DESCRIPTION OF THE IRON ORES. 
71 
contact ore contains parallel streaks of a yellow clayey-looking 
material. On examination this resolves itself into a mixture of iron 
carbonate, iron sulphate, and^lass, and probably some residual clay. 
Some of the narrow ore veins in the andesite possess a comb structure 
formed by the meeting and interlocking of apatite crystals projected 
from the walls (see fig. 10), sometimes not entirely closing the vein. 
In the ore breccias the cements are magnetite, limonite, calcite, and 
quartz. At the Milner mine and elsewhere the magnetite has been 
deposited first about the fragments, here consisting of quartzite, then 
hematite, then limonite, but exception-ally in the same locality the 
reverse order appears. 
The texture of the ore as a whole is good for furnace use. The 
harder ores will need crushing:. 
Fig. 10. — Vein of magnetite in andesite. The ore, indicated by the fine dots, does not quite fill the 
opening. Crystals of apatite penetrate the ore and interlock across the opening. One-half 
natural size. 
For the following information concerning the composition of the 
ores the writers are indebted to Mr. Fred Lerch, of Biwabik, Minn., 
and to Mr. R. N. Dickman, of Chicago, 111., both of whom have 
exhaustively sampled the ores of the district for commercial purposes. 
Corroborative figures were obtained from other commercial sources, 
and in a few cases analyses were made for the writers. In all, about 
200 analyses from 400 samples of ores have been available, about two- 
thirds of them containing determinations only of iron, silica, and 
phosphorus, and one-third showing the percentages of all the common 
elements. 
The average composition of the ores of the Iron Springs district, 
determined by combining all available analyses of the ores of the dis- 
trict from surface and pits, is as follows: 
Average composition of iron ores of the Iron Springs district. 
Percent. Percent. 
5G Copper 0.027 
Sulphur 057 
Manganese L96 
Soda I. L9 
Potassa SO 
Iron 
Silica 7 
Phosphorus 
Lime and magnesia 4 
Alumina 1 
Water 3 
