84 IRON ORES OF IRON SPRINGS DISTRICT, UTAH. 
deposits lack clay characteristic of residual deposits. If the slight 
amount carried off during weathering be assumed to be available for 
the development of ore deposits, there seems to be no reason why 
limestone of this low percentage of iron should yield sufficient ore for 
ore deposits in the particular localities where they now occur and not 
in others where the limestone contains as much iron. 
SUMMARY OF MINERAL ASSOCIATIONS OF ORES IN 
RELATION TO ORIGIN. 
The first effect of the andesite laccolith intrusions was the develop- 
ment of the silicated contact phase of limestone containing the 
minerals of column 1 in the following table. Slightly later, veins 
containing much the same association of minerals cut andesite and 
limestone (column 3). About the same time came the introduction of 
ore-bearing solutions in veins both in andesite and limestone and also 
replacing limestone (column 2). The minerals deposited are much 
the same as those previously developed in the contact limestone, 
though albite and orthoclase, present in the contact phase, have not 
been found in the ore, while apatite and garnet are more abundant in 
association with the ores than elsewhere in the contact phase. So 
similar are the groups of minerals developed up to this point and so 
close their association that they can not be sharply separated. There 
can be little doubt that they are developed under no greatly varying 
conditions with insignificant time intervals. According to Lind- 
gren's classification, the minerals of these groups are characteristic 
both of products of aqueo-igneous solutions, like pegmatites, and of 
products of aqueous solutions, in the lower contact zone. Criteria do 
not seem to be available in the Iron Springs district for clearly sepa- 
rating the two classes. The evidence appears to indicate that they 
all result from the andesite intrusion, principally through the trans- 
fer of pneumatolytic vapors, but that in the limestone contact they 
are also developed by simple elimination of lime and magnesia, and 
the recrystallization of the residue. 
Later, solutions from the lavas introduced another and clearly 
distinguishable group of minerals, listed in column 5. These are 
found principally near the contact of the lavas with the prelava 
erosion surface, and were developed, therefore, under essentially 
surface conditions. They correspond closely to the minerals listed 
by Lindgren a as characteristic of these conditions. 
aLindgren, Waldemar, The relation of ore deposition to physical conditions, Econ. Geol., vol. 2, 
1907, pp. 122-125. 
