Petrology and Geochemistry of the Harlan , Kellioka , and Darby Coals from the Louellen 7 . 5-Minute Quadrangle , Harlan County , Kentucky

The Harlan, Kellioka, and Darby coals in Harlan County, Kentucky, have been among the highest quality coals mined in the Central Appalachians. The Middle Pennsylvanian coals are correlative with the Upper Elkhorn No. 1 to Upper Elkhorn No. 31⁄2 coals to the northwest of the Pine Mountain thrust fault. Much of the mining traditionally was controlled by captive, steel-company-owned mines and the coal was part of the high volatile A bituminous portion of the coking coal blend. Overall, the coals are generally low-ash and low-sulfur, contributing to their desirability as metallurgical coals. We did observe variation both in geochemistry, such as individual lithologies with significant P2O5/Ba + Sr/Rare earth concentrations, and in maceral content between the lithotypes in the mine sections.


Introduction
Harlan County, Kentucky, has had a long, colorful, and, at times, violent mining history [1][2][3].None of that would have been the case without a base of extensive reserves of high quality coal, much of it directed towards the metallurgical coal market and mined at steel-company-owned mines [4,5].
In this investigation, we examined the petrology and chemistry of coals in Harlan County southeast of Pine Mountain, on the Pine Mountain thrust sheet (Figure 1).In particular, we appraised, in ascending order, the Harlan, Kellioka, and Darby coals of the Pikeville Formation of the Middle Pennsylvanian Breathitt Group (Figure 2).These coals were traditionally some of the better coking coal reserves.The study coals are the approximate correlatives of the Upper Elkhorn No. 1 and Upper Elkhorn No. 2, Upper Elkhorn No. 3 or Van Lear, and the Upper Elkhorn No. 3½ coals, respectively, to the northwest of Pine Mountain [6].The underlying Path Fork coal, the correlative of the Blue Gem and Pond Creek coals on the northwest side of the Pine Mountain thrust fault, was investigated by Hatton et al. [7].Below the Path Fork, the Grundy Formation Hance coal, correlative of the Manchester and many other coals on the northwest side of the Pine Mountain thrust fault, was studied by Esterle and Ferm [8] as well as Hubbard et al. [9].The study areas for the Path Fork and Hance coals, however, although on the thrust sheet, were to the southwest of the present study area.The environments of deposition for Kentucky coals have been investigated by the Kentucky Geological Survey and the University of Kentucky Center for Applied Energy Research [7,9,[11][12][13][14]; John Ferm and his students at various universities, most recently (1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999) at the University of Kentucky (for example: Esterle and Ferm [8]); and outside researchers [15,16].With the exception of Esterle and Ferm [8], Hatton et al. [7], and Hubbard et al. [9], the studies emphasized settings to the northwest of Pine Mountain.Much of the mining of the coals preceded the 1980s and 1990s studies noted above.As such, the current examination of coals collected in the 1980s represents one of the few detailed studies of Harlan County coals.The environments of deposition for Kentucky coals have been investigated by the Kentucky Geological Survey and the University of Kentucky Center for Applied Energy Research [7,9,[11][12][13][14]; John Ferm and his students at various universities, most recently (1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999) at the University of Kentucky (for example: Esterle and Ferm [8]); and outside researchers [15,16].With the exception of Esterle and Ferm [8], Hatton et al. [7], and Hubbard et al. [9], the studies emphasized settings to the northwest of Pine Mountain.Much of the mining of the coals preceded the 1980s and 1990s studies noted above.As such, the current examination of coals collected in the 1980s represents one of the few detailed studies of Harlan County coals.The environments of deposition for Kentucky coals have been investigated by the Kentucky Geological Survey and the University of Kentucky Center for Applied Energy Research [7,9,[11][12][13][14]; John Ferm and his students at various universities, most recently (1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999) at the University of Kentucky (for example: Esterle and Ferm [8]); and outside researchers [15,16].With the exception of Esterle and Ferm [8], Hatton et al. [7], and Hubbard et al. [9], the studies emphasized settings to the northwest of Pine Mountain.Much of the mining of the coals preceded the 1980s and 1990s studies noted above.As such, the current examination of coals collected in the 1980s represents one of the few detailed studies of Harlan County coals.

Methods
Samples were collected both at mines and from company-supplied cores in the 1980s (The samples from the 1980s represent the last widespread availability of mine samples and the serendipitous availability of core samples.Aside from shifts in mining, the CAER sampling interests shifted to other coals) (locations on Figure 1).The coals were collected as whole coal and bench samples, excluding rock partings greater than about 1-cm thick.The proximate and sulfur analyses were conducted at the University of Kentucky Center for Applied Energy Research (CAER) following ASTM procedures.Major oxides were analyzed at the CAER by X-ray fluorescence following procedures outlined by Hower and Bland [17].All of the latter analyses were done shortly after sampling.Inductively coupled plasma mass spectrometry (X series II ICP-MS, ThermoFisher, Waltham, MA, USA), in pulse counting mode (three points per peak), was used to determine trace elements in the coal ash samples obtained from raw coals at 815 ˝C.The ICP-MS analyses were conducted at the China University of Mining and Technology (Beijing) on ash samples provided by the CAER.For ICP-MS analysis, samples were digested using an UltraClave Microwave High Pressure Reactor (Milestone, Milano, Italy) [18].The digestion reagents for each 50-mg coal ash sample are 2-mL 65% HNO 3 and 5-mL 40% HF [18].The Guaranteed-Reagent HNO 3 and HF for sample digestion were further purified by sub-boiling distillation.Arsenic and Selenium were determined by ICP-MS using collision cell technology (CCT) in order to avoid disturbance of polyatomic ions [19].Multi-element standards (Inorganic Ventures: CCS-1, CCS-4, CCS-5, and CCS-6; NIST 2685b and Chinese standard reference GBW 07114) were used for calibration of trace element concentrations.The method detection limit (MDL) for each of the trace elements, calculated as three times the standard deviation of the average from the blank samples (n = 10), is listed in Table 1.Maceral analysis, originally done shortly after the sampling, was re-examined for this study following the ICCP nomenclature [20,21].The petrology was done using Leitz Orthoplan microscopes with oil-immersion, reflected-light, 50-x objectives on particulate pellets prepared to a final 0.05-µm-alumina polish.The reflectance was measured using a 547-nm bandpass filter and a 9-µm-diameter measuring spot with a photomultiplier calibrated against a series of glass reflectance standards in the range of the coal reflectances.

Proximate and Sulfur Analysis
The Harlan coal is the thickest of the three coals investigated; with two of the sections exceeding 2.72 m.The Harlan ash yield is higher and more variable than in the Kellioka and Darby coals (Table 2), discussed below.Several samples exceed 20% ash yield, with sample 6400 having 53% ash yield, sufficient to classify it as carbonaceous shale.On the whole-coal basis, the Harlan coal is a low-to medium-S coal, also higher than in the other two coals; exceeding 2% S in the 23.8%-ash-yield sample 6384.With the relative increase in sulfur compared to the other two coals, we can infer that the Harlan peat was subjected to a more significant marine influence.The nature and extent of such an influence is difficult to discern with just three detailed sections.With the exception of this study, the Harlan coal has not been studied in the same detail as some other eastern Kentucky coals (see Introduction).The mined Harlan coal, destined for the metallurgical market, was beneficiated prior to shipment from the facility; therefore, much of the high-ash and high-S coal was not included in those shipments.The ash yield of Harlan coals varies somewhat in our samples depending upon the decisions made about sampling benches.For example, in retrospect, sample 6400 perhaps should not have been included in the whole-coal sample although it would have been part of the mined section along with other partings and portions of the roof and floor.As noted above, coal beneficiation would eliminate many of the higher mineral matter particles, producing a low-ash product.
With the exception of the lower bench at both of the benched sites, the ash yield of the Kellioka coals is less than 5%; sulfur content is generally low, exceeding 0.9% only in the top two benches at both sites and the basal bench at site 6360.The Darby has a low-ash, low-S content, with the exception of the thin top lithotype (sample 6367) at site 6366 with 7.44% ash yield and 36.4% total vitrinite (ash-free basis).

Petrology
The petrology of the coals is presented on Table 3.The lithologic profile of the Harlan coal is shown in Figure 3.Despite some similarities between nearby sites, particularly between seam sections 6378 and 6392, the continuity is not as great as we have seen in studies of the Pond Creek and Blue Gem coals [22,23], the Fire Clay coal [12,24,25], although significant short-distance, few-hundred-meter variation is known to occur in other economically important eastern Kentucky coals [23,26].
The total vitrinite in the whole Harlan coals ranges from 58% to 75% (mineral-included basis), the lowest being in sample 6273 owing to the high mineral content.There is a wide variety of maceral distributions among the bench/lithotype samples.This is well illustrated in the low-mineral matter samples 6399 and 6398 of the 6392 sequence.The sample 6399 bright clarain, bench 7 of 11, has 81.6% total vitrinite.In contrast, sample 6398, the thin, 3.05-cm durain directly overlying 6399, has 31.2%vitrinite, 31.6%inertinite, and 36.6% liptinite.With a few exceptions, such as sample 6357 with less than 41% total vitrinite and sample 6364 with less than 48% total vitrinite, the Kellioka coal samples have over 60% vitrinite.The highest vitrinite is found in the relatively high-S upper benches.The inertinite assemblages in the Kellioka coals are dominated by varying amounts of fusinite, semifusinite, micrinite, and inertodetrinite.Macrinite is most abundant in the low-vitrinite lithologies 6357 and 6364, at 6.4% and 4.6% (mineral-free basis), with 2.2% and 2.4% macrinite found in samples 6355 and 6356, respectively, the lithologies with 63%-65% vitrinite.The liptinite assemblages in the Kellioka coals are dominated by sporinite with lesser amounts of resinite and cutinite.
The whole-coal Darby samples all have at least 68.9% total vitrinite (ash-free basis) and none of the other lithotypes have less than 55% vitrinite.The inertinite is generally a function of varying amounts of fusinite, semifusinite, micrinite, and inertodetrinite.Macrinite exceeds 1.5% only in the whole coal sample 6267 and the lithotype sample 6367.The liptinite assemblages in the Darby samples are dominated by sporinite with lesser amounts of resinite and minor amounts of cutinite.

Elemental Geochemistry
Table 4 lists the concentrations of major-element oxides and trace elements in the samples from the Harlan, Kellioka, and Darby coals.Compared to average values for world hard coals reported by Ketris and Yudovich [26] and based on the enrichment classification of elements in coal outlined by Dai et al. [27], only the averages of Co in the Harlan coals and As in the Kellioka coals are slightly enriched, with CC (CC = ratio of element concentration in investigated coals vs. world hard coals) 2.10 and 2.02, respectively.Lithium and Cu in the Harlan coals have CC of 1.60 and 1.84, respectively.The average concentrations of other trace elements in the three coals are either close to or depleted relative to the averages of the same elements for the world hard coals (Figure 4).Particularly, the concentrations of quite a number of trace elements in Kellioka and Darby coals are depleted (Figure 4).According to Dai et al. [27], elemental concentrations in coal can be classified as six levels relative to the averages for world coals, unusually enriched (CC > 100), significantly enriched (10 < CC < 100), enriched(5 < CC < 10); slightly enriched (2 < CC < 5); close to the average values for world hard coals (0.5 < CC < 2), and depleted (CC < 0.5).With a few exceptions, such as sample 6357 with less than 41% total vitrinite and sample 6364 with less than 48% total vitrinite, the Kellioka coal samples have over 60% vitrinite.The highest vitrinite is found in the relatively high-S upper benches.The inertinite assemblages in the Kellioka coals are dominated by varying amounts of fusinite, semifusinite, micrinite, and inertodetrinite.Macrinite is most abundant in the low-vitrinite lithologies 6357 and 6364, at 6.4% and 4.6% (mineral-free basis), with 2.2% and 2.4% macrinite found in samples 6355 and 6356, respectively, the lithologies with 63%-65% vitrinite.The liptinite assemblages in the Kellioka coals are dominated by sporinite with lesser amounts of resinite and cutinite.
The whole-coal Darby samples all have at least 68.9% total vitrinite (ash-free basis) and none of the other lithotypes have less than 55% vitrinite.The inertinite is generally a function of varying amounts of fusinite, semifusinite, micrinite, and inertodetrinite.Macrinite exceeds 1.5% only in the whole coal sample 6267 and the lithotype sample 6367.The liptinite assemblages in the Darby samples are dominated by sporinite with lesser amounts of resinite and minor amounts of cutinite.

Elemental Geochemistry
Table 4 lists the concentrations of major-element oxides and trace elements in the samples from the Harlan, Kellioka, and Darby coals.Compared to average values for world hard coals reported by Ketris and Yudovich [26] and based on the enrichment classification of elements in coal outlined by Dai et al. [27], only the averages of Co in the Harlan coals and As in the Kellioka coals are slightly enriched, with CC (CC = ratio of element concentration in investigated coals vs. world hard coals) 2.10 and 2.02, respectively.Lithium and Cu in the Harlan coals have CC of 1.60 and 1.84, respectively.The average concentrations of other trace elements in the three coals are either close to or depleted relative to the averages of the same elements for the world hard coals (Figure 4).Particularly, the concentrations of quite a number of trace elements in Kellioka and Darby coals are depleted (Figure 4).According to Dai et al. [27], elemental concentrations in coal can be classified as six levels relative to the averages for world coals, unusually enriched (CC > 100), significantly enriched (10 < CC < 100), enriched(5 < CC < 10); slightly enriched (2 < CC < 5); close to the average values for world hard coals (0.5 < CC < 2), and depleted (CC < 0.5).Because the three coals have relatively low ash yields and most of the trace elements in the coals have inorganic affinity, the concentration of trace elements in ashes of the three coals were compared to the averages of the same elements for the world coal ash reported by Ketris and Yudovich [26].Elements including Li, Co, Cu, As, and Ta in the Harlan coal ashes, elements P, Co, Cu, As, Sr, Ba, Ta, and Pb in the Kellika coal ashes, and elements Be, Co, Ni, Cu, Ga, Ge, Sr, Y, Mo, Sn, Sb, Ba, and Tl in the Darby coal ashes are relatively enriched (Figure 5).Because the three coals have relatively low ash yields and most of the trace elements in the coals have inorganic affinity, the concentration of trace elements in ashes of the three coals were compared to the averages of the same elements for the world coal ash reported by Ketris and Yudovich [26].Elements including Li, Co, Cu, As, and Ta in the Harlan coal ashes, elements P, Co, Cu, As, Sr, Ba, Ta, and Pb in the Kellika coal ashes, and elements Be, Co, Ni, Cu, Ga, Ge, Sr, Y, Mo, Sn, Sb, Ba, and Tl in the Darby coal ashes are relatively enriched (Figure 5).The correlation coefficient (r = 0.59) of Li and ash yield in the Harlan coals indicates an inorganic affinity.Further, lithium positively correlated to Mg (r = 0.74), SiO2 (r = 0.61), Al2O3 (r = 0.740), and K2O (r = 0.84), indicatingit is mainly associated with clay minerals (e.g., kaolinite, mixed-layer illite/smectite, or illite).
The Cu in the Harlan coals is positively correlated to Ash (r = 0.87), Al2O3 (r = 0.77), SiO2 (r = 0.80), and K2O (r = 0.76), but has a weak correlation coefficient with total sulfur (r = 0.37), indicating Cu mainly occurs in clay minerals.The correlation coefficient of Co and ash is 0.41, indicating that Co has a dominant inorganic association and a small proportion may be associated with organic matter.
The concentrations of As in Kellioka coals and coal ashes are 16.8 and 378 µg/g respectively, much higher than their averages for world hard coals and coal ashes (9 and 46 µg/g, respectively [26].The adverse effects on environment of arsenic in Kellioka coals should be of concern.The correlation coefficient of As-St (r = 0.77) and As-Fe2O3 (r = 0.63), and Fe-St (r = 0.85) (Figure 6) of the Kellioka coals indicate that As is mainly associated with pyrite.
With exceptions of Li, Cu, and Co in the Harlan coals, and As in the Kellioka coals, the remaining elements in the three coals are either close to or lower than the averages for world hard coals [26], and most of them have an inorganic affinity (Figure 7).However, some elements including Be, Ga, Ge, Sr, Mo, Sn, and W have different modes of occurrence in the three coals.For example: The correlation coefficient of Be and ash yield in the Harlan and Darby coals(r = 0.17, and r = −0.14, respectively) show an organic-inorganic mixed affinity (also see Figure 8).Be in the Kellioka coals, however, showed inorganic affinity (r = 0.95; Figure 8).The correlation coefficient (r = 0.59) of Li and ash yield in the Harlan coals indicates an inorganic affinity.Further, lithium positively correlated to Mg (r = 0.74), SiO 2 (r = 0.61), Al 2 O 3 (r = 0.740), and K 2 O (r = 0.84), indicatingit is mainly associated with clay minerals (e.g., kaolinite, mixed-layer illite/smectite, or illite).
The Cu in the Harlan coals is positively correlated to Ash (r = 0.87), Al 2 O 3 (r = 0.77), SiO 2 (r = 0.80), and K 2 O (r = 0.76), but has a weak correlation coefficient with total sulfur (r = 0.37), indicating Cu mainly occurs in clay minerals.The correlation coefficient of Co and ash is 0.41, indicating that Co has a dominant inorganic association and a small proportion may be associated with organic matter.
The concentrations of As in Kellioka coals and coal ashes are 16.8 and 378 µg/g respectively, much higher than their averages for world hard coals and coal ashes (9 and 46 µg/g, respectively [26].The adverse effects on environment of arsenic in Kellioka coals should be of concern.The correlation coefficient of As-St (r = 0.77) and As-Fe 2 O 3 (r = 0.63), and Fe-St (r = 0.85) (Figure 6) of the Kellioka coals indicate that As is mainly associated with pyrite.
With exceptions of Li, Cu, and Co in the Harlan coals, and As in the Kellioka coals, the remaining elements in the three coals are either close to or lower than the averages for world hard coals [26], and most of them have an inorganic affinity (Figure 7).However, some elements including Be, Ga, Ge, Sr, Mo, Sn, and W have different modes of occurrence in the three coals.For example: The correlation coefficient of Be and ash yield in the Harlan and Darby coals (r = 0.17, and r = ´0.14, respectively) show an organic-inorganic mixed affinity (also see Figure 8).Be in the Kellioka coals, however, showed inorganic affinity (r = 0.95; Figure 8).Gallium in the Harlan and Kellioka coals shows an inorganic affinity (r = 0.84 and r = 0.99 respectively; Figure 8D,E), but in the Darby coals it has an organic-inorganic mixed affinity (r = 0.17; Figure 8F).
Germanium, Sr, and Mo in the three coals show an organic-inorganic mixed affinity (Figure 8).Although the correlation coefficient of Ge and ash yield in Kellioka coals is high (r = 0.98; Figure 8H), there are only two points fall in the area with Ge concentration higher than 8 µg/g.However, twelve scattered points fall in the area of Ge concentration of less than 1.6µg/g, showing an organic-inorganic mixed affinity.The correlation coefficient of Sr and ash yield in the Kellioka is also high (r = 0.77), the scattered points in the Figure 8K (only one point with high Sr concentration, 587µg/g) also indicate a mixed affinity.
Tin and W show an inorganic affinity in the Harlan and Kellioka coals but have an inorganic-organic mixed affinity in the Darby coals (Figure 8).
Although the average concentrations of most of trace elements in the three coals are not enriched relative to the averages of the world coals, some trace elements are relatively enriched in some benches of each coal seam.For example, see Sections 3.3.1-3.3.3 below.

The Harlan coals
The Harlan geochemistry has hints of the high values of certain minor element associations noted in other coals, such as TiO 2 + Zr, V + Cr, and Ba + Sr (such as the Darby for the latter association, see below).The TiO 2 + Zr has been found to be associated with detrital minerals in the basal benches of some coals [17,28]; V + Cr, possibly in association with clay minerals, can be enriched in the top bench; and Ba and Sr can be associated with phosphates and carbonates [28,29].The fourth benches in both sections 6378 and 6392, bench 6 of 9 of section 6378, and bench 8 of 11 of section 6392 have some of the higher Cr and V values.In all cases, these benches underlie a parting, an event nearly as significant as the final demise of the coal [13], therefore, also an event likely to be marked by the same geochemical indicators as the top of the coal.
The Ba + Sr content exceeds 6000 ppm in sample 6401, but this is considerably lower than the high values encountered in the Darby coal (see below).Certain benches in the 6378 section also have >1000 ppm (ash basis) Ba and/or Sr, in some cases corresponding with P 2 O 5 > 0.5% (ash basis).The Rare earth elements + Y (REY) content is not high by what might be considered to be potential commercial standards (perhaps 900 ppm on the ash basis) [30].We note, however, that the samples with REY >600 ppm correspond to the samples with P 2 O 5 >0.5%, not surprising since the REY are often found in phosphate minerals.

The Kellioka coals
The high-Fe 2 O 3 content generally occurs in the top two benches, the higher pyritic S lithologies.These are also the benches with the highest As concentrations, up to 1231 ppm As and 0.39% S py (both on ash basis) in sample 6354.The third benches from the top at both sites, samples 6355 and 6363, are the highest CaO samples.Very little mineral matter is evident in microscopic examination and carbonates are not among the microscopic minerals.The concentrations of Sr, Ba, and REY are generally highest in the same samples, for example >11000 ppm Sr + Ba and 929 ppm REY in sample 6364, corresponding to a phosphate concentration of 3.50% (all on the ash basis).

The Darby coals
The samples generally have a relatively high amount of Ba + Sr, with sample 6264 (sample 3 of 4 from the 6261 series) exceeding 14560 ppm and sample 6370 (sample 4 of 5 from the 6366 series) having >11000 ppm Ba + Sr (both on the ash basis).Such levels of Ba + Sr might be attributable to associations with carbonates or phosphates.Neither sample has the highest REY content of the Darby samples, nearly 1700 ppm in sample 6262 (bench 1 or 4 from the 6261 series).Without further microbeam-based mineralogy studies, we cannot be certain about the association.Vanadium and Cr, known in other coals to be associated with clays and frequently observed in the uppermost lithotype of many coal beds [31,32], are highest in the top lithology of both bench suites.Germanium and Ga are relatively high in the upper and lower benches of the 6261 series.Germanium is known to be enriched in coal lithotypes bordering the roof, floor, or partings [33].
The concentrations of rare earth elements (Table 5) in the three coals are lower than the averages for the world coals [26]; Figure 4), but their concentrations in coal ashes are close to the average for the world coal ash (Ketris and Yudovich [26]; Figure 5).The three coal seams have different REY distribution patterns: (1) With the exceptions of some samples (samples 6387, 6386, and 6383 in Figure 9C; samples in Figure 9D; samples 6397 and 6398 in Figure 9E; samples 6399, 6402, and 6403 in Figure 9F), the REY in the Harlan coals are characterized by M-type enrichment.
(2) The Kellioka coal samples do not show much fractionation among the L-, M-, and H-REY, with the exception of sample 6358, which has a distinct H-REY enrichment type (Figure 10).
(3) With a few exceptions of samples 6264, 6370, 6371, and 6369, which a slight M-REY enrichment, the Darby coal samples are enriched in heavy REY relative to the upper continental crust [35] (Figure 11).Vanadium and Cr, known in other coals to be associated with clays and frequently observed in the uppermost lithotype of many coal beds [31,32], are highest in the top lithology of both bench suites.Germanium and Ga are relatively high in the upper and lower benches of the 6261 series.Germanium is known to be enriched in coal lithotypes bordering the roof, floor, or partings [33].
The concentrations of rare earth elements (Table 5) in the three coals are lower than the averages for the world coals [26]; Figure 4), but their concentrations in coal ashes are close to the average for the world coal ash (Ketris and Yudovich [26]; Figure 5).The three coal seams have different REY distribution patterns: (1) With the exceptions of some samples (samples 6387, 6386, and 6383 in Figure 9C; samples in Figure 9D; samples 6397 and 6398 in Figure 9E; samples 6399, 6402, and 6403 in Figure 9F), the REY in the Harlan coals are characterized by M-type enrichment.
(2) The Kellioka coal samples do not show much fractionation among the L-, M-, and H-REY, with the exception of sample 6358, which has a distinct H-REY enrichment type (Figure 10).
(       Geochemical influences were likely to have been complex.Aside from the expected terrigenous influx at the time of deposition, the region was subject to the influence of hydrothermal fluids during diagenesis.This is most notable on the footwall side of the Pine Mountain thrust fault where an enhanced coal rank compared to correlative coals on the thrust sheet (as we are studying here), albeit all within the high volatile A bituminous rank range, are accompanied by enhanced levels of Cl and Hg and other trace metals [34].While not previously demonstrated, it is possible that the coals on the Pine Mountain thrust sheet could have been similarly influenced, if not from fluids squeezed out in advance of the Pine Mountain thrust sheet, then by fluid flow influenced by thrust faults to the southeast in Virginia.Examination of the Al2O3 vs. TiO2 plot (Figure 12) provides a view of another aspect of mineral influx.The Harlan benches have a much wider distribution than the Kellioka or Darby benches, having both higher and lower Al2O3 and lower TiO2 than the other coals.Among the Darby samples with the highest TiO2, bench samples 6262 and 6368 have strikingly different REY  Geochemical influences were likely to have been complex.Aside from the expected terrigenous influx at the time of deposition, the region was subject to the influence of hydrothermal fluids during diagenesis.This is most notable on the footwall side of the Pine Mountain thrust fault where an enhanced coal rank compared to correlative coals on the thrust sheet (as we are studying here), albeit all within the high volatile A bituminous rank range, are accompanied by enhanced levels of Cl and Hg and other trace metals [34].While not previously demonstrated, it is possible that the coals on the Pine Mountain thrust sheet could have been similarly influenced, if not from fluids squeezed out in advance of the Pine Mountain thrust sheet, then by fluid flow influenced by thrust faults to the southeast in Virginia.Examination of the Al2O3 vs. TiO2 plot (Figure 12) provides a view of another aspect of mineral influx.The Harlan benches have a much wider distribution than the Kellioka or Darby benches, having both higher and lower Al2O3 and lower TiO2 than the other coals.Among the Darby samples with the highest TiO2, bench samples 6262 and 6368 have strikingly different REY Geochemical influences were likely to have been complex.Aside from the expected terrigenous influx at the time of deposition, the region was subject to the influence of hydrothermal fluids during diagenesis.This is most notable on the footwall side of the Pine Mountain thrust fault where an enhanced coal rank compared to correlative coals on the thrust sheet (as we are studying here), albeit all within the high volatile A bituminous rank range, are accompanied by enhanced levels of Cl and Hg and other trace metals [34].While not previously demonstrated, it is possible that the coals on the Pine Mountain thrust sheet could have been similarly influenced, if not from fluids squeezed out in advance of the Pine Mountain thrust sheet, then by fluid flow influenced by thrust faults to the southeast in Virginia.Examination of the Al 2 O 3 vs.TiO 2 plot (Figure 12) provides a view of another aspect of mineral influx.The Harlan benches have a much wider distribution than the Kellioka or Darby benches, having both higher and lower Al 2 O 3 and lower TiO 2 than the other coals.Among the Darby samples with the highest TiO 2 , bench samples 6262 and 6368 have strikingly different REY distributions than any of the other benches Minerals 2015, 5, 894-918 among the three coals.In particular, the Y concentration versus the UCC baseline value is high.Relative to other Darby benches, the P 2 O 5 is also high, suggesting that an influx of Y-(and REY) bearing phosphates could have accompanied the TiO 2 influx.TiO 2 -mineral/Phosphate/Zircon sediments are common in detrital (often the basal coal) lithotypes [17,25,26,[36][37][38][39][40][41][42][43].

Summary
The Harlan, Kellioka, and Darby coals have traditionally been among the more important coal resources in Harlan County, Kentucky.
The Harlan coal is the thickest and has the highest ash and sulfur content of the three coals in the study.In practice, the ash and sulfur content could be reduced by beneficiation.An enrichment of TiO2 + Zr in the basal lithotype and V + Cr in the top lithotype and in lithologies immediately below partings is similar to occurrences seen in other eastern Kentucky coals.The lithotypes with REY >600 ppm correspond to concentrations of P2O5 > 0.5%.Much of the Harlan coal has an M-type REY distribution pattern (after Seredin and Dai [30]).
The Kellioka coal generally has less than 5% ash yield and a sulfur content <0.9% in most lithotypes.Pyritic S is highest in the uppermost two lithotypes and, in the 6360 section, in the basal lithotype.Concentrations of Sr + Ba > 11000 ppm, accompanied by 929 ppm REY, occur in a lithotype with 3.50% P2O5.The Kellioka samples generally do not have REY patterns corresponding to the Seredin and Dai [30] distributions.
The Darby coal is generally low-ash and low-sulfur.The Ba + Sr content exceeds 14,560 ppm (ash basis) in one sample and has relatively high values in other lithotypes.While a carbonate or phosphate association might be the source of the elements, there is no direct mineral evidence for such an association in this coal.The highest REY content, nearly 1700 ppm, does not correspond to the highest Sr + Ba.A few of the Darby samples show an M-type distribution, with most samples enriched in heavy REY elements.As with the Harlan coal, the V + Cr is highest in the uppermost lithotype in both benched sections.

Minerals 2015, 5 , 2 Figure 1 .
Figure 1.Location of the sample sites in Harlan County, Kentucky.For multiple-bench/multiple-lithotype samples, the site is designated by the sample number of the accompanying whole-coal sample.

Figure 1 . 2 Figure 1 .
Figure 1.Location of the sample sites in Harlan County, Kentucky.For multiple-bench/multiple-lithotype samples, the site is designated by the sample number of the accompanying whole-coal sample.

Figure 3 .
Figure 3. Lithologic sections of the Harlan coal.For the 6255, 6378, and 6392 sequences, the tick marks along the right edge indicate the boundaries of the sampled intervals and the associated numbers represent the bench number.The blank spaces between coal benches indicate non-coal rock intervals.See the tables for the correlation between the bench and sample numbers.

Figure 3 .
Figure 3. Lithologic sections of the Harlan coal.For the 6255, 6378, and 6392 sequences, the tick marks along the right edge indicate the boundaries of the sampled intervals and the associated numbers represent the bench number.The blank spaces between coal benches indicate non-coal rock intervals.See the tables for the correlation between the bench and sample numbers.

Figure 4 .
Figure 4. Concentration coefficients of trace elements in the coals studied.(A) Harlan; (B) Kellioka; (C) Darby.Concentration coefficients (CC) are the ratio of the trace-element concentrations in the coal samples vs. world hard coals reported by Ketris and Yudovich [26].Figure 4. Concentration coefficients of trace elements in the coals studied.(A) Harlan; (B) Kellioka; (C) Darby.Concentration coefficients (CC) are the ratio of the trace-element concentrations in the coal samples vs. world hard coals reported by Ketris and Yudovich [26].

Figure 4 .
Figure 4. Concentration coefficients of trace elements in the coals studied.(A) Harlan; (B) Kellioka; (C) Darby.Concentration coefficients (CC) are the ratio of the trace-element concentrations in the coal samples vs. world hard coals reported by Ketris and Yudovich [26].Figure 4. Concentration coefficients of trace elements in the coals studied.(A) Harlan; (B) Kellioka; (C) Darby.Concentration coefficients (CC) are the ratio of the trace-element concentrations in the coal samples vs. world hard coals reported by Ketris and Yudovich [26].

Figure 5 .
Figure 5. Concentration coefficients of trace elements in the coal ashes studied.(A) Harlan; (B) Kellioka; (C) Darby.Concentration coefficients (CC) are the ratio of the trace-element concentrations in the coal ash samples vs. world coal ash reported by Ketris and Yudovich [26].

Figure 5 .
Figure 5. Concentration coefficients of trace elements in the coal ashes studied.(A) Harlan; (B) Kellioka; (C) Darby.Concentration coefficients (CC) are the ratio of the trace-element concentrations in the coal ash samples vs. world coal ash reported by Ketris and Yudovich [26].

Figure 7 .
Figure 7. Correlation coefficient of trace elements and ash yield of the coals in Harlan, Kellioka, and Darby.

Figure 7 .
Figure 7. Correlation coefficient of trace elements and ash yield of the coals in Harlan, Kellioka, and Darby.Figure 7. Correlation coefficient of trace elements and ash yield of the coals in Harlan, Kellioka, and Darby.

Figure 7 .Figure 8 .
Figure 7. Correlation coefficient of trace elements and ash yield of the coals in Harlan, Kellioka, and Darby.Figure 7. Correlation coefficient of trace elements and ash yield of the coals in Harlan, Kellioka, and Darby.

Figure 8 .
Figure 8. Relations of ash yield and some selected trace elements in the coals in Harlan, Kellioka, and Darby.Figure 8. Relations of ash yield and some selected trace elements in the coals in Harlan, Kellioka, and Darby.

Figure 8 .
Figure 8. Relations of ash yield and some selected trace elements in the coals in Harlan, Kellioka, and Darby.Figure 8. Relations of ash yield and some selected trace elements in the coals in Harlan, Kellioka, and Darby.

Minerals 2015, 5 ,
page-page19 ) With a few exceptions of samples 6264, 6370, 6371, and 6369, which a slight M-REY enrichment, the Darby coal samples are enriched in heavy REY relative to the upper continental crust [35] (Figure11).

Figure 9 .
Figure 9. Distribution patterns of REY in Harlan coals.REY concentrations are normalized by those in the Upper Continental Crust [35].

Figure 9 .
Figure 9. Distribution patterns of REY in Harlan coals.REY concentrations are normalized by those in the Upper Continental Crust [35].

Figure 10 .
Figure 10.Distribution patterns of REY in Kellioka coals.REY concentrations are normalized by those in the Upper Continental Crust [35].

Figure 11 .
Figure 11.Distribution patterns of REY in Darby coals.REY concentrationsare normalized by those in the Upper Continental Crust [35].

Figure 10 . 21 Figure 10 .
Figure 10.Distribution patterns of REY in Kellioka coals.REY concentrations are normalized by those in the Upper Continental Crust [35].

Figure 11 .
Figure 11.Distribution patterns of REY in Darby coals.REY concentrationsare normalized by those in the Upper Continental Crust [35].

Figure 11 .
Figure 11.Distribution patterns of REY in Darby coals.REY concentrationsare normalized by those in the Upper Continental Crust [35].

Table 4 .
Percentages of major-element oxides and chlorine (%) and concentrations of trace elements (µg/g) in coals from Harlan, Kellioka, and Darby (on whole coal basis).Bdl-below detection limit; nd-ot determined.

Table 5 .
Concentrations of rare earth elements and yttrium (µg/g) in coals from Harlan, Kellioka, and Darby (on whole coal basis).