U-Pb Age Constraints on Magmatism and Mineralization in the Northern Great Basin, Nevada

A U-Pb dating study was undertaken to establish an absolute
age framework for intrusive rocks spatially associated with sediment-
hosted disseminated gold deposits in the northern Great Basin
of Nevada. Forty-four samples were processed, including suites
from the Goldstrike/Meikle, Bald Mountain, Gold Acres/Cortez,
Jerritt Canyon and Ruby Hill areas, as well a suite of regional samples.
Crystallization ages have been established for twenty-six of
these samples; the remainder either did not yield datable minerals or
displayed such complex U-Pb systematics that an age could not be
confidently assigned. Results of the study indicate that at least four
discrete and apparently short-lived magmatic events occurred in the
northern Great Basin in Mesozoic and Early Tertiary time; these are
dated at ~186 Ma, ~162-156 Ma, 113-105 Ma, and 38-33 Ma. The
latter three episodes are widely recognized based upon published
geochronologic data. In contrast, the late Early Jurassic magmatic
activity, documented in the Bald Mountain area, has not previously
been recognized this far east of the magmatic arc; the regional significance
and extent of this activity is unknown. A variety of ore
deposits, including base metal porphyry, skarns and mantos and possibly
distal disseminated sediment-hosted Au-Ag, are spatially and
genetically associated with intrusions of Middle Jurassic and Early
Cretaceous age in the Goldstrike, Bald Mountain, and Ruby Hill
areas. Early Tertiary magmatism is temporally associated with classic
Carlin-type mineralization in many districts and with distal disseminated
styles of deposits in the Battle Mountain district and elsewhere.
When compared to U-Pb ages, many published K-Ar ages on
relatively unaltered rock units outside of the main hydrothermal centers
in the northern Great Basin are shown to be reasonably reliable.
In contrast, K-Ar and some Ar-Ar ages from within mineralized districts
have commonly been disturbed and variably reset by the
hydrothermal processes.