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

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

Indicated/inferred resource of 8.65 Moz Au (340 Mt @ 0.8 g/t)

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

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

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

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

1. Geological Setting ca. 2741 Ma Chester Intrusive Complex (CIC): multiphase high-level intrusion of tonalitediorite CIC Intrudes mafic metavolcanic rocks of Arbutus Formation ca. 2739 Ma overlying felsic to intermediate metavolcanic rocks of the Yeo Formation after Ayer and Chartrand (2011), Berger (2011)

Côté Gold deposit 2. Exploration History

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

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

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

3. Textures

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

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

5. Distribution of Mineralization Breccia bodies

5. Distribution of Mineralization agmatic breccia Hydrothermal breccia

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

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

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 ± 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

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

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

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

Breccia 6. Sericite Alteration Sheeted vein

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

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

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

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

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

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

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

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

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

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 2736.1 ± 11.4 Ma

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

7. Geochronology- Molybdenite E-W sheeted vein E-W sheeted veins predate lamprophyre dike and shearing event; Re-Os age of 2746.8 ± 11.4 Ma.

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

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.

8. Deposit model Poulsen et al. (2000)

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; 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).

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