| Abstract: | This investigation of the Eagle Mountain Mine area, though cursory, revealed new
structural, alteration, and stratigraphic relations. Eagle Mountain ores were previously an
important source of iron to the western U. S. Ore (where fresh) is magnetite-pyrite rock
forming two stratabound horizons virtually continuous for 11 km.
Gneissic basement rocks are overlain by two sedimentary units, separated by
unconformities. The lower unit contains carbonate rocks and quartzite; the ‘vitreous
quartzite‘ of previous workers, however, is an alteration feature rather than a stratigraphic
one. The upper unit contains thick conglomerates. This layered sequence of rocks is
deformed into a west-plunging anticline. Intrusion by Jurassic quartz monzonite
apparently followed this deformation.
Quartz monzonite forms a branching network of sills, some of which dilate the
contact between the upper and lower sedimentary sequences. Intrusion resulted in
extensive, mostly-anhydrous skarns, but stratabound iron ore is just as closely related to
some other features: 1) regional alteration of quartz monzonite, with iron ore adjacent to
little-altered rocks along the boundary between sodic and potassic domains, 2) the two
unconformities, which apparently formed stratigraphic traps for precipitation of
stratabound iron ores, 3) a north-facing monoclinal plane between folds, which was
preferentially replaced.
Iron ore replaces a variety of host rocks along the two unconformities, forming
massive to globular bodies, and its mineralogy correlates with deuteric alteration features,
not anhydrous skarn. Its pyrite contains as much as 3% cobalt.
Iron was only one of five elements that showed mobility in this region on a scale
that suggests basic crustal processes. The others in probable order of flux magnitude are
silica, magnesium, sodium, and potassium, to form regionally distributed ?vitreous
quartzite?, dolomite, and secondary feldspars, respectively. |
| Genre: | USGS Numbered Series |
| ProdID: | 31394 |
| Citation Author: | Force, Eric R. |
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| Citation Language: | ENGLISH |
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| Citation Phsyical Description: | 17 p. |
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| Citation Series: | Open-File Report |
| Citation Series Code: | OFR |
| Citation Series Number: | 2001-237 |
| Citation Search Results Text: | Eagle Mountain Mine- geology of the former Kaiser Steel Operation in Riverside County, California; 2001; OFR; 2001-237; Force, Eric R. |
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| Citation Year: | 2001 |
| Type: | citation/reference |
| Text: | Eagle Mountain Mine- geology of the former Kaiser Steel Operation in Riverside County, California; 2001; OFR; 2001-237; Force, Eric R. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/usgs_thumb.jpg |
| URL (INDEX PAGE): | http://geopubs.wr.usgs.gov/open-file/of01-237/ |
| Date Other: | Tue, 1 Jan 2002 00:00 -0600 |
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