﻿REPORT OF THE DIRECTOR I9IO II3 



The Kiruna deposits were undoubtedly the most instructive in 

 regard to considerations of ore-genesis that we saw in Sweden. 

 There were few members of the excursion, apparently, who were not 

 impressed by the evidences in favor of the igneous derivation of 

 the magnetites, however much individual opinion may have varied 

 in regard to the exact process by which the ore came to occupy its 

 present position. The undoubtedly igneous character of the wall 

 rocks, the structures exhibited by the ore itself, the dikes of apatite 

 connected with the same and found in the porphyry, and the apoph- 

 yses of ore in the footwall of Kiirunavaara and more notably in 

 the surrounding porphyry of Tuolluvaara, seemed conclusive on 

 that score. These features have been admirably set forth in the 

 monograph by Doctor Geijer already quoted, and further discussion 

 of them here may be spared. 



As to the precise construction to be placed upon the evidences, 

 for a theoretical explanation of the ore genesis, the views of the 

 Swedish geologists and others who have studied the district are 

 somewhat at variance, though many accord on the more essential 

 points. Hogbom, Sjogren, Stutzer and Geijer agree that the magne- 

 tites have been derived from the porphyries and that their concen- 

 tration primarily has been due to magnetic differentiation. But these 

 authorities take issue on the problems connected with the subsequent 

 history of the ores for which it is possible to give several versions: 

 the magnetites may have cooled in place along with the wall rocks ; 

 again, they may have been forced up through the partially or com- 

 pletely cooled rocks in the form of dikes like those of pegmatite; 

 or they may have flowed out on the surface as lava sheets in an in- 

 terval between the eruption of the foot-wall and hanging-wall por- 

 phyries. Of course the different views do not conflict with the val- 

 idity of the general principle, and it is not improbable that the se- 

 quence of events with respect to the several deposits may be explain- 

 able in more than one way. 



The relations of the Kiirunavaara-Luossovaara ores seem excep- 

 tional in that the two walls have a somewhat different composition — 

 the hanging being classed as a quartz porphyry and the foot as a 

 syenite porphyry — though the variation is not large. For these 

 deposits Backstrom and later De Launay would assign a pneumato- 

 lytic-aqueous origin, according to which the iron was brought up 

 in the form of vapors and precipitated at the surface in the presence 

 of water during the interval of the two porphyry eruptions which 

 are believed to have been submarine. This explanation involves the 



