Evaluating the Intrusion-Related Model for the Archean Low-Grade, High- Tonnage Côté Gold Au(-Cu) Deposit

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1 Evaluating the Intrusion-Related Model for the Archean Low-Grade, High- Tonnage Côté Gold Au(-Cu) Deposit L.R. Katz, D.J. Kontak, Laurentian University, B. Dubé, V. McNicoll, Geological Survey of Canada R.A. Creaser, University of Alberta

2 Indicated/inferred resource of 8.65 Moz Au ( g/t)

3 Indicated/inferred resource of 8.65 Moz Au ( g/t)

4 Three distict gold-rich metallogenic events in the Abitibi Robert (2001)

5 Côté Gold represents a new metallogenic event Intrusionrelated 2740 Ma Robert (2001)

6 Outline 1) Regional geological setting 2) Exploration history 3) Deposit geology 4) Geochemistry of host rocks 5) Distribution and nature of mineralization 6) Alteration types 7) Geochronology of alteration and mineralization 8) Deposit model 9) Summary and conclusions

7 1. Geological Setting Modified after Dubé and Gosselin (2007)

8 1. Geological Setting ca Ma Chester Intrusive Complex (CIC): multiphase high-level intrusion of tonalitediorite CIC Intrudes mafic metavolcanic rocks of Arbutus Formation ca Ma overlying felsic to intermediate metavolcanic rocks of the Yeo Formation after Ayer and Chartrand (2011), Berger (2011)

9 1. Geological Setting ca Ma Chester Intrusive Complex (CIC): multiphase high-level intrusion of tonalitediorite CIC Intrudes mafic metavolcanic rocks of Arbutus Formation ca Ma overlying felsic to intermediate metavolcanic rocks of the Yeo Formation after Ayer and Chartrand (2011), Berger (2011)

2739 Ma overlying felsic to intermediate metavolcanic

10 1. Geological Setting ca Ma Chester Intrusive Complex (CIC): multiphase high-level intrusion of tonalitediorite CIC Intrudes mafic metavolcanic rocks of Arbutus Formation ca Ma overlying felsic to intermediate metavolcanic rocks of the Yeo Formation Arbutus Formation Yeo Formation after Ayer and Chartrand (2011), Berger (2011)

11 Côté Gold deposit 2. Exploration History

12 3. Deposit Geology Hosted in CIC tonalite (I) diorite tonalite (II); Breccias of magmatic and magmatichydrothermal origin intrude tonalitediorite complex.

13 Tonalite intruded by diorite 3. Field Relationships Diorite intruded by quartz diorite Diorite intruded by tonalite

14 Tonalite intruded by diorite 3. Field Relationships Diorite intruded by quartz diorite Tonalite Diorite I II Diorite intruded by tonalite

15 3. Textures

16 3. Textures 2.3 g/t Au 0.8 g/t Au

$tonalite Relatively unfractionated$ chondrite-normalized REE patterns Similar to

17 4. Geochemistry- Tonalite and Diorite Low-Al tonalite Relatively unfractionated chondrite-normalized REE patterns Similar to other low-al composite intrusions found below VMS-type deposits

18 5. Distribution of Mineralization Breccia bodies

19 5. Distribution of Mineralization agmatic breccia Hydrothermal breccia

20 5. Nature of Mineralization 1) Disseminated: Matrix of magmatic and hydrothermal biotite breccia Altered tonalite/diorite VG Moly 2) Vein-controlled: Discrete stockwork Sheeted

21 6. Alteration Amphibole Biotite Sericite Sodic Epidote Early Late Diorite Breccia matrix Tonalite Breccia Tonalite

6. Amphibole Alteration Assemblage: - Hbl ± Qz

Vein-controlled: Amphibole vein Albite rim

22 6. Amphibole Alteration Assemblage: - Hbl ± Qz ± Ttn ± Ap ± Mag ± Bt ± Ab ± Py ± Ccp - Mineralogically similar to dioritic rocks of CIC Diorite Style: - Breccia-hosted - Vein-controlled: Amphibole vein Albite rim Distribution: - Restricted to deep and central parts of the deposit

6. Biotite Alteration Assemblage: Bt ± Qz ±

Hydrothermal biotite breccia is centered on

23 6. Biotite Alteration Assemblage: Bt ± Qz ± Mag ± Ep ± Aln ± Cb ± Ap ± Ttn ± Bst ± Fl ± Py ± Ccp ± Gn ± Sp Style: Breccia hosted/disseminated/ veins Distribution: Hydrothermal biotite breccia is centered on the deposit Disseminated and vein extend outwards from breccia

24 Breccia matrix 6. Biotite Alteration Assemblage: Bt ± Qz ± Mag ± Ep ± Aln ± Cb ± Ap ± Ttn ± Bst ± Fl ± Py ± Ccp ± Gn ± Sp Breccia matrix Style: Breccia hosted/disseminated/ veins Distribution: Hydrothermal biotite breccia is centered on the deposit Disseminated and vein extend outwards from breccia

veins Distribution: Hydrothermal biotite

25 Breccia matrix 6. Biotite Alteration Assemblage: Bt ± Qz ± Mag ± Ep ± Aln ± Cb ± Ap ± Ttn ± Bst ± Fl ± Py ± Ccp ± Gn ± Sp Style: Breccia hosted/disseminated/ veins Distribution: Hydrothermal biotite breccia is centered on the deposit Disseminated and vein extend outwards from breccia

$fractures and replacement Overprints$ biotite alteration Distribution:

26 6. Sericite Alteration Assemblage: Mus ± Qz ± Cb ± Py ± Ccp Replacement Sheeted vein Style: Borders veins, fractures and replacement Overprints biotite alteration Distribution: Most intense in in core and weak distally

27 Breccia 6. Sericite Alteration Sheeted vein

28 Breccia 6. Sericite Alteration Sheeted vein

6. Sodic Alteration Assemblage: - Ab ± Qz

29 6. Sodic Alteration Assemblage: - Ab ± Qz ± Cb ± Ttn ± Ilm ± Chl Style: - Vein-controlled - Replacement of plagioclase and mafic minerals Spatial distribution: - Strong and pervasive in center of deposit - Overprints sericite alteration and not as widespread

30 6. Epidote Alteration Assemblage: Ep ± Qtz ± Cb ± Chl ± Py ± Ccp Style: Vein-controlled Replacement of plagioclase and mafic minerals Distribution: Restricted to north of deposit

31 N 6. Distribution of Alteration Paleo-tectonic top Amphibole veins and breccias Paleo-tectonic bottom

32 N 6. Distribution of Alteration Paleo-tectonic top Biotite breccia with outward veins and disseminations Paleo-tectonic bottom

33 N 6. Distribution of Alteration Paleo-tectonic top Sericite alteration Paleo-tectonic bottom

34 6. Distribution of Alteration N Paleo-tectonic top Epidote alteration Sodic alteration Paleo-tectonic bottom

35 7. Geochronology- Hydrothermal Stage LA ICP-MS method Amphibole hydrothermal event constrained to 2745 ± 3 Ma

36 7. Geochronology- Hydrothermal Stage LA ICP-MS method LA ICP-MS method

37 7. Geochronology- Molybdenite Two Re-Os ages at 2739 ± 7 Ma (Kontak et al., 2013) Skidder Outcrop DDH E09-01 (Box 46)

38 7. Geochronology- Molybdenite Moly Moly Au Au grew with pyrrhotite (Po) and occurs along cleavage planes in Molybdenite (Mol) and is interpreted to be syn- to post-molybdenite; Re-Os age of ± 11.4 Ma

39 7. Geochronology- Molybdenite E-W sheeted veins predate lamprophyre dike and shearing event;

40 7. Geochronology- Molybdenite E-W sheeted vein E-W sheeted veins predate lamprophyre dike and shearing event; Re-Os age of ± 11.4 Ma.

41 7. Geochronology- Molybdenite Côté Gold deposit E-W sheeted veins in and outside deposit predate shearing; confirmed by Re-Os age and structural study

42 8. Deposit Model Hosted by a high-level low-al tonalite and diorite; Amphibole, biotite and sericite alteration are the result of Fe- Mg-Ca-K metasomatism derived from diorite; Oxidized mineral assemblage (pyrite-magnetite-chalcopyritepyrrhotite); Overlap of magmatic and hydrothermal events at 2740 Ma.

43 8. Deposit model Poulsen et al. (2000)

44 8. Deposit model Poulsen et al. (2000)

45 8. Deposit Model Can the Côté Gold deposit be equated to a porphyrytype deposit? Tectonic setting/ environment Côté Gold deposit Subvolcanic; possible back-arc environment Depth Shallow ~1 to 5 km Porphyry deposits Oceanic or continental arc (and back arc); transtensional to moderately extensional Host rocks Tholeiitic to calc-alkaline; tonalite and water-rich diorite Calc-alkaline; water-rich; felsic to intermediate intrusion Alteration types Amphibole, biotite, sericite, sodic, epidote Calcic-sodic, potassic, phyllic, propylitic, argillic Alteration zonation Deep amphibole; central biotite breccia; overprinted by sericite; epidote restricted to north Deep calcic-sodic; central potassic; overprinted by sericite; surrounded by propylitic Mineralization styles Breccia-hosted, veins, disseminated Vein, breccia, disseminated Mineral associations Py, ccp Py, ccp, bn Sillitoe (2010) Metal associations Au ± Cu ± (Mo-Ag-Te-Bi- Zn) Cu ± Mo ± Au ± Ag ± (Zn- Pb-Ag) Timing Syn-genetic with intrusion Syn-genetic with intrusion

9. Summary and Conclusions Low-grade (~1g/t), large-tonnage Au deposit; CIC is a high-level, subvolcanic, 2741 Ma low-al tonalite-diorite complex similar to other low-al composite intrusions;

46 9. Summary and Conclusions Low-grade (~1g/t), large-tonnage Au deposit; CIC is a high-level, subvolcanic, 2741 Ma low-al tonalite-diorite complex similar to other low-al composite intrusions; Amphibole biotite sericite alteration the result of magmatically derived fluids; alteration is zoned on deposit scale; Alteration and mineralization is constrained to 2740 Ma (U-Pb titanite, Re-Os molybdenite) and overlaps with the age of intrusive complex; Côté Gold represents an Archean analogue to porphyry-type deposits in which a magmatic-hydrothermal system developed from an intermediate dioritic magma, resulting in mineralization coincident with the formation of distinct hydrothermal alteration types (amphibole, biotite, sericite).

47 Thank you

The 2740 Ma Côté Gold Au(-Cu) deposit, Canada: Example of porphyry-type magmatic-hydrothermal ore-forming processes in the Archean

The 2740 Ma Côté Gold Au(-Cu) deposit, Canada: Example of porphyry-type magmatic-hydrothermal ore-forming processes in the Archean Daniel J. Kontak, Laura Katz, Laurentian University Benoit Dubé, Geological