82 IRON ORES OF IRON SPRINGS DISTRICT, UTAH. 
here, but is present elsewhere in the same associations and was prob- 
ably also introduced by the lava waters. 
So obvious and striking are the effects of the extrusion of the 
lavas upon the principal ore deposits of the lower slopes of the 
laccoliths that the question was raised in the field study whether 
this concentration could not have been the principal and perhaps 
the only one, but the evidence seems to be conclusive that the con- 
centration under the influence of the Tertiary lavas was after all 
relatively slight. Limestones in contact with the lava, but away 
from the andesite, do not carry iron-ore deposits, although reddened 
and silicified by solutions from the overlying lava. The minerals 
(barite, galena, copper carbonates, etc.) deposited in the ore by 
these solutions are distinctly later than the main mass of the ore, 
which is intimately associated with heavy anhydrous silicates char- 
acteristic of deep-seated intrusions. The coarse recrystallization 
of the ore under the lava influence seems to be shallow and the 
recrystallized ore to be superposed upon ore of finer and softer 
texture. 
It seems a reasonably safe conclusion that during and following 
the lava extrusions both hot meteoric waters and waters contributed 
by the lavas flowed down the andesite slopes, that they were inter- 
mingled, and that the results of their work are not to be closely 
discriminated. The contribution of minerals from the lavas, however, 
would seem to require emphasis on the effectiveness of the waters 
from them. 
ALTERATIONS SUBSEQUENT TO TERTIARY ERUPTIONS. 
Observation has not yet gone below water level, so that a com- 
parison of the ores of the weathered and unweathered zones can not 
be made. In general the characteristics of the ore are determined 
by conditions other than weathering. However, the ores as a whole 
are more porous near the erosion surface than below in pits. There 
is less calcite above than there is below. It is inferred that there has 
been leaching of the calcite above and perhaps redeposition below. 
The calcite is partly in fine granular form, incrusting ore and rock 
surfaces, and is similar in appearance to carbonate seen about some 
of the old vents of hot springs in this district. The possibility is 
therefore suggested that the solution and redistribution of the calcium 
carbonate went on partly through the agency of warm waters during 
the period of the cooling of the lava. However, redistribution is yet 
going on, through the agency of cold meteoric water, with sufficient 
rapidity to incrust rapidly changing erosion surfaces. 
The magnetite commonly alters to limonite and hematite, in thin 
incrusting films, not directly at the surface, but in the solution 
cavities and in fissures near the surface, This alteration seems to 
