Resources II: Iron Mining

Iron is a must have resource for a D&D civilization. I want to explore how iron can be found, and what other elements are found with it. I'm particularly interested in what kinds of things generally appear together. This will help me design a system for generating consistent placement of resources.

Iron has been mined for a long time. I found this article, about a Nasca ore mine, fascinating.

There are five major types of ore containing iron. There are some general trends that can help place them.

• Hematite. This is probably the most common form. It usually occurs in banded iron formations in sedimentary rock. You can also use hematite to produce various ochres, specifically in the colors of yellow, red, purple, sienna, and umber, depending on the concentration of impurities.
• Magnetite. Sometimes found in sands, but largely igneous and metamorphic rocks. It's also a good source of magnesium.
• Siderite. A poor source of iron, so I'll pretend it doesnt exist.
• Limonite. This is found in a class of soils called laterite soils. They are often found on plateaus, and contain large amounts of clay, aluminum (unknown to ancient peoples), and sometimes nickel. It's also useful for yellow ochre. More importantly, gold is often found in limonite deposits. It's generally formed in areas with alternating wet and dry seasons.
• Goethite. Commonly found in bogs, an early source of iron for the Welsh and Norse. The generation of bogs is something I'm still trying to figure out. While most of the other ores must be dug up, goethite can literally be picked up by hand out of the muck. In addition, a bog that's been picked clean generally replenishes every 50 years or so as the iron from deposits continues to coalesce. Yields brown ochre.

There is also meteoric iron, but it is so rare that any weapon made from it would certainly be an artifact and therefore priceless in any game.

Goethite and limonite are the lowest-tech and lowest-yield sources. When the limonite is worked, it actually turns into hematite. So these will be the first available in the tech system. Hematite and magnetite are harder to get and require more infrastructure and technology to extract iron from the raw ore. I need to do more thinking about what levels to assign to each of these resources. Of course, it requires additional knowledge to extract nickel and magnesium.

I'm thinking that to get a good idea of the distribution of some of these ores, I need a better system for figuring out the distribution of the different types of rock.

Resources discussed: hematite, magnetite, limonite, bog iron, clay, nickel, yellow ochre, red ochre, purple ochre, sienna ochre, umber ochre, magnesium, gold,