Address to Section C, Geology. 455 
still immense ore body of Luossayaara. At Kiruna the ore rises to 
the height of 816 feet above the surface of the lake, and it varies in 
thickness from 80 to 500 feet, with an average thickness of about 
230 feet. According to the report by Professor Walfrid Petersson,’ 
submitted this year to the Swedish Parliament, Kirunavaara contains 
200 million tons of ore above lake-level, and Luossavaara another 
223 million tons. The ore is high-grade. According to Lundbohm 
60 per cent. of the trial pits showed a yield varying from 67 to 71 per 
cent. of iron, and 21 per cent. of them showed a yield of from 60 to 67 
per cent. of iron. The average of nineteen analyses published in 
Professor Petersson’s recent report gives the contents of iron as 
64°15 per cent. Unlike the Taberg and Routivaara ores, the per- 
centage of titanium is very low; thus in nineteen analyses given by 
Petersson the average of titanic acid is only ‘23 per cent., and it 
varies in the specimens from -04 to °8 per cent. 
The ore lies between two series of acid rocks, which have been very 
differently interpreted, but will no doubt be fully explained by the 
researches now in progress under the direction of Mr. Lundbohm. 
The rocks were first called halleflinta, as by Fredholm, and regarded 
as of sedimentary origin. They are now accepted as an igneous series, 
associated with some conglomerates, slates, and quartzites. The ore 
body itself is bounded on both sides by porphyrites, of which that on 
the lower or western side is more basic than that overlying the ore to 
the east. The basic western porphyrite is in contact with a soda- 
augite syenite of which the relations are still uncertain. Interbedded 
with the overlying eastern porphyrite are rocks that appear to be 
volcanic tuffs, and both in the tuffs and in the upper porphyrite are 
fragments of the Kiruna ore. 
Three main theories of the genesis of the Kiruna ores have been 
proposed. Their sedimentary origin was urged on the ground that 
they occur regularly interstratified in a series of altered sediments, 
and that the ores, therefore, are also sedimentary. This view may be 
promptly dismissed, since the adjacent rocks are igneous. 
The second theory has been advanced independently by Professor de 
Launay and Dr. Helge Backstrom : according to them the porphyrites 
above and below the iron ores are lava-flows, and the ore was 
a superficial formation deposited in an interval between the volcanic 
eruptions. According to de Launay the iron was raised to the surface 
as emanations of iron chloride and iron sulphide; the iron was 
deposited as oxide, and most of it subsequently reduced to magnetite 
during the metamorphism of the district. 
The third theory—that the ores are of direct igneous origin—has 
been maintained by Léfstrand, Hogbom, and Stutzer; according to 
them the ores are segregations of magnetite from the acid igneous 
rocks in which they occur. The segregation theory has been opposed, 
amongst others, by de Launay and Vogt. Thus, de Launay maintains 
that the segregation would have been impossible in such fluid lavas as 
the Kiruna porphyrites, and is improbable, since there is no transition 
between the ore and the barren rock. 
1 Bihang till Rikd. Prot., 1907, 1 Saml., 1 Afd., 84 Haft, No. 107, pp. 213, 217. 
