A mining enterprise where the ores were composed principally of iron pyrites (much decomposed), in a quartz matrix, with native gold in very irregular grains. Some portions, however, carried their metallic value in a matrix of calcite and siderite. The mill in which the ores were treated consisted of two 800-lb. stamps, two amalgamating-plates, four pans, two automatic washers, two Frue vanners, and the necessary accessories for assaying, retorting and refining gold. The plant, originally erected with American capital, and directed by competent Americans, passed into the hands of Mexican owners. On taking charge of the business I found on hand a large amount of ore assaying 35 grammes of gold per metric ton (about 1 oz. Troy per ton of 2000 lbs.); but the company was losing money, and was about to abandon the business.
Obviously, the difficulty lay in the treatment of the ore. The extraction of gold scarcely reached one-tenth of the assay-value ; the loss of mercury was considerable; and high freight-charges excluded the alternative of exporting the ores.
This situation naturally suggested that amalgamation was not applicable to these ores, and that a more appropriate method must be adopted.
The cyanide- and chlorination-methods had been tried already, without practically satisfactory results. For the first few months I employed a combined system, extracting a part of the gold by direct amalgamation, and cyaniding the concentrates. This saved 32 per cent, of the assay-value, but the cost of milling still exceeded the proceeds. Meanwhile I observed that on certain occasions during the amalgamation there was a very perceptible escape of hydrogen sulphide. This I could not satisfactorily explain; but, on the other hand, it accounted for the great loss of mercury which had made amalgamation so expensive and ineffective.
To remedy this (and also diminish the great quantity of cyanide of potassium that had to be used, especially when the gangue of the mineral was calcite), I began with a reverberatory roasting of the crude ore delivered to the mill, and a subsequent washing with water, until the latter came off perfectly clear. The operations of amalgamation, concentration and cyaniding were then performed as before, and the result was a gold-extraction of 63 per cent, of the assay-value, with a loss of 11 per cent, of the mercury used.
This loss surprised me; nevertheless, under these conditions the milling of the ores began to be remunerative, and I could afford to study the subject with more leisure and less anxiety. On further investigation, the gold which had escaped amalgamation was found to be in a peculiar state of aggregation, reminding one strongly of the “ platinum sponge ” in its tendency to condense some gases. I think that the gold could be found there in another form also, analogous to so-called “ black platinum.”
Once this fact was discovered, the explanation of the previous phenomena was not difficult. The very finely-divided sponge and black gold, coming into contact with the mercury, provoked an energetic electro-chemical action; and this decomposed a relatively large quantity of water, the oxygen of which was absorbed by the sponge, while the hydrogen, combining with the sulphur of the pyrite, produced hydrogen sulphide. Of the latter, a part escaped as free gas, and a part attacked the mercury, producing mercury sulphide, which explains the great loss of that metal.
Of course the actual reactions are much more complicated than this rough statement; but the principal result, the formation of mercury sulphide, has been conclusively proved by analysis. The loss of the gold is also explained, whenever the sponge or the black gold is present under such conditions as to operate like the electro-positive element of an electric couple ; that is to say, when it will receive, condense and hold oxygen, and be returned by the electro-negative element of the couple in question.
The investigation was continued, to find a method of treatment which would both reduce the loss of mercury and increase the extraction of gold. Since the gold occurred in the gangue in grains of varying size, sometimes, but not always, impalpable, it seemed impossible to dispense with amalgamation entirely. On the other hand, a subsequent cyaniding was impaired by the foregoing pulverizing with stamps, which gave a large amount of slimes, through which it was difficult to pass the cyanide solutions. Moreover, these solutions were immediately transformed into carbonates and ammonia salts, and the consumption of cyanide was excessive. Treatment with chlorine was also difficult, and by neither of the two methods was I able, in my laboratory experiments, to obtain more than 40 per cent, of the assay-value.
I resolved, therefore, to continue experimentally the amalgamation, supplemented at first with cyaniding, and prefaced with roasting, as above described. Having abundance of hydraulic power, I began the use, with certain modifications, of the Siemens and Halske method of precipitating the gold. This increased by 15 per cent, of the assay-value the extraction of gold, and also reduced the expense of treatment. Precipitation with zinc was therefore abandoned. The increased extraction was undoubtedly occasioned by the employment of the electric current, since the treatment had not been otherwise modified, and the average composition of the ores had not changed. A comparative experiment, in which a given lot of concentrates was cyanided, and one part was treated with zinc-precipitation, and the other with the electric current instead, entirely confirmed this hypothesis. In the first case 60 per cent., and in the second 66.30 per cent, of the assay-value was obtained.
The examination of various works on electro-metallurgy and electricity furnished me with little or nothing in the way of further guidance, except certain hints as to the movements of bodies and substances in solution, produced by the electric current, and the irregular decomposition of the electrodes, which seemed to indicate the key to the problem. Without recapitulating here the statements of Parret, Becquerel, De la Hive, Wiedemann, Jurgensen, Quincke, Herschel, and Nobilli, I will simply say that their investigations, together with my own experience, led me to attempt the treatment of the ores in question by amalgamation only, with the aid of the electric current.
Before devising a process of my own, however, I tried those of Body, B. C. Moloy, and others, without satisfactory results. Finally, after some experiment and change in my first apparatus, I perfected a method by which the loss of mercury was reduced to 0.08 per cent., and the extraction of gold brought up to 95 per cent, of the assay-value, while the cost of treatment was lowered until it only amounted to $0.42 per ton for crushing, and $0.19 for amalgamation and the electric current.
At first, this method consisted in reverberatory roasting of the ore and washing abundantly with water, then passing it through the mortars, where it was pulverized and began to amalgamate. The mortars were provided with interior amalgamating-plates, in communication with the poles of a dynamo that produced a current of 150 amperes, 14 volts. The two stamp-batteries discharged into a common channel, in which; side by side, were placed the large amalgamating-plates, one communicating with the positive pole, the other with the negative. This arrangement gave encouraging results; but in view of the energetic decomposition of water which attended it, the electro-motive power was diminished by subdividing the amalgamation-plates and uniting them, not in series, but in tension. This produced the much-desired result. The liberation of gases diminished considerably, and the loss of mercury became insignificant.
Similar dispositions were made for the pans and the washers. Over the wooden shoes were placed amalgamating-plates 2 decim. square, and on the side-walls of the buckets similar plates 0.5 m. square, united, in tension, with the poles of the dynamos, in such a manner that the electro-motive power would not exceed 1.5 volts. Later, the aggregate surface of the plates was enlarged to some 15 m. square, which gave the best results. A further increase of surface would have been useless.
On an average, 9 tons of ore were treated every 24 hours; the extraction of gold was 94 per cent., and the loss of mercury was insignificant.
Still later experiments led to the abandonment of the preliminary roasting of the ore; and this resulted in the maximum gold-extraction of 95 per cent, of the assay-value.
The Patio Process
Subsequently, I had occasion to occupy myself with the treatment of ores by the patio process. The ores consisted of a quartz mass, carrying a mixture in variable proportions of miargyrite, polybasite, silver-glance, pyrites, oxides of iron and manganese, and finally some native silver and calcite; zinc-blende was occasionally present.
The plant comprised 50 stamps of 850 lbs.; 30 arrastres; 4 mechanical washers; a patio (yard) with a capacity of 1360 tons; and corresponding apparatus, operated by abundant hydraulic power.
All the theories known to me regarding the reactions of the patio process are inconsistent with the phenomena observed in practice. As a consequence, the process, empirically, and more or less ignorantly, performed, has often been unfairly discarded by reason of failures due in reality, not to its principles, but to its improper application.
Frederick Sonneschmid, who was sent to Mexico by Charles III. of Spain, with the idea of introducing there the German methods of treating silver-ores, did not hesitate to report that the patio process was superior to the barrel-amalgamation developed by Born and his successors.
The theory of Sonneschmid, based upon twelve years of practice in Mexico, may be stated as follows :
Sonneschmid assumed that the magistral, in which he regarded the copper sulphate as the chief operative reagent, liberated from the salt hydrochloric acid, which transformed to silver chloride the metallic or sulphuretted silver contained in the ores; and that this silver chloride, in the presence of the excess of salt or hydrochloric acid, was reduced to the metallic state, and amalgamated with part of the mercury, giving up its hydrochloric acid to another part, to form mercury chloride. In addition to the mechanical loss of mercury in the process, there was thus a double chemical loss, due to the formation of mercury chloride, partly by the hydrochloric acid from the silver, and partly by the free hydrochloric acid in the mass.
This theory, as further developed, but not essentially changed, by Karsten, Rammelsberg and Regnault, has been generally adopted. Up to a certain point, it explains the most important phenomena of the process.
The consumption of mercury in this process is generally measured in its proportion to the amount of silver obtained. A loss of 12 oz. of mercury per mark (= 8 oz.) of silver extracted is generally considered good practice; and it is commonly reckoned that of the 12 oz., 8 constitute the chemical loss, and 4 the mechanical. But when docile ores are intelligently and carefully treated, the loss of mercury may be less than 8.25 oz. per 8 oz. of silver—a fact which disproves the theory that the silver chloride is reduced wholly by the mercury; since this loss is much smaller than the chemical equivalent involved in such a reaction.
Experiments made at the Hacienda, de Regia, by my father, Eng’r Miguel Bustamente, showed that, when the quantity of salt was augmented, and the treatment was slightly “ cold,” the total loss of mercury never exceeded 4 oz. per mark of silver extracted.
By another series of experiments, made to ascertain the influence of the impurities of the sulphates of copper employed, he demonstrated that the English sulphate of copper, the purest used in Mexico, did not give as good results as the acid sulphate of copper produced by the Mints in treating gold; and, finally, that the most effective and economical of all is the impure sulphate of copper, with a large quantity of iron, known as “ magistral,” and obtained by the roasting of chalcopyrite.
These results, repeatedly confirmed by myself and others, likewise contradict the generally admitted principles and theories cited above.
The fact is, that some of the reactions pointed out by theoretical chemists take place; but there are a multitude of other reactions which may and do also occur; and the accessory ingredients of the ore have no less (and probably even more) influence in the patio than in other reduction-methods, because the latter may neutralize, by means of appropriate mixture of charges, some of the elements disturbing the desired reaction; whereas in the patio no one has taken pains to make such mixtures, but all are content simply to divide the ores into “ docile ” and “ rebellious.”
This is not surprising, since the greater number of plants are in the hands of ordinary amalgamating-workmen, ignorant of chemistry and mineralogy, and attached to the routine practice of their fathers. Regular docimastic assays are rarely maintained, and still more rarely used with advantage as checks or guides in daily operations. The assays of the residue are carelessly made, and the treatment is generally guesswork. Nevertheless, the general results in treating “ docile ” ores are good. If the loss of mercury could always be kept down to 4 oz. per mark of silver obtained, and the extraction of silver and gold up to 95 per cent, of the assay-value, and if this could be done with a larger proportion of the “ rebellious ” ores, the patio would be the ideal method for this country.
Some ten years ago, as a student of metallurgy, I presented, in my examination-thesis, a theory of the patio process which I wish now to re-state, without pretending that it solves the whole problem, but believing that it takes account of certain reactions, constantly occurring in the process, which have been overlooked hitherto, though they have a marked influence on the results of the treatment.
The first chemical operation upon “ docile ” ores is the salting (ensalmorar), which consists in the addition of chloride of sodium (from 1.5 to 4 per cent, of the weight of the ore). The salt should be as pure as possible, as its quality has a marked influence on the consumption of sulphate of copper afterwards, and on the pureness of the silver, as well as on the time spent in making up the torta.
In the majority of cases I have found the use of an excess of nearly pure salt to result in greater silver-extraction, saving of time in the treatment, and notable diminution of the loss of mercury.
After the mixing (repaso), which may be done by peons, horses, rollers, pans, cradles, Archimedean screw, Chilean alacran, arrastres, etc., comes the “ incorporation ” of the sulphate of copper, or the magistral, and then of the mercury. The quantity of copper sulphate added (varying from 1.5 to 6 per cent, of the weight of the ore) depends upon many circumstances, the principal being the dullness of the workmen and the good or bad quality of the impure sulphate employed. The quantity of mercury added is calculated to be 4 or 5 times the weight of silver expected to be obtained at the end of the operation.
The exact estimate of the quantity of sulphate of copper to be employed is of great importance. If too little is added, the treatment is checked; the sulphate is converted into suboxide of copper; and the mercury, floured and oxidized, cannot be easily recovered by washing the torta without some injurious change in the compounds of silver.
If, on the other hand, the sulphate be in excess, the chloride reactions are very energetic, the mercury being rapidly converted into chloride (with liberation of 62.8 cal; of heat) ; whereas, the formation of silver chloride (liberating only 29.2 cal.) cannot take place. By subsequent reactions and outside influences, among which are the admitted effects of light and organic matter, a portion of the mercury is converted into an oxide, which is, like calomel, almost insoluble in the more or less concentrated solution of salt to which the principal reactions of the patio process are ascribed. A considerable loss of mercury is thus caused; and the compounds of silver are so transformed or rendered inert as to hinder their reduction, and produce the indications known to the workmen as those of “ hot ” treatment.
The addition, as a remedy, of lime, ashes, precipitated copper, etc., cools the torta, and destroys the calomel which may have been formed; but it neither reduces the oxidized mercury nor modifies the passivity of the argentiferous compounds.
All the current theories of the patio attribute to cupric or to cuprous chloride the chloridization of the silver in the ore —the copper becoming a sulphide or sulph-antimonide, etc. But many trustworthy laboratory experiments have disproved this proposition. The test is not difficult. Place pure pulverized argentite in a beaker; add cupric chloride in more or less concentrated solution; and the result is nil, as could have been foretold from the principles of thermo-chemistry; since the heat of formation of the chloride of silver is only 29.2 cal., while that of cupric chloride is much greater, namely, 71.2 cal. Adding chloride of sodium makes no difference, even after three months. But on the further addition of iron, or metallic zinc in shavings, an almost instantaneous reaction follows; and the more intense the light during the experiment the more energetic will be this reaction. The black silver sulphide is changed to white. This reaction, no doubt, led Kroncke to employ the cuprous chloride in the method which bears his name. When an excess of iron or zinc is added, the energetic reaction rapidly deposits metallic silver—which is not surprising.
This experiment, studied in the light of Berthelot’s thermo-chemical law, confirms the conclusion that the reaction is not a simple chloridization of the silver by the cuprous chloride (the formation heat of the latter being but 29.2, while that of the former is 62.2 cal.), but is in large part due to the metallic iron (or zinc). This conclusion can be further supported by similar experiment, in which cuprous silver is used instead of cupric chloride. The resulting reaction is very slow, and quite insignificant.
On the other hand, the hypothesis of the effective agency of the iron encounters at once the objection that, apart from American pan-amalgamation, the various silver-amalgamation processes do not involve a large consumption of iron; and, moreover, that they produce silver of much higher purity than that obtained in pans, which rarely assays as much as 0.750 fine. It is true that the crushing of ore with modern apparatus exposes it to a certain quantity of iron; that the animals which tramp the tortas are shod with iron; but these factors cannot be significant; since, both formerly and to this day, crushing in stone arrastres and the trampling of the torta by men are performed in remote mining districts of Mexico, with technical results not greatly, if at all, inferior to those of more modern practice.
These objections led me to a series of laboratory experiments which, I think, demonstrate:
the formation of ferric chloride (Fe2Cl6), the formation-heat of which, in solution, is 255.4 cal.;
its subsequent reduction to a lower chloride, with liberation of chlorine, which, acting in the nascent state upon the compounds of silver, transforms them into chlorides;
the reaction of these chlorides upon the hydrated oxides in the mixture of ore and reagents, and on the metallic iron, resulting in metallic silver with a new formation of chloride of iron, releasing oxygen, and probably affecting a partial regeneration of sulphate of copper;
a new formation of chlorides of copper and a continuation of these reactions until the termination of the treatment. This is a resume of my theory of the patio process.
What is the role of the copper in these reactions ? Its presence is certainly indispensable. It has always been supposed to play the double role of the chlorination of the compounds of silver and its own sulphatization. As to the latter reaction: the formation-heat of the sulphate of silver is 3 cal.; that of the sulphate of copper 20.8 cal.; and that of the sulphate of iron, in the most unfavorable case, 41.6 cal. Undoubtedly, therefore, if iron oxide be present, this last reaction will be the one to take place. The state of division of this sulphate of iron; the liberation of oxygen in the formation of perchlorides from the oxides of iron contained in all ores; the humidity ; the action of light and of atmospheric agents;—all contribute to the formation of the, sulphate of iron, liberating 94.4, and not to that of copper, liberating only 57 cal. This is only an application of the well-known principle of “maximum work.”
Continuing: the formation-heat of the chloride of sodium (NaCl) is 58.5; that of sodium sulphide, dissolved, 186.8; that of iron sulphide 94.4; and that of copper sulphide 57 cal. The latter, therefore, will undoubtedly be most easily attacked by the chloride of sodium, since it requires the smallest number of calories to make it resign to the sodium its sulphuric acid, with formation, undoubtedly, of proto-chlorate of copper, which liberates 71.2 cal.
This simple comparison of the formation-heats shows at once the usefulness of the sulphate of copper in the patio process, and also explains the small success of those experimenters who have, in practice, substituted sulphate of iron. The presence of copper is, moreover, of the utmost importance for the preservation of mercury in the metallic state, after the oxides of iron have been transformed into proto-chlorides; the formation-heat of the corrosive sublimate being only 59.6 cal.
It remains to be explained why the “magistral” (i.e., the sulphates of copper and iron obtained by the reverberatory roasting of chalcopyrite) yields, in this process, better results than the English sulphate of copper, chemically the purest in the market. This explanation is very simple, and completes my theory of the patio process.
All those who have practiced photography have witnessed the effect of light in reducing the silver-salts and transforming the proto- into the per-salts of iron; also the strong solvent action of iron perchloride upon the salts of silver—especially silver chloride, whether it has or has not been affected by light. The solvent power of iron perchloride upon silver chloride is greatly superior to that of the chloride of sodium, though the latter may be more generally known; and it naturally facilitates and accelerates the reactions in the patio. In particular, the chlorination and consequent loss of mercury is diminished, for two reasons:
because the quantity of chloride of copper formed is made relatively small; and
because the proto- and perchloride of iron immediately formed, instead, from the sulphate of iron of the magistral, directly aid in attacking the argentiferous compounds.
The reduction to silver of the dissolved silver chloride may be effected either:
through the precipitation of silver as an unstable oxide by the oxides of iron naturally existing or artificially formed in the ore, or
by the conversion of silver proto-chloride into perchloride, leaving free silver, which amalgamates with the mercury, eluding in this way further chlorination and solution.
Consequently, mercury should not be chemically lost in this treatment. In fact, the necessary chemical loss has often been shown in practice to be imaginary. The mechanical loss is the only inevitable one.
The two principal signs observed in the usual tests which have hitherto served, and will doubtless continue to serve as a practical guide in the operation of the patio process, confirm part of the theory here presented.
The test of a “ cold ” torta, made immediately after the incorporation by trampling, shows mercury, sometimes in part more or less confluent, but usually in small drops, or in the exceedingly fine state of division (floured) which we call liz. Rubbing this together, and then attempting to strain it by squeezing, we obtain scarcely any signs of amalgam. The mercury is very white, resembling its natural color, or tending more or less to a yellowish color on the surface, owing (as the experts say) to the formation of sub-oxide of copper. The film of this oxide, covering the surface of the mercury, is undoubtedly due to the decomposition of the chloride of copper by the oxides of iron in the ore; and the quantity of chlorine thus liberated from the copper salt is not sufficient to form the needed amount of perchloride of iron, which, acting in the nascent state, and favored by the heat liberated in its own formation, is the true agent in the chloridization of the silver-compounds. Hence the “ coldness ” of the torta, with the unfavorable conditions which that implies. This phenomenon led me to suspect for the first time the important part played in the patio process by the iron oxides and salts of the ore.
On the other hand, the torta is “ hot” when an excess of sulphate of copper has been added. In this case, perchloricle of iron is very rapidly formed, and tends to be reduced with similar rapidity to the proto-chloride, converting the mercury to calomel (Hg2Cl2), until the reaction provoked by the immoderate use of sulphate of copper has terminated. In this case, practically all the reagents employed are consumed in the chlorination of the mercury, without useful result. The greater part, if not the whole, of the iron oxides in the ores is changed to proto-chloride; and if, after the over-heated torta has cooled, pure sulphate of copper be employed to continue the treatment, much difficulty will be experienced in recovering the conditions lost.
Inventors, reasoning upon the reactions of the Freiberg barrel-amalgamation, have proposed the use of metallic iron in the various phases of the patio process, as a means of minimizing the loss of mercury. The main result of such a measure has been the requirement of a larger quantity of sulphate of copper, together with delay in the progress of the treatment. The reason is easily seen : the metallic iron precipitates metallic copper, and this reaction cools the torta. The consumption of mercury increases instead of diminishing.
In view of these facts and considerations, it is, in my judgment, the best practice to conduct the treatment of the torta moderately and with vigilance, and, upon the least sign of excessive heat, to apply the remedy at once, in the form of a quantity (calculated as exactly as possible) of lime, precipitated copper, or ashes, to forestall the effects of a “ hot ” torta upon the mercury.
As already observed, the proper amount of sulphate of copper required in this process for any particular ore should be as carefully determined, according to the law of chemical equivalents, as the amount and nature of flux required in a smelting process. And it follows that for this process, as for smelting, different ores might be so mixed, after proper analysis of each, as to diminish the necessary amount, or increase the effectiveness of the metallurgical reagents added. Empirical mixtures of “ docile ” and “ rebellious ” ores are known to have given excellent results in many Mexican localities; and there is a wide and promising field for the thorough study and systematic application of this practice, which would raise it from the plane of local tradition or happy accident to that of definite purpose and fore-knowledge.
In this, as in other respects, the Mexican amalgamation-process has never had opportunity to exhibit its full technical and economical capacity. I firmly believe that it can successfully compete with smelting, especially in a country like ours, in which, by reason of topographical conditions and the cost of fuel, freights will always be high.
With regard to methods for diminishing the loss of mercury and amalgam, I would here recall the experiments in connection with the amalgamation of gold, described in the first part of this paper. I have similarly employed the electric current in connection with the patio process also—not to affect the treatment itself, but to join the metallic particles. The result was, as I had expected, the same as that which had been accomplished with gold. The quantity of silver and mercury recovered was considerably increased; and I succeeded in saving 97 per cent, of the humid-assay value of silver with a loss of only 5.1 per cent of the mercury employed.
The apparatus consisted of a series of amalgamated copper plates connected to the poles of the dynamo, and grouped in tension, so as to obtain, per sq. meter of surface, from one to two volts and 40 amperes of current. These plates were so suspended by means of the canals and inside of the drain of the patio in such a manner as to interrupt, to a certain extent, the free passage of the slimes and water, but without seriously hindering or complicating the washing of the torta. I am fully conscious that, after more than seven years spent in establishing facts, overcoming difficulties, and perfecting details, my work in the economic utilization of the facts and theories set forth above is, like my attempt to state them here, still far from complete and satisfactory. Nevertheless, this paper, begun two years ago, is now published, in the hope that the suggestions and experiments of others may aid in the improvement and the due recognition of our Mexican patio process, so little understood, so often undervalued, and so worthy of a better fame and fate.
Collahuasi Copper Mine
The oxide circuit flowsheet involves both leaching to recover the contained copper and electro-winning to produce copper cathodes.
XO___XO Mineral processing as example
The ore is a free-milling conglomerate with negligible sulphide content. Rocks near the surface have been affected by a high degree of weathering which is associated with increased porosity and increased heap leach dissolution and recovery. The North Heap Leach facility was commissioned in 1998 to process the initial highly porous ore and the construction of the Phase V heap leach pad was completed in 2009. As the mine gets deeper, so the percentage of weathered ore amenable to heap leaching decreases. This justified the construction of the CIL plant in 2004 and its subsequent expansion, commissioned in January 2009. The CIL milling process provides a 97% recovery which is not possible when using heap leaching for the harder, unweathered ore, the percentage of which increases over the LoM.
The North Heap Leach facility employs three stages of crushing prior to agglomeration. Post primary crushing through a gyratory crusher, a series of overland conveyors transport the undersize material to the agglomeration stockpile where it joins the final product. Secondary crushing product is fed to the tertiary hopper via a series of conveyors. The oversize material from the upper and lower decks (32 mm and 22 mm respectively) feed the tertiary crushers and the discharge from the tertiary crushers is conveyed back to the tertiary bin. The undersize material from the tertiary screens joins the final crushing product to the agglomeration stockpile.
CIL plant flow diagram
The agglomeration process involves the addition of 4 kg/t of cement to the crushed rock to bind the fine material and produce agglomerate that remains stacked and porous on the heap leach pads. Following agglomeration, the ore is transferred by conveyor and stacked on the leach pads by a stacking conveyor.
The heaps are irrigated with a cyanide solution which dissolves the gold as it percolates through the heaps. The pregnant solution is collected on the layer of geotextile that lines the base of the heaps and is pumped through a series of ponds to the adsorption/desorption/recovery (ADR) plant. Here the gold is adsorbed onto activated carbon, removed from the carbon by acid wash, and recovered using electro-winning. All gold produced at the North facility is smelted at the smelt house using diesel-fired furnaces.
The CIL process route has a gyratory crusher that feeds two crushed ore stockpiles, each with a live capacity of 45,000 tonnes (30 hours). Underneath each stockpile is a reclaim tunnel, with apron feeders that feed onto a conveyor belt. These in turn feed the milling circuit, which consists of a semi-autogenous grinding (SAG) and ball mill. Recycle crushing is in closed circuit with the SAG mill that has 14 MW of installed power (2 x 7,000 kW twin-drive motors). The ball mill has 14 MW of installed power (2 x 7,000 kW twin drive-motors) and is in close circuit with the cyclone cluster. The milling circuit is operated at a capacity of 1,450 tph.
The CIL circuit consists of two trains of eight tanks in series, which are fed from a common leach tank. The loaded carbon passes into a 15-tonne acid wash column. The gold is recovered from the loaded carbon in two 15-tonne elution circuits. Gold is recovered from solution by electro-winning and smelted in an induction furnace at the CIL smelt house.
Copper Facts
Copper the Metal
Copper Fact 1
Copper is a mineral and an element essential to our everyday lives. It is a major industrial metal because
of its high ductility, malleability, thermal and electrical conductivity and resistance to corrosion. It is an
essential nutrient in our daily diet. And, its antimicrobial property is becoming increasingly important to
the prevention of infection. It ranks third after iron and aluminum in terms of quantities consumed in
the USA.
Copper Fact 2
The U.S. Geological Survey (USGS) estimates that every American born in 2008 will use 1,309 pounds of
copper during their lifetime for necessities, lifestyles and health.
Copper Fact 3
Known land-based resources of copper are estimated to be 1.6 billion metric tons of copper (USGS,
2004). United States copper production largely comes from deposits in Arizona, Utah, New Mexico,
Nevada and Montana. Twenty mines account for about 99% of production.
Copper Fact 4
Copper is element number 29 on the Periodic Table of Elements. It is considered a semi-precious,
nonferrous, malleable metal with many hundreds of applications in the areas of electricity and
electronics, plumbing, building construction and architecture, industry, transportation, and consumer
and health products.
Copper Fact 5
Pure copper's melting point is 1,981°F (1,083°C, 1356°K). Its most important properties include superior
heat transfer, electrical conductivity and corrosion resistance.
Copper Fact 6
Copper is easily alloyed with other metals. Currently, there are more than 570 copper alloys listed with
the American Society for Testing and Materials International. They are identi旋�ed by numbers preceded
by a "C" and are assigned and reviewed by the Copper Development Association for ASTM. More than
350 of them have been acknowledged by the U.S. Environmental Protection Agency as antimicrobial.
Copper Mining Process Flow Chart Lovely Mining Basics. Copper Mining Process Flow Chart Lovely Mining Basics photos and pictures collection. we make it and here these list of awesome picture for your inspiration and informational purpose regarding the Copper Mining Process Flow Chart Lovely Mining Copper Mining Process Flow Chart Lovely Mining Basics.
Copper Mining Process Flow Chart Lovely Mining Basics.
XO___XO XXX
The Many Uses of Gold
The Most Useful Metal
Of all the minerals mined from the Earth, none is more useful than gold. Its usefulness is derived from a diversity of special properties. Gold conducts electricity, does not tarnish, is very easy to work, can be drawn into wire, can be hammered into thin sheets, alloys with many other metals, can be melted and cast into highly detailed shapes, has a wonderful color and a brilliant luster. Gold is a memorable metal that occupies a special place in the human mind.
Gold nuggets: Gold nuggets found in a stream can easily be hammered into shapes, combined, and worked with primitive tools into ornamental objects.
A Bit of Gold History
When Spanish explorers first arrived in the "New World" they met the native South Americans. These two cultures had been separated by a vast ocean, they had never touched one another, they spoke different languages and lived entirely different lives. Yet they had one thing in common - they both held gold in highest esteem and used it to make some of their most important objects.
Throughout the history of our planet, almost every established culture has used gold to symbolize power, beauty, purity, and accomplishment. Today we continue to use gold for our most significant objects: wedding rings, Olympic medals, Oscars, Grammys, money, crucifixes and ecclesiastical art. No other substance of the same rarity holds a more visible and prominent place in our society.
Gold ring: Gold ring with colored stone. Image copyright iStockphoto.com / Krzysztof Gorski.
Gold rings: Gold rings of different color. Image copyright iStockphoto.com / Martin McCarthy.
Colors of gold-silver-copper alloys: Different metal colors that can be produced by alloying different amounts of gold, silver, and copper. Image by Metallos, used here under a GNU Free Documentation License.
Jewelry: The Primary Use of Gold
Gold has been used to make ornamental objects and jewelry for thousands of years. Gold nuggets found in a stream are very easy to work and were probably one of the first metals used by humans. Today, most of the gold that is newly mined or recycled is used in the manufacture of jewelry. About 78% of the gold consumed each year is used in the manufacture of jewelry.
Special properties of gold make it perfect for manufacturing jewelry. These include: very high luster; desirable yellow color; tarnish resistance; ability to be drawn into wires, hammered into sheets, or cast into shapes. These are all properties of an attractive metal that is easily worked into beautiful objects. Another extremely important factor that demands the use of gold as a jewelry metal is tradition. Important objects are expected to be made from gold.
Pure gold is too soft to stand up to the stresses applied to many jewelry items. Craftsmen learned that alloying gold with other metals such as copper, silver, and platinum would increase its durability. Since then most gold used to make jewelry is an alloy of gold with one or more other metals.
The alloys of gold have a lower value per unit of weight than pure gold. A standard of trade known as "karatage" was developed to designate the gold content of these alloys. Pure gold is known as 24 karat gold and is almost always marked with "24K". An alloy that is 50% gold by weight is known as 12 karat gold (12/24ths) and is marked with "12K". An alloy that contains 75% gold by weight is 18 karat (18/24 = 75%) and marked "18K". In general, high-karat jewelry is softer and more resistant to tarnish, while low-karat jewelry is stronger and less resistant to tarnish - especially when in contact with perspiration.
Alloying gold with other metals changes the color of the finished products (see illustration). An alloy of 75% gold, 16% silver and 9% copper yields yellow gold. White gold is an alloy of 75% gold, 4% silver, 4% copper and 17% palladium. Other alloys yield pink, green, peach and even black-colored metals.
Gold bullion: Fine gold metal is usually cast into small bars for easy handling, exchange, and storage. USDOJ Image.
Gold coins: United States Gold Coins. Image copyright iStockphoto / Donald Swartz.
Financial Gold: Coinage, Bullion, Backing
Because gold is highly valued and in very limited supply, it has long been used as a medium of exchange or money. The first known use of gold in transactions dates back over 6000 years. Early transactions were done using pieces of gold or pieces of silver. The rarity, usefulness, and desirability of gold make it a substance of long-term value. Gold works well for this purpose because it has a high value, is durable, portable, and easily divisible.
Some early printings of paper money were backed by gold held in safekeeping for every unit of money that was placed in circulation. The United States once used a "gold standard" and maintained a stockpile of gold to back every dollar in circulation. Under this gold standard, any person could present paper currency to the government and demand in exchange an equal value of gold. The gold standard was once used by many nations, but it eventually became too cumbersome and is no longer used by any nation.
2017 Gold Production
Country
Metric Tons
China
440
Australia
300
Russia
255
United States
245
Canada
180
Peru
155
South Africa
145
Mexico
110
Uzbekistan
100
Brazil
85
Ghana
80
Indonesia
80
Kazakhstan
70
Papua New Guinea
60
Other Countries
845
The values above are estimated gold production in metric tons. Data from USGS Mineral Commodity Summaries.
The gold used as a financial backing for currency was most often held in the form of gold bars, also known as "gold bullion." The use of gold bars kept manufacturing costs to a minimum and allowed convenient handling and storage. Today many governments, individuals, and institutions hold investments of gold in the convenient form of bullion.
The first gold coins were minted under the order of King Croesus of Lydia (a region of present-day Turkey) in about 560 BC. Gold coins were commonly used in transactions up through the early 1900s, when paper currency became a more common form of exchange. Gold coins were issued in two types of units. Some were denominated in units of currency, such as dollars, while others were issued in standard weights, such as ounces or grams.
Today gold coins are no longer in wide use for financial transactions. However, gold coins issued in specific weights are popular ways for people to purchase and own small amounts of gold for investment. Gold coins are also issued as "commemorative" items. Many people enjoy these commemorative coins because they have both a collectible value and a precious metal value.
Gold use in electronics: Gold parts are used in cell phones and many other electronics. Image copyright iStockphoto / Matjaz Boncina.
The best way to learn about minerals is to study with a collection of small specimens that you can handle, examine, and observe their properties. Inexpensive mineral collections are available in the Geology.com Store.
Uses of Gold in Electronics
The most important industrial use of gold is in the manufacture of electronics. Solid state electronic devices use very low voltages and currents which are easily interrupted by corrosion or tarnish at the contact points. Gold is the highly efficient conductor that can carry these tiny currents and remain free of corrosion. Electronic components made with gold are highly reliable. Gold is used in connectors, switch and relay contacts, soldered joints, connecting wires and connection strips.
A small amount of gold is used in almost every sophisticated electronic device. This includes cell phones, calculators, personal digital assistants, global positioning system (GPS) units, and other small electronic devices. Most large electronic appliances such as television sets also contain gold.
One challenge with the use of gold in very small quantities in very small devices is loss of the metal from society. Nearly one billion cell phones are produced each year, and most of them contain about fifty cents worth of gold. Their average lifetime is under two years, and very few are currently recycled. Although the amount of gold is small in each device, their enormous numbers translate into a lot of unrecycled gold.
Gold computer connections: Gold in a computer memory chip. Image copyright iStockphoto / Teresa Azevedo.
Uses of Gold in Computers
Gold is used in many places in the standard desktop or laptop computer. The rapid and accurate transmission of digital information through the computer and from one component to another requires an efficient and reliable conductor. Gold meets these requirements better than any other metal. The importance of high quality and reliable performance justifies the high cost.
Edge connectors used to mount microprocessor and memory chips onto the motherboard and the plug-and-socket connectors used to attach cables all contain gold. The gold in these components is generally electroplated onto other metals and alloyed with small amounts of nickel or cobalt to increase durability.
Dental gold: A crown made from dental gold alloy. Image copyright iStockphoto / choicegraphx.
Uses of Gold in Dentistry
How would iron work as a dental filling? Not very well... your dentist would need blacksmithing tools, your smile would be rusty a few days after a filling, and you would need to get used to the taste of iron. Even at much higher expense, gold is used in dentistry because of its superior performance and aesthetic appeal. Gold alloys are used for fillings, crowns, bridges, and orthodontic appliances. Gold is used in dentistry because it is chemically inert, nonallergenic, and easy for the dentist to work.
Gold is known to have been used in dentistry as early as 700 B.C. Etruscan "dentists" used gold wire to fasten replacement teeth into the mouths of their patients. Gold was probably used to fill cavities in ancient times; however, there is no documentation or archaeological evidence for this use of gold until a little over 1000 years ago.
Gold was much more generously used in dentistry up until the late 1970s. The sharp run-up of gold prices at that time motivated the development of substitute materials. However, the amount of gold used in dentistry is starting to rise again. Some motivation for this comes from concerns that less inert metals might have an adverse effect on long-term health.
Medical uses of gold: Gold is used in some surgical instruments. Image copyright iStockphoto / atbaei.
Medical Uses of Gold
Gold is used as a drug to treat a small number of medical conditions. Injections of weak solutions of sodium aurothiomalate or aurothioglucose are sometimes used to treat rheumatoid arthritis. Particles of a radioactive gold isotope are implanted in tissues to serve as a radiation source in the treatment of certain cancers.
Small amounts of gold are used to remedy a condition known as lagophthalmos, which is an inability of a person to close their eyes completely. This condition is treated by implanting small amounts of gold in the upper eyelid. The implanted gold "weights" the eyelid, and the force of gravity helps the eyelid close fully.
Radioactive gold is used in diagnosis. It is injected in a colloidal solution that can be tracked as a beta emitter as it passes through the body. Many surgical instruments, electronic equipment, and life-support devices are made using small amounts of gold. Gold is nonreactive in the instruments and is highly reliable in the electronic equipment and life-support devices.
Gold use in aerospace: Gold is used in satellite components. Image copyright iStockphoto / pete stopher.
Gold-coated telescope mirror: Photo of one of the James Webb Space Telescope's primary mirror segments being coated with gold by Quantum Coating Incorporated. Photo by Drew Noel, NASA.
Uses of Gold in Aerospace
If you are going to spend billions of dollars on a vehicle that when launched will travel on a voyage where the possibility of lubrication, maintenance and repair is absolutely zero, then building it with extremely dependable materials is essential. This is exactly why gold is used in hundreds of ways in every space vehicle that NASA launches.
Gold is used in circuitry because it is a dependable conductor and connector. In addition, many parts of every space vehicle are fitted with gold-coated polyester film. This film reflects infrared radiation and helps stabilize the temperature of the spacecraft. Without this coating, dark colored parts of the spacecraft would absorb significant amounts of heat.
Gold is also used as a lubricant between mechanical parts. In the vacuum of space, organic lubricants would volatilize and they would be broken down by the intense radiation beyond Earth's atmosphere. Gold has a very low shear strength, and a thin film of gold between critical moving parts serves as a lubricant - the gold molecules slip past one another under the forces of friction and that provides a lubricant action.
Gold use in awards: Gold Medal. Image copyright iStockphoto / Olivier Blondeaui.
Uses of Gold in Awards & Status Symbols
What metal is used to make the crown worn by a king? Gold! This metal is selected for use because gold is THE metal of highest esteem. It would make no sense to make a king's crown out of steel - even though steel is the strongest metal. Gold is chosen for use in a king's crown because it is the metal associated with highest esteem and status.
Gold is associated with many positive qualities. Purity is another quality associated with gold. For this reason, gold is the metal of choice for religious objects. Crosses, communion ware, and other religious symbols are made with gold for this reason.
Gold is also used as the first place winner's medal or trophy in almost any type of contest. First-place winners at the Olympic Games are given gold medals. The Academy Awards Oscars are gold awards. Music's Grammy Awards are made of gold. All of these important achievements are honored with awards made of gold.
Gold used in glass: Gold is used in specialty building glass. Image copyright iStockphoto / Cezar Serbanescu.
Uses of Gold in Glassmaking
Gold has many uses in the production of glass. The most basic use in glassmaking is that of a pigment. A small amount of gold, if suspended in the glass when it is annealed, will produce a rich ruby color.
Gold is also used when making specialty glass for climate-controlled buildings and cases. A small amount of gold dispersed within the glass or coated onto the glass surface will reflect solar radiation outward, helping the buildings stay cool in the summer, and reflect internal heat inward, helping them stay warm in winter.
The visor on the helmet of an astronaut's space suit is coated with a very thin film of gold. This thin film reflects much of the very intense solar radiation of space, protecting the astronaut's eyes and skin.
Gold church dome: Gold dome of a church. Image copyright iStockphoto / Constantine Vishnevsky.
Gold Gilding and Gold Leaf
Gold has the highest malleability of any metal. This enables gold to be beaten into sheets that are only a few millionths of an inch thick. These thin sheets, known as "gold leaf" can be applied over the irregular surfaces of picture frames, molding, or furniture.
Gold leaf is also used on the external and internal surfaces of buildings. This provides a durable and corrosion-resistant covering. One of the most eye-catching uses of gold leaf is on the domes of religious buildings and other important structures. The cost of this "roofing material" is very high per square foot; however, the cost of the gold is only a few percent of the total project cost. Most of the cost goes to the labor of highly skilled artisans who apply the gold leaf.
Prague orloj: Prague Astronomical Clock in the Czech Republic. Image copyright iStockphoto / Kelly Borsheim.
Future Uses of Gold
Gold is too expensive to use by chance. Instead it is used deliberately and only when less expensive substitutes cannot be identified. As a result, once a use is found for gold it is rarely abandoned for another metal. This means that the number of uses for gold have been increasing over time.
Most of the ways that gold is used today have been developed only during the last two or three decades. This trend will likely continue. As our society requires more sophisticated and reliable materials, our uses for gold will increase. This combination of growing demand, few substitutes, and limited supply will cause the value and importance of gold to increase steadily over time. It is truly a metal of the future.
Substitutes for Gold and Reductions in Use
Because of its rarity and high price, manufacturers are always looking for ways to reduce the amount of gold required to make an object or substitute a less expensive metal in its place. Base metals clad with gold alloys have long been used as a way to reduce the amount of gold used in jewelry and electrical connections. These items are constantly being redesigned to reduce the amount of gold required and to maintain their utility standards. Palladium, platinum, and silver are the most common substitutes for gold that closely retain its desired properties.
Measurement of Gold and Other Metals in Electronic and Automotive Waste Using Gamma Activation Analysis
CSIRO is developing the method of gamma activation analysis (GAA) for the rapid, non-destructive analysis of gold and other metals in mineral ores. Samples are irradiated with high-energy X-rays produced using a linear electron accelerator, resulting in activation of target elements. The gamma-rays emitted during the decays of the radioactive products of these activation reactions can be analyzed to determine the sample composition. Both the incident X-rays and emitted gamma-rays are sufficiently penetrating to allow large, heterogeneous samples to be analyzed directly without sampling or pre-treatment. We have recently conducted a preliminary study to investigate the application of the GAA method to the analysis of bulk electronic and automotive waste materials supplied by the SMaRT Centre at the University of New South Wales. The electronic waste gold contents vary from 80 to more than 800 parts-per-million (ppm), and silver contents range from 250–350 ppm; no gold or silver is observed in the automotive waste material. Consequently, the metal value of these waste materials is highly variable and can reach up to US$30,000 per tonne. Qualitative analysis demonstrates that the GAA method is capable of detecting a range of other economically and environmentally important elements in these samples, including copper, bromine, tin, lead, and tantalum. The speed and simplicity of the GAA method make it well suited to rapid waste characterization.
Electronic or e-waste is an umbrella term covering discarded electrical and electronic equipment that has reached the end of its life cycle, cannot be reused, and has ceased to be of any value to its owner. In 2014, around 41.8 million metric tonnes of e-waste was produced worldwide, with 468,000 metric tonnes produced in Australia alone. The amount of e-waste being produced around the world is expected to grow by 4–5 % each year up to 2018 . E-waste is the fastest growing form of waste in Australia, with the rate of production currently increasing 3 times more quickly than any other waste type .
E-waste covers an extensive range of products from large white goods through to small personal electronic devices. A wide variety of e-waste products results in an extremely heterogeneous physical composition. E-waste can contain many metals in differing concentrations that can be recyclable, hazardous, or precious . The most common metals by weight fraction include iron, copper, aluminum, nickel, zinc, and tin. Hazardous substances in e-waste include lead, mercury, arsenic, cadmium, and beryllium, among others. Precious metals such as gold, silver, and palladium are also found in small quantities, generally parts-per-million levels, but may constitute a significant fraction of the recycling value. Motives for recycling e-waste include reducing landfill volumes, preventing the leaching of toxic substances such as lead and mercury into the environment, and the recovery of valuable resources.
Using current (Sep. 2015) metal prices sourced from the metalprices.com website, we have calculated both the overall metal values of these different e-waste streams and the contributions from individual elements. These results are shown in Table 1.
Table 1
Average compositions of e-waste samples taken from [4, 5] and contributions to total metal value (US$) calculated using Sep. 2015 prices
Element
Mobile phone e-waste
Computer e-waste
Television e-waste
Wt%
Value %
Wt%
Value %
Wt%
Value %
Copper
12.8
3.0
20.0
6.9
10.0
23.2
Aluminum
–
–
5.0
0.5
10.0
6.9
Iron
6.5
0.1
7.0
0.2
28.0
4.8
Lead
0.6
<0.1
1.5
0.2
1.0
0.7
Nickel
1.5
0.7
1.0
0.6
0.3
1.3
Tin
1.0
0.7
2.9
2.6
1.4
9.0
Silver
0.363
7.6
0.1
2.8
0.028
5.8
Gold
0.0347
54.3
0.025
53.2
0.0017
26.3
Palladium
0.0151
33.5
0.011
33.0
0.0010
22.0
Total value per tonne
$23,000
$16,900
$2300
It is immediately apparent that the metal value of e-waste is dominated by the precious metal content, especially gold and palladium. Only in materials relatively deficient in precious metals does copper make a significant contribution. The value of the other metals is generally low. As the precious metal content of different e-waste streams is so variable, the overall metal value also varies by more than a factor of 10.
Printed circuit boards (PCBs) form an important component of e-waste. PCBs typically comprise non-metals (plastics, epoxy, resins, and glasses) and metals (mainly copper, tin, iron, lead, and nickel, with parts-per-million concentrations of precious metals). Several of these metals may be present at significantly higher levels than conventional ore deposits, making PCBs a particularly interesting resource for recycling. Table 2 shows the comparison of typical concentrations of some metals found in PCBs with levels in commercial ores, with data taken from Bizzo et al. [6] and Viet et al. [7]. Concentrations of copper and gold are typically one and two orders of magnitude higher, respectively, in PCBs than in ore deposits.
Table 2
Comparison of metal content of typical ores and printed circuit board (PCB) waste taken from [6, 7]; concentrations are in % unless indicated otherwise
Metal
Typical ore (%)
PCBs (%)
Copper
0.5–3.0
12.0–29.0
Zinc
1.7–6.4
0.1–2.7
Tin
0.2–0.85
1.1–4.8
Lead
0.3–7.5
1.3–3.9
Iron
30–60
0.1–11.4
Nickel
0.7–2.0
0.3–1.6
Gold
<5 ppm
29–1120 ppm
Silver
<500 ppm
100–5200 ppm
When vehicles are recycled, approximately 75 % of material is separated, including lubricants, tyres, metals, and plastics. The remaining fraction is mechanically processed to produce ASR, a complex and highly heterogeneous mixture comprising plastics, rubber and elastomers, textiles, and metals and glass. The waste may also contain toxic and hazardous materials including chlorine and sulfur compounds, contaminated oil, polyvinyl chloride (PVC), and toxic metals. One study found that ASR samples contained up to 2930 ppm of copper, 550 ppm of nickel, 10,200 ppm of lead, and 13,200 ppm of zinc, making it unsuitable for some landfills [8].
A method capable of accurately analyzing the metal content of waste samples would find widespread application, both for valuing waste prior to recycling and verifying levels of hazardous metals before final disposal. The heterogeneous nature of e-waste and ASR, and the need for automated analysis of large numbers of samples to support industrial-scale recycling present particular challenges.
Rapidly and accurately assaying high-value elements in bulk samples is also important for the minerals industry. The method of gamma activation analysis (GAA) has been recognized as one solution [9, 10, 11] to this problem. A complement to the more commonly used neutron activation analysis, GAA involves irradiating samples with a high-energy X-ray beam to induce nuclear reactions in target elements. This induced radioactivity can be measured and related back to the elemental composition of the sample being analyzed.
Our work [12] has focused on improving the sensitivity and accuracy of the GAA method, particularly for the analysis of trace elements such as gold. In this preliminary study, we explore the application of the GAA technique to the analysis of gold, silver, and other elements in waste materials.
We particularly concentrate on activation reactions with very short half-lives that allow analysis to be completed in a few minutes. A secondary advantage of using short half-life reactions is that residual activity of samples after analysis is very low. For example, surface dose rates are generally unmeasurable above natural background about 1 hour after the measurement process is completed, and calculated radioisotope levels are below recommended clearance levels [13].
Electronic and Automotive Waste Samples
Electronic waste primarily consists of PCBs, solder, and electronic components. PCBs comprise a substrate material with copper layers on one or both surfaces, etched to form conductive tracks. Electronic components may be mounted on one or both sides of the board. Multi-layer boards are also commonly encountered, which include additional internal copper conducting layers to facilitate more complex circuit layouts.
Substrates for circuit board construction comprise a stiffening material bonded with a resin; fire retardants, often bromine-based, may also be added. Older, lower-cost substrate materials use cellulose-paper as the stiffening material and a phenolic or epoxy resin. The most commonly used substrate material, known as FR4, is a fiber-glass epoxy-resin composite. The electronic components mounted onto the circuit boards are made from a wide range of materials, including many metals and ceramics. Precious metals commonly used in the fabrication of these components include gold, silver, the platinum group elements (including platinum, palladium, ruthenium, rhodium, and iridium), and tantalum. The solder used to connect components to the circuit board may contain significant concentrations of lead, tin, copper, silver, bismuth, indium, zinc, and antinomy.
The electronic waste samples used for this study were sourced from the recycling unit of the University of New South Wales in Sydney, Australia. Three samples of randomly selected PCBs from discarded computer monitors and processing units were chosen.
Sample (a) was taken from a cathode ray tube (CRT) monitor. This was a single-sided, paper/resin laminate PCB. The entire board was shredded using a knife mill into approximately 5 mm pieces. Sample (b) was taken from a PCB inside a flat-panel LCD monitor. It was a double-sided board with a polymer substrate. Sample (c) was taken from a computer motherboard; it had a multi-layer, fiber-glass-based construction. Samples 2 and 3 were found to be too hard to shred using the knife mill, so the boards were manually broken into pieces measuring about 10 mm.
The fourth sample chosen for testing was automotive shredded residue (ASR), sourced from OneSteel Recycling based in Newcastle, NSW, Australia. The material received had a particle top size of approximately 5 mm and was measured as received.
Figure 1 shows the electronic waste and ASR samples in the form in which they were analyzed.
Photographs of electronic and automotive waste samples used for gamma activation analysis tests
Conclusions
We have demonstrated that gamma activation analysis provides a powerful tool for analyzing both valuable and hazardous elements in waste materials. The advantages of GAA include the following:
True, bulk analysis of large and heterogeneous samples
Rapid measurement, with no sample preparation required, and results available in a few minutes
Excellent sensitivity for economically and environmentally important elements, including gold, silver, copper, tin, bromine, and lead.
The use of Monte Carlo-based radiation transport modeling allows calibration information to be readily transferred between different sample types, facilitating calibration of a GAA system using commercially available standards.
We are currently working to establish a commercial GAA facility in Australia for routine analysis of gold, silver, copper, and other elements in mineral ores. Such a facility would be equally applicable for valuing the metal content of samples of waste materials, and for monitoring processing and extraction operations.
XO___XO XXX = Composition of Planet Mars
Mars is the "Red Planet" for a very good reason: its surface is made of a thick layer of oxidized iron dust and rocks of the same color. Maybe another name for Mars could be "Rusty." But the ruddy surface does not tell the whole story of the composition of this world.
Dusty crust
The dust that covers the surface of Mars is fine like talcum powder. Beneath the layer of dust, the Martian crust consists mostly of volcanic basalt rock. The soil of Mars also holds nutrients such as sodium, potassium, chloride and magnesium. The crust is between 6 and 30 miles (10 and 50 kilometers) thick, according to NASA.
Mars' crust is thought to be one piece. Unlike Earth, the red planet has no tectonic plates that ride on the mantle to reshape the terrain. Since there is little to no movement in the crust, molten rock flowed to the surface at the same point for successive eruptions, building up into the huge volcanoes that dot the Martian surface.
Dusty, glass-rich sand dunes like these found just south of the north polar ice cap could cover much of Mars. (False color image)
Credit: NASA/JPL/University of Arizona
That doesn't mean the crust sits quietly. New research has found that powerful landslides may speed down Martian slopes at up to 450 mph (725 km/h).
"The calculated velocity of landslides (often well in excess of 100 m/s and up to 200 m/s at peak) compares well with velocity estimates based on the run-up of the landslides on mounds," researchers wrote in a study published in The European Physical Journal Plus.
"We conclude that ice may have been an important medium of lubrication of landslides on Mars, even in equatorial areas like Valles Marineris" (the Grand Canyon of Mars).
Any life that ever existed on Mars would have had to cope with the radiation, perhaps by thriving underground. While astronomers continue to search for past or present signs of biology on Mars, no convincing evidence has yet been found.
Elemental abundances can be determined remotely by orbiting spacecraft. This map shows the surface concentration (by weight percent) of the element silicon based on data from the Gamma Ray Spectrometer (GRS) Suite on the Mars Odyssey spacecraft. Similar maps exist for a number of other elements.
Also like Earth, Mars is a differentiated planet, meaning that it has a central core made up of metallic iron and nickel surrounded by a less dense, silicate mantle and crust.[4] The planet's distinctive red colour is due to the oxidation of iron on its surface.
Much of what we know about the elemental composition of Mars comes from orbiting spacecraft and landers. (See Exploration of Mars for list.) Most of these spacecraft carry spectrometers and other instruments to measure the surface composition of Mars by either remote sensing from orbit or in situ analyses on the surface. We also have many actual samples of Mars in the form of meteorites that have made their way to Earth. Martian meteorites (often called SNC's, for Shergottites, Nakhlites, and Chassignites[5]—the groups of meteorites first shown to have a martian origin) provide data on the chemical composition of Mars' crust and interior that would not otherwise be available except through a sample return mission.
Based on these data sources, scientists think that the most abundant chemical elements in the Martian crust, besides silicon and oxygen, are iron, magnesium, aluminum, calcium, and potassium. These elements are major components of the minerals comprising igneous rocks.[6] The elements titanium, chromium, manganese, sulfur, phosphorus, sodium, and chlorine are less abundant[7][8] but are still important components of many accessory minerals[9] in rocks and of secondary minerals (weathering products) in the dust and soils (the regolith). Hydrogen is present as water (H2O) ice and in hydrated minerals. Carbon occurs as carbon dioxide (CO2) in the atmosphere and sometimes as dry ice at the poles. An unknown amount of carbon is also stored in carbonates. Molecular nitrogen (N2) makes up 2.7 percent of the atmosphere. As far as we know, organic compounds are absent[10]except for a trace of methane detected in the atmosphere.[11][12]
On 16 December 2014, NASA reported the Curiosity rover detected a "tenfold spike", likely localized, in the amount of methane in the Martian atmosphere. Sample measurements taken "a dozen times over 20 months" showed increases in late 2013 and early 2014, averaging "7 parts of methane per billion in the atmosphere." Before and after that, readings averaged around one-tenth that level.[13][14]
The elemental composition of Mars is different from Earth′s in several significant ways. First, Martian meteorite analysis suggests that the planet's mantle is about twice as rich in iron as the Earth's mantle.[15][16] Second, its core is richer in sulphur.[17] Third, the Martian mantle is richer in potassium and phosphorus than Earth's and fourth, the Martian crust contains a higher percentage of volatile elements such as sulphur and chlorine than the Earth's crust does. Many of these conclusions are supported by in situ analyses of rocks and soils on the Martian surface.[18]
Mars is fundamentally an igneous planet. Rocks on the surface and in the crust consist predominantly of minerals that crystallize from magma. Most of our current knowledge about the mineral composition of Mars comes from spectroscopic data from orbiting spacecraft, in situ analyses of rocks and soils from six landing sites, and study of the Martian meteorites.[19] Spectrometers currently in orbit include THEMIS (Mars Odyssey), OMEGA (Mars Express), and CRISM (Mars Reconnaissance Orbiter). The two Mars exploration rovers each carry an Alpha Particle X-ray Spectrometer (APXS), a thermal emission spectrometer (Mini-TES), and Mössbauer spectrometer to identify minerals on the surface.
The dark areas of Mars are characterised by the mafic rock-forming minerals olivine, pyroxene, and plagioclasefeldspar. These minerals are the primary constituents of basalt, a dark volcanic rock that also makes up the Earth's oceanic crust and the lunar maria.
Mars Odyssey THEMIS false-colour image of olivine basalts in the Valles Marineris. Layers rich in olivine appear purple.
The mineral olivine occurs all over the planet, but some of the largest concentrations are in Nili Fossae, an area containing Noachian-aged rocks. Another large olivine-rich outcrop is in Ganges Chasma, an eastern side chasm of Valles Marineris (pictured).[21] Olivine weathers rapidly into clay minerals in the presence of liquid water. Therefore, areas with large outcroppings of olivine-bearing rock indicate that liquid water has not been abundant since the rocks formed.[5]
Pyroxene minerals are also widespread across the surface. Both low-calcium (ortho-) and high-calcium (clino-) pyroxenes are present, with the high-calcium varieties associated with younger volcanic shields and the low-calcium forms (enstatite) more common in the old highland terrain. Because enstatite melts at a higher temperature than its high-calcium cousin, some researchers have argued that its presence in the highlands indicates that older magmas on Mars had higher temperatures than younger ones.[22]
Between 1997 and 2006, the Thermal Emission Spectrometer (TES) on the Mars Global Surveyor (MGS) spacecraft mapped the global mineral composition of the planet.[23] TES identified two global-scale volcanic units on Mars. Surface Type 1 (ST1) characterises the Noachian-aged highlands and consists of unaltered plagioclase- and clinopyroxene-rich basalts. Surface Type 2 (ST2) is common in the younger plains north of the dichotomy boundary and is more silica rich than ST1.
The lavas of ST2 have been interpreted as andesites or basaltic andesites, indicating the lavas in the northern plains originated from more chemically evolved, volatile-rich magmas.[24] (See Igneous differentiation and Fractional crystallization.) However, other researchers have suggested that ST2 represents weathered basalts with thin coatings of silica glass or other secondary minerals that formed through interaction with water- or ice-bearing materials.[25]
True intermediate and felsic rocks are present on Mars, but exposures are uncommon. Both TES and the Thermal Emission Imaging System (THEMIS) on the Mars Odyssey spacecraft have identified high-silica rocks in Syrtis Major and near the southwestern rim of the crater Antoniadi. The rocks have spectra resembling quartz-rich dacites and granitoids, suggesting that at least some parts of the Martian crust may have a diversity of igneous rocks similar to Earth's.[26] Some geophysical evidence suggests that the bulk of the Martian crust may actually consist of basaltic andesite or andesite. The andesitic crust is hidden by overlying basaltic lavas that dominate the surface composition but are volumetrically minor.[4]
Rocks studied by Spirit Rover in Gusev crater can be classified in different ways. The amounts and types of minerals make the rocks primitive basalts—also called picritic basalts. The rocks are similar to ancient terrestrial rocks called basaltic komatiites. Rocks of the plains also resemble the basaltic shergottites, meteorites which came from Mars. One classification system compares the amount of alkali elements to the amount of silica on a graph; in this system, Gusev plains rocks lie near the junction of basalt, picrobasalt, and tephite. The Irvine-Barager classification calls them basalts.[27]
Curiosity rover - view of "Sheepbed" mudstone (lower left) and surroundings (February 14, 2013).
In the journal Science from September 2013, researchers described a different type of rock called "Jake M" or "Jake Matijevic (rock),” It was the first rock analyzed by the Alpha Particle X-ray Spectrometer instrument on the Curiosity rover, and it was different from other known martian igneous rocks as it is alkaline (>15% normative nepheline) and relatively fractionated. Jake M is similar to terrestrial mugearites, a rock type typically found at ocean islands and continental rifts. Jake M's discovery may mean that alkaline magmas may be more common on Mars than on Earth and that Curiosity could encounter even more fractionated alkaline rocks (for example, phonolites and trachytes).[31]
On December 9, 2013, NASA researchers described, in a series of six articles in the journal Science, many new discoveries from the Curiosity rover. Possible organics were found that could not be explained by contamination.[32][33] Although the organic carbon was probably from Mars, it can all be explained by dust and meteorites that have landed on the planet.[34][35][36] Because much of the carbon was released at a relatively low temperature in Curiosity’s Sample Analysis at Mars (SAM) instrument package, it probably did not come from carbonates in the sample. The carbon could be from organisms, but this has not been proven. This organic-bearing material was obtained by drilling 5 centimeters deep in a site called Yellowknife Bay into a rock called “Sheepbed mudstone”. The samples were named John Klein and Cumberland. Microbes could be living on Mars by obtaining energy from chemical imbalances between minerals in a process called chemolithotrophy which means “eating rock.”[37] However, in this process only a very tiny amount of carbon is involved — much less than was found at Yellowknife Bay.[38][39]
Using SAM’s mass spectrometer, scientists measured isotopes of helium, neon, and argon that cosmic rays produce as they go through rock. The fewer of these isotopes they find, the more recently the rock has been exposed near the surface. The 4-billion-year-old lakebed rock drilled by Curiosity was uncovered between 30 million and 110 million years ago by winds which sandblasted away 2 meters of overlying rock. Next, they hope to find a site tens of millions of years younger by drilling close to an overhanging outcrop.[40]
The absorbed dose and dose equivalent from galactic cosmic rays and solar energetic particles on the Martian surface for ~300 days of observations during the current solar maximum was measured. These measurements are necessary for human missions to the surface of Mars, to provide microbial survival times of any possible extant or past life, and to determine how long potential organic biosignatures can be preserved. This study estimates that a few meters drill is necessary to access possible biomolecules.[41] The actual absorbed dose measured by the Radiation Assessment Detector (RAD) is 76 mGy/yr at the surface. Based on these measurements, for a round trip Mars surface mission with 180 days (each way) cruise, and 500 days on the Martian surface for this current solar cycle, an astronaut would be exposed to a total mission dose equivalent of ~1.01 sievert. Exposure to 1 sievert is associated with a 5 percent increase in risk for developing fatal cancer. NASA's current lifetime limit for increased risk for its astronauts operating in low-Earth orbit is 3 percent.[42] Maximum shielding from galactic cosmic rays can be obtained with about 3 meters of Martian soil.[43]
The samples examined were probably once mud that for millions to tens of millions of years could have hosted living organisms. This wet environment had neutral pH, low salinity, and variable redox states of both iron and sulfur species.[34][44][45][46] These types of iron and sulfur could have been used by living organisms.[47]C, H, O, S, N, and P were measured directly as key biogenic elements, and by inference, P is assumed to have been there as well.[37][39] The two samples, John Klein and Cumberland, contain basaltic minerals, Ca-sulfates, Fe oxide/hydroxides, Fe-sulfides, amorphous material, and trioctahedral smectites (a type of clay). Basaltic minerals in the mudstone are similar to those in nearby aeoliandeposits. However, the mudstone has far less Fe-forsterite plus magnetite, so Fe-forsterite (type of olivine) was probably altered to form smectite (a type of clay) and magnetite.[48] A Late Noachian/EarlyHesperian or younger age indicates that clay mineral formation on Mars extended beyond Noachian time; therefore, in this location neutral pH lasted longer than previously thought.[44]
Much of the Martian surface is deeply covered by dust as fine as talcum powder. The global predominance of dust obscures the underlying bedrock, making spectroscopic identification of primary minerals impossible from orbit over many areas of the planet. The red/orange appearance of the dust is caused by iron(III) oxide (nanophase Fe2O3) and the iron(III) oxide-hydroxide mineral goethite.[51]
The global dust cover and the presence of other wind-blown sediments has made soil compositions remarkably uniform across the Martian surface. Analysis of soil samples from the Viking landers in 1976, Pathfinder, and the Mars Exploration rovers show nearly identical mineral compositions from widely separated locations around the planet.[53] The soils consist of finely broken up basaltic rock fragments and are highly enriched in sulphur and chlorine, probably derived from volcanic gas emissions.[54]
Opaline silica and iron sulphate minerals form in acidic (low pH) solutions. Sulphates have been found in a variety of locations, including near Juventae Chasma, Ius Chasma, Melas Chasma, Candor Chasma, and Ganges Chasma. These sites all contain fluvial landforms indicating that abundant water was once present.[55] Spirit rover discovered sulfates and goethite in the Columbia Hills.[56][57]
Some of the mineral classes detected may have formed in environments suitable (i.e., enough water and the proper pH) for life. The mineral smectite (a phyllosilicate) forms in near-neutral waters. Phyllosilicates and carbonates are good for preserving organic matter, so they may contain evidence of past life.[58][59] Sulfate deposits preserve chemical and morphological fossils, and fossils of microorganisms form in iron oxides like hematite.[60] The presence of opaline silica points toward a hydrothermal environment that could support life. Silica is also excellent for preserving evidence of microbes.[61]
Huygens Crater with circle showing place where carbonate was discovered. This deposit may represent a time when Mars had abundant liquid water on its surface. Scale bar is 250 km long.
Layered sedimentary deposits are widespread on Mars. These deposits probably consist of both sedimentary rock and poorly indurated or unconsolidated sediments. Thick sedimentary deposits occur in the interior of several canyons in Valles Marineris, within large craters in Arabia and Meridiani Planum (see Henry Crater for example), and probably comprise much of the deposits in the northern lowlands (e.g., Vastitas Borealis Formation). The Mars Exploration Rover Opportunity landed in an area containing cross-bedded (mainly eolian) sandstones (Burns formation[62]). Fluvial-deltaic deposits are present in Eberswalde Crater and elsewhere, and photogeologic evidence suggests that many craters and low lying intercrater areas in the southern highlands contain Noachian-aged lake sediments.
While the possibility of carbonates on Mars has been of great interest to exobiologists and geochemists alike, there was little evidence for significant quantities of carbonate deposits on the surface. In the summer of 2008, the TEGA and WCL experiments on the 2007 Phoenix Mars lander found between 3–5wt% (percent by weight) calcite (CaCO3) and an alkaline soil.[63] In 2010, analyses by the Mars Exploration Rover Spirit identified outcrops rich in magnesium-iron carbonate (16–34 wt%) in the Columbia Hills of Gusev crater. The magnesium-iron carbonate most likely precipitated from carbonate-bearing solutions under hydrothermal conditions at near-neutral pH in association with volcanic activity during the Noachian Period.[64]
Carbonates (calcium or iron carbonates) were discovered in a crater on the rim of Huygens Crater, located in the Iapygia quadrangle. The impact on the rim exposed material that had been dug up from the impact that created Huygens. These minerals represent evidence that Mars once had a thicker carbon dioxide atmosphere with abundant moisture, since these kind of carbonates only form when there is a lot of water. They were found with the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter. Earlier, the instrument had detected clay minerals. The carbonates were found near the clay minerals. Both of these minerals form in wet environments. It is supposed that billions of years ago Mars was much warmer and wetter. At that time, carbonates would have formed from water and the carbon dioxide-rich atmosphere. Later the deposits of carbonate would have been buried. The double impact has now exposed the minerals. Earth has vast carbonate deposits in the form of limestone.[65]
Spirit Rover discoveries in the Aeolis quadrangle
The rocks on the plains of Gusev are a type of basalt. They contain the mineralsolivine, pyroxene, plagioclase, and magnetite, and they look like volcanic basalt as they are fine-grained with irregular holes (geologists would say they have vesicles and vugs).Much of the soil on the plains came from the breakdown of the local rocks. Fairly high levels of nickel were found in some soils; probably from meteorites.[68] Analysis shows that the rocks have been slightly altered by tiny amounts of water. Outside coatings and cracks inside the rocks suggest water deposited minerals, maybe bromine compounds. All the rocks contain a fine coating of dust and one or more harder rinds of material. One type can be brushed off, while another needed to be ground off by the Rock Abrasion Tool (RAT).[69]
There are a variety of rocks in the Columbia Hills (Mars), some of which have been altered by water, but not by very much water.
The dust in Gusev Crater is the same as dust all around the planet. All the dust was found to be magnetic. Moreover, Spirit found the magnetism was caused by the mineral magnetite, especially magnetite that contained the element titanium. One magnet was able to completely divert all dust hence all Martian dust is thought to be magnetic.[52] The spectra of the dust was similar to spectra of bright, low thermal inertia regions like Tharsis and Arabia that have been detected by orbiting satellites. A thin layer of dust, maybe less than one millimeter thick covers all surfaces. Something in it contains a small amount of chemically bound water.[70][71]
Plains
Adirondack
Above: An approximate true-color view of Adirondack, taken by Spirit's pancam. Right:Digital camera image (from Spirit's Pancam) of Adirondack after a RAT grind (Spirit's rock grinding tool)
Observations of rocks on the plains show they contain the minerals pyroxene, olivine, plagioclase, and magnetite. These rocks can be classified in different ways. The amounts and types of minerals make the rocks primitive basalts—also called picritic basalts. The rocks are similar to ancient terrestrial rocks called basaltic komatiites. Rocks of the plains also resemble the basaltic shergottites, meteorites which came from Mars. One classification system compares the amount of alkali elements to the amount of silica on a graph; in this system, Gusev plains rocks lie near the junction of basalt, picrobasalt, and tephite. The Irvine-Barager classification calls them basalts.[27] Plain's rocks have been very slightly altered, probably by thin films of water because they are softer and contain veins of light colored material that may be bromine compounds, as well as coatings or rinds. It is thought that small amounts of water may have gotten into cracks inducing mineralization processes).[27][67] Coatings on the rocks may have occurred when rocks were buried and interacted with thin films of water and dust. One sign that they were altered was that it was easier to grind these rocks compared to the same types of rocks found on Earth.
The first rock that Spirit studied was Adirondack. It turned out to be typical of the other rocks on the plains.
Columbia Hills
Scientists found a variety of rock types in the Columbia Hills, and they placed them into six different categories. The six are: Adirondack, Clovis, Wishstone, Peace, Watchtower, Backstay, and Independence. They are named after a prominent rock in each group. Their chemical compositions, as measured by APXS, are significantly different from each other.[72] Most importantly, all of the rocks in Columbia Hills show various degrees of alteration due to aqueous fluids.[73] They are enriched in the elements phosphorus, sulfur, chlorine, and bromine—all of which can be carried around in water solutions. The Columbia Hills' rocks contain basaltic glass, along with varying amounts of olivine and sulfates.[74][56] The olivine abundance varies inversely with the amount of sulfates. This is exactly what is expected because water destroys olivine but helps to produce sulfates.
The Clovis group is especially interesting because the Mossbauer spectrometer (MB) detected goethite in it.[57] Goethite forms only in the presence of water, so its discovery is the first direct evidence of past water in the Columbia Hills's rocks. In addition, the MB spectra of rocks and outcrops displayed a strong decline in olivine presence, although the rocks probably once contained much olivine.[75] Olivine is a marker for the lack of water because it easily decomposes in the presence of water. Sulfate was found, and it needs water to form. Wishstone contained a great deal of plagioclase, some olivine, and anhydrate (a sulfate). Peace rocks showed sulfur and strong evidence for bound water, so hydrated sulfates are suspected. Watchtower class rocks lack olivine consequently they may have been altered by water. The Independence class showed some signs of clay (perhaps montmorillonite a member of the smectite group). Clays require fairly long term exposure to water to form. One type of soil, called Paso Robles, from the Columbia Hills, may be an evaporate deposit because it contains large amounts of sulfur, phosphorus, calcium, and iron.[76] Also, MB found that much of the iron in Paso Robles soil was of the oxidized, Fe+++form, which would happen if water had been present.[70]
Towards the middle of the six-year mission (a mission that was supposed to last only 90 days), large amounts of pure silica were found in the soil. The silica could have come from the interaction of soil with acid vapors produced by volcanic activity in the presence of water or from water in a hot spring environment.[77]
After Spirit stopped working scientists studied old data from the Miniature Thermal Emission Spectrometer, or Mini-TES and confirmed the presence of large amounts of carbonate-rich rocks, which means that regions of the planet may have once harbored water. The carbonates were discovered in an outcrop of rocks called "Comanche."[78][79]
In summary, Spirit found evidence of slight weathering on the plains of Gusev, but no evidence that a lake was there. However, in the Columbia Hills there was clear evidence for a moderate amount of aqueous weathering. The evidence included sulfates and the minerals goethite and carbonates which only form in the presence of water. It is believed that Gusev crater may have held a lake long ago, but it has since been covered by igneous materials. All the dust contains a magnetic component which was identified as magnetite with some titanium. Furthermore, the thin coating of dust that covers everything on Mars is the same in all parts of Mars.
Opportunity rover discoveries in the Margaritifer Sinus quadrangle
This image, taken by the microscopic imager, reveals shiny, spherical objects embedded within the trench wall
"Blueberries" (hematite spheres) on a rocky outcrop at Eagle Crater. Note the merged triplet in the upper left.
Drawing showing how "blueberries" came to cover much of surface in Meridiani Planum.
The rock "Berry Bowl".
Opportunity Rover found that the soil at Meridiani Planum was very similar to the soil at Gusev crater and Ares Vallis; however in many places at Meridiani the soil was covered with round, hard, gray spherules that were named "blueberries."[80] These blueberries were found to be composed almost entirely of the mineral hematite. It was decided that the spectra signal spotted from orbit by Mars Odyssey was produced by these spherules. After further study it was decided that the blueberries were concretions formed in the ground by water.[70] Over time, these concretions weathered from what was overlying rock, and then became concentrated on the surface as a lag deposit. The concentration of spherules in bedrock could have produced the observed blueberry covering from the weathering of as little as one meter of rock.[81][82] Most of the soil consisted of olivine basalt sands that did not come from the local rocks. The sand may have been transported from somewhere else.[83]
Minerals in dust
A Mossbauer spectrum was made of the dust that gathered on Opportunity's capture magnet. The results suggested that the magnetic component of the dust was titanomagnetite, rather than just plain magnetite, as was once thought. A small amount of olivine was also detected which was interpreted as indicating a long arid period on the planet. On the other hand, a small amount of hematite that was present meant that there may have been liquid water for a short time in the early history of the planet.[84] Because the Rock Abrasion Tool (RAT) found it easy to grind into the bedrocks, it is thought that the rocks are much softer than the rocks at Gusev crater.
Bedrock minerals
Few rocks were visible on the surface where Opportunity landed, but bedrock that was exposed in craters was examined by the suite of instruments on the Rover.[85] Bedrock rocks were found to be sedimentary rocks with a high concentration of sulfur in the form of calcium and magnesium sulfates. Some of the sulfates that may be present in bedrocks are kieserite, sulfate anhydrate, bassanite, hexahydrite, epsomite, and gypsum. Salts, such as halite, bischofite, antarcticite, bloedite, vanthoffite, or gluberite may also be present.[86][87]
"Homestake" formation
The rocks contained the sulfates had a light tone compared to isolated rocks and rocks examined by landers/rovers at other locations on Mars. The spectra of these light toned rocks, containing hydrated sulfates, were similar to spectra taken by the Thermal Emission Spectrometer on board the Mars Global Surveyor. The same spectrum is found over a large area, so it is believed that water once appeared over a wide region, not just in the area explored by Opportunity Rover.[88]
The Alpha Particle X-ray Spectrometer (APXS) found rather high levels of phosphorus in the rocks. Similar high levels were found by other rovers at Ares Vallis and Gusev Crater, so it has been hypothesized that the mantle of Mars may be phosphorus-rich.[89] The minerals in the rocks could have originated by acid weathering of basalt. Because the solubility of phosphorus is related to the solubility of uranium, thorium, and rare earth elements, they are all also expected to be enriched in rocks.[90]
When Opportunity rover traveled to the rim of Endeavour crater, it soon found a white vein that was later identified as being pure gypsum.[91][92] It was formed when water carrying gypsum in solution deposited the mineral in a crack in the rock. A picture of this vein, called "Homestake" formation, is shown below.
Evidence of water
Cross-bedding features in rock "Last Chance".
Voids or "vugs" inside the rock
Heat Shield Rock was the first meteorite ever identified on another planet.
Heat shield, with Heat Shield Rock just above and to the left in the background.
Examination in 2004 of Meridiani rocks, showed the first strong in situ evidence for past water by detecting the mineral jarosite, which only forms in water. This discovery proved that water once existed in Meridiani Planum.[93] In addition, some rocks showed small laminations (layers) with shapes that are only made by gently flowing water.[94] The first such laminations were found in a rock called "The Dells." Geologists would say that the cross-stratification showed festoon geometry from transport in subaqueous ripples.[87] A picture of cross-stratification, also called cross-bedding, is shown on the left.
Box-shaped holes in some rocks were caused by sulfates forming large crystals, and then when the crystals later dissolved, holes, called vugs, were left behind.[94] The concentration of the element bromine in rocks was highly variable probably because it is very soluble. Water may have concentrated it in places before it evaporated. Another mechanism for concentrating highly soluble bromine compounds is frost deposition at night that would form very thin films of water that would concentrate bromine in certain spots.[80]
Rock from impact
One rock, "Bounce Rock," found sitting on the sandy plains was found to be ejecta from an impact crater. Its chemistry was different from the bedrocks. Containing mostly pyroxene and plagioclase and no olivine, it closely resembled a part, Lithology B, of the shergottite meteorite EETA 79001, a meteorite known to have come from Mars. Bounce rock received its name by being near an airbag bounce mark.[81]
Meteorites
Opportunity Rover found meteorites just sitting on the plains. The first one analyzed with Opportunity's instruments was called "Heatshield Rock," as it was found near where Opportunity's heatshield landed. Examination with the Miniature Thermal Emission Spectrometer (Mini-TES), Mossbauer spectrometer, and APXS lead researchers to, classify it as an IAB meteorite. The APXS determined it was composed of 93% iron and 7% nickel. The cobble named "Fig Tree Barberton" is thought to be a stony or stony-iron meteorite (mesosiderite silicate),[95] while "Allan Hills," and "Zhong Shan" may be iron meteorites.
Geological history
Observations at the site have led scientists to believe that the area was flooded with water a number of times and was subjected to evaporation and desiccation.[81] In the process sulfates were deposited. After sulfates cemented the sediments, hematite concretions grew by precipitation from groundwater. Some sulfates formed into large crystals which later dissolved to leave vugs. Several lines of evidence point toward an arid climate in the past billion years or so, but a climate supporting water, at least for a time, in the distant past.[96]
Curiosity Rover discoveries in the Aeolis quadrangle
On September 27, 2012, NASA scientists announced that the Curiosity rover found evidence for an ancient streambed suggesting a "vigorous flow" of water on Mars.[1][2][3]
On 16 December 2014, NASA reported the Curiosity rover detected a "tenfold spike", likely localized, in the amount of methane in the Martian atmosphere. Sample measurements taken "a dozen times over 20 months" showed increases in late 2013 and early 2014, averaging "7 parts of methane per billion in the atmosphere." Before and after that, readings averaged around one-tenth that level.[13][14]
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Notes: * = linked article is about the mission that encountered this rock; M = Meteorite - (
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