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露天开采(Surface-Mining).ppt

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1、Surface Mining Chapter 2 Planning and Design of Surface Mining,2.1 Definition of Mining Parameters(采矿参数),2.2 Ultimate Pit Definition (最终境界),2.3 Open pit Optimization ( 露天坑优化),2.4 Optimum production scheduling(最优开采计划),2.5 Materials handling Ex-Mine,2.6 Waste disposal,2.1 Definition of mining paramete

2、rs 2.1.1 Introduction Many factors govern the size and shape of an open pit. These must be properly understood and used in the planning of any open pit operation. The following are the key items affecting the pit design: geology地质, grade品位, localization of the mineralization矿床地点, extent of the depos

3、it矿床大小, topography地貌, property boundaries开采界限, production rates, bench height台阶高度,(9) pit slopes边坡角, (10) road grades线路坡度, (11) mining costs, (12) processing costs选矿,(13) metal recovery金属回收率, (14) marketing considerations, (15) strip ratios 剥采比, (16) cutoff grade 回采品位.2.1.2 Bench heightThe bench hei

4、ght is the vertical distance between each horizontal level of the pit. The elements of a bench are illustrated in Fig. 1. Unless geological conditions dictate otherwise, all benches should have the same height.,The height will depend on : the physical characteristics of the deposit, the degree of se

5、lectivity required in separating the ore the size and type of equipment to meet the production requirements climatic conditions.The bench height should be set as high as possible within the limits of the size and type of equipment selected for the desired production. The bench should not be so high

6、that it will present safety problems of towering banks of blasted or un-blasted material. The bench height in open pit mines will normally range from 15m in large copper mines to as little as 1 m in uranium mines.,2.1.3 Pit slopes(边坡角)The slope of the pit wall边坡 is one of the major elements affectin

7、g the size and shape of the pit. The pit slope helps determine the amount of waste that must be moved to mine ore. The pit wall needs to remain stable as long as mining activity is in that area. The stability of the pit walls should be analyzed as carefully as possible.,Rock strength, faults断层, join

8、ts节理, presence of water,and other geologic information are key factors in theevaluation of the proper slope angle边坡角.The physical characteristics of the deposit cause the pitslope to change with rock type, sector location, elevation,or orientation走向 within the pit. Fig. 2 illustrates how the pit slo

9、pes may vary in thedeposit.A proper slope evaluation will give the slope that allowsthe pit walls to remain stable.,The pit slope analysis determines the angle to be used between the roads in the pit.,The pit walls should be set as steep as possible to minimize the strip ratio剥采比.,The overall pit sl

10、ope平均边坡角 used for design must be flatter to allow for the road system in the ultimate pit最终境界.,Fig 3 and Fig 4 show the need to design the pit with alesser slope to allow for roads.,Fig. 3 has been designed with a 450 angle for the pit walls.The pit in Fig. 4 uses the same pit bottom坑底 and the 450 i

11、nter-ramp slope 路间边坡between the roads, but, a road has been added. So the overall pit slope is lesser the the inter-ramp slope.In the example, almost 50% more tonnage must be moved to mine the same pit bottom.In the early design of a pit a lesser pit slope can be used to allow for the road system.,T

12、he pit in Fig. 5 was designed with an overall slope of 380.The overall slope to use will depend on the width, grade坡度, and anticipated placement位置 of the road. Fig. 6 shows a vertical section of a pit wall from Fig.4. The inter-ramp angle is projected from the pit bottomupward to the original ground

13、 surface at point B. The overall pit slope angle 平均边坡角is the angle fromthe toe of the bottom bench to the crest of the top bench(台阶上缘,台阶坡顶线).Point A shows the intercept交点 of the overall pit slopeangle with the original ground surface地表.,2.1.4 Cutoff grade(开采边界品位)Cutoff grade is any grade that for an

14、y specific reason is usedto separate any two courses of action. The reason used in setting a cutoff grade usually incorporates the economic characteristics of the project.When mining, the operator must make a decision as towhether the next block of material should be mined andprocessed选矿, mined and

15、stockpiled堆存, mined 开挖(toexpose ore) and sent to the waste dump废石场, or not mined at all. The grade of the block is used to make this decision.,For any block to be deliberately mined, it must pay for the costs of mining, processing, and marketing. The grade of material that can pay for this(the costi

16、ng, processing and marketing) but for no stripping(剥离) is the breakeven(损 益平衡点) mining cutoff grade(经济合理开采品位) .A second cutoff grade次级边界品位 can be used for blocks that are below the mining cutoff grade and would not be mined for their own value. These blocks may be mined as waste by deeper ore blocks

17、.The cost of mining these blocks is paid for by the deeper ore.,The final destination of these blocks is then only influencedby costs for the blocks once they have been mined. The blocks can be processed at this point if they can pay forjust the processing and marketing costs.In mining phase the cut

18、off grade calculation would includethe drilling凿岩, blasting爆破, loading铲装, and hauling运输 costs.,The processing costs would cover crushing破碎, conveying,运输 grinding磨矿, and concentrating选矿costs.The marketing costs could include concentrate handling精矿处理, smelting冶炼, refining精炼 and transportation运输. Addit

19、ional direct costs for royalties矿山资源费 and taxeswould also be included. Overhead costs ( 企业一般管理成本) should also be addedto the calculation. Depreciation(通货膨胀) is used in the calculation forthe purpose of setting the pit size.,Table 1 is the calculation of the mining cutoff grade for acopper project wi

20、th the following parameters: 30 kt/d (33000 st pd) of ore mined for 20years$300,000,000 capital cost (include replacement capital) $1.00 mining cost per ton of ore$0.95 mining cost per ton of waste$3.00 processing cost per ton of ore$1.00 general and administrative (G&A) cost per ton of ore$0.75 fre

21、ight, smelter, and refining (FSR) cost per kilogramof copper85% overall copper recovery,The results are shown graphically in Fig. 8. Note that the cutoff grade will increase as the costs increase.The difference between the mining cutoff grade and the milling cutoff grade is shown in Fig.9.,2.1.5 Str

22、ip Ratio The strip ratio is the ratio of the number of tons of waste that must moved for one ton of ore to be mined. The results of a pit design will determine the tons of waste and ore that the pit contains. The ratio of waste and ore for the design will give the average strip ratio for that pit. T

23、he average strip ratio differs from the breakeven strip ratio 经济合理剥采比或盈亏平衡剥采比 used to design the pit.,The breakeven(不赚不赔的) strip ratio(盈亏平衡剥采比)refers only to the last increment mined along the pit wall.The strip ratio is calculated for the point at which breakevenoccurs and the necessary stripping i

24、s paid for by the netvalue of the ore removed.The calculation for the breakeven strip ratio (BESR) is B BESR = (A-B)/CWhereA revenue per ton of oreB production cost per ton of ore ( includingall costs to the point of sale, excluding stripping) C Stripping cost per ton of waste,In certain studies a m

25、inimum profit requirement is includedin the formula.BESR = A- (B+D)/CWhere D = minimum profit per ton of ore.Table 2 contains the information for calculation the strip ratio for the example used in calculating the cutoff grade previously. The results are shown graphically in Fig. 10.,Return,Return,R

26、eturn,Return,Return,Return,Return,A surface intercept of pit wall if roads are included. B surface intercept of pit wall if roads are not included,Average pit slope angle,Slope angle between roads,Original ground surface,Return,Return,Return,Return,Return,Strip ratio (waste: ore),2.2 Ultimate Pit De

27、finition (最终境界) 2.2.1 Introduction As the first step for long or short-range planning, the limits of the open pit must be set. The limits(ultimate pit) define the amount of ore minable, the metal content金属量, and the associated amount of waste to be moved during the life of the operation.The size, ge

28、ometry, and location of the ultimate pit are import in planning tailings areas尾矿库, waste dumps废石 场, access roads开拓坑道, concentrating plants选场, and all other surface facilities.,Knowledge gained from designing the ultimate pit also aids in guiding future exploration work.The material contained in the

29、pit will meet two objectives. A block will not be mined unless it can pay all costs for its mining, processing, and marketing and for stripping剥离 the waste above the block.For conservation保护of resources, any block meeting the first objective will be included in the pit.( 满足条件的矿石应包括在开采范围内)The result

30、of these objectives is the design that will maximize the total profit of the pit based on the physicaland economic parameters used. As these parameters change in the future, the pit design may also change.,2.2.2 Manual DesignThe usual method of manual design starts with the three types of vertical s

31、ections shown in Fig.1,1.Cross sections spaced at regular intervals parallel to each other and normal to(垂直)the long axis of the ore body. These will provide most of the pit definition and may number from 10 to perhaps 30, depending on the size and shape of the deposit and on the information availab

32、le.2.Longitudinal section along the long axis of the ore body to help define the pit limit at the ends 两端of the ore body.3.Radical sections help define the pit limits at the end of the of the ore body.,Each section should show ore grades, surface topography, geology (if needed to set the pit limits用

33、于确定露天境界), and structural controls (if needed to set the pit limits), and any other information that will limit the pit (e.g. ownership boundaries).The stripping ratio is used to set the pit limits on each section. (refer to the 采矿学P323327)The pit limits are placed on each section independently using

34、 the proper pit slope angle.,The pit limits are placed on the section at a point where the grade of ore can pay for mining the waste above it. When the line for the pit limit has been drawn on the section, the grade of the ore along the line is calculated and the lengths of the ore and waste are mea

35、sured.The ratio of the waste and ore is calculated and compared to the breakeven stripping ratio经济合理剥采比 for the grade of ore along the pit limit.If the calculated stripping ratio is less than the allowable stripping ratio, the pit limit is expanded. If the calculated stripping ratio is greater, the

36、pit limit is contracted.,This process continues on the section until the pit limit is set at a point where the calculated stripping ratio and breakeven stripping ratio are equal. In Fig. 2, the grade on the right side of the pit was estimated to be 0.6% Cu. At a price of $2.25 per kg of copper, the

37、breakeven stripping ratio from Fig. 3 is 1.3: 1. The line for the pit limit was found using the required pit slope and located at the point that gave a waste: ore ratio of 1.3:1. At the limit,On the left side of the section, the pit limit for the 0.7% Cu grade was similarly determined using a breake

38、ven stripping ratio of 2.7:1. Fig. 2, Fig. 3 If the grade of ore changed as the pit limit line was moved, the breakeven stripping ratio to use would also change. The pit limits are established on the longitudinal section in the same manner with the same stripping ratio curves.,The pit limits for the

39、 radial section are handled with a different stripping ratio curve, however. As shown in Fig. 4, the cross sections and the longitudinal section represent a slice along the pit wall with the base length as the surface intercept. The radial section represents a narrow portion of the pit at the base a

40、nd much wider portion at the surface intercept.,The next step in the manual design is to transfer the pitlimits from each section to a single plan map of the deposit.The elevation标高 and location of the pit bottom坑底 and the surface intercepts交点 from each section are transferred. The resultant plan ma

41、p will show a very irregular pattern of the elevation and outline of the pit bottom and of the surface intercepts. The bottom must be manually smoothed to conform to the section information.,Starting with the smoothed pit bottom, the engineer will develop the outline 轮廓for each bench at the point mi

42、dway between the bench toe台阶坡底线 and the crest坡顶线. The engineer manually expands the pit from the bottom with the following criteria: The breakeven stripping ratios for adjacent sections mayneed to be averaged. 两个相邻断面的经济合理剥采比平均化 The allowable pit slopes must be obeyed遵守. If the road system is designe

43、d at the same time, the inter-ramp angle路间坡角 used. If the preliminary design does not show the roads, theoutline for the bench midpoints 台阶中点will be based onthe flatter overall pit slope that allows for roads.,Possible unstable patterns in the pit should be avoided. Simple geometric patterns on each

44、 bench make the designing easier. When the pit plan has been developed, the results should be reviewed to determine if the breakeven stripping ratios have been satisfied.,2.2.3 Computer MethodsAs should be appreciated, the manual design of a pit gets the planning engineer closely involved with the d

45、esign and increases the engineers knowledge of the deposit. The procedure is cumbersome, though, and is difficult to use on large or complex deposits.,Drawback of manual design is that if any of the design parameters change, the entire process may have to be repeated. Another drawback to the method

46、of manual design is that the pit may be well designed on each section, but, when the sections are joined and the pit is smoothed, the result may not yield the best overall pit.,2.2.4 Lerchs-Grossman methodThe two-dimensional Lerchs-Grossman method will design on a vertical section the pit outline gi

47、ving the maximum net profit. The method is appealing because it eliminates the trial-and-error process of manually designing the pit on each section. The method is also convenient for computer processing.The results must still be transferred to a pit plan map露天坑计划图 and manually smoothed and checked.

48、 The example in Fig. 5 represents a vertical section through a block model of the deposit.,There are three steps in Lerchs-Grossman method.Step 1: Add the values down each column of blocks and enter these numbers into the corresponding blocks in Fig. 7. Step 2: Start with the top block in the left c

49、olumn and work down each column. Step 3. Scan the top row for the maximum total value. For example the optimal pit would have a value of $13. This is the total net return of the optimal pit. The Fig. 7 shows the pit outlined on the section.,2.2.5 Floating cone methodIf the grade of the base is above

50、 the mining cutoff grade, the expansion is projected upward to the top level of the model as in Fig. 8. The resulting cone is formed using the appropriate pit slope angles. If the total revenues are greater than the total costs for the blocks in the cone, the cone has a positive net value and is economic to mine.A second block is then examined, as shown in Fig. 9. Each block in the deposit is examined in turn as a base block of a cone.,

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