t>^.^. ' !* > -I ' * ^ •' ' ,>''"" '. . '■ .■».;■- J ' ' . ' l' ^^:'>- N . ' ^'"' °- <^<-^^%\ c°\:^^^'^°o /\^i/% '»i.t* -^^6* 3> • ,«> ^f*-, •*.* ^v* "^ ""H/Jfl^Ny* aV ^-> ^"'V. V V, 4 5^ k-A ,>°..:^^-X ./.-aii-X ./.•i.;^.>o >'\.t^. V /,-iij..\ ■^^-0^ "•v<^ V ^^••\/ '^o.;'*^-\^o'> ^''^ -'^••~"- '"^ ^''^:*^CV'" V^-ri'. >« r -^o^ ,.-.-, Ok*"-*. ♦ aV -S*^ . -^fv t'?^ » 4 O **'■ oil"' '^.i. * ^c • ^V \ .0 b V °., *.T .^ ., ♦ O J* » o V C" V iP-n*., *'•••*% /^.r^^^-^o, .-^*\'^>''*^ .^^ o. . '^^ A* »*^fe'. ^ <» •'TV.* ,0 '^^c, 'o . » ' <. ♦'T:: • , ^j>. -ov^ ^o-n.. V rA^ J^ * o • ' • ♦ '^ ^ov" ^-.. ^•^-0^ *-■••■ ^* J-^' . >0 -•-'e. <. *'Trv* .0 '-*>.- _< <»•_ ."i .^■^ / '*. UH nO a,^Z\ This publication has been cataloged as follows: Hrabik, Joseph A Economic evaluation of borehole and conventional mining systems in phosphate deposits. (Bureau of Mines information circular ; 8929) Bibliography: p. 16, Supt. of Docs, no.: 1 28.27:8929. 1. Phosphate mines and mining. 2. Borehole mining. I. Godesky, Douglas J. II. Title. III. Series: Information circular (United States. Bureau of Mines) : 892Q. TN295A]4 ITN913] 622s [622'. 3641 83-600001 m '-i^.^ CONTENTS Page Abstract 1 '^ Introduction 2 , Acknowledgments 2 r~ Resource availability 3 I Deposit assumptions........... 3 Borehole mining system 3 nO Geologic considerations 6 ^ Conventional mining systems 6 ^ Benef iciation system 8 ~^^ Environmental considerations 8 ^ Economic evaluation 9 (J Borehole mining capital cos t 11 Borehole mining operating cost... 11 Conventional mining capital cost 12 Conventional mining operating cost 13 Benef iciation system capital cost 14 Benef iciation system operating cost 14 Conclusions 14 Suggestions for further investigation 15 References 16 Appendix A. — Mining and benef iciation parameters 17 Appendix B. — Borehole mining system capital and operating costs 18 Appendix C. — Conventional mining system capital and operating costs 20 Appendix D. — Benef iciation system capital and operating costs 24 Appendix E. — Cash flow analysis 25 ILLUSTRATIONS 1. Prototype borehole mining system 4 2. Conventional mining systems 7 3. Economic comparison — borehole mining versus conventional mining at 1.6 million short tons of product per year 10 4. Economic comparison — borehole mining versus conventional mining at 3.3 million short tons of product per year 11 5. Economic comparison — borehole raining versus conventional mining at 5.0 million short tons of product per year 11 TABLES 1. Borehole mining system economic evaluation results 9 2. Conventional mining system economic evaluation results 10 rv] B-1. Estimated capital requirements, borehole raining system 18 tx} B-2. Estiraated annual operating costs, borehole raining system 19 ^ C-1. Estiraated capital requirements, conventional raining systems 20 ^ C-2. Estimated annual operating costs, conventional mining system, at 1.6 _ million short tons of product per year 21 C-3. Estimated annual operating costs, conventional mining system, at 3.3 million short tons of product per year 22 .,„ C-4. Estimated annual operating costs, conventional mining system, at 5.0' dl million short tons of product per year 23 D-1. Estimated capital requirements, benef iciation system 24 D-2. Estimated annual operating costs, benef iciation system 24 ii TABLES — CONTINUED Page E-1. Cash flow analysis at 50-ft overburden and 1.6 million short tons of product per year 25 E-2. Cash flow analysis at 100-ft overburden and 1.6 million short tons of product per year 26 E-3. Cash flow analysis at 150-ft overburden and 1.6 million short tons of product per year 27 E-4. Cash flow analysis at 50-ft overburden and 3.3 million short tons of product per year 28 E-5. Cash flow analysis at 100-ft overburden and 3.3 million short tons of product per year 29 E-6. Cash flow analysis at 150-ft overburden and 3.3 million short tons of product per year 30 E-7. Cash flow analysis at 50-ft overburden and 5.0 million short tons of product per year 31 E-8. Cash flow analysis at 100-ft overburden and 5.0 million short tons of product per year 32 E-9. Cash flow analysis at 150-ft overburden and 5.0 million short tons of product per year 33 E-10. Cash flow analysis, borehole mining, at 230-ft overburden and 1.6 mil- lion short tons of product per year. 34 E-11. Cash flow analysis, borehole mining, at 230-ft overburden and 3.3 mil- lion short tons of product per year 34 E-12. Cash flow analysis, borehole mining, at 230-ft overburden and 5.0 mil- lion short tons of product per year. 34 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT bhp brake horsepower psi pound per square inch ft foot rpm revolution per minute gpm gallon per minute scfm standard cubic foot per minute hp horsepower tph ton per hour h hour V ac volt, alternating in inch current kW-h kilowatt hour yd yard lb pound yd 3 cubic yard lb/ft3 pound per cubic foot yr year pet percent ECONOMIC EVALUATION OF BOREHOLE AND CONVENTIONAL MINING SYSTEMS IN PHOSPHATE DEPOSITS By Joseph At Hrabik and Douglas J, Godesky ABSTRACT The Bureau of Mines compared the feasibility of mining deep phosphate deposits by a borehole mining system with mining by proven conventional techniques. An economic comparison of the borehole mining system with conventional dragline and bucket wheel excavator mining systems was com- pleted at various mining depths and production rates. Hypothetical phosphate deposits, with various overburden thicknesses and reserve ton- nages, were defined. Geologic conditions necessary for the application of the borehole system were identified. Discounted cash flow analyses based on derived capital and operating costs were used to generate rates of return and product prices. Borehole mining was found to be more economical where overburden thickness was 150 ft or greater; however, at 50- and 100-ft thicknesses, conventional surface mining was more economical. Overburden thickness has a great effect on the economic feasiblity of the conventional mining systems but less effect on the economics of borehole mining. Economies of scale are only realized in conventional mining, since larger equip- ment is employed to achieve greater production, whereas increased pro- duction from borehole mining is achieved using additional equipment units. A comparison of the environmental effects of borehole and conventional surface mining systems showed that borehole mining is environmentally more desirable. ^Mining engineer, Eastern Field Operations Center, Bureau of Mines, Pittsburgh, PA. ^Physical scientist. Eastern Field Operations Center, Bureau of Mines, Pittsburgh, PA. INTRODUCTION The phosphate mining industry of the United States is centralized in Florida where shallow sedimentary deposits have lent themselves to open pit mining. To- tal mining depths of less than 60 ft have made dragline mining the standard method of removing overburden and extracting phosphate ore (matrix) . In areas where thicker unconsolidated overburden is en- countered, dredges and bucket wheel ex- cavators can be employed to assist in the removal of overburden. As shallow phosphate reserves are de- pleted, deeper deposits are being consid- ered for development. Recovery of these deeper deposits by conventional surface mining methods would require the removal of thick overburden that could result in higher costs as well as increased envi- ronmental disturbance. Some of the deep deposits, such as those in northeastern Florida, are immediately overlain by beds of semiconsolidated to consolidated rock. Under these circumstances, borehole min- ing may be a technologically and econom- ically viable alternative to conventional mining. This Bureau of Mines study evaluates the economics of borehole and conven- tional mining systems as applied to the recovery of hypothetical phosphate de- posits. The extent of these deposits is assumed to be sufficient to justify capi- tal expenditures at various production rates. Borehole mining is a proposed method of recovering ore without overburden remov- al. The development of the borehole min- ing system for recovering a variety of minerals began early in the 20th century and continues to the present day. The most recent work was carried out by the Bureau of Mines under contract J0205038 (4_).3 The applicability of the borehole mining system for recovering phosphate matrix was tested using the Bureau's experimental borehole mining equipment at Agrico Chemical Co.'s property in St, Johns County, Florida. A prototype bore- hole mining system with updated specifi- cations was designed as part of the con- tract, and is the basis for the borehole mining parameters and costs used in this study. The prototype system has not yet been built or tested. A beneficiation process is proposed to concentrate primary phosphate matrix sim- ilar to that found in northeastern Flor- ida. This high-grade phosphate matrix contains little pebble material and has a clay content averaging about 25 pet. Washing and double-stage flotation is proposed to produce a marketable phos- phate rock product. The beneficiation process is assumed to utilize advanced clay dewatering methods to reduce dis- posal area volume requirements. Results of the economic evaluation, at various mining depths and produc- tion rates , are graphically illustrated. These graphs can aid in the selection of a mining method whenever actual geo- logic conditions are similar to the hypo- thetical deposit situations depicted in this study. The graphs may also be help- ful in assessing the sensitivity of mine economics to depth and production rate variations. ACKNOWLEDGMENTS Thanks are extended to Dr. G. S. Knoke, research scientist. Flow Industries, Inc., Kent, WA, and Dr. G. A. Savanick, physicist. Bureau of Mines, Minneapolis, MN, for providing technical details and costing parameters of the prototype bore- hole mining system. Grateful acknowledg- ment is made to Mr. M. F. Dibble, mana- ger, new projects, Agrico Chemical Co., Tulsa, OK, and Mr. C. K. Brown, senior staff geologist, Agrico Chemical Co., Mulberry, FL, for their cooperation and technical assistance. Consultation with Mr. J. M. Williams, vice president and Underlined numbers in parentheses re- fer to items in the list of references preceding the appendixes. general manager, Zellars-Williams , Inc., Lakeland, FL, greatly contributed to the analysis of conventional alternatives. surface mining RESOURCE AVAILABILITY Phosphate deposits suitable for recov- ery by the borehole mining system are lo- cated at structurally and cyclically fa- vorable depositional sites along the southeastern coastal plain of the United States. The borehole mining system, if commercially applicable, could result in the recovery of billions of tons of phos- phate resources. DEPOSIT ASSUMPTIONS For the purposes of this evaluation, criteria for a set of hypothetical depos- its were established. Borehole and con- ventional dragline and bucket wheel min- ing systems were applied to the same criteria. All deposits described are hypotheti- cal and are not intended to accurately represent actual geologic, mining, or economic situations. The hypothetical deposits were constructed to serve the purposes of this study. The phosphate matrix was assumed to be 20 ft thick and lying beneath either 50, 100, 150, or 230 ft of overburden. The 50 ft of overburden immediately above the phosphate matrix was assumed to contain consolidated carbonate beds and semicon- solidated materials. The upper portion of the overburden contained unconsoli- dated sand, shell fragments, and clay. The reserves were sufficient to support 20-yr mine lives at production rates of 1.6, 3.3, or 5.0 million short tons of product per year. 4 The deposits were assumed to be later- ally extensive and consistent in quality, bed thickness, and depth. Such deposits are known to exist in parts of northeast- ern Florida at depths of 200 to 300 ft. Basic deposit assumptions are summarized in appendix A along with mine and mill operating parameters. BOREHOLE MINING SYSTEM Borehole mining is a method of recover- ing phosphate matrix without the removal of overburden. With the proposed bore- hole mining system, a borehole mining tool is lowered to the phosphate horizon through a predrilled, steel-cased bore- hole. A rotating water jet on the tool disintegrates the phosphate matrix while a jet pump at the lower end of the tool pumps the resulting slurry to the sur- face. The slurry is then transported to a beneficiation plant by pipeline. The resulting cavity is backfilled with waste material pumped back from the plant. Figure 1 illustrates a prototype borehole mining unit. Mining unit specifications and operating parameters are summarized in appendix A. The borehole mining tool is composed of mining, standard, and Kelly sections. The mining section, which houses the cut- ting jet and jet pump, operates within the phosphate horizon. Standard sections contain the pipes that deliver water and air down to the mining section and carry slurry up to the surface. A Kelly sec- tion with a three-passage swivel directs the water, air, and slurry flow through the top standard section. All sections are approximately 20 ft long and 8 in. in diameter. The overall length of the tool can be adjusted by the addition or remov- al of standard sections, which are in- stalled between the Kelly and mining sections. ^Production values are rounded for text reporting purposes. Precise production values used in cost calculations are 1,666,590, 3,333,180, and 5,000,135 short tons of product per year. Tool sections Tool section storage racit Air compressor Turntable Vertical slurry pump Slurry to process p lant Slurry tank Electrical power box Water supply Hydraulic wincti Derrick Hydraulic power package Kelly section Motor starter box Vertical turbine water pump Cutting jet Borehole cavity FIGURE 1. - Prototype borehole mining system. (Coiirtesy Flow Industries, Inc.) Operations for borehole mining in- clude site preparation, borehole drill- ing, equipment set up, mining, back- filling, and reclamation. Each deposit will require site-specific mining proce- dures to maximize matrix recovery. During site preparation, bulldozers clear vegetation, level the mining areas, and establish access roads. The borehole drilling locations and sequence of mining the borehole cavities are then marked by a survey crew. Drill rigs, casing trucks, and a fork- lift truck are used to drill and case the production boreholes. Holes are drilled to the bottom of the matrix and cased from the top of the ore horizon to the surface. The prototype borehole mining tool described in this study requires a 12-in-diameter cased borehole. A tight fit between the casing and competent strata above the matrix would be estab- lished through the use of mechanical or cement seals or expandable packing de- vices. This would prevent water from be- ing forced into the annulus between the casing and the drill-hole wall and erod- ing the cavity roof. Borehole drilling is conducted on a staggered grid pattern. Mining on a staggered grid pattern permits greater matrix recovery than mining on a square pattern while maintaining the same mini- mum spacing between boreholes. A 70-ft spacing between boreholes would effect a final barrier of 10 ft between mined-out cavities. Barriers must be maintained so that phosphate slurry is not washed into previously mined cavities. Mining recovery is estimated to be 66.6 pet. Future testing may demonstrate that min- ing recovery may be increased by modify- ing the shape of cavities or reducing the cavity spacing. The borehole mining unit, consisting of the mining tool, derrick, pumps, and re- mote controls, mounted on a crawler base, is positioned over a cased borehole. The mining tool components are bolted togeth- er and lowered to the phosphate horizon. A hydraulic winch attached to the top of the derrick lowers and raises the mining tool. Pumps and compressors on the mining unit deliver water and air through the Kelly and standard sections to the cut- ting jet and the jet pump. A single cut- ting jet operates at 1,200 psi to disin- tegrate the phosphate matrix and form a slurry. Air is directed out of the cut- ting jet nozzle creating a shield that improves the jet's penetration through the flooded cavity and increases cutting distance. The cutting jet slides verti- cally within the mining tool to reach ma- trix from the base to the roof of the phosphate horizon. A turntable on the surface rotates the tool 360° during min- ing. Slurry flows to the jet pump in- takes at the lower end of the mining sec- tion and is pumped to the surface. At the surface, the slurry is transported to the benef iciation plant by pipeline. Matrix surrounding the cavity may slough in toward the mining tool as slur- ry is removed. Material would lie at an undetermined angle of repose from the bottom of the cavity near the jet pump to the outer perimeter of the cavity. The final cavity would be bowl-shaped with an average radius of 30 ft. Application of the borehole mining tool would not be limited by depth. The high- er ground water pressure associated with a deeper deposit would assist in the pumping of slurry to the surface. Minor adjustments of pumping power would be re- quired to overcome the additional fric- tion between the slurry and the standard section pipeline when mining depth is Increased. Most of the water used in mining, slurry transportation, and benef iciation would be recycled. A small portion of the water used would be lost owing to evaporation. The borehole cavities would receive ground water inflow to partially balance water loss in the other parts of the system. Only small quantities of deep-well, makeup water would be needed. After approximately 50 h of mining, the solids content of the slurry drops, indicating that the borehole cavity is mined out. The borehole tool is then withdrawn from the hole. Sections are separated and stored on a vertical rack. The mining unit is then moved to the next borehole location and the tool is again lowered to the phosphate bed. Total time required to withdraw the tool, move, and lower the tool down the next borehole varies from 3 to 5 h depending upon hole depth. One person operates each mining unit with extra personnel available to with- draw the tool and help move it between boreholes. A maintenance crew performs all maintenance and repair work and keeps a stock of spare parts and supplies on hand. Supervisors manage the mining, plan the moves, monitor progress, and keep the operation fully staffed and in production. One supervisor would be required to manage six direct labor employees . Clay and sand tailings would be gen- erated during the benef iciation process. Dewatered clay and sand tailings are com- bined and pumped from the benef iciation plant to the mining area where a backfill rig refills the borehole cavities O ) . Backfilling reduces or eliminates the possibility of surface subsidence and provides a means of disposing of both the clay and sands. The higher density clay-sand mixture, when introduced below clear water, does not mix with overlying water. The dis- posal of the wastes into the borehole cavity displaces relatively clear ground water, which would subsequently be recov- ered from the top of the borehole and re- circulated for plant use. In the final stages of backfilling, the steel casing is pulled from the hole and reused. The Florida Department of Envi- ronmental Regulations currently requires concrete sealing of the borehole with the steel casing in place. The department has waived this requirement for future borehole mining experiments. Reclamation following borehole mining would be minimal when compared with that required for surface mining opera- tions. Minor regrading and scarifying would be done by bulldozers , followed by revegetation with natural grasses and shrubs. As in conventional surface min- ing, approximately three growing sea- sons of reclamation area maintenance would be required to assure successful revegetation. The capacity of the proposed borehole mining unit is assumed to be 50 short tons of matrix per hour. Higher produc- tion can be achieved by increasing the number of mining units. Economies of scale do not apply to this system because different capacity tools have not been developed. GEOLOGIC CONSIDERATIONS The phosphate industry in the Southeast is currently surface mining phosphate de- posits with overburden thicknesses of up to 110 ft. Such overburden consists of unconsolidated sand and clay with no com- petent beds. Initial tests conducted for the Bureau indicated that for the suc- cessful application of borehole mining, a relatively competent rock bed must imme- diately overlie the phosphate matrix. A coiiq)etent bed prevents contamination of the matrix with sand and clay overburden that would otherwise cave into the bore- hole cavities. Primary phosphate deposits, those with no secondary reworking, facilitate mining by the borehole method. Primary deposits are very uniform in occurrence, quality, and thickness , which makes exploration data easier to interpret and mining easi- er to plan. This results in less explo- ration drilling. Since primary deposits contain only minor quantities of pebble, a more pumpable slurry results and the performance of the slurry pumping system is improved. While conclusive experiments have not been run, clay lenses within the matrix are believed to break up and then fall to the cavity floor as the matrix is mined; the larger fragments would then accumu- late on the cavity floor. This action would reduce the actual clay content of the material elevated to the surface and improve the overall phosphate grade of the recovered matrix. The grain size of the matrix particles and other primary depositional features of the bed may influence the shape of the borehole cavities. Owing to depositional variations, borehole cavities may assume irregular, noncircular shapes. CONVENTIONAL MINING SYSTEMS The hypothetical deposits described in this study can also be recovered by conventional mining technology. The sur- face mining system employed depends upon the thickness and character of the over- burden. Various overburden situations are addressed in three generalized cases. A cross section illustrating the three case situations is shown in figure 2. Site preparation work would be required in all three cases. Clearing vegetation, building access roads , and leveling min- ing areas would be accomplished by bulldozers. In case 1 , the 20-f t phosphate bed is overlain by 50 ft of interbedded carbon- ates, sands, and clays. A dragline V^MlWrnWiifc Surface 3^5F Unconsolidated sand and clay to be removed using bucket wheel excavators Unconsolidated sand and clay and semi consolidated material to be- removed by dragline 50ft Consolidated limestone interbedded with semi consolidated materials- to be removed by dragline """^s^^^^s^BMSMMSS^M 50ft 0,.^. -^ 1^^^^' y?? k%k 'J ^" '-^- ^mis^^^Sl^^P ' '^s'^oVO'-rtRy^ ^ - '?i?.2a ^^^i^^^^^fe^ ' ' ' "^ Phosphate matrix to be removed by 20^^ dragline j ?^aa^ Case 3 FIGURE 2. = Conventional mining systems. (Not to scale) removes this overburden and casts it into a previously mined cut to expose the phosphate matrix. The same dragline ex- cavates the matrix and transfers it to a slurry pit. In the slurry pit, water jets break, up the friable ore, creating a slurry that is pumped to a benef iciation plant. For case 2, an additional 50 ft of semlconsolidated overburden lies above the case 1 overburden, resulting in a to- tal overburden depth of 100 ft. A drag- line operating from the surface removes overburden and mines the matrix as de- scribed in case 1. For case 3, 50 ft of unconsolidated sand and clay lies above the case 2 over- burden, resulting in a total overburden depth of 150 ft. The top 50 ft of over- burden is stripped by two bucket wheel excavators, conveyed around the pit, and spread over mined out areas by stacker- reclaimers. Removal of the semi- consolidated overburden and phosphate matrix recovery proceeds as described in case 1. Reclamation involves casting overburden into mined-out cuts along with waste material from the benef iciation plant. A mixture of thickened clay slimes and sand tailings from the benef iciation plant is transported by pipeline to the mining area and backfilled into mined-out cuts. Draglines or dozers cover the waste with overburden material. Reasonable ground stability is expected since the amount of dewatered slimes and tailings is small compared with the amount of overburden cover. Topsoil is spread over the re- graded areas. The reclaimed land is suitable for agriculture or pasture. The ground surface would be stable enough to support most residential and industrial construction. Each case was evaluated at various production rates. Economies of scale are anticipated since draglines and bucket wheel excavators are available in different sizes. Conventional mining operating parameters are suimnarized in appendix A. BENEFICIATION SYSTEM The benef iciation processes for the primary phosphate matrix produced by borehole mining and conventional mining are identical. The operating parameters and recovery rates for benef iciation are based upon metallurgical tests. The major steps of the benef iciation process are washing and flotation. Wash- ing removes the clay fraction transport- ed with the matrix, A double-stage flotation circuit upgrades the washed feed. The grain size of feed is consist- ent, with 95 pet in the minus 35- to plus 200-mesh range. Owing to the grain size and high feed grade, 92 pet phos- phate recovery is achieved in the double- float circuit. Since some phosphate is lost in the washing circuit, an overall phosphate recovery of 85.7 pet is expect- ed. The resulting product output ton- nage equals about 46 pet of matrix input. The general operating parameters for the benef iciation system are summarized in appendix A. Waste clays produced during washing are thickened in clay holding ponds con- structed near the plant. Advanced de- watering methods are employed to minimize the pond retention time. It is assumed that 1 yr of clay settling capacity would be required. Thickened clay slimes are combined with sand tailings from flotation, pumped to the mining areas , and backfilled into mined-out cuts or borehole cavities. ENVIRONMENTAL CONSIDERATIONS Surface mining of phosphate has been occurring in central Florida for more than 90 yr. Very rugged landscapes and large above-grade clay dewatering ponds mark the locations of unreclaimed surface mining operations , and regulations now require the reclamation of surface mining areas for agricultural and recreational uses. Borehole mining may become a more envi- ronmentally acceptable alternative method for recovering phosphate, since commer- cial application of the borehole mining system eliminates the need for the remov- al of overburden material. Actual land disturbance is limited to clearing of vegetation and minor leveling of mining areas. The need to backfill and grade spoil piles, and the associated costs, are eliminated. Site cleanup and revege- tation are the only reclamation proce- dures required. Phosphate benef iciation yields sand tailings and water-retentive clay waste (clay) materials. The clay in central Florida, prior to dewatering, occupies between 1.25 and 2.0 times more volume than the unmined phosphate matrix (^-^) . The resulting extra volume of waste material is currently stored in above-grade clay dewatering ponds for ex- tended periods of time. Traditional methods of disposing of wastes, especially clays, ^re now being discouraged. The Florida Department of Environmental Regulation (2^) currently takes the position that because the "storage of waste clays for long periods of time interferes with expeditious rec- lamation and above grade storage of clays takes otherwise useful land out of pro- duction and raises potential health and safety problems , below grade storage and rapid reclamation techniques are encour- aged." In the future, surface mining operations will employ additional mechan- ical and chemical methods to reduce the clay volume, mix the clay with sand tail- ings , and backfill the waste into mined- out cuts. In borehole mining the waste is backfilled into mined-out cavities. Long-term above-grade waste storage is thus avoided. Water used in borehole mining and benef iciation is recirculated within the system. A large quantity of water is made available through the clay dewater- ing process. Ground water, infiltrat- ing borehole cavities at a slow rate, would be pumped from the cavities in the slurry. Ground water forced out of the cavity during backfilling would be pumped to the benef iciation plant for use. It is assumed that sufficient water is gen- erated during clay dewatering and mining for use throughout the system. Earlier studies indicated that bore- hole mining has not affected local water tables (4_) . fers remained tal boreholes sealed. The To insure that the aqui- undamaged, the experimen- in St. Johns County were steel casings were left in place and the boreholes were sealed with concrete from the top of the cavity to the surface. If this procedure is required in a large-scale operation, operating costs would be prohibitively high. The cooperation of government agencies would be required to reevaluate the need for sealing and develop lower cost alternatives. Significant controversy exists concern- ing the health hazard associated with ra- don levels on reclaimed phosphate lands following surface mining. The borehole mining system would minimize this ex- posure. Since the overburden is not disturbed, a significant earth buffer would remain intact above unrecovered uranium-enriched phosphate strata between boreholes and benef iciation wastes that are backfilled into mined-out borehole cavities. ECONOMIC EVALUATION An economic evaluation of borehole and conventional mining systems at selected production rates of 1.6, 3.3, and 5.0 million short tons of product per yearS was conducted at overburden depths of 50, 100, 150, and 230 ft for the borehole system, and 50, 100, and 150 ft for the conventional system. The 230-f t over- burden depth represents mining conditions in northern Florida and the depth for which Flow Industries, Inc., and Agrico -'See footnote 4. Chemical Co. provided borehole mining data. Mine and mill capital and operat- ing costs were estimated for these pro- duction rates and deposit depths. Discounted cash flow analyses were used to generate rates of return and product prices based on 20-yr project lives (1). Details of the analyses are given in appendix E. The results of the economic evaluations of the borehole mining system are presented in table 1 and those of the conventional mining system are presented TABLE 1. - Borehole mining system economic evaluation results Overburden, Capital costs Operating costs ' Rate of return, 2 pet Price 1 ft Break even 20-pct rate Mine | Mill Mine | Mill of return 1,666,590 SHORT TONS OF PRODUCT PER YEAR 50. 100. 150. 230. $45,598,000 46,094,000 46,591,000 47,385,000 $36 36 36 36 ,202,000 ,202,000 ,202,000 ,202,000 111. 64 12.40 13.17 14.39 $1.70 1.70 1.70 1.70 19.32 18.61 17.89 16.72 $16.26 17.08 17.89 19.20 $30.74 31.51 32.28 33.51 3,333,180 SHORT TONS OF PRODUCT PER YEAR 50. 100. 150. 230. $91,357,000 92,350,000 93,343,000 94,932,000 $55 55 55 55 ,122,000 ,122,000 ,122,000 ,122,000 11.83 12.60 13.36 14.59 $1.59 1.59 1.59 1.59 20.91 20.15 19.39 18.13 $16.13 16.96 17.77 19.08 $29.08 29.85 30.61 31.85 5 , 000 ,135 SHORT TONS OF PRODUCT PER YEAR 50. 100. 150. 230. $137,151,000 138,613,000 140,103,000 142,486,000 $70 70 70 70 ,518,000 ,518,000 ,518,000 ,518,000 11.90 12.67 13.43 14.66 'Per short ton of phosphate rock product. 2Discounted cash flow rate of return at $30 $1.54 1.54 1.54 1.54 21.77 21.01 20.22 18.92 $16.06 16.86 17.67 18.98 $28.28 29.03 29.79 31.02 per short ton of phosphate rock product. 10 TABLE 2, - Conventional mining system economic evaluation results Overburden, Capital costs Operating costs' Rate of return, 2 pet Price 1 ft Break even 20-pct rate Mine | Mill Mine | Mill of return 1,666,590 SHORT TONS OF PRODUCT PER YEAR 50. 100. 150. $59,161,000 75,178,000 126,053,000 $36,202,000 36,202,000 36,202,000 $5.09 6.40 12.60 $1.70 1.70 1.70 22.70 19.87 11.19 $10.18 12.19 20.13 $26.70 30.17 43.04 3,333,180 SHORT TONS OF PRODUCT PER YEAR 50. 100. 150. $113,733,000 128,057,000 210,129,000 $55,122,000 55,122,000 55 , 122,000 $4.39 5.06 9.40 $1.59 1.59 1.59 25.38 23.86 16.05 $8.98 9.94 15.66 $23.87 25.51 35.29 5,000,135 SHORT TONS OF PRODUCT PER YEAR 50. 100. 150. 168,575,000 $70,518,000 $3.75 $1.54 26.96 $8.04 $22.32 179,023,000 70,518,000 4.64 1.54 25.74 9.14 23.63 287,725,000 70,518,000 8.24 1.54 18.38 13.95 32.05 'Per short ton of phosphate rock product. ^Discounted cash flow rate of return at $30 per short ton of phosphate rock product. in table 2. Mill capital and operating costs are also summarized in tables 1 and 2. Operating costs do not include depre- ciation, depletion, and other noncash flow items. The cost of initial deposit explora- tion is not included in capital cost es- timations. Development of a uniform phosphate resource over a broad area usually involves exploratory drilling of low density. Initial exploration cost for a particular tract is therefore small relative to other capital investments and would be the same for both systems. Premining control drilling is included in the borehole and conventional mining operating costs. Legal, environmental impact statement, permitting, and interest costs are not included in the mine or mill capital cost estimations. Salvage values were esti- mated as 10 pet of the initial capital investments for plant and equipment. Straight-line depreciation of plant and equipment was employed. Working capital for the borehole, conventional, and benef iciation systems equals 90 days operating cost. All cost estimates are adjusted to January 1981 dollars using Bureau of Labor Statistics cost indexes. Eco- nomic comparisons of the mining sys- tems are illustrated in figures 3, 4, and 5. ■ 1 ' ' ' ' 1 ' ' ' •— ^\ ■ \. ■ ^T^ ^Borehole mining : \ : Conventional mining — ^ \ —1 : ^ .1 , , , \ 50 100 150 200 OVERBURDEN THICKNESS, ft 250 FIGURE 3. " Economic comparison— borehole mining versus conventional mining at 1.6 mil- lion short tons of product per year. Discounted cash flow rate of return at $30 per short ton of phosphate rock product. 11 20 15 Conventional mining Borehole mining 50 100 150 200 25 OVERBURDEN THICKNESS, ft FIGURE 4. ■ Economic comparison— borehole mining versus conventional mining at 3.3 mil- lion short tons of product per year. Discounted cash flow rate of return at $30 per short ton of phosphate rock product. 30 25 20 50 100 150 200 250 OVERBURDEN THICKNESS, ft FIGURE 5. ' Economic comparison-borehole mining versus conventional mining at 5.0 mil- lion short tons of product per year. Discounted cash flow rate of return at $30 per short ton of phosphate rock product. BOREHOLE MINING CAPITAL COST Capital costs for the borehole mining system include land acquisition, the borehole mining units, miscellaneous mining equipment, and working capital. Details of the borehole mining capital cost are presented in appendix B. ' ' ' ' 1 ' ' ' ' 1 ' ■ \. .^Conventionol mining Borehole mining ^'^^^^: , ... 1 .... 1 , . . . 1 . . . , 1 . . . . Land acquisition costs are based on an estimated cost of $1 per short ton of product recovered over the 20-yr life of the operation, thereby relating land val- ue directly to the value of the recovera- ble phosphate. When commercially available, a proto- type borehole mining unit, capable of operating at 230 ft of overburden, is estimated to cost $700,000. This cost represents a fixed cost for the surface unit, Kelly, and mining sections and a variable cost for the standard sections. The standard section length and cost vary with the mining depth. The total borehole mining unit cost is obtained by multiplying the single unit cost, based upon deposit depth, by the number of units required. The number of units re- quired is based upon the mine capacity, a mining rate of 50 short tons per hour, a utilization level of 24 h per day, and the effective availability of the min- ing unit, which varies with deposit depth. A 10-pct contingency cost is then added to the total mining unit capital cost. Borehole mining units are not re- placed during the life of the mine and are depreciated over the first 15 yr of operation. The miscellaneous mining equipment cost is based upon an estimated cost of $40,000 per unit multiplied by the number of units. A 10-pct contingency factor is then added. Miscellaneous mining equip- ment is replaced after 10 yr of opera- tion. Costs are depreciated over the first 8 yr of use. BOREHOLE MINING OPERATING COST Operating cost for the borehole mining system is composed of 14 cost elements and details are present in appendix B. Site preparation cost is estimated at $2,326 per acre. The acreage required for each operation is based upon the operating schedule, matrix density, and the mining recovery. Drilling, casing, and sealing cost in- cludes premining control drilling, bore- hole drilling, and borehole casing and 12 sealing costs. Control drilling is based upon a hole density of 0.4 hole per acre, deposit depth, and an estimated average cost of $3,50 per foot for core drilling and gamma ray logging. The operating labor cost is based on an estimated labor rate of $12 per hour, as applied to the number of employees and the operating schedule. Site reclamation cost, including cav- ity backfilling, is based on an esti- mate of $1.50 per short ton of material backfilled. The slurry transportation cost is based on an estimated cost of $0.18 per short ton-mile, multiplied by the tonnage of ore and waste transported and by the av- erage transportation distance. The annual support and maintenance la- bor costs are estimated to be 80 and 25 pet, respectively, of the annual operat- ing labor cost. Supervisory labor costs are estimated as a percentage of the total annual oper- ating labor, support labor, and mainte- nance labor costs. The percentages used at the 1.6, 3.3, and 5.0 million short ton per year production rates are 20, 15, and 10 pet, respectively. Payroll benefits and payroll overhead cost elements are estimated as 30 and 40 pet, respectively, of the total of all four labor cost elements. The prototype unit is estimated to require power for the cutting jet, slurry pump, and other smaller pumps, for a total of 2,400 bhp which includes a 300-bhp variance with mining depth. The estimated annual power cost equals $580,682 per unit plus a variable cost per unit of $332 per foot of total mining depth. The annual maintenance supply cost is estimated at $30,000 per unit, operating on a 330 day per year schedule. This cost is adjusted to the 365 day per year schedule and multiplied by the number of units required. The health and safety cost is based on an annual cost estimate of $190,000 per year for 10 units operating for 330 days per year. This cost is adjusted to the required number of units and proposed operating schedule. The fixed costs attributed to mining are estimated to be 85 pet of the total annual mineral severance tax, local tax- es, and insurance cost. Severance tax, after ad valorem tax credit and reclama- tion rebate, is estimated at $1.21 per short ton of product. Local taxes and insurance are estimated at $0.58 per short ton of product. The operating cost, per short ton of product, is then obtained by dividing the total annual operating cost by the annual product tonnage. CONVENTIONAL MINING CAPITAL COST Capital costs for the conventional min- ing system included land acquisition, mine equipment, draglines and bucket wheel excavators, and working capital. Details of the conventional mining capi- tal cost are presented in appendix C. Land acquisition costs are equal to the land acquisition costs for the borehole mining system at the same production rate. Although mining recovery is higher for the conventional system, and less acreage is required, the costs are equiv- alent since they are based upon $1 per short ton of product recovered over the life of the mine. Mine equipment and dragline and bucket wheel excavator costs are based on cost estimates developed by industry and pub- lished sources. Costing models were fol- lowed for all calculations involving draglines and related expenses (_7) . At 13 150-ft overburden depths, where bucket wheel excavators are required, separate additional capital costs are developed. Mine equipment costs include the sup- port equipment for the dragline and buck- et wheel excavation systems. Some ele- ments of the initial base mine capital cost estimates required adjusting accord- ing to the following formula: New mine capital cost = Base mine capital cost r New mine capacity 1 ^ '^ |_ Base mine capacity] This scaling formula is based upon the assumption that capital costs are expo- nentially related to production capacity. Dragline capital costs are based upon the number of draglines required, the dragline sizes, and equipment manufactur- er's suggested costs. The proposed over- burden depths and production rates deter- mined the quantity and size of the equipment. The total bucket wheel system cost is based upon an estimated system cost of $108,535,540 for moving 28.7 million bank cubic yards of overburden per year. This cost is scaled to the proposed production rates using the 0.7 exponential scaling formula. Costs of the bucket wheel ex- cavators, conveyor systems, and stacker reclaimers are estimated to be 90 pet of the total bucket wheel system cost and are allocated to the dragline and bucket wheel excavator cost category. The re- maining 10 pet is for support equipment and is attributed to the mine equipment cost category. Items included under mine equipment cost are replaced after the first 10 yr of production. They are depreciated over the first 8 yr of use. Draglines and bucket wheel excavators are not replaced during the 20-yr production periods. They are depreciated over the first 15 yr of operation. CONVENTIONAL MINING OPERATING COST Operating costs for the conventional mining systems are composed of 18 cost elements and details are presented in appendix C. The estimated dragline oper- ating costs and related expenses were calculated using cost models developed by Zellars-Williams , Inc. (_7). The bucket wheel excavator system annual operating costs are based upon known system costs scaled to the proposed production rates and other factors. The two most important controlling fac- tors in the cost evaluation are the phos- phate reserve grade and characteristics and the mine capacity. Matrix pumping distances and mine recovery are examples of miscellaneous factors considered in the cost model. The power cost element is composed of dragline, slurry pit, and pumping power requirements. A power cost rate of $0.0416 per kilowatt hour is used to ob- tain the total annual power cost. The outside services cost element is composed of mine site preparation costs plus reclamation costs. Mine site prep- aration and reclamation costs are esti- mated at $708 and $2,500 per acre, respectively. Matrix pipeline cost is estimated at $34 per foot. The cost of premining con- trol drilling, gamma ray logging, and core analysis is estimated at $3.50 per foot. A drilling density of 0.4 hole per acre is used. Severance tax, after ad valorem tax credit and reclamation rebate, is esti- mated at $1.21 per short ton of product. Local taxes and insurance are estimated at $0.54 per short ton of product plus a 4-pct sales tax. The operating cost, per short ton of product, is then obtained by dividing the total annual operating cost by the annual product tonnage. 14 BENEFICIATION SYSTEM CAPITAL COST Capital costs for the benef iciation system included mill plant capital and working capital. Details are presented in appendix D. At each production rate, the benef iciation processes and associ- ated capital costs are equal for the borehole and conventional mining systems. Mill plant capital cost is estimated at $35,500,000 for a 1.6 million short ton per year plant. This cost is scaled to the other production rates using an ex- ponential scaling factor of 0.6 in the following formula: New mill capital cost product for a plant producing 1.6 million short tons per year. This estimate is reduced by the plant depreciation cost, with a final estimate being $1.43 per short ton of product (for power, labor, and reagents). Reagents are estimated to be 60 pet of this cost, while the power and labor cost category is estimated at 40 pet. The power and labor cost element is scaled to adjust for other proposed pro- duction rates. The scaling method used is based upon the assxamption that operat- ing cost is exponentially related to the production capacity of the mill. The formula used is = Base mill capital cost 4 New mill capacity Base mill capacity 0.6 BENEFICIATION SYSTEM OPERATING COST Operating costs for the beneficiation system included power and labor, rea- gents, and fixed costs. Details are pre- sented in appendix D. At each production rate, the beneficiation processes and associated operating costs are equal for the borehole and conventional mining sys- tems. Mill operating cost for power, labor, reagents, and depreciation is es- timated at $2.50 per short ton of New mill power and labor cost = Base mill power and labor cost r Base mill capacity" New mill capacity ,J..3_ The fixed costs attributed to benefici- ation are estimated to be 15 pet of the total annual mineral severance tax, local taxes, and insurance cost. Severance tax, after ad valorem tax credit and reclamation rebate, is estimated at $1.21 per short ton of product. Local taxes and insurance are estimated at $0.58 per short ton. CONCLUSIONS Based on the economic evaluation of the borehole and conventional mining sys- tems , borehole mining systems are eco- nomically superior for the recovery of deep bedded phosphate deposits. However, the recovery of shallow phosphate depos- its by conventional mining is econom- ically more attractive than by borehole mining. Conventional surface mining with 50 and 100 ft of overburden is more economical (i.e., has a higher rate of return) than borehole mining at all three production rates examined. At 150 ft of overburden, borehole mining is economically superior at all production rates. Only the bore- hole mining system was evaluated at a 230-ft overburden thickness. The eco- nomic attractiveness (as measured by rate of return) of the conventional mining systems falls rapidly between 100 and 150 ft of overburden owing to significantly higher capital and operating costs. By extrapolating the data, rate of return for conventional mining with 230 ft of overburden is expected to be prohibitive- ly low, perhaps negative, at a product price of $30 per short ton. The borehole mining system maintains a high level of economic attractiveness at 150 and 230 ft of overburden. 15 Conventional phosphate mines in Florida typically achieve rates of return between 15 and 20 pet. The operations evaluated in this study attain comparable levels of profitability except for low produc- tion conventional mining with 150 ft of overburden. Borehole mining is environmentally more desirable for recovering phosphate de- posits than conventional surface mining alternatives. The surface area disturbed at any time during borehole mining is minimal. Borehole mining recovers the phosphate matrix without disturbing the material overlying the ore. Reclamation work required to restore the surface after borehole mining is limited to minor regrading and revegetation. The borehole mining system is an eco- nomically and environmentally attractive method of recovering phosphate under cer- tain geologic conditions. With the in- creasing need to mine deeper phosphate deposits, development of borehole mining technology should progress and in the future may supply a significant share of the demand for phosphate. SUGGESTIONS FOR FURTHER INVESTIGATION 1 . Exploration or evaluation of areas where borehole mining can be applied to recover phosphate. - Examine various mining tool diameters to find the optimum diameter tool and borehole. - Delineate phosphate potential in ar- eas where borehole mining can be applied. - Assess the potential of applying borehole mining to offshore phosphate deposits. 2. Testing the application of bore- hole mining under various overburden conditions. - Improve maneuverability of the water jet nozzle to increase mobility and cut- ting radius. - Redesign mining tool to increase unit production and maximize mining recovery. Evaluate possible economies of scale if production rate per unit exceeds 50 short tons of matrix per hour. - Determine cavity roof competence needed to prevent cavity collapse. - Test application of borehole mining methods in areas with no relatively com- petent overburden. 3. Improve mechanical efficiency of borehole mining equipment. - Determine possible borehole cavity shapes, sizes, and spacings; estimate associated mining recovery rates. - Evaluate to required between the ore zone. what extent a seal is the casing and top of 16 REFERENCES 1. Davidoff , R. L. Supply Analysis Model (SAM): A Minerals Availability System Methodology. BuMines IC 8820, 1980, pp. 14-15. 2. Florida Department of Natural Resources. Florida Statutes. Chapter 16C - 16: Mine Reclamation. Florida Di- vision of Resource Management, amended Oct. 6, 1980. 3. Marvin, M. H, , G. S. Knoke, and W. R. Archibald. Backfilling of Cavi- ties Produced in Borehole Mining Opera- tions (contract J0285037, Flow Indus- tries, Inc.). BuMines OFR 4-81, 1979, 78 pp.; NTIS PB 81-171308. 4. Scott, L. E. Borehole Mining of Phosphate Ores (contract J0205038, Flow Industries, Inc.). BuMines OFR 138-82, August 1981, 215 pp.; NTIS PB 82-257841. 5. Timberlake, R. C. Building Land With Phosphate Wastes. Min. Eng. , v. 21, No. 12, December 1969, pp. 38-40. 6. U.S. Bureau of Mines, Staff. The Florida Phosphate Slimes Problem. IC 8668, 1975, 41 pp. 7. Zellars, M. E., and J. M. Williams. Evaluation of the Phosphate Deposits of Florida Using the Minerals Availabil- ity System (contract J0377000, Zellars- Williams, Inc.). BxiMines OFR 112-78, June 1978, 199 pp.; NTIS PB 286 648/ AS. 17 APPENDIX A. — MINING AND BENEFICIATION PARAMETERS Basic deposit assumptions Matrix thickness ft. . Matrix density Ib/f t3. . Average overburden density. .Ib/ft^. . Matrix grade, pet: Bone phosphate of lime ' P205- Pebble content of matrix pet.. Clay content of matrix pet.. Matrix "X"^ yd^.. U pet BPL = 0.458 pet P205. ^Matrix per short ton of product. 20 88 36.25 16.59 25 1.84 General operating parameters Recovery, pet: Washing Flotation Overall benef iciation Product grade, pet: Bone phosphate of lime ' Borehole mining unit — Specifications Operating shifts per day Utilization level h. Operating days per year Mine life yr. U pet BPL = 0.458 pet P2O5. and approximate operating parameters Average unit mining rate. . . .tph. . 50 Tool rotation rate rpm. . 10 Mining tool diameter in.. 8 Standard section length ft.. 20 Cutting jet: Flow rate gpm. . 1,000 Pressure psl. . 1,200 Power hp . . 1,000 Electric motors (500 hp, 2,300 V ac) 2 Jet pump : Flow rate gpm. . 500 Pressure psl. . 1 ,200 Power (for 250-ft mining depth) hp. . 500 Electric motor (500 hp) 1 Air compressor: Flow rate scfm.. 1,500 Pressure psi. . 250 Power hp. . 400 Electric motor (400 hp, 2,300 V ac) 1 Borehole and conventional mining parameters at three production rates Slurry pump: Discharge flow rate gpm.. Power hp. . Electric motor (150 hp, 2,300 V ac) Slurry tank capacity gal.. Water tank capacity gal.. Hydraulic power package hp.. Hydraulic electric motor (200 hp, 2,300 V ac Size of mining unit ft.. Approximate unit weight (tanks empty, no sections). Average cavity radius Cavity separation. . . . Borehole separation. . Operating factor Move and setup ..lb. ..ft. ..ft. ..ft. .pet. ...h. 93.1 92.0 85.7 68.00 31.14 3 24 365 20 1,600 150 1 500 2,000 200 10 by 10 by 30 150,000 30 10 70 90 3-5 Annual product output, short tons. Borehole mining parameters: Dally product output short tons.. Dally matrix production do. . . . Mining units Area mined per year acres . . Total area mined in 20 yr do.... Mining recovery pet. . Conventional mining parameters: Daily product output short tons.. Daily matrix production do.... Number of draglines and capacity at — 50-f t overburden 100-f t overburden 150-f t overburden' Area mined per year acres.. Total area mined in 20 yr do.... Mining recovery pet. . 'Bucket wheel excavators used also. 1, 666,590 3, 333,180 5, 000,135 4,566 9,132 13,698 10,000 20,000 30,000 10 20 30 143 286 429 2,860 5,720 8,580 66.6 66.6 66.6 4,566 9,132 13,698 10,000 20,000 30,000 1, 35 yd3 2. 35 yd 3 2, 52 yd 3 2, 31 yd3 3, 41 yd3 4. 46 yd 3 2, 31 yd3 3, 41 yd3 4. 46 yd 3 112 224 336 2,240 4,480 6,720 85.0 85.0 85.0 18 APPENDIX B. --BOREHOLE MINING SYSTEM CAPITAL AND OPERATING COSTS TABLE B-1. - Estimated capital requirements, borehole mining system Overburden, ft. 50 100 150 230 1,666,590 SHORT TONS OF PRODUCT PER YEAR Acquisition ' $33,332,000 7,047,000 440,000 4,779,000 $33,332,000 7,228,000 440,000 5,094,000 $33,332,000 7,410,000 440,000 5,409,000 $33,332,000 7,700,000 10 mining units. ............. Miscellaneous mining equipment . .....••. .......... 440,000 Working capital2 5,913,000 Total 45,598,000 46,094,000 46,591,000 47,385,000 3,333,180 SHORT TONS OF PRODUCT PER YEAR Acquisition '.......•......... $66,664,000 14,093,000 880,000 9,720,000 $66,664,000 14,456,000 880,000 10,350,000 $66,664,000 14,819,000 880,000 10,980,000 $66,664,000 15,400,000 20 mining units. ............. Miscellaneous mining equipment Working capital^ 880,000 11,988,000 Total 91,357,000 92,350,000 93,343,000 94,932,000 Acquisition 1 30 mining units Miscellaneous mining equipment Working capital^ Total 5,000,135 SHORT TONS OF PRODUCT PER YEAR 'Cost of property requi ^Working capital equals $100,003,000 21,140,000 1,320,000 14,688,000 137,151,000 $100,003 21,684 1,320 15,606 ,000 ,000 ,000 ,000 138,613,000 $100,003,000 22,229,000 1,320,000 16,551,000 140,103,000 $100,003,000 23,100,000 1,320,000 18,063,000 142,486.000 red for 20-yr operation. 90 days' operating cost. 19 TABLE B-2. - Estimated annual operating costs, borehole mining system Overburden, ft. 50 100 150 230 1,666,590 SHORT TONS OF PRODUCT PER YEAR Site preparation Drilling, casing, and Operating labor Support labor Maintenance labor Supervisory labor Payroll benefits Payroll overhead Power , Maintenance supplies.. Health and safety Site reclamation Slurry transportation. Fixed costs Total sealing. $332 1,558 1,051 840 262 430 775 1,034 6,039 331 210 2,975 1,014 2,535 19,393 558 368 200 960 800 992 786 381 220 820 152 115 014 717 083 $332 2,668 1,051 840 262 430 775 1,034 6,205 331 210 2,975 1,014 2,535 20,669 558 628 200 960 800 992 786 381 220 820 152 115 014 717 343 $332 3,778 1,051 840 262 430 775 1,034 6,371 331 210 2,975 1,014 2,535 21,945 558 888 200 960 800 992 786 381 220 820 152 115 014 717 603 $332 5,555 1,051 840 262 430 775 1,034 6,636 331 210 2,975 1,014 2,535 23,987 3,333,180 SHORT TONS OF PRODUCT PER YEAR Site preparation Drilling, casing, and sealing. Operating labor Support labor Maintenance labor Supervisory labor Payroll benefits Payroll overhead. Power Maintenance supplies Health and safety Site reclamation. Slurry transportation Fixed costs Total $665 3,116 2,102 1,681 525 646 1,486 1,982 2,078 663 420 5,950 3,042 5,071 116 736 400 920 600 488 922 563 440 640 300 230 041 433 39,433 829 $665 5,337 2,102 1,681 525 646 1,486 1,982 12,410 663 420 5,950 3,042 5,071 116 256 400 920 600 488 922 563 440 640 300 230 041 433 41,986 349 $665 7,557 2,102 1,681 525 646 1,486 1,982 12,742 663 420 5,950 3,042 5,071 116 776 400 920 600 488 922 563 440 640 300 230 041 433 44,538 869 $665 11,110 2,102 1,681 525 646 1,486 1,982 13,273 663 420 5,950 3,042 5,071 48,622 5,000,135 SHORT TONS OF PRODUCT PER YEAR Site preparation Drilling, casing, and sealing. Operating labor Support labor Maintenance labor Supervisory labor Payroll benefits Payroll overhead Power Maintenance supplies Health and safety Site reclamation Slurry transportation Fixed costs Total $997 4,675 3,153 2,522 788 646 2,133 2,844 18,117 995 630 8,924 5,475 7,607 674 104 600 880 400 488 410 547 660 460 450 798 556 706 59,513 733 $997 8,005 3,153 2,522 788 646 2,133 2,844 18,615 995 630 8,924 5,475 7,607 674 884 600 880 400 488 410 547 660 460 450 798 556 706 63,342 513 $997 11,336 3,153 2,522 788 646 2,133 2,844 19,113 995 630 8,924 5,475 7,607 674 664 600 880 400 488 410 547 660 460 450 798 556 706 67,171 293 $997 16,665 3,153 2,522 788 646 2,133 2,844 19,910 995 630 8,924 5,475 7,607 73,297 20 APPENDIX C. —CONVENTIONAL MINING SYSTEM CAPITAL AND OPERATING COSTS TABLE C-1. - Estimated capital requirements, conventional mining systems Overburden, ft. 50 100 150 1,666,590 SHORT TONS OF PRODUCT PER YEAR Acquisition ' Mine equipment Draglines and bucket wheel excavators Working capital^ , Total. $33,332,000 14,262,000 9,479,000 2,088,000 59,161,000 $33 22 17 2 ,332,000 ,103,000 ,115,000 ,628,000 75,178,000 $33,332,000 26,936,000 60,610,000 5,175,000 126,053,000 3,333,180 SHORT TONS OF PRODUCT PER YEAR Acquisition^ , Mining equipment , Draglines and bucket wheel Working capital^ , Total , excavators. $66,664,000 24,511,000 18,958,000 3,600,000 113,733,000 $66 28 28 4 ,664,000 ,798,000 ,437,000 ,158,000 128,057,000 $66,664,000 36,649,000 99,094,000 7.722,000 210,129,000 5,000,135 SHORT TONS OF PRODUCT PER YEAR Acquisition ^ Mine equipment Draglines and bucket wheel excavators.... Working capital^ , Total 'Cost of property required ^Working capital equals 90 $100,003,000 26,566,000 37,389,000 4,617,000 168,575,000 $100 35 37 5 ,003,000 ,380,000 ,916,000 ,724,000 179,023,000 $100,003,000 45,807,000 131,763,000 10,152,000 287,725,000 for 20-yr operation, days' operating cost. 21 TABLE C-2. - Estimated annual operating costs, conventional mining system, at 1.6 million short tons of product per year' Overburden, ft. 50 100 150 DRAGLINE SYSTEM Direct: Power, Fuel. . Supplies Mobile mine support equipment Outside services Direct operating labor Direct production supervision. Maintenance labor Maintenance supervision Maintenance parts and supplies Replacement mine pipe Payroll overhead Indirect: Administrative, technical, and clerical labor... Administrative payroll overhead Facilities maintenance and supplies General overhead Fixed: Local taxes Insurance BUCKET WHEEL EXCAVATOR SYSTEM Direct: Power. Maintenance supplies Operating and maintenance labor Indirect: Administrative, technical, and clerical labor, facilities maintenance and supplies Fixed: Local taxes and insurance Total $901,938 58,771 328,213 333,037 359,293 892,079 380,605 270,091 159,648 1,172,478 120,972 411,283 397,526 95,435 24,638 31,694 2,511,152 33,332 NAp NAp NAp NAp NAp $1,005,908 82,280 382,532 466,252 359,293 1,227,241 520,784 397,526 234,339 1,873,659 241,944 575,907 514,341 123,470 31,859 42,835 2,558,546 33,332 NAp NAp NAp NAp NAp $1,005,908 82,280 382,532 466,252 359,293 1,227,241 520,784 397,526 234,339 1,873,659 241,944 575,907 514,341 123,470 31,859 46,755 2,558,546 33,332 1,418,549 4,038,390 3,003,741 1,547,685 309,537 8,482,185 10,672,048 20,993,870 NAp Not applicable. 'Precise production value, 1,666,590 short tons. 22 TABLE C-3. - Estimated annual operating costs, conventional mining system, at 3.3 million short tons of product per year' Overburden , ft DRAGLINE SYSTEM Direct: Power Fuel Supplies Mobile mine support equipment Outside services Direct operating labor Direct production supervision Maintenance labor Maintenance supervision. Maintenance parts and supplies Replacement mine pipe Payroll overhead Indirect: Administrative, technical, and clerical labor... Administrative payroll overhead Facilities maintenance and supplies General overhead Fixed: Local taxes Insurance BUCKET WHEEL EXCAVATOR SYSTEM Direct: Power Maintenance supplies Operating and maintenance labor Indirect: Administrative, technical, and clerical labor, facilities maintenance and supplies Fixed: Local taxes and insurance Total NAp Not applicable. 'Precise production value, 3,333,180 short tons. 50 100 150 $1,925,765 82,280 490,972 466,252 718,586 1,227,241 520,784 397,526 234,339 1,873,659 349,476 575,907 514,341 123,470 31,859 45,971 4,985,850 66,664 NAp NAp NAp NAp NAp $2,106,357 105,788 544,627 599,467 718,586 1,562,404 659,263 524,961 300,534 2,488,121 524,213 737,883 631,864 151,648 39,151 61,103 5,027,432 66,664 NAp NAp NAp NAp NAp $2,106,357 105,788 544,627 599,467 718,586 1,562,404 659,263 524,961 300,534 2,488,121 524,213 737,883 631,864 151,648 39,151 68,943 5,027,432 66,664 2,306,316 6,565,727 3,003,741 2,172,399 434,480 14,630,942 16,850,066 31,340,569 23 TABLE C-4. - Estimated annual operating costs, conventional mining system, at 5.0 million short tons of product per year' Overburden, ft DRAGLINE SYSTEM Direct: Power Fuel Supplies Mobile mine support equipment Outside services Direct operating labor Direct production supervision Maintenance labor Maintenance supervision Maintenance parts and supplies Replacement mine pipe Payroll overhead Indirect: Administrative, technical, and clerical labor... Administrative payroll overhead Facilities maintenance and supplies General overhead Fixed: Local taxes Insurance BUCKET WHEEL EXCAVATOR SYSTEM Direct: Power Maintenance supplies Operating and maintenance labor Indirect: Administrative, technical, and clerical labor, facilities maintenance and supplies. Fixed: Local taxes and insurance Total NAp Not applicable. 'Precise production value, 5,000,135 short tons. 50 100 150 $2,994,996 82,280 635,591 466,252 1,077,878 1,227,241 520,784 397,526 234,339 1,873,659 430,124 575,907 514,341 123,470 31,859 52,977 7,415,325 100,003 NAp NAp NAp NAp NAp $3,265,884 129,297 742,901 732,681 1,077,878 1,897,566 797,734 652,396 369,072 3,101,507 860,247 898,472 749,382 179,852 46,433 79,361 7,498,490 100,003 NAp NAp NAp NAp NAp $3,265,884 129,297 742,901 732,681 1,077,878 1,897,566 797,734 652,396 369,072 3,101,507 860,247 898,472 749,382 179,852 46,433 91,121 7,498,490 100,003 3,057,864 8,705,272 3,003,741 2,701,258 540,252 18,754,552 23,179,156 41,199,303 24 APPENDIX D.~BENEFICIATION SYSTEM CAPITAL AND OPERATING COSTS TABLE D-1, - Estimated capital requirements, benef iciation system Annual mining rate, short tons of product Mill plant Working capital ^ Total 1,666,590. 3,333,180. 5,000,135. $35,500,000 53,808,000 68,628,000 $702,000 1,314,000 1,890,000 $36,202,000 55,122,000 70,518,000 Working capital equals 90 days' operating cost. TABLE D-2. - Estimated annual operating costs, benef iciation system Short tons of product | 1,666,590 [ 3,333,180 5,000,135 ANNUAL COST Power and labor. Reagents. Fixed costs Total $949,956 1,433,268 447,479 2,830,703 $1,533,263 2,866,535 894,959 5,294,757 $2,050,055 4,300,116 1,342,536 7.692,707 COST PER SHORT TON OF PRODUCT' Power and labor Reagents Fixed costs Total 'Rounded to the nearest cent. $0.57 .86 .27 1.70 $0.46 .86 .27 1.59 $0.41 .86 .27 1.54 25 APPENDIX E.— CASH FLOW ANALYSIS TABLE E-1. - Cash flow analysis at 50-ft overburden and 1.6 million short tons of product per year (Based on annual revenue of $49,995,506) Borehole mining Conventional mining Continuous Continuous Year Capital Cash flow rate of Capital Cash flow rate of expenditure return, ' pet expenditure return, ' pet 0^ $56,998,666 -$56,998,666 $56,998,666 -$56,998,666 1 24,801,333 -4,621,091 38,364,333 -10,131,711 2 18,593,989 25,020,969 3 18,939,770 25,366,750 4 18,939,770 25,366,750 3.43 5 18,939,770 4.88 25,366,750 10.27 6 18,939,770 9.28 25,366,750 14.32 7 18,939,770 12.15 25,366,750 16.91 8 18,939,770 14.11 25,366,750 18.63 9 18,915,664 15.49 24,585,359 19.79 10 18,915,664 16.49 24,585,359 20.62 11 440,000 17,326,678 17.17 14,262,000 11,875,593 20.92 12 17,722,678 17.70 24,711,393 21.39 13 17,722,678 18.11 24,711,393 21.74 14 17,722,678 18.42 24,711,393 22.00 15 17,722,678 18.67 24,711,639 22.20 16 17,170,993 18.86 24,088,639 22.36 17 16,825,212 19.00 23,742,858 22.47 18 16,479,432 19.12 23,397,077 22.56 19 16,455,325 19.21 22,615,686 22.62 203 -9,823,000 26,278,325 19.32 -10,139,000 32,754,686 22.70 1 Discounted eash flow rate of return at $30 per short ton of phosphate rock product, 2Year equals total preproduction years. ^Equipment value and working capital salvaged in year 20. 26 TABLE E-2. - Cash flow analysis at 100-ft overburden and 1.6 million short tons of product per year (Based on annual revenue of $49,995,506) Borehole mining Conventional mining Continuous Continuous Year Capital Cash flow rate of Capital Cash flow rate of expenditure return, ' pet expenditure return, ' pet 02 $56,998,666 -$56,998,666 $56,998,666 -$56,998,666 1 25,297,333 -5,749,057 54,381,333 -25,071,775 2 17,943,924 24,550,205 3 18,289,705 24,895,986 4 18,289,705 24,895,986 5 18,289,705 3.61 24,895,986 5.08 6 18,289,705 8.16 24,895,986 9.87 7 18,289,705 11.12 24,895,986 12.93 8 18,289,705 13.15 24,895,986 14.98 9 18,265,598 14.56 23,685,000 16.35 10 18,265,598 15.63 23,685,000 17.34 11 440,000 16,601,714 16.34 22,103,000 4,235,581 17.48 12 16,997,714 16.89 24,128,281 18.09 13 16,997,714 17.32 24,128,281 18.55 14 16,997,714 17.65 24,128,281 18.90 15 16,997,714 17.91 24,128,281 19.17 16 16,440,738 18.11 23,282,417 19.38 17 16,094,957 18.26 22,936,636 19.54 18 15,749,176 18.38 22,590,855 19.66 19 15,725,070 18.48 21,379,869 19.75 203 -10,156,000 25,881,070 18.61 -13,011,000 34,390,869 19.87 iDiscoun ted cash flovg rate of retur n at $30 per short ton of phosphate rock product. ^Year equals total preproduction years. ^Equipment value and working capital salvaged in year 20. 27 TABLE E-3. - Cash flow analysis at 150-ft overburden and 1.6 million short tons of product per year (Based on annual revenue of $49,995,506) Borehole mining Conventional mini ng Continuous Continuous Year Capital Cash flow rate of Capital Cash flow rate of expenditure return, ' pet expenditure return, ' pet 02 $56,998,666 -$56,998,666 $56,998,666 -$56,998,666 1 25,794,333 -6,877,890 105,256,333 -80,195,134 2 17,293,891 25,127,728 3 17,639,672 22,109,579 4 17,639,672 21,132,638 5 17,639,672 2.31 21,132,638 6 17,639,672 7.00 21,132,638 7 17,639,672 10.07 21,132,638 8 17,639,672 12.17 21,132,638 2.35 9 17,615,565 13.66 19,656,906 4.57 10 17,615,565 14.75 19,656,906 6.23 11 440,000 15,895,508 15.49 26,936,000 -4,420,477 5.91 12 16,291,508 16.06 19,821,923 7.16 13 16,291,508 16.51 19,821,923 8.12 14 16,291,508 16.86 19,821,923 8.88 15 16,291,508 17.13 19,821,923 9.48 16 15,729,207 17.35 17,705,118 9.91 17 15,383,426 17.51 17,359,337 10.26 18 15,037,645 17.64 17,013,556 10.55 19 15,013,539 17.75 15,537,825 10.77 203 -10,489,000 25,502,539 17.89 -20,875,000 36,412,825 11.19 ^Discounted cash flow rate of return at $30 per short ton of phosphate rock product, ^Year equals total preproduction years. 3Equipment value and working capital salvaged in year 20. 28 TABLE E-4. - Cash flow analysis at 50-ft overburden and 3.3 million short tons of product per year (Based on annual revenue of $99,991,012) Borehole mining Conventional mining Continuous Continuous Year Capital Cash flow rate of Capital Cash flow rate of expenditure return, ' pet expenditure return, ' pet 02 $102,536,000 -$102,536,000 $102,536,000 -$102,536,000 1 43,943,000 -4,492,214 66,319,000 -9,849,125 2 36,683,963 50,853,452 3 37,208,040 51,377,529 4 37,208,040 1.00 51,377,529 8.55 5 37,208,040 7.74 51,377,529 14.64 6 37,208,040 11.82 51,377,529 18.24 7 37,208,040 14.47 51,377,529 20.51 8 37,208,040 16.27 51,377,529 22.01 9 37,159,827 17.53 50,034,626 23.01 10 37,159,827 18.43 50,034,626 23.71 11 880,000 33,981,855 19.05 24,511,000 28,156,710 24.00 12 34,773,855 19.52 50,216,610 24.38 13 34,773,855 19.87 50,216,610 24.66 14 34,773,855 20.15 50,216,610 24.87 15 34,773,855 20.36 50,216,610 25.02 16 33,837,971 20.52 49,138,586 25.14 17 33,313,894 20.65 48,614,510 25.22 18 32,789,817 20.74 48,090,433 25.29 19 32,741,604 20.82 46,747,530 25.33 203 -18,001,000 50,742,604 20.91 -17,094,000 63,841,530 25.38 'Discounted cash flow rate of return at $30 per short ton of phosphate rock product, ^Year equals total preproduction years. 3Equipment value and working capital salvaged in year 20. 29 TABLE E-5. - Cash flow analysis at 100-ft overburden and 3.3 million short tons of product per year (Based on annual revenue of $99,991,012) Borehole mining Conventional mining Continuous Continuous Year Capital Cash flow rate of Capital Cash flow rate of expenditure return, ' pet expenditure return, ' pet 0^ $102,536,000 -$102,536,000 $102,536,000 -$102,536,000 1 44,936,000 -6,749,045 80,643,000 -23,445,615 2 35,383,832 50,204,362 3 35,907,909 50,728,439 4 35,907,909 50,728,439 5.32 5 35,907,909 6.44 50,728,439 12.00 6 35,907,909 10.66 50,728,439 15.94 7 35,907,909 13.40 50,728,439 18.42 8 35,907,909 15.27 50,728,439 20.08 9 35,859,696 16.58 49,150,680 21.18 10 35,859,696 17.53 49,150,680 21.96 11 880,000 32,531,928 18.17 28,798,000 23,536,973 22.24 12 33,323,928 18.66 49,455,173 22.67 13 33,323,928 19.04 49,455,173 22.99 14 33,323,928 19.33 49,455,173 23.24 15 33,323,928 19.56 49,455,173 23.42 16 32,377,460 19.73 48,100,176 23.55 17 31,853,383 19.86 47,576,099 23.66 18 31,329,306 19.97 47,052,022 23.73 19 31,281,093 20.05 45,474,264 23.79 203.... -18,668,000 49,949,093 20.15 -19,458,000 64,932,264 23.86 'Discoun ted cash flow rate of returi 1 at $30 per short ton of phosphate rock product. ^Year equals total preproduction years. ^Equipment value and working capital salvaged in year 20. 30 TABLE E-6. - Cash flow analysis at 150-ft overburden and 3.3 million short tons of product per year (Based on annual revenue of $99,991,012) Borehole mining Conventional mining Year Capital expenditure 02.... 1 2 3 4 5 6 7...., 8 9 10 11...., 12...., 13 14 15 16 17 18 19 203..., Cash flow Continuous rate of return, ' pet Capital expenditure Cash flow Continuous rate of return, ' pet $102,536,000 45,929,000 880,000 -19,334,000 -$102,536,000 -9,005,843 34,083,734 34,607,81 34,607,81 34,607,81 34,607,81 34,607,81 34,607,81 34,559,598 34,559,598 31,119,483 31,911,483 31,911,483 31,911,483 31,911,483 30,954,398 30,430,321 29,906,244 29,858,031 49,192,031 5.10 9.47 12.31 14.25 15.62 16.61 17.27 17.79 18.19 18.50 18.74 18.92 19.07 19.18 19.27 19.39 $102,536,000 162,715,000 36,649,000 -31,657,000 -$102,536,000 -102,945,041 45,642,310 45,808,300 45,808,300 45,808,300 45,808,300 45,808,300 45,808,300 43,800,399 43,800,399 10,801,954 43,786,054 43,786,054 43,786,054 43,786,054 40,366,437 39,842,360 39,318,283 37,310,382 68,967,382 2.77 6.68 9.32 11.11 12.41 12.66 13.49 14.13 14.62 15.01 15.29 15.52 15.70 15.84 16.05 'Discounted cash flow rate of return at $30 per short ton of phosphate rock product, ^Year equals total preproduction years. ^Equipment value and working capital salvaged in year 20. 31 TABLE E-7. - Cash flow analysis at 50-ft overburden and 5.0 million short tons of product per year (Based on annual revenue of $149,986,517) Borehole mining Conventional mining Continuous Continuous Year Capital Cash flow rate of Capital Cash flow rate of expenditure return, ' pet expenditure return, ' pet 02 $145,755,000 -$145,755,000 $145,755,000 -$145,755,000 1 61,914,000 -3,324,061 93,338,000 -7,787,912 2 54,724,763 77,535,412 3 55,393,187 78,203,836 0.44 4 55,393,187 2.75 78,203,836 11.29 5 55,393,187 9.24 78,203,836 17.01 6 55,393,187 13.16 78,203,836 20.38 7 55,393,187 15.70 78,203,836 22.49 8 55,393,187 17.41 78,203,836 23.88 9 55,320,867 18.61 76,748,375 24.80 10 55,320,867 19.47 76,748,375 25.45 11 1,320,000 50,553,909 20.04 26,566,000 52,721,578 25.76 12 51,741,909 20.48 76,630,978 26.10 13 51,741,909 20.82 76,630,978 26.34 14 51,741,909 21.07 76,630,978 26.52 15 51,741,909 21.27 76,630,978 26.66 16 50,455,775 21.42 74,870,050 26.75 17 49,787,351 21.53 74,201,627 26.82 18 49,118,927 21.62 73,533,203 26.88 19 49,046,608 21.69 72,077,743 26.92 203 -25,820,000 74,866,608 21.77 -22,424,000 94,510,743 26.96 'Discounted eash flow rate of return at $30 per short ^Year equals total preproduction years. 3Equipment value and working capital salvaged in year ton of phosphate rock product. 20. 32 TABLE E-8. - Cash flow analysis at 100-ft overburden and 5.0 million short tons of product per year (Based on annual revenue of $149,986,517) Borehole mining Conventional mining Continuous Continuous Year Capital Cash flow rate of Capital Cash flow rate of expenditure return, 1 pet expenditure return, ' pet 0^ $145,755,000 -$145,755,000 $145,755,000 -$145,755,000 1 63,376,000 -6,625,651 103,786,000 -19,106,615 2 52,830,773 75,730,609 3 53,499,196 76,399,033 4 53,499,196 1.27 76,399,033 9.01 5 53,499,196 7.96 76,399,033 15.10 6 53,499,196 12.01 76,399,033 18.68 7 53,499,196 14.64 76,399,033 20.94 8 53,499,196 16.42 76,399,033 22.42 9 53,426,877 17.67 74,460,651 23.41 10 53,426,877 18.57 74,460,651 24.11 11 1,320,000 48,435,225 19.17 35,380,000 42,759,481 24.40 12 49,623,225 19.63 74,601,481 24.77 13 49,623,225 19.99 74,601,481 25.04 14 49,623,225 20.26 74,601,481 25.24 15 49,623,225 20.46 74,601,481 25.39 16 48,321,182 20.62 72,825,164 25.50 17 47,652,758 20.74 72,156,741 25.59 18 46,984,334 20.84 71,488,317 25.65 19 46,912,015 20.92 69,549,935 25.69 203 -26,792,000 73,704,015 21.01 -25,346,000 94,895,935 25.74 'Discounted cash flow rate of return at $30 per short ton of phosphate rock product, ^Year equals total preproduction years. 3Equipment value and working capital salvaged in year 20. 33 TABLE E-9. - Cash flow analysis at 150-ft overburden and 5.0 million short tons of product per year (Based on annual revenue of $149,986,517) Borehole mining Conventional mining Continuous Continuous Year Capital Cash flow rate of Capital Cash flow rate of expenditure return, ' pet expenditure return, ' pet 02 145,755,000 -$145,755,000 $145,755,000 -$145,755,000 1 64,866,000 -10,011,315 212,488,000 -123,280,186 2 50,880,609 69,831,638 3 51,549,032 70,500,062 4 51,549,032 70,500,062 5 51,549,032 6.60 70,500,062 1.28 6 51,549,032 10.80 70,500,062 6.77 7 51,549,032 13.53 70,500,062 10.25 8 51,549,032 15.38 70,500,062 12.58 9 51,476,713 16.68 67,990,429 14.16 10 51,476,713 17.63 67,990,429 15.31 11 1,320,000 46,316,540 18.25 45,807,000 26,521,260 15.65 12 47,504,540 18.74 67,747,560 16.33 13 47,504,540 19.11 67,747,560 16.86 14 47,504,540 19.40 67,747,560 17.26 15 47,504,540 19.62 67,747,560 17.57 16 46,186,589 19.79 63,229,012 17.80 17 45,518,165 19.93 62,560,588 17.98 18 44,849,741 20.03 61,892,164 18.12 19 44,777,422 20.11 59,382,532 18.23 203 -27,792,000 72,569,422 20.22 -41,244,000 100,626,532 18.38 'Discounted eash flow rate of return at $30 per short ^Year equals total preproduction years. ^Equipment value and working capital salvaged in year ton of phosphate rock product. 20. 34 TABLE E-10. - Cash flow analysis, borehole mining, at 230-ft overburden and 1.6 million short tons of product per year (Based on annual revenue of $49,995,506) Year Capital Cash flow Continuous rate Year Capital Cash flow Continuous rate expenditure of return, ' pet expenditure of return, ' pet 0^... $56,998,666 -$56,998,666 U 440,000 14,743,062 14.08 1.... 26,588,333 -8,682,988 12 15,139,062 14.70 2.... 16,253,793 13 15,139,062 15.18 3 16,599,573 14 15.139,062 15.56 4 16,599,573 15 15,139,062 15.86 5 16,599,573 0.14 16 14,568,288 16.10 6 16,599,573 5.08 17 14,222,507 16.28 7 16,599,573 8.32 18 13,876,726 16.42 8.... 16,599,573 10.55 19 13,852,620 16.54 9 16,575,467 12.13 203... -11,022,000 24,874.620 16.72 10 16,575,467 13.30 'Discounted cash flow rate of return at $30 per short ton of phosphate rock product. ^Year equals total preproduction years. ^Equipment value and working capital salvaged in year 20. TABLE E-11. - Cash flow analysis, borehole mining, at 230-ft overburden and 3.3 million short tons of product per year (Based on annual revenue of $99,991,012) Year Capital Cash flow Continuous rate Year Capital Cash flow Continuous rate expenditure of return, ' pet expenditure of return, ' pet 0^... $102,536,000 -$102,536,000 11 880.000 28,814,625 15.80 1 47,518,000 -12,616,907 12 29,606,625 16.36 2 32,003,570 13 29,606.625 16.79 3 32,527,647 14 29,606,625 17.13 4 32,527,647 15 29,606,625 17.39 5 32.527,647 2.87 16 28,632,560 17.60 6 32,527,647 7.48 17 28,108.483 17.76 7 32,527,647 10.49 18.... 27,584.406 17.88 8 32,527,647 12.56 19 27,536,193 17.99 9 32,479,434 14.20 203... -20.400,000 47,936,193 18.13 10 32,479,434 15.09 'Discounted cash flow rate of return at $30 per short ton of phosphate rock product. ^Year equals total preproduction years. ^Equipment value and working capital salvaged in year 20. TABLE E-12. - Cash flow analysis, borehole mining, at 230-ft overburden and 5.0 million short tons of product per year (Based on annual revenue of $149,986,517) Year Capital Cash flow Continuous rate Year Capital Cash flow Continuous rate expenditure of return, ' pet expenditure of return, ' pet 0^... $145,755,000 -$145,755,000 11 1,320,000 42,859,237 16.75 1.... 67.249.000 -15,427,477 12 44,047,237 17.27 2 47,760,347 13 44,047,237 17.68 3 48.428.770 14 44,047,237 17.99 4 48,428,770 15 44,047,237 18.24 5.... 48,428,770 4.34 16 42,703,832 18.43 6 48,428,770 8.78 17 42,035,408 18.58 7 48,428,770 11.68 18 41,366,984 18.70 8 48,428,770 13.66 19 41,294,665 18.79 9 48.356,451 15.06 203... -29.391.000 70,685,665 18.92 10 48,356,451 16.07 'Discounted cash flow rate of return at $30 per shor ^Year equals total preproduction years. 3Equipment value and working capital salvaged in yea t ton of phosphate rock product, r 20. 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