Folded-faulted magnetite-quartz banded iron formation in the Precambrian of Ontario, Canada.

Whitish = quartz-rich Dark gray = magnetite-rich

The outcrop seen here consists of BIFs - banded iron formations. BIFs are unusual, dense sedimentary rocks consisting of alternating layers of iron-rich oxides and iron-rich silicates. Most BIFs are Proterozoic in age (although some are Late Archean), and do not form today - they're “extinct”! Many specific varieties of iron formation are known, and some are given special rock names. For example, jaspilite is an attractive reddish & silvery gray banded rock consisting of hematite, red chert (“jasper”), and specular hematite or magnetite. This outcrop has magnetite-quartz BIF.

Because of their age, most BIFs have been around long enough to have been subjected to one or more orogenic (mountain-building) events. As such, most BIFs are folded, faulted, and/or metamorphosed to varying degrees.

BIFs are known from around the world, but some of the most famous & extensive BIF deposits are found in the vicinity of North America’s Lake Superior Basin. Many BIFs have economic concentrations of iron and are mined. BIFs are the most important variety of iron ore on Earth.

The rocks at this locality have small-scale folds and faults. Published literature refers to the folding here as soft-sediment deformation.

The outcrop surface here was glacially eroded and smoothed during the Pleistocene Ice Age.

Stratigraphy: Temagami Iron-Formation, lower Neoarchean, ~2.736 Ga