Pelican Narrows Project - Update

Transcription

1 Pelican Narrows Project - Update R. Maxeiner and N. Rayner Objective of Pelican Narrows project Overview of previously completed geochronology and regional geology Quick review of geology of the Kakinagimak area New geochron results (collaboration with Nicole Rayner) Plans for this summer

2 Objectives Not mapped since late 1960s; existing maps lack differentiation of volcanic, plutonic and sedimentary protoliths, as well as the identification of VMS-type alteration assemblages; (claims in area by HBED, Foran, Athapap Gold, Murgor Resources) Constrain ages of volcanic succession and plutonic components using geochronology; Try to re-address problems regarding age relationship of sedimentary succession in transition zone between KD and FFD; Compile work by Ashton et al. and new work to provide a 1:100,000 scale map for area of new geophysical survey. Ashton et al. (91-95)

3 U-Pb zircon ages (TIMS and SHRIMP) Jan granite 1773 ±9 Ma (n=1); Ma (n=7); 1826 Ma syntectonic qtz diorite and 1830 enderbite; Ma pre- to syntectonic qtz monzonite and granite (n=2); Ma granodioriteleucotonalite (n=3); Rhyolite 1873 ±9 Ma (Scimitar Lk) Ma Sask Craton granitoids/gabbro (n=6); (2 nd episode of zircon growth at 2443 Ma in Q- gneiss); 3117 ±4 Ma Q-gneiss (leucocratic granitoids) SHRIMP; from Ashton et al. (1999; 2005; CJES) Rayner et al. (2005) Previous Geochronology

4 : Unusual grey foliated m-gr tonalite 2-3 km2 homogeneous intrusion Different from typical gneissic tonalite and granodiorite: f-gr to m-gr, contains patchy hbl-bearing partial melt Plag, biotite>hornblende, titanite, apatite, microcline, opaque Previous Geochronology

5 Previous Geochronology : synvolcanic tonalite (Heaman and Ashton, 1992) two multigrain (n=10) fractions ppm U (moderate) Pb 207/206 ages 1835 (3.4 disc), 1864 (4.4 disc)

6 :?sample location Foliated to gneissic leucotonalite Predates all observed deformation Sample contained little leucosome Previous Geochronology

7 Previous Geochronology : gneissic leucotonalite (Heaman et al., 1993) tiny colourless prisms and needles four fractions; 3 fractions give /-4 Ma largest single grain gives Pb207/Pb206 age of 1863 Ma; lowest U (323) and Th (14) ->?inher. meaningless lower intercept 1789 titanite age

8 Previous Geochronology : Attitti Lk Felsic Gneiss (w 10-15% leucosome; some incorporated in sample) (Heaman and Ashton, 1992) heterogeneous zircon population; high U ( ppm) 1807 Ma +3/-2 upper intercept based on four fractions

9 Geology Kakinagimak LEGEND me me Syn- to Post-tectonic Plutons Granite pegmatite Leucogranodiorite, leucogranite?missi Group Feldspathic psammite and derived diatexite Arc and Successor Arc Plutons Cornell Bay Gabbro, microgabbro Quartz monzonite Quartz diorite, diorite and diorite gneiss Gneissic to migmatitic granodiorite-tonalite Homogeneous biotite granodiorite Homogeneous hornblende granodiorite? Amisk Collage Sedimentary Rocks Migmatitic Pelite / derived diatexite Migmatitic psammopelite-(pelite) Migmatitic psammite-(psammopelite) Impure marble, quartzite Quartzite Migmatitic calcic psammopelite Volcanic and Associated Rocks Heterogeneous calcic psammopelite, psammite and intermediate volcanic tuff Altered felsic volcanic, volcaniclastic rocks Felsic volcanic, volcaniclastic, subvolcanic rocks Intermediate volcanic and volcaniclastic rocks Mafic calc-silicate rock Mafic volcanic and volcaniclastic rocks Upper amphibolite facies conditions: 6.6 to 7.9 kbar and temperatures of 630 to 725 C (Ashton and Digel, 1992) mn mn mn Galbraith Bentz Bay (Attitti ) Kilometres McCall Grindley McWilliams File Bay Kakinagimak Gifford Bay Dezort Scott Keep Cawsey Schotts deposit Schotts N

10 Geology Kakinagimak Amisk Collage: Volcanic rocks (? Ga) Upper amphibolite facies (local partial melt) Mafic-felsic f-gr hbl-bi +-cpx gneisses Locally compositionally layered / transposed Locally sulphide bearing / gnt-anth alteration Local chert and exhalative horizons; me me Cornell Bay?Amisk Collage Volcanic and Associated Rocks Heterogeneous calcic psammopelite, psammite and intermediate volcanic tuff Altered felsic volcanic, volcaniclastic rocks Felsic volcanic, volcaniclastic, subvolcanic rocks Intermediate volcanic and volcaniclastic rocks mn mn mn Galbraith Bentz Bay (Attitti ) Kilometres McCall Grindley McWilliams File Bay Kakinagimak Gifford Bay Dezort Scott Keep Cawsey Schotts deposit Schotts N Mafic calc -silicate rock Mafic volcanic and volcaniclastic rocks

11 Geology Kakinagimak Amisk Collage: Sedimentary rocks (?>1.87 Ga;?Burntwood Group) Upper amphibolite facies (migmatite to diatexite) F- to m-gr garnet-biotite-graphite +-hbl gneisses Locally compositionally layered (psp-pelitic) Local quartzite layers, one o/c of marble and qtzt me me Cornell Bay?Amisk Collage Sedimentary Rocks Migmatitic Pelite / derived diatexite Migmatitic psammopelite -(pelite) Migmatitic psammite -(psammopelite) mn mn mn Galbraith Bentz Bay (Attitti ) McCall Grindley McWilliams Kakinagimak Gifford Bay Dezort Scott Keep Cawsey Schotts deposit N Impure marble, quartzite Kilometres File Bay Schotts Quartzite Migmatitic calcic psammopelite

12 Geology Kakinagimak Arc and Successor Arc Plutons (? Ga) Most abundant: Gneissic to migmatitic granodiorite-tonalite bodies; Intrude the volcanic succession on map scale; local amphibolitic xenoliths; = calc-alkaline granodioritic to gabbroic plutons from Flin Flon area; M- to c-gr, compositionally variable, heterogeneous orthogneisses with inclusions and boudinaged dykes; partially melted; Arc and Successor Arc Plutons Gabbro, microgabbro Quartz monzonite Quartz diorite, diorite and diorite gneiss Gneissic to migmatitic granodiorite-tonalite - Homogeneous biotite granodiorite Homogeneous hornblende granodiorite mn mn mn Galbraith Bentz Bay (Attitti ) Kilometres McCall Grindley McWilliams File Bay me me Cornell Bay Kakinagimak Gifford Bay Dezort Scott Keep Cawsey Schotts deposit Schotts N

13 Geology Kakinagimak?Missi Group (?1.84 Ga) magnetite-garnet bearing quartzofeldspathic rocks Gradational from f-gr layered quartzofeldspathic gneiss into homogeneous c-gr diatexite with garnet (~2%), magnetite (~2%), biotite, hornblende, tourmaline, and apatite me me Cornell Bay? Missi Group Feldspathic psammite and derived diatexite mn mn mn Galbraith Bentz Bay (Attitti ) McCall Grindley McWilliams Kakinagimak Gifford Bay Dezort Scott Keep Cawsey Schotts deposit N Kilometres File Bay Schotts

14 Geology Kakinagimak Syn- to post-tectonic plutons (?1.81 Ga) white to pink leucogranodioritic to leucogranitic rocks medium to coarse grained, homogeneous, and weakly to moderately foliated (NE-dipping) Weakly developed NE-dipping foliation may suggest that N-trending inferred crustal melts were emplaced late during D2 in an extensional orientation, related to northeast-southwest directed shortening. Syn - to Post -tectonic Plutons Granite pegmatite mn mn mn Galbraith Bentz Bay (Attitti ) McCall Grindley McWilliams me me Cornell Bay Kakinagimak Gifford Bay Dezort Scott Keep Cawsey N Leucogranodiorite, leucogranite Schotts deposit Kilometres File Bay Schotts

15 me me Structural Geology F4 F3 D0 Cornell Bay F2 F1 F mn mn mn Galbraith Bentz Bay (Attitti ) McCall Grindley Kakinagimak McWilliams Cawsey Dezort Gifford Early Folds Bay (?F2) Scott Keep N Schotts deposit Kilometres File Bay F3 Schotts

16 New Geochronology Results

17 New Geochronology Results Sample RM feldspar porphyry- F-gr, homogeneous, fsp-phyric; Fairly massive; 2-3 km2 unit;?intrusive into surrounding volcanic rocks : Synvolcanic tonalite (Heaman and Ashton, 1992) - two multigrain (n=10) fractions ppm U (moderate) - Pb 7/6 ages 1835 (3.4 disc), 1864 (4.4 disc)

18 New Geochronology Results Sample RM feldspar porphyry- Previous attempt 7/6:1835 Ma, 1864 Ma Two populations: low U cores: Ma high U overgrowth: Ma Feldspar Porphyry - RM (lab # z9364) Pb/ U High U zircon, typically overgrowths approx Ga, not a single statistical population Difficulty in resolving inheritance/incomplete recrystallization of igneous zircon and Pb-loss Zoned, lower U zircon Weighted mean: 1846 ±7 Ma (2sigma) n=31; MSWD = 1.19; probability of fit = 22% Pb/ 235 U

19 New Geochronology Results

20 New Geochronology Results Sample RM porphyritic intermediate volcanic- Fine grained, hbl-bearing, plag-phyric, trachytic, strongly lineated intermediate volcanic rock; Weak comp. layering. Results: High U overgrowths dated by SHRIMP give an age of 1808 ± 4 Ma interpreted as the metamorphic age; Low U zircon present as cores and entire zircon grains were dated by TIMS to be 1831 ± 2 Ma and are interpreted as the crystallization age.

21 New Geochronology Results Kakinagimak area ( Ma Ma) Puffy Dacite ( Ma) Machado et al., 1999 Felsic dykes, Meridian (1847 & 1839 Ma) Stern and Lucas, 1994 Selected other 1840ish ages in Flin Flon Domain after Syme et al. (1998)

22 New Geochronology Results

23 New Geochronology Results Sample RM anatectic leucogranite- M-gr, homogeneous, bi-bearing, colour index <5; Gradational into granodiorite gneisses (?derived from it)

24 New Geochronology Results Sample RM anatectic leucogranite- Red ellipses: high U overgrowths 1807 ± 8 Ma, crystallization age; Blue ellipses: earlier generation of high U overgrowths 1868 ± 6 Ma, interpreted to be inherited from tonalite host; Green ellipses: low U cores ca Ga, represents additional inherited component(s). 206 Pb/ 238 U data-point error ellipses are 68.3% conf ( Pb/ 235 U

25 Summary/Discussion Confirmed ~1807 Ma metamorphism and emplacement of anatectic leucogranite melt sheets Subvolcanic rocks: 1831 Ma; 1848 Ma (successor arc; feeders to Missi volcanism???); still missing the Flin Flon volcanic ages Ma zircon growth in leucogranite: inherited grains recording crystallization of granodiorite suite or earlier metamorphic event related to formation of Flin Flon Glennie Complex at 1870 Ma 1957 Ma cluster (ranging from ) : inherited grains, but uncertain origin; possible indication of older volcanoplutonic rocks?

26 Tentative plans for the summer 7-person crew: Ryan Morelli, Monica Cliveti, Lindsay Richan, Kirby Ebel, Carson Turnbull, Andrew Smith, Ralf 1 st week in June: plan Hanson field trip June: coverage mapping with 3 mapping crews on Wiki July: separate camps for 2 weeks; mid summer breaks August: Kisseynew transition; geochron sampling; field trip. Geochron sampling focus: old volcanic rocks; old sedimentary rocks; potential Missi Group rocks;