| Title | The Lemoine auriferous volcanogenic massive sulfide deposit, Chibougamau camp, Abitibi Greenstone Belt, Quebec, Canada: geology and genesis |
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| Author | Mercier-Langevin, P; Lafrance, B; Bécu, V; Dubé, B; Kjarsgaard, I; Guha, J |
| Source | Archean volcanism, magmatism and ore deposits; by Mercier-Langevin, P (ed.); Hannington, M (ed.); Gibson, H (ed.); Houlé, M (ed.); Dubé, B (ed.); Monecke, T (ed.); Goutier, J (ed.); Economic geology and
the bulletin of the Society of Economic Geologists vol. 109, no. 1, 2014 p. 231-269, https://doi.org/10.2113/econgeo.109.1.231 |
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| Year | 2014 |
| Alt Series | Earth Sciences Sector, Contribution Series 20120014 |
| Publisher | Society of Economic Geologists |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Province | Quebec |
| NTS | 32G/09; 32G/10; 32G/15; 32G/16 |
| Area | Chibougamau |
| Lat/Long WENS | -75.0000 -74.0000 50.0000 49.5000 |
| Subjects | metallic minerals; structural geology; igneous and metamorphic petrology; geochemistry; volcanogenic deposits; sulphide deposits; Archean; metallogeny; alteration; mineral assemblages; metamorphism;
greenschist facies; deformation; chlorite; sericite; epidote; chloritoid; tectonic setting; gold; mineralization; hydrothermal alteration; hydrothermal deposits; lithology; volcanic rocks; rhyolites; dacites; andesites; basalts; gabbros; porphyries;
geochemical analyses; trace element geochemistry; major element geochemistry; Abitibi greenstone belt; Lemoine deposit; Waconichi Formation; Lemoine Member; Precambrian |
| Illustrations | geological sketch maps; geochemical analyses |
| Program | Targeted Geoscience Initiative (TGI-4) Volcanogenic Massive Sulfide Ore Systems |
| Program | Targeted Geoscience Initiative (TGI-4) Gold Ore Systems |
| Released | 2013 11 19 |
| Abstract | The Lemoine auriferous volcanogenic massive sulfide deposit (0.76 Mt at 4.6 g/t Au, 4.2 wt % Cu, and 9.5 wt % Zn) is part of the Chibougamau camp located in the northeastern part of the Abitibi
greenstone belt. The deposit is hosted by a steeply dipping, S-facing homoclinal volcanic succession (~2729-2726 Ma Waconichi Formation, Lemoine Member) composed of effusive and intrusive tholeiitic rhyolites and andesites cut by comagmatic diorite
and gabbro dikes and overlain by transitional to mildly calc-alkaline basalts, andesites, and rhyolites.
Seven predominant synvolcanic alteration assemblages, now intensely deformed and metamorphosed to upper greenschist facies, were defined based
on their mineralogy and position relative to ore. Albite-quartz, sericite-carbonate, sericite-chlorite, sericite-chlorite-(Zn), and chlorite-sericite-epidote-carbonate assemblages define semiconcordant zones that are stacked from the paleoseafloor to
the deep footwall. In contrast, chlorite and chlorite-sericite-chloritoid assemblages overprint the other alteration zones and form subconcordant to now transposed discordant zones in the deposit footwall. Most alteration assemblages are
characterized by relative SiO2, CaO, and Na2O mass losses and relative FeO, MgO, K2O, and CO2 mass gains. Whole-rock oxygen isotopes indicate that the temperatures of alteration ranged from ~100° to 150°C (sericite-carbonate assemblage) to >=350°C
(sericite-chlorite, chlorite-sericite-chloritoid, and chlorite assemblages). The chlorite-sericite-chloritoid assemblage, and to some extent the sericite-chlorite assemblage, are associated with strong to near total depletion of light rare earth
elements possibly due to reaction with Cl-bearing, mildly acidic fluids at depth in the ore-forming hydrothermal system.
The sulfide lens was formed in part on the seafloor and in part by subseafloor replacement. The massive sulfides are
particularly rich in Bi, suggesting a possible magmatic input into the Lemoine ore-forming hydrothermal system. High Bi concentrations in the mineralizing system are likely to have enhanced Au precipitation by scavenging the precious metal from the
hydrothermal fluids. The Au-rich nature of the Lemoine auriferous volcanogenic massive sulfide deposit can be explained by a combination of very efficient metal transport, highly effective capture of metals at or near the seafloor, and a possible
magmatic contribution to the hydrothermal system. |
| GEOSCAN ID | 291366 |
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