Geology and ore deposits of the Casto quadrangle, Idaho

Bulletin 854



The study of the Casto quadrangle was undertaken as the first item in a project to obtain more thorough knowledge of the general geology of southcentral Idaho on which to base study of the ore deposits of t he region. The quadrangle conta ins fragmentary exposures of Algonkian and Paleozoic sedimentary rocks, extensive deposits of old volcanic strata, presumably Permian, not heretofore recognized in this part of Idaho, and a thick succession of Oligocene(?) lava and pyroclastic rocks. The Idaho batholith and its satellites extend into the quadrangle, and in addition there a re large masses of Tertiary granitic rock, not previously distinguished in Idaho, and many Tertiary dikes, some of which are genetically associated with contact-metamorphic deposits. The area contains injection gneiss of complex origin, largely related to the Idaho batholith but in part resulting from injection by ~he Tertiary granitic rocks under relatively light load. Orogenic movement took place in Algonkian, Paleozoic, and Tertiary time. There is a summit peneplain or par tial peneplain of Tertiary, perhaps Pliocene age, and the erosional history since its elevation has been complex. The ore deposits include lodes and placers. The lodes are related to both the Idaho batholith and the Tert iary intrusive rocks and have yielded gold and copper ore of a total value of about 1,000,000. Placers, largely formed in an interglacial inter val, have yielded about an equal amount. There has been some prospecting but almost no production since 1916.

Study Area

Publication type Report
Publication Subtype USGS Numbered Series
Title Geology and ore deposits of the Casto quadrangle, Idaho
Series title Bulletin
Series number 854
DOI 10.3133/b854
Year Published 1934
Language English
Publisher U.S. Government Printing Office
Description Report: 135 p.; 1 Plate: 18.48 x 27.70 inches
Country United States
State Idaho
Other Geospatial Challis National Forest, Salmon National Forest
Online Only (Y/N) N
Additional Online Files (Y/N) N
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