Gold is one of the most sought after metals on earth because of its high value.The high value of gold means that a deposit does not need to be very large in order to be economically mined. This is great news for miners but can complicate matters for prospectors due to the difficulty of identifying deposits. Gold is often found in ores composed of rock with very small particles.
Ore with grades of gold as low as 0.5 parts per million may be worth mining but a grade of at least 30 ppm is necessary for it to be visible to the naked eye. This means that the gold in most mines is invisible. Because viewing individual grains of gold can be a challenge, prospecting by finding grains of gold through conventional sampling can be nearly impossible.
Finding Gold Deposits
In order to find deposits, prospectors use geophysical data to narrow down their region of interest meaning that it is very easy to miss worthwhile gold deposits. Working on a small scale is also problematic because it is so easy to miss deposits. Luckily, new techniques have been developed to enhance the chances of prospectors being able to identify and find new gold deposits.
Gold extraction requires a combination of comminution, mineral processing, hydrometallurgical and pyrometallurgical processes to be performed on the ore. Gold grain morphology takes advantage of the malleable nature of gold as well as the fact that the surface shape of gold changes as it travels further from the source in order to determine the location of its source.
Types of Gold Samples
Gold samples are classified into three categories:
This classification refers to gold grains that have maintained their primary shape and surface textures and identifies grains which have traveled less than 500 meters from the gold source.
Grains with evidence of mild reshaping are referred to as modified and have traveled 1-1000 meters from the source.
Pieces which have traveled more than 1000 meters from the source become worn down and lose their original shape.
In any given sample of 30-50 kg, all of the gold grains would be sorted out and assessed according to these classifications. If the sample area turns up a significant amount of gold grains, further exploration will be completed. A 50 kg sample with a gold concentration of 0.5 ppm would only hold 5 grains of gold. Using normal geochemical analysis, only about 50 grams of the sample would go to the lab and it is unlikely that the limit gold grains would be included or discovered.
This is why gold morphology is such an obvious breakthrough: it allows prospectors to find all gold grains in their samples and track those grains back to their source.
“When you have high counts of pristine and modified gold grains, you know that you are close to a bedrock source of gold. High amounts of pristine and modified gold grains in a sample almost always lead to a bedrock source of gold.”
President of Diamonds North
The current high value of gold makes gold grain morphology an excellent gold exploration method to find economically feasible gold deposits effectively.
Robert D Lagrone is a passionate mining engineer from Toronto, Canada. He loves sharing his knowledge with others. Outside work, he loves to travel and read books. He writes guest blogs for several blogging sites. Follow him at [email protected]