86 IRON ORES OF IRON SPRINGS DISTRICT, UTAH. 
(3) Erosion, developing mountains with andesite cores, encircled 
by belts of sediments at uniform elevations on the slopes, except 
where displaced by faults, or where cut back by differential erosion. 
The areas between the mountains were left with low relief. The ores 
were exposed and partly eroded, calcite, apatite and perhaps other 
gangue materials were leached and redeposited below. There was 
more or less oxidation and hydration of the ores along fissures beneath 
the surface. 
(4) Extrusion of the Tertiary lavas over the entire area, furnishing 
hot magmatic waters and heat to meteoric waters, and thereby 
developing coarsely crystalline magnetite and hematite in the ore 
deposits and especially at the surface, leaching the gangue materials 
so far as they were left by weathering near the surface, and depositing 
in the cavities chalcedony and to a slight extent magnetite, hematite, 
limonite, siderite, chlorite, barite, calcite, galena, and the copper 
carbonates. 
(5) Erosion, reexhuming the andesite mountains from under the 
lavas and bringing to light the sediments and ores on the slopes; this 
was accompanied by local surface oxidation and hydration of the ores 
and leaching of the gangue materials, chiefly calcite, but also apatite. 
Differential erosion caused the ore in some cases to stand above the 
adjacent rocks, and in others, where the hard cap was cut off, brought 
the softer underlying ores well down to the level of adjacent rocks. 
(6) Preceding and accompanying (5) occurred faulting of the ore 
deposits, developing structural relations not in all cases to be distin- 
guished from those determined by faulting before deposition of the 
ores. 
BEARING OF THE THEORY OF ORIGIN UPON FURTHER 
EXPLORATION. 
Exploration has not yet demonstrated the depth of the ore deposits. 
The greatest known depth is at the Pinto group of pits, south of 
Iron Mountain, where 130 feet is known from the pits and topography. 
At the Desert Mound drilling may have gone deeper, but the records 
are not available to the writers. 
If the theory of the writers as to the origin of the ore is correct, 
there are certain fairly well-based inferences to be drawn as to depth 
and shape of the ore deposits. 
If the ore-bearing fissures in the andesite are true stretch fissures 
determined by the crystallization of the lavas, it may be inferred that 
they will show the same features with depth as at the surface; that is, 
curving, pinching out, branching and occurrence in parallel sets. 
There seems to be no reason why these vein deposits should not go 
to a very considerable depth, this being determined by the depth to 
which Assuring had occurred at the time of the extrusion of the 
ore-bearing solutions. 
