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ng the desired productivity and thus directly impacts the economics of the project the cavability may be established through empirical comparisons of the rock mass to other known caving operations numerical modeling or both a key aspect of the cave design is the hydraulic radius hr which is a calculation of the ...
undercutting process post undercutting usually places the undercut level drifts directly over the extraction level drifts and at the top of the major apex long hole drilling and blasting is required for the formation of the drawbell in all cases but is sequenced differently according to method pre and advance unde...
nts are staggered and therefore the temporary fringe drifts are not straight in addition the boundaries of the panels in a large deposit become problematic such problems occur because if a fringe drift is established between panels the width of the pillar between the herringbone layouts on either side of the fringe...
motecontrolled or automated lhds thereby eliminating any risk to the operators service ventilation level the service ventilation level is typical of a larger footprint mine and is primarily a way to provide intake and exhaust ventilation across the production footprint for the undercut extraction and haulage levels...
n be removed from the traffic flow fairly easily thereby reducing production shortfalls another advantage of a truck haulage level is the ability to modify designs easily over the course of time if new reserves or discoveries come into play the main disadvantages of truck haulage include significantly smaller payloa...
s of the finger raises forming pillars that will later be long holed and blasted to initiate the caving action transfer raises are driven between the haulage and the grizzly level with a loading chute at the haulage level and grizzly rails for sizing at the grizzly level after the undercut has been blasted broken or...
ut and drawbell post undercutting post or conventional undercutting refers to undercut drillingand blasting after development of the underlying extraction level has been completed figure 13 10 4 drawbells are also prepared ahead of the undercut blasting production blocks can be brought into production more quickly...
y an advance undercut only extends ahead by the length of one drawbell thereby keeping the active cave close to the leading edge of the cave front if the caved undercut is left to sit for too long before taking the drawbell beneath it can begin to compact and accept the weight of the ground above the abutment str...
is prohibitively high a separate haulage level is employed as the panel and drawpoints are being constructed the relevant orepasses ore handling systems and ventilation infrastructure must keep pace orepasses can be drop raised raise climbed mechanically or manually or raise bored down to a handling level th...
130 000 t d el teniente chile those upper limits will continue to grow as more and more of the large open pit mines in the world transition to underground mining and the technology for large scale underground production improves mines are being planned today that will exceed 150 000 t d when at full production s...
the production capacity of the mine is not overestimated another major consideration in determining the optimal production rate for a caving operation is the manner in which the cave is advanced in the ore body large deposits cannot be caved in a single pass because the advance of the cave front is slowed by the limi...
r larger mines determines how the production blocks interact with each other as the mine life progresses it is critical to devise an opening sequence that is geotechnically sound otherwise the production goals and perhaps even the mine itself can be put at risk the mining sequence on a large footprint cave will ...
sting the larger rocks ventilation there are several components to ventilating a caving operation that bear particular attention planning these components into a general scheme early on will reduce operational trouble at a later stage because multiple lhds will be operating in parallel galleries sufficient air must...
cally be managed from a remote control center the automated equipment operates in isolated areas to prevent worker machine interface issues automation is employed to improve productivities and reduce exposure of operators to injury in certain mines the risk of rock bursting or wet muck rushes is great enough to warr...
ar another large caving operation plans for trains with two 40 t locomotives and 24 cars at 30 t per car rail systems lend themselves very well to automation and in the right environment can have much lower operating costs than haul trucks several varieties of long hole drills exist and newer computerized version...
t equipment for rail haulage operations typically includes smaller 12 t locomotives often diesel powered so as to be independent from issues with the electrical power supply functions handled include shift change track repair cleanup under ore chutes switching and marshalling electrical and control maintenance ...
those issues it is therefore important for cave management to understand and react to those issues special draw orders for specific drawpoints might be issued to address those issues for example a hung up drawpoint might be causing excessive weight in a production drift so orders are implemented to prioritize bla...
production can be 10 15 years capital estimates are typically divided into the following capital development which includes all preproduction and production buildup development and infrastructure required to bring the mine to its sustainable full production rate and sustaining capital work required on long ter...
ns infrastructure requirements maturity of the mine depth and so on labor block caving mines can be highly mechanized and efficient operations commonly achieving more tonnage per workershift than any other underground method and potentially producing many times more tonnage per worker shift the initial labor re...
t process is beyond the scope of this chapter but an informative section on operational hazards and risk assessment for block caving can be found in chapters 10 and 11 of block caving geomechanics brown 2003 as with any mining project a detailed risk assessment is required typically a qualitative risk analysis is...
and the released energy cannot be absorbed in slips or fractures rock bursts will usually occur only in strong brittle rocks such as quartzite or granite effects include violent fracture and expulsion of rock from and near the boundaries of excavations and the full or partial closure of mining excavations damage c...
nce of the undercutting are key components to the caving performance should the chosen design prove to be unstable large portions of the production area could be lost and ground repair would be extensive leading to lost or delayed production caving rate if lower than expected ramp up will be delayed cave s...
of the mineral s in question does not change in hydrometallurgical processing however chemical reactions invariably occur these systems are operated at ambient or elevated temperatures depending on the kinetics of the processes the ultimate goal in the production of metals is to yield metals in their purest form...
for the buyers or engineers who will treat this concentrate further to extract the metal values to achieve this goal economic assessments of all possible technological alternatives must be conducted economic concerns table 14 1 2 summarizes the total u s supply and recycled supply of selected metals in 1996 alth...
tic and electrostatic concentration are used extensively in the industry froth flotation the surface properties of minerals composition and electrical charge are used in combination with collectors which are heterogeneous compounds containing a polar component and a nonpolar component for selective separations o...
ning chalcopyrite and molybdenite is shown in figure 14 1 5 after grinding and classification pulp is fed to rougher flotation the rougher tailings are thickened and sent to a tailings dam the rougher concentrate is classified and the oversize is reground cyclone overflow is fed to cleaner flotation and the clea...
cuit that entailed staged crushing followed by open circuit rod milling and closed circuit ball milling modern equipment has blurred this concept with autogenous grinding semiautogenous grinding ag sag mills and high pressure grinding rolls hpgrs in particular spanning a broad range of comminution applications...
asting in conjunction with the overall economics of shovel productivity primary crusher throughput and downstream comminution efficiency efficient blasting is effective at both decreasing top size as well as improved fines generation in general the following conclusions can be drawn staggered patterns versus s...
ft the haulage burden from a mobile equipment fleet to conveyors and more economically transport material mined to either ore or overburden stockpiles the evolution of larger truck sizes along with a general trend of steeper and deeper pits have tended to disfavor in pit crushing and conveying however these can of...
nerable to damage through introduction of incompressible foreign objects notably ground engagement tools and tramp metal in cases where direct dumping is used protection is limited to tools such as cameras and image analysis software useful for detection of the loss of shovel teeth spotters and the installation...
h oversize fed to a tertiary crushing circuit operating in closed circuit with screens the product of a standard tertiary crushing plant is nominally 100 passing 13 mm the basic design of a tertiary crushing plant secondary crushers in open circuit with tertiary crushers in closed circuit with screens along with ...
maintenance can be readily sourced or developed throughput for the machines used is largely volumetrically controlled as such plant throughput is relatively insensitive to changes in feed hardness or feed size distribution though the amount of comminution work and power drawn by the machines is clearly affected ...
4 papua indonesia presented in figure 14 2 7 has registered monthly tonnages averaging more than 125 000 t d 138 000 stpd with single day performances in excess of 150 000 t d 165 000 stpd although common convention generally refers to highaspect ratio mills as sag mills with diameter to effective grinding...
r draw produces a finer grind and has a higher unit power input kilowatt hours per ton than a sag circuit milling the same ore in the presence of suitable ore an ag circuit can provide substantial operating cost savings due to a reduction in grinding media expenditure and liner wear in broad terms this makes sa...
in the design for future pebble crushing expansions today every ag sag flow sheet conceived is likely to seriously consider the inclusion of a pebble crusher circuit for certain ore types particularly those with a chert andesite or other hard component that develops a critically sized material that constrains mi...
g the challenge of feed size is that for many ores the overall coarseness of the primary crusher product is correlated to feed hardness larger more competent material consumes mill volume and limits throughput to counteract this effect many circuits including troilus quebec kidston queensland australia ra...
is typically required of ag sag circuit operation as is more advanced process control to maintain steady state operation with different operator advanced process control regimes based on different ore types additionally very hard ores can severely constrain ag sag mill throughput in such cases the circuits can ...
ss standpoint hpgrs produce a product with substantially more fines 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 a sag circuit than a conventional crushing circuit reducing the required amount of power in the ball mill circu...
condary milling for those circuits requiring secondary grinding most circuits aside from heap leach operations and single stage ag sag circuits the use of wet ball mills has remained the standard unit operation most such circuits use ball mills in closed circuit with hydrocyclones however closing circuits with fi...
opriate design for recirculating load is beyond the scope of this chapter milling efficiency typically increases with closed circuit operation and will often increase to a certain level with increasing circulating load after a certain point the grinding efficiency declines with increasing recirculating load also a...
ic need and subsequently marketed although not all operations require this stage of grinding for those that do it is often a critical unit operation although the mills are smaller in size than mills for primary and secondary grinding unit energy input ranging from 5 to 40 kw h t for tertiary mill feed often excee...
or tertiary grinding they are widely used in lime slaking and in concentrate regrind applications pin mills of either nonfluidizing or fluidizing tip speed are generally the next mill considered at progressively finer grinds to a nominal grind size with a p80 of 5 m isamills are established as a versatile fine gr...
can have effects including agglomeration or increased galvanic activity for example the use of specialized electroformed nickel subsieves which offer precisely sized apertures for sieves at sizes less than 20 m is restricted for copper concentrates because of rapid galvanic action with the sieve itself technique...
ind below a maximum particle size is important when this requirement is overriding certain grinding equipment listed in order of coarser grinds and lower fines generation can be used center discharge rod mills end peripheral discharge rod mills overflow rod mills and grate discharge ball mills in quarrying and...
ife capital costs operating costs delivery time for major components and plant location are all factors in process selection given ore characterization data alternative circuit designs to accomplish the required comminution can be developed capital and operating cost estimates for each circuit alternative allow ...
lated the traditional bond work index is perhaps the best known but similar indices are calculated by other tests grindability tests that reach a locked cycle equilibrium or steady state continuous operation are a better indicator of actual mill performance than batch tests the design methodology for hpgrs using a ...
ariables that can be reasonably tested the amount of sample required and the logistics and expense of sample acquisition a number of tests have been developed over the years with various strengths and weaknesses this is partly a reflection of proprietary design approaches by various companies and designers and per...
rget and ore breakage characteristics for an ore body most appropriately evaluated as a range and ideally based on a preliminary mine plan a number of circuit designs can be prepared for evaluation based on circuit specifications ore characteristics downstream processes location operator preferences and scopi...
on at the desired operating conditions conversely motors with rated power outputs larger than could ever be drawn have been installed leading to confusion on the part of designers and operators who believed that this power should be available for grinding much of the art of power estimation was converted to direct ...
ant performance simulation is a powerful tool that offers the ability to evaluate circuit response for a range of operating conditions and of a given circuit for a range of feed types and readily compare a number of circuit options it can also provide a great deal of useful process information in terms of the volum...
which will change based on ore hardness and size distribution for crushers or hpgrs though the feed rate is fixed based on volumetric throughput at a given aperture and the power drawn varies as a function of the ore characteristics regardless a design methodology that considers designing the primary milling sta...
us grinding are often designed to accommodate semiautogenous grinding either for operational flexibility or with the anticipation of milling future ore bodies a case study of an operation with a versatile single stage ag sag circuit is brunswick larsen et al 2001 when using the largest mills available a single sa...
ting both differences in capital and operating costs and in performance between plant types qualitative considerations include location operator preference equipment lead times and the like selection of motor and drive types for tumbling mills is a specialized topic in itself for larger mills nominally more tha...
ia size and density the use of ore as ag media was reviewed previously in the ag sag circuits section pebble milling a form of secondary milling most often uses oversize material extracted from the primary milling circuit as media this is most often done in applications with higher ore densities and can represe...
owatt hours per ton is a good metric for comparison the use of liner handlers to reline mills is now standard practice and the use of larger machines has facilitated consolidation of liner parts the world s current largest liner handler is in use at pt freeport indonesia the machine s 7 250 kg capacity has allowed...
ffort may seem to be an easy target to achieve both cost and carbon footprint benefits in many cases though the incremental comminution effort required for the incremental value recovery is less than the energy requirement to recover a like quantity of values from a freshly mined ton of ore from an energy perspecti...
wo minerals to be separated is used as the medium of separation particles of higher and lower specific gravities than the medium move in opposite directions this technique requires only a small difference in specific gravities of the minerals for effective separation heavy or dense medium separation methods are abso...
the pulsation of the bed may be achieved by means of a plunger or by admitting compressed air at regular short intervals into a limb of a u shaped tank light material is generally discarded through a gate positioned opposite to the feed end gaudin 1939 suggested that three segregation mechanisms may take place wi...
ramic ragging may be selected from a range of specific gravities from 1 6 to 5 0 ipjs have been used across many mineral types including gold sulfides tin coal and diamonds figure 14 4 3 shows a schematic diagram of an ipj ipjs are available in a range of sizes handling 2 to 100 t h of feed material the solids ...
found wider application in the coal industry as this method does not use process water with the advantage of eliminating the need to dewater fines or manage slurry confinement particulate emissions have been minimized by the inclusion of fabric dust collectors the new units use a punch plate instead of a fine wire m...
near the center column several cone pairs may be stacked on top of each other to increase the quality of the separation cones are operated continuously figure 14 4 6 shows a schematic diagram of a reichert cone riffled sluice riffled sluices are commonly used by artisan miners to recover gold the segregated gold o...
slow forward stroke and a rapid return the feed slurry enters through a port at the top corner and is distributed over the flat surface because of the vibratory motion wash water is introduced along the top edge of the table surface washing the particles down the slope heavy mineral particles get trapped between t...
vices that use this technique are called centrifugal concentrators two devices that have found wide applications in recovering fine gold and other minerals are the knelson and falcon concentrators knelson concentrator knelson concentrators as shown in figure 14 4 9 are comprised of a slightly conical shaped rotatin...
in precious metal recovery plants in continuous devices at the top of the bowl is a ring of specially designed concentrate flow hoppers followed by pneumatically controlled variable orifice valves these valves allow for a constant stream of concentrate to be produced the continuous concentrator is able to vary ma...
type of material to be separated the heavy medium suspension should be nonsettling which requires the solid particles to be sufficiently small for coal the most commonly used are magnetite and barite as the medium density should be less than the ash density for ore separations more dense solid materials such as...
the diameter of the cyclone the diameters of these hmcs range from about 0 5 m to 1 4 m and have capacities up to 500 t h the relative density of the overflow stream should be between 3 and 12 lower than that of the feed stream dyna whirlpool separator the dwp also imparts a centrifugal acceleration to the feed p...
solution is used generally an organic solvent may be used to dilute the reagents to a required specific gravity caution should be exercised in handling these reagents as most of them are toxic the data from these tests are presented as washability curves that essentially indicate the grade and recovery of the concen...
froth flotation applications changes in the settings of one factor such as feed rate will automatically cause changes in other parts of the system such as flotation rate particle size recovery airflow rate and pulp density as a result it is difficult to study the effects of any single factor in isolation and...
nts naturally hydrophobic materials include hydrocarbons and nonpolar solids such as elemental sulfur coal is a good example of a material that is normally naturally hydrophobic because it is mostly composed of hydrocarbons chemical treatments to render a surface hydrophobic are essentially methods for selectively ...
oth flotation chemicals are needed both to control the relative hydrophobicities of the particles and to maintain the proper froth characteristics therefore many different reagents are involved in the froth flotation process with the selection of reagents depending on the specific mineral mixtures being treated kl...
l it is also possible to float naturally hydrophobic minerals such as molybdenite elemental sulfur and talc with nonionic collectors nonionic collectors can also be used as extenders for other collectors if another more expensive collector makes a surface partially hydrophobic adding a nonpolar oil will often ...