A 3k-Year-Old Copper Smelting Site Could Be Key to Understanding Origins of Iron

Leadville Colorado was the site of a very minor gold rush, that mostly produced large piles of lead tailings.

Until someone noticed the lead tailings were not lead, but oxidized silver.

I have only assayed samples from the iron cap. You would not expect to find much in that part of the formation but it still came in at 1-2g/ton. There is a large area of visually striking bornite[0] that I have not yet been able to properly sample which is roughly the area you would expect the gold to concentrate. It is in the walls of a narrow, deep canyon at high elevation. The region was mined for gold/copper a century ago, so the existence is not surprising.

The location makes access extremely challenging. It requires 3 hours of hiking, assuming you are fit, and borderline technical mountaineering once you get close to the site. The lower parts of the canyon are also under tens of meters of ice most of the year, which creates a separate set of safety issues. When these mountains were prospected in the 1920s, it would have been underneath a deep permanent snow field. I've visited some of the old gold mines in the area for calibration and this deposit appears substantially larger than those.

The discovery was accidental. I was looking for a waterfall I had seen on satellite imagery in the backcountry and came across an enormous chunk of molybdenite[1] while climbing across granite scree. I made several trips to find the source of the molybdenite higher up the mountains, which I never did, but while searching for that I localized a bunch of other beautiful sulfide/oxide mineral specimens to the above canyon. It gives me a great excuse to explore parts of the mountains no one has been into before.

[0] https://en.wikipedia.org/wiki/Bornite

[1] https://en.wikipedia.org/wiki/Molybdenite

The improvement of ideas over time is a rather complex process.

It's multiple things working together. Typically you have to have an excess of calories which leads to free time in at least part of the population. While the 'fear of change' as gods fault is more of a post ad hoc rationalization of the horizon problem. That is any change in behaviors in the good times could lead to death in the hard times. Moving away from what works has risks.

One big advantage of iron is that you can forge it. Bronze has to be cast or cold worked (with annealing steps as necessary). You can't forge weld bronze either, so you need to braze/solder parts together. A skilled blacksmith can forge things from iron quickly and with little waste. It's especially important for things like nails and arrowheads that are needed in mass quantities.

Very minor semantic nitpick as a metallurgist, martensitic and austenitic are not terms that distinguish the ductility of the metal, they are ways the atoms organize into crystal structures (which do have an effect on hardness/ductility).

Austenite is one of the high temperature crystal structures of iron, and is not usually seen at room temperature except in certain non-heat-treatable stainless steels, and in highly alloyed steels some small amounts of retained austenite remains that doesn't get the chance to transform due to low cooling rates and suppressed M_f temperatures. Martensite forms by rapidly cooling austenite without giving the atoms the ability to re-organize into their preferred structure (ferrite, pearlite, or cementite depending on the carbon concentration). This transformation actually changes the size of the crystal matrix, which locks in a ton of internal stress as atoms want to move around but can't. All of this internal stress must then be overcome by an external stress to move the atoms around, resulting in a much harder material.

Martensite requires extremely fast cooling rates (on the order of 100s of degrees/second), which is why most carbon steels are quenched to harden them. These cooling rates are only able to be achieved a little ways into the bulk of the material, so you usually end up with a hardened case made of martensite, and a softer more ductile core that is usually pearlite (layers of ferrite [pure iron] and cementite [iron carbide]) that form due to the slower cooling in the core. This is usually actually more desirable than an entirely through hardened piece, as the hard surface can resist wear and indentation, while the soft core increases the ductility and toughness which reduces the risk of fracture.

> Where there was copper, there was no tin, and vice versa.

There were some exceptions on the British Isles. Even some mines that had both.

>We also know that different populations have different distributions -- slightly different standard deviations, sometimes vastly different means.

Citation needed. This is at a minimum, highly controversial.

And I think the claim is that the distribution was more or less the same, not that they were all uniformly intelligent.

> This is all a digression from the main claims, so I'd prefer that people don't pull on this thread

You want to say your piece and get no back-chat?

Romans started to hit people with iron swords at a certain date, influencing the history of Europe substantially, so the origin of that iron age is interesting. Elsewhere, a copper smelting site of 500 BC would be interesting: consider the Moche, in Peru, who independently had a sort of bronze age around that time while Europe was into iron. (I don't think they did anything much with their bronze because they were too preoccupied with body fluids and erotic pottery.)

They found ancient inhabitants of Georgia using iron ore as flux for copper smelting, so it's a theory of how they went from one to the other. It's not terribly exciting but it beats "they tried smelting rocks at random to see if anything good would happen".

i have zero background in this topic.. but if i were to guess there are >100x more ceramic kilns than there are bronze smelters

if some people chucked random ores into ceramic kilns, maybe one would get out some iron slag and then iterate from there

theres a great blog series about making iron.

https://acoup.blog/2020/09/18/collections-iron-how-did-they-...

its easy on paper, but when you get into the details its actually tricky

The author is a professor of ancient history at Oxford University. What makes you think it is political? A book can specialise in Western history without having a hidden agenda.

Based on reading the Guardian review (that predictably praises it and seems to be written by someone who doesn't know much history) and a much better review on a website run, weirdly enough, by Christians (written by someone who does know history), I would agree.

The first half of the quality review praises the good parts of the book, the second half is where the meat is.

It is probably a useful book if you don't know much about the classical world but it doesn't seem like one should take one's politics from it.

Quality review:

https://www.thegospelcoalition.org/reviews/how-world-made-we...

Low quality review:

https://www.theguardian.com/books/2024/feb/28/how-the-world-...

Many years ago, my roommate was working on his PhD in geology while my history obsession was in full bloom and we talked about this a little. He made some interesting points about iron versus copper supply and how its relative abundance meant that some cultures would have had access to iron long before access to copper.

The transition to iron was very slow and some places kept using bronze for centuries. There’s also no single point (known) for where the Iron Age started. In Nigeria, for example, it seems most likely that Nok people worked with iron first and had no significant Copper or Bronze Age.

I think that the closest answer is that we don’t know for sure, but evidence seems to show that the path to iron followed different paths in different parts of the world. In some cases, the copper industry would have been heavily involved. In other places, an iron industry seemed to take shape before a copper industry, so the developments would have been independent.