The behaviour of gold in Hemlo Mines Ltd. grinding circuit

This paper compares the behaviour of gold and ore in the grinding circuit of Hemlo Mines Ltd. Particular attention is given to grinding kinetics, classification behaviour, and liberation. For grinding kinetics, laboratory grinding of gold flakes and silica, 840 \im to 1200 \an in size (14/20 mesh), was also performed to provide a standard for comparison and to study in a controlled environment the mechanisms of breakage, folding, smearing and impacting.
Grinding kinetics were characterized at laboratory scale with breakage and selection functions. The breakage function showed that 75% of gold disappearing from the 840 \an to 1200 \an class reported to the 600 \an to 840 pm; this figure is much higher than for silica (46%) or most other minerals, and implies that comparatively fewer fine fragments are produced from the breakage of gold flakes, on account of gold's malleability. The selection function of silica was four times that of gold. At plant scale, the ratio of the selection function of ore and gold increased from 6 for at 50 \an to 100 nm to 20 at 500 urn to 1000 \an.
Observation of original flakes and their fragments with the scanning electron microscope showed that the main mechanism of "grinding" from the 840 pm to 1200 /j.m to the 600 \an to 840 p.m class was folding rather than actual breakage. This was confirmed by a measure of individual flake weight. The postulated breakage cycle is that relatively globular flakes become increasingly serrated through grinding; they can then regain their original shape through folding and reflattening into cylindrical and spherical shapes, as the majority does; however, some fragments will at this point undergo actual breakage. Photograhic evidence is presented to support the proposed mechanisms.
Smearing of gold unto silica was observed when silica was ground after a gold, and embedding of silica into gold flakes when gold was ground after a silica. Both mechanisms occur whenever gold and harder minerals are jointly ground, and result in "un-liberation" of gold. It is postulated that smearing of gold onto other minerals plays an important role in explaining how gravity recovery can increase over-all gold metallurgy, especially when used ahead of flotation.
Classification of gold in the primary hydrocyclones takes place at a much finer cut-size than ore, 20 jj.m vs 57 \an. This and the slower grinding kinetics result in high gold circulating loads in the primary loop, 6700%, and a gold content in the primary cyclone underflow ((PCUF) is twenty-four times that of the ore. The gold size distribution for primary cyclone overflow is much finer than that of the ore, although they are essentially similar in the PCUF.
Liberation, or more accurately "gravity recoverability", was assessed with a 7.5 cm (3 in.) Knelson concentrator. It varied between the thirties for the primary mill discharge and two cyclone overflows, to highs of 89% and 92 % for the PCUF and secondary mill discharge.
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Publication: CIM Bulletin
Author(s): Veronique Falmagne
Issue: 955
Volume: 84
Year: 1991
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Summary: This paper reviews the development of new designs in extensible and high angle conveyor systems. These aim to overcome the limitations of prior alternative concepts in design. The application of such systems in strip, terrace, open pit and mountain mining is reviewed.
Publication: CIM Bulletin
Author(s): A. Richmond, T. Atkinson, M. Scoble
Issue: 955
Volume: 84
Year: 1991
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Summary: The Williams Mine is Canada's largest gold producer, with annual production of some 500 000 ounces of gold from two million tonnes of ore. Highly mechanized and automated underground mining practices are utilized at the property in order to help achieve high levels of productivity and the most cost-effective mining possible.
Planning and design parameters for the underground ore handling system at the Williams Mine are described in this paper. Particular reference is made to the consideration...
Publication: CIM Bulletin
Author(s): Henry Smith, Stu Brown
Issue: 955
Volume: 84
Year: 1991
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Summary: Exploration and development of mineral resources in developing countries by Canadian-based multinational mining companies is becoming increasingly common. One problem being encountered is that the objectives of the governments of developing countries can differ from those of developed countries. These objectives are not always consistent with maximizing returns from the projects, which can create conflicts between the mining company's responsibility to its shareholders and the desire to be a...
Publication: CIM Bulletin
Author(s): Robert B. Parsons
Issue: 955
Volume: 84
Year: 1991
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Summary: Minnova Inc. has five operating divisions thoughout Canada. One of them is Lac Dufault which was established in 1964.
Lac Dufault is located 15 km north of Rouyn-Noranda, in what is known as Noranda volcanic centre, in northwestern Quebec. For more than 25 years, Lac Dufault has produced copper, zinc, gold and silver from four different mines: Norbec, Mitten-bach, Corbet and now Ansil.
Ansil, officially in production since July 1989, is one of the deepest mines presently in production in...
Publication: CIM Bulletin
Author(s): J. Desrosiers
Issue: 955
Volume: 84
Year: 1991
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Summary: British Steel has increased its usage of stainless steel for bunker, silo and chute linings to reduce maintenance costs and improve productivity.
A generation of low cost 12% Cr steels has been specifically developed to satisfy the needs of hardness, flow promotion and through life costing which are demanded by bulk solids handling industries.The range of stainless steels include: a very hard martensitic grade which is particularly suitable for high stress applications where impact and...
Publication: CIM Bulletin
Author(s): J. Peace, J.R. Fletcher
Issue: 955
Volume: 84
Year: 1991
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Summary: Comme l'exploitation d'un gisement a grande profondeur represente un defl de faille et que la profondeur a laquelle se situe celui d'Ansil varie de 1200 m a 1460 m, nous avons du mettre en place une infrastructure de surface d'envergure incluant un treuil de production et un chevalement d'une tres grande capacite. De meme, I'infrastructure sous terre a eteproposee en tenant compte de cefait important; d'ailleurs, I'excavation de deuxpuits circu-laires dont I'un est en beton et acier et...
Publication: CIM Bulletin
Author(s): Richard Samson
Issue: 955
Volume: 84
Year: 1991
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Summary: Epithermal Zn-Pb-Cu-Ag-Au quartz-carbonate-barite veins at the Silver Queen mine near Owen Lake, west-central British Columbia, are hosted by Late Cretaceous Tip Top Hill andesitic volcanic rocks. The veins form a rectilinear northwest-northeast pattern that differs slightly from regional structural trends. The main northwest-trending veins are oriented very close to the trend of regional northwest faults, but the crossing veins tend to be more east-northeasterly (070 degrees) compared to a...
Publication: CIM Bulletin
Author(s): C.H.B. Leitch, H.L. Cheng, C.T. Hood, A.J. Sinclair
Issue: 955
Volume: 84
Year: 1991
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