The Oil Drum

As a student, I once worked in White Pine. A most unusual copper mine. Its use of the room-and-pillar underground mining technique resembled that in a coal mine. They were considering moving to longwall mining (continuous), also typical of coal mines (more difficult and expensive, but doesn't waste the 40% of the ore in the pillars). Although some native copper (and native silver) was present in the ore, most of the copper values were in Cu-sulfide, enriched in silver, within the shale. Native copper was far more typical of the so-called amygaloidal copper mines further up the Peninsula, in an older basalt horizon. These also were highly atypical deposits.

Stated metal reserves are always limited (many states tax them, and exploration beyond immediate needs is generally not cost effective). Iron is an extremely abundant metal (why we use so much of it) and one that is relatively cheap to recover (why it is priced in dollars per ton rather than dollars per gram). One reason it is so cheap is that the oxide can be reduced to metallic form relatively easily, using only charcoal or coal. We are NEVER going to run out of that metal in particular, but it will become more expensive as energy costs increase, or as alternatives to fossil fuels are required by law. Quickly expanding production of any commodity can be difficult (and risky in case of a recession), as evidenced by present shortages. Steel may be in temporary short supply, but pass a strong magnet through almost any dry river or beach sand and you can convince yourself that magnetic iron oxide ore (magnetite) is nearly everywhere. (So-called black sands contain the most magnetite.)

That stated, and before Kayakguy gets on my case, I should mention that most of the high grade iron ore presently being mined, called iron formation or taconite, is something of a geological rarity. Like petroleum, it was formed over a limited time span under rather special conditions. This time span occurred 2.5 billion years ago, and the special conditions are thought to involve the very first oxygenation of the earth's atmosphere and uppermost ocean, by increasingly abundant single celled plants (photosynthesizing algae, similar to the ones that later dominated petroleum production). This oxygen pollution event (in terms of what the atmosphere had previously been like) progressively precipitated (as iron oxides) most of the reduced (ferrous) iron that had been dissolved in the oceans. After about 2 billion years ago, there was very little iron left (and the oceans have been rather deficient in iron ever since - why iron fertilization has been suggested to assist organic carbonate precipitation). Smaller iron oxide deposits, some quite high grade, form by many other processes, and variable amounts of iron oxide occur in most rocks and sediments. So iron won't run out, but once the taconite mines are exhausted, iron and steel costs should increase.

Taconite itself has only been the preferred source for iron relatively recently. Previously, nearly pure iron oxide (red rust or hematite), locally formed at the surface by weathering of taconite, was the preferred ore. Incipient exhaustion of these hematite ores led to investigation of much lower grade siliceous taconite. It was discovered that grinding and roasting of taconite made its iron minerals alter to magnetite, which could easily be upgraded with a magnet. Thus the iron industry was reborn.

Economists apparently assume that some similar miracle involving tar sands or oil shale will happen to save the oil industry, a possiblility that many here delight in discounting. Using energy to produce valuable metals (for, e.g., tools, weapons, or structures) is not quite the same math as using energy simply to produce energy.