Hello Planetary Pals,
This week’s blog post is a combination of a couple of my interests and passions; I have a love for both history and also a passion for all things geology. I figured this topic, on mining techniques of the past would be interesting to discover. I specifically chose this time period because it is the most interesting to me. In these times, writing was not very widespread, and what little documents exist rarely focus on something so base as mining. Instead, a majority of the knowledge regarding this topic comes from archaeology and experimental reconstructions. Mining techniques have evolved over time and humans have always needed to access and exploit their surrounding natural resources.
The most ancient human technologies such as stone-crafting and pottery-making could be achieved through simple surface quarrying. They could take surface deposits of clay and fire them for pottery or rusted hematite deposits to use as pigment for cave paintings. Eventually these paleolithic humans looked further than merely surface deposits. Flint tools and wares were especially valuable to these humans, and they soo figured out how to quarry for them. Archeological finds of small shafts and adits follow chert deposits into hillsides in many areas of Europe dating to this era, indicating that paleolithic humans had figured out basic mining techniques.
Even these neolithic humans found value in the rare and beautiful minerals such as gold. Since gold is unreactive and difficult to oxidize, it is often found in it’s native form. Ancient humans used the same techniques that panners use today when looking for placer deposits of gold in rivers and alluvium .
Following the Neolithic age was the Chalcolithic age, the age of copper use by humans. Humans could work native copper rather easily into tools and weapons, however in Europe, these kinds of deposits are rather rare. Instead, humans began to master the technique of smelting. Smelting is not easy, and it is not merely melting the ore. Instead, it is a chemical reaction, utilizing knowledge of oxidation and reduction in order to pull the unwanted material away from the desired metal. For instance, to smelt malachite, it is heated in an oxidizing environment according to:
CuCO3Cu(OH)2 → 2 CuO + CO2 + H2O
after which the CuO is heated in a reducing environment to remove the oxygen, leaving behind the pure copper:
2 CuO + C → 2 Cu + CO2
The earliest evidence of this type of basic smelting is found in Serbia. Waste slag pills were found at the archeological site and showed that humans had figured out smelting by at least 5000 BC. The Chalcolithic was relatively short-lived in Europe, as metallurgical techniques (or possibly metallurgical accidents) soon made the formation of Bronze possible, starting the Bronze Age. Being able to smelt and use Bronze had a significant impact on the development of Ancient Europe. Weapons and tools could be stronger and longer lasting, and were desirable trade items that allowed civilizations to prosper.
These periods of prehistory end with the Iron Age. This period is defined by the beginnings of iron ore smelting and the end of unwritten history. Iron ore is much more difficult to produce than bronze and was a prohibiting factor in development until technologically superior furnaces could be developed to maintain the high temperatures required. Unlike copper and tin, which are uncommon materials, iron is abundant in almost any region. Therefore, once the technology to produce iron was developed, it was quickly adopted by most civilizations. The Iron Age is said to end in a region once recorded history began there, though iron was by far the most common material manufactured for centuries after the iron age “ended” in a region.
Roman ingenuity in mining allowed for the support of such a large and prosperous empire. Important metals needed to sustain the empire such as lead, copper, silver, and gold, were mined with new and innovative techniques. Other than looking in placer deposits for native metals, they explored vast underground mines in the search for ore.
One common method of mining was called fire-setting. In this method, a pile of wood is stacked against the rock and set ablaze. The fire heats up the rock to a high temperature. Next, after the fire is out, the miners would throw water on the rock. This induces thermal fracturing as the rock rapidly cools. The cracks created by this quenching allow it to be pried open easier and allows ore to be broken into small pieces to be easier to transport. This method was typically very destructive to the local environment due to the volume of trees that needed to be cut down.
A third method of mining used by the Romans is known as hushing. Roman engineers would create canals or aqueducts to a potential mine site and fill up large reservoirs of water. Once the reservoir was full they would release the water in a torrential wave. The roaring water escaping from the large reservoir would tear through the soil and overburden, leaving the bare bedrock behind. With the large tracts of bedrock now exposed, it could be prospected for gold-bearing veins or other ores. This method was also environmentally unsound, and often conflicts would arise over the romans diverting a river away from a community’s water supply.
Roman open pit mines were common, however underground mines were also employed if the ore was especially rich. These mines were dangerous, only a meter or so large in spots, and often filled with noxious gasses that would kill miners. There were often many adits drilled into a mine to allow for an exchange of oxygen, and bellow and windscoops were also used to pump in air. Mines also often filled up with water seeping in from the water table. To combat this the romans created special water wheels that would carry water up and out of the mine.
The fall of the Roman Empire would impact the mining industry of Europe for centuries. Continued Germanic and Slavic invasions and conquests of the Early Medieval Period made it difficult to maintain mines. Manpower was lost in wars, technology was slow to progress, and capital was not invested in these dangerous and risky areas. With decreased incentive to trade, the people of the early medieval period would mine areas close to their villages, and often with less efficient techniques than had been used by the Romans.
One interesting source of iron, especially for the Norse, was bog iron. Bog iron is formed b iron precipitating out of water in the reducing environment of peat swamps, sometimes also facilitated by bacterial fixing. Typically these are the mineral goethite, and they are typically very oxidized. Long sticks would be used to poke through the muck of the swamp to find nodules of the precipitated iron. This type of metal was common in Scandinavia and exploited extensively by the Norse. In L’Anse aux Meadows, bog iron was used to sustain the colony. Bog iron is also renewable as new precipitates form about once in a generation.
The High Middle Ages were a prosperous period in Europe and once again, mining was able to continue effectively. Population growth and increased wealth fueled the industry to better meet the new demand for metals. As well, advancements in medieval armor meant that more metal needed to be mined to outfit soldiers. After the printing press was invented, mining techniques could be spread faster and further across Europe and the world. An example of this is the publication of Agricola’s De Re Metallica, which was the first in depth and detailed depiction of late medieval mining techniques. This helped to standardize practices everywhere. Despite this growth, by the end of the middle ages and with the discovery of the new world, mining in Europe took a downturn, based on the amazing array of unexploited natural resources in North and South America.