Nederlandse Goudpan Vereniging

"De metalen gewonnen door mijnen, zoals zilver, goud, enzovoort, komen uit water."

Theophrastus

Wetenschap in de Klassieke periode was meestal beperkt tot speculatie. De pre-Aristotelianen verklaarden de oorsprong van het universum en natuurlijke phenomenen in het licht van de vier basiselementen - aarde, water, lucht en vuur. Deze theorie, die waarschijnlijk haar oorsprong vond in de oude civilisatie van de Indus Vallei, werd overgenomen door de vroege Babylonische natuurwetenschappers en doorgeven aan de vroege Griekse filosofen, waarvan Empedocles (ca. 490-430 v Chr.) vaak de geaccrediteerd wordt voor het verfijnen van deze theorie. Aristoteles omarmde de vier elementen theorie en voegde er nog een concept aan toe, namelijk ether.

Tijdens de pre-Helleense en Helleense tijden werd er in het hele Middenlandse Zee gebied, in Klein Azië en op andere plekken in West en Noord Europa en in Afrika en Azië, uitvoerig goud en zilver gemijnd. Er is veel literatuur over oude mijnwerken in deze gebieden. Deze worden alle samengevat door Rickard (1932), Davies (1935) en Healy (1978).

Door bewijs geleverd door de vele afzettingen en storthopen in Egypte, het Aegeisch gebied, Turkijë (Anatolië), Iran, India en andere regionen, lijkt erop dat in het begin het meeste goud uit eluviale en alluviale placers kwam; Toen deze placers later uitgeput raakten, werden de geoxideerde zones van goud houdende kwarts en sulfide afzettingen geëploiteerd, eerst door open groeves en later door ondergrondse werken. Brandzetting werd veel gebruikt door de Grieken en Romeinen in de ondergrondse mijnen.

Plinius stelde in zijn Historia Naturalis, dat azijn beter was dan water bij afschrikken en afbreken van het hete gesteente. Door problemen met water en ventilatie was de diepte van exploitatie van het gesteente gelimiteerd tot ongeveer 200 meter in de meeste gouddragende gebieden. Slaven en gevangenen deden de mijnwerzaamheden. Goudzoekmethodes waren ruw en voor het belangrijkste deel gebaseerd op visuele tekenen van de aanwezigheid van goud in kwarts float, in dagzomen van kwarts, in gossans, in bodems en verweerde overblijfselen, en in de sedimenten van stromen en rivieren. Er werd veel in het wilde weg gegraven bij het zoeken naar goud. Dit wordt ondersteund door het feit dat er in de meeste goude mijngebieden veel ondiepe schachten en Pliny, in his Historia naturalis, claimed that vinegar was better than water in quenching and disintegrating the hot rock. Because of water and ventilation problems, the depth of exploitation of bedrock deposits was limited, probably to 200 m or less in most auriferous regions. Slaves and convicts did all mining. Prospecting knowledge was crude and was based principally on visual signs of the presence of gold in quartz float, in exposures in quartz outcrops, in gossans, nearby soils and weathered residuum, and in the sediments of streams and rivers. Much gophering was employed in prospecting, evidenced by an abundance of pits and shallow shafts in most of the ancient mining areas of the Aegean, Turkey, Egypt, India (Kolar), and elsewhere. The gold pan appears to have been employed for testing gossans, soils, and alluvium and for winning the metal since the earliest times. Likewise, the rocker and sluice with riffles, animal fleeces, or mats for trapping the gold seem to have been in use almost from the begin ning of placer gold mining. The animal (sheep or goat) fleeces were dried and the gold was then shaken out of them into pans for further concentration. When ulex (a prickly plant of the furze or gorse family) was used, it was burned and the gold washed out of the ashes.

Some placer operations employed the boulder-riffle method of concentrating the gold; in this method boulders were arranged in such a way that as the water rushed along carrying the gold, it swirled around the boulders, depositing the nuggets and dust in the slack-water zones around and between the boulders. After an appropriate interval, the sluicing water was turned off or diverted to allow the cleanup. Stretches of streams with natural riffles, such as slate and schist beds and folia oriented at right angles to the stream direction, also appear to have been employed in some placer areas. In large placer operations, especially where high-level (terrace) gravels were exploited by the Romans, as along the Sil in Northwestern Spain and the Vrbas in Yugoslavia, hushing (booming) was employed. This method frequently required aqueducts and canals several kilometres in length for transport of the water to the crude monitors. Where bedrock quartz deposits were exploited, the separation of the native gold from the d ross, mainly quartz, was accomplished by hand picking, followed by crushing and grinding in stone mortars, querns, and crude "hour glass" and other types of mills, and finally by washing on sloping boards or flat rocks. These "washeries" can be seen in pictorial form on walls and tablets in Egyptian tombs and in a dilapidated condition in a number of ancient mining regions in Greece, Egypt, and the Middle East.

"The mountain torrents are said to bring down gold, and these barbarians (Soanes) catch it in troughs (sluices) perforated with holes and in fleecy skins." Strabo's reference is probably to the river Phasis (the present Rioni in Georgia, draining from the Caucasus), which drained the Colchis region, supposedly one of the goals of the Argonauts in the legend of Jason. Describing the gold deposits of Egypt and Nubia Strabo quotes Agatharchides of Cnidus (c. 132 B.C.) freely and gives us an insight into the geological setting of some of the deposits. In an interpretative translation we learn: "There (in Egypt and Nubia) the rock is black and full of streaks and veins of a mineral with a remarkable whiteness the lustre of which surpasses the most brilliant natural materials."

Obviously, Strabo, like Diodorus Siculus, is speaking of gold-quartz stockworks in greenstones (amphibolites) or in black slates or schists. The white mineral is probably milky quartz. These interpretations are supported by recent work in Sudan (Fletcher, 1985; Gaskell, 1985).

A number of Roman writers have left works of interest to geologists and mineralogists. Lucretius (99-55 B.C.) author of De rerum natura, a famous philosophical work, describes many natural phenomena but mentions gold and mineral deposits in only a cursory manner. Vitruvius (c. 27 B.C.), the renowned Roman military engineer and architect, likewise treats the subject of mineral deposits and gold only briefly in his De architecture. Pliny the Elder (A.D. 23-79) was the only Roman to engage in extensive natural history studies; of all the classical writers he alone has given us a documentation of the works of earlier ledge of minerals and mineral deposits writers and a summary of the know extant at the beginning of our era. His extensive travels, as a onetime cavalry officer and later prefect (admiral) of the Roman Fleet under Vespasian, are recorded in thirty-seven books in his encyclopaedic Historia naturalis. This famous treatise was suddenly terminated by Pliny's death as a martyr to science when he was suff ocated by volcanic gases as he sought to study the cause of the violent eruption of Vesuvius in A.D. 79.

The Historia naturalis is a great assemblage of fact, fancy, and fiction written from both observation and hearsay. Where observation prevails, the narrative is precise and logical; where hearsay predominates much of the text is fanciful and sometimes bizarre. Book 33 treats of the natural history of metals, and in it the first section is reserved for gold.

After a long discourse on the avarice of man for gold, the wearing of gold rings and other golden adornments, coinage, other uses of gold, and the special qualities of gold, Pliny turns to methods of discovering and mining gold ores. In the translation of Rackman (1968, p. 53) with my explanations in parentheses we read:

"Gold in our part of the world-not to speak of the Indian gold obtained from ants or the gold dug up by griffins in Scythia is obtained in three ways: in the detritus of rivers, for instance in the Tagus in Spain, the Po in Italy, the Maritza (Hebrus) in Thrace, the Sarabat (Pactolus) in Asia Minor and the Ganges in India; and there is no gold that is in a more perfect state, as it is thoroughly polished by the mere friction of the current. Another method is by sinking shafts; or it is sought for in the fallen debris of mountains. Each of these methods must be described. People seeking for gold begin by getting up (searching for) segullum -that is the name for earth that indicates the presence of gold. (Beneath) this is a pocket of sand, which is washed, and from the sediment left an estimate of the vein is made. Sometimes by a rare piece of luck a pocket is found immediately, on the surface of the earth, as occurred recently in Dalmatia when Nero was emperor, one yielding fifty pounds weight of gold a day. Gold found in this way in the surface crust is called talutium if there is also auriferous earth underneath. The otherwise dry, barren mountains of the Spanish provinces, which produce nothing else whatever is forced into fertility in regard to this commodity.

Gold dug up from shafts is called 'channelled' or 'trenched' gold; it is found sticking to the grit (gangue) of marble, not in the way in which it gleams in the lapis lazuli of the East and the stone of Thebes and in other precious stones, but sparkling in the folds of the marble. These channels of veins wander to and fro along the sides of the shafts. . . . The third method will have outdone the achievements of the Giants. By means of galleries driven for long distances the mountains are mined by the light of lamps."

In a following passage, Pliny deals with the constitution of gold. In the translation by Rackman (1968, p. 53) we read:

"All gold contains silver in various proportions, a tenth part in some cases, an eighth in others. In one mine only, that of Callaecia called the Albucrara mine, the proportion of silver found is one thirty-sixth, and consequently this one is more valuable than all the others. Wherever the proportion of silver is one-fifth, the ore is called electrum; grains of this are found in 'channelled' gold."

The reference to the Indian gold ants and the Scythian griffins comes from Herodotus and is a tale spun through the ages down to the present day, being repeated and analyzed by Strabo and Pliny and by T. A. Rickard as late as 1930. Adams (1938) discusses the probable origin of the tale in detail. My personal opinion is that in ancient times someone found eluvial gold particles in ant (termite) mounds somewhere in Asia, from whence sprung the fable of the gold-digging ants. In this respect, it was well known by the old prospectors that ants would collect splendid particles of metals and minerals such as gold and galena. Some birds have a similar penchant. The griffin tale from Scythia may be similarly based on the circumstance that the spoil near certain animal burrows (e.g., marmot) in auriferous regions may contain particles of gold.

The material called segullum (or segutilum in some Latin versions) should probably be translated as gossan. Segullo is still used by Castilian (Spanish) prospectors to define the gossanous material capping certain auriferous deposits. I can find no translation for the Latin word talutium (or talutatium in some versions); I suspect that nuggety or eluvial was meant. The use of marble for the gangue of gold veins is evidently an error; quartz was obviously meant. Channelled gold in the second excerpt should be translated as vein gold.

In a later passage, Pliny deals with the oxidation processes of copper minerals in gold veins. In the translation given by Bailey (1929, pt. 1, p. 105) it is stated: "Chrysocolla is an exudation found in the shafts, which we have already mentioned. It oozes down the vein of gold, and its muddy substance is congealed under the influence of the winter cold until it is as hard as pumice. It is well established that the best quality forms in copper mines and the next best in silver mines. It occurs in lead mines also, but this kind is inferior to that found in gold mines. In all these mines, however, it is also prepared artificially (though its worth is far below that of the natural product) by leading a gentle stream of water into the vein all through the winter until the month of June, and evaporating the extract in June and July. It is therefore perfectly clear that chrysocolla is none other than a decomposition product of a vein of metal."

There has been considerable discussion by classic scholars about the identity of chrysocolla. The modern chrysocolla is a copper silicate, and Pliny may have meant this mineral in some cases; more generally, however, the mineral in question was probably malachite or azurite, the green and blue copper carbonates. The reference to the precipitation mechanism as due to winter cold follows from the ancient idea that many minerals were congealed (frozen) from water analogous to the formation of ice. This passage is one of the first references in the geological literature to oxidation phenomena in mineral (gold) deposits.

The last of the classical Roman writers to briefly refer to gold deposits was Seneca (A.D. 3-65) contemporary of Pliny and tutor to Nero. In his Quaestiones naturales he says in (an interpretative) translation: "In the earth there are some kinds of moisture that harden when fully formed. From these arise all metalliferous deposits from which our avarice seeks gold and silver." This passage suggests that Seneca followed Theophrastus in his view of the origin of gold (deposits) from water.

Early Indian (Hindu) manuscripts mention gold in many contexts but deal only in the simplest of generalities with the origin of the various types of deposits from which the precious metal was obtained. The Rig- Veda, first of the books of the sacred Sanskrit scriptures of the Hindus, composed about 1500 B.C., contains several references to gold and silver but gives only the barest details about the geology of the metals (Ray, 1904, 1925; Bhagvat, 1933). In the Arthashastra of Chanakya or Kautilya (fourth century B.C.) there are further details about gold and silver, but these are concerned principally with the mining, metallurgy, and testing of the two metals. Mention is made, however, of the occurrence of gold ores in mountains and of the different types of auriferous ores - unmixed yellow (probably pyritic ore?), red and reddish yellow (limonitic ore?), and some with a bluish colour on fractures (oxidized copper sulphide ore). Nodules (nuggets) and needles of gold are also described from placers. Several c olour types of gold are mentioned -that with a blue shade, silvery (electrum), thorn-apple like (red), and pure (the colour of the pollen of the lotus). The early Indian peoples mined gold extensively from bedrock deposits and obtained the metal from placers in many of the rivers of the Indian Peninsula. Mining of the bedrock deposits was carried out principally in the oxidized zones of auriferous veins and disseminations in sheared zones and iron-formations, as is evident from very ancient workings in the famous Kolar field in south India. Some of these workings probably provided gold to the early Indus Valley civilization of 4000-3000 B.C. (Ray, 1948).

Allchin (1962) has reviewed the evidence of early gold mining in India and the methods employed in winning the precious metal. He has concluded from archaeological evidence and C-14 dating that placer mining in India was widespread long before the Christian Era and that large-scale bedrock mining (principally in the oxidized zones but also in some cases in the hard rock) in southern India began with the Mauryan colonization of the Deccan about the end of the fourth century B.C. The Hutti and Kolar fields appear to have been first prospected and mined about the beginning of the Christian era.

It seems strange that the Greeks, Romans, and Indians never developed any precise scientific theories on the origin of gold and other types of deposits despite the fact that gold was mined from its principal deposits (excluding the quartz-pebble conglomerates) throughout their empires for many centuries. It has been said that the Roman in general, and the Roman (mining) engineer in particular, was a very practical man and not given to speculation and theories; the same can be said of the Greek but only in part. Natural phenomena interested the Greeks but their philosophers were concerned more with speculations on the great manifestations of nature rather than with mundane things such as gold veins. Another factor, it is said, revolves about the use of slaves in Greek, Roman, and Indian mining ventures. To engage in the earthy tasks of mining (and geology) was deemed to be below the elite and generally considered to be disparaging of one's station in life. Therefore, Greek, Roman, and Indian writers provide l ittle if any observational detail on geological and geochemical processes. Their knowledge of minerals was limited to only a few species and their familiarity with rocks was essentially negligible. Therefore, they could not have logically evolved any systematic theories for the origin of (gold) veins and other types of deposits.

References and selected bibliography

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