I collected this in 1967, during my PhD program, when I went on an economic geology trip with Dr. Bill Kelly and Dr. Stewart Turneaure to Upper Michigan. This geological find was new to me, as was beautiful white snow on autumn colors in the 3rd week of September. (THIS is why we do geology). It was during this trip that we discovered that you could ask Dr. Turneaure about any part of the train schedules (departures and arrivals) between any two cities of your choice in the eastern United States, and the Midwest. For example, what train will be available on a Sunday afternoon, to take you from Chicago to St. Louis? He would rattle off the name of the 'line' and the times. Scary. The courses Dr. Turneaure taught on ore deposits geology, mining geology, and Precambrian geology were full of detail,…and insight.
Some of the native copper in the deposits of northern Michigan occurs as vesicle ‘cement’ in granule conglomerates. The atmospheric and ground-water chemical conditions that existed at that place and at that time were highly anomalous to what we experience today. What does it take, for example, to precipitate NATIVE copper, and not some silicate or carbonate or oxide of copper? Someone will have to explain to me how a granule conglomerate becomes ‘cemented’ with native copper. I imagine that when the gravel that became the conglomerate was buried deeply, copper-bearing solutions moved through the relatively porous material and deposited native copper in the available open space. Very unconventional.
Age & Formation
Calumet Conglomerate is the host for the native copper, late Mesoproterozoic, ~ 1.1 Ga.