US2536869A - Mining method - Google Patents

Description

P. B. BUCKY MINING METHOD Jan. 2, 1951 s sheets-sheet 1 Filed June 22, 1946 FIG. 2

,INVENTOR: Phlllp B. Bucky ORNEYS.

Jan. 2, 1951- P. B. BUCKY MINING METHOD Filed June -212, 1946 3 Sheets-Sheet 2 INVENTOR Phili B. Buck Byfwgmwlpmm y #M AT ORNEYS P. B. BUCKY .MINING MTHOD Jan. 2, 1951 :s sheets-sheet s Filed June 22k, 1946 INVENTORI Philip B. Bucky BY: Qu ad @mi fi@ ATTORN YS Patented Jan. 2, 1951 UNITED STATES rATENT OFFICE MINING METHOD Philip B. Bucky, Larchmont, N. Y. Application June 22, 1946, Serial No. 678,614

13 Claims.

This invention provides a new and economical method for mining ore that may be used for Working both underground deposits and those that crop on the surface. The new method is particularly satisfactory for mining orebodies in regions where the orebody and the ground in which it occurs tends to spall or fail into open spacesy and where wall failure dilutes the broken ore with waste rock. However, it may be used for mining any deposit where it is advantageous to provide support for the ground during or after mining operations. The invention further provides for obtaining improved ore fragmentation in the stope being mined, and for withdrawing the ore from the stopes without dilution by waste rock or ll.

The preferred embodiment of the new method may be termed the shrink-fill method of mining, as it involves rst breaking the ground by a modied shrinkage method of stoping, and then introducing Waste ll at the top of the stope as the fragmented ore is withdrawn from the bottom and as its upper surface subsides within the stope. However, other methods than shrinkage methods may be used, in appropriate cases, to break the ground.

Many dilferent methods for extracting ore from mineral deposits are knoWn and employed. The choice of the particular method to be used in mining any given ore deposit is mainly a matter of selecting the most economical method to which the deposit lends itself, taking into account such factors as richness of the ore, the ease with which it may be broken to permit its withdrawal, the size of the deposit, and the mechanical strength of both the orebody and the ground within which the deposit occurs. Shrinkage methods of mining often are employed. A typical shrinkage method involves digging into the deposit at a, depth below its upper surface, and breaking the ore down from the roof of the working space. If the surrounding ground is strong, it is generally su'icient to continue breaking ore from the roof of the stope and withdrawing the broken ore from the bottom of the stope at the proper rate to provide working space for the men until the upper limit of the stope is reached. During the ore-breaking operations the upper surface of the broken ore serves as the floor of the working space, and withdrawal of the broken ore is regulated to maintain a working space of proper height. Thereafter the broken ore is simply withdrawn from the stope, leaving an open cavity underground.

If the surrounding ground is not suciently (or cavity) is formed within it, some method of supporting the ground and/or preventing dilution of the ore must be provided. This is also important in regions where precautions must be taken against ultimate surface subsidence, because even strong ground may ultimately cave into open emptied stopes.

Numerous methods for supporting the surrounding ground from which ore has been mined are known and employed. Some such methods involve extensive use of timbers to support the ground during mining operations and subsequently. Often the spaces between the timbers are lled with waste rock after the ore has been extracted to provide permanent support for the ground. Considerable handling of small batches of broken ore and lill material usually is required in mining by these methods. The timbering and the handling of ore and ll make such methods expensive, and consequently they are generally used only for mining high grade deposits.

In the so-called cut-and-ll method, the ore is usually broken from the stope roof (as in the typical shrinkage method described above), and after one cut of ore has been taken from the roof of the working space and has been withdrawn by shovelling, scraping, or other means, waste ll is introduced to take the place of the ore removed and to raise the floor of the Working space high enough to permit another cut to be taken. This method saves the expense of timbering, but involves laborious handling of broken ore and waste fill Caving methods which involve breaking the ore simply by allowing it to cave into an undercut opening are generally the most economical methods for underground mining, but such methods can be used only where the ore is of such character as to break properly by caving, and where surface subsidence of the ground is not important.

The new mining method provided by the pres- 'ent invention is generally applicable where shrinkage, cut-and-ll, block caving, and similar methods have heretofore been employed, and is also applicable in many instances where extensive timbering, or timbering and iill, has been considered necessary to support the surrounding ground.

Briefly the new method comprises breaking the ore throughout the height of a stope within an orebody and withdrawing the broken ore by gravity flow through a chute at the stope bottom. In a preferred embodiment of the invention, the ore is broken down from the solid mass of ore in 3 place while the space between it and the previously broken ore is very much smaller thanv ha been maintained in heretofore known mining methods. In general the upper surface of the column of broken ore in the stope is maintained sunciently close to the lower surface of the overhanging unbroken ore so that any space therebetween is no greater than will be filled substantially completely by material broken in the succeeding, 'blasting (orefbreaking) step. Advantageously, i'some cases the upperl surface'of the broken ore may at all times be maintained substantially in contact with the roof formed 'by the overhanging mass of unbroken ore. In this manner, the force of the blasting operation by which the solid ore is broken also 'contributes to further fragmenting the underlying already broken ore. The drilling andother mining oper'- ations are conducted from working positions within a rather smallamanway, so that working onditions are` safer than is possible when the miing'operatidns 'are conducted in relatively large underground open working spaces.

VAlflfterthe ore has been broken throughout the height of the stope, waste ll is added at the t"9D of theA stope at v'substantially the same rate as thebro'len ore4 is withdrawn through' the chute at the bottom of the stopejand asv the upper surface of theI broken ore subsides therein. Thus the )st'ipe'v 'maintained substantially full of broken'inateriall'tore or fill) at all times.

o "Withdrawal 'offthe broken ore through the chute 'at the` bottom, ofthe stope is continued, with continuing addition of waste ll at the top of the stope', until'theinterface beween the orez andthe waste reaches the level'at which the angle' from the ore withdrawal chute to the laterally most'rmte part of the ore-ll interface `is less tljran'A 'about '10 to the horizontal. Further. withdrawals of ore by gravity ow then vare'n'iost advantageously. made through another chute locatezd'at a point such that said angle is appreciably greaterthan about 70.

The new methodl is generally more economical andin its preferred embodiment may be ernployed with greater safety than is generally the case'with 'heretofore known mining methods such as those briefly described above. The new method is `e..pp' licable'to orebodies which dip but gently from the horizontal and equally to orebodies which dip steeply. It may be employed successfully in mining lange orebodies of great width and length,l as well as in mining relatively small orebod'ie's. VIt is especially useful in mining ore from deposits occurring: in ground which is weak and tends to. cave or spall in open stopes, and where provision must therefore be made to avoid oontamination of the ore and to provide supportfor the ground, but it may also be used in regions where the ground is strong. The new mining method is peculiarly eifective for preventing rook bursts, a type ofground failure that often occurs in open mining cavities in strong ground. However, the new method may be employed in mining ore from deposits in strong ground, even where'rock bursts donot occur, in order to insure permanently against caving and surface subsidence after the deposit has been mined out.

The invention is described in some detail be low' with l reference "to the embodiments diagrammed in the accompanying drawings. These embodiments illustrate characteristic and pre- 4 be made in adapting the new method to particu; lar ore deposits. In the drawings,

Figs. 1, 2, 3 and 4 show successive stages in mining ore by the new method from a steeply dipping, rather narrow deposit; and

Fig. 5 shows an adaptation of the new method to the mining of ore from an essentially horizontal deposit of considerable extent that outcrops on the surface.

In theembodimentshown in 'gss 1 to 4, ore is being minedby the new metho from a steeply dipping deposit or orebody I0. Preparatory to mining the ore, crosscuts Il are driven from the mi' e shaft (not shown) to the orebody. Level dril s l2 also are driven alongside the orebody at vertical intervals of say 50 to 300 or more feet to permit ready aocess to the orebody. Crosscuts 3 extend out Afrom 'these level drifts into the orebody. Ore chutes I4 are driven upwardly from the level drifts l2 into the ore deposit at an angle preferably somewhat greater, than tho, angle of repose. of broken orefrom the orebody.

After the preliminary de velopmenh'theore.in r

the stope that has been markedE out by, the development work is broken su'iciently 'so vtljatit may liow by gravity through .the chutes .MI into mine cars for transporting it. to the mine shaft, through which itis hoisted tothe surface. The Chutes "|24 are 0f -g'ursa pronged with the usual gates to control the flow of broken ore .from the stope, i'

Breaking the ore maybe accomplished in, any desired fashion. -It. *forv examplal broken by the conventional shrinlagegmzethod,deseribed above, or if the fore. sldf proper, aving, qualityfit may be broken by a caving method. Generallm however, I prefer to employ the modified and'v improved shrinkage method illi'lstrated in" the drawings and` described below. Figs. 1 to l showsuccessive. stages in the. progress of. ore-breaking operations. Enr purposes, of

illustration, it-is assumedthat the ore is to-be broken in a series of stones, arrang'edone above the other, and each of about the height from one level drift l2` to the next 'level drift above. In carrying out the method, a raise l5 is Vr'st` driven along the foot wall of the orebody throughout the height of the stope, from one working'level to the next above. As shown in Fig. 1, the. raise o l5 has been completed throughout thehe'ight'of the upper stope and a considerable portion of the ore l5: in thisvstope has already been broken. The corresponding raise in the stope neigt beldv/,s in the course of being driven. upwardlyv .Tfhe raises t5, provide .the working space from with-in which the ore-breaking operations are conducted, and may be placed wherever, and in whatever numbers, most advantageous.forworkingfthe deposit. "Y n Before breaking Ore Within a Stasera geen face at the bottom of the stope is 5ot`1ta-inerl, by excavating an opening IJ, s ay siate eight feet in height. extending'. advantageously'from the foot wall to the. hanging wall thea-lengthof the stope. Drill holes l.8 thenare drivenacross the orebody from the raise, I5 atan appropriate distance above the bottom surfape of the unbroken ore in the stope. The drill holes are loaded, tamped and fired to blast the ore down from the roof. A limited and controlled amount. of broken ore then is withdrawn through the chute I4. The amount withdrawn is considerably less than has heretofore been considered,neo;ssary, and ingeneral is such that any, space. .thereby created b etween the @Per safes-e f=hebr1eersand subside from the top of the stope.

the lower surface of the ovrhanging unbroken mass (such as-the spaces I'Ia in the upper and intermediate stopes in Figs. 1 and 3) is no greater in volume than will be filled by ore broken in the next succeeding blasting operation. In some cases the amount of ore withdrawn is no greater than sumcient to create voids in the mass of broken ore, without lowering the upper surface of the broken ore substantially out of contact with the .overhanging roof of unbroken ore (as.

practical to the still unbroken roof of ore in place. This advantage is that the force of the blast not only breaks ore from the solid roof, but serves also to cause additional fragmentation of the broken ore lying directly below the roof. The improved fragmentation of the ore thereby obtained reduces any tendency for the ore to be blocked in the chutes by large lumps, and otherwise facilitates handling the ore underground. It also facilitates crushing and grinding in subsequent preparation of the ore for treatment to recover its valuable components. Another advantage is that the working space is within the confines of the raise I5. The mining operations can be conducted from this position with greater safety than is possible if such operations must be conducted from working positions in an underground opening of substantial extent. Still another advantage is that the stope is maintained full or nearly full of material at all times, without such open spaces as normally are provided for working purposes, so that the walls of the stope, and to a considerable extent the roof of .unbroken ore, are well supported at all times throughout the mining operations. Spalling of weak walls and'consequent dilution of the ore, and rock bursts such as occur in strong ground, are thereby prevented.

The appearance of the workings after all of the ore has been broken in the upper stope and as ore-breaking operations are commencing in the intermediate stope is shown in Fig. 2. Advantageously the roof I9 of the upper stope is shaped as shown in the drawings, so that it forms an langle with the horizontal greater than the angle of repose of the flll material subsequently to be introduced. The ore from this stope may now be withdrawn as required through the upper chute I 4, and may be transported to the mine shaft for hoisting to the surface.

Concurrently with or subsequently to breaking the ore in the upper stope, ore-breaking operations may be similarly carried out in the intermediate or lower stopes, as illustrated in Figs. 2, 3 and 4. The only difference in procedure in working in the lower stope, as compared with working in the uppermost stope, is that the orebreaking operations in the lower stope are carriedfall the way up to the point of breaking through into the stope next above.

After the ore has been broken all the way to the top of the uppermost stope, continued withdrawal of broken ore through the chutes I4 will cause the upper surface of the broken ore I6 to Thissubsidence willcreate an open cavity within the ore deposit. If this open cavityassumes substantial proportions, the surrounding ground, particularly if it is weak or tends to spall, is likely to cave into the opening thus created, mix with the ore, and lessen its value. Such caving may also render development drifts in the caved region unusable and tend to cause subsidence of the earth at the surface of the ground. Large openings greatly increase the hazard of rock bursts, and may preventmining in adjacent unworked sections of the orebody.

To prevent such diinculties due to large openings underground, waste ll is introduced into the stope through a suitable opening or chute leading to the' apex of its inclined roof I9. The waste ll is supplied to the top of the stope at substantially the same rate and in substantially the same amount as broken ore is withdrawn through the chute or chutes I4 and as the upper surface of the broken ore subsides within the stope. The amount of waste fill thus introduced is sufficient to maintain the stope in which Vthe ore has been broken substantially full of broken material (ll or ore) at all times. The ll and broken ore prevent caving or spalling of the surrounding ground to any appreciable extent, when the ground is weak, and prevent rock bursts when the ore and surrounding rock are strong.

By forming the roof I9 of the stope at an angle greater than the angle of repose of the lll material, fill introduced at the apex of the roof will ow out against the roof and provide support for it as well as for the walls of the deposit.

Any available material may be used as ll. Barren rock from development drifts, or tailings from a concentrator plant located near the mine, often are available and are well-suited for use as ll. The fill-may be brought to the stope through the upper level drift I2 and crosscut I3, and may be dumped into the stope through waste chutes provided for this purpose. If desired, such waste chutes may extend all the way to the surface of the ground, so that fill may be introduced into the stope directly from the surface.

I have found that the waste fill may be added directly on top of the broken ore, and that as the ore is withdrawn through the chutes with consequent subsidence of the interface between the waste fill and ore, little or no intermixture of the waste with the ore will occur until the ore-fill interface approaches the chute more closely than a predeterminable distance. This distance is the height the interface must be above the ore chute so that the angle from the chute to the laterally most remote part of the interface is 70 (more or less, as best determined by experiment). When withdrawing ore that has been broken throughout the height of several successive stopes, as illustrated in the drawings, I therefore prefer to regulate withdrawing of the ore as follows:

When the interface between the ore and ll has subsided in the upper stope to a level where the angle from the upper stope chute to the laterally most remote part of the interface is no more than about '70 to the horizontal, fwithdrawal of ore through that chute. is discontinued. The upper limit of the dotted line 20 in Fig. 3 indicates the level of the ore-fill interface at the time when withdrawal of ore through the upper chutes I4 is discontinued.

The angle indicated above to be about 70 does not under all circumstances have precisely this value. It may vary considerably one way or the other, depending in general on the now charac tetsties; of; tbehrokenf oie, but ordinerlie it. is.

chuteyinquestion as4 the. interface 'subsidesfeveniyf In the case -of a, Wide stone; served.- bvseveral chutes on the same level, the laterallymost remote? part, ottbeiinterfaee in thedirection f another chute-may, bel taken aspbeing; along a lineemidway between;the chutes.

After the, interface between theIY ore and waste ll has-.reached theV level belowA which it is inadvisablesto continue-withdrawing ore throuehthe uppenchute l I 4,1, further withdrawal Aofthev .lonoken oremay' be; eiectedthrough the; chute. at the bottom of the; nextglower stope'lthe intermediate stone. as shown, in the drawings), When the subsiding interface between the 4 ore and; ll reaches the level- (indicated by thegupperylimit oigthevdotted line 2l in Fig. 4) where the-angle from this chute to thelaterally. vmost; remote part ofatheinterfacejs again '70moreor less, withdrawalV through-nthe, intermediate, chute is. discontinued,- and-further withdrawalzisfeffected as through the-chuteat thetbottom of the. lowermost stope, after` the solid portionbetween stopes is fragmented;

As'. a result-:of the. aboverdescribed procedure. for withdraw-ingthis ore,v the -subsiding interface between-.the ore and added retains substantiall'ytthe.I shape.v of-the: top of Vthe. upper stope aftiwhich the;.ll' is, added, untilthe.v interface reaches the..y level 4at* which i the angle.- from, the lowerrnosti chute.. to the*A laterally 1 mostremote part of. the :interfaceI isabout 70.

In .withdrawing the -ore .through the; chute or chutes at the bottom vof :the lowermoststepe,l the withdrawal may be continuedeven after the interface between the-ore -and-ifill hasl subsided to below the level `.corresponding `to thatfatwhich withdrawal operations.- through .the higher level chutes. were. discontinued... Indeed, withdrawal through.4 thelowermost chute may continue until waste illxshowsinthe orefchute, which then indicates-that,substantially all .of :the-ore has. been withdrawn from thel stope, and that it contains little but-waste ll. Therewill, however, remain a:.vol11me.122 e of ore (occupying. the region .below tha-dotted line. 23-iin Fig. 4), which cannotzbe withdrawn bygravity flowthroug-h the'lower-most chute i4; This-tore,- andiany smalLunderlying massfofiunbroken ore, maybe either left inzplace onminedfbyspecialmethods.

Thenew mining methodas describedaboue may be used to. mine concurrently several stopes within the-same. ore,bod`\7. For example; in mining a steeply dipping orebody such as illustrated i'n- Rigs. 1 izo-4, mining operations mayibeproceeding in stopes ait-several ,levels at the. same time; In this way, the rate Aat -which ore-is mined from the, deposit maybe-increasedi The height off'the stope to be `:worked may-.fin factbe. determined in part=from the numberof different stopes thatiit is desired to lworkeoncurrently for, purposes-of obtaining.aflargedaily output-of-.ore`

Fig. 5 illustrates an adaptation off the new method to mining conourrentlyin several adjacent stopes-in -anessentially horizontal .orebody which outcrops on. the-surface-- As :shown in this figure. the orebodytis of -heig-ht Hfand adjacent iopessl; 32,-' 33 and-34eme in variousstages'ot Werktage. eimainhaulaeewar sdrvenin the reels 44 beneath-the orebodxt and f. ore chutes- 3 64 extend :from it :int o the.1 orebodyi- StopeA 34; shown in the drawings has been markedfput and-prepared for mini-ngl by driving-:a manway-raise- BJ :through the-stone.V and opening the: ore-chutes :36;but ore-breakinghas net bef euniinthis-stope.. In istopef?. .ore-isbeing broken by-z a..sl1ri nkage-. methode of. the characterv dee scribed.- previously. 'Ihefworking spacefr orebreakingoperationsris in@ the manway raises; 3.1: Drill .holes 38. are. made fromsetups in the; raises 31; (they. may beemade by long-hole. diamond drills). to :permitxplacing Loi;the fexplosive: charges in'. the overhanging solid ore. Broken ore 45;` is withdrawn from ,the stope through the chutes-w35 asrequiredto create voids-.inthe mass ofi-broken ore.- aiter. eaohiilast,4 as. described: above.Y The bottom oteaehstope is :shownformedl witha sloping bottom so `thatthe ore'1 may feedtdireotly into .chutesandinto the earsor conveyor on the main .haulage drift 35i stopezrisfshown as it appears after theore has been-.broken all the wayv-to the surface-and initial addition of liill has been-:placed on top. `of it, During subsequent operationsA in this .stope,

ore is. withdrawn by lgravity ow through chutes 3=leadingto the mainhaulagewaydi Waste ll is introduced atithe-surfacel at substantially the samerat-eas broken ore-is withdrawn,A so as to maintain A`the-storie Afull-atv all 'times of broken material.

The-left-lrandstope I is shown 'in Fig. 5 as it appearsafter' nearl-yf. all of-the-broken-ore therein has--been-Withdrawn throughthe orel chutes 35 communicating with=-themain haulageway; Waste1lhas= been introduced at substantially the lsame rate as broken oreV has been withdrawn, so that the stope has been maintained full of broken-- material. The fill isintroducedrdirectly ony top of` the# broken ore, as I havefound that no -timbervrnatting or-other` separating means at the interface GG of broken ore and il is necessary to prevent-dilution oftheore by the ll as the ore is v.vlthdrawn and as the interfacel $9 subsides within the stope. In fact; Withdrawal-lof theore results in quite even subsidence of the interface et' between the broken ore and iili, withvv little'or no intermingling-of these broken materials. After completion of the ore-drawing operations (when wast-eA appears in the ore chute), some broken ore 4i and some solidore 42 may. still remain in the stope (as shown for examplein stope 3i) These residual volumes fof ore are small, and maybe left in place or may be mined-by special methods.

An important feature of' the stoping operations illustrated inlii'g 5'is the maintenance of partitions 43.0 f ore in' placeb'etweerithe stopes 3f, 32, 33; etc, These partitions (which consti? tute only a small portion of the o're body) pref vent'lziroken ore in one stope from' intermingling by'cross flowwithwaste fill added to an adjacent stope, with consequent dilution of the broken ore. In theabsence of partitions, cross ilowwill occur both during the orefbreaking operations andsubsequently, if the mining operations in one stope are substantially. farther advanced than in, the vadjacent stope. In addition to resulti'ng in dilutionof the broken ore, such cross flow. would seriously hamper conduct of the miningvoperations. The partitions 43, besides preventing cross flow of ,fill 'and broken ore, serve as pillars .for helping support the ore. in place whileore-breaking operations are' in progress.

1 'If it is desired to recover all of the ore from the orebody and not leave any ore in place as part-itions, it is often possible to erect timber partitions in the course of the ore-breaking operations. When this is done, substantially all of the ore in the deposit may be broken and recovered,

but in such event the distance between broken ore and roof must be increased and drilling may take place in the stope (as in conventional shrinkage-stoping operations). It is also possible to add cementing material (such as Portland cement) to the fill material at the stope boundaries, to enable the fill to stand, and when this is done mining operations may be conducted in a subsequently worked adjacent stope so as to break and extract al1 of the ore up to the cemented fill. This procedure also avoids the need for leaving any partitions of ore in place.

To insure substantially complete extraction of the broken ore from the stope when mining in accordance with the method described herein, it is sometimes advantageous if the bottom of the stope inclines downwardly to a bottom apex at an angle best determined by experiment, but which approximates 70 to the horizontal. The ore chute should of course communicate with the stope through this bottom apex. This angle is indicated in Fig. 5 as that of the boundary between the residual volume of broken ore 4I and the added waste ll in stope 3l. So long as the interface between the broken ore and added fill is suflciently high above the bottom of the stope, it will subside substantially horizontally as the ore is withdrawn. Near the bottom of the stope, however, the broken material, if followed by ll, funnels to the ore chute at an angle of about 70, more or less. As the substantially horizontal interface between the broken ore and fill enters the region toward the bottom of the stope where this funneling occurs, it too willrbegin to assume a funnel shape with its apex pointing downwardly toward the ore chute. If the bottom of the stope is horizontal, or less than the above stated angle, some broken ore then will remain in place while waste fill funnels through it to the ore chute. By sloping the bottom of the stope at 70 or such other angle near 70 as is indicated by experiment, there will be no opportunity for this funnel of broken ore to form and in ccnsequence no broken ore will be left in the stope. With stopes having a properly7 sloped bottom, the appearance of waste ll in the ore chute is a sign that essentially all of the broken ore has been extracted. If the ore is of sufficient value, the

sloping bottom of the stope may be formed entirely in the barren rock underlying the ore deposit, and all of the ore may then be broken and extracted.

The new mining method herein described, by providingV for addition of waste fill at the top of the stope as broken ore is withdrawn from the bottom, greatly simplifies the mining operations. In contrast to the cut-and-ll method of mining, the new method avoids the need for much hand mucking or scraping of ore, and handling and evening of added ll. Yet it is generally applicable to mining in orebodies adapted to the cut-and-ll method. It is also applicable in some cases to orebodies heretofore mined by stopes heaviy timbered to support the surrounding ground. When adapted to such orebodies, the new method saves greaty on the amount of timber required and on the cost of installing the timber.

Once stoping operations reach the point where rlll is introduced, ore may be withdrawn steadily and at any desired rate from the stope'untl virtually all of the ore has been extracted. No heretofore known method that provides adequate support for the surrounding ground has achieved this advantage. In general, the economies effected in mining operations conducted in accordance with the invention are greater than can be achieved under comparable conditions by any other method which provides effective and permanent support for the surrounding ground.

It is of course 'evident that the advantages of some features of the invention may be had without making full use of all of the features of the complete new method. For example, it is possible to derive the benefits of adding ll at the top of the stope while withdrawing ore from the bottom regardless of what method of breaking the ore was employed. Hence if desired ordinary shrinkage stoping, caving, or other conventional orebreaking procedure may be followed. Similarly Y the benefits of the improved ore-breaking procedure herein described may be obtained without adding fill at the top of the stope after completing the ore-breaking operations, if there is no objection to leaving an open empty stope underground.

The significant features and advantages'of the new mining method herein described may be briefly summarized as follows:

The modified shrinkage method for breaking the ore that is advantageously (but not necessarily) employed in connection with the other features of the invention is principally characterized by withdrawing a minimum amount of ore through the chutes after each blasting operation. The amount withdrawn is considerably less than heretofore considered necessary and in many cases need not result in lowering the upper surface of the broken ore substantially out of contact with the overhanging unbroken ore. It is desirable to have the distance between broken ore and unbroken roof as little as possible. With this procedure the following benets accrue:

1. The men always work in a small relatively safe space, such as the raises shown in the drawings, and not under a large open span in a stope. In addition, a minimum number of openings is required to work an orebody by the new method, and the openings required are of minimum dimensions. This makes the new method particularly safe, and reduces to a minimum the amount of expense involved in Ventilating and cooling the mine workings.

2. The broken ore not only provides support for the walls of the deposit, but to some extent may also provide support for the roof of unbroken material.

3. The force of the explosive is not only expended in breaking ore down from the solid mass, but also serves to further fragment the broken material lying in the stope. In consequence, less secondary breaking of ore in the mine (as required, for example, to open plugged chutes) is necessary, and crushing of the ore taken from the mine is simplified. In addition, the ore broken down from the roof is better fragmented, because it is broken against the jagged upper surface of the previously broken ore.

The addition of waste ll at the top of the stope after all of the ore therein has been broken, at substantially the same ratefas broken ore is withdrawn at the bottom of the stope, is the characteristic feature of the invention for providing support for the surrounding ground after com- 121 pletion ofthev orebreakingk operations. procedure leads. to the following advantages:

1. Ample support. is providedl for the ground without the-need for excessive handling ofwaste lill-and without the` use oftimbers.

v2. In weak ground, the` support providedby the added iill prevents spalling of waste material from the walls ofthe deposit, and prevents caving ofv the ground,- which if it occurred woud result in diluting and lessening the value .of the broken ore.

3: In strong ground, the added fill prevents rock bursts that are apt to occur in large underground openings, especially at considerable depths. The new procedure for adding lill, especially when used in conjunction with the herein-described procedurefor breaking the ore, makes it unnecessary to form any large open spaces underground at any stage of-v the mining operations, and-so makes it feasible to conduct miningoperations atv muchgreaterrdepths than have heretofore been possible in ground-that is subject to rook-bursts.

4: The added ll, of course, is highly effective for-preventing surface subsidence during or after mining operations.

' The adaptation of the new miningmethod described in conjunction with Fig. 5. has the following particular advantages:

1. It makes it possibletominein a considerablenumber of closely spaced stopes and enables the mining operations in each stope to proceed independently offthosein adjacent stopes. Most of the load involved in supporting the surrounding ground is borne bythe' broken ore and added lll, soA that the partitions of ore in place may be. very thin. If desired, even thesev thin partitions may be extracted by erecting timber partitions-or cementing theadded fill along theboundaries of the stope.

2. If applied to underground mining, this method permits substantially complete' extraction of ore from large and extended. ore bodies without caving or surface subsidence.

This

3. When applied to surface outcropping deposits, as particularly illustrated in. Fig. 5, the new method may be used to supplant open-cut mining, or may be used in conjunction with opencut mining to remove the valuable ore along the side slopes of the open cut without having to rer move large amounts of waste ground or overburden to prevent caving. of side slopes into the open cut. This of course' results in increased recovery of ore with decreased mining of waste material from the side slopes.

Most adaptations of the new method to either underground or surface cropping deposits leadto the following general advantages:

1. A Working pattern for the orebody that is independent of the number of solidV block faces in juxtaposition may be developed.

2. Economic Working of orebodies which when cavedl produce fragments of a size difficult to handle underground is facilitated.

In general, the new method may be applied advantag'eouslyv to replace, or to be used in conjunction with, such heretofore known mining methods as shrinkage stoping, cut-and-ll stoping, top slicing, sublevel caving, block. caving, and open-cut mining.

I-claim:

l. The method ot mining ore from an underground deposit in ground requiringsupport which comprises breaking the ore in a stope'within the deposit. sufficiently to withdrawal from said stope bygravity flow, forming thexroofo the stope at an angle to the horizontal substantially as great as the angle of reposeof. available waste ll, introducing such waste fill into said stope. at the top thereof, and continuously supplyingsuch iill to the stope in substantially the sameamount and at substantially the same rate as broken ore subsides from the top and is Awithdrawn from the bottom of said stope, whereby the walls and roof of the stope are at all times supported by broken ore or added fill.

2. In the mining of ore from adeposit in which ore in a stope in the deposit is broken and the broken ore is withdrawn from the bottom of said stope with consequent subsidence of its upper surface, the improvement which comprises form.- ing the roof of the stope at an angle to the horizontal at least as great asA the angle of repose of available waste fill, and adding such. Waste fill directly to the subsiding upper surface of the broken ore and continuingV the addition ofsuch waste ll continuously in substantially the amount required to maintain said stope full to the roof with broken material at all times.

3. The method of miningore from a. deposit which comprises marking oif within thedeposit a stope of substantial height; and ofA less Width thanthe width of the deposit, breaking the ore within said stope and withdrawingV it from the bottom thereof, forming the roof of the stope at an angle to the horizontal at. least asv great as the angle of repose of available ll material, adding such waste fill at the top of the stope at substantially the same rate as the upper surface of the broken ore subsides therefrom and in amount sudlicient to keep the stope fullv to the roof at all times with addedA ll, similarly working a horizontally adjacent stopewithin the deposit, and maintaining between the. stopes a partition capable of preventing admixture by cross flow of ll added to one stope with ore broken in the adjacent stope.

4. The method of mining ore from an under.- ground deposit which comprises breaking ore. in a stope within the deposit, withdrawing. the broken ore from adjacent the bottom of the stope, forming the roof of the stope at an angle to the horizontal substantially as great as the angle of repose of available ll material, and introducing such Waste ll into the top of said stope through the apex of the angular roof thereof at a rate substantially equal to the rate at which broken ore is withdrawn from said stope and as its upper surface subsides therein, the added fillbeing at all time's maintained in substantial contact with the roof of the stope so as to provide support therefor as well as forA the stope side walls.

5. The method of withdrawing broken ore from an underground stope and` providing support for the surrounding ground which comprises withdrawing the broken ore from the bottom ofthe stope and adding waste ll at thel to'p thereof directly to the upper surface of the broken ore, said Waste fill being added as the upper. surface of the broken ore subsides and, in amount sufficient to keep the stope substantially. full ofbroken material at all times, the added fill being at all times. maintained in contact with the. roof. of the stope so asv to provide support therefor as well as for the stope side walls. y

` 6. rThe method of mining ore from a deposit in ground requiring supprt which comprises forming a manway. extendingA upwardly through the height of a stope within the deposit and, an ore chute communicating, with the deposit adjacent the bottom of said stope, drilling from the manway into the deposit above the chute, breaking the ore by blasting from the drill holes, withdrawing the broken ore through the chute only in controlled limited amount such that voids are created in the mass of broken ore without lowering its upper surface substantially out of contact with the overhanging unbroken ore, and continuing breaking of the ore in said manner to the top of the stope, the stope below the unbroken ore being maintained substantially full of broken ore at all times during ore-breaking operations.

7. In a method of mining ore from a stope containing broken ore in the lower portion thereof and unbroken ore above, involving blasting ore from the lower portion of the unbroken ore mass downwardly against said upper surface of the broken ore, the improvement which comprises performing the blasting operation while the upper surface of the broken ore is in contact with the overhanging unbroken ore, whereby the force of the blast further fragments the already broken ore as well as breaking a further quantity of ore.

8. The method of mining ore from a stope containing broken ore in the lower portion thereof and unbroken ore above,lwhich comprises plas*- ing ore from the lower portion of the unbroken ore mass downwardly against the upper surface of the broken ore, maintaining the upper surface of the broken ore at all times substantially in contact with the lower surface of the overhanging mass of unbroken ore so that no extended open space is permitted to form-between the unbroken ore and the underlying broken ore, whereby the blasting operation contributes to further fragmentation of the already broken ore, then withdrawing suicient broken ore from the lower portion of the stope to create fresh voids in the column of broken ore without creating any extended open space between its upper surface and the lower surface of the still unbroken ore, and repeating the sequence of operations.

9. The method of mining ore from a stope which comprises forming a manway extending upwardly through the stope, drilling substantially laterally from the manway into the lower portion of the mass of unbroken ore in the stope, blasting the ore downwardly from the drill holes, and withdrawing broken ore from the lower portion of the stope in controlled limited amounts sufficient only to create voids in the mass of broken ore without lowering its upper surface substantially out of contact with the lower surface of the still unbroken ore.

10. The method of mining ore from a stope which comprises forming a manway extending upwardly through the stope, maintaining the stope substantially full at all times of broken and unbroken ore with the upper surface of the column of broken ore in contact with the lower surface of the unbroken ore, and conducting all ore-breaking operations from working positions within the manway.

11. The method of mining ore from a deposit in ground requiring support which comprises forming a substantially vertical column of broken ore of considerable height within the deposit, forming a number of vertically spaced ore chutes communicating with and intermediate the ends of the deposit, withdrawing ore from said column through a rst of said chutes at a point well above the bottom of that part of the deposit to be worked, adding waste ll at the top of said column at substantially the same rate as broken ore is withdrawn so as to maintain at all times a full column of broken material, discontinuing withdrawal of broken ore through said first chute before the interface of broken ore and ll has subsided to the level where the angle from the chute to the laterally most remote part of said interface is less than about to the horizontal, breaking the ore of any barrier between said rst chute and the next lower chute, and continuing withdrawal of the ore from said column through said next lower chute.

12. The method of mining ore from a deposit in ground requiring support which ccmprises breaking the ore throughout the height of an upper stope within the depcsit, forming an ore chute communicating with the bottom of the upper stope, withdrawing broken ore from said upper stope through said chute and adding waste fill at the top of said stope as the upper surface of broken ore subsides therein so that the stope is kept substantially full of broken material at all times, breaking the ore throughout the height of a second stope immediately below and communieating directly with said upper stope, discontinuing withdrawal of ore through the chute at the bottom of said upper'stope before the interface of broken ore and ll has subsided to the level where the angle from said chute to the laterally most remote part of said interface is less than about 70 to the horizontal, forming a second chute at the bottom of said second stope and making further withdrawals of broken ore through said chute at the bottom of said second stope.

13. In extracting ore from a deposit in which a column of ore has been broken and is being withdrawn by gravity flow through a chute, and where waste ll is added at the top of said column as the upper surface of the broken ore subsides, the improvement which comprises discontinuing withdrawal of the broken ore through' the chute before the interface between the broken ore and ll has subsided to the level where the angle from said chute to the laterally most remote part of said interface is less than about 70 to the horizontal, forming a second chute in communication with said column of ore and located at a point such that the angle between said second chute and the part of the interface laterally most remote from said second chute is appreciably greater than about 70, and making any further withdrawals of ore by gravity flow through said second chute.

PHILIP B. BUCKY.

REFERENCES CITED The following references are of record in the le of this patent:

Mining Engineers Handbook (3rd Ed. 1941), by Robert Peele, published by John Wiley & Sons, Inc., section 10-I pages 287, 290, 291, 292, 359 and 360.

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