As others have stated in their answers, there is no evidence, so far, that there is gold on Mars. We can't say there is or there isn't gold on Mars, we just haven't found any yet. We also don't know if gold were to exist, if it occurs in concentrated deposits, amenable to mining, or whether it's disseminated.
Gold hasn't been the focus of the exploration of Mars because it's not important enough, ... yet. Geological resources for construction materials and energy are currently more important.
If gold were discovered and mined on Mars, one question that needs to be asked is, "what do you do with it?". Do you send to Earth to be stored in a secure vault? Why?
Formation of Gold Deposits ... On Earth
There are three ways gold deposits are formed on Earth.
- Circulating Ground Waters.
- Gold bearing solutions expelled from magma as it cools,
precipitating minerals as they move into surrounding cooler rocks.
- High temperatures and high pressures in mountain building regions
resulting in chemical reactions that change rocks to new mineral
All these processes require ground water as a transporting medium to concentrate gold and minerals.
Despite the suggestion that Mars once had oceans. We know nothing of ancient ground waters on Mars.
Mining on Mars
Before successful mining can occur, mineral exploration must be undertaken to determine the size and richness of any gold deposit. Currently on Earth this requires the use of exploration drilling rigs to outline the extent of any deposit. Drilling samples will need to be taken and assayed for gold content. Getting the drilling and assaying equipment to Mars will be expensive. All the equipment might be needed to be sent to Mars in parts and assembled there.
If we assume gold is present on Mars and that the deposits are large enough & rich enough (contain a lot of gold) how do they get mined? The answer depends on the nature of the deposit:
- Nuggets on or just below the surface.
- Locked within rocks, near the surface and potentially amenable to
open pit (surface mining) techniques.
- Locked within rocks, but deep below the surface of the planet and
only mineable by underground methods.
Nuggets could be scooped up from the surface but open pit or underground mines will require heavy mining equipment. How does the equipment get to Mars? Transported from Earth in parts and assembled on Mars, which is very expensive; or does it get made on Mars from locally sourced minerals and locally constructed factories. This will be expensive and take a lot of time to achieve.
With exploration and mining there will be the issue of energy needed to power all the equipment. Unless large areas of the planet are sacrificed to photovoltaic arrays nuclear electric generators will be needed.
I speculate that batteries will not sufficient to power the heavy equipment for prolonged periods. This then leaves the use of power cables from a nuclear generator to power the equipment.
All of this is getting complex and expensive.
Mining produces dust, which on Mars will be a safety and operational problem because of impeded visibility and the affect on the equipment, particularly bearings and any rotating equipment.
On Earth, water is used to suppress dust. This then begs the question, "will there be sufficient water to suppress dust and can it be sacrificed for such a purpose?".
If the gold is locked within rock, will drill and blast techniques be used to break up the rock, or will grinding methods be used (adapting techniques used by tunnel boring machines)?
If drill and blast methods are used will explosives be transported from Earth or will they be made on Mars? More complexity and expense.
One method that could be used, if conditions were suitable is in-situ leaching. This requires the deposit to be drilled in a regular pattern and a dissolving solution to be pumped down some holes to dissolve the gold and the solution to then be pumped up other holes and the enriched liquor to be treated to remove the gold.
One problem with this technique is there may be minerals other than gold that could be preferentially leached leaving the gold in place underground. If marcasite (a form of iron pyrite) is present it will be leached in preference to any gold that may be present.
Treatment of Gold Bearing Ore
Now, assuming gold on Mars can easily be delineated during exploration and the ore mined, how is the gold then extracted from the fragmented rock?
The two main methods would be via a processing plant such as a carbon in pulp (CIP) or carbon in leach (CIL). Both require the use of cyanide to dissolve the gold and carbon to absorb the dissolved gold.
A cheaper method, that takes longer to recover the gold is heap leaching. This requires the fragmented gold bearing ore to be deposited into long mounds and a gold dissolving liquor (cyanide based) to be continuously dripped or sprinkled on the heap. As the dissolving liquor removes gold from the heap, it is collected from the pond at the bottom of the heap and treated further.
Problems with using this method on Mars are the cold temperatures and the thinness of the atmosphere and its low pressure and the potential for any water based solution/liquor to simply evaporate. This might be mitigated by enclosing the heaps in warmed pressurized containment structures.
All this is expensive and would require trained personnel.
Irrespective of whether a CIP plant of a heap leach pad is used the gold would then need to be electroplated and turned into bars for transport. This would required the use of electricity during the electroplating process and a source of heat would be needed to melt the gold and pour it into bars.
All this is costly enough on Earth, on Mars it will be more expensive because everything will need to be transported there simply to get the gold off the planet.