MINERALOGICALMAGAZINE,SEPTEMBER

I979,

VOL. 4 3 , PP.

389-95

Cobalt-, nickel-, and iron-bearing
sulpharsenides from the North of England
R. A. IXER, C. J. STANLEY, AND D. J. VAUGHAN
Department of Geological Sciences, University of Aston in Birmingham, Birmingham B4 7ET
SUMMARY. Within the Alston Orefield of the North
Pennines, glaucodot and gersdorffite have been found insamples from Tynebottom Mine, Garrigill, and zoned
gersdorffite has been found from Nenthead and the Great
Sulphur Vein. At Scar Crag in the English Lake District,glaucodot and alloclase (the first reported occurrence inthe United Kingdom) occur associated with arsenopyrite
and minor cobaltite and skutterudite. The mineralogy
and parageneses of these associations have been studied
by ore microscopy, X-ray powder photography, andelectron probe microanalysis.
Electron probe microanalysis shows a considerable
range in nickel content in the sulpharsenides from the
Alston Orefield with a relatively constant Co:Fe ratio.
Samples from Scar Crag contain no nickel but exhibit
almost a complete range of Co:Fe ratios from FeAsS to
CoAsS. The compositions of the Alston Orefield sulpharsenides, in particular, show them to be metastablephases when compared with data from synthetic studies.
At Tynebottom Mine, glaucodot and gersdorffite overgrow arsenical marcasite, and at Nenthead and the Great
Sulphur Vein, early pyrite framboids or euhedra act as
cores to zoned gersdorffite crystals. The Scar Cragsulpharsenides occur in a quartz chlorite apatite veinwith the glaucodot and alloclase as overgrowths on
arsenopyrite.
In the case of the Scar Crag association, considerationof the compositions of coexisting phases, together with
precise determinations of the arsenic content of thearsenopyrites, has permitted speculation regarding temperatures and sulphur activities during ore formation.
Estimated ranges are Tc. 400 ~~ and as2 ~ m-9-I0 11 bar. The occurrence of the sulpharsenides in the
Alston Orefield correlates with further geochemical differences compared to other Pennine ores, differences thathave been linked to higher temperatures of formation
and a magmatic contribution to the ore-forming fluid.
The Scar Crag mineralization may be related to a postulated stock intrusion beneath Causey Pike and thegeographical proximity of the Alston and Scar Cragoccurrences does suggest the possibility of a genetic link.

SULPHARSENIDE minerals of cobalt, nickel, andiron have been found in two distinct associations
within the Alston Block area of the N o r t hPennines; cobalt and iron-bearing sulpharsenides
have also been found in ore samples from Scar
Crag in the English Lake District. The corn-

Copyright the Mineralogical Society

positions, mineral properties, associations, andparageneses of these newly reported phases arepresented here, together with some speculations as
to the conditions of formation of the assemblages.
At Tynebottom Mine, Garrigill [ N Y 739 418],
glaucodot and gersdorffite have been found insamples collected from dump materials. The occurrence of cobalt-bearing minerals from Tynebottom
Mine confirms the suggestion by D u n h a m (1948) of
the presence of an 'unknown cobalt arsenide orcobalt sulphide', which was made on the basis ofabundant erythrite around the mine. A second
association, which contains zoned crystals of
gersdorffite, occurs both in material collected from
Nenthead [ N Y 79 ~ 436] and from the Great
Sulphur Vein [NY 74 ~ 39o]. The mineralization at
Scar Crag [ N Y 2o6o 2o7o] in the Lake District
contains glaucodot and alloclase associated witharsenopyrite and minor amounts of cobaltite andskutterudite. This is the first authenticated occurrence of alloclase in the United Kingdom. Samples
collected from surface exposures and obtained
from the Kingsbury Collection at the British
Museum have been studied in this work.
The geological setting of the mineral veins of the
Alston Block and their general mineralogy has been
discussed in detail by D u n h a m (1948). The Scar
Crag Vein (also known as the 'Cobalt Vein')outcrops above the footpath from Braithwaite
village to Sail and Scar Crag in Long Comb, about
one kilometre to the west of Causey Pike. Strens0962) considered that the vein, which trends a few
degrees east of north, was emplaced along a preBala tear fault in Mosser-Kirkstile slates of the
Skiddaw Slates Group. Although minor amountsof cobalt- and nickel-bearing phases have beenfound at Coniston (Russell, I925) and at Dale Head(by C. J. S.), the over-all assemblages are different
from those at Scar Crag, which appears to bea unique association for the Lake District.
Unsuccessful attempts to extract cobalt at Scar
Crag have been recorded by Postlethwaite (I913).
Experimental methods. Samples have beenstudied using reflected light microscopy andR. A. I X E R

39~

selected areas analysed by electron microprobe.
The instrument used was a Cambridge Microscan V employing .an accelerating voltage of
15 kV. Standards used were synthetic sulphides
and sulpharsenides and the results were corrected by standard procedures. Certain samples
were also examined by X-ray powder (DebyeScherrer) photography using Co radiation. Veinmaterial from Scar Crag was also examined inthin section.
Mineral data. At Tynebottom Mine, glaucodot
and gersdorffite overgrowths on arsenical marcasite occur within a quartz, calcite, and ankerite
gangue. The arsenical marcasite forms I-2 cm byo.2 cm laths, which are randomly oriented orcollected into sheaf-like aggregates or rarely intolarge (2- 5 cm) anhedra (see fig. I). In oil immersion,it has a distinct green-white to pink-brown reflection pleochroism and a strong, green to brownanisotropy. The laths show a fine diamond-shaped

E T AL.

FIG. I. Photomicrograph of a polished section showing
euhedral subhedral sulpharsenide overgrowths on lathcrystal of arsenical marcasite, Tynebottom Mine,
Garrigill.

TABLE I. Representative electron microprobe analyses of cobalt, nickel, and iron-bearing sulpharsenides(All data in wt. ~.)Locality/Mineral Species

Fe

Co

Ni

As

S

Total

Arsenical marcasite

39.83
39.77
44.I9

3.34
3-75
0.88

1-24
1.14
o.12

8.60
8.68
4-13

46.67
46.44
50.55

99.68
99.79
99.87

Gersdorffite

4.86
3-35
2.36

11.45
11.88
7-03

t9.28
21.39
24.49

46.70
44.84
45.95

20.02
19.57
18.82

lO2.3o1Ol.O498.65

Glaucodot

12.o4
9.86
I 1.29I 1.24

22.o3
2i.o6
23.68
24.27

2.22
5.80
1.71
1.56

45.69
43.98
42.27
40.41

20.64
21.93
21.59
23.92

IO2.62IO2.62
IO0.54
101.41

Arsenopyrite

34.7
35.o
34.2

0.3
o.3
0.4

----

44.6
45-4
46.7

t9,7
2o.i
I9.I

99.3
lOO.8
lOO.4

Alloclase

4.8
4-9
4.8
5.9
6.4
6.1
6.8
5.6
5 .6
6.7
8.0

32.0
32.0
30.9
29-5
29.8
29. 5
29. 4
3o.1
30-4
28.2
27.1

--------~
--

46.6
46.4
46-3
47-3
45.7
47.4
45.9
47-3
47.5
48-1
48.3

18.o
17.3
I7.4
I6.9
17.8
16.9
18.9
18.4
17.7
16-9
16.8

lOl. 5
IOO.6
99-4
99.6
99-7
99-9
lOl.O
IOl.5
IOI.2
99.9
I00.2

Glaucodot

II. 9
I5.8
13.4
12.8
24.0.
24. 5
22.4

23.61
19.4
22. 3
23.2
10.6
IO.7
12.8

--------

46.2
46.3
45.8
46.2
45-4
46.1
46.7

19.4
I9.1
18.8
19.1
19.I
17.9
I7.2

IOI.l
ioo.6
lOO.3
1OI.3
99 -I
99.2
99.1

Alston Block ( Tynebottom Mine)

Lake District (Scar Crag)--

Cobaltian Arsenopyrite

28.2

5.9

--

47.o

18.7

99.8

Cobaltite

2.0

33.6

--

44.7

I9.O

99-3

Skutterudite

2.7

I9.5

--

77.2

1.7

lO1.1

S U L P H A R S E N I D E S FROM THE NORTH OF E N G L A N D
cleavage in addition to later fracturing and individual marcasite rhombs are composed of acomplex intergrowth of small (< 5/~m) domains.
Compared to normal marcasite it has a lower
reflectivity and the yellow component of the reflection pleochroism is absent. Electron microprobe
analysis (Table I) shows the marcasite commonly
contains in excess of 8 wt. ~o arsenic as well as 3-4
wt. ~o cobalt and c. ~ wt. ~ nickel. Along the widthof the marcasite laths, oriented tabular aggregatesof pyrite or pyritohedra (5-2o pm diameter) occur.
The pyrite itself encloses small pyrrhotine ( < 5 pm)
inclusions.
The cobalt-, nickel-, and iron-bearing sulpharsenides at Tynebottom form subhedral to euhedral
overgrowths (up to 4o pm in width) on the edges offractured marcasite or heal internal fractures. The
overgrowths have two, or sometimes three, optically distinct phases, which have been identified byelectron microprobe analysis. The relationships
between these phases and the distribution of Co,
Ni, Fe, As, and S between them are illustrated in fig.
2. The outermost phase has been identified as
gersdorffite by electron microprobe analysis (seeTable I). It displays a good cubic cleavage, cubic
habit and is pink-yellow in colour under the ore
microscope. It is isotropic to weakly anisotropic.
The analytical data (Table I) show dominant nickel(c. I7-24 wt.~o) with lesser cobalt (c. 7-~2 wt.~o)and minor iron (c. 2-6 wt. ~). The phase within thishas been identified as glaucodot by electron microprobe analysis (and X-ray powder diffraction). It
contains dominant cobalt (c. I9-24 wt.Yo) withlesser iron (c. 9-12 wt.~o) and minor amounts ofnickel (c. I-6 wt. ~o). This glaucodot exhibits slightpink to yellow-pink reflection pleochroism andmoderate anisotropy. Both phases take a goodpolish and have reflectivities a little below that ofpyrite on qualitative observation.
A thin zone, adjacent to the enclosed arsenicalmarcasite, appears an optically distinct third phasein some parts of the sections as it has a lower

39I

reflectivity. The electron microprobe data, however, show that this phase has the composition of
gersdorffite (fig. 2, Table I). Frequently, the sulpharsenide overgrowths display optical continuity
with the enclosed marcasite. Minor amounts ofeuhedral gersdorffite (c. Io/~m diameter) also occur
associated with anhedral chalcopyrite grains (c. 2o#m diameter).
In the material collected from the Great Sulphur
Vein and from workings at Nenthead, euhedral
zoned gersdorffite crystals have been found inquartz in association with anhedral chalcopyrite
and pyrite. The gersdorffite was identified initiallyon the basis of its optical properties in comparison
with the Tynebottom Mine material. Electron
microprobe analysis showed the presence of major
nickel, sulphur, and arsenic with some cobalt andiron, but it was not possible to obtain quantitative
data for these small grains. Gersdorffite occurs as
small (5-Io/~m) discrete, lilac-white euhedral crystals within vein quartz and calcite, and withinmineralized shaley limestones. Associated opaqueminerals are chalcopyrite, galena, pyrite, and marcasite. The gersdorffite euhedra display cubic habit
and cleavage (triangular polishing pits), and exhibit
faint zoning characterized by colour differences(lilac to pink) and differences in reflectivity andhardness. The zoning is difficult to see in freshly
polished material but the colour differences between zones gradually become enhanced. The zone
boundaries follow the crystal outlines andfrequently more than one (c. 2-3 pm wide) zone ispresent. The zoning is too fine in scale to enable
compositional differences between zones to be
determined by microprobe analysis. Small pyrite
framboids or euhedra act as cores to many
gersdorffite crystals and the gersdorffite itself iscommonly enclosed and replaced by galena andchalcopyrite.
At Scar Crag, cobalt-iron sulpharsenide minerals
occur with arsenopyrite in a quartz-chloriteapatite vein. Quartz is by far the most dominant

FIG. 2. Electron microprobe X-ray scanning micrographs of a bladed crystal of arsenical marcasite with sulpharsenide overgrowths (bottom), Tynebottom Mine, Garrigill: (a) sulphur K~; (b) arsenic K~;(c) cobalt K~;(d) nickel K~;(e) iron K~.

392

R . A . IXER E T AL.

FIG. 3. Photomicrographs of polished sections of material from Scar Crag: (a, left)Arsenopyrite(bottom) overgrown by
alloclasewith cobaltite euhedra developed along a fracture in alloclase.(b, right) Zoning in glaucodot shown by etchingwith saturated ferric chloride solution (high-cobalt glaucodot is less etched than low-cobalt glaucodot and cobaltian
arsenopyrite).

vein mineral; early quartz is often euhedral andwith a zoned arrangement of inclusions. Rutile
occurs within quartz either as radiating bunches offine needles (< ioo pm in length) or as subhedralgrains (< 3o pm). Small amounts of tourmaline
showing blue-brown pleochroism occur as subhedral to euhedral grains (< 4oo pm) associatedwith early quartz. Abundant apatite occurs as large
euhedra (< 5 cm in some specimens) growing
inwards from the vein margins, and chlorite is also
common. Arsenopyrite is the most abundantopaque mineral present, occurring as large euhedral and subhedral grains and aggregates ( < 3ram). Electron microprobe analysis (Table I) showsthat the arsenopyrite always contains some cobalt(usually < I ~o) and slight zoning is evident inpolished section. This zonation could be related to
the variations in S:As ratio but this was notobserved in electron microprobe data, andKretschmar and Scott (1976) have pointed out that
'optically zoned arsenopyrites are not necessarily
compositionally zoned'. The arsenopyrite is overgrown by glaucodot or, more commonly, alloclase.
Electron microprobe data for both phases arepresented in Table I. In contrast to the Alston
area sulpharsenides, no nickel is present in theseminerals and there is a much greater variation in

the Fe:Co ratio, which was relatively constant in
the former samples (Table I, fig. 4).
The identification of glaucodot and alloclase at
Scar Crag has been substantiated by X-ray powder
FeAs S34~o-

Co As S 3oo" 4oo"

soo"

soo 9

4oo"

3oo'

NiAs S

FIG. 4. Compositions of cobalt-, nickel-,and iron-bearing
sulpharsenides from northern England plotted (in atomic
per cent) on the ternary diagram FeAsS CoAsS-NiAsS(xScar Crag phases; o Tynebottom phases). Also shown are
the solid solution limits experimentally determined byKlemm 0965).

S U L P H A R S E N I D E S F R O M THE N O R T H OF E N G L A N D
photography. The X-ray powder data obtained forglaucodot are closely comparable to published data
and distinctly different to data obtained for the
more cobalt-rich alloclase. Comparison of the data
for Scar Crag alloclase with that published by
Kingston (i97I) and by Petruk et al. 0 9 7 0 for thetype material and samples from Cobalt, Ontario,
respectively, support the identification. Although,as illustrated by our analysis, alloclase is a generally
more cobalt-rich sulpharsenide than glaucodot,
there is no evidence of a clear break in compositionin the CoAsS-FeAsS solid solution series (fig. 4).
The distinction between glaucodot and alloclase
must be made on the basis of crystal structure,glaucodot being of orthorhombic space group
Cmmrn (Ferguson, i946), whereas alloclase fromthe type locality is now known to be monoclinic, ofspace group P21 (Scott and Nowacki, I976).
Although alloclase is not easily distinguished inpolished section, it does have slightly lower polishing hardness and reflectivity than arsenopyrite andexhibits purple/mauve-greenish olive anisotropic
tints under partly crossed nicols; arsenopyrite
exhibits blue and orange tints whereas the colours
exhibited by glaucodot are much less intense greys
and browns.
As well as anhedral overgrowths ( < 5oo/~m) on
arsenopyrite, alloclase occasionally forms ( < IOO/~m) subhedra. It also sometimes encloses grains ofskutterudite ( < 2o #m) as confirmed by microprobe analysis (Table I). Cobaltite, also confirmed
by electron microprobe (Table I) occurs as smalleuhedra ( < 5o pm) at the outer margin of thealloclase, at the boundary between alloclase
and arsenopyrite or along fractures in these twominerals. Other minerals observed are: marcasite,which rarely overgrows alloclase; native bismuth,which occurs as inclusions in arsenopyrite andearly quartz; bismuthinite, which occurs along
fractures in arsenopyrite and alloclase and at grainboundaries; and a few small ( < 2o /lm) molybdenite fibres.
Certain of the Scar Crag specimens exhibit a finezonal texture with individual zones having compositions of cobaltian arsenopyrite, glaucodot, andalloclase. This faint zonation is best seen underpartly crossed nicols and is enhanced by etching.
Although previous studies of the mineralization at
Scar Crag have resulted in reports of scheelite(Kingsbury and Hartley, I957) and 1611ingite(Strens, 1962), neither of these minerals was foundin the present study, despite considerable searching.
Mineral parageneses. At the Tynebottom Mine,the earliest phases are pyrite with very minor
associated pyrrhotine. These are succeeded by thearsenical marcasite, which is in turn overgrown by
the sulpharsenides--gersdorffite and glaucodot.

393

Some euhedral gersdorffite is also associated withlater chalcopyrite and very minor arsenopyrite
occurs within the carbonate gangue. Oxidation of
the pyrite to limonite and of the gersdorffite toerythrite has occurred as a result of weathering,
especially along cleavages.
The paragenesis at Nenthead and the Great
Sulphur Vein is of early pyrite framboids or euhedra
acting as cores to gersdorffite crystals, which havein turn been enclosed and replaced by galena andchalcopyrite. Weathering has resulted in the alteration of chalcopyrite to covelline, blaubleibendercovelline, and limonite along cleavages and crystal
edges; of galena to anglesite and covelline orcerussite and chalcosine; and of gersdorffite tolimonite.
PARAGENETICDIAGRAM

quartzmuscovite
apatitetourmaline
futileDmchloritearsenopyrite
glaucodot
olloclasite

cobaltite
skutteruditemmarcasite

bismuthbismuthinite
molybdenlte--?

pyritehaematitescoroditepsiJomelane
erythHne. . . . . .

FIG. 5. The mineral paragenesis at Scar Crag, Lake
District.
The Scar Crag paragenesis is illustrated in fig. 5.
Quartz, rutile, tourmaline, and apatite appear tohave been the first minerals introduced into the veinwith minor muscovite, now mostly replaced bychlorite. Quartz was probably deposited throughout the main period of ore mineralization. The
major ore minerals were deposited at the same timeor shortly after these early minerals and arsenopyrite was the first of these phases. Arsenopyrite isovergrown (but not replaced) by later glaucodot
and alloclase. Skutterudite occasionally is foundenclosed by alloclase; cobaltite and marcasite
formed later than alloclase. Native bismuth occurs
within arsenopyrite and early quartz, bismuthinite
is a slightly later phase. Minor molybdenite andpyrite occur as late minerals in the primary
assemblage. There has been extensive later
replacement of arsenopyrite by scorodite and394

R. A. IXER E T AL.

some replacement by hematite. Psilomelane is the main phase of sulpharsenide formation can befound as a coating on joint planes and erythrite approximately estimated by the formation ofhas resulted from weathering of the cobalti- native bismuth and bismuthinite at this time (fig. 5).
ferous sulpharsenides.
In fig. 6, the bismuth-bismuthinite sulphidation
Discussion. Very little data are available on phasecurve (Barton and Skinner, i967) is plotted on arelations in the ternary system FeAsS-CoAsS- diagram showing variation of log as~ with temperaNiAsS (or its constituent binary systems). Klemm ture; also plotted are the limits of temperature and(I965) has investigated equilibrium solid solution sulphur activity defined by the range of As content
limits in the dry FeAsS-CoAsS-NiAsS system as a in Scar Crag arsenopyrite. Sulphidation curves forfunction of temperature and his results are shown certain F e - A s - S phases are also shown along within fig. 4, together with the sulpharsenide com- the curve for the sulphidation of pyrrhotine topositions determined in this work. According to pyrite.
these data, most of the su!pharsenides found in thiswork should form only above 3oo ~ and many
only above 5oo ~ A few analyses represent com.,,
positions that cannot be synthesized in the dry
system. Estimates of the temperatures of mineraliz-6
ation in the Alston orefield (from fluid inclusionZand isotope studies) indicate appreciably lower
temperatures than 300 ~ (c. IOO-2OO ~1966; Smith, 1974). The sulpharsenide assemblages
from the Alston orefield are certainly metastable,
like the bravoites that are a significant minor
feature of the mineralization of the South Pennines-12
2. 31,55 at %Arsenic-13(Ixer, 1978). Klemm (1965) suggested widespreadmetastability of glaucodot by comparison of his
experimental work with analyses from the literature.
%0
'
560
1,8
1"7
1~
1.5
1.4
1.3
1"2
1.1
The arsenopyrite in the mineral assemblage at
Temperoture I O 0 0 / T (K)Scar Crag can be employed as a geothermometer
through determination of S:As ratios provided an FIG. 6. Plot of sulphur activity (log10as) against temperaindependent estimate can be made of sulphur ture (Iooo/T K) for sulphidation equilibria relevant toactivity during ore formation. This technique, the Scar Crag assemblages. Also shown are sulphidation
based on the work of Kretschmar and Scott (1976), curves for arsenopyrite of limiting As: S ratios observed inthose assemblages.
also requires that the arsenopyrite be from anequilibrium as -buffered assemblage and contains a
The early sulpharsenide assemblage appears to
combined minor element content < I ~/o. Since theScar Crag arsenopyrite generally only contains have been in equilibrium with bismuth and to have
< o.5 ~o Co, the latter criterion is fulfilled. The formed under the temperature (c. 4oo ~ and as2 (c.
Io -9 arm) conditions defined by the field 'A' in fig.
question of equilibrium is much more difficult toassess, but it would seem worth while to apply the 6. Later assemblages see the appearance of bistechnique and then critically evaluate the results. muthinite and cobaltite (which Maurel and Picot,
Accurate determination of the wt. ~ As in the Scar i973, relate to increasing S:As ratio). This could
Crag arsenopyrite samples is also essential and two correspond to an increase in as2 or, more likely, justmethods have been employed here. Careful a drop in temperature. The eventual appearance
measurement of the position of the dl31 line in X- of pyrite ties in with falling temperature and conray powder diffraction data enables the determi- ditions closer to those shown by field 'B' (Tc. 3o0
native curve of Kretschmar and Scott (1976) to be ~ as2 c. IO- 12 atm). Although arsenopyrites of theused (the equation A t o m i c ~ As--866.67 d131- composition range determined could coexist with
1381.2 defines this curve). The measured d 131 values bismuth at much lower values of as2 and somewhat
gave a range of 1.63o-1.63] A which leads to a lower temperature, this seems unlikely in view ofrange in at. ~ As = 32.42-31.55. These results are the subsequent appearance of bismuthinite, cobaltin good agreement with those obtained by the ite, and pyrite. The conditions of ore formation
second method, electron microprobe analysis using indicated here are well within the 'main-line' ore
synthetic arsenopyrite as a standard (if pure arsenic fluid environment outlined by Holland (I965) andis used as a standard, results are up to 2 ~o different other workers. The only comparable vein in thedue to differences in As coordination and bonding Lake District occurs in the Carrock Fell Tungsten
between element and sulpharsenide). The as2 during deposit where Shepherd et al. (I973) obtained

SULPHARSENIDESF R O M THE N O R T H O F E N G L A N D

temperatures of 295 ~ (assuming 800 bar pressure)from fluid inclusions in mineralized quartz.
A factor of importance in the occurrence of thesesulpharsenides in the Alston orefield is their complete absence from samples studied from the
Derbyshire orefield of the South Pennines (Ixer and
Townley, 1978 ). Other notable mineralogical differences between the two orefields include thepresence of pyrrhotine in the Alston ores as acharacteristic and early sulphide but its rarity in theSouth Pennines, an.d the occurrence within only the
Alston galenas of a n u m b e r of small ( < 2 /~m)crystallographically orientated inclusions, which
probably account for the high silver and arsenicvalues reported by Small (I977). This correlateswith other geochemical differences shown by the
Alston orefield, such as a marked enrichment of
rare-earth elements in fluorite (Smith, I974), which
has been suggested to indicate a magmatic contribution to the ore-forming fluid (Rogers, i978 ).
Fluid inclusion data from the Alston ores also
indicate higher temperatures of formation andgreater potassium content than the other Pennine
orefields (Smith, 1974; Sawkins, 1966; Rogers,I978).
The origin of the Scar Crag mineralization could
be linked to the possible existence of a stock-like
intrusion beneath Causey Pike (Rose, 1955). The
slates in this area have been altered to a lighter andharder rock with minute dark spots and thislithology, termed Blakefell Mudstone (Eastwood etal., 193 I), has been interpreted as the metamorphic
aureole of the supposed intrusion. Although there
are certainly differences in the temperatures ofsulpharsenide mineralization in the Alston orefield
and at Scar Crag, and probably differences in age,
their geographical proximity does suggest apossible genetic link.
Acknowledgements. We thank the British Museum(Natural History) and the staff of the Mineralogy
Department, particularly Peter Embrey, for access tomaterial in the Kingsbury Collection. Some preliminary
studies of sulpharsenides from the North Pennines were
undertaken by Mr R. Townley as part of a research

395

projecf at Aston University. One of us (C. J. S.) acknowledges the support of theUniversity of Aston in theform of a postgraduate studentship. We thank Cathy
Kennedy for typing the manuscript and Beverley Parker
for preparation of the diagrams.
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Reinhart and Winston, New York.
Dunham (K. C.), 1948. Geology of the Northern Pennine
Orefield, 1, HMSO.
Eastwood (T.), Hollingworth (S. E.), Rose (W. C. C.), andTrotter (F. M.), 1968. The Geology of the Countryaround Cockermouth and Caldbeck. H.M.S.O.
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Petruk (W.), Harris (D. C.), and Stewart (J. M.), 197 I. Can.
Mineral. 11, x49-86.
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[Manuscript received 5 January I979]