40 Minnesota Academy of Science 



lor hundreds of years the only dwellers in the district. The cli- 

 mate is severe, the yearly average temperature being about 37° 

 Fan. Winter lasts from the first of October to the end of May, and 

 the snowfall is heavy. Kiruna is now a well-built town of about 

 7800 inhabitants. An elctric railway carries the miners to the foot 

 of the mountain, and covered tramways or inclines take them up to 

 the working faces. Hitherto the work of quarrying the ore has not 

 been attended by any unusual problems, but as depth increases and 

 the amount of rock to be mined becomes more nearly equal to the 

 tonnage of ore, there will be an opportunity for the display of en- 

 gineering skill of a high order. The average dip of the ore is about 

 55° to the east, and the foot wall rock as well as the hanging is 

 already being mined in considerable quantity. 



The ore is massive and dry, and the rocks above and beneath 

 are likewise solid and fresh crystalline rock. Hence, the ground 

 stands well and only an occasional pillar is needed even in large 

 excavations. 



The grade of the ore is high. Indeed, the Swedish ores constitute 

 one of the most important sources of high-grade iron ore in sight to- 

 day. The chief impurity is phosphorus in the form of apatite. This, 

 however is so plentiful that instead of being detrimental it becomes 

 an important asset. By the use of the Thomas-Gilchrist process the 

 phosphorus is saved and converted into phosphoric fertilizer. Indeed, 

 the Germans pay about as much for a unit of phosphorus as for a 

 unit of iron. In this respect again we would do well to take a les- 

 son from European practice. There is no one material resource at 

 once so valuable and necessary and so scarce as phosphorus. I am 

 inclined to the opinion that our phosphate products should all be by 

 law retained within our own borders; and that we should avail our- 

 selves of the opportunity to buy and utilize more of these Swedish 

 high phospnorus ores. At present our seaboard iron furnaces im- 

 port from Kiruna a certain grade of low-phosphorus, high-in-iron 

 ores. The ore thus far produced from this Arctic Circle mine has 

 averaged as follows : 



Grade A 1,141,302 tons Average 69.63 Fe 0.024 Phos 

 B 67,387 " "■ G9.25 " 0.G7 



C 371,854 " " G8.60 " 0.1G2 



D 7,003,158 " " G2.48 " 1.88 



F 278,966 " '« 59.34 " 2.78 



G 708,636 " " 57.77 " 3.09 



The amount of titanic acid in the ores is generally less than 

 0.5%; and the sulphur averages 0.05 or less. 



But little is known concerning the geological age of the Kiruna 

 ore and the surrounding sedimentary and igneous rocks. They are 

 presumed to be pre-cambrian and post-archean. The geology of the 

 ore deposits is complex and most interesting, and has been made 

 the subject of careful study by Lundbohm and Geijer. 



It is a remarkable fact that the great ore bodies of Kirunavaara 

 and Luossavaara, (which lies a mile or two farther north, almost in 

 line of strike), occur between two beds of porphyries, of rather 

 similar composition. The foot wall consists of syenitic rocks with 



