| Description |
vii, 80 leaves : illustrations, photographs, maps ; 29 cm |
| Summary |
"The purpose of this investigation was to determine the unusually complex geology of a little-known area south of the Eldorado mining district, southern Clark County, Nevada. The area, mapped at a scale of 1:24000, comprises a segment of the northerly-trending Eldorado mountains in the southeast corner of the Great Basin. This rugged desert area is on a drainage divide between the Great Basin and the Colorado River. The rocks of the area consist of Precambrian gneisses and schists invaded by successive generations of Upper Cretaceous (?) - Tertiary igneous rocks. The older rocks, mainly biotite-chlorite gneisses, have resulted from high-grade regional metamorphism followed by partial retrograde effects. A medium-grained quartz monzonite grades migmatically into these rocks. A later, essentially contemporaneous complex of acidic rocks, chiefly fine-grained quarts monzonite and rhyolite-andesite porphyry, occur as a large easterly-trending pluton, and numerous dike swarms and chonoliths. Intermediate-basic intrusions, chiefly of andesite-latite porphyry, follow in close succession. Andesite flows locally occur in the north, nonconformably overlying gneiss and quartz monzonite. Quaternary surficial deposits cover parts of the area. The gneissic foliation, extremely variable in trend and attitude, tends to parallel the strike of the large pluton near the gneiss-pluton contact. A profusion of dike swarms, joints and faults are present in the area. These all show preferred trends, chiefly northerly. The most prominent faults uplift the western part of the Eldorado Mountains, i.e. the Ireteba Peaks, above the surrounding country. The periods of igneous intrusion and fracturing overlapped. A few mineralized fissure zones (epithermal gold-silver-quartz), cutting andesite, gneiss and schist, are concentrated in the northern part of the area"--Abstract, leaves ii-iii. |
|
