Alluvial Gold Mining from Argonauts to Agricola ^†

Abstract

This work examines alluvial gold deposit mining and processing methods from the Argonautic expedition until the Renaissance. According to Greek mythology, the mountain rivers of Colchis (Georgia) carried coarse sand and gold particles, which were washed in special wooden sluice boxes. The finer fractions were held in the lower part of the device, which was lined with sheepskin. Using a sheepskin to extract gold from riverbeds gave rise to the myth of the Golden Fleece. Afterwards, during the Roman Empire period, the mining of alluvial gold was performed manually until the discovery of hydraulic mining, a technique that contributed to a massive increase in production. At the same time, the Romans employed various techniques to separate the metals from the total mass of the ore. Gold refining was carried out through cupellation and the mercury amalgamation process. During the Renaissance, Georgius Bauer Agricola wrote De Re Metallica, one of the essential machinery books in mining in the 16th century. He developed a new type of pump to remove water, the uncontrolled flow of which caused significant problems in the underground mining process. The bucket chain pump, the “pater noster” pump, and the piston pump are some of the most innovative devices he presented in his work. Also, Agricola extensively referenced the recovery techniques for gold and other precious metals during the Archaic period that helped preserve the myth of the Argonautic expedition and the Golden Fleece.

1. Introduction

Gold has been known for at least 5000 years and was initially extracted from alluvial deposits. The precious metal has been valued exceptionally highly by all societies throughout human history for different reasons. The Argonautic expedition, the Roman Empire period, and the Renaissance were among the most critical chronological periods in the development and foundation of the mining and processing of alluvial gold deposits with particular innovations for those times [1].

The primary purpose of the present report is to document the evolution of alluvial gold deposit mining and processing methods, from the Argonauts to the Renaissance. The initial extraction of gold from riverbeds by the Argonauts, the use of the “ground sluicing” and hydraulic mining methods by the Romans and Agricola’s remarkable systems are some of the most fundamental processes that will be recorded, among others, in this report. The particular innovations, as well as the technical characteristics of the devices, will be analyzed extensively based on bibliographical references of those times [2].

2. The Argonautic Expedition and the Recovery of Gold from Colchis Riverbeds (1330 BC)

The Caucasus Mountains have had a strong relationship with gold for millennia. According to myths recounted by Greek and Roman writers, the legendary hero Jason was sent on an impossible mission to find the Golden Fleece in Colchis (a part of today’s west Georgia) [3,4].

The method employed was the processing of coarse sand and gold particles carried from the mountain rivers of Colchis (Svaneti Province). The sands were washed using special wooden sluice boxes, and the finer fractions were held in the lower part of the device, which was lined with sheepskin. This superb unique system gave rise to the myth of the Golden Fleece (also known as «χρυσόμαλλον δέρας» in ancient Greek), which originated in a land that abounded in silver palaces and golden halls of ancient kings. Their thick fur trapped the gold the water carried away as nuggets or dust, taking on a golden glow. This method was widespread during the Bronze Age and was the same as that used on the Phasis River (now Rioni) at Colchis (Figure 1) [1].

The Argonauts, on their return to Iolkos, avoided the Aegean and followed the sea routes of the central Mediterranean and the rivers of southern Europe. They passed through the great mining centers along the Danube located mainly in the areas of Ai Bunar (Bulgaria) and Rudna Glava (Serbia), where copper was mined, to Transylvania, where there were large deposits of gold, as well as through the southwestern part of Danube (Erzgebirge, Germany). From there, the Argo sailed, via the Adriatic, to the Rhone and the Eridanos (river in northern Europe mentioned in Greek mythology and historiography), and through the rivers south of the Alps, on whose banks were concentrated deposits of copper, iron, lead, and gold. The Argonauts reached Egypt and finally the Aegean, stopping in Crete and Thera, which was the intermediate station for imports from the Aegean to Crete (Figure 2) [6].

Based on surveys of Svaneti Province’s ore deposits, most of the gold reserves have been mined in the past. At the same time, the intensive erosion cycle of the current era, which was caused by abundant rainfall and extensive glacial periods, led to the rapid uplift of the Svaneti section of the Greater Caucasus, favoring rapid gold replenishment in the present-day rivers. This scenario of active enrichment of the riverine pebbles in the region is a key geological datum indicating high-quality gold mining activity in the historical past and present. Consequently, the exploration in the Svaneti area provides sufficient evidence to verify the myth that the Colchis is described as “a gold-rich country” [5].

3. The Roman Empire and the First Need for Massive Alluvial Gold Mining (27 BC-476 AD)

The expansion of the Roman Empire indicated that the demand for metals was high and therefore, more sources had to be found. Most of the gold mined in the territories of the Roman Empire, including the conquered areas, was mainly used to support the army and its infrastructure. However, gold evolved and became one of the most central pillars of Roman civilization. It was not only the currency of the time, but also a measure of wealth and even a lever of global trade.

For the most part, gold and other metals were mined by hand. Then, however, the hydraulic mining method was invented, a technique that contributed to the massive increase in production. This is an ancient mining technology in which a torrent of water removes debris and reveals mineral veins. In its most profitable mining period, it is estimated that the Roman Empire produced up to 9 tons of gold per year [7]. This production is equivalent to over half a billion USD in annual gold revenue based on today’s gold prices.

Figure 3 (left) depicts the stages of exploiting alluvial gold deposits using hydraulic power. In particular, it depicts the water tank (from which water is fed to the mining area through a channel), the use of trenches for moving the conglomerates to the lower section, the miners removing the larger boulders manually, and the sluice box devices used to wash the conglomerates and separate gold particles with different sizes. In general, this specific technique is known as “ground sluicing” and it was particularly suited for mining deposits with a thickness ranging from 4 to 6 m. When dealing with dry soils, they would create 6 to 8 converging trenches, each inclined at a 5% angle relative to the horizontal plane [8]. By utilizing the force of running water, the miners would push the alluvial deposits towards the trench walls, gradually driving them downwards along the slope. The pebbles were washed and removed from the trench while the flowing water carried the sand and clay away, directing them towards the outlet. Consequently, the heavier fraction of the material settled at the bottom of the trenches, allowing for the recovery of gold grains through concentration pans (Figure 3 right) [9].

The Romans used various techniques to separate the metals from the total mass of the ore. In particular, gold was refined either by heating it for a long time in the presence of other (metallic or non-metallic) substances (refining, by cementation process) or by the process of amalgamation with mercury, one of the oldest methods of gold extraction. It involves the dissolution of Au from Hg and then the distillation of Hg from the Au-Hg alloy, producing spongy gold and mercury vapor [10].

4. The Innovative Machines of Georgius Bauer Agricola during the Renaissance (1494–1556)

During the early Renaissance (15th century AD), mining and metallurgy developed significantly. The writers Georgius Agricola and Vannoccio Biringuccio were the ones who provided most of the information on metallurgy and mining of this period. Their two main works, Pirotechnia (1540) and De Re Metallica (1556), cover most of the topics related to mining and metallurgy. These works became standard textbooks for the next two centuries [11]. In the sixth book of De Re Metallica, Agricola analyzes the devices used in underground mining [12]. In it, one can find meticulous descriptions of the systems by which water is pumped from wells. The three innovative types of pumps that Agricola presents for the first time are the following (Figure 4) [12]:

• Bucket-line pumps (Figure 4a);
• Pater noster pumps (Figure 4b);
• Piston pumps (Figure 4c).

The bucket line pump [13] has been recorded since ancient Greek and Roman times, and was also used during the Middle Ages. Generally, wheel pumps are divided into two categories: the Egyptian wheel (noria) and the bucket chain pump, which are the most commonly used. The noria pump consists of a large wheel with buckets fixed on its periphery. The buckets (or containers) fill with water when they pass through the stream and deposit it just before reaching the top. When the water had to be lifted to a great height or when the streams were too deep, the device received a suitable transformation. More specifically, the buckets were connected by a strap at the top and bottom of the riser. Thus, this device had no defined limitations on the power rates it could process. Agricola describes many different types of wheel pumps, while the primary type is manually operated with a suitable gear system, which acts as a reducer (Figure 4a).

The pater noster pumps [13] consist of a chain with a closed loop that moves inside a tube, made of perforated wood logs. The chain slides inside the pipe by means of a pulley, which is fitted onto the shaft of the water wheel. The first type of device operated using an overflow water wheel and was equipped with circular discs spaced approximately 2 m apart along the length of the chain. The drainage depth that could be achieved with the pater noster pump was estimated at 70 m using an 8 m diameter wheel, while if a 10 m diameter wheel was applied, the depth could reach up to 80 m. The pater noster pump described by Agricola is shown in Figure 4b.

Single-acting piston pumps are based on the operating principle of the hydraulic pump of Ctesibius (3rd century BC). Agricola analyzed different types of pistons, obviously improved in design compared to their counterparts of the previous centuries. These had valves of much better construction, and the sealing between the tube and the piston was improved. The basic type of piston pump is manually operated, performing the reciprocating motion of the drive rod without the use of levers. Impressive alluvial deposits in the De Re Metallica project illustrate many piston pump types. In particular, a pump made of two connected parallel tubes and the pistons driven by a horizontal crankshaft are mentioned extensively. In fact, the pumps were constructed from a log, and were carefully drilled and machined with a special tool in the area of the piston stroke. Another system involved the use of three parallel pumps. In this arrangement, the mechanism for converting rotary to reciprocating motion rested on a rotating shaft, which was particularly common in those days. In this way, water was drained from wells up to a depth of about 30 m (Figure 4c) [13].

Agricola made sketches and described water pumps that were used in various machines to demonstrate his proposed methods of extracting metals from their ores. In Chapter VIII of his translated book, De Re Metallica, Agricola provided detailed pictorial descriptions of the equipment and procedures used. His focus was mainly on the methods of washing and isolating metal from gangue. The book contained forty-nine exquisite illustrations of troughs, sluices, launders, weirs, and ditches used to direct the ore and combine it with water for separation. The equipment was designed to separate fine grains from lumps. The troughs and launders featured different mechanisms such as cleats, rifles, skins, cloth, twigs, and sieves, while some were lined with boards. Additionally, the book demonstrated the art of whirling bowls with various capturing devices. Rakes, brooms, hoes, and trowels were also used as agitators (Figure 5) [5].

5. Conclusions

The periods of the Argonautic expedition and the Roman Empire were the beginning of the evolution of methods and procedures in the mining and processing of alluvial gold deposits. Thus, the first concerted attempt to document the procedures applied in mining alluvial gold deposits can be seen in De Re Metallica. The publication of this book marked the beginning of the transition between the philosophical side of metallurgy and science based on empirically determined observations. Thus, De Re Metallica represents the first attempt to describe the nature, location, and means of obtaining and purifying metals derived from experience and experimentation. This is reflected in the ability to replicate the processes and experiments as they unfold and in the accuracy and detail with which they are described. It is observed that even today, in the industrially advanced era, the technologies applied are based on the earlier innovative methods of the previous centuries.