Origin of gold in placer deposits of the Sierra Nevada Foothills, California

Documents presented here offer an alternative theory for the origin of gold in the Early Tertiary river sediments located in the Sierra Foothills of California. The fundamental concept presented here is not really new but it was largely forgotten for numerous decades. The re-introduction of this topic is promoted by Odin Christensen who has presented this alternative gold genesis theory to numerous geologic associations and academic forums. That Power Point presentation and notes are included here.  In addition, a recent paper expounding this theory presented to the 2015 Symposium of the Geological Society of Nevada is available here as well.


Gold Nuggets—Evidence of Past Climates and Former Landscapes

This is a Power Point slide presentation by Odin Christensen given to the Geological Society of Nevada as well as other geological associations.  Odin is a metallic minerals exploration geologist with considerable experience with Nevada gold deposits as well as international gold exploration experience.  Christensen re-introduces an alternative theory and mechanism to account for the high concentrations of placer gold nuggets in the Early Tertiary river sediments of California as well as other similar placer deposits in Alaska and the Yukon Territories.  He outlines the geochemical processes that operate to concentrate gold in various horizons of very mature lateritic soil profiles under intense chemical weathering conditions.  These lateritic soils are generally classified as Oxisols.  Kaolinite is the dominant pedogenic clay mineral in these mature soils.

Today, this supergene gold concentration process can be observed operating in tropical regions in low latitudes throughout the world such as South America and Africa.  The Early Eocene was a period of globally warm and wet conditions and kaolinitic Oxisols are known to have formed in high latitudes during that time.  Thus, this mechanism is a plausible explanation for the occurrence of gold nuggets in Early Tertiary rivers that traversed and drained regions of Nevada known largely for disseminated gold deposits.

Also included here is a paper about supergene gold enrichment in very mature lateritic residual soils in Australia which are sources of some of the largest gold nuggets yet found.

The concept or notion of the supergene enrichment in mature soils to account for the origin of placer gold in Northern California and Oregon’s ancient and modern river systems has been postulated before.  In fact, workers from the very earliest days of the study of California’s rich placer gold deposits proposed that theory.  Included here is an earlier paper by Evans (1981) from the Engineering and Mining Journal, outlining the concept that the earlier workers contemplated. This is one of the references listed in Christensen’s reference list below.

Christensen, Odin D., Christopher D.Henry, and Jim Wood, 2015, Origin of gold in placer deposits of the Sierra Nevada Foothills, California, Geological Society of Nevada Symposium 2015.  view here

Christensen, Odin, 2014, Gold Nuggets—Evidence of Past Climates and Former Landscapes, Geological Society of Nevada, February 21, 2014.

          Power Point slide show (pdf)    view here

          Slide show Notes (pdf)             view here

          Topic Reference List                view here

Hughes, Martin J., et. al., Lateritic Weathering and Secondary Gold    view here

Evans, 1981, Laterization as a Possible Contributor to Gold Placers, Engineering and Mining Journal, p.86-91.      view here