Goldtutor,
Thank you for your inquiry, the following response has been provided by African Gold.
Regards,
Agoracom
"The conventional wisdom was that these nuggets were the weathered product of veins in bedrock which oxidized and slowly deteriorated over a long period of time. The difficulty with this idea is that, in most cases, the original (lode) gold deposit that underlies these nugget contains no gold grains that are any where near as large. In other words, the gold at depth in the fresh (parent) bedrock is quite fine in comparison to what you see in the weathered zone. This conundrum has been encountered in many places that have been subject to tropical weathering.Geologists now believe that the nuggets may have formed when an original, much smaller nugget acted as a seed onto which additional gold was deposited from water slowly migrating through the weathered zone. In other words, the original nugget acted as a nucleus on which new gold precipitated. This requires a fair amount of additional gold in the surrounding area as the distance of migration is probably not that great (maybe a few tens of metres). The evidence that supports this idea includes the fact that many such nuggets do in fact contain growth rings. The amount of gold versus other metals, mainly silver, varies from the centre of the nugget to the margins. This lack of homogeneity indicates some type of growth phenomena."
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