This open-file report contains the slide presentation (Power Point) prepared for the May 15-18, 2005 Geological Society of Nevada Symposium "Window to the World", in Reno. A detailed description of the study will be published in the Symposium Proceedings. A brief explanation is presented below and exemplified by the slides.

Carlin-type sedimentary rock-hosted gold deposits in Nevada have made the state one of the main gold producers in the world. About 100 Carlin-type deposits are known along two northwest linear trends in north-central Nevada-the Carlin and Battle Mountain-Eureka trends, as well as in two smaller clusters, the Getchell trend and Jerritt Canyon district. These deposits have produced more than 2,000 metric tonnes of gold, mainly from the prominent Carlin trend.

The unique geologic characteristics of Carlin-type gold deposits and a clear dissimilarity between them and other types of gold deposits remain obvious but basically inexplicable. 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 gold-concentrating 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 possible 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) absence of Mesozoic and Cenozoic intrusive rocks in the deposit vicinity, and (3) presence of stratabound mineralization in the form of conformable tabular, lenticular, and ribbon-shaped 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-km-long 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 the 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, covering 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 motions appear to corroborate the assumption that original sedimentary-exhalative (SEDEX) gold concentrating processes might have been initiated by hot spot activity-i.e., the stratabound Carlin-type deposits with related synsedimentary local uplifts suggest a specific Paleozoic hot spot that initiated failed amagmatic rifting and related synsedimentary gold influx into Paleozoic basins at the western margin of the craton.