Diamond Exploration Education and Useful Information

Diamond Creation and Kimberlite

 

Diamonds are created 150-300 kilometers below the surface of the earth, in areas of pressure higher than 40 thousand atmospheres, and temperatures of 950–1400 degrees Celsius.  Type 2A diamonds are formed at even greater depths of 400-600km below the surface in subduction zones, and it is thought that this is where large diamonds like the Nipissing Diamond originate.  Diamondiferous kimberlite pipes are brought to surface as a result of carbon dioxide gas accumulating over diamond creation zones, then and pushing its way up through deep cracks and faults in the earth’s crust, ending in a violent eruption. Diamonds and other gemstones are brought from the mantle below, to the surface through this process. Once the magma cools, a kimberlite pipe is formed, which is where the majority of diamonds can be found on earth.

 

Geological Requirements for Kimberlite

 

Broadly speaking, continental cratons are where most diamondiferous kimberlite pipes are found. Regional kimberlite locations are highly correlated with major structural faults, and more locally with cross faults.  They are often discovered at contact points between different types of rocks, and usually appear in close proximity to other kimberlite pipes.  Therefore, almost every new kimberlite discovery has lead to other nearby kimberlite discoveries in each respective region.

 

Glaciation and Kimberlite Pipe Topography

 

On average, roughly every 100,000 years, the earth experiences an ice age, where massive glaciers blanket the land. The most recent glacial period ended roughly 11,000 years ago, and covered the majority of North America.  A glacier is formed as ice accumulates over time, reaching heights of up to 3km.  The immense weight of a glacier crushes everything below, and the pressure creates a thin layer of water on the earth’s surface, allowing for glacial movement.  As glaciers travel, they gouge out softer layers of rock, such as kimberlite, more than the harder layers, such as granite.  Once glaciers melt, they leave depressions in areas where kimberlites have come to surface, often resulting in circular-shaped lakes or swamps above the pipes.  Glaciers also leave striations in any exposed bedrock, which indicate the direction of the most recent glacial movements.

 

Kimberlite Indicator Minerals

 

After glaciers gauge out kimberlite, they then melt and recede, depositing pulverized kimberlite materials down-ice in new locations from their kimberlite origin. Diamonds aren’t the only gems that are discovered in kimberlite pipes.  There are various other minerals such as Chrome Pyrope Garnets, Eclogetic Garnets, Chromites, Mg-Ilmenite, Chrome Diopsides, and Olivine (Forsterite), that when discovered, can be used to estimate the locations of their kimberlite origins.  In areas of glaciation, using glacial striae, explorers can track kimberlite indicator minerals in reverse to the glacial movements, until they no longer find significant numbers of those indicator minerals.  This is the main method of determining if a kimberlite source is in close proximity.

 

Soil Gas Hydrocarbon (SGH) Sampling

 

SGH sampling is a method of detecting buried inorganic material deposits, such as kimberlite, by measuring non-gaseous hydrocarbon compounds that have been synthesized by bacteria feeding on the target.  Microbes decompose and release various specific hydrocarbons, which are diffused through the overburden to the surface.  Discovery of specific ratios can indicate if a surface location is above, or in close proximity to, a kimberlite pipe.  SGH can help detect mineral deposits up to 500m at depth, but in the case of potential kimberlites on RJK’s land claims, overburden is generally only between 2-5m above the bedrock, with a maximum of 20m.  Activation laboratories LTD stated that DeBeers Canada use SGH over any prospective Kimberlite as it reduces their drill program by 50%. Of the companies that have tried SGH, over 90% have observed success in determining their targets.

 

Geophysics of Kimberlite Pipes

 

Geophysics utilize magnetic, EM (electromagnetic) and gravity in to determine relative differences of the physical signatures of the earth.  This is particularly useful in diamond exploration, as each method tends to work well on kimberlite pipes, which often, but not always, have properties that are different relative to the surrounding rock.  Kimberlite pipes can appear as either magnetic highs, or magnetic lows, depending on the position of the earth’s poles at that moment of the kimberlite eruption.  However, some diamondiferous kimberlite pipes have been discovered with little to no geophysical signature.  Interpretation of geophysical data can offer guidance on the size and shape of anomalies, as well as insight on where to position drill holes.

 

Drilling for Kimberlite

 

Once kimberlite targets are identified using the methods listed above, drilling the target is necessary to determine if the target contains kimberlite, and whether there is potential for diamonds.  On rare occasions, if kimberlite outcrop is discovered on the surface, samples can be collected from those areas for analysis. If kimberlite is found, continued drilling is used to determine the diamond grade and dimensions of the pipe.

 

Caustic Fusion and Testing for Large Stones

 

Caustic fusion is a process to separate any diamonds from their kimberlite host rocks.  Kimberlite drill core is loaded into stainless steel vessels with caustic soda set to high temperatures, which dissolves the material around the diamonds. After a set period of time, the solution is drained and screened, liberating the diamonds.  If caustic fusion results are positive, a bulk sample of the kimberlite deposit is taken to determine the diamond grade of the kimberlite pipe, as well as search for the presence of large stones.  Economics thereafter are determined by samples milled in a pilot mill for diamond recovery, and if results are favourable, full production may occur.