Implications of stratabound Carlin-type gold deposits in Paleozoic rocks of north-central Nevada

On the basis of mineralogical-geochemical data and related implications, as well as
general geological considerations, SEDEX gold accumulations in the Great Basin might
have been a Paleozoic precursor event in many Carlin-type gold deposits whose origins
subsequently were masked because of multiphase Mesozoic and Cenozoic tectonism and
magmatism. This paper examines important geological characteristics that relate to
inferred formation of primary stratiform and (or) stratabound SEDEX disseminated
gold accumulations in Carlin-type deposits of north-central Nevada, and that correspond
to well-developed models of polymetallic SEDEX deposits. The latter provide the fundamental
criteria for a filtering of the entire population of more than 100 Carlin-type
deposits in the Great Basin in order to select those deposits that are considered to have
remnants of synsedimentary features. Three filters were used to screen Carlin-type gold
deposits: (1) their occurrence in epicratonic sedimentary strata with or without growth
faults, (2) predominant absence of Mesozoic and Cenozoic intrusive rocks in the deposit
vicinity, and (3) presence of stratabound type of mineralization comprised of conformable
tabular, lenticular, and ribbon-shaped ore bodies associated with feeder channels.
Sequential application of these three filters results in 25 Carlin-type deposits that
might contain evidence of synsedimentary gold mineralization. These deposits are
evenly distributed in the Jerritt Canyon district and along an approximately 300-kmlong
NW belt including the Carlin trend and the southern part of the Battle Mountain-
Eureka trend. The selected group includes only stratabound deposits that are
present in Paleozoic autochtonous or parautochthonous sedimentary strata belonging
to the eastern assemblage carbonate platform in east-central Nevada, in spite of
widespread lithological and facies diversity in these host rocks. These deposits clearly
contain volumetrically significant, well-developed stratabound disseminated gold
mineralization and are minimally disturbed by faults and (or) magmatic effects.
Comparative examination of the settings of the 25 deposits shows a steady southward
stratigraphic ascent of mineralized sequences from Upper Ordovician and Lower
Silurian Hanson Creek Formation to Early and Late Mississippian Joana Limestone
and Chainman Shale, involving an inferred mineralizing time span from 460 to 325
Ma. In addition, the Carlin and Battle Mountain-Eureka trends parallel the general
drift direction of North America (Laurentia plate) during 400 to 325 Ma. Local and
regional time-stratigraphic features compared with data on paleocontinental movements
appear to corroborate the assumption that original sedimentary-exhalative
(SEDEX) gold ore-forming processes might have been initiated by hot spot activity—
i.e., the stratabound Carlin-type deposits themselves suggest a specific Paleozoic hot
spot that initiated failed amagmatic rifting and related synsedimentary gold influx
into a basin at the western margin of the craton.