34 Minnesota Academy of Science 



ganese and iron ores. Here, as elsewhere in central Sweden, the 

 ore-bearing formation is the crystalline schists. They are here chief- 

 dolomite, which is characteristically banded by lime magnesia sili- 

 cates, except adjacent to the ore and skol. 



The ores occur in stockworks, usually containing both iron and 

 manganese. There appears to be a tendency to scatter and diminish 

 in importance at moderate depth. The gangue of the iron ore shoots 

 is called "skarn" and is of varied color and mineral composition, 

 containing gray-green malacolite, brown and black garnets and fer- 

 ruginous quartz. There are also unimportant deposits of sulphide 

 ores of copper, iron, lead and zinc. Many skol layers or bands 

 bound the ore and extend thro the adjacent rocks. In some in- 

 stances these skols are squeezed and altered greenstone dikes that 

 seem to have been present before the ore was deposited, and to 

 ly granulite and dolomite. Closely associated is a gneissic granite. 

 Two varieties of younger intrusive granite dikes occur, and various 

 still later diorite and diabase dikes. Pure dolomite bears such a 

 constant relation to the ore or skol formations that it is concluded 

 that the ore-.depositing agencies had a marked effect also upon the 

 have formed a boundary to it or determined its extent. In other 

 cases the skols are more or less micaceous and represent trans- 

 formed granulite or leptite. Still other occurrences resemble very 

 old shear zones or fault planes whose filling has been transformed 

 into crystalline rock material. Still later fracturing has occurred, 

 and the cracks have been filled with calcite and other secondary 

 minerals. 



In this same neighborhood are also the mines of Norberg, Flog- 

 berget and Persberg. The principal features of interest are the 

 "skarn" ores and the calcareous ores, the former of which are horn- 

 blendic magnetites and the latter serpentinous and amphiboliferous 

 limestones intermingled with small patches and lenses of skarn ore, 



Persberg is one of the oldest mining fields in Vermlands Bergs- 

 lag. Mining dates back to the 13th century; and the first mining- 

 privileges were granted by King Eric the Pomeranian in 1413. The 

 Bergmaster's report for 1637 states that "the whole mountain is 

 nothing but ore, and of mighty richness, and can be smelted with- 

 out flux," from which it can be seen that the art of writing mining 

 prospectuses based largely upon the imagination did not originate 

 in the United States. The total output of the Persberg mines is 

 estimated at less than 4,000,000 tons. Fifty years ago the annual 

 production was about 50,000 tons. At the present time it is about 

 30,000 tons. The ore is of excellent quality and has contributed 

 largely to the reputation of Swedish iron in the world's market. 

 The best grade of ore contains 55V 2 Fe, 0.001—0.004% P; and the 

 second grade 45% Fe and 0.005 — 0.01% P. The sulphur content varies 

 from 0.012 to 0.025%. The deepest workings are now about 

 1,000 feet. Machine drilling was first started in Sweden at Pers- 

 berg in 18G4-1866. These mines . were well described by Linnaeus 

 about 1740. Powder for blasting was introduced about 1720. 



The skarn ores are believed by Sjogren to owe their origin to 

 the metamorphic influence of greenstones upon limestones. There 

 are, however, considerable ore-deposits which are, so far as can be 



