Gold mining equipment mexico

Gold mining equipment mexico

Although the outlook for gold mining is much improved, those who are interested in working or financing gold properties should not be unduly optimistic. Many gold deposits in New Mexico and elsewhere are still too low grade to be worked successfully, It is possible to obtain picked samples from many worthless deposits which give assay returns far greater than the average of the material that can be mined. A vein a quarter of an inch wide may actually contain S 1,000 to the ton in gold, but when diluted with the adjacent country rock that must be mined with it, the resulting ore would have a gross value of less than S8 a ton. Mining, transportation and treatment expenses for ore of this grade in many places would exceed the metal value, and mining could be carried on only at a loss. Gold gravels which would pay handsomely if at the surface may be fatally handicapped by barren over-burden that must be removed before they can be reached. Placer ground that would be workable with abundant water near at hand may be valueless because of the scarcity of water or the cost of bringing it to the deposits.

New Mexico has suffered greatly from the promostion of ill-advised mining projects. Unquestionably, many statements regarding mineral deposits in the State have been made by promoters and others which would not be substantiated by efficient investigations of the deposits. Before any gold mining program requiring a large or even moderate expenditure in advance of actual production is adopted, the deposit should be carefully examined by a reliable mining engineer or mining geologist and a favorable report received from him. Particularly in the case of placer deposits the examination should include thorough, systematic and accurate sampling. The examination may cost hundreds or even thousands of dollars, but if it proves the property to be non-commercial, many times its cost in useless expenditures will be saved. If favorable, it should contain information of much value to the owners regarding the character and grade of the deposit and proper methods of mining and treatment. A favorable report does not necessarily assure profitable mining, but it should indicate a reasonable probability of successful operation.

MINING AND TREATMENT OF PLACER MATERIAL

Shallow placer material is mined in open cuts with picks and shovels, plows and horse scrapers, power scrapers, drag-line excavators, and power shovels; and worthless overburden, if not too thick is removed by one of these methods. The gravel is transported to the gold-saving plant mechanically or by running water. Deep pay streaks can be worked by drift mining without disturbing the overlying material but at relatively increased cost.

The simplest apparatus for recovering gold from placers is the miner’s pan, and it is indispensable in prospecting, Its capacity is small – about one cubic yard per day – but in the hands of a skillful operator it is quite efficient. A surprising amount of gold has been obtained by its use.

The rocker is used in prospecting and in working small placer deposits. The gravel is passed through the machine with a rocking motion, and the gold collects against riffles or on an apron. The rocker is easily and cheaply constructed and obtains good gold recoveries with a moderate amount of water. It gives best results when operated by two men, who can handle from three to five cubic yards of gravel per day with it.

The sluicing method of recovering gold is practiced where the deposit is of at least moderate size and water is abundant. The sluice (also called riffle box) is a slightly inclined trough with cross-pieces or other obstructions in the bottom, called riffles. The gravel is deposited in the head box at the upper end and washed through the sluice with water. The gold collects in front of the riffles. Mercury is sometimes used to aid in collecting the gold.

Placer gold that is granular and not too fine can be recovered effectively by running the closely-sized sand over a standard concentrating table,

Several wet machines have been placed on the market recently which recover the gold from placers with a reduced amount of water. Dry placer machines, in the operation of which no water is required, do not save as much gold as wet machines, and they have not been satisfactory with many gravels, If these machines are sufficiently improved they may be used successfully at certain deposits where the water problem is serious.

Hydraulic mining consists of excavating the gravel deposit by directing a stream of water under considerable pressure against it, washing the material to a sluice through which it passes and in which the gold is caught, and disposing of the tailings. The most important requirements for this type of mining are an ample supply of cheap water under high pressure, sufficient grade on bed-rock for the sluices, and adequate dump room for the tailings. The disposal of the tailings may entail difficulties in agricultural areas. Under favorable conditions hydraulic mining is much less expensive than hand methods or ordinary sluicing.

The gold dredge is a scow supplied with a mechanical excavator and elevator – usually a digging ladder and an endless system of buckets – screening and washing plant, and gold-saving equipment. This method is suitable to extensive river-bar and gravel-plain placers which are fairly thick and have a level bedrock. The dredge must operate while floating on the water, and hence the conditions must be such that a pond for it can be maintained. Numerous large boulders in the gravel may seriously interfere with dredging operations. Dredges are expensive, but they handle material at a lower cost per cubic yard than is possible by any other method.

MIKING AND MILLING OF GOLD ORES

Lode gold ores are ordinarily mined in the same manner as the lode deposits of other metals having the same size, shape and physical characteristics. A discussion of methods is beyond the scope of this report,

Gold ores consist of (a) shipping ores, or those rich enough in gold to be shipped to a smelter, and (b) milling ores, or those too low in gold content to stand transportation and smelter treatment costs, but which can be profitably milled near the deposit and the resulting bullion or other product marketed. Some ores that are below shipping grade as mined can be hand sorted, and a product obtained that is acceptable at the smelter. At most gold deposits the amount of milling ore is many times larger than the shipping ore. Most of the ore taken from New Mexico gold mines has been milled.

Many gold mills have been constructed and then operated for only a few weeks or months because of a deficiency in the amount or value of the ore, or both. It is never advisable to construct a mill until a sufficient quantity of ore of satisfactory grade is blocked out to justify its cost, and only after experimental work has definitely indicated the best milling process.

The most important milling methods for gold ores are amalgamation, cyanidation and concentration, In the amalgamation process the ore is usually crushed in a stamp mill and the gold collected by mercury. This process is only adaptable to free-milling ores – those in which the gold is in the native form. This class of ore is usually confined to the oxidized zone, and the deeper sulphide ores may not be amenable to this process. The amalgam, consisting of mercury and gold, is retorted, and the residue containing the gold is melted into bars, in which form it is sold. Silver in the native form is also recovered by this process.

In the cyanide process the ore is ground to the necessary fineness and the gold is dissolved in an alkaline solution of potassium or sodium cyanide. From the solution the gold is precipitated by zinc shavings or zinc dust. The precipitate is run through a filter press and melted into bullion bars for the market. Cyanidation is effective for the recovery of both gold and silver in the native form and also when contained in the sulphides and other minerals. Copper in the ore may interfere with cyaniding.

In some mills gold ores are concentrated by gravity methods or flotation, and the concentrates are sold to a smelter. Payment is made by the smelter not only for the gold and silver in the concentrates but for certain other metals if present in sufficient amounts. For many ores some combination of the above methods gives best results.

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