No abstract

No abstract

No abstract

Page Tertiary and Quaternary rocks______________________________________ E36 Gila Conglomerate___________________________________________ Quaternary deposits.______________________________________________ Older alluvium________________________________________________ Pediment gravels_____-________________________________________ Younger alluvium_____________________________________________ Talus. _____________________________________ Tufa.______________-_______________________ Structure. ________________________________________________________ Folds_______________.____________________ Deer Creek syncline.______________________________________ Dicks Spring Canyon syncline_____________________________ Other folds_______________________________________ Thrust faults___-______________-_-_-_-_-_-_-____________ Reed Basin thrust.________________________________________ Thrust northwest of Coolidge Dam__________________________ Thrust in Dicks Spring Canyon.____________________________ High-angle faults ______________________________________________ Red Rooster-Quartzite Mountain fault zone_________________ Dicks Spring fault______________-__________________________ Mescal Creek fault._______________________________________ Hawk Canyon fault______________________________________ Bull Basin fault.______________________________ Other faults_.-________________________________ Ore deposits ______________________________________________________ Christmas mine__-____________-__-___-_-__-_______________ History._________________________________________________ Geology__________________________________________________ Ore bodies________________________________________________ Geologic controls of the mineralization.__________________ Iron deposit-__________________________-_____l_______________-Geologic history___________________________________________________ References cited_________________________________________________ Index________________________________________________________ 5.

The rocks exposed in the Jackson Mountains, a prominent range near the center of Hurnboldt County, Nev., record the effects of a Late Cretaceous to early Tertiary orogeny. Such an orogeny has been assumed to have affected all of the Great Basin, but the rock record is sufficiently complete to provide positive dating in only a few areas, such as the Jackson Mountains. The oldest rocks in the range are the Permian or earlier volcanic rocks of the Happy Creek volcanic series, which make up most of the northern half of the range. In a few places the Happy Creek volcanic series grades upward into undivided Permian and Triassic rocks, which consist of interbedded clastic sedimentary rocks, mafic volcanic rocks, and some shaly and 'siliceous limestone. The Happy Creek volcanic series is also overlain by an unnamed predominantly limestone unit of Triassic age. A phyllite and slate unit of probable Triassic age is in fault contact with the Permian and Triassic undivided rocks. At several other localities the Happy Creek volcanic rocks are overlain by the King Lear formation of Early Cretaceous age or by the Pansy Lee conglomerate of Cretaceous or Tertiary age; these two units are of chief importance in dating the Cretaceous and possibly early Tertiary erogenic events. The King Lear formation consists of locally derived pebble and boulder conglomerate and interbedded siltstone and graywacke, and lenses of limestone. The Pansy Lee conglomerate is a pebble conglomerate with considerable interbedded coarse-grained sandstone. The pebbles consist of chert and quartzite completely unlike rocks now exposed in the Jackson Mountains. Dioritic rocks were intruded both before and after the King Lear formation was deposited. Granodioritic intrusive bodies in the range cut rocks no younger than Triassic, but the granodiorite is believed to be of Late Cretaceous or early Tertiary age. Tertiary intrusive and extrusive volcanic rocks and sedimentary rocks are widely distributed along the east side and south end of the range. The most extensive tectonic feature of the Jackson Mountains is the Deer Creek thrust, which is discontinuously exposed from Rattlesnake Canyon northeastward to the north side of Deer Creek Peak. The thrust has brought the Happy Creek volcanic series over the King Lear and Pansy Lee formations, and is thus of Late Cretaceous or early Tertiary age. An earlier period of possible Cretaceous deformation is shown by a northeastward-plunging syncline in the King Lear formation on the southeast side of King Lear Peak. Dl D2 CONTRIBUTIONS TO GENERAL GEOLOGY Pre-Cretaceous deformation is shown by a tight fold in limestone of the undivided Permian and Triassic unit beneath the King Lear formation at the mouth of Rattlesnake Canyon. The late Tertiary deformation was almost exclusively a response to vertical stresses, which generally produced high-angle faults rather than folds. The range has probably been uplifted principally by displacement on faults that are buried beneath the alluvium some distance to the east and west of the...