Mine Site Geology
The lower Proterozoic pile of felsic to intermediate tuffs, flows and minor sedimentary rocks have been metamorphosed to greenschist facies and have been tilted just past vertical and thus the overturned package dips steeply to the north while it strikes roughly N50E. The stratigraphic footwall is composed of three main units: a quartz-eye tuff, a metadacite and an andalusite-biotite schist. The andalusite-biotite schist is in contact with the main ore horizon. Unlike many massive sulfide ores, there is no evidence for a well defined feeder zone or alteration pipe. The geology is shown in simplified form in Figure 1.
The ore horizon is composed of a lower quartz-sericite schist hosting the massive ore and lapilli tuffs and a fine grained tuff overlying the ore. The stratigraphic hanging wall is generally more mafic and is composed of chlorite phyllites, metadacites and a biotite-feldspar unit.
The most striking feature of the Flambeau deposit which makes it unique in the world is the development of up to several hundred feet of Precambrian supergene enrichment. This enriched ore was capped by the Cambrian Mt. Simon sandstone which preserved the deposit during the last glaciation. The Mt. Simon was nearly breached by the glacial erosion - the lack of significant preserved gossan or supergene enriched ore at, for instance, Crandon can be directly attributed to the lack of the capping sandstone at the other properties. (Minor supergene enriched ore is present at Crandon.) Reports during the earliest stripping record the presence of blocks of quartzite in the gossan - the Barron quartzite outcrops not too far to the west of Ladysmith and may have covered the Ladysmith area in the Middle Precambrian. If this is true then the supergene enrichment may have occurred in the middle or even lower Proterozoic - not the Eocambrian as commonly accepted.