﻿REPORT OF THE DIRECTOR I9IO 1\J 



innumerable small lenses. The division of the ore and wall rocks 

 is, however, quite sharp. 



At Dannemora, Norberg and Langban we saw some typical de- 

 posits of such low-phosphorus ores as have been the mainstay of 

 the Swedish iron industry since the middle ages. The association 

 of magnetites with limestones, observed in some occurrences, has 

 few parallels apparently outside of Sweden, and there are no similar 

 deposits, of any importance at least, within our own State. 



The Dannemora deposits have the form of vertical shoots, or 

 stocks as they are referred to by Professor Sjogren in the guide to 

 the district, and occur within a small belt of dolomitic limestone 

 that is in turn surrounded by gneiss. The limestone belt is scarcely 

 two miles long and a quarter of a mile wide. The gneiss belongs 

 to the halleflinta variety, with a dense ground mass, and is believed 

 to be a crushed quartz-porphyry. Of later age than either of these 

 rocks are granite in large intrusions and dikes of several kinds, the 

 latter only coming in contact with the ore. The magnetite is mixed 

 with silicates, chiefly amphibole and pyroxene, and much of it is 

 too low grade to be used directly in the furnace. Like many of 

 the low-phosphorous ores which we saw, it has a very fine texture. 



A somewhat related occurrence of magnetite is represented by 

 the southern mine group (called Klackbergsfaltet) at Norberg. 

 Lenses of dolomite are included in a fine-grained gneiss (leptite) 

 and together are arranged in a discontinuous belt that follows the 

 general country strike. Smaller lenses of magnetite are found here 

 and there either wholly within the dolomite or along its contact 

 with the gneiss. 



The ores are high in lime and contain several per cent of man- 

 ganese in the form of carbonate. An unusual ingredient of magne- 

 tites, noted in this place, is graphite which coats the natural joint 

 surfaces so that the ore when seen in mass looks like so much coal. 



The phosphorus content is remarkably low, on the average about 

 .002 or .003 per cent. The iron runs from 40 to 50 per cent, but 

 as there is an excess of fluxing constituents the grade is really 

 better than the iron percentages indicate. 



Another series of magnetites at Norberg is represented by the 

 skarn ores which are directly bounded by leptite or else form pockets 

 and irregular bodies within lenticular masses of the same skarn 

 minerals that compose the gangue. These minerals are chiefly 

 amphibole, pyroxene and garnet. The association and the presence 

 of considerable calcite at times suggest that the deposits are geneti- 



