Chemistry of zeolites and zeolitic tuffs from a Pliocene lacustrine deposit near Durkee, Baker County, Oregon
Zeolites in an unnamed Pliocene lacustrine and fluviatile deposit near Durkee were first mentioned by Eakle (1898). He described a new zeolite, erionite, from a small opal quarry in a "rhyolite" (welded ash-flow tuff) about 6 km southeast of Durkee. Eakle, unfortunately, provided only a vague description of the type locality of erionite; and more than half a century passed before the type locality was rediscovered by L. W. Staples, and additional specimens were compared with Eakle's original material (Staples and Gard, 1959). Prior to the late 1950's, the Durkee locality was the only confirmed occurrence of erionite in the world. Our investigation of the zeolites and the diagenesis of tuffaceous rocks near Durkee began late in 1970 after a brief reconnaissance early in that year showed an abundance and variety of authigenic zeolites in silicic tuffs of the lacustrine deposit. Field studies continued intermittently until 1972, and laboratory studies continued intermittently until 1976. Preliminary findings have been published in two brief reports (Sheppard and Gude, 1975; Gude and Sheppard, 1978). This present report is concerned only with the chemistry of certain zeolitic tuffs from the Durkee deposit and with the chemistry of chabazite, clinoptilolite, and erionite that were separated from six of the tuffs.