By Gregory M. Molinda 

,$?@-% 

kV, ' .. #\ 

I., - - t,. r 

UNITED STATES DEPARTMENT OF THE INTERIOR F- 
Report of Investigations 9186 

Investigation of Methane Occurrence 

and Outbursts in the Cote Blanche 

Domal Salt Mine, Louisiana 

By Gregory M. Molinda 

UNITED STATES DEPARTMENT OF THE INTERIOR 

Donald Paul Hodel, Secretary 

BUREAU OF MINES 

T S Ary, Director 
L~brary of Congress Cataloging in Publication Data : 

i 

r 

Molinda, G. M. (Gregory M.) 

Investigation of methane occurrence and outbursts in the Cote Blanche domal 

salt mine, Louisiana. 

(Report of investigations; 9186) 

Bibliography: p. 20 

Supt. of Docs. no. : I 28.23: 9186. 

1. Methane-Louisiana-Cote Blanche Island. 2. Salt mines and miningLouisiana--Cote Blanche Island. 3. Mine gases--Louisiana--Cote Blanche Island. 

I. Title. 11. Series: Report of investigations (United States. Bureau of Mines) ; 

9186. 

TN23.U43 [TN305] 622 s [622'.363'0976342] 88-600113 

A 
CONTENTS 

I 

Abstra~t.......................*...~......~................................... 

Introducti~n.......................~.......................................... 

Nature of outbursts at the Cote Blanche Mine......................*......*.... 

Geology of the Cote Blanche salt dome......................................... 

Methane content of the Cote Blanche salt dome.....................*......*.*.. 

Relationship of geologic properties of salt domes to outbursts...........*.... 

Salt layering and structure................................................. 

Salt crystal size........................................................... 

Salt composition............................................................ 

Using geologic mapping and methane content sampling for prediction of gassy 

zones.............. ...................................*....*.*................ 

Methane control strategies.........*.*..**.................................... 18 

Summary ....................................................................... 19 

Conclusions.........~.~..............e..~~..~~~........................ 20 

References...................~.......~..~~~.~~~..~~.............~..... 20 

1 ILLUSTRATIONS 

Location of study area showing active and inactive domal salt mines in 

gulf coast area...............................................e......e.e 3 

Location of outbursts in Cote Blanche Mine............................*. Pocket 

Multiple outbursts showing concentric fracturing known as onionskin 

texture and bull's-eye termination...................................... 4 

Cross section of mining advance showing outburst cavity removal by 

successive production blasts............................................ 4 

Location of outbursts that occurred during bench mining at Cote Blanche 

Mine.................e....~...................................... Pocket 

Mine map showing outbursts and their relationship to layering structure, 

salt crystal size, and methane content, study area l.................. .. 6 

Mine map showing outbursts and their relationship to layering structure, 

salt crystal size, and methane content, study area 2.................... 7 

Geologic map of Cote Blanche Mine................................*... Pocket 

Salt layering and distribution of sandy beds.....................*...... Pocket 

Generalized structure map of Cote Blanche Mine......................... .. 8 

Overturned beds at Cote Blanche Mine..................................... 9 

Vertical sandstone unit showing typical pinch and swell boundinage 

structure...................~........................................ 10 

Grain size distribution plot of sediment dissolved out of included 

~andstone.................~.~.....~~~~.~....~.... 10 

Photomicrograph of salt crystal showing entrained gas bubbles............ 11 

Location of outbursts and salt samples with methane content in Cote 

Blanche Mine...................................~~................ Pocket 

Outbursts confined between anhydrite layers........................*.*... 14 

Distribution of salt crystal size versus methane content at Cote Blanche 

TABLES 

1. Mineralogic composition of salt-free sediment from selected samples, Cote 

Blanche salt mine...............*..**.*................................. 9 

2. Methane content and location of selected samples, Cote Blanche salt mine. 13 

3. Procedures for predicting gassy conditions.........*..................... 18 
UNIT OF MEASURE ABBREVIATIONS USED IN THS REPORT 

cm centimeter g gram 

cm3 cubic centimeter in inch 

ft foot mm millimeter 

ft2 square foot Pet percent 

ft3 cubic foot Yr year 

f t 3 / d cubic foot per day 
INVESTIGATION OF METHANE OCCURRENCE AND OUTBURSTS IN THE 

COTE BLANCHE DOMAL SALT MINE, LOUISIANA 

By Gregory M. ~olinda' 

ABSTRACT 

The Bureau of Mines conducted an investigation into the occurrence of 

outbursts of salt known to be responsible for explosions, fatalities, 

and damage in domal salt mines. The purpose of the investigation was to 

develop a basis for predicting these outbursts based on geologic and 

associated physical properties of salt. 

The investigation was conducted at the Cote Blanche salt mine in 

southern Louisiana. Because outbursts are the primary mode of methane 

emission into the mine, more than 80 outbursts, ranging in size from 1 

to 50 ft in diameter have been mapped. These outbursts generally are 

aligned and elongate parallel to the direction of salt layering. More 

than 200 salt samples, both random and selected, were tested for methane 

content. It was found that outburst zones are well correlated with high 

methane content. Detailed mapping also revealed that the zones are well 

defined, with salt crystal size abruptly increasing upon entry into the 

zone. The intensity of folding and kinking of the salt layering within 

the outburst zone also appears to increase. An interbedded sand layer 

occurring throughout the mine does not appear to be a significant source 

of methane. However, fine-grained salt may be related to outburst 

occurrence. 

' ~eolo~ist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
INTRODUCTION 

The Bureau of Mines has developed a 

laboratory test for determining methane 

content in rock salt samples, and has 

evaluated emission characteristics of 

various forms of salt. This Bureau report assesses the usefulness of these 

tests, various geologic parameters, and 

rock salt properties in predicting the 

potential for occurence of outbursts in 

domal salt deposits. 

The occurrence of hydrocarbons within 

salt structures has been observed for 

many years from exploration drill holes 

into these structures by both the oil and 

gas and salt mining industries (I).~ 

Many gas occurrences have been encountered, but mostly during underground mining. In one domal salt mine, more than 

90 pct of the gas contained in a recovered sample is methane (2). The remainder consists of higher hydrocarbons, 

02, N2, and C02. 

The character of methane emission in 

salt mines is different than in coal 

mines. Instead of the continuous bleed 

of gas from the face, roof, and rib as 

in coal mines, methane in domal salt is 

emitted mainly as an instantaneous release of gas from salt broken during 

blasting of production faces. Gas has 

also been known to bleed from natural 

fractures in salt, from blast drill 

holes, or from undercutting a face in 

preparation for blasting. In at least 

one instance where a continuous miner was 

used, gas was emitted (1,000-8,000 ft3/d) 

through the face and ribs, migrating primarily along layering within the salt 

(2). When compared with coal mines, some 

of which routinely emit several million 

cubic feet of methane per day, it is seen 

that methane sources in salt mines rarely 

amount to a significant volume of methane 

and are readily diluted by the ventilation system. This has led to the belief 

that rock salt is essentially 

'underlined numbers in parentheses ref er to items in the list of references at 

the end of this report. 

impermeable, and that hazardous methane 

emissions generally occur only during 

face blasting (1). 

Hazardous emissions of methane occur 

infrequently during production blasting. 

These emissions characteristically take 

the form of outbursts. An outburst, as 

it applies to rock salt mining, can be 

defined as an unexpected, nearly instantaneous expulsion of gas and rock salt 

from a production face. The results of 

outbursts, normally conical cavities, are 

created by the expulsion of broken rock 

salt and gas into the previously mined 

opening. These conical or cylindrical 

cavities generally range in size from 

1 ft to tens of feet in diameter, and can 

be more than 270 ft high. Average outburst cavity heights may be 10 to 20 ft, 

and they are almost always propagated 

upward. They commonly occur at either 

the rib-roof junction or strictly into 

the roof. Only rarely has a cavity 

extended into the floor. 

It is thought that most outbursts are 

at least partly the result of rapid release of high-pressure gas. In the gulf 

coast region the gas is mainly methane. 

Methane, hydrogen sulfide, and carbon 

dioxide have been noted in Polish salt 

mines for centuries (A). Outbursts at 

the now-flooded Winnfield salt mine in 

Louisiana were thought to be driven by 

pressurized C02, as were occurrences in 

several European salt mines. The fatal 

mine disaster at the Belle Isle Mine in 

1979 proved that high-pressure methane in 

large quantities could be emitted (L, 5- - 5). It is estimated that more than 

600,000 f t3 of methane was emitted instantaneously from the outburst that 

caused that disaster (1). 

How methane was incorporated in salt 

domes is uncertain. Methane may have 

been entrained in the salt mass shortly 

after it became mobile, or gas under high 

pressure from deeply buried organic sediments overlying the evaporite sequence 

may have been incorporated into the 

rising salt plume. This gas may have 
become isolated in pressurized zones and 

was carried within the salt stock towards 

the surface. 

Previous work has shown a relationship 

between anomalous salt zones and gas 

occurence (2-3, 5). Kupfer describes 

internal anomalous zones as the area 

between adjacent salt stocks where rock 

has been included, (7 ). Another anomalous 

zone is the contact' of salt stocks with 

bordering strata. When mining approaches 

these large internal or boundary areas, 

the methane content of salt increases as 

well as does outburst frequency. Not all 

structure, and gas history may vary 

greatly from one dome to the next. 

Geologic factors that caused changes 

in crystal texture, structure of the 

distorted strata, and geochemical characteristics are probably responsible for 

the occurrence of high-pressure zones, as 

well as the actual outbursts. Mechanical deformation related to cavern development may also play a role, but is 

beyond the scope of this report. This 

report presents the results of detailed 

geologic mapping and sampling of rock 

salt for methane content and applies 

gulf coast salt mines intersect these these results to aid in the prediction of 

anomalous zones, and the composition, outbursts. 

NATURE OF OUTBURSTS AT THE COTE BLANCHE MINE 

The Cote Blanche Mine, one of five 

remaining domal salt mines in the gulf 

coast region, is located approximately 30 

miles south of New Iberia, in southern 

Louisiana (fig. 1). This mine has been 

in operation since 1961, using a roomand-pillar scheme. Rooms are normally 55 

ft wide, square pillars are 100 ft on a 

side, with a first-cut room height of 25 

it. A second or bench cut is then removed by blasting out the floor, making a 

total room height of 80 ft. The mining 

are extracted by undercutting and blasting. The salt is then screened and 

crushed underground and brought to the 

surface on a skip, where it is loaded on 

barges by a conveyor belt system. 

More than 80 outbursts have been observed at the Cote Blanche Mine. They 

occur throughout the 1,365-ft mine level, 

but they tend to be concentrated in relatively small areas. Most outbursts and 

the largest in size are clustered in the 

northeast quadrant and the southern half 

plan is nearly a perfect gridwork and has of the mine (fig. 2). Outbursts can be 

not changed since the mine opened. Faces identified by a characteristic conical 

shape with concentric fracturing or 

KEY 

AR I onionskin texture (fig. 3). They range 

t----- Active mines in size from 1 ft in diameter to the 

kt Inactive mines 

Grand Saline largest observed out burst, which was over 

N i Winnfield ) i 50 ft in diameter and reached a height of 

LI/ 

I AL 

over 50 ft. In one benched area of the 

MS \ mine (22 LS), outbursts occur diagonally 

'I LA { I on either side of an entry. 3 If these 

TX I ----- two cavities are from the same outburst 

occurrence, as is expected, the total 

outburst length would be over 100 ft. 

3~ine location is designated by a grid 

Mexico Belle Isle work system as shown in figure 2. Crosso m 50 cuts or entries separated by a hyphen 

Scale, rn~les (e.g., I-JN) indicate a location between 

FIGURE 1.-Location of study area showing active and inactive the crosscut or entry; N and S indicate 

domal salt mines in gulf coast area. northern and southern part of the mine. 
0 

w 

10 

Scale, ft 

FIGURE 3.-Multiple outbursts showing concentric fracturing 

known as onionskin texture and bull's-eye termination. 

east between entries 25 and 26 when out

bursts were encountered. Mining was 

halted at this point. Ten years later 

mining was resumed and outbursts were 

immediately encountered. Gas pressure 

had not been substantially relieved during a lOyr period. 

Outburst 

I Blast I Blast I Blast I Blast 

0 25 Face advance 

____C 

f IGURE 4.- Cross section of mining advance showing outburst cavity removal by successive production blasts. 
GEOLOGY OF THE COTE BLANCHE SALT DOME 

The Cote Blanche salt dome is one of 

the famous five island salt domes. These 

domes form a line trending roughly NW-SE 

for 60 miles just south of New Iberia, LA 

(fig. 1). They are diapiric salt structures originating in the Louann Formation 

of Permian-Jurassic age (9). It has been 

thought that the Cote ~ianche dome is 

formed from at least two salt spines that 

moved relative to each other, leaving a 

marked overhang to the north (10). In 

contrast to the other four island salt 

domes, there is no underground evidence 

of an internal boundary zone at the Cote 

Gianche Mine that would indiczte the convergence of two or more salt plumes. 

Kupfer reports bedding parallel to the 

domal margin in the southeastern part of 

several reasons. First, they follow 

closely the trend of salt layering in 

occurrences throughout the mine; second, 

they maintain a fairly constant thickness 

(1-6 ft); third, the contact between the 

sand and the adjacent salt is very sharp; 

and fourth, the sand has a fairly consistent mineralogic composition. This sand 

unit is one of the few marker beds in the 

complexly folded salt strata. Another 

marker bed is a black, carbonaceous silt 

clay member (fig. 8). 

Figure 9 shows the distribution of sand 

throughout the mine. Based on these 

marker beds and structural mapping, it 

appears that although local folding is 

complex, the axis of a large fold runs 

from the northwest to the center of the 

the mine (10). This appears to be the mine and turns southward. Since the 

only indication of a possible boundary strata are nearly vertical, the best dezone within the mine limits. This type 

of zone is caused by vertical dome movement and results in drag of adjacent rock 

and salt layers. 

As in all of the other Louisiana five 

island salt domes, the internal structure 

is nearly vertical, although locally salt 

beds have been observed to roll over to 

nearly 45' from horizontal. Mapping 

shows internal structure to be extremely 

complex (figs. 6-7). The alternating 

bands of light and dark salt are considered to be original bedding from the 

evaporite sequence (1 - 0). Sediment inclusions occur mainly in the form of an 

interbedded sand, as opposed to the massive incorporation of elastic and organic 

debris in anomalous zones. These sandy 

beds are considered original bedding for 

scription of the structure may be as a 

vertical, elliptical cylinder, open to 

the northwest. Folding in the northern 

half of the mine appears to be broader 

and more open with the fold limbs approaching each other and tightening as 

the axis is followed southward (fig. 10). 

This interpretation is supported by previous mapping (10). 

The interbeddz sand occurs discontinuously. It may be persistent over several 

crosscuts then disappears and reappears 

after skipping a crosscut. It occurs as 

a sequence of up to two closely spaced 

thin exposures from 1 to 6 ft thick (6 

LN). It is possible the exposures are 

from the same complexly folded bed (6 LN) 

(fig. 11). It is possible that all of the 

sandstone in the mine is from the same 
FIGURE 6.-Mine map showing outbursts and their relationship to layering structure, salt crystal size, and methane content, 

study area 1. 
complex folding of domal strata, the bed 

could have folded back on itself in the 

area around 22 ON and continued south 

through the center of the dome. The 

sandstone bed should be continuous but it 

is absent probably because of vertical 

shearing, which may leave the sheared 

portion of the bed either above or below 

the mined horizon. 

The sandy beds, in many instances, 

occur as blocky cobbles up to 4 ft in 

diameter. These blocks sometimes form a 

collapse breccia. At 8-9 PN it appears 

that the potash matrix was partially dissolved, allowing the sand bed to collapse 

and brecciate. A boudinage structure 

also commonly occurs (fig. 12). Boudinage structure is characterized by sausagelike shapes caused by pinching and 

swelling deformation. These rolled and 

stretched blocks are a result of vertical 

transport. In one instance, a thin (2-in 

thick) continuous clay band parallels the 

boudinage structure, attesting to the 

coherency of the clay layer relative to 

vertical flowage the clay grains flattened out and stretched, maintaining the 

strata continuity. The nonplastic quartz 

grains separated and formed the boudinage 

structure. 

The sand occurs as both unconsolidated 

sediment and as sandstone blocks with KC1 

as the cement for both blocks and grains. 

The amount of sand within the layer varies from 60 pct to only a few percent. 

The sediment is sometimes replaced by a 

pinkish-orange sylvinite, a mixture of 

halite and KC1 minerals* The amount of 

KC1 is approximately 7 to 10 pct. Kupfer 

states that this association of KC1 and 

sand is not unexpected in the original 

environment of deposition if it is 

assumed that the sand and KC1 are both 

primary bedding (7). The potash mineral, 

sylvite, is quite-common and is precipitated from a brine solution when evaporation rates are high, possibly because of 

high winds. In such an arid climate, 

large amounts of sand and silt could be 

blown into the evaporite basin. 
FIGURE 10.-Generalized structure map of Cote Blanche Mine. 

Table 1 shows the mineralogic composi- generally sandstone or siltstone with a 

tion of dissolved-out (salt-free) clas- small percentage of metamorphic fragtics from seven sediment samples. Quartz ments. Other components include mica, 

is the predominant mineral, with up to aragonite, calcite, dolomite, and chert. 

25 pct rock fragments as the next most Some anhydrite is found, but although an 

frequent component. Rock fragments are insoluble, it is not a detrital mineral. 
FIGURE 11.-Overturned beds at Cote Blanche Mine. 

TABLE 1. - Mineralogic composition of salt-free sediment from selected samples, 

Cote Blanche salt mine, percent 

Sample Quartz I Feldspar I Rock fragment I Other I Location 

7......................... 1 7 8 6 1 15 1 1 1 7- 8 KN 

'Shale, eiltstone, sandstone, metasediments. 

.......................... I 7 4 0 25 I 1 1 10 I-JN 
GRAIN SIZE, mm 

FIGURE 13.-Grain size distribution plot of sediment dissolved 

out of included sandstone. 

The average grain size is fine to very 

fine sand with many grains being rounded 

to well rounded. Figure 13 is an average 

grain size distribution plot developed 

from standard sieve analysis for the 

sandstone. The samples average 10 to 15 

pct of sediment in the silt size or 

smaller range. The extreme rounding, 

sphericity, and frosting of the quartz 

grains, and the grain size distribution, 

support the theory of aeolian transport 

into the evaporite basin. These parameters were evaluated by standard 

part of the mine associated with outbursts . No such association was 

observed with this clay layer. 

Occurring principally in the southern 

part of the mine is a zone of hard, finegrained salt (f ig. 8). This salt is 

extremely f ine-grained and brittle and 

has a characteristic ringing sound when 

struck. Kupfer described the zone as 

"yellow massive saltt1 (10). This zone 

can be traced from 14 DS to 18 PS. It is 

best exposed in the ventilation tunnel at 

ES, where it is associated with brine 

seepage and chemical impurities. This 

salt is particularly difficult to mine 

because of its hardness. It is difficult 

to drill and blast as well as to crush. 

The salt occurs in a zone as an interbedded normal salt and fine-grained salt. 

The zone appears to be over 300 ft wide 

at its northern termination at 14 DS, and 

tapers to 20 ft at 18 PS. It is also 

known sporadically in the northern part 

of the mine at 15 ON, 18 QN. 

There is a distinctive jointing pattern 

associated with this fine-grained salt, 
FIGURE 14.-Photomicrograph of salt crystal showing entrained gas bubbles. 
expelled is generally enough to fill the 

cavity . Previous Bureau work has shown that 

high methane content and outburst occurrence in domal salt are related (G). 

Even though outbursts are not exclusively 

related to methane content, this property 

can be used as an early warning device. 

The Cote Blanche Mine currently uses a 

field-adapted dissolution test for methane. This test was developed by the 

Bureau and relates noise levels given off 

by the salt when methane is released to 

methane content. Salt is dissolved in 

fresh water and a microphone records the 

popping sound generated by the pressurized wthane. These noise levels have 

been calibrated to methane content using 

the standard dissolution test also developed by the Bureau (12). The test has 

been shown to be usefx in alerting mine 

personnel to gassy conditions. At Cote 

Blanche, a new level is being planned 

above the present level. Since strata 

continuity is near vertical in salt 

domes, methane-enriched zones can be 

projected vertically. So by charting 

methane content on one level, this same 

information may be used as an aid to 

reducing hazards on another level. 

Salt samples from Cote Blanche Mine 

have been tested for methane content in 

order to characterize the nature of methane occurrence. Two hundred nineteen 

salt samples have been tested for methane 

content at Cote Blanche. Many of the 

gassy areas of the mine have been sampled 

as well as a random sampling for control. 

Methane content ranged from 0.0 to 8.7 

cm3 CH4 per 100 g NaC1. A salt sample is 

considered methane enriched when more 

than 0.30 cm3 CH4 per 100 g NaCl is masured (11). Some of the methane contents 

at ~ote~lanche are among the highest 

measured in the Gulf Coast basin. Table 

2 shows some of the methane content Samples at Cote Blanche, their locations, 

and salt type. It can be seen that most 

of the highest methane contents are taken 

directly from outburst cavities or from 

salt ejected from those cavities. The 

lower methane concent rations are mainly 

taken from normal or run-ofmine salt. 

In addition, the frequency of higher 

hydrocarbons increases with methane 

content. This relationship was also 

indicated by Schatzel (1 1). 

Figure 15 shows the-distribution of 

salt samples and their associated methane 

contents over the mine area. The major 

outburst areas (26 MN, 25 GN, 31 GN, and 

21 MS) all have high methane contents 

associated with samples drawn from the 

outbursts themselves or the broken salt 

ejected from the outburst cavity. This 

observation is consistent with findings 

at other domal salt mines in the area 

(11). This relationship indicates that 

routine sampling for methane content can 

be an effective way of indicating outburst potential. 

Schatzel (11) determined that there is 

a relationship between the type of salt 

and volume of associated methane. There 

are three types of rock salt; normal, 

anomalous, and outburst. Normal salt is 

pure halite with rare inclusions. This 

salt normally has no methane associated 

with it. Anomalous salt contains sediment, organic, or chemical impurities. 

This type of salt normally is more likely 

to be methane enriched, but this is not 

true of anomalous salt tested at Cote 

Blanche. Outburst salt is rock salt collected directly from an outburst cavity, 

or from broken salt ejected from such a 

cavity. Most samples of this salt type 

show methane enrichment; as do outburst 

samples from Cote Blanche. Most normal 

salt samples from Cote Blanche have a low 

methane content. Samples were also collected systematically across the mine 

along entries BN, CN, and HN; two grab 

samples per pillar (fig. 15). Most of 

these samples show little methane enrichment, supporting the observation that 

methane occurs in discrete zones, rather 

than being disseminated uniformly. 

At Cote Blanche, methane enrichment In 

salt samples has occurred in areas where 

no outbursts occur. Examples include the 

decline from the face mined level to the 

bench level (13-18 AN). Methane was 

encountered continuously during the 

development of this slope. Methane was 

emitted during face drilling and undercut ting operations. Another area of 

methane enrichment is the ventilation 

tunnel between 16 and 18 ES. Here, brine 

and methane were encountered during 
TABLE 2. - Methane content and location of selected salt samples, Cote Blanche 

salt mine 

0. do.......... 

NA............ 1 NA............ 

, AnolMlous. .... , NA............ 

I NA............ 

Outburst...... 

Normal.. ...... Outburst.. .... NA............ 

@itburst.. 3.3 c 

. .do.. ........ 0. do.......... 

. .do.. ........ Normal.. ...... Outburst.. .... NA............ 

Normal.. ...... 0. do.......... 

NA............ 

Outburst.. .... . .do.. ........ NA............ 

Outburst.. .... . .do.. ........ NA............ 

NA............ 

NA.....w...... 

Ch4 per 100 g 

NaC1, cm3 

2.029 

Higher hydrocarbons I Mine location 

22 HN 

26 EN 

31 FN 

31 FN 

32 HN 

26 LN 

20 GN 

25 GN 

23 HN 

31 GN 

25 EN 

31 GN 

31 CN 

25-26 GN 

25 GN 

26 L-MN 

25 GN 

18 GN 

26 LN 

18-19 GS 

21 NS 

26 GN 

26 GN 

26 MN 

21 NS 

26 GN 

21 DN 

22 LS 

26 GN 

37 ........... 1 Normal.... .... 1 8.783 I C2H6, C3H8, C4H109 C5H17 1 22 Ls 

NA Not available. 

tunnel advancement through impure, dark- important factor. Other factors may inbanded salt. The presence of methane is clude rock strength, or strata.weakening 

indicated by popping salt, large crystal due to geologic or mechanical events. 

size, and actual emissions in a number of Inherently weak salt (folded or sheared), 

areas devoid of outbursts. While methane o r s a l t weakened mechanically because of 

under pressure appears necessary to overloading of undersized pillars, may be 

outburst occurrence- in the gulf coast, it more susceptible to blowouts in highappears that this is not the only gas-pressure zones. 

RELATIONSHIP OF GEOLOGIC PROPERTIES OF SALT DOMES TO OUTBURSTS 

Three other geologic associations of in detail. Mapped features include outsalt were investigated to determine if burst size, shape, and location; salt 

they could be used to predict outburst crystal size and the variation of that 

potential. These include large-scale and crystal size with proximity to outbursts; 

local structural layering, salt crystal and salt banding direction and distursize, and salt composition. Two outburst bance related to outbursts. Salt samples 

areas at Cote Blanche Mine were mapped were collected in the study areas and 
tested for methane content to determine 

relative gassiness. 

SALT LAYERING AND STRUCTURE 

Large geologic structures in the mine 

are indicated by the orientation of 

alternating light and dark salt layers. 

This layering trends northwest on the 

west side of the mine and northeast on 

the east side and ranges from 45" to vertical and overturned (fig. 8). An example of overturned beds occurs at 5-6 LN 

(fig. 11). Here, the layers overturned 

in the roof and give the false impression 

of multiple sandy beds, which are actually one bed. Dips average 75" to 85" from 

horizontal. Outbursts tend to occur 

along linear trends that parallel largescale layering. In the southern part of 

the mine a series of outbursts follow a 

linear trend approximately N 30" E, from 

JS to NS. This direction parallels the 

salt layering. In the east-central part 

of the mine, from EN to EN, another 

series of outbursts also parallels layering that trends N 10" E. At 17-18 MS 

three outbursts (ellipsoid shaped; 15 by 

7 ft, combination of two; 15 by 5 ft) 

parallel fine-grained salt beds that 

trend N 20" W. In study area 1, the 

series of outbursts also parallel local 

layering, which trends almost N 30" E 

(fig. 6). Finally, in study area 2, from 

FN to HN, the line of outbursts closely 

parallels layering that runs approximately due north (fig. 7). 

The intensity of layering disturbance 

appears to increase near an outburst 

occurrence. Two outburst areas were 

mapped in detail. These indicate the 

complexity of local layering, and show 

the location of outbursts up to 50 ft 

wide (figs. 6-7). Figure 6 shows the 

structural detail that can be seen in the 

roof in study area 1. The tight isoclinal folding increases in complexity nearest the outburst area and immediately 

around it. Study area 2 also exhibits 

complex folding and shearing nearest the 

outburst area, as well as salt beds that 

dip to nearly 45". These zones of comfolding intensity in some areas, there 

are numerous examples of complexly folded 

beds where no outbursts occur. Therefore, the use of folding and folding 

intensity as a predictive tool is not 

supported. 

Locally two situations appear to show 

structural control of layering over outburst occurrence. In the southern part 

of the mine (21 MS), several outbursts 

are confined between two black anhydrite 

layers. The location and direction of 

propagation of these outbursts is probably controlled by the vertical anhydrite 

layers (fig. 16). In one instance a 

3- to 4-ft-diam outburst is confined 

between two anhydrite-rich layers, and 

forms a pipe extending into the roof to 

an unknown height. In another instance, 

at 18-1/2 FS, a small outburst (2- to 3- 

ft diam) is confined between two finegrained salt bands. These layers appear 

to be confining the gas and acting as 

barriers. 

SALT CRYSTAL SIZE 

It is widely suspected by the Gulf 

Coast mining industry that large salt 

crystals are related to high methane content. At Cote Blanche, where the decline 

plex folding extend 100 to 150 ft beyond 

the outburst area in all directions. FIGURE 16.-Outbursts confined between anhydrite (black 

Although outbursts may occur related to salt) layers. 
salt crystal size versus methane content 

for 219 samples from all over the Cote 

Blanche Mine. The middle axis of individual grains was measured and an average 

grain size was estimated for each sample. 

The grain size was then plotted versus 

methane content, which was obtained for 

each sample. The normal grain size at 

Cote Blanche is approximately 118 to 1/4 

in. Most samples in this size range had 

little variation in grain size. This 

grain size is characterized by low methane content with the relative proportion 

of normal size samples decreasing as 

methane content increases. The larger 

grain sizes (>0.50 in) showed much more 

variation in the range of grain sizes. 

These size ranges also were related to 

increasing methane content. 

In both study areas located in the 

northeastern part of the mine, salt crystal size was mapped in proximity to the 

outburst zone. There is a noticeable 

increase in crystal size in a zone that 

parallels the trend of the outburst zone 

METHANE CONTENT, cm3 per 

l OOg NaCl 

FIGURE 17.-Distribution of salt crystal size versus methane 

content at Cote Blanche Mine. 
commonly reach 6 to 8 in, compared with 

the normal crystal size of 1/8 to 1/4 in. 

The texture is poikiloblastic, with 

smaller grains serving as matrix for the 

oversized salt grains. The zone is well 

defined and appears as a vertical envelope around the linear outburst trend. 

In study area 2, the zone includes all 

the outbursts and a region up to 50 ft 

away. In study area 1, all but one of 

the mapped outbursts are included within 

the coarse. crystal zone. The boundary 

between coarse and normal salt crystals 

extends up to50 ftfrom the lineof 

outbursts. 

The occurrence of methane in bench 

holes drilled in the floor along entry GN 

generally coincides with the boundary of 

the coarse crystal-gassy zone. Methane 

concentrations of over 1 pct were measured at the bench floor hole collars 125 

f t from the outburst zone. A concentration of nearly 5 pct was measured emitting from a hole drilled 1 h earlier at a 

site 100 ft from the outburst zone. 

This well-defined zone of large crystals is not unusual in this salt mine or 

others in the area. Muehlberger reports 

a similar zone with halite crystals up to 

100 ft long at the Grand Saline Mine 

(13). Salt purity is also well correlated with crystal size. Generally, the 

larger the crystal the purer the salt. 

It is possible that these areas are zones 

of recrystallization due to permeating 

brine in anomalous zones. Methane, as 

well as brine, may be entrapped within 

large crystals, and on the crystal boundaries. These pods then become isolated 

by differential movement. 

Most of the areas in which outbursts 

occur have larger than normal crystal 

sizes. In addition, most of the areas in 

which high methane contents have been 

measured also have large salt crystals. 

In study areas 1 and 2, salt samples 

have been tested for methane content and 

these values plotted along with salt 

crystal size (figs. 6-7). Study area 

1 shows that seven samples within the 

coarse crystal zone were enriched in 

methane, with the highest methane content 

being 3.2 cm3 per 100 g NaC1. Only one 

sample outside the coarse-normal crystal 

boundary was shown to be enriched in 

methane, and this value is associated 

with an outburst. Methane contents within the coarse crystal boundary range are 

more than 150 times those outside the 

zone. Study area 2 shows six samples 

within the coarse crystal zone that were 

enriched in methane, with the highest 

being over 6.1 cm3 per 100 g NaC1. This 

concentration is also more than 150 times 

that of a sample just outside the zone 

(0.0363 cm3 CH4 per 100 g NaC1). These 

methane enrichments correlate very well 

with the occurrence of coarse crystal 

salt and outbursts. Such detailed mapping and sampling is necessary in order 

to document the abrupt changes in crystal 

texture and methane content that take 

place in the complexly folded salt dome. 

The use of salt crystal size along with 

routine methane content testing can be 

valuable in predicting the approach to a 

gassy area. But it must be realized that 

even if all the criteria indicate the 

approach to a gassy area, mining may 

already be very close to an outburstprone area. Face advance could be as 

close as 50 ft to a high-pressure zone 

before changes in methane content and 

texture indicate a potential hazardous 

situation. 

SALT COMPOSITION 

There are several instances where included sediment, fine-grained salt, and 

outbursts occur together. At 23 JS, a 

sandy KC1 bed (6-12 in thick) bends 

sharply (fig. 9). On the inside of this 

bend an outburst occurred. The outburst 

cavity, approximately 15 ft in diameter 

and 5 ft high, appears to be confined by 

the sandy bed on one side. Another outburst, approximately the same size, 

occurred along this same sandy bed at 23 

KS. At 22 ON an outburst (15- to 20-ft 

in diam, 8 ft deep) occurred on the 

inside of tight fold of a sandy bed (6 in 

thick). Parallel to the sandy bed is a 

thin (6 in) carbonaceous silt clay layer 

and a bed of fine-grained salt (6 in). 

There are other i-nstances (18-19 ON, 24 

MN-NN) where outbursts and sandstone 

occur in proximity to each other (within 

100 ft), but in none of these cases does 

it appear that the sandstone, in many 
instances merely unconsolidated sediment, 

acts as a significant source or conduit 

for methane. Most of the outbursts and 

outburst areas occurred where there is no 

sign of bedded sediment. 

The fine-grained salt trend, extending 

from ES to OS in the southeastern portion 

of the mine, is associated with hydrocarbons in several locations. At 18 MS, 

four outbursts, three approximately 15 by 

8 by 5 ft and one approximately 3 ft in 

diameter, occurred in the roof and rib. 

These outbursts are aligned parallel to 

the f ine-grained salt layering. Another 

outburst at 18-1/2 FS is confined between 

two glassy salt layers. At 18 ES, there 

is a petroleum seep in the rib. At 17 DS 

a fracture that bled methane occurred at 

the roof -rib junction. The mine operators flared gas from the bleeder for more 

than 1 yr to avoid a hazardous accumulation (10). This gas vent exits the 

northern boundary of the fine-grained 

salt trend. The ventilation tunnel (16- 

18 ES), in which wet, gassy conditions 

occur, also cuts through the zone of 

hard, fine-grained salt. 

1 USING GEOLOGIC MAPPING AND METHANE CONTENT SAMPLING FOR PREDICTION OF GASSY ZONES 

?.. 

Lne investigation of the geolcgic properties of the Cote Blanche salt dome is 

aimed at determining how these properties 

relate to methane-rich zones and then, 

using the properties with significant 

relationships, it is hoped to predict 

the occurrence of these zones in advance 

of mining. It was necessary to map the 

location and trend of existing methanerich zones in order to realize how methane occurs, and its extent and distribution within the mine. Methane-rich zones 

can be indicated by outbursts, methane 

emissions, high methane content, very 

coarse salt crystals, and wet impure salt 

zones. At other domal salt mines in 

southern Louisiana, it has been hypothesized that methane is related to boundary 

zones of anomalous impure salt, which 

mark the transition between salt stocks. 

These zones appear to at least be sources 

of methane, and could possibly be conduits for gas migration from remote 

areas, possibly outside the dome. At 

Cote Blanche no such boundary zones have 

been exposed by mining. A series of thin 

sand beds are the only included sediment 

occurrences and these are determined not 

to be significant sources of methane. 

It was also found that lines of outbursts parallel large and small structural features in the dome* T5e major 

structural pattern is a large eliiptical 

fold that has an axis which rucs from the 

northwest to the center of the nine and 

turns southward along entry 20-21 (fig. 

10). The series of sandy beds cccurring 

throughout the mine can be used as inarker 

beds for structural mapping. By documenting the large-scale as well as the 

small-scale structural trends (study 

areas 1 and 2), projection of linear 

trends of gassy zones may be possible. 

If methane-rich zones do show linear 

properties they may also be projected 

vertically, since vertical continuity is 

consistent in salt domes. 

Detailed mapping of salt crystal size 

has shown that methane-rich zones are 

indicated by large salt crystals, and 

possibly distorted and kinked layering. 

These zones are also linear, can be as 

narrow as 200 ft wide, and are abruptly 

separated from normal size salt crystals 

(18-14 in Routine documentation of 

salt crystal size can also indicate if 

trends are present, and forecast the 

approach to a gassy zone. It was also 

found that methane enrichment and large 

salt crystals occur commonly in other 

parts of the mine where no outbursts 

occur. It appears that some additional 

parameter is important to outburst occurrence. Fossibly, the mehcanical properties of rock salt are important in the 

generation of outburst conditions. 

Geologic mapping should be done shortly 

after blasting before diesel soot deposits obscures roof and rib structures. 

Soot buildup occurs within a few months. 

Field zapping should be done on no 

smaller than 1 in = 100 ft base maps. 

This will allow most of the complex 

structural detail to be included. Accurate sketches of roof and rib banding 

should be made, as well as actual strike 
TABLE 3. - Procedures for predicting gassy conditions 

Mapping....... Outbursts (size and shape). 

Banding sketch in roof (1 in = 100 ft base map). 

Bed attitude measure (strike and dip). 

Crystal texture (even grained, poikiloblastic), average crystal size, 

crystal shape. 

Composition--sediment, inclusions (attitude, bedded, foreign), chemical changes (color, taste). 

Sampling..... . Methane content of salt--standard dissolution, acoustic field dissolution (several representative samples per face). 

Bottle sample for methane from bleeder or drill hole. 

Drilling. ..... Exploration hole--200-300 ft in advance. 

Core log--crystal texture composition. 

Reservoir tests-methane content of core, methane flow, formation 

pressure packing, packing intervals, recovery time after shut-in. 

Gas composition analysis. 

and dip readings taken. Special attention should be taken to map grain size, 

disturbed banding, and rapidly changing 

bed attitude. Several measurements (bed 

attitude, grain size) per intersection 

are necessary. Any unusual features, 

such as sediment inclusions, thick black 

bands, yellow salt, petroleum or brine 

seeps, potash trends, or outbursts, 

should be mapped and appropriate bearing 

taken. Mapping of salt impurities will 

also be very useful for production 

-quality. 

The mapping of texture includes an 

overall statement of type of texture; 

whether the salt is even grained or 

poikiloblastic. Mapping crystal size 

usually means estimating since access is 

limited. It is necessary to make many 

observations in order to arrive at a representative grain size. This high frequency of observation is also necessary 

since crystal size changes rapidly. 

Methane content of salt should be 

determined at each production face. At 

least one sample could be taken from the 

face on each of four corners and one in 

the middle. This could be accomplished 

during the face loading part of the mining cycle when access is available from 

the jumbo drill platforms. These samples 

could be processed in as little 5 min 

each by the acoustic dissolution test. 

Results from these tests could be used to 

build a three-dimensional model of methane concentrations. 

Information can also be gained from 

drill hole data. Long exploration coreholes can be logged for salt composition 

and purity, crystal size, and methane 

content. Also, the disking of core from 

exploration holes has been used to indicate high-pressure gas zones. Oriented 

properly, by knowing existing geologic 

trends, these holes may delineate potential problem areas. In addition, reservoir properties, such as formation pressure and gas flow may be determined. 

Table 3 shows the necessary predictive 

procedures. 

Although the existence of any single 

criterion may not be sufficient to indicate gassiness, it appears that the 

probability of encountering outbursts is 

greatly increased when all three of the 

following criteria are observed: 

1. High methane content. 

2. Unusually large salt crystal size. 

3. Increased tightness of folds and 

kinking. 

METHANE CONTROL STRATEGIES 

Once sufficient mapping and sampling must be implemented to control potential 

data have been obtained to delineate po- emission of methane into the mine. 

tential methane-rich zones, some strategy Iannacchione (3) - found that boreholes 
drilled into gassy salt zones built pressures rapidly when shut in, but that 

these pressures were also rapidly dissipated. Additionally, the holes had relatively low gas flows. Therefore attempts 

at long-range gas drainage by horizontal 

holes would fail in the impermeable salt 

strata. Local drainage might possibly 

have some success. If long exploration 

holes identified methane-rich zones, it 

may be possible to fracture the zone with 

packed charges, and increase permeability 

for methane drainage, and possibly allow 

some stress relief. 

If advance warning of the approach to 

methane-rich zones is provided, then face 

ventilation can be adjusted to dilute 

methane emissions. Also, additional 

methane monitors can be positioned so 

that adequate gas concentration information will be known before personnel are 

admitted back into mine. Finally, avoidance of the potentially hazardous area is 

an option if the hazard is sufficiently 

great. 

SUMMARY 

Approximately 75 pct of the Cote 

Blanche Mine has been mapped for outbursts and sediment inclusions. Approximately 25 pct of the mine has been mapped 

for salt bedding attitude. Two outburst 

areas were mapped in detail for outburst 

size and- shape, salt layering, and salt 

crystal size, and closely sampled for 

salt methane content. Seven sediment 

samples were analyzed petrographically 

and complete grain size distributions 

were developed for 10 other sediment 

samples. 

The mapping and sampling programs at 

Cote Blanche salt mine have shown the 

importance of consistent documentation of 

methane occurrences in understanding the 

extent to which methane is distributed. 

Additionally, several relationships were 

observed that will aid in the prediction 

of gassy zones in advance of mining. 

Methane-rich zones occur as isolated 

linear trends that contact abruptly with 

normal nongassy salt. In two instances 

the zones were approximately 100 to 200 

ft wide, and paralleled a line of outbursts. The gassy zones were identified 

by methane contents more than 150 times 

those outside the zone. Large salt crystals are also known to be related to 

gassy zones, and these large crystals 

delineate the methane-rich zones in the 

study areas. Local salt layering was 

more disturbed in the immediate outburst 

area, and may be diagnostic, but more 

detailed evidence is needed. By mapping 

salt lithology it was observed that 

included sediment did not act as a 

significant source or conduit for methane 

into the Cote Blanche Mine, as it had 

been hypothesized in other domal mines in 

the area. A zone of hard, fine-grained 

salt had numerous methane occurrences 

(outbursts, methane bleeder, petroleum 

seep), suggesting some genetic relationship. Routine methane content testing 

and mapping is an effective way of quickly determining the gassiness of a sample 

and, by projection, a region. 

Mapping has revealed the basic geologic 

structure of the salt dome, as well as 

provided the first documentation of the 

complete extent of outbursting in the 

mine. More than 80 outbursts, ranging in 

size from 1 ft in diameter to more than 

50 ft in diameter have been mapped. They 

tend to occur along linear trends that 

parallel salt layering direction. Unlike 

the other salt mines in the area, outbursts have occurred during bench mining, 

and possibly two have propagated 

downward. 

The other modes of occurrence of methane at the mine include the bleeding of 

methane from face and bench blastholes, 

bleeding from undercuts before blasting, 

and the infrequent venting of methane 

from natural or blast-induced fractures. 

The prediction of gassy conditions in 

advance of mining can be accomplished by 

careful methane testing of blasted faces. 

Information on the methane content can 

also identify large-scale trends of gasbearing salt. Since outbursts tend to 

follow local structural trends, geologic 

mapping is necessary to predict the 
direction of potential outbursts. This also show changes in folding intensity, 

mapping must be accomplished shortly salt crystal size, and methane content 

after mining, before diesel soot obscures information, which can allow prediction 

much of the information. Mapping will of gassy zones. 

CONCLUSIONS 

1. Methane-rich zones at Cote Blanche 

occur along linear trends that roughly 

parallel salt layering. The outbursts 

that punctuate some of the zones tend to 

occur in clusters, with small outbursts 

being important because they indicate 

favorable conditions for the formation of 

large outbursts. These linear trends can 

be projected vertically, which will aid 

in mine planning on multiple ieveis. 

2. Methane-rich zones were found to 

occur abruptly; sometimes being delineated by sharp contacts such as salt 

bands. This means that mining advance 

can be very near a high-pressure gas zone 

without the operators being aware. 

3. Very large, well-formed salt crystals of widely varying size distribution 

have been shown to indicate high methane 

content. These zones of high methane 

content commonly occur throughout the 

mine. Most do not have outbursts 

associated with them. They should be 

documented for purposes of establishing 

minewide trends. Run-of mine salt crystals are normally 1/8 to 1/4 in across 

and methane free. 

4. Measurement of pillar size at one 

outburst area did not appear to show that 

this parameter was related to outburst 

occurrence. 

5. me best predictive techniques 

include consistent mapping and sampling 

for methane content. Another method is 

drilling long exploration holes in 

advance of mining for reservoir properties, core disking, and salt 

composition. 

6. Standard long-hole gas drainage 

techniques will be ineffective in the 

naturally impermeable salt. It may be 

possible to induce local permeability 

with packed charges. 

REFERENCES 

1. Plimpton, H. G., R. K. Foster, 

J. S. Risbeck, R. P. Rutherford, R. F. 

King, G. L. Buf fington, and W. C. Traweek. Final Report of Mine Explosion 

Disaster, Belle Isle Mine, Cargill, Inc., 

Franklin, St. Mary Parish, Louisiana. 

MSHA Accident Invest. Rep., 1980, 

156 pp. 

2. Iannacchione, A. T., R. Ha Grau 

111, A. Sainato, T. M. Kohler, and S. J. 

Schatzel. Assessment of Methane Hazards 

in an Anomalous Zone of a Gulf Coast Salt 

Dome. BuMines RI 8861, 1984, 26 pp. 

3. Iannacchione, A. T., G. L. Finfinger, T. M. Kohler, and D. M. Hyman. 

Investigation of Methane Emissions From 

an Advancing Face in the Belle Isle Domal 

Salt Mine, Louisiana. BuMines RI 8723, 

1982, 24 pp. 

4. Wiesliczka, M. J. Tourist's Guidebook. Cracow Tourist Information and 

Advertising Centre, Cracow, 1977, 62 pp. ; 

available upon request from G. Molinda, 

BuMines, Pittsburgh, PA. 

5. Belchic, H. C. The Winnfield Salt 

Dome, Winn Parish, Louisiana. Sec. in 

Interior Salt Domes and Tertiary Stratigraphy of Northern Louisiana, Shreveport 

Geol. Soc. (Shreveport, LA), 1960, 

pp. 29-47. 

6. Thoms, R. L., and J. D. Martinez. 

Blowouts in Domal Salt. Paper in Fifth 

Symposium on Salt (Hamburg, West Germany, 

Yay 29-June 1, 1978). North. OH Geol. 

Soc. (Cleveland, OH) v. 1, 1980, pp. 119- 

134. 

7. Kupfer, D. H. Shear Zones Inside 

Gulf Salt Stocks Help To Delineate Spines 

of Movement. AAPG Bull., v. 60, 1976, 

pp. 1434-1447. 

8. MSHA Storage Task Force. Fact 

Finding Investigation of Southern Louisiana Salt Domes-Weeks Island, Cote Blanche 

Island, Jefferson Island, Belle Isle, 
Avery Island. 1978, 40 pp.; available 

upon request from G. Molinda, BuMines, 

Pittsburgh, PA. 

9. Halbouty, M. T. Salt Domes: Gulf 

Region, United States and Mexico. Gulf 

Publ. Co. (Houston, TX), 1967, 425 pp. 

10. Golder Associates (Houston, TX). 

Geotechnical Study of Cote Blanche Is land 

Salt Mine--Summary Volume, New Iberia, 

Louisiana. Rep. to Gulf Interstate Eng. 

Co., v. 2, appendix 11, Oct. 1977, 

62 PP. 

11. Schatzel, S. J., and D. M. Hyman. 

Methane Content of Gulf Coast Domal Rock 

Salt. BuMines RI 8889, 1984, 18 pp. 

12. Hyman, D. M. Methodology for 

Determining Occluded Gas Contents in 

Domal Rock Salt. BuMines RI 8700, 1982, 

11 PP* 

13. Muehlberger, W. R., and P. S. 

Claybaugh. Internal Structure and Pe trofabrics of Gulf Coast Salt Domes. Sec. 

in Diapirism and Diapirs-A Symposium. 

AAPG mem., 1968, pp. 90-98. 
LEGEND 

a* Outburst 

F lnoccessible area 

FIGURE 2.-CoaUon 01 oulbuntr In Cote 8lmcha Min. 
LEGEND 

-0- Outburst 

Bench mined area 

EZl Foce mined only 

0 400 800 t11rI 

Scale, ft 

oobooooo 

FIGURE S.-Locrtion of outbursts that occurred during bmch mlnlng at Cote Blanche Mine. 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

-J 

- 

- 

- 

- 

- 

- 

-RN 

-ON 

PN 

-ON 

NN 

MN 

-LN 

-KN 

-JN 

-IN 

HN 

-GN 

FN 

-EN 

DN 

CN 

BN 

-AN 

Main East 

-AS 

-8s 

-CS 

-DS 

-ES 

F S 

-GS 

-HS 

I S 

S 

KS 

L S 

-MS 

-NS 

-0s 

P S 

0 S 

R S 

S S 

S 
om KC1 

Fine grained salt 

Black carbonaceous silt cloy 

---- Inferred cmtact 

o Methane bleeder 

0 400 800 #.#.I 

Scale, ft 

-ES 

-FS 

-GS 

- H s 

IS 

-JS 

-KS 

-LS 

- MS 

- NS 

- 0s 

- P S 

-as 

- RS 

- S S 

-1 S 

FIGURE L-G.ologk IIUp ot Coh Bllmh. Mim. 
LEGEND 

A Salt layering 

Or Sandy bed 

'--- Inferred contoct 

DS 

- E S 

-FS 

-GS 

-ti S 

-is 

-JS 

- K S 

-LS 

-MS 

-NS 

-0s 

FIGURE 9.-Ssn lryerlng and dialribution of undy beds. 
LEGEND 

@ Outburst 

Methane content, cm per l OOg NaCI : 

A 0.0 10 0.3 (low) 

0.3 to 1.0 (medium 1 

0 > 1.0 (high) 

Scale, f t 

FIGURE 15.-Location of outbursls and MR aampler with methane content In Cole Blanche Mine