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Gold During the Transition to Modern Scientific Views

Even so in hot Countries, all that part of the subterranean vapours, which here is condensed into Lead, and other base mettalls, can there have no leave to congeale, by reason of the heate: but is all or most part therof exhaled out of the Mines, leaving behind the royall metalls, whose property is to coagulate with heat: whereas the property of the base metalls is to evapourate with heate and to congeale with cold.

The contrary opinion to this; namely that the substance of the best metals are convertible into royal mettals by heate and digestion, hath filled the world with false Books and receipts in Alchimy, and haih caused many men to spend much money, labour, study, and charges to no purpose."

We learn from this chapter that Plattes still adhered to the astral theory that postulated that the sun had considerable influence on the localization of gold deposits, for he repeatedly advises search for the precious metal in the hot (tropical) countries. His explanation of the nature of gold is partly alchemical although he denies the alchemical theories of transmutation. His subterraneous vapour (exhalative) theory of the origin of gold veins seems to have been derived from the speculations of the Greeks. For the origin of placer gold, Plattes comes down explicitly on the side of the mechanical weathering origin of placer gold.

A contemporary of Plattes, Edward Jorden (1569-1632), studied hot springs extensively, and in his great work Discourse of Naturall Bathes and Minerall Waters (1631) came to the conclusion that the internal heat of the earth was due to natural causes and not to a vast internal coal-fired conflagration or to the penetration of the surfs rays. For the origin of vein minerals, he advocated a fermentation process based on the "metallic seed" or "seminary spirit" of the minerals of the earth:
"There is a Seminarie Spirit of all minerals in the bowels of the earth, which meeting with convenient matter, and adiuuant causes, is not idle, but doth proceed to produce minerals, according to the nature of it, and the matter which it meets withall: which matter it workes upon like a ferment, and by his motion procures an actuall heate, as an instrument to further his work; which actuall heate is increased by the fermentation of the matter."

There is in this statement, shorn of its alchemical connotations, the seeds of the metamorphic secretion theory of endogenic mineral deposits.

Views similar to those of Jorden were published in 1671 by John Webster in his Metallographa (A History of Metals). He inclined to the view that metals, including gold, grew (or were generated) in the earth; he called it the vegetability of metals. Webster gives a number of reasons for his views, among which the following may be mentioned:

"A third reason I take to be this, To prove that Metals are generated: That whosoever hath diligently considered the manner how most metals do lie in their wombs, or beds, which for the most part are hard Rocks, Cliffs, and Stones, or things equivalently as hard as they, as lank and spare, must necessarily conclude, that they could never have penetrated the Clefts, Chinks, and porous places of such hard bodies, but that before their entrance into those cavities, they were in principis solutis, either in form of water, or vapours, and steams. And then were those steams, or that water produced before their induration into a Metalline form, and after concocted and maturated into several forms of Metals; which is an analogous, if not an univocal generation; otherwise they could never be found in such streight passages, and narrow cavities, as all experience doth testifie they are."

One sees from this excerpt that Webster, despite his other quaint ideas, had a grasp of the rudiments of the hydrothermal theory. Later in his treatise, he asked a number of pertinent questions about the growth or generation of metals; some of these questions have been elucidated in modern times by a knowledge of oxidation and reduction, secondary enrichment, and other processes in mineral deposits.

The first treatise on the geology and metallurgy of ores originating in the Americas is the El arte de los metales written by Alvaro Alonzo Barba in 1637 at Potosi, Bolivia, and printed in Madrid, Spain, in 1640. Padre Barba was curate of the parish of San Bernardo, Potosi, for many years; he read widely on natural science and traveled extensively in the silver and gold camps in and near his parish. His great work was reprinted twice, in 1675 and in 1729, and was translated into English, French, and German; in English, the last translation is by Douglass and Mathewson (1923). Barba's work fell under the harsh scrutiny of the Inquisition in the latter part of the seventeenth century, was banned, and was burned, evidently because of his (alchemical) ideas on transmutation of the metals and because in certain passages he used the collective word Nature rather than God as the creator of ores. One of these particular passages in chapter 18 on the creation of metals follows from the translation by Douglass and Mathewson (1923):

"Many of the generality of People, in order to avoid profound Discussion, say that in the beginning of the World God created Ores in the form in which they to-day exist and are found in their Veins. This is an offence to Nature, denying to her, without any Reason, the productive Virtue she possesses in all other sublunar things. Furthermore, experience in many parts of the World has proved the contrary. As an example and proof of this, it is sufficient to note what is brought to pass before the eyes of all, in Ilua (Elba), an island near Tuscany, where Iron abounds. After the Men have worked the Veins to the greatest possible Depth, they return the Earth and dumps to the workings; within a period of not more than ten or fifteen Years great quantities of Ore are taken out, into which the dumps and Earth have been converted. The same thing, in the opinion of many, happens in this rich Hill of Potosi. Be this as it may be, we all have seen that Stones which years ago were left in the mines because they contained no Silver, having afterwards been taken out, yielded Silver so continuously and abundantly that it can be attributed only to the perpetual Creation of Silver."

One may think at first reading that Barba is dealing in fantasy when describing the modern day creation of iron and silver ores. Not so. It is well known that iron springs derived from the oxidation of iron ores readily precipitate limonite; similarly with silver in Bolivia and elsewhere, oxidation of lean argentiferous ores yields soluble silver, which on migrating downward and coming in contact with pyrite and other sulphides in veins is precipitated. Barba mentions many such Examples of oxidation and secondary enrichment in his famous treatise. In fact the geological part of his treatise when shorn of alchemical connotations represents the first modern attempt to explain oxidation and reduction in metallic veins.

In his explanation of the origin of metals and their gangue minerals Barba follows the Peripatetics. Again from the translation of Douglass and Mathewson (1923) we read:

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This document is in the public domain.

March, 2011