SHORTCOMMUNICATIONSM I N E R A L O G I C A L M A G A Z I N E , MARCH 1 9 7 8 , VOL. 4 2, PP. 1 4 9 - 5 0

The distribution of bravoite and nickeliferous
marcasite in central Britain
BRAVOITE and nickeliferous pyrite as primaryphases have two major low-temperature associations. Firstly, they occur within the P b Zn-baryte-fluorite deposits of the Mississippi
Valley type. The bravoite is paragenetically early,
either being diagenetic as in the Cave-in-Rockdistrict of Illinois (Park, I967), or epigenetic as atMillclose mine (Bannister, 194o ) and Masson Hill(Ixer, I974) in south-east Derbyshire and Dirtlow
Rake and Treak Cliff in northern Derbyshire (Lunnet al., I974).
Secondly, they occur within mineralized red-bed
sandstone deposits of a more variable mineralogy.
These include the highly zoned bravoites from theP b - Z n deposits within the Bunter sandstones ofMechernich, Eifel, and of Maubach, Rhineland,Germany (Baumann, I976), occurrences within theZ n - C u - P b - C o - N i deposits of the Permo-Triassic
sandstones of Beyr6de quarry, southern France(Wahbi et al., I973) and the C u - N i deposits of theDevonian of the Voronezh region U.S.S.R.
(Ageykin et al., I969). They also occur in an alliedclass of deposits, those formed from leached redbeds. Here bravoite can occur epigenetically as in
the Magnet Cove Mine, Walton-Cheverie area,Nova Scotia (Boyle, I97I), Or syngenetically as atFredericktown, Missouri (El Baz et al., I963).
Townley (~976) has shown the first association tobe common, and the second association to bepresent, in central Britain. Optically identifiablebravoite and nickeliferous pyrite have been foundin fifty-six localities throughout the South Pennine
Orefield including the outlying anticlines ofAshover and Crich and the anomalous copper areaof Ecton. It is normally the earliest sulphide,occurring as lilac or brown subhedra associatedwith pyrite, marcasite, chalcopyrite, sphalerite, andgalena and more rarely with millerite (Ashover),pyrrhotine and tetrahedrite (Millclose mine), andbornite (Odin mine). Bravoite also occurs as small( < 20/~m) inclusions of zoned euhedra surroundedby pyrite and marcasite rims and within fluorite,
calcite, baryte, and quartz. This paragenesis appears to be remarkably uniform, a fact reflected in
the chemical compositions of these sulphides.
Comparison of the available analyses of nickel andcobalt contents of bravoites are given in Table I
and show consistently low cobalt values of less than1"5 wt ~o and a range of nickel values mainly withinlO-2O w t ~ nickel.
At eleven localities, notably at Winster, Oxclosemine, Dirtlow Rake, and Odin mine, marcasite
enclosing bravoite displays faint anomalous lilac
and brown colours associated with grain boundaries, or coloured bands and zones, often ascontinuations of zoning within the enclosed bravoite. These bands cross-cut twin and grain boundaries. Electron microprobe analyses (Table II)show these coloured marcasites to be nickeliferous.
The nickel and cobalt values are similar to those

TABLE I. Ranges of nickel and cobalt content for Derbyshire bravoites

Ni wt
Co wt ~oNo. of anal.

Millclose
Mine

OxcloseMine

Winster

Shuttle Rake

Dirtlow
Rakei6.2o-i6.69
tr.-i.40

i2.i3-i8.92
o'83-I'22

7-6-24.83
tr.-o'29

5.99-I3.OI
tr.

Io.o7-I4.59
tr.-o'91

24436YAnalyst

Hey in Bannister(I94o)
Vaughan (I969)

Ixer (I974)

Townley (I976)

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TABLE I I . Microprobe analyses of nickeliferous marcasites
Dirtlow
Rake

Winster.Xr

Ni wt ~oCo wt ~oFe wt ~
S wt ~oTotal

I'57
n.d.
43"oI
53"29
97"87
Faint zoning

6"39
n.d.
4o"16
53.68
IOO'23
Deep violet

obtained by Desborough et al. (I97O) for hydrothermal nickeliferous marcasites from the Sudbury
Basin.
Essentially similar bravoite associations havebeen identified elsewhere, such as at eight new
localities in the Askrigg Block (including the Swaledale, Arkengarthdale, and Greenhow areas), one in
the Alston Block (at Nenthead) and two in theMendip Hills (at Haydon Grange and Green Ore).
These localities augment those at Clitheroe andRimington, Lancashire, and in Wensleydale andWharfedale described by Rogers and Ixer in L u n net al. (I974).
Only one example of the red-bed association hasbeen investigated, the copper mineralization at
Alderley Edge, Cheshire. Nickeliferous and cohaltian wad has been described from this locality(Warrington, t965). Material from the undoubtedly epigenetic lead-zinc mineralization fromEngine Vein and the stratiform copper mineralization both contain early zoned bravoites. Theyoccur as small ( < Io #m) euhedra (without pyrite
and marcasite rims) apparently as inclusions in
detrital quartz grains, or more commonly as larger
20-3 ~ # m zoned subhedra associated with thegalena, chalcopyrite, chalcosine, or carbonate
cements, in a similar m a n n e r to the Voronezh
mineralization.
It has now been established, therefore, thatbravoite is a widespread accessory mineral in thelow-temperature mineralization of central Britain.
Its distribution outside this area is as yet unknown,
although the occurrence of other nickel minerals,
notably ullmannite and nickeline in the North
Department of Geological Sciences
University of Aston in Birmingham
Gosta Green, Birmingham B4 7ET

5"98
n.d.
38.78
53"3798"I3
Lilac bando'I3
n.d.
47"o75r67
98"87
UncolouredPennine Orefield of Co. D u r h a m (Dunham, I948)
suggests a wider distribution.
Acknowledgement. Thanks are due to Dr. D. J. Vaughan
for critically reading the manuscript.
REFERENCES
Ageykin (A. S.), Chernyshov (N. M.), Molotkov (S. P.),
and Bukovshin (V. V.), I969. Intern. Geol. Rev. 11,I32-4.
Bannister (F. A.), t94o. Mineral. Mag. 25, 609-I4.
Baumann (L.), 2976. Introduction to Ore Deposits. Scot.
Academic Press.
Boyle (R. W.), 297t. Geol. Surv. Can. Bull. 166, 82-4.
Desborough (G. A.) and Larson (R. A.), I97o. Econ. Geol.
65, 728-3o.
Dunham (K. C.), I948. Geology of the Northern Pennine
Orefield, 1, H.M.S.O.
E1 Baz (F.) and Amstutz (G. C.), I963. Mineral. Soc. Am.
Spec. Paper, 1, t9o- 7.
Ixer (R. A.), I974. Mineral. Mag. 39, 812-25.
Lunn (P. E.), Rogers (P. J.), and Ixer (R. A.), I974. Bull.
Peak Dist. Mines Hist. Soc. 5, 332-4.
Park (W. C.), r967. Miner. Deposita, 2, 372 6.
Townley (R.), Unpublished M.Phil. thesis, University ofAston in Birmingham.
Wahbi (Y.), Picot (P.), and Tallon (F.), 2973. Bull. Soc.fr.
Mineral. Crystallogr. 96, 23I-2.
Warrington (G.), I965. Mercian Geol. 1, I I I-29.
Vaughan (D. J.), t969. Am. Mineral. 54, 1o75-83.
[Manuscript received I6 March I977;
revised 8 July I977]
Copyright the Mineralogical Society
ROBERT A. IXER