Monday, November 18, 2013

A Short Course on Hard Rock Gold (Part 4)

 (Canadian hard rock miners drilling a "face.")

In many respects, hard rock gold mining is a vastly different undertaking than your run-of-the-mill small-scale placer mining operation. One of the most difficult and expensive aspects of hard rock gold mining is actually developing a mine once you've located and claimed it.

Before I get to the heart of the matter here, I'd like to reiterate that my main emphasis in this series of posts is targeted toward small-scale gold miners and mining operations. In my mind, small scale means non-commercial, non-corporate, and devoid of any of the large-scale trappings of those two types of operations in terms of personnel, payrolls, equipment, and machinery.

Hard Rock Mining Terms

You're probably familiar with some hard rock mining terms but I suspect a good percentage of you aren't, so let's review some key terms before I get into an involved discussion of mine development:

Adit: Typically, the spot where a horizontal passage or shaft comes to the surface.

(Old mine adit in my neck of the woods.)

Assay: Process of analyzing ore to determine its precious metals content. Chemical and fire assays are used by most small-scale miners.

"Coyote" hole: Shallow, hand-dug excavation used to determine gold values or to extract gold samples.

Drift: Horizontal mine passageway or tunnel.

Excavation:  Large-scale "coyote" hole. Could be dug by hand or by heavy equipment.

"Face:" Frontal area where drilling, blasting, and excavating takes place. Sometimes called the front or frontal wall.

Headframe: Sometimes known as a "winze" in its simplest form, a headframe is metal or wooden structure used for lifting material to the surface from a vertical mine shaft.

(Mine headframe.)

Mercury (Hg): Also known as "quicksilver" by the old timers, mercury was used (and still is in some instances) for bonding small particles of gold together into amalgam. (Hg is a potent neuro-toxin if ingested or absorbed through the skin. It is also highly poisonous if vapors are inhaled while "burning" off the Hg from amalgam using acids like nitric. Never attempt the latter in enclosed spaces.)

Portal: Entrance to a tunnel, adit, or mine.

Prospect pit:  Exploratory excavation or hole dug while searching for gold vein or placer material. Similar to a "coyote" hole or shallow excavation.

"Raise:" Secondary mine shaft excavated vertically to connect one horizontal shaft to another.

(Looking down a mine "raise.")

"Rake:" Timber support placed at an angle.

Shaft: Vertical or sloped opening providing access to various mine levels.

"Square Set:" Mine wall and overhang bracing using squared timbers notched and interlaced in a honeycomb system.


Stamp Mill: Machine or mill with mechanical or electric "stamps" or pestles for crushing ore into fine powder.

Stope: An upward-trending excavation of inclined vein material that can't be accessed by other shafts or drifts.

Tailings: Barren, refuse rock (coarse tailings) or processed material (fine tailings) from hard rock mining operations. (Note that many fine tailings from old mining operations have been cyanide leached and can still present a health hazard.)

Tunnel: Horizontal underground passage with openings at both ends.

 (10-stamp mill.)

Overhang: "Roof" area above a miner. Sometimes called the top wall.

Walls: Sides of a shaft or tunnel.

That should hold you all for a bit. In my next post on this subject, we'll discuss the dynamics of developing a hard rock gold mine. Until then, be safe and keep on grinning.

(c) Jim Rocha (J.R.) 2013

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


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