Coal Reserves of the Matewan
Quadrangle, Kentucky -A Coal Recoverability StudyU.S. Geological Survey Circular 9355
APPENDIX B.-ASSUMPTIONS
MINING METHODS
Local and practical mining methods were employed in the feasibility type mine planning. Four surface mining methods were examined: area stripping, mountain top removal, contour stripping, and auger mining. Contour stripping, auger mining, and mountain top removal were considered applicable; area stripping was not. Continuous miner and longwall operations were planned for deep mining, due to their high productivity, but conventional mining was not considered; however, it is recognized that conventional methods (drill, cut, and shoot) would have to be employed where geological conditions dictated. Recovery rates were determined for the applicable mining methods, and for the deep mining methods simple regression curves were fitted to the accumulated data for production rates; these were used to assign production rates for the deep mining methods by configuration and mining height. Surface transportation of coal, both washed and run-of-mine (ROM), was addressed by measuring haulage distances to known wash plant locations and rail loadouts.
Mine Recovery Factors
For many years a convenient rule of thumb of 50% has been used when estimating the amount of recoverable reserves in a loosely defined resource or mining area. This type of average does not consider either the minability of deposits, changes in technology, or changes in demand for coal. It is impossible to predict accurately the eventual recoverability of all coal deposits; however, a current average of recoverabilities depicting today's technology and economics will be useful for estimating deposits that are presently minable.
Lowrie (20)1 makes a very good observation that bears repeating.
"The rationale, traditionally, for using the convenient Figure of 50 percent as an acceptable approximation of average recovery is that it compensated for losses which were not ordinarily included at individual mines. This is an indefinite generalization which allows broad interpretation and perhaps erroneous exclusion of potentially recoverable deposits. Marginal deposits or those not ordinarily considered profitable or minable today, such as those behind prior workings, of poor quality, under adverse physical conditions, undermined, or underlying surface structures and so on, may be minable later rather than lost. Subsequent reevaluation of deposits as a result of changes in technology and economics should be made from a category other than lost, which has a permanent connotation. Definitive evaluation of losses attendant in mining such deposits should be deferred until the time of exploitation."
Each mining method considered for this project demonstrates a recovery unique to that particular method. For this reason, variations of each method were investigated. The investigation included creating several "typical" models and calculating the recoveries, analyzing published and unpublished recovery data from government and industry sources, and drawing upon personal experience.
Recovery Considerations
The mining methods considered in this report are:
1. Contour strip (surface), with two coal thickness categories: 12 in to 36 in, and greater than 36 in.
2. Auger (surface), with two coal thickness categories: 12 in to 36 in, and greater than 36 in.
3. Continuous miner, five entry system (underground), using two different pillar sizes: 40 ft by 40 ft, and 80 ft by 120 ft.
4. Longwall, three entry development (underground), using two different pillar sizes: 40 ft by 40 ft, and actual mine plan dimensions.
The following definitions that pertain to coal recovery, as used for this study, are derived from the USGS (21):
1. Recoverable coal.-The coal that is or can be extracted from a coal bed during mining. The term "recoverable" should be used in combination with "resources" and not with "reserves."
2. Recovery percent.-The percentage of coal extracted from a bed where the total tonnage originally in the bed is equal to 100%.
3. Recovery factor.-The estimated or actual percentage of coal, expressed as a decimal, that can be or was extracted from the coal originally in a bed or beds of an area, mine, district, field, basin, region, province, township, quadrangle, county, State, political province, nation, and (or) the world.
Six factors that are identified as significantly affecting recovery percentages in underground mines (20) are:
1. Pillaring system.
2. Top rock and conditions.
3. Bottom rock and conditions.
4. Marketability.
5. Coalbed thickness.
6. Productivity.
Thirteen factors that are identified as significantly affecting recovery percentages in strip mines (22) are:
1. Top coal removed with overburden.
2. Bottom coal left in place.
3. Coal lost in ribs between cuts.
4. Losses due to partings.
5. Losses due to other factors, such as equipment limitations and spillage.
6. Outcrops (coal exposed to weathering's degradation).
7. Utility, railway, and highway rights-of-way.
8. Streams.
9. Underground workings.
10. Oil and gas wells.
11. Property lines.
12. Buildings.
13. Other, such as landslide areas and cemeteries.
Five factors that are identified as significantly affecting recovery percentages in auger operations (22) are:
1. Auger diameter.
2. Auger spacing.
3. Average auger penetration.
4. Coalbed thickness.
5. Length of coalbed available for auguring.
Recovery Determination
A "typical" mine plan was drafted to scale with
sufficient detail to incorporate the standard pillars, entries,
and development works necessary to provide a representative
scenario of the particular mining type under study. The mine plan
was digitized, using the GSMAP computer program (23), to provide
two dimensional digital information of the mine plan. The
digitized data was reproduced on paper by a pen plotter to verify
its accuracy. The areas of all pillars were then calculated by
the GSMAP program. The accuracy and methodology of digitizing
using GSMAP was checked on three seams using multiple-pass
planimetering. The mining and restriction areas were nearly
identical between methods.
Standard, or "average," recovery factors were
established for each of several conditions and mining methods. It
is recognized these are not, and cannot be considered, definitive
under all conditions, but reflect today's technology and economic
conditions more accurately than the often used 50% factor.
The following mine recovery factors are used for this study:
1. For contour strip mines.-78% where the coal seam is less than 36 in thick, and 93% where the coal seam is greater than 36 in thick.
2. For auger mines.-30%.
3. For continuous miner mines.-62% where the pillars are 40 ft by 40 ft, and 57% where the pillars are 80 ft by 120 ft.
4. For longwall mines.-84% where the pillars are 40 ft by 40 ft, and 78% where the pillars vary in size.
Recovery Model Dependencies
The resource recoverability calculations consist of the entire process of determining, from raw data, the amount and salability of coal from the area in question. The viability and accuracy of the calculations and associated modeling is dependent upon (1) the existence of a proven geologic model of the coal bed, (2) mining methods, (3) mining recovery, (4) mining sequence, (5) coal quality, and (6) dilution factors. Also influencing the model are coal washability parameters, wash plant recovery, mine size optimization, equipment configurations, land ownership, and all of the various environmental, social, and technical restrictions to mining. Equally important is the care with which the data is collected and used. Throughout the modeling process, utmost care was taken to assure that current, state-of-the-art methods were employed and that error was minimized.
Production Rates
The rate of production for surface and underground mining
operations has long been discussed, studied, and computerized.
Information on many of the factors influencing production within
a specific coal seam, as shown in table B-1,
were not available during the data collection. Rather than
calculate idealized production rates from the influencing
factors, actual ROM production rates from Bureau evaluations and
from industry and government publications were used. Contour
strip and auger mining production rates were determined from mine
evaluations and heavy equipment production charts and were fairly
constant. Production rates for deep mining methods employing
continuous miners or longwalls varied over a wide range. Longwall
productivity appeared to correlate with mining height, and linear
regression analysis proved this assumption to be correct, with
very little scatter of the data points from the mean. Continuous
miner productivity was found to have fairly good correlation to
mining height after other mining factors had been accounted for.
These other factors (e.g., available spare or standby equipment,
supersections, remote controlled equipment, extremely good mining
conditions, and retreat pillar robbing) foster significantly
higher production rates than normal. Development mining,
development for longwalls, and some captive mines, have lower
than normal production rates. When the mine circumstances were
addressed, the continuous mining productivity could be broken out
into high, normal, and low production rates, and linear
regression analysis suggested good correlation between mining
height and production rate. These regression analyses are shown
in figures B-1-A through B-lD.
Average production rates were determined for several ranges of
mining heights and mining methods. Tables B-2
and B-3 show the production rates used
in this study. These seam height configurations were used to
specify production equipment sizing and capital costs for the
mine costing models.
Mine Design
A feasibility program utilizing the three main Upper Elkhorn
seams was begun in 1989. Isopach maps of the coal, interburden,
overburden, previously mined areas, and land use restrictions
were obtained from the USGS. Generalized mine plans were
developed and the close proximity of the three seams to each
other allowed the interaction from seam to seam to be studied
during mine planning. This feasibility study demonstrated that
preliminary mine plans and restrictions could be merged and an
estimate of the recoverable resources could be made. Based on
these findings, the program was expanded to include the remaining
minable seams in the Matewan quadrangle and to develop mining
cost models that would allow estimates of the economically
recoverable resources.
The surface mining configuration was planned to operate with two
separate fleets of equipment in two different locations at the
same time. This procedure utilized support equipment, enhanced
coal production and blending, and allowed sequencing of auger
mining. The planning process assumed common ownership of surface
and mineral rights and assumed that mining would be done in a
logical, orderly manner for maximum recovery of the resource.
Only contour stripping methods were applied in the Matewan
quadrangle. Neither area mining nor mountain top removal was
planned. The production parameters in contour stripping were
dependent upon seam thickness. Seams 36 in thick or greater were
assumed to have stripping rates of 6,500 BCY per shift, whereas
seams that ranged in thickness from 12 in to 36 in had stripping
rates of 5,200 BCY per shift. Mine bench widths varied, but a
minimum of 80 ft was used for all stripping. The 80-ft minimum
width allowed endloaders to safely load trucks and provided the
trucks with enough room to turn around on the bench. Since the
average ground slope is about 26' (48.8%), the minimum bench
width could be maintained with seam thicknesses of less than 24
in. These conditions, along with the thin - interburden between
many of the seams, would allow multiple seam stripping. For this
reason, the 80-ft minimum width bench was used for all
strip-minable resources with seam thicknesses between 12 in and
24 in. During the surface planning, logical portal locations were
noted for underground development. Surface mine production was
evaluated using a work schedule of 8 hours per shift, 2 shifts
per day, 5 days per week (240 days per year). It was assumed that
the surface mining equipment would develop the
"face-up" area for the deep mine portals, mine offices,
and applicable stockpile areas. Reclamation plans would be
developed that would leave enough bench area for production haul
roads from the deep mine stockpiles.
Auger mining followed closely behind the stripping operations and
utilized the coal production equipment and support equipment. It
was assumed that the stripping operation left the highwall and
bench in a condition that would require little maintenance by the
auger operations. Twin-headed augers were the chief production
equipment, having a compliment of drill heads and auger steel
matched to the coal seam thickness. Average recovery rates of 30%
and average depth of holes of 60 ft were assumed. Highwall
miners, while not specified, could be an option for the thicker
seams.
Deep mine development was laid out with five mains, 18 ft to 20
ft wide, having normal offset barrier pillars and production
panels employing room-and-pillar mining methods laid out at right
angles to the mains. Submains were laid out beneath and parallel
to the mountain ridges (spurs). Minimum panel widths were five
entries; as the panels approached the outcrop, the minimum
advance was with two entries. Only mining with continuous miners
and longw@ was considered. The use of conventional roomand-pillar
mining (drill, cut, and shoot) is fairly common in the Matewan
quadrangle; however, wherever possible, operators are turning to
continuous miners. Also, it is recognized that some coal seams
are best mined by conventional methods due to particular
geological conditions. That information was not available to the
authors in the detail necessary for planning; therefore,
conventional mining methods were not addressed in this study. The
optimum-size operation was assumed to be two continuous miner
production units for continuous mining methods, and two
continuous miners and one longwafl panel for a longwall
operation. Minimum mining heights for continuous miners was set
at 24 in of seam thickness and 5 in of out-of-seam dilution. The
longwar minimum seam thickness was 42 in, with 3 in of
out-of-seam dilution. Because of mining height restrictions on
equipment, continuous miner operations had four separate height
ranges: 24 to 42 in, 42 to 72 in, 72 to 96 in, and greater than
96 in. Also because of restrictions on equipment, longwall mining
had three mining heights: 42 to 72 in, 72 to 96 in, and greater
that 96 in. Equipment specifications, capitation, production,
etc., were all determined by these mining heights in the recovery
and costing models. In addition to the minimum thickness of 42 in
of seam height for longwalls, at present a machine size
limitation (motor to horsepower limitations), panels were laid
out with three entries on both sides of the panel, a minimum
width of 550 ft, and a minimum length of 4,000 ft. Areas
considered for longwah mining had to contain enough coal resource
to depreciate the longwar equipment used in that seam. AR deep
mine production was scheduled for 8 hours per day, 2 shifts per
day, 5 days per week (240 days per year). Production rates are
noted in tables 5 and 6 by mining method and height.
Development methodology for the basic mine plans. is listed
below:
1. Understanding of the coalbed to be planned and the supe@acent and subjacent minable seams.
2. Identification of the effect of the land use restrictions on the subject bed.
3. Ground slope determination, along the outcrop, to outline areas having an undisturbed slope greater than 32'-for technical restrictions and for determining the highwall stripping ratio cutoff.
4. Surface mine design using the maximum 20:1 highwall ratio to determine the bench widths and stripping areas. Where the highwall ratio could be greater than 20:1, a minimum bench width of 80 ft was used.
5. Auger mining planned to coordinate with the stripping. Production tonnages were calculated by bench length, seam thickness, depth of auger holes, and normal recovery rate.
6. Underground mine development planned using working site areas prepared during stripping. Mains and submains were planned to be driven parallel to and beneath the mountain ridges.
7. Evaluation of seams for areas that met or exceeded the minimum longwall criteria. When a potential longwaff area was found, the panels were laid out and the continuous miner plans were designed around the longwaff plan.
8. Integration of the coal-haulage zone map with the mine plans. Original resources, restrictions, and minable resources were calculated for each haulage zone.
Using the above guidelines, the first mine plan maps were constructed for the Upper Elkhorn 3B seam (fig. B-2). Planning for the Upper Elkhorn 3D seam followed, and conflicts between the mining plans for the 3B and 3D seams were resolved where necessary (i.e., where the interburden between the two seams was less than 40 ft). Next, the Upper Elkhorn 3.5 seam was planned. Since the interburden between the 3.5 and 3D seams exceeded 40 ft in thickness, there were no mining plan conflicts between these seams; however, the interburden between the Upper Elkhorn 3.5 and Williamson seams was thinner than 40 ft in many areas and caused major mining plan conflicts between the two seams. In this same way, mine plan maps of the other eighteen coal seams were subsequently constructed.
SURFACE TRANSPORTATION
Topography in the Matewan quadrangle is rugged, having valley wall slopes ranging from 1Y to 320 (27% to 639o) and valley floors sloping from r to 13" (4% to 23%). Four major ridges control the watersheds in the quadrangle. During the initial tour and investigation of the quadrangle, the authors noted that coal was not transported over these main ridges. Indeed, only one ridge was crossed by a paved highway. Therefore, for the sake of efficiency, local practice was for all loaded trucks to haul coal downhill by the most convenient route to their destinations. Locations of preparation plants and train loadouts were obtained from the DSMRE permit maps. State, Federal, and county roads were located on the USGS 7-1/2-minute topographic map. After reviewing the geology and the potential for mining within the different watersheds, the quadrangle was divided into 16 haulage zones (fig. B-3). The geographical center of all minable coal beds was located in each haulage zone and assumed to be the mine coal stockpiling area. Haulage distances were estimated from the stockpile area to the closest preparation plant and/or rail loadout. In this haulage scenario, the following assumptions were made
1. The closest wash plant always had the capacity to handle the delivered ROM coal. 2. Only wash plants with rail loadouts were used, thus eliminating double handling of the coal. Studies were conducted to see if the costs would be less to haul to a nearby mine washing facility, clean the coal reload the trucks, and then haul to a rail facility. However, none of the Matewanquadrangle coal seams contained enough ash to justify loading the coal in a truck the second time. Of course, this justification is valid only if enough washing capacity is available from facilities with rail loading capabilities.
3. No new washing facilities were necessary; however, it was assumed that all wash plants were operated at high efficiency rates, with idealized labor needs, and at normal operating costs.
4. All surface haulage of coal was done by contractor owned- and-operated trucks. Coal haulage contract costs for the southeast Kentucky, southern West Virginia, and southwestern Virginia areas were calculated as a fixed cost per truck plus a cost per ton-mile. These are included in the mine cost models as a basis for calculating the coal haulage costs. Escalating factors are used in the models to keep costs on a current level. Table 7 shows the oneway haulage distance and the cost assigned to each zone, for the Matewan quadrangle, as used in this study.
The next recovery calculation deals with cleaning (washing) the ROM product to produce a salable product, The preparation plant recovery, and the resulting salable product, are calculated for each haulage zone by mining method and seam thickness category (tables B5-B8). Review of the central Appalachian coal quality data, modern coal preparation plants, and coal spot and contract markets provided a basis for the models. The following items were of considerable importance:
1. Coal washing did not significantly improve the sulfur content in the salable product (i.e., most of the sulfur was tied up in the organic material, not as pyrite; therefore, it could not be easily removed).
2. Most of the modern preparation facilities examined had processes that would recover an average of 94% of the available coal from the ROM tonnage and would substitute only 6% of the parting material for coal in the final washed product. These average figures were incorporated into the recovery model because definitive density and washability information was not available in sufficient detail for most seams in the quadrangle.
3. The assumed cutoff between washed and direct-shipped coal was based on an ash content of 9%, or greater, in the ROM product. In-seam parting material and out-of-seam dilution were assumed to be 100% ash. Parting material density was assumed to be 2,400 tons per acre-foot. Coal was assumed to have a density of 1,800 tons per acre-foot.
The total recoverable resource is calculated by subtracting from the total original resource (including coal, inseam parting, and mining dilution) previously mined-out and/or abandoned resources and resources unavailable due to environmental, technical, and barrier restrictions.
From the minable resources for each mining method, the associated mining and washing losses are subtracted. This results in the amount of recoverable resource that is available for sale, with no quality or mining cost restrictions included. Table B-9 exhibits the results of the recovery calculations for one seam. The recoverable resources-by haulage zone, mining method, and seam thickness category are then used in the mine costing models to generate the operating costs for these recoverable coal tonnages.
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