68 
IRON OHES Or IRON SPRINGS DISTRICT. UTAH. 
a soft clay retaining andesite texture. The contacts may be vertical 
or inclined, but arc commonly somewhat steeply inclined away from 
the andesite. 
These simple relations of ore to wall rock, are complicated to a con- 
siderable extent by faulting, probably to a larger extent than has 
500 feet 
Fig. 4. — Cross section of Desert Mound contact deposit, a, Iron ore; b, laccolithic andesite; c, Home- 
stake limestone; d, altered Ilomestake limestone; e, Pinto sandstone. 
been proved. Because of the faulting the ore may be nearly or quite 
surrounded by andesite or by limestone or by any combination of 
these rocks. The map (PL II) indicates the effect of the faulting on 
the surface distribution. Its effect is probably equally marked on 
the third dimension. 
Fig. 5. — Cross section of Great Western fissure veins, a, Iron ore; b, laccolithic andesite. 
The faulting is in considerable part earlier than the ore deposition, 
as shown by the fact that the fault breccias are cemented by ore. 
The Desert Mound and the Marshall claim in The Three Peaks area 
afford good illustrations. Other faults are distinctly later than the 
deposition of the ore, as on the Chesapeake claim and others on the 
500 feet 
Fig. r>.— Cross section of Lindsay Hill contact deposit, a, Iron ore; b, laccolithic andesite; c, Home- 
stake limestone; d, altered Homestake limestone. 
slope and on the top of Iron Mountain. The earlier and the later 
faulting are not certainly to be distinguished in all places in the pres- 
ent state of development of the deposits, for the structural relations 
developed are in part similar in the two cases. The age of the late 
