Re: Gold Mill Overview (drwgs)*

Hi, Steve -

Several years ago the geologist father of one of my closest friends gave me an ancient book that he had no real use for, as he worked for Union Oil — not the Golden Cycle Mine. 'The Metallurgy of Gold' was written by M. Eissler in 1888;  I have a very tattered copy of the 5th Edition, published in 1900 to cover all of the 'latest developments' in the mining and refining of gold. Most of its more than 600 pages of very small print focus on the chemistry needed to extract gold from difficult ores, but there are also over 300 diagrams and 45 photographic plates, most of which illustrate the equipment used in the mills where this chemistry was employed, including several photos of mining complexes similar to the photo which Scott posted above.

It would be impossible to even outline the contents of the book here – just the table of contents is eight pages long – but here's my stab at a very simplistic overview of what goes on in the main building:

In general, mills were built on hillsides so that gravity would assist in moving the ore through the successive steps used to extract the gold. The first diagram below shows the cross-section of a typical mill of about 1895. Starting at the top, the ore is dumped from a push cart or mine car into a bin, where it is then fed into a crusher which reduces the rocks to pebbles about the size of walnuts. Once small enough to pass through a sizing grid, these pebbles fall into a second bin from which they are gradually fed into the batteries of stamp mills. The output of the stamps, a fine powder that was kept moist to keep it from blowing away, was then fed - and re-fed - through a series of various types of concentrators until most of worthless rock had been washed away; the resultant concentrate was then shipped to smelters for final processing.
(See [ngdiscussion.net] etc. posted earlier this week by Larry and others.)


A large mill might have a half-dozen receiving bins and crushers, and 150 or more stamps; the round-the-clock pounding of the stamps made sleeping difficult in a mining camp - it's no wonder that 90-proof 'sleeping potion' was so popular.


The Vanner concentrator was just one brand of many similar machines - basically just mechanized versions of large gold pans, with riffles, where water flowing over the constantly-shaking tables helped float the lighter rock and sand away from the heavier gold (and silver, zinc, etc.). The final steps might have mercury added to amalgamate the finest particles of gold; this was collected on a regular basis and the mercury boiled off to recover the gold. In later years, cyanide solutions were also used to help separate the gold from other minerals.


I'm sure there are others who post here who will catch my errors, and fill in some of the gaps in the above.

- Russ

* 'drwgs' = 'drawings', not 'Denver Rio Western Grande System'.    



Edited 3 time(s). Last edit at 02/27/2010 11:04AM by Russo Loco.