983

Sideronatrite from mineralized cavities in the Rising Sun
colliery, Backworth, Northumberland
By B. A. O. RANDALL, B.Sc., Ph.D., and J. M. JONES, M.Sc., Ph.D.
Department of Geology, University of Newcastle upon Tyne
[Read 9 June 1966]

Summary. Two unusual cavities at a Northumberland colliery are described.
Although apparently of tectonic origin they do not seem to be related to any majer
fault. Sideronatrite, not previously recorded in this country, is thought to result
from the alteration of the marcasite and pyrite lining the cavities by undergroundsaline waters. These waters are the source of the baryte and gypsum that are also
found in the cavities and of the salt stalactites in the disused roadways of thecolliery.
WO cavities were encountered in June 1960 during work in theBrockwell coal seam, 1220 ft below sea level, at the Rising Sun
colliery, Northumberland; grid reference 431401/567640. They werebrought to the authors' attention as a result of their inquiries into thepresence of cavities within igneous dykes in the Northumberland coalfield. Through the courtesy of the National Coal Board the authors
visited the Rising Sun colliery on 29 April 1965 and examined thecavities though work in t h a t district of the mine had ceased.
The two cavities are close together but at slightly different levels. Thelower, more easterly one is largely below the floor of the roadway while
the upper is entirely above the level of the roof (see fig. 1).
The lower cavity, which is elongate north-south, is 36 ft in length witha maximum width of 6 ft 6 in. and height of 9 ft. I t can be enteredthrough a low passage or ' c u n d y ' , the top of which is only I ft 6 in. above
the floor of the roadway. The roof of the cavity is flat and uniform, being
formed by a bedding plane in sandstone, b u t the floor is uneven and iscomposed of fallen debris.
The main chamber contains two pools of water, a few feet deep, which
are separated b y a ridge of rock debris. The water in the pools was foundto be at 24"5 ~ C despite the fact t h a t cold water from other workings in
the pit was being pumped into the cavity. The high air temperature of
26 ~ C probably results from the reduction of forced ventilation in thedisused workings. I t is, however, reported t h a t when the cavity was first
discovered a shallow stream of hot saline water flowed through it. ThisTB. A. O. RANDALLAND a. M. 5ONES ON

984

s~,
9:..

oclU
.

9 . . . . . . ~ . . .

.... , - . . . . . . .~. . . . . , . . . .

Cold water~.: ."

covet,//.

18
I, \ \ \\\\\\Water ~I\, \ \ \ \ \\\ Co,,op.ed.a,,\ \ \ ~9 LOWER CAVITY&_\ ~-~--~-\\~__---(b) PLAN
0\\\\ \\ \\ \\\,\\\'\ /no mineralisation\_~4 ~ ~ ~' o ~ ~ -''iA'~-_~~--~\. . . .

........
so, .... IsIOreet,, ~ \\ \ \ UPPERCAWTY..~..,.~.,~ \,..~ \ 0bo,,eroof"" Z? "'..'[;::~" of ro0dw0,/

Hode about 30 ~Av/
Yellow s t o f o q m i t e ~ - ~..._._._.~.~.

(c) TRANSVERSE SECTION
OF LOWER CAVITY

1~

Nineralisec ~ 1 1 ~Level of
Roa__dwo_y__',-4--Oriqinol wall before collapse

FIc. I. Sketch illustrations of the Rising Sun cavities.

SIDERONATRITEFROMNORTHUMBERLAND

985

flow of water has now been upset by the colliery drainage but saline
water is still pumped from the pit for barium extraction.
The walls of the cavity are almost vertical and appear to be controlled
by the natural joint planes of the sandstone, although the western portion has an upward extension that hades to the east at about 30 ~ . It isprobable that all the walls and roof of the original cavity were mineralized but subsequent collapse of the roof and eastern wall has altered theshape of the cavity and exposed uncoated sediments.
The western wall is covered with botryoidal marcasite and pyrite,
which in turn is coated with a thin (1 ram) coating of rust-redpowdery
material. The development of the botryoidal sulphides shows marked
horizontal structures, as if its growth had been controlled by varying
water levels (see fig. 2).
The upper cavity, which lies some six or seven yards to the west of thelower one, is irregular in shape and could only be penetrated for a shortdistance; the entry is from the roof of the roadway. It extends upwards
about 12 ft and has an estimated length of 14 ft in a north-south direction, i.e. at right angles to the roadway. The width is extremely variable
reaching a visible maximum of only 4 ft. Although previously there had
been an accumulation of gas in the cavity it was relatively gas free at thetime of the visit.
The upper cavity appears to be entirely lined with botryoidal sulphides, but in contrast to the lower cavity many of the growths are of apendant nature. This is probably due to the more vertical attitude of thewalls and similar pendants may well have formed part of the original
roof lining in the lower cavity. The sulphides again show a marked horizontal structure but are much more 'yellow' than their counterparts inthe lower chamber, although some have an extremely thin red veneer.
In places the sulphides are coated by a fungoid-like growth of a yelloworange mineral, later identified as sideronatrite.
Specimens collected from the cavity are mainly of brecciated sandy
siltstone coated with sulphides. In addition, a few unmineralized fragments of shale and coal were found lying on the floor.
The cavity seems to be an expansion of a one-inch vein, which isvisible in the roof and north wall of the roadway. Below the cavity in thesouth wall of the roadway there are a series of ~-89in. veins hading 20-30 ~E and in the coal seam, 8 ft below the cavity, there are a few minor faults
with downthrows to the east of 89in. and 1 in.
The sulphides. The principal minerals in both cavities are marcasite
and pyrite, the former predominating. These minerals form a skin on the986

B. A. O. R A N D A L L AN]) J . M. J O N E S ON

walls of the cavities t h a t is variable in thickness b u t rarely exceeds oneinch, although some of the pendant growths of the upper cavity are more
massive. The sulphides are botryoidal b u t have grown in such a mannert h a t all the bulbous masses are aligned horizontally. When specimens ofthe sulphide layer are polished both radial and concentric growths arevisible and it is seen t h a t while most of the material is marcasite, pyriteis present as thin concentric layers within the main mass.

0L

6i~chestIlFins. 2 and 3: Fro. 2 (left). Drawing of botryoidal sulphides from lower cavity
showing marked horizontal structure.
FIG. 3 (right). Hemispherical shells of halite on wooden pillar.
Some of the sulphide from the upper cavity has a dull tarnished surface while other material is covered b y a thin red film. Unfortunately thelatter was too thin to collect without excessive contamination. X-ray
photographs of material scratched from the surface indicated only marcasite with a little gypsum.
Baryte. A thin deposit of rust-coloured material covers most of thesulphides of the lower cavity. An X-ray powder photograph of thismaterial showed t h a t baryte was the dominant material but gave noindication of the presence of any iron bearing mineral. A t first sight thisseems surprising but many strongly coloured rocks, such as the Penrith
sandstone, may contain only 1 % of total iron as F%0~ (Waugh, 1965).
Optical examination of this material confirmed the presence of baryte

SIDERONATRITE FROM NORTHUMBERLAND

987

although much of it was almost opaque because of iron staining. Spectrographic analysis indicated the presence of many elements in addition
to barium in particular strontium and sodium. It seems probable that thestrontium is replacing barium in the baryte and that the sodium indicates the presence of a minute quantity of halite.
Sideronatrite is found in moderate quantity encrusting some of thesulphide in the upper cavity. It is lemon-yellow to orange in colour andoccurs in composite masses of spherical shape up to ~ in. in diameter.
The individual crystals, which are about 1 mm in length, are prismaticand appear to be terminated by macrodomes. There is a dominant {010}cleavage and the two refractive indices (y and fi) measured on it are
1.584 and 1.526 ; y is pale yellow, and fl almost colourless. These properties agree well with those given by Larsen and Berman (1934).
The density of the mineral, which is insoluble in cold water, was determined by suspension in a graded density column used in conjunction
with a goniometer (Jones, 1961) and was found to be 2"045. This figure isconsiderably less than the value usually quoted for this mineral, 2.152.35 (Palaehe et al., 1951). X-ray powder photographs yield d-spacingsthat agree very closely with published data (Cesbron, 1964; Van Tassel,]956).
When heated in water the sideronatrite broke down with the formation of a red-brown flocculant material that on X-ray examination
proved to be natrojarosite.
Gypsum. A small fragile stalagmite (89in.) of yellowish material foundin the westerly upward extension of the lower cavity proved to be composed of gypsum. Small crystals of gypsum were also found adhering to
the surface of some of the sulphides from the upper cavity.
Calcite. Small quantities of calcite were located between the sulphidelayer and the wall material in the upper cavity. These appear to havebeen formed prior to the main sulphide mineralization.
Halite. All the specimens collected from the cavity were cleaned in cold
water in the laboratory to remove pit dirt. Upon drying a thin encrustation of halite was visible on many of them, especially those composed
mainly of sandstone, proving that the rocks in this vicinity have been
impregnated by underground saline waters.
Large numbers of salt stalactites were seen in the disused roadwaythat leads to the cavity. Some of the more massive of these stalactites areup to 189in. in diameter and cubic salt forms are visible on their attachment areas. Most, however, are only ~ in. to 89in. in diameter even though
they may be several feet in length, and on occasion extend from ceiling

988

B.A.O. ~A~CDALLA ~ D J. M. JO~ES ON

to floor. Nearly all the stalactites have a circular central cavity runningtheir entire length such that the very narrow ones are virtually thinwalled tubes.
Salt, in the form of extremely thin-walled hemispherical shells, about
the size of raindrops, was also found attached to the walls and timbers of
the roadway (see fig. 3).

The origin of the cavity
The cavities described in this paper cannot really be compared eitherwith those described by Randall and Jones (1966) in the dykes of theNorthumberland Coalfield or with eaves in carbonate rocks, which owe
their origin to solution. Although it is considered that their formationmust arise from tectonic movement they do not appear to be in any way
related to a maior fault. In the roadway section only small faults withthrows of less than one inch are visible in the vicinity of the cavity but
there are reports of minor faulting a little further east.
There are many indications of transcurrent fault movement in Northumberland (Robson, 1964), so that it is possible that the apparently
minor faults near the cavity could have important lateral components,
not visible because of the horizontal nature of the strata. If transcurrent
movement can be visualized in this instance, then irregularities on thefault plane would perufit the development of cavities.
The lower cavity is developed in a homogeneous fine-grained sandstone. In thin section it is seen to be a compact rock with a mosaic-likestructure due to the secondary growth of quartz around the original sandgrains. In addition the rock contains small areas rich in minute baryte
crystals. The rock is both compact and competent and sufficiently strong
to withstand the rock creep that at this depth would tend to fill thecavity; such movement is indicated by the buckled metal girders in theroadway. The wall-rock of the upper cavity was inaccessible but material
collected from it did include sulphide coated brecciated mudstone andsandy shale.

The mineralization
Since the principal minerals of the cavity are pyrite and marcasite,both ubiquitous in the Coal Measures, it is thought most probable thatthey have been derived from the adjacent rocks and concentrated in thecavities by circulating ground-waters. There seems to be no need to propose any unusually high temperatures for this process. Cavities in thedykes of the coalfield also contain these minerals (Randall and Jones,

SIDERONATRITE FROM NORTHUMBERLAND

9891966) and these too are ascribed to a low temperature transference ofmaterial. The marked horizontal structure developed in the sulphides of
the Rising Sun cavities, which is absent in the deposits of the other cavities, suggests t h a t there has been a frequently fluctuating water level.
I t is tempting to t r y to equate the sulphide mineralization of these cavities with t h a t of the Sleekburn Dyke cavity (Randall, 1953), which mustbe Tertiary or younger in age. However, such correlation seems untenable and it is felt t h a t no estimate can be made as to the age of thismineralization.
The other minerals in the cavity have resulted from the alteration of
the sulphides or from the underground saline waters. Sideronatrite,
although well known in the iron deposits of Chile (Bandy, 1938; Van
Tassel, 1956; Cesbron, ]964), has not been recorded previously inBritain. I t has, however, been found in Belgian coal-mines both onwooden pit-props and as patches in sandstone (Van Tassel, 1956) andmore recently in Israel (Sass, Nathan, and Nissenbaum, ]965). The morenormal weathering product of iron sulphides is jarosite, which is recorded
from m a n y localities (Cosgrove and Hodson, 1963). I t seems probablet h a t the formation of sideronatrite, in this instance, is related to thesaline nature of the underground waters (Anderson, 1945) and probably
to the moderately high air temperatures (26 ~ C and over) recorded in thisp a r t of the pit. The association of this mineral with the gypsum, baryte,and halite can hardly be fortuitous.
A t one time the cavities and the roadway were flooded and the very
rapid erosion of the iron work in the roadway leaves little doubt t h a t thiswas saline water. The formation of the sulphates is probably due tothe breakdown of the sulphides producing sulphurie acid, which thenreacted with the material contained in the saline water to produce
sideronatrite, baryte, and gypsum. The halite, which is found both as
stalactites and as a general impregnation of the specimens, would beproduced wherever there was evaporation of the saline water; certainly
the hemispherical shells of salt found on the roadway walls and timbers
were formed in this manner.
Acknowledgements. Whilst all opinions expressed are those of the authors, thanks
are due to the National Coal Board for permission to publish this article. The authors
are particularly grateful to the officials of the Rising Sun colliery and the Group
Surveyors for information regarding the presence of the cavities and for their hospitality and assistance at the time of the visit.

References
ANDERSON(W.), 1945. Geol. Mag., vol. 82, pp. 267-273.
BANDY (M. (].), 1938. Amer. Min., vol. 23, pp. 669-760.

990~. A. O. RANDALL AND J. M. JONES ON SIDERONATRITECESBRON (F.), 1964. Bull. Soc. f'ran~. Min. Crist., voh 87, pp. 125-143.
COSGROVE (M. E.) and HO~SON (F.), 1963. Proc. uGeoh Soc., voh 34, pp. 8190.
JONES (J. M.), 1961. Journ. Sci. Instr., voh 38, pp. 303-304.
LARSEN (E. S.) and BERMAN (H.), 1934. U.S. Geol. Surv. Bull. no. 848, p. 101.
PALACHE (C.), BERIvIAN (H.), a n d FRONDEL (C,), 1951. D a n a ' s System of Mineralogy.
7th edn., vol. 2, pp. 604-605.
I~AI~!DALL(B. A. O.), 1953. Min. Mag., vol. 30, pp. 246-253.
and JONES (J. M.), 1966. Trans. Inst. Mining Eng., voh 125, pp. 309-317.
RoBsoN (D. A.), 1964. Proc. Yorks. Geol. Soc., voh 34, pp. 293-308.
SAss (E.), NATHAN (A.), a n d NlSSENEAUM (A.), 1965. Min. Mag., -col. 35, pp. 84-87.
VA)I TASSEL (R.), 1956. Bull. Inst. Roy. Sci. Nat. Belg., vol. 32, no. 51. [M.A. 13-370]
WAUGH (B.), 1965. Diagenetic and environmental studies of Permo-Triassic sedim e n t s in the Vale of Eden. Unpublished Ph.D. thesis, University of Newcastle
upon Tyne.
--[Manuscript received 19 March 1966.]