Abstract

Hydrothermal solutions mainly of hypogene origin are believed to be responsible for the formation of collapse features, their associated alteration effects, and the accompanying mineralization at and near Temple Mountain, Utah. The collapse features are characterized by: (1) a central core, consisting of blocks and fragments of downdropped broken strata; (2) a structural basin in surrounding strata; (3) marked alteration effects which differ in core and border. The collapse features, 11 of which are noted, range from less than 100 feet in diameter to more than 1000 feet and with three exceptions consist of a Moss Back core in Moenkopi country rock. Even the three exceptions represent a similar process. The writers believe that the collapse structures were formed by the removal of the underlying carbonate rocks (Kaibab Limestone and lower and middle Moenkopi Formation), which resulted in downdropping of the higher strata and sagging of the surrounding beds to form the enclosing basin.

At the Temple Mountain collapse Wingate and Moss Back sandstone blocks have been dropped several hundreds of feet and are enclosed in structural basins of Moenkopi and Chinle strata. Drilling records reveal that the carbonate constituents of the underlying Kaibab Limestone have been removed. Alteration effects within the collapsed core and the surrounding country rock from the top of the Coconino Sandstone through the Wingate Sandstone include argillization, carbonatization (dolomitization), and ferrugination (sideritization and hematitization); the uranium mineralization following consists chiefly of emplacement of pyrite, urano-organic ore, and late alteration effects, chiefly alunitization.

Mineral relationships indicate that hydrothermal solutions dominated in processes of the development of the collapse features and in the alteration and mineralization.

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