Gold Hill: Anatomy of a Gold Mine EarthCache

Typically, gold mining in a region starts when someone discovers gold “lying around” on the ground or in a stream. This was the case with the first gold find in North Carolina, in 1799, at what was to eventually become the Reed Gold Mine in Cabarrus County, about 18 miles southwest of where you are standing in Gold Hill. In 1823, Dennis Olmstead conducted a geological and mineralogical survey of the State of North Carolina. This was the first geological survey in the United States having to do with mineral deposits. His survey focused heavily on the gold bearing rock in the region of Gold Hill. Shortly thereafter, in 1824, gold was discovered in Gold Hill.

Initially, gold mining begins with the easy pickings: Placer mining. Placer (pronounced “plasser”) mining is possible because heavy particles have weathered out of previously solid rocks. Such weathered out particles are known as a “deposit”. Gold is very heavy; it has a specific gravity of 19.3, meaning that it is 19.3 times heavier than water. Because they are so heavy, these particles can be separated from lighter materials (sand, clay, etc.) by running water, or even air from a bellows in some cases.

Besides placer deposits, the other type of gold deposits is “lode” deposits, and these are found imbedded in rock, usually quartz, as is the case at Gold Hill.¹ The unfortunate fact facing all placer miners is that easy pickings tend to be captured early – once they were gone, underground, hard rock mining was the only alternative available to those early miners. Extensive mining began in 1842 and continued through the late 1850s, and then stopped almost completely during the Civil War period. Later, new mining and ore-processing techniques allowed mining to resume and continue sporadically into the early 1900’s.

Microscopic flakes of gold are widely distributed under the surface of much of the earth, but are mostly in very tiny amounts. Geological faults, fractures in rocks, contraction and cracking in some types of rocks, and other factors can combine to concentrate previously dispersed flakes, to the extent that mining them becomes economically feasible.¹

At Gold Hill, the gold particles were carried by hot liquids that filled cracks and fissures within the “country rock”. Heat and pressure drove off most of the water and other “volatiles”, leaving behind “veins” of solid quartz. Those gold particles were now within hard, solid quartz. When placer mining (think of a fellow with a shallow pan or bucket, panning for gold) was initially replaced by underground mining, the latter form of mining was merely a bunch of pits dug into the earth. Actually, such an open pit is a quarry, not a mine. Besides making the area nightmarishly ugly, it was also extremely hard work, and the rewards were meager.

Eventually, the transition to truly underground mining took place. Such mining greatly increased the complexities of getting the ore out of the ground. Equipment, materials, experienced mining engineers and miners, and – most importantly – lots and lots of money, were all needed. And all had to be in place before the first ounce of ore was mined.

So…, what would an underground mine at Gold Hill have looked like, and what would its parts be called? This is a schematic drawing of the Randolph ore vein and the mine that was developed to extract that ore. It is from the Laney book of 1910, and was reproduced for us by the North Carolina Geological Survey.

The Randolph Mine
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Cross section of the Randolph Mine, which was built to exploit a major vein of gold-bearing ore.   Hit the Back arrow to return to the EarthCache listing.

Shaft.  A primary vertical or non-vertical opening through mine strata used for ventilation or drainage and/or for hoisting of personnel or materials; connects the surface with underground workings.² Everything that enters (miners, supplies, equipment) or leaves (miners, ore, country rock, water) a mine does so thru the shaft. At large, sophisticated mines, there may have been more than one shaft, with one for, say, miners and water pipes, and another for rock and ore.

Level. At (usually) pre-determined intervals, a horizontal tunnel will depart from the shaft. It is hoped that such a straight line tunnel will intersect a vein of ore-bearing material.²

Drift.  A horizontal passage underground. A drift follows the vein, as distinguished from a crosscut that intersects it, or a level or gallery, which may do either.²

Winze.  (A) secondary or tertiary vertical or near-vertical opening sunk from a point inside a mine for the purpose of connecting with a lower level or of exploring the ground for a limited depth below a level.  If miners were exploiting a vein (using a drift), and the vein went downward, they would begin a winze, in order to follow the vein.²

Whim. A vertical horse-powered drum used as a hoist in a mine.³  These were replaced by more sophisticated headframe gearing and winding arrangements when steam-powered lifts were introduced.

Headframe.  The above-ground whim or sophisticated lift and emptying hardware and structure over the shaft.³ As mining became more productive and volumes of ore and rock increased dramatically, the headframe, or head house, became a large, imposing structure, usually dominating the surrounding area.

Stope. An excavation in the form of steps made by the mining of ore from steeply inclined or vertical veins.³  This is an old term, and is not used today.  An area of worked over ore would be referred to as “stoped” on mine diagrams.  Imagine a cavernous area underground where the ore has been completely extracted and sent to the surface for crushing.

Mining Difficulties

It is well to remember the difficulties encountered by the mining companies as they attempted to get the ore mined and out of the ground.

Water was a constant problem, as ground water continuously seeped into the mine shaft and lower levels. Piping systems, driven by state-of-the-art steam powered pumps, ran 24x7 in order to keep the mines relatively dry and safe.

Shafts, drifts, stopes, etc., were all structurally different, and went thru varying types of rock and ore. Miners and engineers had to know how each structure needed to be stabilized and made safe. Here is a beautiful illustration from Laney that shows how technically and mechanically complicated the timber supports (known correctly as cribbing) had to be:

Extensive cribbing in the Randolph Mine
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Obviously, a lot of knowledge and hard work had to take place for this degree of structure. Hit the Back arrow to return to the EarthCache listing.

The biggest challenge facing the engineers and miners was the sad fact that the gold at Gold Hill was not highly concentrated, and they had to try and go after those ore-bearing bodies with the highest concentration of gold.

Notes:

1. There is no attempt herein to detail the geological processes behind the emplaced gold and the quartz veins, as the purpose of this EarthCache is to explain the structural parts of a typical, underground, historical gold mine.

2. Definitions thanks to http://www.coalEducation.org

3. Definitions thanks to http://www.thefreedictionary.com

Logging Questions:

     Send me an e-mail – not part of your log – responding to the following:

1. Make the subject of the e-mail “GC1XQRB Gold Hill: Anatomy of a Gold Mine”

2. How many people were in your party?

3.  At Gold Hill, very hot, silica-rich fluid was emplaced deep underground. This fluid carried elemental silver, copper, gold and atoms of other elements, and it filled cracks and seams within the country rock of the region.

Stand on the top of the stairway leading down into the Miller Mine shaft. As you start down the stairs, look at the first three rocks on your right (the ones cemented in place along the top of the wall of the stairwell). These are country rock from the mine, and although it’s hard to believe, all three of these are the same basic rock type:  Compacted and consolidated ocean floor sediments referred to as the Floyd Church Mudstone.  Obviously, these three specimens must have been subjected to different environments.

 Describe some of the differences between the three, comparing:

    i. color

    ii. apparent hardness (but please don’t hit the rocks or try to break them)

    iii. foliation (Look for thin, horizontal layering – a sign of metamorphism)

    iv. alteration (Hot fluids, which may contain gold and other minerals and atoms, alter the country rock with which they come in contact. This type of alteration actually changes the composition and alignment of the minerals, often making a completely new type of rock.)

Bibliography:

Bradley, P. Senior Geologist, North Carolina Geological Survey. Personal correspondence, 2009.

Hopkins, V. Vice President of the Historic Gold Hill and Mines Foundation, Inc., and Chair, History Committee of the Foundation. Personal correspondence, 2009.

Knapp, R. F., and Glass, B. D. Gold Mining in North Carolina. Office of Archives and History, North Carolina Department of Cultural Resources, 1999.

Laney, F. B. The Gold Hill Mining District of North Carolina. Bulletin 21, North Carolina Geological and Economical Survey. 1910.

Stewart, K. G., and Roberson, M-R. Exploring the Geology of the Carolinas. University of North Carolina Press, 2007.

          
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