| Abstract: | The Midnite mine is one of only two mines in the United States currently producing uranium from discordant deposits in crystalline host rocks. Ore bodies are in metamorphosed steeply dipping Precambrian pelitic and calcareous rocks of a roof pendant adjacent to a Cretaceous(?) porphyritic quartz monzonite pluton. Production during 14 years, of operation has been about 8 million pounds of U3O8 from oxidized and reduced ores averaging 0.23 percent U3O8.
Uranium deposits are generally tabular in form and dimensions range up to 380 m long, 210 m wide, and 50 m thick. Deposits are bounded on at least one side by unmineralized intrusive ribs of granitic rock, and thickest mineralized zones invariably occur at depressions in the intrusive contact. Upper limits of some deposits are nearly horizontal, and upper elevations of adjacent mineralized zones separated by ribs of granite are similar. Near surface ore is predominantly autunite, but ore at depth consists of pitchblende and coffinite with abundant pyrite and marcasite. Uranium minerals occur as .disseminations along foliation, replacements, and stockwork fracture-fillings.
No stratigraphic controls on ore deposition are recognized. Rather, mineralized zones cut across lithologic boundaries if permeability is adequate. Most ore is in muscovite schist and mica phyllite, but important deposits occur in calc-silicate hornfels. Amphibolite sills and mid-Tertiary dacite dikes locally, carry ore where intensely fractured. High content of iron and sulfur, contained chiefly in FeS2, appear to be an important feature of favorable host rocks.
Geometry of deposits, structural, and geochemical features suggest that uranium minerals were deposited over a span of time from late Cretaceous to late Tertiary. Ore occurs in but is not offset by a shear zone that displaces mid-Tertiary rocks.. Economic zones of uranium are interpreted to have been secondarily enriched in late Tertiary time by downward and lateral migration of uranium into permeable zones where deposition was influenced by ground water controls and minerals that could reduce or neutralize uranium-bearing solutions. |
| Genre: | USGS Numbered Series |
| ProdID: | 15141 |
| Citation Author: | Nash, J. Thomas; Lehrman, Norman J. |
| Citation Contributing Office: | |
| Citation Datum: | |
| Citation Day: | |
| Citation Edition: | - |
| Citation Editor: | |
| Citation End Page: | |
| Citation Issue: | |
| Citation Keywords: | |
| Citation Language: | ENGLISH |
| Citation Larger Work Title: | |
| Citation LatN: | |
| Citation LatS: | |
| Citation LonE: | |
| Citation LonW: | |
| Citation Month: | |
| Citation No Pagination: | |
| Citation Number Of Pages: | |
| Citation Online Only Flag: | |
| Citation Phsyical Description: | 36 leaves :ill., maps ;27 cm. |
| Citation Projection: | |
| Citation Public Comments: | |
| Citation Publisher: | U.S. Geological Survey], |
| Citation Series: | Open-File Report |
| Citation Series Code: | OFR |
| Citation Series Number: | 75-402 |
| Citation Search Results Text: | Geology of the Midnite uranium mine, Stevens County, Washington; a preliminary report; 1975; OFR; 75-402; Nash, J. Thomas; Lehrman, Norman J. |
| Citation Start Page: | |
| Citation Volume: | |
| Citation Year: | 1975 |
| Type: | citation/reference |
| Text: | Geology of the Midnite uranium mine, Stevens County, Washington; a preliminary report; 1975; OFR; 75-402; Nash, J. Thomas; Lehrman, Norman J. |
| URL (THUMBNAIL): | http://pubs.usgs.gov/of/1975/0402/report-thumb.jpg |
| URL (DOCUMENT): | http://pubs.usgs.gov/of/1975/0402/report.pdf |
| Date Other: | Sat, 1 Jan 1994 00:00 -0600 |
| Publisher: | U.S. Geological Survey], |
