Geochronologic studies in the Grants mineral belt

Conference · Tue Jan 01 04:00:00 EST 1980 · Mem. - N.M. Bur. Mines Miner. Resour.; (United States)

OSTI ID:6385187

Brookins, D G

Geologic observation coupled with radiometric age dating can be used to assess ages of ore formation and, in some cases, ages of sedimentation in the Grants mineral belt. Rb-Sr studies indicate the earliest mineralization is trend ore at Ambrosia Lake and Smith Lake, dated at 139 +- 9.5 m.y. This date is similar to that for barren-rock montmorillonite from the Jackpile sandstone (Late Jurassic): 142 +- 14 m.y.; it may be used, with caution, to indicate the minimum age of sedimentation for the Morrison Formation. Geologic evidence indicates epigenetic rather than syngenetic ore formation. Barren-rock montmorillonites from Ambrosia Lake yield a poorly defined isochron of 132 +- 26 m.y. Early formed ore at the Jackpile-Paguate mine, Laguna district, was remobilized and reprecipitated at 113 +- 7 m.y. This date is older than the range of dates for the Dakota Formation (Cretaceous) and Mancos Shale. The 113 +- 7 m.y. mid-Cretaceous date for the Jackpile-Paguate ore is consistent with geologic evidence; geologic control suggests that other ore deposits are post-Late Jurassic but pre-Dakota Formation. Based on geologic evidence, mineralization in the Dakota Formation is thought to be very young. Laramide mineralization (60 to 70 m.y.) is evidenced by the presence of some stack ore. At least one uranium deposit, located partly in oxidized ground at the main redox front of the Grants mineral belt, may represent Tertiary mineralization; the clay-mineral Rb-Sr systematics of this deposit have been severely perturbed. Younger mineralization is indicated by U-Pb dates on uranophane (9 to 10 m.y.), and Pleistocene mineralization is noted for some ore. U-Pb dates of U/sup 4 +/ -rich ore minerals cluster between 80 and 100 m.y., although some are as old as 140 to 150 m.y. K-Ar dates on clay minerals range from 49 to 138 m.y. The reasons for this scatter are not known, although loss of radiogenic /sup 40/Ar due to burial is probable.

• Research Organization: Univ. of New Mexico, Albuquerque
• OSTI ID: 6385187
• Report Number(s): CONF-7905120-
• Conference Information: Journal Name: Mem. - N.M. Bur. Mines Miner. Resour.; (United States) Journal Volume: 38
• Country of Publication: United States
• Language: English

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