Bulletin No. 24. The Geology of the Rove Formation and Associated Intrusives in Northeastern Minnesota

Abstract

In the large area of Rove formation along the boundary of north- eastern Minnesota and Ontario there have been two important silver mines, both on the Ontario side of the boundary - Silver Islet and Silver Mountain. The existence of a number of smaller mines and prospects makes it certain that mineralization of this kind occurred over a wide area, and several other mineral occurrences have long been known; but no other important deposits have been developed. Since much of the area is concealed under glacial deposits and since only a reconnaissance geological survey had been made in the part of the area that lies in Minnesota, it seemed advisable to survey the area in more detail. An effort was made to map and study all large outcrops and most of the smaller ones, to record where the veins are and what is their nature, to map the formations more closely than before, and on these records to base an estimate of the probable mineral prospects of the district. The Gunflint iron-bearing formation, which has been treated before, is here referred to only incidentally. The Minnesota area of Rove slate is a narrow strip south of the international boundary from Pigeon Point to a few miles west of Gunflint Lake in Cook County. Since the base of the formation trends northeast into Ontario and the beds dip south, it is believed that eastern outcrops in Minnesota are at a higher horizon than those near Gunflint Lake.