Hi Chris! My e-mail doesn't receive, and the boffins who installed it haven't the slightest idea why. I am not gifted with a huge amount of patience for cyber-ethereal stuff, so until they can solve the problem without deleting everything and installing it anew, it can stay broken.
As regards your questions - yes and no. In RAB drilling (rotary air blast), lighter particles may get to the surface faster than heavier particles, and you can see them pass out the top of the receiving cyclone into the air (as dust) while the heavier stuff falls out the bottom into a bag. If there is fine free gold in the hole, out it goes with the dust. However, the air pressure is very high, so everything comes out at once - the side benefit, and a very important one in reverse circulation (water) drilling is that the head doesn't clog up. Since everything is carried in suspension in an RC hole, nothing is lost, unless fine gold is carried in the water through the mesh size of the sieve. You would know whether this was likely by the type of deposit you are drilling off.
Samples are accurate for depth and lithology. Companies choose RC or RAB drilling over core drilling because it is much cheaper and gives a look at stratigraphy at low cost. However, your 'sample' is a little square of very clean gravel you map through a handlens or binocular microscope. If you need more information you have to find the bag with the sample, frequently out of thousands (hopefully you have an assistant). The Ujina discovery, for example, was two sequential squares of very clean gravel with (even under high power) a lot of little black specks in a white/clear matrix. Core drilling proved it to be 5% chalcocite in quartz-carbonate altered andesite.
Companies that drill off prospects with RC or RAB rigs with no plans to follow up with diamond holes always have a hard time convincing me they know what they are doing.
Hope this helps.
Ujina |
