TIMING CONSTRAINTS AND PARAGENESIS OF MINERALIZING EVENTS AT THE CRESTAURUM GOLD DEPOSIT, YELLOWKNIFE GREENSTONE BELT, NWT, CANADA

The Crestaurum shear zone-hosted lode gold deposit is located 14km north of Yellowknife, Northwest Territories, Canada, in the late Archean Yellowknife Greenstone Belt of the southwestern Slave Structural Province. The 035°/55° SE shear zone transects metamorphosed basalts (ca. >2722 Ma), mixed felsic volcaniclastics, and post-volcanic gabbro and QFP dikes (ca. 2670 Ma). The metamorphic grade of the host rocks are greenschist to the east and transitional to amphibolite grade towards a polyphase tonalite to the west. The shear zone has a reverse sense of movement as indicated by steeply pitching stretching lineations, boudinaged quartz veins, and C-S fabric relationships. Regional and local fabric relationships confine the mineralization to syn- to late-D2 (~2590 Ma).

Multiple layered quartz veins and multiple generations of mineralization are evidence for a composite history. Sulfide mineralization in the gold-bearing quartz and quartz-carbonate veins include pyrite + stibnite + arsenopyrite + sulfosalts ± sphalerite ± chalcopyrite. Visible gold is physically and chemically associated with pyrite, stibnite, and sulfosalts. Refractory gold is associated with arsenopyrite. Host rock alteration in the shear zone includes carbonate + pyrite + chlorite ± sericite ± biotite ± tourmaline. Other gold-bearing quartz veins in the area trend at 270° and are base-metal rich. They contain sphalerite + galena + pyrrhotite + pyrite ± arsenopyrite ± chalcopyrite and reflect a separate mineralizing event from the Crestaurum Shear Zone.

Early mineralizing events in the area include syn-volcanic pyrite + pyrrhotite stockworks, magnetite-bearing banded iron formation, and post-volcanic quartz vein-hosted molybdenite within the tonalite west of the Crestaurum Shear Zone. This molybdenite mineralization has been dated by Re-Os at ca. 2680 ± 19 Ma and is significantly older than the syn- to late-D2 Crestaurum mineralization. On the local scale, these older mineralizing events are candidates as proto-ores for the Crestaurum deposit.