Lefty, there is a small diamond exploration company that is drilling in certain areas where indicator minerals have been found in creeks and streams. From what I have heard they have identified some areas of interest. But the areas are most likely in strategic farmland reserves or have tight envirnomental controls so in my opinion the prospects of mining are low. There is also a rumour of a kimberlite pipe up in the mountains somewhere that is linked with the Bones Knob volcanic system that has yielded some small diamonds. I assume it is either of low grade importance or is in National Park lands which is why there hasn't been any further full scale exploitation.
Most of the Atherton Tablelands is, in my opinion, rich in gems. My theory is that vast deposits where covered in very thick layers of basalt lava. This lava has broken down to the high quality red soils the region is famous for. In some places farmers have sunk bores up to 100 ft before hitting bed rock. Some places there is a still thick, solid basalt lava flows that haven't broken down yet. The volcanic activity finished up only 15,000 years ago so geologically speaking the region isn't old enough for erosion to strip the top soils, erode the underlying rock and concentrate the gems.
Many of the outer parts of the region i.e. Herberton, Innot hot springs, Mt Garnet etc don't have the thick lava flows. This means erosion has had time to effect the host rocks directly for longer. That's why (in a general sense) there has been such significant concentrations of tin, topaz and limited pockets of sapphires discovered in those areas. I'm sure there are sapphire pipes containing million of carats buried under the lava flows. But, without being able to see whats under the soils we will never know. Random drilling is like shooting the ocean with a rifle in the hope of hitting a fish. Pointless.
There is big deposits of corundum, garnets, tourmaline, topaz, peridot, aquamarine etc to be had West and North of the Tablelands but the country out that way is vast and hard and some of the places are just to bloody dangerous to go without explicit knowledge of the area and the people that inhabit it. There is a lot of shady shite that goes on up here. This is probably why so little exploration is done by the general fossicking community.
