Is it practical to extract elements from the salt remnants of Martian oceans and lakes?

Question

Modern human civilization needs many elements to function. Our mining efforts are based on extensive logistics and the ability to transport ores from excavation sites to processing facilities over enormous distances.

For Mars, it is not practical at almost any stage of colonization, as it is impossible to settle anywhere without habitat construction and transport infrastructure, both of which require resources. There are no roads, no water transport, and no airborne transport.

Earth could supply at first, but it is so costly that it might not be worth it, as the tyranny of the rocket equation persists.

However, oceans on Earth have a lot of elements dissolved in them and, provided hypothesis about martian oceans holds, won't the salt remnants of martian oceans and lakes be the ultimate ore to mine?

P.S. I would greatly appreciate any papers and articles about this as I haven't found much. The only remotely relevant topic is brine mining for lithium and other elements here on Earth.

Answer 1

Answer: unlikely

For an ore deposit to be economically viable, the element(s) of interest need to be high enough concentration. This usually requires some geologic process to concentrate minerals from their low background concentration. The minerals in ocean water are mostly in low, uniform concentration so deposits formed from evaporated Mars oceans would be expected to reflect this.

However, Mars has signs of past tectonic activity. https://en.wikipedia.org/wiki/Tectonics_of_Mars The processes which have produced ore bodies on earth may have been operating on Mars in the past as well

Ore deposits are rock volumes containing selected elements in sufficient concentration and quantity that they can be extracted economically. Except for Fe and Al, all technically important metals and other elements are scarce, in total constituting less than ~1% of the Earth's crust. Depending on the element and its mineralogy, a 10- to 10 000-fold enrichment is required for economic extraction today. Such extreme element concentration involves a combination of processes operating in concert, which explains why ore deposits have similar characteristics but are relatively rare.

Selective element enrichment generally includes steps of

(1)dissolution of elements from common crustal or mantle rocks,

(2)physical transport by a mobile phase such as a melt or an aqueous fluid, and

(3) chemical precipitation in distinct minerals forming the ore deposit.

Element transport by hydrothermal fluid (a water-rich agent that can flow through permeable and commonly fractured rocks) is particularly efficient and chemically selective.

https://www.sciencedirect.com/topics/earth-and-planetary-sciences/ore-deposit

Answer 2

@Woody is correct in stating that concentration of elements in a deposit is critical to the economical viability of extracting any element.

Oceans on Earth contain 20 million tons of gold, but according to webpage you reference, the concentration of gold in the oceans is 4 × 10^-6 mg/L. Another way of expressing this is the concentration is 4 × 10^-9 g/L. Given that 1 gram of water has a volume of about 1 cubic centimeter, this concentration is about 4 parts per billion (ppb). To obtain 4 grams of gold one needs to process 1 billion grams (1000 t) of ocean. It's why it is uneconomic to extract gold from the oceans. Viable large scale open cut mines mine gold with a concentrations measuring in the parts per million. Underground mines need higher concentrations to be viable. The concentration of other metals in the oceans is similarly small.

Now, lets assume all of Earth's ocean evaporate and all the elements they contain are deposited on the floor of the former oceans. Keeping it simple, all that gold would be deposited on the floors of the Pacific, Indian, Atlantic, Southern and Arctic oceans. That's a huge area to dig up to get 20 Mt of gold.

Mining (digging) is only one part of the process, The majority of elements occur as minerals and once mined they must be processed in metallurgical plants to obtain the minerals and metals required.

This leads to the problem of grain sizes of the minerals mined and processed. Minerals formed from evaporation of water are generally small. If grinding is required, small grain sizes are very problematic, which leads to higher costs for processing and extraction.

Mining and processing are energy intensive activities. Sources of energy on Mars, in the quantities required, will be another challenge and cost.

Whatever the situation on Earth, things on Mars won't be easier.