A synthesis of the aeromagnetic data (Fig. 3) reveals several important features:

1. The most striking feature on the aeromagnetic maps ( McRitchie, 1971 c; Hetu and

Holman, 1995; GSC, 1988, for the Bissett area only) are discontinuous strings of linear,

very strong positive anomalies along the northern and eastern margin of the Rice Lake

belt, northwest of Bissett along the Wanipigow River, in the Wallace Lake-Siderock

Lake area and between Moore Lake and Garner Lake. They are caused by oxide facies

banded iron-formation. The absence of similar anomalies elsewhere in the supracrustal

belt sets these sedimentary and the associated rocks apart from the remainder of the

belt. As described below these iron-formations and the associated rocks are part of a

pre-2.8 Ga platformal assemblage, predating and largely in fault contact with the

younger dominantly volcanogenic assemblages of the Rice Lake Group.

2. A second order of regional, but lower amplitude, positive anomalies marks the

larger younger (

2.73 Ga) granitic intrusions in the greenstone belt and the

metasedimentary gneiss belt to the south. Particularly their margins are magnetically

defined, e. g. the belt-central Ross River pluton, because of contrasts with adjacent

volcanic rocks.

3. Strings of distinctly oval positive anomalies along the northern margin of the belt

between Lake Winnipeg and Bissett are caused by serpentinites. These are spatially

associated with the Wanipigow Fault. The textures of these bodies do not definitively

indicate their origin but it is possible that they represent komatiites which have been

tectonically re-intruded along late fault structures.

4. A large strong magnetic anomaly in the Garner Lake area is caused by the Garner

Lake layered mafic/ultramafic intrusion.

5. A feature that is particularly noticeable on the

is the

weakening, or disappearance, of positive magnetic anomalies in a northerly trending

strip, extending from approximately 5 km west of Bissett to the eastern shore of Rice

Lake. This termination appears to be in part related to the disappearance (or

discontinuity) of iron formation, but the regional feature may be an expression of the

breakdown of magnetite during impregnation with reducing fluids. There is some