Mining - Chilean Drag-Mill and Rockers
The machinery used for separating gold consisted of the Chilean mill for crushing and grinding after having been broken by hammers, the Tyrolese bowls, the drag-mill, and the Burke rockers.
The Chilean mill was used from ancient times and when it worked it worked, put it relied on precision, which was not always provided. It needed a consistent source of power and adequate water. The millstones could only be cut and shaped by an experienced mason. The mill consisted of two vertical millstones in a watertight base of bed stone. They were attached by a shaft in such a way that they had two motions. They rolled on their edges while rotating clockwise on the shaft. As the mill crushed the rock, water was introduced that would wash away the ore and allow the heavier gold to sink to the bottom. At that point the amalgamation process was begun. Quicksilver lined the base of the mill and the gold amalgamated with the quicksilver, which was then baked in a retort and the quicksilver separated out again. After that the gold was formed into bars and taken to the mint. The work for a Chilean mill was 70 bushels of ore a day and the mills ran for 24 hours.
The drag mill was an inexpensive mill, but more efficient at removing gold from ore. The main drawback of the drag mill was the time it took to grind the ore to powder. The ore was crushed, decomposed in “stirrers,” passed into the Tyrolese bowls, which after a sudden half revolution allowed the sand to run off with the water and leave the gold in the bottom. The resultant mud then went on to the rocker cradles for the amalgamation process.
No. 2102 – published by Theodore Buerbaum, Salisbury, N.C. – Germany.
Nitze, Henry B. C. and H.A.J. Wilkens Gold Mining in North Carolina: and Adjacent South Appalachian Regions Raleigh, N.C.: Guy V. Barnes, Public Printer, 1897 (North Carolina Geological Survey Bulletin #10)
Glass, Brent D. King Midas and Old Rip: the Gold Hill Mining District of North Carolina UNC-Chapel Hill Dissertation, 1980