[sup 40]Ar/[sup 39]Ar isotopic dates from the Cripple Creek gold-Telluride district, Colorado: Constraints on the timing of magmatism and mineralization

Conference · Thu Apr 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5022858

Kelley, K D; Snee, L W ^[1]; Thompson, T B ^[2]

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1. Geological Survey, Denver, CO (United States)
2. Colorado State Univ., Fort Collins, CO (United States). Dept. of Earth Resources

The Cripple Creek district is within a Tertiary diatreme-intrusive complex, a steep-walled basin in Proterozoic pelitic and igneous rocks that is filled with terrigenous sedimentary rocks, volcanic and hydrothermal breccias, and tuffs. The orebodies occur as veins in Proterozoic and Tertiary rocks or as deposits localized within hydrothermal breccia bodies or disseminated in diatreme breccias. [sup 40]Ar/[sup 39]Ar dates from igneous rocks demonstrate the approximately contemporaneous emplacement of the most differentiated phonolitic rocks. Three sanidine samples from phonolite yield apparent ages ranging from 30.9 [+-] 0.1 to 31.8 [+-] 0.1 Ma (1 sigma). Biotite and sanidine age spectra from relatively less differentiated tephriphonolite are discordant; the emplacement age is estimated to be between 31.4 [+-] 0.1 and 32.5 [+-] 0.1 Ma. A maximum age of 31.5 [+-] 0.1 Ma was obtained on a whole-rock sample of trachyandesite. The mafic phonolitic rocks are relatively younger. A sample of the Isabella dike, a phonotephrite dike cutting phonolite, yields a whole-rock age of 28.7 [+-] 0.04 Ma. The data suggest that mineralization both predates and postdates emplacement of the mafic phonolitic rocks. Hydrothermal biotite in a vein cutting phonolite yields an age of 29.9 [+-] 0.1 Ma. The age spectrum of adularia from a vein cutting volcaniclastic rocks is difficult to interpret due to the presence of excess argon, but an age is estimated to be between 29.5 and 30.4 Ma. In the vicinity of the phonotephrite dike, field evidence suggests that vein mineralization postdates emplacement of the dike; potassium feldspar from potassium altered phonolite in the vicinity of mineralized rock yields ages of 28.2 [+-] 0.1 and 28.8 [+-] 0.1 Ma.

• OSTI ID: 5022858
• Report Number(s): CONF-9305259--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
ARGON 39
ARGON 40
ARGON ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CENOZOIC ERA
COLORADO
DEVELOPED COUNTRIES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FELDSPARS
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGY
GOLD ORES
HYDROTHERMAL SYNTHESIS
IGNEOUS ROCKS
ISOTOPE DATING
ISOTOPES
LIGHT NUCLEI
MAGMATISM
MINERALIZATION
MINERALS
NORTH AMERICA
NUCLEI
ORES
PETROGENESIS
PETROLOGY
RADIOISOTOPES
ROCKS
SILICATE MINERALS
STABLE ISOTOPES
SYNTHESIS
TERTIARY PERIOD
USA
YEARS LIVING RADIOISOTOPES