Geology of the East Bull Lake gabbro–anorthosite pluton, Algoma District, Ontario

Abstract

The East Bull Lake Pluton, a layered gabbro–anorthosite intrusion 90 km west of Sudbury, Ontario, is in an inward-dipping lopolith and is 780 m thick in the centre and elliptical in plan view (13.5 km × 3.5 km). It intruded Archean metavolcanic and metaplutonic rocks of the Superior Province during the Early Proterozoic (2480 Ma).The intrusion consistes of a basal anorthositic unit, succeeded by rhythmic-layered gabbro, troctolite, layered gabbro, and massive and dendritic gabbro units. It is offset by the west-northwest-striking, subvertical Folson Lake fault. South of this fault, only anorthosite and massive and dendritic gabbro are exposed. North of the fault, subsurface lithologies intersected by me boreholes correlate with surface lithologies. Troctolite, the most distinctive marker that can be correlated between boreholes and surface exposures, confirms the general attitude and shape of the layers and lopolith.Chemical composition of the intrusion ranges from high-Mg tholeiite to calc-alkaline high-alumina basalts.Fractures occur in several preferred orientations, the most common being northwesterly, subparallel to the Folson Lake fault, numerous mafic dykes, and topographic lineaments. Complex fracture-filling and alteration mineralogies formed under a wide range of P–T conditions representative of epidote-amphibolite – greenschist facies, pumpellyite–prehnite facies, zeolite facies, and low-temperature rock–water interaction processes.The last movement on the Folson Lake fault was a dextral strike slip of up to 3.0 km that postdates most mafic dykes.

Analysis of Crystalline Rock Permeability Versus Depth in a Canadian Precambrian Rock Setting

“…The East Bull Lake Research Area (RA‐7) was located ∼25 km north of Massey, Ontario in the Algoma District (Bottomley et al., 1986; McCrank et al., 1985). It was located in the Superior province near the Southern province (Pearson, 1984).…”

“…Research began at this site in 1980 and was conducted until 1992 (Whitaker et al., 1994). The research at this site was focused on mapping the shape of the pluton, the distribution of rock types, and the characteristics of faults and fractures (McCrank et al., 1985). Later on, the research was expanded to study the hydrogeological characteristics, hydrogeochemical characteristics, and the evolutionary processes of groundwater (Bottomley et al., 1986).…”

The East Bull Lake Intrusive Suite: Remnants of a 2.48 GaLarge Igneous and Metallogenic Province in the Sudbury Area of the CanadianShield

“…1); however, contact relationships between rocks of the East Bull Lake suite and the Huronian Supergroup are either faulted or equivocal. Consequently, it is not known for certain whether the rocks of the East Bull Lake suite intruded the Huronian Supergroup or whether they were unconformably overlain by it, or both (e.g., Card, 1978;McCrank et al, 1989;Peck et al, 1993). Emplacement of the East Bull Lake suite bodies, subsequent eruption of volcanic rocks of the Huronian Supergroup, and formation of the depositional basin later filled by Huronian Supergroup sediments is attributed by most authors (e.g., Card et al, 1972;Young, 1983;Fahrig, 1987;Hoffman, 1989;Bennett et al, 1991;Heaman, 1997;Card and Poulsen, 2000;Ernst and Buchan, 2001) to an intracontinental rifting event resulting from a mantle plume centered near Sudbury.…”

“…Table 2 summarizes the geochronology of the suite. The three largest intrusions are the East Bull Lake, Agnew Lake, and River Valley intrusions, all of which have been mapped in the last decade in whole or in part at either a 1:10,000 or 1:20,000 scale (Chubb, 1994;Peck et al, 1995;Vogel, 1996;Easton and Hrominchuk, 2001a, b), with accompanying petrological, geochemical, or economic studies (James and Born, 1985;McCrank et al, 1989;Peck et al, 1993Peck et al, , 1995Chubb, 1994;Vogel, 1996;Vogel et al, 1998aVogel et al, , b, 1999Easton and Hrominchuk, 1999;Hrominchuk, 1999Hrominchuk, , 2000. The preserved size of the intrusions varies from 1 to >150 km 2 ( Table 1).…”