Heavy minerals and substances which do not bond with silicon or oxygen (such as gold, platinum, and radioactive sources) mostly sunk to earth's core long ago. Iron exists on the earth bonded to oxygen, silicon and sulfur, but never in its free form. Much of the good stuff we do get actually comes from earth's asteroid craters. About half the world's nickel, for example, comes from a mining area in Canada called the Sudbury Astrobleme where an asteroid hit the earth long ago. The Sudbury Astrobleme also produces platinum group metals which are separated from its nickel mass.
With asteroids in space, you get free ore. Good (pure, free) ore requires very little processing.
Free metal concentrations in stony meteorites are about 20%. M-type asteroids are over 90% metal. C-type asteroids have 5% to 20% water.
"... a two-kilometer-wide asteroid holds more metal than all the ore mined on Earth since the beginning of civilization."
usra.edu (pdf)
Mining a near asteroid is the cheapest and quickest way to go and we can melt, mold, cast, assemble, and construct just about anything.
The Minor Planet Center is a good source of information on minor planets (asteroids).
We might include harpoons, spikes, stakes, anchors, and cables for staying attached to and moving around the asteroid, containers and bags to hold material for uploading to processing equipment, aluminum foil to make oven mirrors, pipes for carrying volatiles, tanks for storing volatiles (we can make there), and solar cell panels for electrical needs.
Different methods can be used for mining the asteroid, including scraping the surface and tunnelling.
At the input chute, the ore is ground up and sieved into different sizes. Mechanical grinders, using a rocking jaw arrangement for coarse crushing and a series of rollers for fine crushing, are arranged in a slowly rotating housing to provide centrigufal movement of the material. Vibrating screens are used to sift the grains for directing them to the proper sized grinders. The streams of material are put thru magnetic fields to separate the nickel-iron metal granules from the silicate grains. Alternatively, the streams can be dropped onto magnetic drums, whereby the silicates and weakly magnetic material deflect off the drum whereas the magnetic granules and pebbles stick to the magnetic drum until the scrape off point. Repeated cycling thru the magnetic field gives highly pure bags of free nickel iron metal. The nonmagnetic material is channelled into a solar oven where the volatiles are cooked out. The oven mirrors can be huge and made of aluminum foil. The volatiles' gaseous form is piped to tanks located in a cold shadow of space. The tanks are put in series so that the furthest one away is coldest. This way, water condenses more in the first one, carbon dioxide and other vapors in the tanks downstream. Fuel can be produced by separating oxygen and hydrogen gases from the mix, or by electrolysis of water. Hydrogen could be chemically bonded with carbon to produce methane fuel. Thin, relatively lightweight spherical tanks can be used to store frozen volatiles. These tanks can be made with some of the nickel iron metal, by use of a solar oven for melting the metal. Ultimately, tanks for storing frozen volatiles for sending to Earth orbit can be manufactured by some of the nickel iron metal, by use of a solar oven for melting the nickel iron metal. A cast can be made from sand or glass-ceramic material from melted leftover ore. Some silicate material from the asteroid will also be used for making glass, fiberglass, ceramics, astercrete, dirt to grow things in, and radiation shielding for habitats and sensitive silicon electronics. Undesired material can be put in a big wastebag container, or sandbags, or cast into bricks by a solar oven, used for shielding the habitat from space radiation, creating more cold shadows, or just removed from the mining operation's space.
Space Radiation Shielding
Extract Oxygen From Water
Saturn's Massive Ring