Trammels based on screen GIT-52MB (ГИТ-52МБ) for lixiviation dump areas of man-made placer gold depo

Currently it is becoming relatively more profitable to extract gold from surficial fine-grained tailings rather than stripping of turfs and to mine deep-seated sands which have moderate washability or high bouldering.

According to current estimates and multiple literatural data to-date prospectors' teams which use conventional washing devices lose between 20 to 50% of gold. Main losses at output of placer gold mine and hardrock gold constitute thin, platy and flour particle gold with the size range of particles from millimetre to several micrones.

Often man-made dump areas are able to compete in terms of gold content and volume with newly opened gold deposits. A considerable national and foreign experience evidencing profitability of repeated commercial exploitation of such objects has already been gained.  A most important advantage of man-made deposits is that the product is already conditioned (it has been lifted upwards from subsurface, desintegrated) for benefication.

Rocks of lixiviation dump areas differ from primary sands of gold-bearing placers; therefore, standard trammels of types ПГШ, ПГБ, ГГМ, etc. are rather poorly performing. There are several reasons therefor.

First of all, lixiviation dump sites differ by comparatively fine material and absence of boulders. As a result, fine-grained tailings are by 90–95% presented with the material finer than 50 mm.

Application of standard hydrocradle machines of type ПГШ for fine-grained tailings of such size is unreasonable. Standard hydrocradle machines have the holing of 80-120 mm, respectively complete lixiviation will go through perforation and will be fed to the sluice. In fact, no benefication of material will take place so far as it will be supplied for washing almost completely. As a result, the sluice will be overloaded and almost all the fine gold from lixiviation will get lost another time.

But if holing of hydrocradle should be reduced to 20-30 mm in order to unload the sluice the performance of screening slumps and the machine shall not provide for acceptable performance rate.

As well, there is no sense to wash lixiviation dump sites using devices of type ГГМ (ППМ). Their main structural element is a strong platy screen able to accept boulders with the size over a metre. For fine-grained tailings without boulders platy screens are not needed and there is no sense to pay for them a high price.

Boxes with drum screens (ПБШ, ПГБ, etc.) suit for fine-grained tailings so far as they allow to separate boulders with size 10-20 mm and thus to reduce the material being fed for further benefication but at low gold content in fine-grained tailing dump area the expensive drum box will have a payback period of several years. Besides, there is no technical necessity to use expensive drum screens on fine-grained tailing dump area so far as fine-grained tailings are easy washable.

Subject to the above said, to disintegrate and to classify fine-grained tailings flat unbalanced throw screens are optimal. They are comparatively inexpensive, provide for good disintegration of easy washable fine-grained tailings at high performance. The best option is a double-deck screen which allows to maximally reduce quantity of material for further benefication. The size of the lower sieve is selected depending on fineness of gold in dump area and processing module which follows the screen.

In 1998 at order of “Nedra Bodaybo” CJSC, “Rudgormash” works specifically developed for placer gold deposits a double-deck screen GIT-52 MB (ГИТ-52 МБ) which has increased length of the sieving part and a number of structural and engineering peculiarities which provide for increased operating reliability, namely:

  • walls of the box are fabricated of wear-resistant steel 10НХД;
  • walls of screens are stiffened by additional faceplates;
  • vibration-resistant bearings are installed in vibrators;
  • packing of bearing units provide for durability in high humidity environment which is characteristic for wet screening;
  • connection of connecting beams with walls is carried out via semiflexible joints;
  • welding joints of sieves with walls are replaced with riveted ones;
  • stiffness of springs is increased.

When operated at a gold-mining works the screen provides for the output rate between 350 and 800 t/hr, whereas the size of separate lumps of the rock being processed may reach 1 m and more. As the upper sieve of the screen grizzly grates serve; the slots are 8, 12, 20, 30, 40, 60, 80,100 mm. They are distinguished by high strength and are designated to separate boulders and cobble roundstone which prevents damage to lower sieves, endures the service life and reduces replacement costs. Metal mesh and polyurethane panels may be installed on the lower tier of the screen.

Description of the operating scheme of sluice box

Rocks is supplied with the use of an excavator or a loading machine through a feed hopper to the vibrating feeding gate ПВ-ПБР-1,2/2,7. An advantage of this type of feeders is that their efficiency can be regulated with the use of a remote control - from zero to maximum.  Regulation is carried out with the use of the frequency converter, without stopping processing lines of the enterprise. Further, the material undergoes separation into fractions on the double-deck screen GIT-52 MB (ГИТ-52 МБ) which technical specifications were presented above, after which the undersize fraction minus 5 - minus 10 mm undergoes benefication stage. Gold in fine-grained tailings of dump areas is various in terms of size and form. They contain a share of “initial” gold which was in the placer gold deposit before its recovery. It gets lost when washing frozen or clay sands due to shortage of water, etc.  But major part of gold in fine-grained tailings is difficult to recover: fineness is primarily 0.25 mm and finer; platy, flake, intergrown with the rock. The choice of benefication equipment is defined subject to both particle-size specifications of gold and weight fraction in fine-grained tailings of high-density minerals: magnetite, iron oxide, iron pyrite, ilmenite, cassiterite, etc.  For fine-grained tailings with minor content of heavy fraction satisfactory recovery of gold can be ensured by sluices. In such a case undersize fraction of screen GIT (ГИТ) may be fed to shallow sluices.

At minor quantity of heavy fraction sluice bed will be quickly stuck; more effective in terms of gold recovery in this case will be ore-dressing machines with continuous output of concentrate: jigging machines (Trud-12 (Труд-12), Trud-6PR (Труд-6ПР)).

Further, the concentrate is additionally ground on MOD-2M (МОД-2М) or MOD-3M (МОД-3М) and then on SKO-7.5 (СКО-7,5).

An important advantage of this sluice box is the possibility to manufacture them both as permanently installed and displaceable.

Sluice trammel with screen GIT-52 MB (ГИТ-52 МБ) successfully operated at placer gold deposit “Ugakhan” in Bodaybo rayon for a period of several years.

In 2007 on the basis of screen GIT-52 MB (ГИТ-52 МБ) in “Zakamensk” LLC (Buryatia) a jigging machine for wolframite placer deposit was constructed. Undersize fraction of lower screen in that machine was supplied to the jigging machine Trud-12 (Труд-12).

In early 2010 a similar construction was purchased by prospectors' team “Gazimur” of Chita oblast.

“Gornaya Promyshlennost” No.3 (91) May-June 2010, “Mining machines” CJSC

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