Eleventh International Geological Congress. 41 



a silica percentage of about GO, the hanging wall of quartz por- 

 phyries with about 70% silica. 



The quartz porphyry is interwoven with innumerable dikes of 

 finely crystalline apatite, generally small, but sometimes more than 

 one meter in thickness. These dikes are often rich in magnetite 

 and hematite. They also often contain much tourmaline and some- 

 times quartz and albite and show flow structures and orientated inter- 

 growths. The quartz porphyry on the eastern side of the ore also 

 contains numerous fragments of magnetite similar to that of the 

 iron mountains. No dikes of magnetite are found cutting the quartz 

 porphyry; but many intersect the syenite on the west. The contact 

 between ore and country rock is generally sharp and distinct. The 

 ore consists chiefly of magnetite; but contains hematite in small ir- 

 regular lumps, in isolated crystals and in small veinlets. The ore 

 is sometimes laminated and intimately banded with alternating las- 

 ers of apatite. Some geologists have mistaken this structure for 

 evidences of sedimentary origin. 



According to the two main theories, this ore is either pneu- 

 matolytic-hydrothermal or magmatic. It occurs in a series of bedded 

 eruptives; is younger than the underlying syenite porphyry and old- 

 er than the overlying quartz porphyry. It was, therefore, formed 

 either by gaseous emanations from the older rocks during an inter- 

 val or pause in the outpouring of solid eruptive matter or is an ac- 

 tual eruptive sheet or dike of magnetite from an acid magma. In 

 either case it is a deposit of rare type and phenomenal importance 



Near the southern border of Lapland is still one more import- 

 ant iron ore district. This is at Gellivare. Iron ore was mined here 

 in the 18th century, being transported by reindeer to small blast 

 furnaces in the vicinity. It was only the invention of the Thomas- 

 Gilchrist process which finally created a demand for these high phos- 

 phorus ores. The production is now about 1,200,000 tons annually. 

 The production to date is about sixteen million tons; and the total 

 estimated tonnage about 270,000,000. The ore is shipped during the 

 summer to Lulea and goes chiefly to Westphalia and to Silesia; 

 some of it also goes to England and America. The Swedish Govern- 

 ment is a partner in the enterprise and the output is limited to 

 about the present amount. 



The geology is even more difficult than at Kiruna, because the 

 rocks are more metamorphosed. It is apparent, however, that they 

 were syenites and syenite porphyries originally, now recrystallized 

 and granulitic or gneissoid. Apatite and titanite are abundant and 

 there is plenty of quartz. Sillimanite and corundum are also pres- 

 ent. There are dikes of metabasites, granites and pegmatites. The 

 granite and pegmatite dikes frequently intersect the ore masses. 

 Skarn breccias are also numerous, presenting in many instances 

 striking structural and mineralogical similarities to the skams of 

 central Sweden. 



The magnetic ore varies from 62% to G9% in iron and from 

 to 5% in phosphorus. Structurally the ore is hard and granular; 

 and there is a parallel banding or striping due to the arrangement 

 of the apatite. 



The main ore belt has a length of about two and a halt miles. 



