Pilbara and Novo Resources: Watermelon Seed Nuggets Mean What?

Quinton Hennigh has apparently recognized the next Witwatersrand according to Bob Moriarty and John Kaiser. The "discovery of the 21st century" is being advanced by the Canadian junior Novo Resources and a growing bandwagon of Australian explorers, Artemis Resources the foremost and original pioneer among them (Artemis holds the ground where outcropping conglomerate beds were prospected with metal detectors leading to the recognition that gold nuggets blanket a significant area). There are a few reasons for thinking the Pilbara Basin in Western Australia near Karratha could turn into a major gold camp, perhaps even on the scale of South Africa's Witwatersrand (which has mined roughly a quarter of the world's gold amounting to some 1.5 billion ounces). One of the reasons is the presence of gold-bearing conglomerates across a wide area overlying Archean basement rocks.

Another reason being bandied about is that a lot of the Pilbara conglomerate gold is in the form of "watermelon seed" nuggets. These nuggets are found in a wide area spanning hundreds of kilometers. Some are saying the nuggets are a sure sign the gold was precipitated from solution in a large acidic (inland?) sea that covered the Archean basement rocks. I am saying such nuggets are found in placers from ancient eroded sources (probably narrow veins and stringers in granite or in mafic dykes) in abundance throughout the major alluvial deposits (Alaska and the Klondike, etc.). Watermelon seed gold is documented as far back as the 1800s.

For example, "In richest Alaska and the gold fields of the Klondike, how they were found ... together with a history of this wonderful land from its discovery to the present day ... and practical information for gold seekers" by Ernest Ingersoll, Henry Wood Elliot, Augustus J. Munson, we are told that:

It is interesting in this connection to know something of the size of the Klondike nuggets, although large nuggets are not necessarily the accompaniment of rich fields. There were four nuggets of the size of duck eggs, and a dozen as large as walnuts, in the gold brought down this summer from Alaska. The big ones are worth about $375 each, and the small ones about $140. There are many thousands of golden bits of the size of watermelon seeds that are worth $1 each, and hundreds of the size of common gravel-stones.

And if we look up the kind of nuggets that are being found in Alaska and the Klondike today, they are still mainly of the "watermelon seed" persuasion (flattened, about a gram in weight). It's the same for California and other places where alluvial placers are still producing gold today. Watermelon seed gold is simply not that uncommon. The sizing is probably the result of lode gold deposits mainly being composed of veining of several millimeter width, which are then eroded and mechanically broken up (gold is soft and rarely survives as a "vein sheet" once freed of its host rock), then folded over and rounded by water flow and transport, and finally flattened by material that piles on top.

So finding lots of watermelon seed nuggets in the Pilbara doesn't decrease the probability that the gold came from a lode source. This is the same process as many of the placers throughout the world, and doesn't really speak kindly for the idea that the Pilbara will turn into another Witwaterstrand. Maybe another California or Klondike gold rush. Not something that would necessarily be mined by a large company because the gold distribution doesn't usually create the advantage of economies of scale by a large operation over that of an individual or small-scale prospector or "fossicker".

As for the high purity of the Pilbara gold somehow indicating that it has a chemical source (deposited by precipitation into a sedimentary basin, suggesting a large extent of the mineralization in a conglomerate horizon or bed instead of localized as it would be in placer channels representing ancient rivers)? Nope. Other parts of Australia are known for high purity nuggets (exceeding 95%) without having been chemically deposited. More likely, the gold purity has to do with the composition of the ore fluids and possibly post-deposition dissolution of impurities.

Disclaimer: This is not investment advice, just an opinion. Consult your own expert.