Baileychlore, the Zn end member of the trioctahedral chlorite

Baileychlore, the Zn end member of the trioctahedral chlorite

American Mineralogist, Volume 73, pages 135-139, 1988
Baileychlore, the Zn endmember of the trioctahedral chlorite series
andGeophysicrjJn".r"ttrt;*[lir,",
Deparrmenr
of Geology
Fn.lNr R-lorp
u.s.A.
53706,
wisconsin
Madison,
Austratian Mineral Development Laboratories,Frewville, South Australia, 5063' Australia
Ansrnacr
Baileychlore occurs as dark green rims on colloform calcite veins within a strongly
oxidized collapse karst-breccia containing altered andesite and garnet-vesuvianiteskarn
clasts at the Red Dome deposit near Chillagoe, Queensland,Australia. Baileychlore is a
new Zn-rich chlorite. The ZnO contents are fairly uniform from 28.2 to 30.5 wto/oat a
depth of 89.6 m in the deposit, with a structural formula of (Zn, 'oFeli'Al'.''Mgo 'uMnfrfr'tro36XSi3
45)Or0(OH)tfor the most Zn-rich analysis.The name is for ProfessorSturges
55Alo
W. Bailey of the University of Wisconsin and is to be used for any trioctahedral chlorite
in which Zn is the dominant divalent octahedral cation.
Baileychlore occurs as fine-grainedtransversefibers exhibiting zoned pleochroic colors
(greento yellow-green)along their length. Refractive indices areot : I .582 and 1 : 1.614.
The measuredand calculateddensitiesare 3. 18(2)and 3. 195g/cm3,respectively.Combined
DrA-rcA curves show a major endotherm at 550'C, a small, double-bottomed endotherm
in the range 680-750 "C, and an exotherm at 850 "C. The X-ray powder pattern is that of
the Ib (B : 97') polytype. The strongestlines (24 given) are ld"b"g.J(hk[)] 14.3(90)(001),
I 30),2.450(35)(203,132),
2.660(50X201,
2;tr),3.573@0X004),
4.600(30X0
7.I 4(100X002),
a n d 1 . 5 4 2 ( 6 0 X 0 6 0 , 3 3 1U) .n i t - c e l l d i m e n s i o n sa r e a : 5 . 3 4 6 ( 3 ) , b : 9 . 2 5 7 ( 4 ) , c :
14.401(7)A, and P : 97.12(5). The symmetry is probably triclinic Cl or Cl because
of semi-random stacking.A one-dimension electron-densityprojection and an asymfor the octahedral
metry value of +1.29 suggesta composition (Znrs'Alo,4D035)058sheetwithin the 2: I layer and (Fe?joAl,e.Mgor.Mnfr$r)'03+for the interlayer sheet.
the Zn end member of the trioctahedral chlorite series,
INrnotucuoN
(Zn'AlXSi'Al)Oro(OH)8' or for any trioctahedral
ideally
Radke et al. (1978) reported chlorite containing 6 to 30
in which Zn is the dominant divalent octahedral
chlorite
wto/oZnO from a drillhole located near Chilhgl", e"ris analogousto clinochlore' the Mg end
The,name
cation'
rralia. Frondel and Ito (1975) previourt' a"r".iUJi'a
and name were approved prior to
mineral
The
..brunsvigite"
"inmember'
(chamosite in ;" ;;;cian, manganoan
publication,by the IMA commission on New Minerals
1975)containingg.Ailio
ferrednomenclatureofBayliss,
M.ileTl Names' Holotype material has been deposzno and9.96 wto/oMno from Franklin, Nr* l..r.v, unJ 1{
with the Smithsonian Institution (NMNH 164430)'
ited
Dunn et al. (19E7) describedthe chlorite lrot'p"-ilu;i.]
Australian Museum (no' 13592)' and the Gethe
Soulh
rpJ.i"r
linfurnaceite from the samegeneralarea as u
at the Universitv of wisconsin' Madison
""*
with up to 24 wto/oZno (primarily tetrahedraD, ii;t;
9t"cv.y5::mr)'
(no'
ouuu/
MnO, and l0o/oMnrO.. The Australian occurrenceis the
only chlorite known to date, however, in which Zn is the
OccunnBNcEt MoRPHOLoGY' AND oRIGIN
dominant divalent octahedral cation present. The ZnO
Baileychlore is known only from one angled drillhole
contents range from 22 to 30 wto/ofor these latter speci(DDH2)
provides
paper
drilled in 1972 to test beneath the Red Dome
a name and additional
mens. The present
Red Dome deposit is located near Mungana
The
for
species.
deposit.
data
this
and
structural
crystallographic
The mineral has been named baileychlore in honor of approximately l5 km west-northwestof Chillagoe,North
ProfessorSturgesW.BaileyoftheDepartmentofGeology Queensland,and is being developedas a gold mine by
and Geophysics,University of Wisconsin, Madison. Pro- Elders ResourcesLtd. The drillhole extends 180 m and
fessorBailey is well known for his researchon the struc- intersectsan assemblageof brecciatedand highly altered
tures and polytypism of chlorites, and he was the first to andesitesand garnet-vesuvianiteskarns.Chlorite haspervasively replaced the andesitesand some of the skarns,
recognizethe structural type to which these particular Zncalcite has replacedgarnet-rich skarns,and at depths beof
rich specimensbelong. Following the nomenclature
Bayliss (1975), baileychlore is to be used as the name for low about 120 m, silicification and alteration to iron ox102-{l 35$02.00
0003-004x/88/0
I 35
136
RULE AND RADKE: BAILEYCHLORE
Cementing minerals include goethite, hematite, chalcocite, malachite, cuprite, native copper, and calcite.
Chlorite occursas matrix material and as a replacement
of andesite and skarn clasts. This chlorite is a zincian
chamosite. Zir.ciar' chamosite from the collapse karstbrecciais also reportedby Smith (1985).Baileychlore,as
distinct from zincian chamosite,has only been identified
in dark green, fibrous veinlets up to I mm wide that
commonly form on the margins of calcite veins.
The primary base- and precious-metal mineralization
at Red Dome is associatedwith calcsilicate skarns and
includes bornite, sphalerite, and various tellurides, including gold and gold-silvertellurides(Torrey et al., 1986).
The zinc chlorites, including baileychlore, have formed
by crystallization of remobilized elementsof the primary
minerals during weathering by meteoric ground water.
Details of this processare discussedby Smith (1985).
Crmnarsrnv
B
photographs
Fig. 1. seIr.r
(by)rims on colof (A) Baileychlore
loformcalcite(cc)veinlets.(B) Transverse
fibersofbaileychlore
(by)adjacentto calcite(cc)vern.
Table 1 presents12 electron-microprobepoint analyses
by Radke et al. (1978) for chlorite from four diferent
depths.Analyses3 to 8 are for the fibrous baileychloreat
a depth of 89.6 m. The ZnO contents of theselatter analysesare fairly uniform from28.2 to 30.5 wt0/0.Allocations
of the analysesto the site occupanciesshown in Table I
are basedon 14 oxygenatoms, assuming8 OH and all Fe
to be ferrous on the basis of qualitative microchemical
tests. Analysis 8 for the most Zn-rich specimen gives a
formula (Zt2 4BF
e2tlA|, rMg - Mnfr.$,Cao,
rEorr)(Si3r2Aloos)
O'.(OH)8. In samplesof low ZnO content, the deficiency
in Zn is compensatedfor by additional Fe2+, and the
chlorite is properly termed zincian chamosite. Baileychlore has an appreciable dioctahedral component in that
about 0.3 ofthe 6 octahedral sites are vacant.
CaO. It is not
All of the analysesshow 0.2 to 1.00/o
known for certain if this is due to calcite impurities or to
Ca in the structure.Ca is not believed to substitute easily
into the chlorite structure, although it is present as an
essentialcomponent in the hybrid chlorite-mica structure
of franklinfurnaceite (Dunn et al., 1987),and there is calcite closely associatedwith the baileychlore. IfCa is excluded from the structure, the formula unit for analysis
8 becomes(Znr roFeljoAl,,,MgoruMn3.6rtr0
36XSi3
s5Aloor)O,.(OH)8. The tetrahedral Al content of baileychlore is
0.44 ro 0.49 atoms (Table l), which is near the lower limit
for the chlorite structure but is characteristicof the structural form (Ib, P: 97') of baileychlore. The structural
formula suggeststhat the octahedral sheetwithin the 2:l
layer also has a net negative charge,becauseofthe presence of vacancies,and that the total layer charge is approximately - 1.0.The MnO contentis low, 0.40loor less
for all specimensanalyzed,and is in contrast to the high
values reported for the zincian chlorites from Franklin,
New Jersey(Frondeland Ito, 1975;Dunn et al., 1987).
ides are extensive.Below about 50 m the sampleshave a
fairly uniform ZnO content between 4 and 6 wto/owith
most or all of the ZninZn-bearing chlorites. Most of the
results presentedin this paper are from pleochroic, dark
green chlorite rims on colloform calcite veins occurring
within the breccia at a depth of 89.6 m. This chlorite has
the highestZnO content noted (28 to 30 wto/o)and at high
magnifications(Fig. l) can be seento form fine transverse
fibers about 3-10 pm in diameter. Native copper is generally intergrown with the calciteand fibrous baileychlore.
The Red Dome brecciais interpretedby Smith (1985)
and Torrey et al. (1986) to be a collapse karst-breccia
formed under weatheringconditions by solution of marble
by meteoric water. The rock types forming the breccia
clasts include skarn, andesite, quartzofeldspathic sandstone,felsic porphyries, and chert; the clastsrangein size
Psvsrcal PROPERTTES
from a few millimeters to 70 m. The matrix is generally
limonitic, goethitic, or chloritic and includes finely lam'It wasnot possibleto obtain completeoptical properties
inated sandstonesdeposited by meteoric ground water. becauseof the fine grain size and fibrous character of
t37
RULE AND RADKE: BAILEYCHLORE
analysisof chlorites(wt%)
TneLe1. Electron-microprobe
DePth
Sample:
sio,
Tio,
At,o3
FeOMnO
MgO
CaO
ZnO
Total
24.4
0.6
17.9
29I
0.1
6.4
O2
6.0
85.4
27.3
0.6
19.6
22.5
0.4
4.7
0.5
10.7
85.8
32.1
n.d
12.5
14.5
0.15
4.7
0.9
28.2
93.1
31.8
n.d.
12.6
14.1
0.13
4.7
0.9
28.8
93.0
32.4
n.d.
12.4
13.7
0.16
4.5
1.0
29j
93.3
32.0
n.d.
12.9
12.5
0.13
4.4
1. 0
30 4
93.3
32j
n.d.
12.5
13.5
0.14
4.6
0.9
29.4
93.1
32.0
n.d.
12.4
12.9
0.15
4.6
1.0
30.5
93.5
si
Al
2 838
1.162
3.087
0.913
J CZb
Al
Zn
Fe
Mg
Mn
Ca
Ti
Total
1.283
0.517
2.893
1.100
0.012
0 028
0.054
5.89
1.695
0.897
2.126
0.785
0.037
0.062
0.005
5.61
1.143
2.293
1.331
o.775
0.014
0110
Number of cations on the basis of Olo(OH)s
Tetrahedralcations (> : 4)
3.524
3.517
3.528
3.558
3.5't2
0.476
0.483
0.472
0.442
0.488
octahedral cations
1.127
1.193
1.154
1.160
1.146
2.478
2.468
2.389
2.361
2.343
1.187
1.145
1.245
1.261
1.300
0.751
0.714
0.748
0.731
0.767
0.014
0 . 0 12
0.013
0 . 0 12
0 . 0 15
0.118
0.114
0j12
0.105
0.114
5.67
5.67
0.472
5.64
97.6m
(320ft)
96.7 m (317ft)
89.6 m (294 ft)
5 1 . 5m ( 1 6 9f t )
5.66
5.65
5.68
25.6
0.6
15.8
26.7
0.15
6.4
0.4
14.2
89.8
25.3
0.4
18.3
22.9
0.16
6.2
0.3
14.4
88.0
11
12
26.2
0.14
16.0
17.6
0.1
5.1
0.5
22.6
88.2
27.4
0.2
16.8
25.4
0.15
5.3
0.45
14.5
90.2
2.919
1.081
2.876
1.'124
3.046
0.954
3.067
0.933
1.043
1.192
2.543
1.082
0.01
5
0.049
1.333
1.208
2.184
1.058
0.01
6
0.034
0.033
5.87
1.235
1.940
1.707
0.883
0.010
0.061
0.012
5.85
1.275
1.196
2.375
0.883
0.014
0.035
0.017
5.82
5.97
others are of zincianchamosite;
Note..Analvstwas p. K. Schultz.Modifiedfrom Radke et al. (1978).Analyses3 to I are of fibrousbaileychlore;
n d. : not determined.
- Total Fe as FeO.
baileychlore. The mean refractive index is about 1.59.
Values of a : 1.582 and t : 1.614 were measuredfor
baileychlore from the 89.6-m depth. The chlorite fibers
exhibit a zoned pleochroic color with the zoning parallel
to the chlorite veins (zoned along the length ofthe fibers)
to produce a colloform-type banding. The zoning is in
shadesof greenand yellow-green.The pleochroismis weak
with the strongestcolors in the darker bands. The measured density of baileychlore from the 89.6-m depth is
3.18(2),which comparesfavorably with a calculateddensity of 3.195 g/cm3for the most Zn-ich material of analysis 8 (Table 1).
Simultaneousore and TGAruns were carried out using
a Rigaku Denki model M8076 instrument. A 50-mg sample of hand-picked and finely gound baileychlore was
used, with an equal amount of calcined alumina as reference.The heating rate was 10 "C/min in a static atmosphereofair. The principal thermal effects(Fig. 2) and
their interpretations are as follows: (l) Ambient to 120
'C: A small broad endotherm accompaniedby a loss of
moisture (-30lo wt loss). (2) 150-200 'C: A very small
ora endotherm and weight lossattributed to loosely combinedwater. (3) 280-330 oC:A very small ore endotherm
and weight loss probably due to a trace ofgoethite contaminant. (4) 400-600 "C: A major prn endotherm and
weight loss due to dehydroxylation ofthe interlayer sheet
of chlorite. (5) 680-750 oC:A very small, broad, doublebottomed endotherm and correspondingweight loss due
to dehydroxylation of the 2:l layer of chlorite. (6) 780880'C: A broad exothermic ore peak with no weight loss.
This is attributed to formation of a high-temperaturealuminosilicate phasefrom the decomposedchlorite at about
.C: The DrA curye showsan in850 'C. (7) 1000-1200
creasingendothermic band with significant weight loss.
This is probably due to sintering of the sample, which
exhibited pronounced shrinkage.
The major feature of the pre curve is the dehydroxylation of the interlayer sheet at 550 "C. The dehydroxylation ofthe 2:l layer is lesswell defined in the range680750 'C, and it is likely that some of its dehydration is
included in the 550 oC endotherm. The endotherms in
general are not as sharp as those from well-crystallized
trioctahedral chlorites and occur at lower temperatures,
presumably because of poorer crystallinity and consequent releaseof water more readily and over a largerange
of temperature.The presenceof octahedral vacanciesin
baileychlore (Table 1) also may afect the curve. Mii{ler
( 1963) noted a large endotherm at 544 "C and two small
endothermsat 680 and 725'C for dioctahedralchlorite.
Srnucrumr- DATA
poorly
crystalline and gives X-ray powis
Baileychlore
der patternsin which the ftkl peaksarebroad. Both DebyeScherrerand difractometer patterns (Table 2) taken with
graphite-monochromatedFeKa and CuKo X-radiation
are recognizableas being characteristicofthe ID (P :97)
polytype as defined by Bailey and Brown (1962). In this
polytype the interlayer sheet is oriented so that its slant
is in the same direction as that of the octahedral sheet
within the 2:l layer. The interlayer is positioned asym-
138
RULE AND RADKE: BAILEYCHLORE
ob+TET.
Fig. 2. Combined DrA-rcA curves for baileychlore
metrically for hydrogenbonding so that is has a b position
relative to the 2:l layer on one side but an a position
relative to the layer on the other side. The presenceofthe
Fig. 3. One-dimensional
projectionusing
electron-density
Ib (P : 97") polytype is consistentwith the composition seven00/ reflections.
The unlabeledpeakat z : 0.35 is a difand mode of origin of this chlorite. Bailey and Brown fractionripple.
(1962)consideredthe Ib (0 :97") polyrypero be the least
stable of the four chlorite structuresknown at that time, dimensional bands and thus of semirandom stacking of
to form at the lowesttemperature,and to have the smallest adjacent layers and interlayers. This is true also for all
substitution oftetrahedral Al for Si.
single crystalsstudied to date of both lb (B : 97) and Ib
Cell dimensions derived by least-squaresrefinement of (B : 90) chlorite from other localities. Bailey and Brown
the X-ray powderdata area: 5.346(3),b : 9.257(4),c :
( I 962) consideredthe symmetry of all chlorites with semi14.401('7)A, and P : 97.12(5)'. Although single crysrals random stackingto be triclinic, Cl or Cl.
are not available, the shapesof the powder-diffraction
It did not prove possibleto make an oriented-clayslide
peaksat d : 4.600 and 1.745 A are suggestiveof two- by settling from a liquid suspensionor by suction through
ceramic tile, even for every dilute suspensionafter disaggregationby ultrasonic treatment. This is probably due
TABLE
2. Baileychlore
X-raypowderdata
to the fibrous nature of baileychlore. The integrated intensities of seven nonoverlapped basal reflections were
4," (A)
4". (A)
measuredfrom an unoriented slide using a Philips X-ray
001
90
14.3
14.290
002
100
7.14
7.145
difractometer with graphite-monochromated CuKa ra003
5
4.76
4.763
diation and a sequenceof %' to l' vertical divergenceslits.
4.628
02;1130
4.600
The intensities were corrected for the Lp factor for ran4.602
004
40
3.s73
3.572
domly oriented crystallites, converted to -F values, and
005
10
2.860
2.858
used
to construct a l-dimensional electron-densitypro2.668
5U
2.660
jection (Fig. 3). Becausethe two octahedral sheetsin the
2.667
2.594
chlorite structureare separatedby c/2, all octahedralcatJ
2.59
2.593
B
ions diffract in phasewith one another for even orders of
2.450
35
2.450
2.449
00/ regardlessof the distribution of cations between the
B
2.27
2.268
two sheets.Comparison of the sum of these observed.F
zvc
2.078
I
15
2.080
^E
values with a similar sum calculated for the octahedral
134
2.076
|
007
2
2.040
2.041
composition of baileychloreyields a scalingfactor to place
206,135
2
B
1.89
1.892
the
observedvalues on an absolute scale.
15:'24:3120
1.745
1.748
D
The peak for the octahedralcations within the 2: I layer
1.737
207,136
10
1.722
1.724
at z : t/zin Figure 3 has greaterelectron density that that
060,33i
60
1.542
1.543
for the octahedralcations ofthe interlayer sheetat z: 0.
062,333,331
za
1.508
1,508
'l.443
209,138
10
1.44
Integration of the areas of these two peaks and scaling
00.10
3
1.428
1.429
relative
to a content of 27 electrons for the resolved in<E
064,335,333
1. 4 1 5
1. 4 1 6
,l
terlayer
OH plane gives a total of 116 electrons, which
065,336,334
136
1.358
261
1.336
may
be
compared
with 125 electrons for the octahedral
20
1.335
402,260
1.334
cation total of analysis 8 of Table I (assuming500/oion't.297
404
20
1.295
262
ization).The excessofelectron densityin the 2:l layer is
1.296
2 0 .0
1 : 13 .i i
1. 1 9 8
1. 1 9 8
27 electrons(9 electronsper cation). Theseelectron-denA/ote.MonochromaticFeKa radiation.Cameradiameter114.6 mm. lnsity values should not be consideredaccuratebecauseof
tensitiesestimatedvisually.B : broad peak.
the availability ofonly seven00/ reflectionsand the con. Two-dimensional
band.
sequentpresenceofFourier termination effects.The data
/G
I*
t-
l'
139
RULE AND RADKE: BAILEYCHLORE
areinternally consistent,however,becausethe heavy-atom
asymmetrycalculatedfrom the 00/ intensitiesis +1.29.
This meansthat there are 1.29more heavy atoms of Zn +
Fe in the 2:l layer than in the interlayer. For this calculation the method of Petruk (1964)was modified by construction ofa graphappropriatefor an averageheavy atom
of ZnourFeo
,r.
It is not possiblewith thesedata to give an unequivocal
distribution ofthe octahedral cations over the two octahedral sheets.However. if the vacanciesare in the trans
M(l) sitesof the 2:1 layer, as in most layer silicates,it is
more likely that the heavier Zn (Z : 30 vs. Z - 26 for
Fe) would also be in the 2:l layer. There is no evidence
for tetrahedralZnfrom Figure 3, in contrast to the Si'Zn,
tetrahedral composition found in franklinfurnaceite by
Dunn et al. (1987). A reasonablecation distribution for
the composition of analysis 8 that satisfiesboth the ob'
served asymmetry and the electron-density values is
(ZnrroAlo,oEorr)0"-for the octahedralsheetof the 2: I
for the interlayer
layer and (Fe?joMnES,Al,orMgoru)'03+
sheet.This gives an asymm€try of +1.29 for the heavy
atoms with 23 more electronsin the octahedraof the 2: I
layer. The net negative chargeof0.45 on the tetrahedral
sheetsis augmentedby a negative charge of 0.58 on the
octahedralsheetfor this distribution to give a net charge
of -1.03 for the 2:l layer as a whole. However, it must
be emphasizedthat other cation distributions are possible
and that resolution of the problem requiresa larger number of 00/ intensities.
by Petroleum ResearchFund Grant 17966'AC2'C, administered by the
American Chemical Society.The ssr.aphotog,raphswere kindly provided
by E. D. Glover.
RrrnnnNcns
Bailey,S.W.,and Brown, B.E.(1962)Chloritepolvtypism:I. Regularand
semi-random oneJayer structures.American Mineralogist, 47, 819850
Bayliss,Peter. (1975) Nomenclature ofthe trioctahedral chlorites' Canadian Mineralogist,13, 178-180.
Dunn, P J., Peacor,D.R., Ramik, R.A., Su, S,C.,and Rouse,R.C. (1987)
Franklinfurnaceite,a Ca-Fe3'-Mnr+-Mn2+ zincosilicateisotypic with
chlorite from Franklin, New Jersey.American Mineralogist, 72' 81281 6 .
Frondel, Clifford, and lto, Jun. (1975) Zinc-rich chlorites from Franklin,
New Jersey.NeuesJahrbuchfilr Mineralogie Abhandlungen,123' lllll5
Miiller, German. (l 963) Zur Kenntnis di-oktaedrischerVierschicht-Phyllosilikate (Sudoit-Reiheder Sudoit-Chlorit-Gruppe). Proceedings,IntemationalClay Conference1963,Stockholm'I, l2l-130.
Petruk, william. (1964)Determination of the heavy atom content in chlorite by meansof the X-ray diffractometer.American Mineralogist' 49,
ol-fl.
Radke, Frank, Schultz,P.K, and Brown, R.N. 1978)Contributionsto
Australasianmineralogy,9, Zinc-rich chlorite from Chillagoe'Queensland. Australian Mineral Development Laboratories Bulletin 23, 2528.
Smith, J.T. (1985) A mineralized solution collapsebreccia, Red Dome,
Mungana,North Queensland.B.Sc.thesis,JamesCook University, North
Queensland,Townsville.
Torrey, C.D., Karjalainen,H., Joyce,P.J., Erceg,M., and Stevens,M'
( I 986) Geotogyand mineralisation of the Red Dome (Mungana) gold
skam deposit, North Queensland,Australia' EGRU Contribution No'
21, Geology Department, JamesCook University, North Queensland,
Townsville.
AcrNowr,rncMENTs
This researchwas supported in part by the Australian Mineral Development Laboratories,in part by NSF Grant EAR-8614868, and in part
Mencn 30, 19E7
Meruscnu'r RBcETvED
SEPrer"lnnn23, 1987
ACCEPTED
M,c,NUSCRIPT