This image was taken from an article, Impacts of Resource Development on Native American Lands by Erin Klauk, at //serc.carleton.edu/research_education/nativelands/ ftbelknap/explorationanddevelopment.html.

Mining Gold by Andy Glass http://www.emporia.edu/earthsci/amber/go340/students/glass

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Gold mining involves large amounts of land and many different areas to mine and process, as well as dump waste. The picture above is of the Zortman-Landusky Mine and shows how a mine might look with leaching pads and waste dumps. The reporting scale below is of the current price of gold taken from Kitco.com. Higher gold prices result in increased mining prospects, and mining companies must weigh hazards associated with mining against potential to increase their respective revenues. Read on for details on mining gold and click on these images or any of the pictures on this webpage for additional relevant information.

Introduction

Contents

Processes for Gold Extraction

Cyanide Leaching
The most common method of extracting gold is to first use explosives to allow removal from the ground, then to use a process known as cyanide leaching (also known as the cyanide process) to extract it from the ore. In cyanide leaching, the extracted material is crushed into grains the size of sand and mixed with a cyanide solution (Ven). The cyanide dissolves the gold from the ore and this solution is collected so the gold can be precipitated out of the ore. The leaching takes place on a leach pad, which can be seen in the picture at the top of the page. For a more detailed chemical explanation of this process, see this www.encyclopedia.com/html/c/cyanidep.asp.

Amalgamation
A second method is the amalgamation process, which uses mercury. This is an older process that is not practical for use with low gold yielding ore, although it may be even more effective than cyanide. Mercury is the oldest chemical used in mining; the amalgamation process was used in ancient Rome and during the California gold rush (Ven). In amalgamation, mud and crushed gravel are mixed with liquid mercury; the gold particles will bind to the mercury (Ven). This mixture (amalgam) of gold and mercury is heated until the mercury evaporates, leaving pure gold. More information on this process can be found at www.encyclopedia.com/html/a/amalgama.asp.

Heap (Dump) Leaching
Where gold occurs in a form that does not require much grinding to free it from other material, a process known as heap or dump leaching can be applied. This is done on crushed ore (dump leaching does not use ground ore, otherwise it is identical) and is generally most suitable for permeable ore types. For less permeable ore types, processes known as agglomeration can be used (www.e-goldprospecting.com/html/gold_leaching.html, Gold Leaching). In leaching, the ore is ground into small chunks, then piled on a clay or plastic lined surface known as the leach pad. It is then irrigated with a leach solution to dissolve the gold, drip irrigation or sprinklers are used to minimize evaporation. After several weeks, the solution flows through the heap, leaches out the gold, which is collected. The solution is returned to the heap to be reused (en.wikipedia.org/wiki/Heap_leaching, Heap Leaching). A diagram of this process is shown below. For more information on heap leaching click on the diagram or go to the homepage of PAMP, a Swiss gold company at www.pamp.com, to learn more about metal refining.


This image was taken from
www.pamp.com/gold_c/Info_site/in_mine/
images/in_mine_us_ct_heapleaching.jpg Vat Leaching
This type of leaching is little more than a flooded dump leach. The gold-bearing ore is placed into an impermeable enclosure and covered in solution. This is primarily for materials that do not respond well to heap leaching but do require grinding to remove the gold. The economics of vat leaching compared to heap systems make this a scarcely used process (Gold Leaching).

Precipitating the Solution

One way of precipitating the gold out of the solution is to add a different metal, which caused the gold to leach out of the solution (Ven). The precipitate is then collected and impurities are removed. Alternatively, a metal cathode could be added. This can be used to apply an electrical current, causing the positively charged gold to precipitate onto the negatively charged cathode. The gold is then melted off the cathode and impurities are removed. The molten gold is then poured into a mold and cooled (Ven ).

Hazards

Discussion

Conclusions

Gold Crusher. Image taken from
http://www.ccvgoldmining.com/Operations/Crushing/crushing.html

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References and Resources

Daniel, Travis. 1999. Everything You Ever Wanted to Know About Gold. URL [http://www.emporia.edu/earthsci/amber/go336/daniel/goldpag2.html]. Date accessed [April 2006].

Encyclopedia.com. 2006. Amalgamation process. The Columbia Encyclopedia, Sixth Edition. URL: http://www.encyclopedia.com/html/a/amalgama.asp.

Encyclopedia.com. 2006. Cyanide process. The Columbia Encyclopedia, Sixth Edition. URL: http://www.encyclopedia.com/html/c/cyanidep.asp.

Gold. URL [http://www.encyclopedia.com/html/g/gold.asp]. Date accessed [April 2006].

Gold Leaching. URL [http://www.e-goldprospecting.com/html/gold_leaching.html]. Date accessed [April 2006].

Heap Leaching. Wikipedia. URL [http://en.wikipedia.org/wiki/Heap_leaching]. Date accessed [April 2006].

PAMP 2006. Heap leaching image. URL: http://www.pamp.com/gold_c/Info_site/in_glos/in_glos_heapleaching.html

Ven, Chris Van de Unknown. Gold Extraction Using Cyanide Leaching. URL [http://tc.engr.wisc.edu/UER/uer97/author4/index.html]. Date accessed [April 2006].

Homestake Gold Mine, South Dakota. Image taken from
http://www.blackhillsattractions.com/pages/attractions/homestakegold.html

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Date created 27 April, 2006; last update 5 May, 2006. © 2006 Andrew Glass. All rights reserved.