Pokegama Quartzite

Just a little north of the mine pit is the "edge of time". In the photos below the hands are indicating the unconformity between the Pokegama Quartzite and the Ely Greenstone. It is an unconformity because of a time difference of about 800 million years. The Ely Greenstone (a chlorite schist) is about 2.7 billion years old and the quartzite is about 1.9 billion years old. The quartzite represents the "basement", the bottom of the iron formation in the Mesabi Range. Everything from this point southward to Lake Superior was at one time a shallow sea. Sand at the edge compressed into the Pokegama Quartzite and stromatolites (a type of blue-green algae) produced oxygen that reacted with the iron in the water to form the iron minerals near the shore.
quartzite greenstone
quartzite greenstone


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1.  MN DNR Minerals Education Workshop Field Trip