Board Thread:Fiction Universe Discussion/@comment-9141454-20150625191138/@comment-1073312-20150626221432

Right lets talk about ores. I think we should create a dedicated article or section on this topic.

Things we should keep in mind is that ore deposits are never pure. The element aluminium has an average crustal abundance of 8% on Earth. With present technology and/or economy, the cut off grade where a deposit of aluminium bearing minerals is 30%. The concentration factor (concentration or ore divided by avg. crustal abundance) is only 3.75, so roughly 4% crustal abundance. Now lets look at gold, it has an abundance of four parts per billion, has a minimal exploitable grade of 0.0001, so has a concentration of 250. That's 4 grams of gold per 1000 tons of rock. The small gold mine produces produces say, 10 million grams of gold. Thinking about that, it makes nanotechnology even less feasible for modern day grading. For an Earth-like planet, you are likely to have a lot of effort and waste heat and mostly worthless waste material. And a lot more effort than is currently used. The way modern economy works, the grading of an ore deposit depends how worthwile it is. Perhaps one day, gold will be so sparse that we will be mining deposits five kilometers deep with an area of ten kilometers. Its possible to work out the area and volume of a mine in comparison to 9.63 million tonnes of processed rock, work out the extraction cost and compare it to nanobots even if they were feasible. Assuming a density 2.5 t m^-3, 9.63000000/2.5*3 equals a volume of 11.556 km. Assuming the area of the largest open mine (I guess 8 square km), that's a depth 512 km, if I'm using the right maths. Planetary strip mining is only a likely possibility for a civilisation stranded on a planet. With asteroids and later cheap transmutation, one might expect that curiously, a civilisation may mine less and less from planets. Perhaps less gold would be mined from the planets by such societies than we currently extract.

But perhaps nanotechnology can be used in smaller scale geonengineering? In nature it typically takes a volume of 0.5 km 3 of water moving through 100 cubic km of rock to deposit 10 tons of gold. Under lots of pressure and temperature, the fluid will transform the rock and precipitate minerals including gold bearing ones. I'm going to put some thinking into this.