard A. Stern teau, ocean island basalt and ‘evolved’ plu- modern N-MORBs, probably due to their 1 Manitoba Energy and Mines, 2 tonic arc. All of the VMS deposits mined to derivation from a highly refractory mantle Geological Survey of Canada date are associated with juvenile arc tectonos- source. tratigraphic assemblages: no economic Cu-Zn The historically non-productive juvenile The Flin Flon greenstone belt in the ju- deposits have been found in the voluminous ocean-floor assemblages include basalt/di- venile (internal) zone of the Paleoproterozoic back-arc basaltic sequences. The first-order abase sequences and related kilometre-scale Trans-Hudson Orogen, northern Manitoba association between juvenile arc rocks and layered mafic-ultramafic bodies. U-Pb zircon and Saskatchewan (Fig. 1), is one of the larg- VMS deposits provides a powerful screen to ages for both the basalts and cumulate com- est Proterozoic volcanic-hosted massive sul- focus exploration in the Flin Flon belt. Con- plexes indicate that the ocean-floor assem- phide (VMS) districts in the world. Produc- sequently, knowledge of the physical (li- blage is coeval with tholeiitic arc volcanism tion plus reserves in 25 Cu-Zn-(Au-Ag) past- thologic, stratigraphic), geochemical and geo- at Flin Flon (ca. 1.904 Ga). The basalts occur and presently-producing mines totals 110 Mt chronological characteristics of the as laterally coherent ‘formations’, 4 to >60 km of sulphide, with a further 23 Mt contained in assemblages in the Amisk collage is crucial in strike length with stratigraphic thicknesses 20 subeconomic deposits.The Flin Flon belt for effective base metal mineral exploration. of 0.3 to 3.0 km, each having characteristic has been calculated to contain more base and 2 The 1.9 Ga juvenile arc assemblages are weathering colour, flow morphology, altera- precious metals per km than any other VMS dominantly mafic (basalt, basaltic andesite), tion assemblage and geochemistry. The ba- district in Canada (J. Franklin, GSC). with <10% rocks of andesite-rhyolite compo- salts are dominantly subalkaline with MgO The local depositional and regional tec- sition. Tholeiitic arc suites tend to be older contents typical of modern MORBs, falling tonic setting of VMS deposits in the Flin Flon (1903-1886 Ma) than calcalkaline (1886- mostly in the range 6-10 wt.%. They have belt have been the focus of investigations for 1882 Ma) and shoshonitic (1885 Ma) suites; higher TiO2, Zr, and Ni compared to the coe- many years. Most recently, the five-year boninites (>1886 Ma) occur only in the Snow val arc volcanic rocks of equivalent MgO. The GSC-Manitoba-Saskatchewan NATMAP Lake arc assemblage. The arc rocks were de- ocean-floor basalts can be subdivided into two Shield Margin Project has built on an exten- posited in a subaqueous environment, but main types, using the ratios of the immobile sive existing geological database to result in a there is clear morphologic evidence (e.g., trace elements: N-type (similar to ‘normal’ much improved understanding of the compo- presence of bubble wall shards, pumice) that MORB);2)E-type(similarto‘enriched’ nents and evolution of the Flin Flon belt. This resedimented pyroclastic rocks may have MORB). Some show no evidence of either a work has demonstrated that the Flin Flon been erupted in a very shallow marine or greenstone belt comprises 1.92-1.88 Ga tec- subaerial setting. Arc sequences commonly tonostratigraphic assemblages derived from a represent a proximal facies with respect to variety of tectonic environments that were source vents, comprising abundant pillowed amalgamated to form an accretionary collage and massive flows, coarse volcaniclastic de- (‘Amisk collage’) prior to the emplacement of bris flow deposits, rare sedimentary interbeds, 1.87-1.83 Ga granitoid plutons (Fig. 1). The and abundant synvolcanic dikes and sills. plutons, and rarely preserved coeval volcanic Stratigraphic sequences are complex and typi- rocks, are associated with younger arc(s) im- cally display a wide variety of rock types with posed on the collage, resulting in the develop- interfingering relationships, lenticular units, ment of a microcontinent by 1.85-1.84 Ga. and abrupt facies variations. Relative to mod- VMS deposits in the Flin Flon belt are ern MORBs, Flin Flon belt arc assemblage hosted by the earlier (1.9 Ga) tectonostrati- rocks have low abundances of Ti, Zr, Hf, Nb, graphic assemblages forming the Amisk col- Y, middle and heavy REEs, Ni and Cr, and are lage. The 1.9 Ga assemblages include juvenile similar to modern oceanic island arc suites. Flin Flon Belt - arc rocks (~60% of the exposed supracrustal For the most primitive Flin Flon arc assem- rocks), juvenile ocean-floor/back-arc rocks blage rocks these values are only 1-2.5x their Manitoba, Canada October 1996 1 1996 – 1997 MDD EXECUTIVE The Gangue No. 54 Following are the MDD Executive and Directors for the 1996-1997 term. Please contact The Gangue is published quarterly by the Mineral Deposits Division, GAC, and is dis- any of these individuals for enquiries, or to suggest initiatives for MDD. tributed to members as part of their member- ship. Chairperson: Cominco Ltd., David Moore 7th Floor 409 Granville St. Vancouver, BC, V6C 1T2. Tel: 604-685-3064; FAX: 604-685-3069 MDD Goals and Objectives The Mineral Deposits Division of the Geo- Vice Chairperson Geological Survey of Canada logical Association of Canada is Canada’s fore- Al Galley 661 - 601 Booth Street most society for promoting the study of mineral Ottawa, ON, K1A 0E8 deposits by supporting local and national meet- Tel: 613-992-7867 E-mail: [email protected] ings, symposia, short courses and field trips. We sponsor the publication of research relating to Past Chairperson & Membership DIAND ore deposits and metallogeny and recognize the Jennifer Pell 4-4914 50th Street, Bellanca Bldg. contributions of outstanding Canadian eco- PO Box 1500, Yellowknife, NT, X1A 2R3 nomic geologists by annually awarding the Tel: 403-669-2640 FAX: 403-873-5763; Duncan Derry and William Harvey Gross med- E-mail: [email protected] als and the Julian Boldy Certificate. Secretary: Inmet Mining Corporation Publication Schedule: Gary S. Wells 3-311 Water Street, Vancouver, BC, V6B 1B8 Tel: 604-681-3771 FAX: 604-681-3360 SUBMISSION PUBLICATION DEADLINE DATE Treasurer: Cathro Exploration Corp. Robert J. Cathro RR#1, Site U-39, Bowen Is., BC, V0N 1G0 December 15 January Tel: 604-947-0038 FAX: 604-947-0038 March 15 April June 15 July Publications: Wolverton Securities September 15 October Art Ettlinger 17th Floor - 701 W. Georgia Street Information for contributors: Vancouver, BC, V7Y 1J5 Tel: 604-662-5248; FAX: 604-662-5205 The objective of this newsletter is primarily to provide a forum for members and other pro- Professional Development Univ. of Windsor, Dept. of Earth Sciences fessionals to voice new ideas, describe interest- Short Courses: 212A Memorial Hall, Windsor, ON ing mineral occurrences or expound on deposit Iain M. Samson Tel: 519-253-4232 ext 2489; FAX: 519-973-7081 models. Articles on ore deposits, deposit mod- E-mail: [email protected] els, news events, field trips, book reviews, con- ferences, reprints of presentations to Professional Development BC Geological Survey companies, mining groups or conferences, or Field Trips: 5 - 1810 Blanshard Street; Victoria, BC, V8T 4J1 other material which may be of interest to the Tel: 604-952-0412 FAX: 604-952-0381; economic geology community are welcomed. Dani Alldrick E-mail: [email protected] Manuscripts should be submitted on IBM- Program Chair: Ottawa ‘97 Mineral Resources Division, GSC, 601 Booth St., formatted diskettes in any major word proces- Al Sangster Ottawa, ON, K1A 0E8. Tel: 613-992-8603; sor format. A printed version should be FAX: 613-996-9820; E-mail: included. Illustrations must be camera-ready [email protected]. (ideally as CDR digital files); photos should be of good quality. Short items dealing with news Program Chair: Quebec City ‘98 Sainte-Foy, Quebec events or meetings can be submitted by FAX, Benoit Dubé Tel: 418- 654-2669 FAX: 418- 654-2615; postal mail or E-mail. E-mail: [email protected]. Newsletter Editor The Gangue, PO Box 8076, Victoria, BC, V8W 3R7 Contributions may be edited Brian Grant Tel: 604-952-0454; FAX: 604-952-0451 for clarity or brevity. E-mail: [email protected] For Information & Submissions: MDD DIRECTORS Brian Grant Terence J. Bottrill (1994 - 1997) Oakville, Ontario Editor - THE GANGUE Tel: 905-842-2893; FAX: 905-842-3614 PO Box 8076, Victoria, BC, V8W 3R7 Pamela L. Schwann (1994 - 1997) La Ronge, Saskatchewan Tel: 604-952-0454 FAX: 604-952-0451 Tel: 306-425-4211 FAX: 306-425-4349 E-mail: [email protected] Marcos Zentilli (1994 - 1997) Halifax, Nova Scotia Tel: 902-494-3873 FAX: 902-494-6889; E-mail: [email protected] Dani Alldrick - Associate Editor Dan Brisbin (1995 - 1998) Timmins, Ontario. E-mail: [email protected] Tel: 705-267-1188 ext 253; FAX: 705-264-6080 E-mail: [email protected] *** Michael J. Downes (1995 - 1998) Toronto, Ontario. The MDD encourages geoscientists to join Tel: 416-869-3578; FAX: 416-869-3359 E-mail: [email protected] the division and contribute to the various Kerry Sparkes (1996 - 1999) St. John’s, Newfoundland programs and activities. Tel: 709-758-1700; FAX: 709-758-1717 Malcolm Robb (1996 - 1999) Yellowknife, Northwest Territories Tel: 403-873-6301; FAX: 403-873-2914 E-mail: [email protected] Paul Archer (1996 - 1999) Quebec City, Quebec Tel: 418-694-9832; FAX: 418-692-3969 Michael Marchand (1996 - 1999) Calgary, Alberta Tel/FAX: 403-282-5105 E-mail: [email protected] 2 The Gangue No.