Mars may contain ores that would be very useful to potential colonists. The abundance of volcanic features together with widespread cratering are strong evidence for a variety of ores. While nothing may be found on Mars that would justify the high cost of transport to Earth, the more ores that future colonists can obtain from Mars, the easier it would be to build colonies there.
How deposits are made Ore deposits are produced with the help of large amounts of heat. On Mars, heat can come from molten rock moving under the ground and from crater impacts. Liquid rock under the ground is called magma. When magma sits in underground chambers, slowly cooling over thousands of years, heavier elements sink. These elements, including copper, chromium, iron, and nickel become concentrated at the bottom. When magma is hot, many elements are free to move. As cooling proceeds, the elements bind with each other to form chemical compounds or minerals. Because some elements do not bond easily to form minerals, they exist freely after nearly all the other elements have bonded into compounds or minerals. The remaining elements are called incompatible elements. Some of them are quite useful to humans. Some examples include niobium, a metal used in producing superconductors and specialty steels, lanthanum and neodymium, and europium for television monitors and energy-efficient LED light bulbs. After the mass of magma has cooled and has mostly frozen or crystallized into a solid, a small amount of liquid rock remains. This liquid bears important substances such as lead, silver, tin, bismuth, and antimony. Sometimes minerals in the magma chamber are so hot that they occupy a gaseous state. Others are mixed with water and sulfur in aqueous solutions. The gases and mineral-rich solutions eventually work their way into cracks and become useful mineral veins. Ore minerals, including the incompatible elements, remain dissolved in the hot solution, then crystallize out when the solution cools. Deposits created by means of these hot solutions are called hydrothermal deposits. Some of Earth's most significant deposits of gold, silver, lead, mercury, zinc, and tungsten started out this way. Nearly all the mines in the northern Black Hills of South Dakota came to be because of hot water deposits of minerals. Cracks often form when a mass of magma cools because magma contracts and hardens when it cools. Cracks occur both in the frozen magma mass and in the surrounding rocks, so ore is deposited in any kind of the rock that happens to be nearby, but the ore minerals first had to be concentrated by way of a molten mass of magma. Research carried out at Louisiana State University found different types of volcanic materials around volcanoes in Elysium Mons. This showed that Mars can have a magma evolution. This leads to the possibility of finding useful minerals for a future human population on Mars."
Molten rock on Mars The presence of many huge volcanoes on Mars shows that large areas were very hot in the past. Olympus Mons is the largest volcano in the Solar System; Ceraunius Tholus, one of its smaller volcanoes, nears the height of Earth's Mount Everest.
There is strong evidence for much more widespread sources of heat in the form of dikes, which indicate that magma traveled under the ground. Dikes take the shape of walls and cut across rock layers. In some cases, dikes on Mars have become exposed by erosion.
Large areas of Mars contain troughs, called fossa, which are classified as grabens by geologists. They stretch thousands of miles out from volcanoes. It is believed that dikes helped with the formation of grabens. Many, maybe most, of the grabens had dikes under them. One would expect dikes and other igneous intrusions on Mars because geologists believe that the amount of liquid rock that moved under the ground is more than what we see on the top in the form of volcanoes and lava flows. On Earth, vast volcanic landscapes are called large igneous provinces (LIPs); such places are sources of nickel, copper, titanium, iron, platinum, palladium, and chromium. Mars's Tharsis region, which contains a group of giant volcanoes, is considered to be a LIP.
Heat from impacts
Besides heat generated by molten rock, Mars has had much heat produced when asteroids impacted its surface making giant craters. The area around a large impact may take hundreds of thousands of years to cool. During that time, ice in the ground will melt, heat, dissolve minerals, then deposit them in cracks or faults that were produced with the impact. Studies on the earth have documented that cracks are produced and that secondary minerals veins are filled in the cracks. Images from satellites orbiting Mars have detected cracks near impact craters. Areas of aqueous and low-grade thermal alteration have been found by the Opportunity Rover on the rim of Endeavour crater. These are found near joints and fractures that allowed deep fluid circulation which caused chemical and thermal alteration of the rocks. So, the area around martian craters may contain a variety of minerals that were produced as an indirect result of an impact.
Heat from impacts results from several processes. Immediately after an impact, there is a rebound off the floor which causes hotter rocks to be uplifted to the surface. However, most of the heat comes from the kinetic energy that is produced during the impact. This enormous heat creates several useful products that may start forming early and then continue for some time. These are called "epigenetic deposits." Circulation of hot mineral-rich fluids in the fractures from the impact cause hydrothermalism. Important examples are the Cu-Ni sulfides at the Sudbury Igneous Complex in Canada. For a number of years, these ores from the Sudbury area had a value of $2 billion each year. The Sudbury formation has provided us with ores of zinc, copper, gold, and lead. Strong evidence for hydrothermalism was reported by a team of researchers studying Auki Crater. This crater contains ridges that may have been produced after fractures formed with an impact. Using instruments on the Mars Reconnaissance Orbiter they found the minerals Smectite, Silica, Zeolite, Serpentine, Carbonate, and Chlorite that are common in impact-induced hydrothermal systems on Earth. There is other evidence of post-impact hydrothermal systems on Mars from other scientists who studied other Martian craters.
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