Small Gold Plant

Gold Leaching Circuits & Equipment

In Leaching for Gold, there is often a tendency to overlook or minimize the importance of the small mine. The small mine of today may develop into the large mine of tomorrow. Under proper management and financing it has as good a chance of yielding a profit as the larger property. Unfortunately large capital is seldom interested in them and they are left to the small groups who are not in a position to obtain the best engineering service. Mills are often erected without proper metallurgical tests and expensive Gold Leaching plant equipment are installed at a time when such large expenditures of capital on the surface is not justified by the underground developments. Careful metallurgical testing on the ore might have disclosed the fact that a simple method of amalgamation or concentration could have been employed and the mill built for a third the cost of a Gold Leaching plant.

By taking advantage of the fact that gold is one of the heaviest metals known and readily forms an amalgam with mercury, an effective but simple and inexpensive plant can be built for most small gold mines. Usually the major percentage of the gold values are in the “native’’ or metallic state and are free at commercial fineness of grinding and can be recovered by some combination of amalgamation and concentration.

Plate amalgamation, where the gold values are caught and held in the quicksilver film on a copper plate is the only step required for a commercial recovery on some few ores. In most cases a portion of the gold is filmed so that it does not amalgamate readily or is contained in ores with other minerals that also amalgamate or “foul” the quicksilver sufficiently to destroy its effectiveness for gold recovery. Here a form of selective concentration such as the Mineral Jigs and blanket tables, is used to concentrate the gold values in a small bulk of high grade concentrates for treatment in an amalgamation barrel or other amalgamator, where the gold is amalgamated and recovered as bullion.

The advantages of these simple plants are many and are not only attractive to the proved small mine but also to those under development. Within recent years many of our well known mines have been developed and brought into large scale production from revenue secured from a small milling plant operating on development ore.

A study of a large number of mills using amalgamation and concentration has disclosed bullion recoveries ranging from 60 per cent to 90 per cent and total recoveries, including concentrates, from 85 per cent to 97 per cent. The average bullion recovery will be about 70 per cent and very often this is of utmost importance as geographic location makes the shipping of the concentrate to a smelting plant undesirable.

While cyanidation is usually favored for treating gold ores to get maximum recovery of the values in bullion form, nevertheless, the fact that an amalgamation plant can be built for approximately one- third of a complete Gold Leaching mill, together with the lower operating costs of the simpler plant, partially offsets the lower recovery. It is customary to impound the tailings from the amalgamation plant and these are cheaply treated when mine developments have justified the erection of the more complete Gold Leaching plant. An amalgamation and concentration plant can be operating intermittently without sacrificing efficiency, and this allows the operation of the plant for only one or two shifts per day to keep the peak power requirements at a minimum as mine compressors can be operated or the hoisting done while the mill is not in operation. The fact that 60 to 90 per cent of the values can be recovered by amalgamation will usually supply sufficient revenue from the mill to pay for development charges and build a reserve for the construction of the complete Gold Leaching plant.

With reasonable care in the design and construction of the original amalgamation and concentration plant all of the equipment can be utilized in the later complete Gold Leaching mill. By using standard equipment it is possible to add the Gold Leaching equipment following the already installed amalgamation and concentration units as these are an essential part of the completed plant.

Other advantages of these simple and inexpensive amalgamation and concentration plants are that they can be successfully operated with unskilled labor as no chemical knowledge or previous experience is necessary. Even flotation has been simplified through the use of “Sub-A” Flotation Cells; this addition of flotation means no marked increase in milling costs, but often a large increase in recovery due to the saving of extremely fine mineral values.

Gold ore bodies can be accurately sampled by milling all of the ore from mine development work and the errors resulting from ordinary sampling methods can be entirely eliminated.

It is interesting to note the numerous dividend paying gold properties, particularly those in Eastern Canada, which have followed the treatment methods shown in the following flowsheets during the development stage and they have gradually added to the equipment as the profits and ore developments warranted. The use of standard proved equipment eliminates the biggest element of chance, and from this nucleus a more efficient and complete plant can be acquired as the flexibility of the equipment permits the change from one flowsheet to another.

We are giving five typical flowsheets used in treating gold ores and are describing the possible applications of these flowsheets, together with their fields of usefulness, and while in each case there is a similarity in equipment, you will note the changes necessary for various type ores. In each case we have endeavored to show the simplest possible plant for best results on each type of ore and to show the improvements that can be made to further increase recoveries at slight additional cost.

Leaching Gold Circuits

Flowsheet_AA

This flowsheet is the lowest in price, and can be used on what are commonly termed as “free milling” gold ores where a high percentage of the values are free and where these values are unlocked at reasonably coarse grinding. This flowsheet is often used for treating high grade pockets. The ball mill is in open circuit and the size of the product to amalgamation plates is controlled by a Spiral Screen on the ball mill discharge. The concentrating table also functions as a classifier and the middling is returned as oversize product for further grinding.

Flowsheet BB

Flowsheet BB has a Mineral Jig and amalgamator in addition to the equipment shown for Flowsheet AA, and is used for an inexpensive plant where values are coarse but minerals are coated or filmed, and will not amalgamate readily on plates. The jig recovers the “rusty” values in a high grade concentrate for “forced” amalgamation treatment in the Amalgamator. On the ores where this flowsheet is applicable, blankets, corduroy, or Gold Matting are usually substituted for amalgamation plates and their concentrate also is treated in the amalgamator with the jig product.

Flowsheet CC

This flowsheet with the ball mill in closed circuit with a classifier, and with the jig in this circuit, will give the highest recovery possible for amalgamation and gravity concentration. The addition of the classifier allows finer grinding and the efficiency of the jig is greatly increased by using it in the closed grinding circuit. This flowsheet not only improves recoveries on ores as described in the previous flowsheets, but is also useful where the minerals are fine and where metallic values are in auriferous sulphides as well as in the free state in the gangue.

Flowsheet DD

There are many gold ores containing oxidized free gold and also values in the sulphides or tellurides; for the latter, flotation must be used on the fine sizes.

The addition of flotation to Flowsheet CC brings recovery to the highest point in Flowsheet DD as flotation recovers the slime values that are normally lost where gravity concentration only is used. The values that can be amalgamated are secured in bullion form from the high grade jig and table concentrates, and the remaining values are recovered in the flotation concentrate. This flowsheet is also necessary where a minor percentage of the gold values are present as metallics at commercial fineness of grinding or where the minerals are friable and easily slimed in fine grinding such as galena or the various telluride minerals.

The addition of flotation does not increase greatly the first cost of the plant, nor does it increase the operating expenses more than a few cents per ton. In a great many cases the additional recovery made by flotation means the difference between operating at a profit and at a loss. Flotation is responsible for the success of many small mining properties today.

Where the isolated location of the mill makes shipping of concentrates prohibitive, many properties store their product until they are justified in installing a complete treatment plant on the ground; current expenses are thus paid through bullion recovered by amalgamation ahead of flotation.

The equipment in this flowsheet is identical to that of DD. Here the ability of the “Sub-A” Flotation Machine to effectively handle a coarse feed is capitalized on to allow the handling of greatly increased tonnages. The ball mill discharge passes in open circuit over the jig, amalgamation plates or blanket tables and the flotation machine. A middling product is returned from the concentrating table and is dewatered in the classifier and returned for regrinding. On tailings, dumps, or low grade ores where it is necessary to handle a larger tonnage, this flowsheet is very effective, and while the recoveries would not be as high as in Flowsheet DD, the loss in recovery is more than offset by the greatly increased tonnage handled and the resultant lower milling cost. With this flowsheet a coarse tailing can be discarded, but slime losses are entirely eliminated as these, together with the granular minerals, are recovered in the flotation machine.

This flexibility of flowsheet is possible only where the “Sub-A” Flotation Machine is used. The (Selective) Mineral Jig is a valuable addition here as the excessive dilution would make it impossible to use any other type of gravity concentration device ahead of flotation. The change from Flowsheet DD to Flowsheet EE can be very easily made to accommodate changes in ore and to allow greater profits from the treatment of any type gold ore encountered.

Typical Gold Milling Flowsheets

The flowsheets on this page were selected to show some of the many different methods of treatment which have been so successfully used in gold installations.

No two ores are exactly alike. What method of treatment will give you the greatest net profit in milling your ore? This can be determined by proper metallurgical tests. They will show the recoveries which may be obtained by various methods of treatment; and the type and cost of equipment required, and the operating cost for each method are then easily established.

From this data, the economic possibilities of the mining and milling project can be established and a milling plant obtained which will assure the best possible results for your particular ore.

Ore tests are conducted on the basis of obtaining the simplest possible flowsheet, using standard, proved equipment. Also, as you will note in the flowsheets shown, this fundamental principle is always followed: “Recover the mineral as soon as it is free.”

  1. Simplest flowsheet for high-grade, “free-milling” ores.
  2. Jig and amalgamation unit recover values not obtained by Flowsheet No. 1.
  3. Classifier in closed circuit increases grinding and jigging efficiency; improves recoveries.
  4. Flotation saves values in sulphides and slimes, not recovered by gravity.
  5. Simple flotation plant with jig to recover metallics in grinding circuit.
  6. Jig recovers non-floating minerals; Unit Cell recovers coarse, bulk concentrate, reduces slime losses.
  7. Small batch cyanidation leaching may be used to obtain all-bullion products.
  8. Jig removes coarse gold ahead of cyanidation, improves recoveries, eliminates erratic tailings.
  9. Combination flotation and cyanidation permits milling both oxides and sulphides.
  10. Leaching for gold of a flotation concentrates to produce all bullion.

    Leaching Gold Flowsheets-1Leaching Gold in Ball-Mill-circuit

Mineral-Jig-with gold Leaching

Gold Leaching Plant

A study of a large number of mills using amalgamation and concentration has disclosed bullion recoveries ranging from 60 per cent to 90 per cent and total recoveries, including concentrates, from 85 per cent to 97 per cent. The average bullion recovery will be about 70 per cent and very often this is of utmost importance as geographic location makes the shipping of the concentrate to a smelting plant undesirable.

While cyanidation is usually favored for treating gold ores to get maximum recovery of the values in bullion form, nevertheless, the fact that an amalgamation plant can be built for approximately one-third of a complete cyanide mill, together with the lower operating costs of the simpler plant, partially offsets the lower recovery. It is customary to impound the tailings from the amalgamation plant and these are cheaply treated when mine developments have justified the erection of the more complete cyanide plant. An amalgamation and concentration plant can be operating intermittently without sacrificing efficiency, and this allows the operation of the plant for only one or two shifts per day to keep the peak power requirements at a minimum as mine compressors can be operated or the hoisting done while the mill is not in operation. The fact that 60 to 80 per cent of the values can be recovered by amalgamation will usually supply sufficient revenue from the mill to pay for development charges and build a reserve for the construction of the complete cyanide plant.

With reasonable care in the design and construction of the original amalgamation and concentration plant all of the equipment can be utilized in the later complete cyanide mill. By using standard equipment it is possible to add the cyanide equipment following the already installed amalgamation and concentration units as these are an essential part of the completed plant.

Other advantages of these simple and inexpensive amalgamation and concentration plants are that they can be successfully operated with unskilled labor as no chemical knowledge or previous experience is necessary. Gold ore bodies can be accurately sampled by milling all of the ore from mine development work and the errors resulting from ordinary sampling methods can be entirely eliminated.

It is interesting to note the numerous dividend paying gold properties, particularly those in Eastern Canada, which have followed the treatment methods shown in the following flowsheets during the development stage and they have gradually added to the equipment as the profits and ore developments warranted. The use of standard proved equipment eliminates the biggest element of chance, and from this nucleus a more efficient and complete plant can be acquired as the flexibility of the equipment permits the change from one flowsheet to another.

We are giving four typical flowsheets used in treating gold ores and are describing the possible applications of these flowsheets, together with their fields of usefulness, and while in each case there is a similarity in equipment, you will note the changes necessary for various type ores. In each case we have endeavoured to show the simplest possible plant for best results on each type of ore and to show the improvements that can be made to further increase recoveries at slight additional cost.

Gold_recovery_circuit_in_small_plant_-Ball_Mill_grinding_Amalgamation_Table_and_Shaking_Table

Small scale gold processing plant AA

small_gold_process_plant_with_ball_mill_jig_gravity_amalgan_and_shaker_table

Small scale gold processing plant BB

This flowsheet is the lowest in price, and can be used on what are commonly termed as “free milling” gold ores where a high percentage of the values are free and where these values are unlocked at reasonably coarse grinding. This flowsheet is often used for treating high grade pockets. The ball mill is in open circuit and the size of the product to amalgamation plates is controlled by a Spiral Screen on the ball mill discharge. The concentrating table also functions as a classifier and the middling is returned as oversize product for further grinding.

small gold recovery plant with gravity concentration and amalgamation

Small scale gold processing plant CC

Flowsheet BB has a Mineral Jig and amalgamator in addition to the equipment shown for Flowsheet AA, and is used for an inexpensive plant where values are coarse but minerals are coated or filmed, and will not amalgamate readily on plates. The jig recovers the “rusty” values in a high grade concentrate for “forced” amalgamation treatment in the Amalgamator. On the ores where this flowsheet is applicable, blankets, corduroy, or Gold Matting are usually substituted for amalgamation plates and their concentrate also is treated in the amalgamator with the jig product.

This flowsheet with the ball mill in closed circuit with a classifier, and with the jig in this circuit, will give the highest recovery possible for amalgamation and gravity concentration. The addition of the classifier allows finer grinding and the efficiency of the jig is greatly increased by using it in the closed grinding circuit. This flowsheet not only improves recoveries on ores as described in the previous flowsheets, but is al£o useful where the minerals are fine and where metallic values are in auriferous sulphides as well as in the free state in the gangue.

small gold process plant with grinding mill gravity jig table anf froth flotation

Small scale gold processing plant DD

There are many gold ores containing oxidized free gold and also values in the sulphides or tellurides; for the latter, flotation must be used on the fine sizes.

The addition of flotation to Flowsheet CC brings recovery to the highest point in Flowsheet DD as flotation recovers the slime values that are normally lost where gravity concentration only is used. The values that can be amalgamated are secured in bullion form from the high grade jig and table concentrates, and the remaining values are recovered in the flotation concentrate. This flowsheet is also necessary where a minor percentage of the gold values are present as metallics at commercial fineness of grinding or where the minerals are friable and easily slimed in fine grinding such as galena or the various telluride minerals.

The addition of flotation does not increase greatly the first cost of the plant, nor does it increase the operating expenses more than a few cents per ton. In a great many cases the additional recovery made by flotation means the difference between operating at a profit and at a loss. Flotation is responsible for the success of many small mining properties today.

small gold process plant with grinding mill gravity jig table middlings to froth flotation

Small scale gold processing plant EE

Where the isolated location of the mill makes shipping of concentrates prohibitive, many properties store their product until they are justified in installing a complete treatment plant on the ground; current expenses are thus paid through bullion recovered by amalgamation ahead of flotation.

The equipment in this flowsheet is identical to that of DD. Here the ability of the Flotation Machine to handle a coarse feed is capitalized on to allow the handling of greatly increased tonnages. The ball mill discharge passes in open circuit over the jig, amalgamation plates or blanket tables and the flotation machine. A middling product is returned from the concentrating table and is dewatered in the classifier and returned for regrinding. On tailings, dumps, or low grade ores where it is necessary to handle a larger tonnage, this flowsheet is very effective, and while the recoveries would not be as high as in Flowsheet DD, the loss in recovery is more than offset by the greatly increased tonnage handled and the resultant lower milling cost. With this flowsheet a coarse tailing can be discarded, but slime losses are entirely eliminated as these, together with the granular minerals, are recovered in the flotation machine.

This flexibility of flowsheet is possible only where the standard “Sub-A” Type Flotation Machine is used. The Mineral Jig is a valuable addition here as the excessive dilution would make it impossible to use any other type of gravity concentration device ahead of flotation. The change from Flowsheet DD to Flowsheet EE can be very easily made to accommodate changes in ore and to allow greater profits from the treatment of any type gold ore encountered.

Gold Leaching Equipment Layout

Gold Leaching Equipment

Gold Leaching Equipment

The 5 Gold Leaching Equipment Flowsheets illustrated above indicate the equipment essential for small cyanide mills of five different tonnages. These flowsheets are all similar with equipment sized for the tonnages shown. They are typical flowsheets for continuous counter-current decantation cyanidation plus a Mineral Jig in the grinding circuit with provisions for amalgamation of the jig concentrates.

The Mineral Jig and Amalgamation Unit have a definite place in cyanide plants as the coarse and granular gold can be readily recovered which may not be completely dissolved by the cyanide solution during the treatment time given to the pulp. The cyanide process has the advantage of producing precious metals in bullion form with the highest net return from those gold and silver ores amenable to cyanidation. The counter – current decantation washing circuit has been found to be a most economical method for removing dissolved precious metals. Washing Tray Thickeners require the minimum floor space and capital costs. In counter – current decantation wash water and barren solution are added in the last thickener units and flow counter to pulp flows, becoming enriched and are finally passed to clarification and precipitation where precious metals are precipitated and recovered.

Easy Gold Plant and Business Expansion

Expanding the Small Gold Plant

The above flowsheets illustrate a method of increasing both capacity and recovery in a small gold plant by several stages. This is typical of the “Pay – As – You – Grow” method of increasing capacity and profits essential in so many small operations. Because each ore has its own individual characteristics it is wise to first start with reliable test data. This is just as important in developing a flowsheet for a small mill as it is for a large plant.

Gold Flowsheet No. 1 shows a typical simple mill for the recovery of gold by amalgamation and by concentrating tables. However, on many ores such a flowsheet gives high losses of both fine gold and sulfide minerals.

Gold Flowsheet No. 2 provides for the addition of “Sub-A” Flotation cells following the amalgamation tables to effect additional recovery of both gold and sulfides in fine and coarse sizes.

Gold Flowsheet No. 3 indicates the addition of a required mill, classifier and extra “Sub-A” Flotation cells to provide for an increase in capacity and improvement in recoveries by regrinding of middling products.

Gold Flowsheet No. 4 shows an increase in flotation capacity to further improve recovery. The additions as illustrated allow an operation to be started on limited capital and gradually to be expanded as conditions warrant.


** Extracted from Memorandum Series No. 47, by C. S. Parsons, Engineer, Ore Dressing and Metallurgical Division, Mines Branch, Department of Mines, Ottawa. Published by permission of the Director, Mines Branch.

***Multiple all financial numbers$ by 8X or 10X to obtain 2016 dollars.


Source: This article is a reproduction of an excerpt of “In the Public Domain” documents held in 911Metallurgy Corp’s private library.[/fusion_builder_column][/fusion_builder_row][/fusion_builder_container]