As a mineral processing engineer, you sure know that it is necessary to draw the gold into wire in order to make gold cloth, gold embroidery, or gold filigree work. Just as it is beaten to form leaf for ornamenting pictures, so also can gold be drawn easily. The same is done with silver and tin, and I believe it could also be done with iron, copper, and brass. Although brass is not so. A description and excellent illustration of this process of casting plates on an inclined bed is given. A rolling mill for the plates is also shown. Most later descriptions of the casting of lead sheets make the bed horizontal and the crosspiece a mere skimmer.
A varnish colored yellow with saffron or otherwise soft as the others, it is seen to spread out and become thin by much hammering, and, because it has a shadow of resemblance to the color of gold, those thin and resonant leaves are made from it that are commonly called tinsel.
In short, wire is drawn of every metal, excepting tin and lead, because of the need of strong bindings which must enter the fire while bound. It can be made in any thinness and length that the craftsman wishes, especially that which is made of gold and silver and which is so long and thin that it is woven into cloth for dresses just like linen and wool, and is embroidered in the company of silk with no distinction.

Goldsmiths also draw gold into wire to make the ornamentation of their works easy and more attractive. These works, brought together and soldered well, are those which are commonly called filigree, whether they be of silver or gold. Brass and steel, which [139^] are stronger things, are also drawn into wires to make strings for musical instruments, as fine or as thick as pleases the one who uses them. To sum up, I do not know that there is in all this work anything notable but a certain experience and great patience.
In this, two procedures are followed. One is drawing with a heavy capstan with a windlass, and the other is with a little drum worked by hand, after having first reduced the bar under the hammer as round and as long as possible. Then it must be annealed and, when annealed, it is usually taken to a small horizontal windlass fitted into a frame, or to [a machine] with the force of a screw, or else a large windlass pivoted vertically. On any of these or other drawing machines the steel drawplates are arranged in firmly fixed blocks of wood. The plates are a haifpalmo long with several rows of holes of successive sizes. In addition, a pair of large tongs with flat, serrated mouths and open legs are needed. These should be held by a stirrup-shaped iron ring which has a hook at the foot to which is attached the end of a belt or rope, the rest of which is wrapped around the small windlass or the large one by turning. In this way the tongs close when you pull them and in that instant take hold of the tip of the ends of the gold or silver wire, which has been,well greased with new wax and put by the craftsman into one of those holes of the drawplate. Then by turning the levers of these instruments with the force of men, the little bars of the said metals are pulled and caused to pass through all the holes of the drawplate one by one.

Since the large instruments do not serve well when the wire has been reduced to a certain point, two drums are pivoted horizontally on a bench and the drawplate is fixed between these two, with little holes of successive sizes so as to make the wire ever finer. By turning one of these drums the desired quantity of wire is wound, passed through the draw- plate, and attached to the other roller. The plate is reversed and the wire put in another hole. Thus, from one hole to another, turning now one drum and now the other, the wire is made to become very fine, always keeping it properly taut so that it may not tangle. When it has been made thus, it is put on other spools. Remember that while you are working it you must always keep it greased with new wax, for besides easing its passage through the holes, this also keeps its color yellow and beautiful.

Finally, in my opinion, this art consists of two things. One is in preparing the drawplates well so that their holes may be kept round. They should be of good and very fine steel. The other is that the gold and silver that you wish to draw be fine, of a soft nature, and that it be kept well annealed to the degree where it can be put on the drum by hand at the start. This method is also followed in drawing every other metal, that is, steel, brass, iron, and copper, but I shall tell you more of iron in detail farther on.

[140] Concerning this drawing of gold and silver I wish to tell you how it is customary to proceed today in almost all works in order to effect a saving of the quautity of gold that would enter the materials that are woven, or in order to alter it for fraud. This wire is also fabricated so that it appears to be all fine gold and actually is almost all silver, for the weight of only one ducat of fine gold is put in every pound; and some, desirous of greater fraud, make the core not even of fine silver but of copper, and gild it. Briefly, to do this a cast bar of copper or fine silver is made, then beaten and made round by the hammer. It should be three-quarters of a braccio long or less. After being well filed and cleaned, a covering of fine ham¬mered gold is soldered over it (or if it is copper you can make this covering of silver) in that quantity by weight that you wish to put on. Solder it on a little furnace with charcoal and with flames of elder, almost bring¬ing it to a melt before rubbing it with a dry stick, as is customary, or with chalcedony or bloodstone so that the applied covering may spread out all over it and everywhere come in contact with the thing with which it is to be soldered. Then it is cooled, annealed again, hammered thin, and it is ready to be put in the drawplate so that you may proceed as I told you above. Certainly if it is not done for fraud, this process is a beautiful thing in this art and worthy of great consideration, especially since the gold that is applied thins out over the thing to which it is soldered and never reveals it on the outside. The wire may be drawn out so fine that the eye can scarcely perceive it, yet it is always very well gilded all over.

This is all concerning the making of wire in which gold or silver is involved, and that of all the others except heavy iron is included in the one demonstrated here. For iron a water-wheel mechanism is built. At the end of a journal there is a bent iron with a ring that has a hook to which a band is attached with a slip knot. A short distance away a block of wood with the drawplate is fixed in the ground. Between the block and the wheel a pit is made in the ground to the depth of a man’s knee. The operator stands in this pit with a pair of large tongs with an iron stirrup, attached to the band, which holds the legs of the tongs so that they close when it is pulled and open when it is released. Letting the water run the wheel, the man, who has tied the band in the middle of the bent axle, lets himself be drawn backwards and then pushes forward. His only care is to seize with the jaws of the tongs die end of the wire that issues from the drawplate with every return that he makes. He sits in the said pit on a board attached at the ends to a beam with two long irons which hold him swinging, so that he moves back and forth as the wheel pushes or pulls and can take hold with the tongs. With this construction iron can be drawn out to any desired length and thickness, if it is annealed often, and also gold, silver, and copper.

In addition to this method, I have seen iron drawn out without a water- wheel mechanism. This other way used horizontal drums, as I told you is done with gold, but for this it is necessary to have the iron very greatly thinned and well annealed. The same could be done with a large wheel for turning it, and if one did not have water it could be done with the motion of a reel or with a horse or man who could move it by walking inside, or with counterweights or other levers that have force. Let what' has been told you of this art suffice.

The earliest metallurgical process for treating silver ores was amalgamation with mercury which was in use in the early 1500's. Closely following was the development of the Patio process for treating ores at Pachuca, Mexico.

Silver often occurs as the native metal and in deposits associated with other metals such as gold, copper, lead and zinc. Principal silver minerals include compounds of sulfur, antimony, arsenic, and copper. Silver chloride, and argentiferous galena are also prime sources.

Native silver and the chloride characterize the oxide zone of most deposits. Native silver can be concentrated, amalgamated, or cyanided. Silver chloride rapidly dissolves in cyanide without oxygen. Oxidized silver ores containing the higher oxides of manganese are generally refractory to metallurgical treatment. A refractory compound of manganese and silver is formed, probably a manganite, which is insoluble in cyanide solutions.

Argentite is the predominant silver mineral. Other important economic minerals are native silver, argentiferous galena, cerargyrite, pyrargyrite and tetrahedrite. Argentite dissolves slowly, the reaction being reversible requires an excess of cyanide. Argentite with disseminated fine grained gold occurring in quartz veins with minor amounts of chalcopyrite and galena may be cyanided directly after grinding, with high silver and gold recoveries. The flowsheet adapted to this type of ore is the Minas de San Luis, Tayoltita cyanide plant, which treats a high grade argentite silver ore containing gold. It is a standard cyanidation circuit but employs long periods of agitation contact for the high silver sulfide content ore.

Lead-zinc base metal semi-oxidized-complex ores in pipes and chimneys are replacement deposits in limestone at El Mochito Mine, Honduras. Mineralization comprises galena, cerussite, anglesite, sphalerite, calamine, and smithsonite. The silver content of about 16 ounces occurs as native silver globs, wire and the mineral argentite. After flotation of lead and zinc concentrates, the tailings are cyanided for gold and silver recovery.

The great Huelva pyritic copper deposits of Spain carry a little gold and silver. At Cerro Colorado, these metals were concentrated above the chalcocite zone into the so-labeled "gossan". This material with a content of 0. 08-0. 09 oz Au and 1.50 oz Ag per ton is amenable to cyanidation.

See Cerro Colorado flowsheet.

In southern Hidalgo, about 60 miles north of Mexico City, are the great silver--gold veins of one of the foremost silver mining districts of the world. Real del Monte, Pachuca. The mineralized area consists of flow rocks and intrusives. The oxidized ores carry pyrites with oxides of iron and manganese and other minerals, silver and gold. The first zone contains auriferous iron oxide, chlorides, and bromides of silver. These ores can be cyanided directly. The lower zone contains pyrite, galena, sphalerite, argentite, and chalcopyrite. The Del Monte flowsheet uses selective flotation to produce a lead, zinc, and pyrite concentrate. The tailings are cyanided.
​

Following the native metal, the tellurides are the most important gold minerals. The tellurides include calaverite and krennerite which contain about 40 percent gold, and sylvanite and hessite with about 25 percent.

The Kalgoorlie, Australian, ores contain free gold and tellurides which occur in Pre-Cambrian rock consisting essentially of schists and quartz-dolerite-greenstones. Auriferous pyrite is also present and the gold is occasionally associated with chalcopyrite, tetrahedrite and arsenopyrite.

The gold in the pyrite is finely divided and requires grinding to about 75 percent passing 200 mesh. The ground product is floated and the concentrate, after cyanidation and filtration, is roasted and recyanided. Flotation tailings are also cyanided.

The ores of the Emperor Mine in Fiji contain gold associated with the telluride minerals sylvanite and hessite. A chemical oxidation step is used in place of roasting to liberate the gold for cyanidation.

Gold with Copper Minerals

Gold is often associated with chalcopyrite in porphyry deposits. When recovered into the copper concentrate, it travels through the smelter and to the refinery where it reports with the anode slimes from electrolytic refining and is subsequently recovered as gold bullion. Gold losses in copper concentrating are about the same as for copper, but are negligible in smelting and refining. Gold occurring in pyrite associated with chalco-pyrite can sometimes be separated by flotation into an auriferous pyritic concentrate for cyanidation as at Benguet Exploration. At the Itogon Suyoc, Palidan Mill, the auriferous pyrite and chalcopyrite are recovered into a bulk flotation concentrate which is then separated into two flotation products; a pyrite concentrate for cyanidation of the gold and a copper concentrate for shipment to a smelter.

At San Manuel, Arizona, the gold follows the molybdenite and this concentrate is treated by a standard type of cyanidation flowsheet.

Gold with Lead and Zinc Minerals

Gold occurring with lead-zinc sulfide ores or copper-lead-zinc ores usually is recovered into the flotation concentrates and shipped to a smelter where gold recovery is high, particularly at lead smelters. Occasionally, free gold may be recovered by amalgamating the concentrate from a jig in the grinding circuit. Gold contained in the flotation tailing is recovered by cyanidation as any residual galena or sphalerite is not harmful to cyanidation.

In this ore classification, the gold occurs both in the free state and disseminated in the sulfides. (Pyrite is found to some degree in most of the world's gold deposits. ) Sulfides tend to decompose in cyanide solutions. Pyrite is the most stable but when pyrrhotite is present trouble is usually experienced both in regard to cyanide consumption and gold extraction. Pyritic flotation concentrates are often reground for gold liberation before cyanidation as at Itogon-Suyoc Itogon, and Pamour. After fine grinding, long periods of agitation are often required to dissolve the gold. Gold-bearing pyrite concentrates are sometimes roasted and cyanided in separate circuits as at Kerr Addison. Also, high grade gold-pyrite flotation concentrates can be shipped to the smelter as is Knob Hill practice. Pyrite and pyrrhotite often occur together creating an overlap in treatment methods.

Gold with Pyrrhotite

Pyrrhotite readily reacts with cyanide to form cyanates and thiocyanates and it readily consumes oxygen. Aeration with lime ahead of cyanidation is usually used on ores in this classification. Aeration for preconditioning is used at Dome, Homestake, Kerr-Addison, and Pamour.

Gold with Arsenopyrite - Arsenic Minerals

Gold is occasionally associated with arsenic minerals as well as pyrite, stibnite, chalcopyrite, etc. Direct cyanidation in these cases is seldom possible. Additionally, when gold is associated with readily soluble arsenic compounds, there is the hazard, in precipitation, of forming arsine, AsH3. In plants where this extremely toxic gas is evolved, special ventilation techniques are required.

Giant Yellowknife produces a refractory flotation concentrate carrying gold in association with arsenopyrite, stibnite, and sulphantimonides of copper, lead and iron. Roasting liberates the sulfide-enclosed gold allowing the calcine to undergo conventional cyanidation. Campbell Red Lake roasts a flotation concentrate ahead of cyanidation.

The properties of gold in ores from the standpoint of recovery are its extremely high specific gravity (15.5 to 19. 3 depending upon amount of alloying metal admixed); the fact that mercury wets it readily in the presence of water (amalgamation); its solubility in dilute aqueous solutions of alkaline cyanides to form relatively stable compounds of the form NaAu(CN)2; and its response, particularly as naturally alloyed, to flotation collectors.

Native Gold Ores

Free milling lode ores are those in which the gold is relatively coarse and amalgamable, the sulfide content is low and nonarsenical, oxidized compounds of bismuth and antimony are absent, and the gangue is substantially free from talc, clay and graphitic constituents. With these ores, there are advantages in extracting as much free gold as possible in the grinding circuit by gravity concentration. Concentration of free gold by gravity is a relatively simple method of recovery and when used in cyanide plants is applied ahead of cyanidation. On lode gold ores, launder traps, hydraulic traps or pulsating jigs are sometimes used in the grinding circuits for recovery of as much as 60 percent of the total gold in the mill feed. The jig hutch product may be continuously discharged onto a shaking riffled table with the concentrate fed in batches to barrel amalgamation. Homestake recovers 20 to 25 percent of the gold in launder traps. Other recovery methods have not been successful because of cable splinters, blasting wire, etc. , in the ore. Woolen blankets have long been used for trapping fine gold particles and particularly for tellurides. Blankets are generally laid overlapping on wide inclined tables.

​From this practice of using blankets came the development of corduroy to entrap gold and a South African version of corduroy is sheet rubber having "V" shaped riffles molded into its surface. The Johnson concentrator, an inclined rotating cylinder, the plane tables, and belt concentrators are lined with this material.

Amalgamation depends upon the wetting and alloying of metallic gold with mercury. Direct amalgamation in which the entire ore stream flows over mercury-covered copper plates has now been generally abandoned to prevent stream pollution. It has been replaced by a concentration step which subjects only a relatively small quantity of high grade concentrate to barrel amalgamation. This method eliminates the tedious cleaning and recoating of the copper plates and reduces the chances for loss through theft. The gravity concentrate is ground for several hours in a small mill or barrel with steel balls or rods before the mercury is added. This form of amalgamation is the simplest and most common method of treating an enriched gold-bearing concentrate. Examples of free gold concentration and amalgamation are shown in the flowsheets of Dome, Homestake, Itogon-Suyoc Palidan, Kalgoorlie, Campbell Red Lake, Blyvooruitzicht, and Vaal Reefs.

Following the recovery of the coarser free gold particles by gravity and barrel amalgamation, the grinding of the ore in cyanide solution with ball or pebble mills is generally practiced. Separate cyanidation of sand and slimes has diminished with the development of closed-circuit fine grinding for "all-slime11 treatment by agitation.

Other Free Milling Ores

Gold mineralization in these ores may occur in a limey siltstone containing intermittent shale beds. Sulfides are seldom seen, but pyrite, galena, sphalerite, chalcopyrite, antimony, mercury and arsenic occur in minute amounts. Gold occurring in micron size is readily amenable to cyanidation as at Carlin and Cortez. Other free milling ores are Benguet, Camflo, Kinross, Kloof, and the new Pueblo Viejo.