high pressure grinding mills in sikkim

minimum wages act, 1948

Minimum Wages Act, 1948 Minimum Wages (Central Advisory Board) Rules, 2011 1. Short title and commencement. 2. Definitions. 3. Constitution of the Central Advisory Board. 4. Term of office of members. 5. Eligibility for re-nomination. 6. Resignation. 7. Cessation of restoration of membership. 8. Meeting. 9. Notice of meetings. 10. Chairman of the meeting. 11. Quorum. 12. Disposal of business. 13. Method of voting. 14. Decision by majority. 15. Proceedings of the meeting. Minimum Wages (Central) Rules, 1950 1. Short title and extent 2. Interpretation 3. Term of office of the members of the Committee and the Advisory Committee 4. Term of office of members of the Board 4-A. Nomination of substitute members 5. Travelling allowance 6. Staff 7. Eligibility for re-nomination of the members of the Committee, Advisory Committee and the Board 8. Resignation of the Chairman and members of the Committee and the Board and filling of the casual vacancies 9. Cessation and restoration of membership 10. Disqualification 11. Meetings 12. Notice of meetings 13. Chairman 14. Quorum 15. Disposal of business 16. Method of voting 17. Proceedings of the meetings 18. Summoning of witnesses and production of documents 19. Expenses of witnesses 20. Mode of computation of the cash value of wages 21. Time and conditions of payment of wages and the deductions permissible from wages 22. Publicity to the minimum wage fixed under the Act 23. Weekly day of rest 24. Number of hours of work which shall constitute a normal working day 24-A. Night shifts 25. Extra wages for overtime 26. Form of registers and records 26-A. Preservation of registers 26-B. Production of registers and other records 26-C. 27. Applications 28. Authorisation 29. Appearance of parties 30. Costs 31. Court-fees 32. Savings Minimum Wages Act, 1948 1. Short title and extent 2. Interpretation 3. Fixing of minimum rates of wages 4. Minimum rate of wages 5. Procedure for fixing and revising minimum wages 6. Advisory committees and sub-committees 7. Advisory Board 8. Central Advisory Board 9. Composition of committees, etc 10. Correction of errors 11. Wages in kind 12. Payment of minimum rates of wages 13. Fixing hours for a normal working day, etc 14. Overtime 15. Wages of worker who works for less than normal working day 16. Wages for two or more classes of work 17. Minimum time rate wages for piece work 18. Maintenance of registers and records 19. Inspectors 20. Claims 21. Single application in respect of a number of employees 22. Penalties for certain offences 22-A. General provision for punishment of other offences 22-B. Cognizance of offences 22-C. offences by companies 22-D. Payment of undisbursed amounts due to employees 22-E. Protection against attachment of assets of employer with Government 22-F. Application of Payment of Wages Act, 1936, to scheduled employments 23. Exemption of employer from liability in certain cases 24. Bar of suits 25. Contracting out 26. Exemptions and exceptions 27. Power of State Government to add to Schedule 28. Power of the Central Government to give directions 29. Power of the Central Government to make rules 30. Power of appropriate Government to make rules 30-A. Rules made by the Central Government to be laid before Parliament 31. Validation of fixation of certain minimum rates of wages The Minimum Wages Act, 1948 (11 OF 1948) 16/753 [15th March, 1948]

(b) to enable a Claims Authority to entertain claims not only in respect of payment of wages which are less than the minimum wages but also in respect of payment of remuneration for days of rest and payment of overtime wages (section 20);

(d) to specify the persons liable to punishment in the case of offences by companies (section 22-C) and to make a general provision for punishment of offences for which no penalty is provided in the Act (section 22-A); and

(i) in relation to any scheduled employment carried on by or under the authority of the [Central Government or a railway administration], or in relation to a mine, oilfield or major port, or any corporation established by [a Central Act], the Central Government, and

(i) in a factory where there is carried on any scheduled employment in respect of which minimum rates of wages have been fixed under this Act, any person named under [clause (f) of sub-section (1) of section 7 of the Factories Act, 1948 (63 of 1948)], as manager of the factory;

(ii) in any scheduled employment under the control of any Government in India in respect of which minimum rates of wages have been fixed under this Act, the person or authority appointed by such Government for the supervision and control of employees or where no person or authority is so appointed, the head of the department;

(iii) in any scheduled employment under any local authority in respect of which minimum rates of wages have been fixed under this Act, the person appointed by such authority for the supervision and control of employees or where no person is so appointed, the chief executive officer of the local authority;

(iv) in any other case where there is carried on any scheduled employment in respect of which minimum rates of wages have been fixed under this Act, any person responsible to the owner for the supervision and control of the employees or for the payment of wages;

[(a) fix the minimum rates of wages payable to employees employed in an employment specified in Part I or Part II of the Schedule and in an employment added to either Part by notification under section 27:

(c) a minimum rate of remuneration to apply in the case of employees employed on piece work for the purpose of securing to such employees a minimum rate of wages on a time work basis (hereinafter referred to as "a guaranteed time rate");

(d) a minimum rate (whether a time rate or a piece rate) to apply in substitution for the minimum rate which would otherwise be applicable, in respect of overtime work done by employees (hereinafter referred to as "overtime rate").

(iv) by such other larger wage-period as may be prescribed, and where such rates are fixed by the day or by the month, the manner of calculating wages for a month or for a day, as the case may be, may be indicated:]

(i) a basic rate of wages and a special allowance at a rate to be adjusted, at such intervals and in such manner as the appropriate Government may direct, to accord as nearly as practicable with the variation in the cost of living index number applicable to such workers (hereinafter referred to as the "cost of living allowance"); or

(ii) a basic rate of wages with or without the cost of living allowance, and the cash value of the concessions in respect of supplies of essential commodities at concession rates, where so authorised; or

(b) by notification in the Official Gazette, publish its proposals for the information of persons likely to be affected thereby and specify a date, not less than two months from the date of the notification, on which the proposals will be taken into consideration.

(b) provide for a day of rest in every period of seven days which shall be allowed to all employees or to any specified class of employees and for the payment of remuneration in respect of such days of rest;

(c) require any person giving out-work and any out-workers, to give any information, which is in his power to give, with respect to the names and addresses of the persons to, for and from whom the work is given out or received, and with respect to the payments to be made for the work;

[(d) seize or take copies of such register, record of wages or notices or portions thereof as he may consider relevant in respect of an offence under this Act which he has reason to believe has been committed by an employer; and]

(i) in the case of a claim arising out of payment of less than the minimum rates of wages, the payment to the employee of the amount by which the minimum wages payable to him exceed the amount actually paid, together with the payment of such compensation as the Authority may think fit, not exceeding ten times the amount of such excess;

(ii) in any other case, the payment of the amount due to the employee, together with the payment of such compensation as the Authority may think fit, not exceeding ten rupees, and the Authority may direct payment of such compensation in cases where the excess or the amount due is paid by the employer to the employee before the disposal of the application.]

(a) under clause (a) of section 22 unless an application in respect of the facts constituting such offence has been presented under section 20 and has been granted wholly or in part, and the appropriate Government or an officer authorised by it in this behalf has sanctioned the making of the complaint;

(a) prescribe the term of office of the members, the procedure to be followed in the conduct of business, the method of voting, the manner of filling up casual vacancies in membership and the quorum necessary for the transaction of business of the committees, sub-committees, [* * *]

(h) prescribe the cases and circumstances in which an employee employed for a period of less than the requisite number of hours constituting a normal working day shall not be entitled to receive wages for a full normal working day;

ygm high pressure grinding mill-vanguard machinery

Product introductionYGM high pressure micro powder mill is referred to as micro powder mill or super fine grinding mill. The high pressure micro grinder is mainly used for the ultra-fine powder processing of more than 500 kinds of materials such as feldspar talc barite marble limestone carbon black and clay.

VANGUARD adopts the high-efficiency impeller energy-saving fan and the working efficiency of which can reach 85% or above while traditional grinding mills equipped with straight blade fan can reach only 62% of air inducing efficiency. Under the equivalent production requirements MTM Medium-speed Grinding Mill can realize better powder separating and lower power consumption.

joyal-high pressure grinding mill,high pressure grinding mill for sales,high pressure grinding mill manufacturer

JOYAL High Pressure Mill is an improved type of Raymond mill. The purpose of the this kind mill is to grind non-flammable and non-explosive materials in the fields of building materials, mining, metallurgies and chemical industry with hardness less than 9.3 in Mohs scale and humidity less than 6 percent.

General:Crushing -- Grinding -- Selecting -- Collecting Detailed:The High-pressure Suspension Mill has the same working principle as Raymond Mill, but its grinding fitting is furnished with 1000 - 1500 kg pressure spring. When the machine works, the grinding roll, under the action of high pressure spring and centrifugal force, rolls close up to grinding ring, its rolling pressure ratio is 1.2 times of Raymond mill given an identical condition, and its output may increase 10% to 20%Please note that when the grinding roller and grinding ring reach a certain degree of abrasion, please adjust the length of high-pressure spring to keep the constant grinding pressure between grinding roller and grinding ring, so as to ensure a stable output and fineness.

high pressure grinding rolls (hpgr) | sgs

HPGR have been used for many years and are emerging as an energy-efficient alternative to conventional and AG/SAG comminution circuits. One of the interesting features of HPGR is its capability to produce a particle size distribution with a greater than typical amount of fines, thus reducing the power requirement for the downstream ball mill. This makes the use of standard ball mill analyses based on the K80 inadequate, unless appropriate corrections are made. (This problem is shared by AG/SAG mill circuits.)

The most appropriate way to get around this data problem is to run the entire circuit at pilot-scale and analyze the data based on the overall power applied in kWh/t. This requires a fair quantity of sample, and the difficulties inherent to performing such a pilot plant make it difficult to come up with reliable conclusions.

The use of a small locked-cycle scale test, such as the Bond ball mill grindability test, was proposed as an alternative way to achieve the same objective in a more controlled manner, and more importantly, with a smaller sample.

SGS has developed a simple methodology that is based on the 0.25 m LABWAL HPGR from Polysius, which has a sample top size of 12.5 mm. Several HPGR tests are performed to assess the effect of operating pressure and moisture content on the performance of the HPGR and the power input to the unit is recorded.

The HPGR product, corresponding to the best condition, is submitted to the standard Bond ball mill grindability test. The Bond ball mill grindability test measures hardness as an index, regardless of the feed size, so it does not give credit for the additional fines. Therefore, the index itself is ignored in the analysis and the results are assessed in terms of throughput rate or specific energy requirement.

The total power for the HPGR system can be compared to that of a conventional circuit, based on the rod and ball mill work indices and the Third Theory of comminution. The power comparison can also be done against AG/SAG mills. This methodology has only been used to scope the potential energy savings of HPGR at small scales.

We conduct HPGR testing in combination with other bench-scale tests and circuit simulation. The use of different test procedures and design methodologies provides you with a bankable solution that is unmatched in its rigor. Contact us to optimize the comminution design for your orebody.

hpgr high pressure grinding rolls

HPGR orhigh-pressure grinding rolls have made broad advances into nonferrous metal mining. The technology is now widely viewed as a primary milling alternative, and there arc a number of large installations commissioned in recent years. After these developments, an HPGR based circuit configuration would often be the base case for certain ore types, such as very hard, abrasive ores.

Though long established in the cement industry, penetration to the hard-rock mining industry was slow , and hampered by high maintenance requirements both for wear surfaces in general, and in particular, high wear on the edge of rolls. HPGRs first made inroads into diamond processing (where rock fracture along grain lines favored a reduction in diamond breakage during comminution), and in the iron-ore industry. Over the course of the past 20 years. HPGR based circuits have become a circuit commonly evaluated, and there are now many circuits in operation.

This industry acceptance has been based on a reduction in the level of overall maintenance effort, an increase in the available size of the units, and the unit operations ability to improve overall comminution efficiency (particularly for harder ore types that can be problematic in a typical SAG circuit). Improvements to wear life and overall availability decreased the overall maintenance effort required. Incorporation of studs on the surface of rolls to allow formation of autogenous wear surfaces, and implementing edge blocks of a long-wearing material for edge protection, have allowed HPGRs to break into the mainstream of mineral processing. These wear-retarding innovations were the focal point of a full-scale trial at Lone Tree (Seidel ct al., 2006). Successful completion of this trial marked somewhat of a turning point in interest in HPGRs for hard-rock applications. Manufacturers have also paid special attention to the bearings, wear surfaces, and the handling of tramp metal through the rolls to improve operational reliability, reduce maintenance, and obtain longer service lives.

The most common HPGRbased circuit involves feeding primary crusher product to a secondary crushing circuit with of cone crushers in closed circuit with screens, followed by tertiary crushing with HPGRs, also operating in closed circuit with screens. The product of these two stages of crushing and screening then passes to secondary milling. In hard-rock metals mining applications, HPGRs are currently in use in tertiary and quaternary crushing applications, as well as in secondary pebble crushing. In many respects, HPGRs replace crushers as a unit operation.

However, from a process standpoint. HPGRs produce a product with substantially more lines (for a given P80) than a crushing circuit. In this regard, the size distribution of an HPGR circuit is much more similar to the product of an SAG circuit than a conventional crushing circuit, reducing the amount of power in the ball-mill circuit required (relative to a crushing circuit).

While HPGRs replace crushing as a unit operation, they represent a much larger installation of power in a given footprint relative to conventional crushers. As such, larger single-line capacities relative to a conventional crushing circuit can he attained. Freeport McMoRans (Freeport) Cerro Verde operation was a ground-breaking installation in that a combination of secondary crushing (using MP1000s), tertiary crushing using HPGRs, and screens replaced what would have been more typically been a large SAG mill feeding a multiple ball-mill circuit (Vanderbeek, 2006). The circuit, commissioned in 2006. was a significant step, and presented an alternative to conventional crushing plants or AG/SAG milling for primary milling applications (see Figure 17.10). Indeed, among the lessons learned for the Cerro Verde circuit w ere techniques to address rolls w ear, maintenance techniques, and elements of the art of operating a comminution circuit of this configuration (Koski et al., 2011).

Newmont Mining Companys Boddington gold project followed on the heels of the Cerro Verde project and, after considerable care and study, selected HPGR comminution, with circuit commissioning in 2009 (Hart et al.. 2011). Using Boddington as a reference for comparing an SAG-based circuit to the selected HPGR-based circuit was widely documented in the literature. The project was commissioned with a similar comminution flowsheet to the Cerro Verde (and also employing four 2.4 x 1.7-m units).

A Cerro Verde expansion used a similar flowsheet as the 2006-commissioned circuit to triple circuit capacity. The expansion circuit includes eight MP1250 cone crushers, eight HPGRs (also 2.4 x 1.7-m units, with 5 MW each), and six ball mills (22 MW each), for installed comminution power of 180 MW. and a nameplate capacity of 240,000 tpd. The expansion circuit was under commissioning and ramp-up in Q4. 2015; combined, the original and expansion Cerro Verde HPGR-based circuits are the largest throughput mill in world.

Like trends in mills, larger equipment sizes continue to evolve. Freeports Morenci operation, for example, commissioned a 3.0 x 2.0-m Metso HPGR (called the hydraulic rolls crusher, or HRC) in an expansion mill circuit in 2014. The circuit has a single-line capacity of over 60,000 tpd. with the single HRC having 11.4 MW of installed power, and operating in conjunction with twin MP1250 cone crushers to feed twin 24 x 40-feet ball mills (26 MW for each of installed power). This single-line capacity approaches that of the larger SAG circuits, with a substantially reduced number of material handling units (feeders, conveyors, screens, chutes) relative to a typical crushing plant, and a more straight-forward plant layout. Notably, the HPGR in this installation (the Metso HRC) made a substantial step forward in process performance with a flanged roll set, w hich eliminates material bypassing the full crushing effect on the edge of rolls, as well as other innovations.

Of note, an HPGR circuits mode of operation is fundamentally different to that of SAG mill. As a largely volumetric machine, the comminution specific energy in an HPGR is a function of the power drawn by the machine at a given rolls pressure setting, divided by the throughput. This has two related effects: firstly, HPGR throughput has relatively little variation based on ore hardness, but it also implies that the specific power input for the HPGR stage is also relatively fixed. As a result, for harder ore types, the product of the HPGR circuit the grind coarsens with harder ore at equivalent throughput. This is typically a positive effect relative to an SAG circuit (where throughput drops with harder ore. but typically achieving an overall finer grind)a coarser grind typically has less impact on revenue (based on a shift on the grindrecover) curve) than a drop in throughput for an SAG circuit. Stated another way, HPGR circuits aremore accommodating of ore variability. Amelunxen et al. (2011) captured this impact well, and converted this variability to NPV estimates relative to an SAG mill circuit (assuming that the SAG was designed based on median ore hardness). Sizing of the secondary milling circuit needs to consider this variability in comminution response in primary milling.

The wear on a rolls surface is a function of the ores abrasivity. Increasing roll speed or pressure increases wear with a given material. Studs allowing the formation of an autogenous wear layer, edge blocks, and cheek plates. Development in these areas continues, with examples including profiling of stud hardness to minimize the bathtub effect (wear of the center of the rolls more rapidly than the outer areas), low-profile edge blocks for installation on worn tires, and improvements in both design and wear materials for cheek plates. As mentioned, the HRC technology takes a different approach through the use of a flanged roll, which in turn also reduces edge wear.

HPGRs typically operate with improved comminution efficiency relative to rotating millsthis effect is typically more pronounced with harder ore types. Also. HPGRs improve observed downstream comminution efficiency. This is attributable to both increased fines generation (which can be corrected for mathematically, as this portion of comminution w ork is actually done by the HPGR. and not downstream unit operation), but also due to what appears to be weakening of the ore. which many researchers attribute to micro-cracking. This effect has been observed by the author in both well-controlled (and fincs-corrected) laboratory tests, and also in plant trials, as well as by other operators and researchers. A typical HPGR-circuit product approaches the lines generation of an SAG-circuit product, both with markedly more fines than a crushing circuit.

Of note is that while the HPGR improves comminution efficiency, the savings in overall circuit power requirements can be reduced or even negated by an increase in conveying and pumping costs relative to large single-line SAG circuits. Put simply, some of the power savings of more efficient comminution is used to transport material through the various unit operations of crushing, HPGR milling, and screening.

Media wear is much less than an SAG circuit in terms of total volume (balls and liners) or as unit consumption in terms of kg/kWh or kg/t. However, although the volume is less, the wear materials are much more highly finishedin economic terms, a high-volume. lower value media is replaced by a low-volume. higher value media. The cost is materials is therefore canceling to a greater or lesser extent. On the other hand, the savings in transport and logistics costs for the reduced volume can be substantial.

A number of trade-off study papers have been published. Very generally, such trade-offs often pit the higher capital cost of an HPGR circuit (with additional unit operations, bells, etc.) to lower comminution energy costs (based on higher comminution efficiency) relative to an SAG circuit. During studies of the Boddington project, comminution power efficiency gain was somewhat offset by increased power for additional conveying and screening units, for an overall net 5% decrease in unit power required for the circuit (Seidel et al., 2006). While the magnitude of the observed power efficiency benefit varies. HPGR circuits demonstrate a consistent benefit, which tends to be more marked for harder ores. Considerations in these trade-off studies also consider the differences in media consumption and overall circuit (not solely comminution) power requirements.

In summary, and relative to an SAG mill primary circuit, HPGRs appear to be most attractive with hard and abrasive ores, and in environments with high power costs. Availabilities are now such that aside from rolls change-outs, which are akin to a mill liner change, the unit rarely controls circuit availability. Overall single-line availabilities comparable to SAG milling can be attained.

HPGR is typically used in a third-stage or fourth-stage crushing application ahead of grinding. You could always try to build a circuit doing 45 m classification, but I suspect your circulating load would be overwhelming. Most HPGR applications in hard rock mining achieve 3000 m to 7000 m product

The largest HPGR Polycom in operation (Figure 5) using a maximum roll diameter of 2.2 meters is processing diamond-bearing rocks in Australia at a maximum feed rate of 600 to 800 mt/h with a top feed size of 150 millimeter (6). This rock material is reduced in one pass to 57% -1 millimeter with a power input of less than 3 kWh/mt.

Polycom HPGR offers particular improvements in the early physical recovery of coarse gold and gold-bearing sulfides through the addition of a PGF Circuit (i.e., Polycom Gravity Separation Flash Flotation).

The Polycom HPGR provides an easy and fast adaptation for throughput and product size through pushbutton changes of the hydraulic pressure. Constant product fineness can be maintained even when variations in ore grindability occur. This is of particular importance to gold operations where variations in particle size of gold and gold-bearing sulfides, silicification, changing rock types or other alteration features present challenges to conventional grinding circuits.

Following are several options for the use of the Polycom high-pressure grinding roll for optimization of gold ore comminution circuits. Specifically the increasing significance of whole ore oxidation treatments of refractory ores will require cost-efficient and optimal liberation of ultrafine precious metals mineralizations.

Additional options for high-pressure grinding roll use in gold ore comminution circuits are illustrated in Figure 11. As indicated by Kapur et al. (1992), high-pressure roll grinding is likely to replace ball mills in increasing numbers in the near future.

Krupp Polysius has developed a rapid and effective test for evaluating a gold ores amenability to high-pressure grinding. All test products are subjected to cyanide leach tests and mineralogical analysis to provide optimal performance data and recommendations for pilot plant work, scale-up and/or plant operation.

high pressure grinding rolls

HPGR roll diameters typically range from 0.5 m to 2.8 m, depending on the supplies, and roll widths vary from 0.2 m to 1.8 m. The aspect ratio of the rolls also varies as a function of manufacturer. Typical HPGR throughput rates range from 20 to 3,000 tph, with installed motor power as high as 3,000 kW per roll. The roll surface is protected with wear-resistant materials, and it has been these that have traditionally stymied HPGR acceptance, but solutions are now in place.

Detailed descriptions of the derivation and formulation of the parameters are given in numerous texts, and as such, the following section provides only a precis of the critical formulas, with some examples of actual relationships from testwork.

When a plant design (with or withoutHigh Pressure Grinding Rolls) is being assembled, every well-equipped engineer will be able to turn to numerous rules of thumb associated with these crushers-even without reference to textbooks or suppliers.

The high pressure grinding roll has established itself in various industries. High pressure grinding rolls has been leading the way for the use of HPGR in the non-ferrous metals mining industry. In comminution circuits of the cement and diamond industry, HPGR has become a standard grinding tool. HPGR has demonstrated economic and technical benefits that are nothing short of spectacular.

HPGR offers operational features such as low wear, high availability, push button control for fineness of grind and throughput, compact size, proven technology and performance guarantees will become pivotal for plant optimization and expansion. The key features of HPGR, the cost-efficient operation due to reduction of power and the even more significant decreases of steel wear cost, have been unchallenged by any other available comminution technology.

Unfortunately, high pressure grinding rolls continue to be confused with conventional roll crushers. HPGR comminution is substantially different from impact, attrition and abrasion comminution as it occurs in crushers, SAG and ball mills. The HPGR comminution occurs in a bed of particles between two counter-rotating rolls where only a limited amount of the ore is in contact with the rolls. The particles are breaking each other in a restricted space with no opportunity to move or escape. Therefore, the comminution efficiency is significantly higher than in conventional crushing and ball mill grinding. The HPGR comminution exhibits two extremely important features in regard to hydrometallurgical dump, heap, thin layer, vat or agitation leach operations:

High-pressure grinding rolls were first applied in the minerals industry in 1985 in cement plants. The main objective for the use of HPGR was the significant energy savings achievable. Today, they are also being used by diamond mines and for the communition of coal as well as for the grinding of slag, iron and chromium concentrates (Figure 4).

If ball milling was completely replaced by HPGR, up to 50% of the energy needed for the dry grinding mill could be saved. In wet grinding, the energy savings are lower, yet still noticeable. Further to the reduction in energy costs, the HPGR also proved to produce higher quality grinding products and/or a better recovery. At present, 165 HPGR Polycom units have been sold worldwide; about 11% of them are operating in the mining industry.

Gold mining operations have, thus far, not utilized the considerable metallurgical and economic benefits offered by HPGR grinding. As is the case with any new processing equipment, a certain acceptance time is required before operators recognize the potential and are willing to modify conventional circuits. Also, while the priority in many grinding operations has been on energy and throughput, gold processing plants, especially, have not recognized the dramatic beneficial effects high-pressure roll grinding has on the gold metallurgy.

Through these recent optimizations and the simplicity of the unit, todays HPGR designs provide high reliability and cost-efficient operations. Coupled with the Polycom HPGR small space requirements, they are ideally suited for comminution plant modifications and upgrades. HPGR Polycom grinding is now being considered for several gold operations in the western United States as well as for refractory gold plants in Australia (Grier, 1992). Judging from other technology improvements and operating practices in gold processing which have come from the cement industry (Marsden et al. 1993), it is almost certain that the remarkable impact high-pressure grinding rolls have made in cement plants will also find its way into gold operations.

Even though there are definitely local preferences to the use of comminution technology, the selection of a cost-efficient, high-recovery crushing and grinding circuit depends predominantly on the compositional characteristics of the gold ore. Therefore, many of the subsequent gold recovery problems are directly related to results of the comminution.

Although considerable progress has been made with optimized conventional and/or innovative gold ore treatment, significant processing problems remain with many ores. They are primarily related to the mineralogy of the ore feed. Further, the mode of occurrence of the gold is essential for the precious metals recovery after comminution (Baum, 1990).

These findings are supported by Mintek (1993) in an evaluation of gold ores from the Pacific Rim which points out that because of the variability and mineralogical complexity of many ores from the southwest Pacific, very careful control of the comminution process is required for optimum results.