ON GOLD AND ITS PRECIPITATION IN QUARTZOSE AND OTHER ROCKS.

Thames Guardian and Mining Record, Volume I, Issue 87, 19 January 1872, Page 3

ON GOLD AND ITS PRECIPITATION IN QUARTZOSE AND OTHER ROCKS.

Tub various theories put forward respecting the origin of gold in quartz veins arc (some of them) ingenious—cacli theory has its believers, just as every candidate for parliamentary honours ; and although they may not enable us to discover large quantities of the precious metal, may yet aid us as stepping-stones towards the truth.

As the most favourite theory of the origin of gold in quartz veins is the 1 igneous’ one, or the upheaval of the gold and quartz whilst both arc in a molten state, and that, therefore, the gold must have existed in the metallic form in the interior of the earth, I will endeavour to show why I think such a theory is unsatisfactory, and opposed to the wellknown laws of gravity.

We hare no direct means of ascertaining the thickness of the earth’s crust, hut assume that it is about 200 miles. Let me take only half that distance, which by-the-by, if true, would make us feel rather uncomfortable—and suppose that at the depth of 100 miles there is an immense mass of liquid scorhc or quartz ; that this has for some time lain in a comparative state of quiescence, until some great volcanic commotion takes place and exerts a pressure from beneath this fluid mass, sufficient to force it upwards through the clefts and crevices of (lie surrounding solidified strata. After a long period this once melted matter congeals and cools. The paits nearest the surface of the eaith and subjected to the influences of the atmosphere and probably watery vapour, solidify and cools perhaps centuries before the portions at greater depths. The gold is supposed to have been ejected simultaneously with the substances composing the reef or quartz vein. My objections to this theory are : 1. That previous to the upheaval, and while the fluid mass was comparatively quiet, if the gold existed in a metallic form, it must have been done so at tho veiy bottom of the cauldron, owing to its greater specilic gravity, which is, say 10, quartz being, say 3. 2. Allowing that the liquid was in a state of ebullition') the great difference in weight would prevent much gold bubbling up near the surface of the lava. 3. That even admitting the gold to have been forced, simultaneously with the quartz, to the very surface of the earth, a long time would elapse before the liquid would congeal; and large masses of gold would rapidly fall through it as soon as the upheaving force ceased to have effect, while the similar particles of the metal would, by molecular attraction, become formed into globules which would every moment increase their size and weight, and tend to hasten their descent immediately after thoir ‘ logger brothers.’ 4. That if the gold were forced up in a ‘ metallic’ form, and such a long time had elapsed before the congealing of the quartz, the deeper we now go into those quartz reefs the less gold wc shall find, because the deeper parts lay longer in a fusion, thereby allowing greater time for a more complete precipitation of the metal.

5. That the gold during its precipitation, is impeded by tiie semi-solidification of the quartz, would he found in globular, semi-globular, and more frequently in pear-shaped masses, and would not bear that rugged and hackly appearance in which we now procure it. Ij. That as quartz veins have generally an inclined position, with foot and hanging walls, the gold during its precipitation would fall ‘perpendicularly,’ and he discovered only in the irregularities ments, and crevices cu th» ‘ * a , jUt- , root wall.’

It may he urged in favour of the popular theory that the immense quantities of gold found in the alluvium proves its correctness, and the molten river had overflowed its hanks, and that whatever portions ot gold had thus gone over with it could not again he precipitated through the reef. This would be perfectly correct if such an overflow had taken place retaining within it ‘ metallic gold.’ It is very probable that what now appeers to he as the surface of the lodes, reefs, or mineral veins were at a very remote place considerably below tho “ then surface. The slow hut sure decomposition of the rocks, and subsequent disintegrations and abrasions, have worn them away to a great extent, and which has resulted in the debris which we find in the gullies and lower adjacent lands. The gold found in such situations has a warer-worn appearance, which does not depend in the slightest degree on the manner in which it was ‘ originally’ deposited in the veins. Supposing the reef to have overflown, at the surface of the earth’s crust, bringing with it gold in a metallic state, we should find at present gold only in that portion which had overflown, and which lias been since carried to a greater or less distance Ilian its outlet.

The liquefaction of that portion which would be left in the main channel would continue for a period long enough for the complete precipitation of all its gold. As an illustration :—lf it were possiblo to force a large quantity of ‘slag,’ or melted scoria;, of specific gravity 3, containing one ton of gold of specific gravity lfi, up through a large, cupola or chimney 100 feet in height, and when the uppermost portions had reached the summit of the chimney allow some to run over, then restrain the ejected force so that the melted matter should entirely fill the chimney, allow it “ only one hour” to become congealed and cooled, I would not give £s'for all the gold that could be f ound above the first twenty feet of the chimney. Possibly some may have fallen over the top, hut it would only he very light particles. Wc will suppose that we can manufacgelatinous fluid, which shall hear the same proportionate specific gravity of quicksilver that melted quartz does to metallic gold. Let a column 200 feet in height he filled from a receptacle at the bottom, and the power that we apply shall be sufficient to force up a lot of quicksilver simultaneously with the liquid. Give it time to become a solid, and how much quicksilver would he found from the height of twenty feet to the top of the column ?

Wc must not suppose that tho gold, if it did exist in the bowels of the earth in a “ melted metallic ” form, was shot up through the other liquids like a hall from a cannon. I will even go so far as to allow that such a thing has been done; those golden halls would have precipitated long before tho solidification of the other materials.

1 have attempted to explain my reasons for opposing the popular theory, principally on the grounds of the difference of specific gravity, and, with all respect for the opinions of others, cannot admit that a lot of ‘ melted metallic ’ gold was kept in stock somewhere below, waiting until the throes of nature troubled her, and she would vomit forth to the surface of the globe. It may now he very naturally asked if, after giving my opinions in opposition to this theory, I can bring forward another which is more feasible and satisfactory. I will endeavour to do so in as concise a manner as possible. I believe that the gold docs not exist in tho interior of the earth as metallic gold, but chiefly as a 1 sulphide of gold,’ and that it lias been forced up in that form from the bottom, gradually losing its sulphur as it approached the surface. Portions of it would become deposited in the crevices and interstices of the heated rock in the form of a powder entirely free from sulphur, and would by heat and pressure he formed into metallic gold. Other portions would he acted on by chlorine (which I consider to he the great natural solvent of gold), and ascending in combination with its dense vapours, find their way through every crevice, and he deposited in the form of a sublimate. It would remain in that condition until the mass of lava had cooled ; then, when water had taken the place previously held by heat, and began to percolate through the vein, these sublimates or chlorides would be dissolved, to he again precipitated by the salts of iron, sulphuretted hydrogen, and other reagents, not forgetting the electro-magnetic currents. No other metal gives up its sulphur more readily than gold. It does not require the time or intense heat which is necessary to some of the other sulphides, and I consider ‘ that’ fact to be the reason why we do not find the sulphides of gold nearer the surface. I believe that at great depths they may exist. The various solvents and reagents necessary to carry on this great chemical experiment are known to exist in enormous quantities in the depths of the earth’s crust. Chlorine would he generated by the sudden inroad of seawater into the" boiling lake, and is probably the cause of those fearful upheavals of lava. Sulphuretted hydrogen and the salts of iron would he generated and formed by the decomposition of the sulphides. It has been generally believed that gold does not enter into combination with sulphur, oxygen, and other substances, which would form it intp ores.

But if compounds of these substances can be made by the chemist in his laboratory, I dot not'see why the same process may not have been carried on in nature, or that the sublimations, solutions, precipitations, and reductions arc not even ‘now’ doing their work. Some compounds of gold aie rapidly decomposed and become metallic by the influence of light. May not such substances have become deposited on the surface of mineral, veins before ‘ light was,’ and have subsequently by light, heat, electro-galvf.nic currents, and pressure, assumed the form of golden nuggets,dust, and spangles ? It must be remembered that those immense manipulations have had probably tens of thousands of years for thoir completion ; and if a chemist in his den can succeed with the aid of a few reagents in forming the sulphides, phosphides, oxides, and chlorides of gold; or can show that two or more of these substances have an affinity for each other, although only infinitesimal, then he may rest assured that nature is conducting the same experiments on a grander scale. She has only allowed us to have jrlimpses of her morlus vperandi, and has lent us a few tiny morsels of reagents and fluxes from her great storehouse, to enable us by great study and sciuntilic research to discover for ourselves her hidden mysteries, so that we may contribute our mites towards the consummation of the happiness of - humanity. —Town and Count- i ,oor Jan. 6. Journal, \ I