Geologie et geochimie de la mine Lamaque, Val d'Or, Quebec

CIM Bulletin, Vol. 76, No. 851, 1983

REAL DAIGNEAULT et GUY PERRAULT, Departement de genie mineral Ecole Polytechnique, Montreal, Que., PAUL BEDARD, Compagnie miniere Lamaque, Val d'Or, Que.

The Lamaque Mine is located in Val d'Or, Quebec; host rocks belong to the Upper Malartic Group (andesites and pyroclastites). Intrusive rocks occur in two manners: small plugs (150 m D) and dykes (ca. 10 m thick). The small plugs contain:1 - diorites and tonalites (Main, East and West plugs) of calc-alkaline derivation: Zr 140ppm, Sr 761 ppm, P2O5 0.31% and (La/Sm)n3.0;2 - diorite (plug no 4) of tholeiitic derivation: Zr 32 ppm, Sr 181 ppm, P2OS 0.27% and (La/Sm)n 1.5.The diorite in plug no. 5 is made up of two parts belonging to each of the above groups. Dyke rocks are feldspar porphyry and quartz-feldspar porphyry and are of calc-alkaline derivation: Zr 83 ppm, Sr 500 ppm and P2O5 0.10%. No. 2 mine ore deposit is made up of flat veins and subver-tical veins in shear zones. The last structural readjustment involved north-south compression; it fractured pre-existing quartz veins and thus made possible their mineralization. Mineralized veins contain quartz, tourmaline, calcite with traces ofscheelite, pyrite and gold; they are lined with thin (2 to 20 cm) alteration rims enriched in carbonates, paragonite, apatite, rutile, sphene and zircon, and ferromagnesian mineral phases have been leached out. The following geochemical migrations are documented:1 -from the alteration rim to the wall rock, K2O, Rb and MgO;2 - from the wall rock to the alteration rim, Na2O;3 - from the wall rock to the vein, SiO2.P2O5, TiO2, Zr, Y, Nb and CaO are enriched in the alteration rim. Andesitic lavas and porphyritic diorite in the vicinity of the veins contain anomalous quantities of gold (40 mg/t); normal gold values in these rocks in non-mineralized areas are approximately 1 mg/t.

Keywords: Géologie régionale, veines, minéralisation aufrière, observation géochimique, intrusifs, cheminées, migration, halos endogènes d'or