Grease Table

GENERAL

The Armstrong Grease Table is a relatively light weight, large capacity machine with a large water recovery and temperature control system.

REQUIREMENTS

For efficient grease recovery the following factors must be adhered to:

1. Only good quality grease must be used. Diamond test the grease before regular use.

2. The spray water and the grease must be of the right temperature (22-24°C)

3. The spray water must be clean and contain less than 100ppm solids.

4. The spray water must contain less than 10ppm combined Na and Mg.

5. The material fed over the grease screen must be correctly sized i.e. 1-2mm, 2-4mm, 4-8mm, 8-16mm, 16-32mm fractions or smaller. This is so that the largest non-diamond particles in the size fraction will not dislodge the smaller diamonds. Larger non diamond particles will also force smaller non diamond particles into the grease if the variation in particle size is too great.

TECHNICAL DETAILS

The grease screen consists of a 1.5mm stainless steel mesh screen tightly suspended between an outer steel frame. The two vibratory motors are fitted to the sides of the frame which allows the water from the spray bars to pass directly into the underlying water tank for re-circulation. The water tank is fitted with baffles to allow for sedimentation and should be cleaned at regular intervals to prevent the build up of solids in the water. The water tank is fitted with a heater element and thermostat to control the water temperature to within the required limits.

OPERATIONAL DETAILS

Grease is applied with a spatula from underneath the screen through the screen cloth between the screen bottom transverse support bars in segments 2 and 4. Sufficient grease is forced through the screen so that the grease protrudes to 1-3mm above the screen. The grease is then smoothed over the surface as required to form a thin layer of grease on top of the screen. This thin grease layer together with any diamonds is easily removed with a spatula to leave a clean remaining layer of grease on the screen surface. Further grease is then forced up through the screen cloth using a spatula to form a new clean layer of grease 1-3mm thick as described above.

'New diamond prospective area in Greenland

A test run with part of the modular plant: a high capacity, vibrating grease table, developed for Avannaa by Gondwanaland Diamonds, South Africa. Courtesy: Avannaa Resources

Avannaa Resources Ltd, operating in Greenland via its fully owned subsidiary Avannaa Exploration Ltd, reports 18 February 2008 (Nicholas Rose, CEO) that it has diamond- tested a dyke in the vicinity of Ataa Sund, central West Greenland, within its licence area no. 2007/52. The 39 kg sample was analysed for its diamond content by SGS Lakefield, Canada, and yielded 102 diamonds with a total weight of 0.013 carat. One stone can be characterized as a macrodiamond with dimensions of 0.83 x 0.66 x 0.53mm, translucent and white with graphite inclusions, while the remaining 101 stones all are microdiamonds. In terms of colour, 95 stones are white and 7 are off white, and in terms of clarity, 62 stones are transparent and 60 translucent. The majority of the stones (76) are crystal fragments suggesting a high probability that larger stones are present. The discovery significantly extends the regional extent of diamond-prospective bedrock in West Greenland, which has primarily focused on the Maniitsoq - Sarfartoq belt 300 kilometers to the south of the Ataa region.

Avannaa will follow up on this discovery in 2008 by bulk sampling the diamondiferous dyke itself and by detailed evaluation of an alluvial diamond target also within its 2007/52 licence area including sampling of up to 500 tonnes of channel facies sands and gravels of the Atane Formation on eastern Disko. The company will also be prospecting for other dykes and plugs of kimberlitic affinity in the Ataa Sund region, where Avannaa has applied for an exploration licence via a newly formed subsidiary Avannaa Diamonds Ltd. The company's other activities in 2008 are targeted at gold and nickel in several existing and new licences in West Greenland. To process sands and gravels on its alluvial diamond project, Avannaa has acquired a light modular plant specially designed for the Atane Formation sediments by Gekko Systems, Australia. This includes a 2 ton/hr in-line pressure jig (IPJ600) equipped with a 5 ton/hr feed trommel and concentrate sorting screens. A high capacity vibrating grease table, with a pre-cleaning scrubber, designed for Avannaa by Gondwanaland Diamonds (South Africa), will make a final processing of the concentrate before delivery to SGS Lakefield for diamond identification and characterisation. The combined processing plant will allow recovery of 0.6 to 12 mm diameter diamonds.'
Copied from MINEX No. 32 - February 2008

Gondwanaland Diamonds

GAVIN ARMSTRONG

The Armstrong vibratory screen system cuts conventional system's power usage.



Gavin Armstrong MD of
Gondwanaland Diamonds

MATERIALS HANDLING

'Vibratory screen system cuts conventional system's electricity usage

By: Leandi Rostoll

Published: 10 Apr 08 - 8:57 in Mining Weekly

Plant, equipment and accessory manufacturer Gondwanaland Diamonds South Africa MD Gavin Armstrong said this week that the company had developed a vibratory screen that could cut conventional screen systems' electricity usage by up to a quarter of the electricity.

The system was developed to be a cost and space effective option, he said in an interview with Mining Weekly.

The Armstrong screens were lighter than conventional screens, had a low profile and could be placed in confined spaces.

The Armstrong conveyor belt, which transports the raw materials to the vibratory screen, was a new concept that completely runs in a pipe protecting the belt and the material transported on the belt from natures elements, he said.

"The belt is easy to replace. By just removing the pulley, the belt can be removed and replaced within ten minutes."

The Armstrong vibratory screen and conveyor belt has been in production for three years and have been used in the diamond mining industry, but can be adapted for other mining industries as well.'
Reproduced here with the permission of Creamer Media's Mining Weekly online

Armstrong Vibratory Screen

The Armstrong vibratory screen, patents 2003/4539 and 2004/9572, consists of a heavy duty 25x75mm rectangular frame to accommodate a standard 2300x920mm woven wire screen. The screen is attached to a square tubing blocked out frame by means of posi-drive screws and rubber-lined metal washers. The vibratory motors are attached to the sides of the screens for maximum screening efficiency and to allow easy fitting of security covers or a cover carrying a number of air fans which converts the screening arrangement into an effective drying screen, with minimum power requirements. The screen can be easily converted into a double or multi deck screen by adding additional decks and larger vibratory motors. This screening system has the following advantages over conventional screens:

1. The screening efficiency is ±60% greater than for poly-deck screens of equivalent size and aperture.

2. The open spaces on the woven wire screens are up to 40% more than that for equivalent poly-deck screens.

3. The screen weight is less than one third that of poly-deck screens of equivalent surface screening area.

4. The power to drive the screen is less than a quarter required for driving the conventional poly-deck screen of the equivalent surface screening area.

5. The screen is compact, of low profile and can be accommodated into smaller spaces than conventional screens which make for ideal use in shipping containers where space is at a premium.

6. The screen is easy to replace, simply undo eight retaining bolts and remove the frame holding the screen in an upward or downward direction. Clean or replace the screen cloth and refit the frame or fit a frame with a new screen mesh. The screen frames and frame bodies are factory produced on accurate jigs so as to be interchangeable.

7. The screens with their side mounted motors are easy to cover for security reasons.

Vibratory Screens