Nederlandse Goudpan Vereniging

"For I know by good and long experience and by
many accurate trials that Quick-silver the most friendly mineral to the
royal metals, can by no means or Artifice whatsoever be fixed and
coagulated into either of the Royal Metals."



Gabriel Plattes, 1639



The interval between the publication of Agricola's De re metallica
(1556) and the great controversy in earth sciences, instigated by Werner
and Hutton and lasting into the early years of the nineteenth century,
marks a time span of nearly three centuries, during which many changes
took place in politics, social structure, economics, and science in
Europe and the newly discovered (i.e., by Europeans) lands of the New
World (Americas), Africa, the Far East, Siberia, and Australasia. The
period witnessed in turn the great events of the aftermath of the
Reformation (1517-1560), the exploration and exploitation of the newly
found lands (Americas, Siberia, Africa, Australia, etc.), the continued
expansion of capitalism and mercantilism, the rise and later decline of
monarchial absolutism in Europe, the emergence of parliamentary monarchy
in England, the Seven Years War (which removed French dominion from
America 1759), the American Revolution (1775-1783), the French
Revolution (1789-1795), and the rise and fall of Napoleon Bonaparte
(1815). Amid all the vicissitudes of the period 1556-1820, there was
steady progress in science. By the closing years of the period a large
body of verifiable knowledge had accumulated in the fields of
mathematics, astronomy, physics, chemistry, and medicine.





In physics and astronomy the revolution begun by Copernicus (1473-1543)
in his De revolutionibus orbium coelestium culminated in Newtons
(1642-1727) monumental Principia, in which the geocentric Ptolemaic
views of the solar system were abolished forever.





Similarly in chemistry the pioneer work of Boyle (1627-1691) in
demolishing the Aristotelian four element theory and establishing the
clear definition of an element and compound and in challenging the
current fanciful alchemical theories in his Sceptical Chymist led
ultimately to the modern view of oxidation-reduction reactions,
enunciated first by Lavoisier (1743-1794); these efforts finally
overthrew the phlogiston theory that had sidetracked chemistry for
almost a century. Technology also advanced greatly during the
seventeenth and eighteenth centuries, particularly in mining methods,
ventilation, and drainage as the demand for metals, especially the
precious metals, grew. Most of this progress in mining technology took
place in central Europe (Erzgebirge) and in England, and from these
regions, many of the ideas of the period about ore-forming processes
would soon originate.



Prospecting and discovery of gold deposits, remained largely a matter
of chance during the transition period, although references in the
literature of the period point to a greater appreciation of the role of
indicators of auriferous deposits, such as quartz, gossans, mineralized
springs, red earths, and depression lineaments along mineralized faults
and fractures. Mining methods were improved over those utilized in the
Late Middle Ages and Renaissance, including particularly the employment
of horsepower on a wider scale during the seventeenth and early part of
the eighteenth centuries and the introduction of the steam engine for
pumping water from deep mines and other tasks during the last half of
the eighteenth century and the early part of the nineteenth. Gunpowder
(black powder) was used more extensively for blasting toward the end of
the period, and there was much improvement in drilling, using handsteel
methods for driving drifts and extracting the ore. Improvements in mine
ventilation, drainage, timbe ring and lighting and in many of the
metallurgical techniques led into those of the modern era. During the
seventeenth century the study of ore deposits suffered a period of
abeyance.





In England Francis Bacon (1561-1626), onetime Lord Chancellor under
James 1, was the foremost philosopher of the time and undoubtedly one of
the greatest prophets of science. He sought to reform all knowledge and
thus create a new learning, and he was a firm advocate of experimental
method and inductive reasoning. Yet, in all of his many works, there is
little of interest for the geologist, except perhaps his speculations on
continental drift, and nothing specifically about mineral deposits.
Rather one has to turn to an agriculturist, Gabriel Plattes, and to a
South American curate, Alvaro Alonzo Barba, to discover the state of the
theories of the origin of ore deposits.





In Plattes A Discovery of Subterraneall Treasure (1639, p. 34)), we
read in the first part of chapter 8 dealing with gold the following
interesting discourse:


"And first, whereas it (gold) is oftentimes found in the sand in
Rivers, let no man thinke that it could be generated there, but that the
swift motion of the water from the high Mountaines, brought it thither,
with earth and altogether, till such time as the motion of the Water
grew more slow: and so according to its property, being not able to
carry forward still both the substances, did still carry the earth with
it, and let the heavier body sinke. Therefore I would have those that
have occasion to deale in the hot Countries where gold is usually
generated, to make triall in all such Rivers which runne from great
Mountains with a swift course in such places, where the motion of the
water beginneth to grow slow."



And later in the chapter (p. 36) we learn Plattes' views on the epigenetic origin of gold from subterranean vapors:



"Now whereas I have formerly affirmed that all mettals in general are
generated of the clammy and gluttenous part of the subterranean vapours,
arising from Bituminous and Sulphurous substances, kindled in the
bowells of the earth: it behooveth me to shew how gold, such a fixed
substance can be found pure of it selfe, and not mixed with other base
mettals.



And the reason of this can be no other, but because that all other
mettalls whatsoever will putrifie in the earth in length of time, and
turne to earth againe; but gold wil never putrifie by reason of his
excellent composition, being made of a Balsamick Sulphur or fatnes,
which is incombustible, and differeth from the Sulphure or fatnes
contained in the other mettals, even as naturall Balsome differeth from
all other oyles, and fat substances: so that though it be an oyle in
shew, yet it will sink in water, whereas all other oyles wil swimme upon
the top of the water...



Now whereas the substance of gold is not subject to putrifie in the
earth by any length of time, it is probable enough that other metalls
might be generated with it at the first, and afterward putrified and
consumed from it in length of time, leaving the gold pure...



And the reason why the hotter the Country is, the richer the Minerals
are, can be no other but the same, that roasted meates are sweeter than
boyled meates, or raw meates: the reason whereof is plaine, for that the
rawish and unsavory part is exhaled by the heate of the fire, leaving
the sweeter part behind.



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 Mat hewson (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 containe d 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:



"It is no wonder that, respecting the matter out of which Metals are
made, there should be such a variety of opinions among Persons
authorized to express them; for it would appear that, by a special
Providence, the Author of Nature wished to hide them in the Depth
wherein they were created, and in the hard Rocks which enclose them, in
order to place some Obstacle to human Ambition. Those who have risen to
the rank of Philosopher through the study of Causes, leave on one side
the raw material as a very remote Principle of Metals, as it is of all
the other corporeal things of the World, and indicate another, also very
remote, which is in part, a certain Humid and Unctuous Exhalation,
together with a certain portion of viscous and greasy Earth, from the
Mixture of which results both Metal and Stones. Thus, if dryness
predominates in the Mixture, Stone results; and if it has a greater
amount of Greasy Water in it, Metal results: this is maintained by
Plato, Aristotle and their followers. From the abundance of th is pure,
shiny Humidity is derived the Lustre of Metals, in which, among the
other elements, Water, as is well known, predominates; and thus they
flow and melt under the action of Heat. From the varied Temperament and
Force of the matter referred to is derived the Diversity of the metals,
of which the purest of all, and Nature's chief effort, is Gold."



Later in his treatise, Barba describes the geological and mineralogical
occurrence of gold in many parts of the Cordillera of South America. Of
the deposits of the Charcas district of Bolivia he says:



"There is no one who has not heard of Carabaya, which is a Region
famous for the abundance and purity of its Gold, its Metal being as fine
as the celebrated Gold of Arabia. It is Gold of twenty-three carats and
three grains. The quantity, which has been, and is still being
extracted, is incredible, although that which has been taken out so far
has been found by People who have looked for it only in the Rivers; only
now are they commencing to work the many rich Veins. Carabaya is
situated alongside of Larecaja, where auriferous Ores abound. In some of
the streams in those Parts, Gold is found in the Form and Colour of
small lead shot, which, when they have been melted, take the red Colour
of Gold, with but little loss through the disappearance of the Crust
which covered them when found. The man who discovered the Gold in this
form did not know what it was until he was enlightened by a Friend whom I
had advised of its true Nature. From Larecaja to Tipuani is a region
occupied by savage Indians, the same having been invaded over twenty
years ago by an Expedition sent to La Paz, I forming part thereof. There
so much Gold is found that the accounts of it would be incredible, were
it not for the many Witnesses who have seen it, and vouch for the fact.




The real name of the city of La Paz, Chaquiyapu, which we have
corrupted into Chuquiabo, means, in the native language of this Country
"Farm" or "Estate" of Gold. Many mine Workings exist there, dating from
the time of the Incas. It is a land well known to be fertile in Gold;
and, during the rainy Season boys find Nuggets in the Streets,
especially in that one which descends by the Monastery of the Dominicans
towards the river. In Coroyco, and other parts of the Andes of
Chuquiabo, there is Gold also in many ravines, grey on the outside like
Lead."



Finally, Barba gives many practical hints on how and where to prospect for gold veins; for instance:



"There is no sure or infallible rule which, without further experiment
or examination, will enable the particular kind of metal contained in a
hill to be determined simply by the Colour of the earth on the surface.
And thus, although the material in which Gold is found is most
frequently Red or dark Yellow, like to brick which has been very much
burnt, veins thereof are frequently found in white Calichal (White
Earth, Kaolin) as in Oruro and Chayanta."



Anyone who has seen the primary, and in places supergene, white and
yellow (clay mineral, alunitic, and propylitic) alteration and the
supergene red (limonitic) and yellow (arositic) oxidation products
associated with (Tertiary) gold deposits will recognize instantly the
value of these guides.



Late in the seventeenth century John Woodward (1665-1728), the English
physician, antiquarian, and collector of fossils, sought to explain the
features of the globe in terms of a flood (the universal Deluge)
released through fractures (perpendicular intervals) from inside the
earth in An Essay Toward a Natural History of the earth and Terrestrial
Bodies, Especially Minerals (1695) and later in The Natural History of
the Earth, Illustrated, Inlarged, and defended (1726). In that second

work, concerning the origin of mineral veins he states:



"Water takes up the particles of metall, which lay before loose, and
separate, in the interstices, and pores of the strata of stone, and
thence carries them into the perpendicular fissures of the strata."



Later Pryce (1778), after examining various theories of origin, explained the tin veins of Cornwall in the following way:



"From this we may reasonably infer, that water, in its passage through
the earth to the principal fissures, imbibes, together with the natural
acids and salts, the mineral and metallick particles, with which the
different strata are impregnated; and meeting, in those fissures,
matters which have nearer affinities with the acid, of course disengages
it, in whole or in part, from the metallick and mineral particles,
which it had held dissolved; and which, on being so disengaged, by the
natural attraction between its parts, forms different ores, more or less
homogeneous, and more or less rich, according to the different
mixtures, which the acid had held dissolved, and the nidus in which it
is deposited. The acid, now impregnated with a new matter, passes on;
till meeting with some other convenient nidus, it lodges in that, and
thereby acquires a fresh impregnation, perhaps at last totally
unmetallick; or, for want of meeting with a proper nidus, appears at the
surface, weakly or strongly tinctured with those pr inciples it had
last imbibed."



These are clearly statements of the lateral secretion theory; they
differ only in detail from the theory postulated by Agricola. Nils
Steensen (Nicholas Steno) (1638-1686), the Danish physician and
theologian, likewise espoused a lateral secretion theory. In his De
solido intra solidum naturaliter contento dissertationis prodromus
(1669) he disputed the Vulgar opinion and the Aristotelian and
alchemical notions about the origin of veins at Creation and
hypothesized that uplifting earth movements created clefts, fissures,
and interstices within the rocks in which mineral matter from the rocks
was precipitated. To quote Steno:



"It is more than probable that all those minerals which fill either the
clefts or expanded spaces of rocks had as their matter the vapour
forced from the rocks themselves... " (Winter, Hobbs, and White, 1968).



Rene Descartes (Renatus Cartesius) (1596-1650), the greatest of the
French philosophers of the seventeenth century, sought to geometrise all
nature. Writing in his Principia philosophiae (1644), he considered the
earth to be a cooled star, the crust of which had been chilled, leaving
a hot anterior. Below the crust he envisaged a metallic shell from
which were exhaled the mineral matters, including gold, that were
chilled and solidified in the faults and fissures in the disrupted outer
crust. It is interesting to observe that these ideas still have some
adherents. The widespread concept that the earth is composed of various
shells (crust, mantle, iron core, etc.) has a similar basis. Likewise,
the idea that some of these shells are sulphidic and metallic and give
rise to mineral deposits has been postulated in recent years,
principally by J. S. Brown in his Ore Genesis, a Metallurgical
Interpretation (1948) and by Quiring (1954), who advocates a gaseous and
liquid ascent of sulphides from a deep sulphide she ll (chalcosphere).



Germany, particularly the region of the Erzgebirge, was the site of
intensive mining during the eighteenth century. Most of the deposits
were veins, and the origin of the fractures in which they occur and the
derivation of their mineral content was the subject of much speculation
among the mining geologists of the time. Much of this speculation was
centred at Freiberg (in Saxony), which later was the site of the
founding of the world famous Bergakademie (1765), among whose celebrated
scholars and students may be mentioned Abraham Gottlob Werner,
Alexander von Humboldt, and Mikhail V. Lomonosov. Only a brief summary
of the various speculations on the origin of veins by a few of the
German mining geologists are considered here, more or less in
chronological order. Henckel (1725, 1727) wrote that mineral veins were
derived from emanations (vapours) derived from three sources:



(1) saline and sulphurous waters arising from deep sources within the
earth, the vapours from these waters having been partly derived from
oceanic water that had gained access to the central fires, was
vaporized, and expelled toward the surface

(2) from various bodies disseminated in the earth's crust, which upon
commingling reacted and yielded vapours that produced the metallic
minerals; and

(3) from the whitening or exhalations of certain minerals already in
existence within the earth, such as pyrite, which when exposed to
oxidation becomes hot and gives off fumes.



One can see in the three sources postulated by this theory the germs of
certain modern concepts concerning the origin of certain types of gold
deposits:



(1) the idea of recycled oceanic and meteoric water as the source of
hydrothermal solutions, particularly with respect to certain Tertiary
(epithermal) gold deposits,

(2) metamorphic secretion, and

(3) oxidation and secondary enrichment.



C. E Zimmerman (1746), a student of Henckel, anticipated the concepts
of metasomatism and replacement and the nineteenth century view of
lateral secretion when he postulated that mineral veins were formed by
the transformation of the rocks enclosing them. His theory was based on
accurate observations of the alteration of the country rocks along
fissures and the complete change of the mineral constituents of the host
rock and their partial replacement by ore and gangue minerals.



A little later Von Oppel (1749) clearly recognized the fundamental
difference between veins and bedded ore deposits. He also emphasized
that veins are localized by structures such as fissures and faults
formed by the desiccation of soft sedimentary rocks or by movements in
the earth's crust, and that these structures existed prior to the
formation of the mineral veins and have definite structural patterns.



Lehmann (1753, 1756) at the middle of the century hypothesized that
vein minerals were deposited in fissures by vapours and exhalations from
the earth's interior, a view similar to that advocated a century
earlier by Descartes. Lehmann further considered veins to be comparable
to the branches of a tree, the roots of which were deeply embedded in
the core of the earth ("The Golden Tree"). Finally, he held that certain
locales and conditions in the earth were more susceptible to
metallization than others; these locales were referred to as the
matrices or wombs of the metals by his predecessors and contemporaries.
He called them the "mothers of metals" or Metalmzittern. This concept is
the first intimation in the literature on mineral deposits about what
we now call metallogenic provinces.



Later in the eighteenth century, C. T. Delius (1770, 1773) denounced
the alchemists for their fantastic theories, inveighed against Lehmann's
metalmzttern theory, and advocated a lateral secretion mechanism for
the concentration of metals in veins, stating that meteoric water heated
by the sun's rays within the rocks was the collector of sparsely
disseminated mineral matter from the country rocks.



Carl Gerhard (1781) held similar ideas but omitted the effect of the
sun. Delius held some unusual views about the continuation of gold veins
at depth. Noting that those of the Siebenburger are rarely auriferous
below about 100 m he concluded that the sun's heat could not penetrate
below this depth, and thus a mechanism for mobilizing the gold from the
enclosing rocks was absent. Delius was, however, an astute observer and
recognized the surface alteration of vein deposits, the development of
gossans, and the formation of a zone of secondary enrichment under
favourable circumstances. He thought these phenomena were due to the
"burning action" of the sun, an incorrect interpretation, and it was not
until early in the present century that the processes of secondary
enrichment were understood and worked out satisfactorily. In Delius's
zonation scheme gossanous material marked by the copper minerals azurite
and malachite, was followed downward by zones respectively rich in
gold, silver, and finally lead, each me tal requiring in turn with depth
less heat from the sun to develop.



During the closing years of the eighteenth century, the effects of
metamorphism seem to have impressed certain writers. Among these were
Charpentier, a professor of mining at Freiberg, and Von Treba, a mining
official of Brunswick, who explained vein deposits as due to Gdhrung
(fermentation) and Faulniss (decomposition) or metamorphism of the
country rocks. Charpentier (1778, 1799), basing his theory on
observations made on the veins of Saxony, conjectured that solutions or
vapours migrating through the rock along minute fissures and cracks had
effected changes in them, developing new minerals and changing strips of
the country rock into veins. Von Treba (1785) held similar views and
thought that veins were simply one of the manifestations of the
processes that changed sediments into schists and gneisses, shales to
slate, and gneisses to granite. These early writers made the first
attempts to explain the relationship of vein deposits to metamorphic
processes. Daubrae (1879) and T. Sterry Hunt (1873a, 1873b, 1897) added
significantly to this concept at a later date, but most investigators
that followed, especially those writing on the magmatic hydrothermal
theory, neglected the important part metamorphism plays in the
concentration of the elements in veins and replacement deposits.



References and selected bibliography

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