APPLICATIONS OF TEXTURAL CHARACTERISTICS TO ORE DRESSING

  • The first stage in ore dressing (or mineral beneficiation) is comminution or size reduction in order to liberate valuable minerals from the gangue.

  • Information on the size and intergrowth relationship (textures) of minerals is of great importance from this point of view.

  • The optimum grain size for effective liberation can only be determined by a careful examination of ore textures in polished sections.

  • Insufficient grinding may result in the loss of valuable minerals in tailings, over grinding wastes energy and produces slimes which also result in losses and are difficult to treat for metal extraction.

  • Furthermore, the efficiency of the grinding processes needs to be monitored by examination of polished grain mounts of the milled product.

  • In considering the problem of liberation of ore minerals, a classification of the textures (without any genetic implications) based on the geometry of their intergrowths and locking relationships is necessitated.

  • Such a classification of textures, incorporating some information on the liberation characteristics, has been suggested by Amstutz.

  • For a geometric classification of ore textures, apart from the type and scale of intergrowths, the nature of the boundary between intergrown particles is also important.

  • This will show whether or not rupturing of larger particles will occur at grain boundaries during grinding.

  • Information regarding fractures and fissures in ore minerals as well as the porosity of the material are also important information which can be obtained from microscopic examination.

  • Such textural features also determine the flotation and leaching methods of ore treatment.

  • Furthermore, the efficiency of liberation can best be assessed by examination of the milled product under the microscope.

  • Examination of each fraction under the microscope permits the estimation of free and mixed grains of ore and gangue minerals, from which can be estimated the percentage liberation of each phase at each size range.

GEOMETRIC CLASSIFICATION OF ORE MINERAL TEXTURES AND THEIR LIBERATION CHARACTERISTICS

Texture/Interlocking: Equigranular, straight, rectilinear, cuspate margins.  Simple locking (Fig 1).

Liberation Properties: Fairly easy liberation.  Common occurrence especially in orthomagmatic and highly metamorphosed and recrystallized ores.  Also in ores showing successive depositional sequence.

Texture/Interlocking: Mutually curving boundaries with negligible interpenetration.  Simple locking (Fig 2).

Liberation Properties: Fairly easy liberation.  Common occurrence in simultaneously crystallized ores where interfacial free energies are similar.

 Texture/Interlocking: Mottled, spotty, careous, with partial penetration.  Relatively simple locking (Fig 3).

Liberation Properties: Fairly easy liberation.  Common occurrence in ores where interreplacement processes have been active.

Texture/Interlocking: Graphic, myrmekitic, visceral locking.  Deep micropenetration (Fig 4).

Liberation Properties: Complete liberation difficult or impossible.  Not common as a major texture in ores.  Produced by exsolution and replacement.  Eg.  Galena/sphalerite and chalcocite/bornite.

 Texture/Interlocking: Disseminated, drop like, emulsion, eutectoidal locking.  Finely dispersed phases (Fig 5)

Liberation Properties: Complete liberation difficult or impossible; chemical treatment often required.  Common occurrence by exsolution (left) Au/arsenopyrite, chalcopyrite/sphalerite; by replacement (right) pyrite/sphalerite.

 Texture/Interlocking: Intergranular rim; coating mantled, enveloped, atoll-like locking (Fig 6).

Liberation Properties: Liberation may be difficult if free grain is continuously enveloped by layer.  Not uncommon, often formed by replacement reaction.  Eg. Hematite film on gold; chalcocite or covellite on pyrite, galena or sphalerite.

Texture/Interlocking: Concentric, spherulitic, scalloped, colloform-layered locking (Fig 7).

Liberation Properties: Liberation fairly difficult or difficult; common occurrence in Fe, Mn, and Al ores.  Also U (pitchblende) intergrained with sulfide.  Usually associated with colloidal precipitation.

Texture/Interlocking: Planar, lamellar, sandwich-type locking.  Lamellae may vary in size (Fig 8).

Liberation Properties: Liberation fairly easy to variable.  Produced by exsolution (Eg.  Cubanite/chalcopyrite, ilmenite/magnetite).  Also by replacement (Eg.  Magnetite and hematite).

Texture/Interlocking: Reticulate (net-like) boxwork.  Finely interpenetrating locking (Fig 9).

Liberation Properties: Liberation variable to difficult.  Common occurrence by replacement (Eg.  bornite/chalcopyrite, anglesite/covellite/galena).  Also by exsolution (Eg.  hematite/ilmenite/magnetite).

 

Notes & Handouts

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