Saturday, March 12, 2016

Developing a Small-Scale Hard-Rock Mine (Part 2)

 (Old timer pushing an ore cart from a small-scale hard-rock mine.)

In this post I'll be continuing on with advice, suggestions, and tips for developing your own hard-rock or lode mine on a small-scale. The principles and practices I'm laying out for you in this series have been proven over time by miners much more adept than myself, so you can take the info provided straight to the bank.

Time and Money Well Spent

Hard-rock gold mining on any scale is not something you want to rush right into...nor is placer mining for that matter. The only urgency you should feel as a small-scale guy or gal is ensuring your find is locked up or claimed for your exploration and development and not subject to another miner coming along and making it his or hers. Otherwise, slow and steady wins the race in the long run. This approach means that the time and money you've invested thus far in your lode claim is well spent and on target for thorough sampling via one or more of the following methods: trenching, pit sampling, or drilling. Let's look at these sampling methods individually:

1. Trenching

There's no rocket science involved in this method folks. It's pick and shovel time with this approach unless you're flush and can afford to run a small Bobcat loader or excavator around your digs. That size of equipment is about as large as you could go and still be considered a small-scale gold miner in my book. You see, I 'm not against equipment that'll do the job, but as I've said many times before, I've never been oriented toward commercial or large-scale gold mining operations. I'm a small-scale gold miner, not a heavy equipment driver, a mechanic, or a mine boss. Anyhoo, let's get back to the gist of things. Trenches are cut or dug to get an idea of the length, width, or area extent of a given outcrop, vein, reef, or blowout. They're also used to determine the presence of intersecting veins or ledges and finally, to gather additional samples for assaying. How wide or deep those trenches are is dependent on any number of factors, not the least of which are your lode mining and sampling experience, knowledge, and abilities. Typical hand-dug lode trenches run to a maximum of 5-7 feet with widths about rarely exceeding 3 feet. There are two reasons for these general sets of measurements: 1) They're about all you're gonna be able to handle on your own or with a pard, and 2) You'll typically get the necessary sampling information you need for small-scale operations using these parameters. Again, you can make shorter work of this trenching approach with small, motorized digging or trenching equipment like the aforementioned Bobcats (some of which are not driven, but hand-operated).

 (Test trench with sample bags nearby.)

Safety Tip: If your trenches are deep (shoulder or head depth or greater), make sure they're stable or you've stabilized them with bracing of one sort or another. No one is gonna even hear you scream when those trench walls collapse and bury your crazy ass alive. Having a pard close by might save your life, but staying away from obvious risks to life and limb is your best friend in mining in general (hard rock or placer).

2. Pit Sampling

I've encountered pit sampling more than any other method when I've been out and about over the years. In certain desert contexts, I've come across hundreds of pits dug to sample horizontally along a ledge or vein as well as vertically up and down a hillside. Just so you know, these pits I'm talking about were ALL dug the hard way, by hand. Oftentimes the old timers dug test pits because the overburden around a ledge or outcrop was just too thick in depth to make trenching feasible. Most small-scale lode pits are 4-5 feet in diameter and can be as deep as 30 feet or more. The deeper the test pit the more important safety issues become, for obvious reasons. Deeper sample pits require shoring of one sort or another, just like trenches.

(Hard-rock sample pit or "coyote hole.")

3. Drilling

This is the most costly approach to hard-rock sampling (just as it is in commercial placer mining) but if you have the means it's also the quickest way to pull core samples. Even in small-scale drilling, samples can be pulled from depths reaching 1,000 feet, although I consider this going way beyond the pale for small-scale guys and gals. However, if you're pretty certain there's good gold ore to be had on your site then drilling for core samples at any depth or angle is warranted. If you hire a driller to do your sampling they typically charge by the foot with extra charges for specialized casings or other odds and ends. If you ever decide to go this route make sure you work out all the cost parameters ahead of time and understand fully what services and gear the driller will supply. Core samples from drilling must be labeled with all pertinent information (date, location, depth, etc.) so that you know where richer zones are and what the overall average of precious metal per ton can be expected after the samples are assayed. I doubt very many of you out there are gonna go the drilling route unless you stumble across rich ground, but I wanted to present this alternative to you just the same.

 (Drilling core samples.)

Ore Values

The value of the ore material you've sampled pretty much dictates whether you'll move forward on your small-scale lode venture or not. Typical gold ore values considered viable for folks like us wanting to develop a lode mine fall in the range of about half a troy ounce per ton on up (average value). The higher the value per ton the better the proposition since you're primarily working by hand or with very small equipment. The old timers rarely worked anything showing less than half an ounce per ton and sometimes passed that value up, particularly when gold was $35.00 (USD) per troy ounce or less. With gold over $1,000.00 an ounce, this value takes on new meaning despite the work involved. Commercial and large-scale operations these days can actually be profitable with gold value averages much lower than this which is why so many large mining corporations are working massive open pit mines delivering only a few grams per ton of material excavated and processed. Also note here that any gold ore you process is probably going to contain other metals as well, like silver, copper, lead, zinc, and so on. It's going to be difficult for a small-scale lode miner to separate and process the gold contained in his or her ore, let alone other metals. That said, here are some bottom line percentage values that are suggested for extracting other metals from your ore:

Copper (Cu): 5%
Lead (Pb): 15%
Silver (Ag): 24 troy ounces per ton of material
Zinc (Zn): 25%

In other words, your ore must display (on average) these percentage values or amounts to make extracting these other metals profitable. The good news here are that these values INCLUDE transport and processing costs (or should, anyway).

That's it for now. There's more to come so stay tuned.

(c) Jim Rocha (J.R.) 2016

Questions? E-mail me at jr872vt90@yahoo.com

1 comment:

  1. Yeah, I cringe when I see people down on their knees up under a ledge digging away like nothing is gonna happen. Especially when the so-called ledge is made up of rounded river rock. When asked if they are concerned, the typical response is "It ain't happened so far. But, I'm watching for it." Famous last words.

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