(Tightly packed gold-bearing gravels...?)
Gold-bearing gravels come in all shapes and sizes...that's a given. What some prospective placer miners fail to realize, however, is that there can be a important difference in their gold-trapping ability.
For the Sake of Learning
Before I get to the heart of the matter let me qualify things here a bit. I'm not focusing my attention on dry placer gravels in this post, despite the fact the deposition principle I'm about to bring to your attention can apply to desert gold locations as well.
Gold Prospecting Books
The main reason for my reluctance to make blanket statements about dry placer gravels here is that gold deposition in those environments tends, once again, to be very spotty or erratic due to the isolated or intermittent nature of water flow in those areas. Although I've come across loosely packed gravels a number of times in dry placers, in the majority of instances tightly packed or "cemented" gravels seem to be the norm in gold areas where running water is intermittent or absent altogether. Yes, this is a generalization of sorts, but for the sake of learning a potentially valuable lesson let's assume it's so.
With that said, let's move on to wet placers where running water hydraulics is the main gold deposition factor. In wet areas placer gold gravel bars, benches, and the very stream gravels themselves can be either loosely consolidated or tightly packed. There doesn't seem to be much middle ground in this observation of mine...typically it's one way or the other (although loosely packed gravels tend to predominate in existing streambeds).
There's a fundamental flaw in tightly packed stream gravels when it comes to gold deposition that should be readily apparent to one and all. Simply put, it's very hard for gold to get trapped in and among tightly packed gravels, especially since most of them are rounded or cobbled. Even at good deposition points, placer gold particles and flakes will invariably skip merrily along right on over tightly packed gravels in favor of areas with better gold-grabbing potential.
Your Best Bet
OK, let's hold up for a second. This doesn't mean that tightly packed stream gravels are completely bereft of gold or can't stop any gold at all. In fact, good gold values that were trapped when those gravels were loosely consolidated may very well lie farther down.
But if you have to make a decision to work either tightly packed or loosely packed gold gravels, it's my view that the latter are your best bet and here's why. Even the most water-worn or cobbled loosely packed gravels can provide numerous small "catch" areas for gold particles to become lodged within. These gold particles and flakes can accumulate there as well.
Common Sense Observation
I can't tell you how many instances like this I've come across in my 33+ years of small-scale mining. If I could magically whisk you away to certain stream locations I've worked in the past I could show you right on the spot what I'm talking about here and you'd be nodding your head and saying, "Yep, I see exactly what you're talking about."
(Or loosely packed gravels?)
This doesn't mean I'm some sort of small-scale mining Einstein. After all, this is a common sense observation that doesn't require a PhD in gold deposition physics to understand. Still, very simple things like these are often overlooked by small-scale gold miners...especially those who are just beginning their mining "careers."
Focus on Loose Gravels
Finally, does Ma Nature always conform to my observations? Or to the laws of deposition physics? No she doesn't. This despite the fact I'm a legend in my own mind and always right. Well...not always right anyway!
I know this is a very simple premise but I thought it valuable enough to bring to your attention. If there's no readily accessible, juicy bedrock to work, focus your attention on those loosely packed gravels because they provide better gold-trapping characteristics.
Good luck to you all.
If you liked this post, you may want to read: "Keep It Simple"
(c) Jim Rocha (J.R.) 2013
Questions? E-mail me at email@example.com