Flowsheet for Barite Processing

Flowsheet for Barite Processing

The barite district cf Scuth-West Sardinia is characterized by the presence of a number of small orebodies scattered over a large area. Because of the karstic genesis, their size, shape and composition are extremely variable thus posing the problem of suitably planning exploration and mining operations in order that the ore may be profitably beneficiated under varying constraints. At the Barega mine different mining methods are implemented according to the characteristics of the orebody and host rocks using simple easily movable equipment. Besides some residual opencast operations, the vein-type mineralizations are generally mined by sublevel stoping or sublevel caving, whereas the more irregular funnel-type masses are exploited by shrinkage stoping. Prcfitability of the operations, which is presently hampered to a certain extent by the fall in market price of oil-drilling barytes, /s subject to the feasibilty of applying tailored low-cost mining methods to each orebody using common equipment as well as to setting up a versatile beneficiation process suitable for each kind cf ore, from easily washable to finely intergrown. After a brief description of the geological features of the Barega mine, the paper illustrates the mining methods currently applied giving some significant data on field operations and the technical and economic reasons underlying the solutions adopted. Loading and hauling problems are also outlined. Processing by jigging and flotation is then illustrated m detail. Finally conclusions are drawn concerning the flexibility of the productive structure in order to accomodate any change in the variables, either internal or external to the system such as the market demand and price for the various utilizations (chemicals, drilling muds, filling agents).

GEOLOGIC OUTLIKE

Concessions of the Barega mine cover almost completely the outcropping formations tpyical of Cambrian series in Sardinia, consisting of sandstones, limestones and shales, in order of deposition.

The series is corrugated by subsequent orogenesis processes and partially eroded so that tougher limestone mountains emerge well above the flatter countryside of weaker shales and sandstones.

Barite orebodies are hosted in the carbonatic rocks; three main groups can be distinguished, according to geometric features and composition:

  • Vein-type orebodies resulting from secondary deposition of barite and accompanying gangues into opened faults or fractures. Barite is often finely intergrown with gangue minerals, especially quartz, and this may render very difficult the processing problem especially as far as concentrate quality is concerned.
  • Column-shaped masses embedded in karstic cavities with variable size, shape and ore composition features. Barite is generally well crystallized wit hvery favouralle intergrowth characteristics so that the run-of-mine is easily amenable to processing;
  • Flat lenses of alluvial metarial, sometimes covered by quartzites, where sharp edged barite pebbles and fragments are intermingled with a clayey soil, altough of a lower grade, ore can be economically processed after desCiros.

The quality of ore reverves has deteriorated substantially over the last few years owing to the fact that in the past beneficiation was focused mainly on richer ores. Presently the proportion of difficult-to-treat ores accounts for about 60 % of the total, thus posing additional processing problems which need to be carefully solved to obtain marketable products with economically acceptable recoveries.

The future of the mine depends on the possibility of discovering new mineralizations outside the boundaries of the traditional area to which exploitation was hitherto confined.

GENERAL FEATURES OF THE MINE

The present mining organization was determined by the features of the available ore reserves, only a small part of which can be mined opencast. Moreover, single orebodies are very variable in size, from a few thousand up to some hundred thousand tonnes of recoverable ore.

As far as rock mechanics is concerned, host rocks are generally strong and competent so that no roof support is normally required in sublevel driftings or haulage ways.

Only occasionally steel frames or concrete vaulting must be used for crossing faults or localized weakness zones, according to needs However there are instances where the hanging wall consists of a thick layer of clayey material which after exposure to air easily caves into the emptied stope creating problems of ore pollution if not carefullv controlled

In the light of the above a very flexible organization is required to face the ever changing mining conditions

The major policy at the mine is to adopt simple and easily movable equipment, adapted to a variety of working conditions so as to allow in most cases both easy maintenance and ready availability For this purpose leg-mounted light drifters are used for development works whereas heavier tools like wagon-drills are employed in pro duction drilling

Face mucking of blasted metariai is accomplished with crawler loaders into ore raises More recently LHD diesel powered vehicles ha ve also been introduced in deeper or remote stops Trucks ar emplo yed for hoisting and haulage up to the processing plant

All such equipment can be used m either opencast or undergro und operations, thus allowing very high utilization coefficients to be attained Similar guide-lines are followed in ore processing, currently the plant can handle materials of diverse characteristics from lean earths to richer ores either well liberated at coarser sizes or linely intergrcwn with the gangue, m fact machine settings and even the flowsheet can be promptly adjusted in order to meet optimum pro cess outcome On average about 650 tonnes ol run-of mine are pro duced daily, this ligure can be increased up to 800 in periods of peak market demand The processing plant has a maximum throughput capacity of 1200 tpd which can be matched by resorting to ore supplied by ex ternal producers In this way the plant was conveived as a custom mill for beneficiatmg ores from the small mineral occurrences in ne ighbounng zones

The labour force of the mine counts some 850 workers including those employed in the processing plant and general services 40 of whom work underground plus supervisors and management making a total of about 100 Yearlv concentrate production presently amounts to about 31 000 tonnes owing to the slump in demand for oil well dri! lings however a peak of 45 000 t has been reached in latter years on account of the verv favourable market situation

UNDERGROUND MINING

Structure of the Mine

An underground structure suitable for trackless mining was designed about 20 years ago, when the outcropping parts of the main orebodies were near depletion rendering opencast mining no longer feasible.

In the transition phase the same kind of equipment was maintained and adapted to the new situtation. Nowadays the technical solutions are basically the same with the improvements suggested by experience gained or proposed by technological progress.

The access ways consist in horizontal crosscuts dug from the hillside at lower levels; as workings deepen it is necassary to drive inclined galleries with a 15-20 m2 cross section, for faulage, service and ventilation. A main incline serves a group of orebodies which account for about 60 % of the available reverves. Orebodies are connected to the incline through short slants at each sublevel; development drift intercommunicating by means of raises or steep ramps are then excavated into the orebodv.

Generally one every four sublevels is used as the haulage way allowing access to 15 tonnes payload trucks.

On account of the extreme variability of both the characteristics of the orebodies and the restrictions to mining, many methods are being used at the Barega mine:

  • Shrinkage stopmg is common practice in small and very irregular veins or for side prominences of bigger orebodies;
  • Sublevel stopmg is widely applied wherever ore and host rocks are competent;
  • Sublevel caving must be adopted in presence of weak hanging wall and in particular when clay layers are too close to the ore-body,
  • Methods with abandoned pilars are preferred when lean zones not worth beneficiatmg are included inside the orebody;
  • Funnel-shaped open pit mining is of course resorted to for outcropping or close-to-surface mineralizations

Development and Sublevel Drifting

As already mentoned, main inclines and haulage ways are opend with a minimum cross section of 15 mJ in order to allow the passage of trucks and the manoeuvering of loaders. Even in this case light equipment is used for drilling, since fast advance rates are not normally needed; if this was the case, a twing-boom jumbo shared with another mine of the same Company is occasionally used for accelerating excavation. Sublevel drifts are dug in a similar way but require a smaller cross area.

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