Copper is a metal, periodic table Cu, that is ductile and an excellent conductor of electricity and heat. Until more of the Martian surface has been prospected, it is impossible to know how much settlements will be able to rely on this metal.
Copper may be found in useful concentrations near thermal vents that could have existed in the early Martian seas. Another possible concentration mechanism would be gravitational separation in molten lava from volcanoes or after asteroid impact.
Aluminium is much more common than copper, by many orders of magnitude. Although it requires more energy to produce it can serve as a good replacement for copper.
Copper on Earth is usually found in ore with concentrations of about 1% (10 000ppm), while volcanic rocks can have concentration between 5 and 25% for alumina, Bauxite has concertation of more than 50% and clays of about 15-30%. Due to low concentration copper ores usually require on site concentration before shipping.
Copper is found either as sulfides, or as oxydes, that require different concentration processes.
On Earth, copper is extracted at a ratio of about 0,6% compared to Iron (1:150). And 1:3 compared to aluminum.
Electrical Wire and Cables
Due to its excellent conductivity, copper is widely used to transmit electricity. Copper is easily drawn into wire. Copper is used extensively in control systems, to conduct communication in standard wire and coaxial wire. This usage is being partly superseded by wireless communications. Aluminium is a commonly used alternative, in particular for larger conductors.
Power transformers are essential for AC power distribution systems. They are large and heavy and require large amounts of copper, although aluminium might be an acceptable substitute. DC converters can replace transformers but also require some copper.
Copper is used extensively as a piping material for potable water, although it is gradually being replaced by plastics. Stainless steel can be a replacement for copper and on Mars requires less energy to produce than plastics.
Copper is used in jewelry and food preparation utensils.
Copper is an essential trace element in food. A typical human body contains 0,000072 kg. For one million persons the copper required would be 72 kg. For an entire ecosystem serving these one million people the amount required might be about ten tonnes (hypothetical ratio of 100:1). Martian regolith might need to be slightly enriched in copper to serve as soil.