Overview of Results from the Greenstone ... - Geology Ontario

Munro–Currie Subproject
The goal of the Munro and Currie townships VMS subprojects of the Discover Abitibi Initiative is to
reach a better understanding of the volcanic stratigraphy in the 2 townships, and of the stratigraphic
position of the volcanogenic mineralization in both. In Munro Township, the mineralization at both the
Potter Mine (formerly known as the Centre Hill Mine) and Potterdoal Mine is hosted in thin
volcaniclastic and sedimentary units at mafic–ultramafic flow contacts; in Currie Township, the
mineralization at the Currie (Tillex) occurrence is hosted in the volcaniclastic and sedimentary units of
the upper Tisdale assemblage.
MUNRO TOWNSHIP
In Munro Township, the Kidd–Munro assemblage rocks consist of subaqueous tholeiitic basalt and
ultramafic flows; felsic and intermediate volcanic rocks are rare. The area is divided into 3 blocks: South
Munro, Central Munro and North Munro. The South Munro block corresponds to the area of the Kidd–
Munro assemblage south of, and including, the southern ultramafic unit cut by the Munro fault zone,
referred to as the “First Komatiitic Lava Succession” (after Johnstone 1991). The Central Munro block
corresponds to the area located between the southern ultramafic unit and the Centre Hill fault. The North
Munro block corresponds to the area located north of the Centre Hill fault (Figure 22; Péloquin, Houlé
and Gibson 2005). The South Munro block is characterized by a basal interlayered spherulitic rhyolite and
basalt unit, followed by a basaltic unit, within which a thin rhyolite unit (the Beatty rhyolite) occurs; the
uppermost unit in the south block is the “First Komatiitic Lava Succession” of Johnstone (1991). The
Central Munro block is characterized by basaltic to komatiitic basaltic units. The difference between the
South and Central Munro blocks lies in the presence of rhyolites and andesites in the former. As the
displacement along the Munro fault and the folding in the area appear to be of limited extent, it is possible
that the South and Central Munro blocks form a continuous stratigraphic sequence consisting of a lower
tholeiitic unit comprised of interlayered tholeiitic basalts, tholeiitic andesites and rhyolites capped by the
“First Komatiitic Lava Succession” (South Munro block), and an upper tholeiitic basalt unit (Central
Munro block) (Péloquin, Houlé and Gibson 2005). The Centre Hill fault between the Central and North
Munro blocks constitutes a major stratigraphic break. In the North Munro block, ultramafic volcanic and
intrusive rocks are dominant. The stratigraphic sequence is interpreted to be repeated 3 times within the
block by folding (the McCool syncline) and faulting (the Warden Hill fault) (Arndt, Naldrett and Pyke
1977; Coad 1976; Johnstone 1991; Epp 1997; Péloquin, Houlé and Gibson 2005). The Potter and
Potterdoal mines are located in the North Munro block: Potter Mine on the south limb of McCool
syncline and Potterdoal in the Warden Hill fault repetition of the north limb of the syncline.
The most complete stratigraphic section is defined at Potter Mine on the south limb of McCool
syncline. There, the volcanic succession is divided into 3 units: 1) a Lower Komatiitic Unit, 2) the Middle
Tholeiitic Unit; and 3) the Upper Komatiitic Unit (Gamble 2000, Gibson and Gamble 2000). The
mineralization at Potter Mine is hosted in the Middle Tholeiitic Unit, which consists of basaltic
volcaniclastic rocks, intact and autobrecciated sills and/or dikes of basalt, thin argillaceous and
carbonaceous sedimentary units, chert, massive sulphide, and lesser komatiitic flows. The sulphides are
hosted within the lapillistone facies of the basaltic volcaniclastic rocks; this facies is interpreted to have
accumulated within a primary graben (Gibson and Gamble 2000).
The magnetic signatures of the stratigraphic succession at Potter Mine can be traced around the
closure of the McCool syncline. North of Potter Mine, on the north limb of the syncline, the succession
observed is a mafic unit, overlain by an ultramafic unit. The units are massive, thick, and coarse grained
and exhibit no internal structure. They were recognized as flows based on the presence of flow-top
breccias (Arndt 1977; Arndt Naldrett and Pyke 1977). These flows, the lateral extensions of the Potter
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