Abstract

A copper deposit about 40 miles southwest of the Coeur d'Alene district, Idaho, shows a marked structural and mineralogical resemblance to the copper deposits of the Ducktown type. It occurs as a replacement along bedding plane fractures and fissures in quartzitic beds of the Belt series and its ore consists chiefly of pyrrhotite, chalcopyrite, and lesser cubanite in a silicate and carbonate gangue. Fracturing repeated several times during mineralization caused deposition in three distinct mineral stages, shown by the partial replacement of one group of minerals by later ones. Minerals deposited during the first stage include the silicates (diopside, tremolite, actinolite, biotite, epidote, tourmaline, microcline, and muscovite), and a little quartz; during the second stage, the carbonate (ferriferous dolomite); and during the third stage, the sulphides (pyrrhotite, chalcopyrite, arsenopyrite, and cubanite), and a little quartz and calcite. Except for its mode of occurrence, the deposit possesses most of the characteristic features of a pyrometasomatic deposit but is, nevertheless, a hypothermal deposit formed probably under exceptionally intense temperature conditions.

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