Date of Award
Master of Science (MS)
In October of 1964 the Topographic Branch of the United States Geological Survey reported difficulties in using magnetic compasses while mapping in the areas of Akra and Hensel, Pembina County, North Dakota. University of North Dakota geologists located anomalies of 67,500 gammas 1.6 lon east of Akra and 71,500 gammas 4 km east of Hensel, the normal magnetic field in this area being about 60,000 gammas. The rock bodies producing the magnetic anomalies were drilled and examination of diamond drill core showed them to consist of oxide and silicate facies iron formation interlayered with quartz-biotite schist of Precambrian age. The core recovered from the Akra site contained mineral assemblages of the greenschist and amphibolite facies of regional metamorphism, the metamorphic grade increasing with depth. The mineral assemblages of the Hensel core indicate amphibolite facies metamorphism. The Precambrian rocks of eastern North Dakota represent the subsurface extension of the Superior Province of the Canadian Shield. This province is characterized by linear greenstone belts of metavolcanics and metasediments separated by areas of intrusive, felsic igneous rocks. Similarities between the Akra and Hensel rock bodies and iron formations exposed on the Canadian Shield suggest deposition during the sedimentary phase of greenstone belt evolution.
Richardson, Ronald E., "Petrography of Precambrian iron formation, Pembina County, North Dakota" (1975). Theses and Dissertations. 245.