Isotopic evidence for timing and mechanism of deposition of the Pb-Ag veins of the Sunshine Mine, Coeur d'Alene district, Idaho
- Univ. of California, Davis, CA (United States). Dept. of Geology
- Geological Survey, Menlo Park, CA (United States)
The Pb-Ag ores of the Sunshine Mine, located in the Coeur d'Alene Mining District of northern Idaho, occur within steeply-dipping, tabular siderite veins that cross-cut the overturned northern limb of the Big Creek Anticline. However, these veins are parallel to the major normal and reverse faults of the Lewis and Clark line that cut through the center of the district, and to the well formed cleavage of the host Belt Supergroup metasediments. The siderite gangue has [delta][sup 18]O values of +13.1 to 17.7% rel SMOW, [delta][sup 13]C values of [minus]9.9 to [minus]6.4% rel PDB, and extremely high initial [sup 87]Sr/[sup 86]Sr ratios of 0.85 to 1.5. Late-stage quartz veins, which sometimes run parallel to the veins but more commonly form cross-cutting ladders, have [delta][sup 18]O [equals] +13.4 to +15.5, and these and the wallrocks are several per mil too low to be in isotopic equilibrium with the siderite. Detailed traverses across two veins show U-shaped'' isotopic trends, with the [delta][sup 13]C and [delta][sup 18]O values being more enriched at vein margins. These small-scale variations were caused by changing fluid composition or temperatures, possibly involving explosive pressure release and CO[sub 2] effervescence during decompression, and account for the lack of a systematic variation of [sup 18]O with depth in the vein systems. The [sup 87]Sr/[sup 86]Sr ratios have a weak negative correlation with the [delta][sup 13]C and [delta][sup 18]O values. The isotopic inhomogeneity of Sr in the veins documents their multi-stage formation, probably from fluid batches derived from different sources. The structural simplicity of the veins supports Sr isotopic evidence that the veins are geologically youthful, and were not formed during the Kootenay orogeny at 850 Ma, nor during deposition and diagenesis of the Belt sediments.
- OSTI ID:
- 5290242
- Report Number(s):
- CONF-9305259-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
Similar Records
Fluid inclusion and isotopic studies of the galena mine, Coeur d'Alene district, ID
Oxygen and hydrogen isotope geochemistry of the Coeur d'Alene mining district, Idaho
Related Subjects
GEOLOGIC DEPOSITS
GEOCHEMISTRY
MINERALIZATION
ORIGIN
IDAHO
LEAD ORES
SILVER ORES
GEOLOGIC FAULTS
GEOLOGIC HISTORY
GEOTHERMOMETRY
ISOTOPE RATIO
PETROCHEMISTRY
PETROGENESIS
SIDERITE
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CHEMISTRY
DEVELOPED COUNTRIES
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOLOGY
IRON CARBONATES
IRON COMPOUNDS
IRON ORES
MINERALS
NORTH AMERICA
ORES
OXYGEN COMPOUNDS
PETROLOGY
TRANSITION ELEMENT COMPOUNDS
USA
580000* - Geosciences