Placer pit design

You’ve found a good prospect!  The test pan shows a piece of gold, or two, or as one test pan we chanced to run showed 18 small pieces of gold!  Experience has taught us to expose several feet of a lateral face to determine the depth of the pay zone, then work horizontally.

Why?  Anyone who has some digging experience, whether post holes or trenches, even digging a garden, has found out how much easier it is to break ground and expand from that broken ground.  A vertical exposure allows you to work forward, which is a lot easier digging than down! A vertical exposure allows you to roll out a good-sized rock that you wouldn't have the strength to lift!

Invariably, as was the case here, weather or the end of the day calls a halt to developing what might be a good prospect.  We’re not young and invincible :) and have way too many obligations to just block out the world and mine! This time it was dusk on a Sunday evening followed by a day of rain…

The delay was a mixed blessing.  It gave us time to discuss and develop a plan of action.  That is the point we’re trying to get across here; make a plan.  Bob worked in different gold mines, and office chatter quite often turned to the gold deposit buried with waste, or under the mill and lab…  We want you to plan better than that, not only for yourself but for the environment!

Let’s go back to the 18-piece test pan prospect.  We had exposed enough to know there was a nice band of gravel and it was probably the source of gold.  Ore exposed was 6-8 inches deep.  Our plan was, obviously, to remove some overburden and run that gravel! 

The nature of the deposit was such that we would remove overburden as we mined into the hill and deposit waste behind us, filling our old workings as we progressed into the deposit.  The rationalization of this would be to never have to re-dig the same material and create as little disturbance as possible. 

I will explain what we see a lot -- throw your rocks and topsoil wherever seems easiest which is often on the bank in front of you!  Think about it… do you want to move that material time and time again?  Do you want to dig the same old rocks back up and move them because you deposited/rolled them where it was easiest?  As you widen your hole, do you want to re-work the waste you’ve already dug once? 

I had called the dusk encroaching and a rainy day a mixed blessing.  As always, there is more to this saga!  We returned two days later to our prospect.  Remember that we had exposed the lateral face to get a jump start on mining.

I can’t even begin to express what we felt when we saw the large hole that had been excavated!  The lateral face was now exposed about 5 feet deep and 12 feet wide!  The dirt and rock they had excavated was, gratefully, piled behind the hole.  They had dug below the pay zone but left a huge amount of overburden to be removed before we could work safely.  We also had to knock down and smooth over their waste pile so we weren’t waist deep in a hole with 5 feet of excavation in front of us and 6 feet of waste piled behind us.  The waste pile  also blocked aceess to the creek, so we would be climbing out of the hole over waste to sluice at the creek about 25 feet away.

We learned several lessons in this experience.  Don’t expose any more than you might work that day… and try to disguise your workings with some fill; we like to arrange some good-sized rocks in the hole to discourage others but also give us an immediate notice if someone does dig in our workings.  Some downed tree branches would serve the same purpose.

This constitutes a good pit design:  Look at your prospect; decide where to deposit waste in relation to future mining and creek access; expose a day’s work and camouflage it when you leave.  You might be able to realize a good day's pay without “giving it away” to everyone else!

A trick we have found helpful.  A digital photo of the lateral exposure can, when downloaded and viewed, give you a better defined view of the workings!  Another helpful tool is to view the workings when they have had a chance to air dry.  This is most helpful in identifying a clay band, it solidifying and oxidizing to expose a defined zone.