Econom/cGeo/ogg
Vol. 84, 1989, pp. 135-142
SCIENTIFIC
COMMUNICATIONS
PALEOZOIC HOT SPRING SINTER IN THE DRUMMOND BASIN, QUEENSLAND, AUSTRALIA
RONALD
CUNNEEN
RGC ExplorationPty. Limited, 16 DouglasStreet,Milton, Queensland4064, Australia
AND RICHARD
H. SILLITOE
8 WestHill Park,HighgateVillage,LondonN6 6ND, England
Introduction
Sinter constructsterraced apronsaround the hot
springdischargesitesof manyactive,high-temperature (>150øC) geothermalsystems,suchas thoseat
SteamboatSpringsin Nevada,Yellowstonein Wyoming, and Wairakei in North Island, New Zealand.
Recentprogressin the understanding
of epithermal
systemshasled to the recognitionthat identicalhot
extensional
grabens(Hutton, 1988) andare interbedded with volcanicrocks(Olgers, 1972).
In the easternpart of the Drummond basin, east
of the Anakieinlier (Fig. 1), the lower,volcanic-dominatedpart of the sequenceis representedby the Sil-
verHillsVolcanics
(Olgers,1972),whichin theMount
Coolon area consistof rhyolitic ignimbrite and tuff
interbedded with lithic and feldspathicsandstone,
springsintercharacterizes
the paleosurfaces
above siltstone,and shale(Grimeset al., 1986).
Sedimentation and volcanism in the Drummond
severalshallowepithermal(or hot spring)gold-silver
basin
ceasedwith the onsetof widespreadmid-Cardeposits(e.g., White and Heropoulos,1983). Wellboniferous
orogeny,duringwhichthe Late Devonianpreservedexampleshavebeen reportedaboveepiearly
Carboniferous
sequenceunderwentopenfoldthermalgold-silverdepositsof middleto late Cenozoicageat McLaughlinin California(Lehrman,1986), ing (Olgers, 1972). The late CarboniferousBulgoHasbrouckMountain (Graney, 1987) and Buckskin nunna Volcanics were deposited unconformably
Mountain (Vikre, 1985) in Nevada, and elsewhere. acrossthe northeasternpart of the Drummondbasin
(Fig. 1) andwere broadlycontemporaneous
In this paper we report the discoveryof identical sequence
with a number of felsic intrusions.
pristinesinterfrom an epithermalsystemof Late Devonianage--to our knowledgethe onlypre-Mesozoic
Local Geology
exampleof unambiguous
sinterdocumentedto date.
The Verbena epithermalsystemwasdevelopedin
The sinterand associatedhydrothermalproductsare
located in the Drummond
basin of east-central
volcanicand sedimentaryrocksassignedby Olgers
Queensland,Australia.The site, centered on latitude (1972) to the Silver Hills Volcanics.As depicted in
three volcanicand
21 ø29'29"S, longitude147ø26'43•'E, is nearthe Ver- Figure 2, we have distinguished
bena (syn.Glen Eva and Glenifer) homestead,some three sedimentaryunitsin andaroundthe mineralized
15 km southeastof Mount Coolonvillage and the area. The volcanicrocks are rhyolitic ignimbrites,
which carryvariableproportionsof pumiceandlithic
nearbygold deposit(Fig. 1).
clasts,andunderwentlittle or no welding.The sediRegional Setting
mentaryrocksare epiclasticand dominatedby lithThe Drummond basin is a structural remnant of a ofeldspathic
sandstone,which is interbeddedwith
largeintracratonicbasinthat developedafterthe mid- subordinatesiltstone,andlocally,with conglomerate.
Devonian Tabberabberanorogeny in the northern The sedimentaryunits displayhigh-anglecrossbedpart of the Tasmanorogeniczone (Fig. 1) of eastern ding and ripple marks,and locallycarry poorly preAustralia(Olgers,1972). The Drummondisa foreland servedfossilsof plant stems.Two of the three sedibasinandprobablyoccupieda back-arcpositionwith mentary units contain sinter horizons,as described
respectto a subaerial,Andean-typevolcanoplutonic below.
The Late Devonian rocks which acted as hosts for
arc farther east (Powell, 1984; Murray, 1986). The
Drummondbasinsequence,of Late Devonianto early the Verbena epithermal systemunderwent gentle
Carboniferousage, was depositedon a basementof foldingduringthe mid-Carboniferous
to producetwo
early and mid-Paleozoicmetamorphicand granitic synclinesand an interveninganticline(Fig. 2). The
rocksandcropsout oversome25,000 km2 (Fig. 1; foldsare characterizedby limbsthat dip mostlyfrom
Olgers, 1972). The sequencecomprisesat least 20ø to 30ø; the foldsplungesoutheast
to east-south12,000 m of mainlyfiuviatilesedimentaryrocks,the eastat 20 ø. No otherrock deformationnor anyfabric
lower, Late Devonianpartsof which accumulatedin developmentwasrecognized.
0361-0128/89/901/135-8 $3.00
13 5
136
SCIENTIFIC COMMUNICATIONS
146c'
km
148o
200
100
.Bimurra
BOWEN
220
BASIN
variousdegreesof pervasivesilicification,especially
of hostsandstone.
Locally,stockworks
are transitional
to hydrothermalbrecciain whichsimilarchalcedony
ispresentasa cementto clasts.The middlesandstone
unit (Fig. 2) isextensivelysilicifiedevenwherestockworkingis poorly developed.Accompanying
hydrothermaleffects,tentativelyconsideredto be marked
by the introductionof illite andsmectite,are largely
maskedby supergenealteration,whichgeneratedkaolinite and subordinatechalky alunite.
The stockworksappearto havebeen overprinted
by a west-northwest-striking
set of steepchalcedony
veins.They cropout poorly, andthosemapped(Fig.
2) aretraceableonlyasalignedfloattrains.Individual
veinsdo not attainwidthsgreaterthan0.5 m andmay
be followed at surface for distances of 5 to 50 m. The
veins exhibit abundant crustification and carbonate-
.,,._,,,I
\
24*
I
replacementtextures(Fig. 3), the latter producedby
hydrothermaldissolutionof lameliarcalcite.More locally, the veinscontainopen spaces,someresulting
fromcalcitedissolution,
thatarelinedwith tiny quartz
crystals.
The sulfide content
of veins and stockworks
is
judged to be low (say,3 vol %) on the basisof the
paucity of supergenelimonite. However, limonite
tendsto be moreabundantin the adjoininghostrocks.
Bulgonunna
Volcanics
vQ
Anakie
Metamomhics
•
ß Gold depositor prospect
O Drummond
Basin
sequence
(outcrop)
FIG. l. Locationsof the Verbena hydrothermal systemand
selectedgold depositsin the Drummondbasin of east-central
Queensland.Geologytaken with slightmodificationfrom Olgers
(1972).
Sinter
The principalexposures
of sinter(Fig. 4A) are in
the middlesandstone
unit (Fig. 2). Two discretesinter
horizonsdip at about20ø southeastward,
andthe up-
permostistraceablealongstrikefor some600 m. Althoughdepositionaldipsof this order havebeen recorded from modern sinter terraces (e.g., Beowawe,
Nevada;Rimstidtand Cole, 1983), the presentattitude of the Verbena sinter is attributed to the effects
The sinter-bearingLate Devonian rocksunderlie of folding.The mostextensivesinterhorizonat surface
a low hill whichis surroundedby lateritizedmesasof exceeds 10 m in thickness whereas the more resedimentary
accumulations,
mainlypaleotalus
of local stricted,lower sinter is 5 m thick. The two are sepprovenance,andRecentalluvium(Fig. 2). The later- aratedby about 1.5 m of sandstoneand siltstone.A
itized paleotalusis consideredas part of the Suttor thinner horizonof sinter,probablyi to 2 m thick, is
unit andcropsout on
Formation,a regionallyextensivedetrital sequence presentin the lowersandstone
the
axis
of
the
anticline
(Fig.
2).
of mid-Tertiary age (e.g., Grimeset al., 1986).
All three beds of sinter are identical texturally to
Hydrothermal Products
their Cenozoicchalcedonicanalogues.
They are well
Chalcedonic veins, stockworks,and sinter at Ver- bedded, composedof dense, laminated, vitreous
benaarepresentin a northwest-trending
zoneranging chalcedony,and displayabundantinterlayercavities
from 400 to 600 m wide and exposedover a strike up to 4 cm long which, althoughirregular in shape,
extent of 1,500 m (Fig. 2). Sinter horizonsoccur in are elongateparallelto the layering(Fig. 4B). Indithe lower and middle sandstone units whereas veins
viduallayersrangein colorfrom white throughgray
and stockworksare most widespread in the middle to tan and orange-brownand are partly translucent.
anduppersandstones
andthe intervening(upper)ig- Brown colorsare due to pigmentationby limonite,
whichalsolinesmanyof the cavities.No sulfideswere
himbrite (Fig. 2).
observed.Thin, irregular intercalationsof silicified
Stockworks and veins
sandwere observedvery locally in the sinter, and
Stockworkscompriseirregular, multidirectional sinterfragmentswere notedin sandstone
abuttingthe
veinletsof dense,massive,porcelaneous
chalcedony, thickestsinter.The sinteris devoidof fragmentaltexup to about 5 cm wide, which are associatedwith tures and crosscuttingfeatures.
SCIENTIFIC COMMUNICATIONS
137
Beddingplanesin the sinterexhibitexternalmoulds than for all the United States sinters listed in Table
of lycopodstems(Fig. 4C andD), randomarraysof 1, and the As valuesare lower than all exceptthose
circularto polygonalcavities(up to 0.5 cmacrossand in the Beowawe,Brady,Coso,and McGinnessHills
0.25 cmdeep)of uncertainorigin(Fig.4E), geyserite sinters,with whichthey are comparable.
"pearls,"andsilicifiedfilamentous
bacterialmats(Fig.
The contentsof Au, Ag, As, and Hg in oxidized
4F). Severalexternalmoldsof lycopodstemswith ex- vein ore from the Wirralie golddepositare an order
ceptionally
well-preserved
ovateleafscars,andin one of magnitudeor moregreaterthanthoserecordedfor
example, leaf molds, too (Fig. 4D), were ex- sinterandvein chalcedonyfrom Verbena(Table 1).
aminedby J. F. Rigbyof the Queensland
Geological However, Sb valuesfrom the two localities are comSurvey.He concluded(writtencommun.,1988) that parable(Table 1).
theyresembleknownDevonian-early
Carboniferous
Environment
of Formation
formsbut probablyrepresenta newspecies.
The bacterial mats are not dissimilar to those described from
Sinter precipitationduring the Late Devonianat
modern sinters (e.g., Yellowstone;Walter et al., Verbena took place in a fiuviatile environmentin
1972).
whichlycopodsflourishedat times.Sinterwasa local
Sinterwasmoreextensivepreviouslyasevidenced facies of the fiuviatile sediments and is believed to
by thepresence
of abundant
angularfragments
ofsin- have accumulatedin drainage channels.Fluviatile
ter, up to 0.5 m in length,in Suttorpaleotalus,es- sedimentationwas interrupted periodicallyby depyroclasticflows.The volpecially400 m westof the principalsinteroutcrops positionof small-volume
(Figs.2 and5). Paleotalus
200 m northoftheprincipal cano-sedimentarypackagelacks featuresindicative
sinter(Fig. 2) containsclastsof distinctivegray-and of proximity to a volcaniccenter. However, recogwhite-bandedsinterunlikeany of that observedin nition of a flow-bandedrhyolite plug and associated
situ.
lavaflowsonly2 km southeast
of the Verbenasystem,
albeit at a higherstratigraphiclevel, suggests
that igLithogeoehemistry
nimbriteeruptionandhydrothermal
activitymayhave
Representativesamplesof sinter from the lower been relatedto an unlocatedandprobablyconcealed
and middle sandstoneunits and of 12 typical chal- rhyolite flow-domecomplex.
The Verbenasintersconstitutea stackedsystem,
cedonyveinsat Verbenawere analyzedfor Au, Ag,
activityclearlyhavingbeenactive,
Hg, As, Sb, andBa by TetchemLabsin Cairns,Aus- withhydrothermal
tralia.Analyses
forAu andAgwereby fire-assay
fusion at least intermittently,during the accumulationof
with an atomicabsorption
finish,the analyticaltech- some600 m of volcanicandepiclasticrocks(Fig. 2).
niquealsousedfor Hg. Arsenic,Sb, andBa were an- Much of the chalcedonyveiningis presentin sandalyzedby X-ray fluorescence.
The resultsare pre- stoneandignimbritewhichare youngerthanthe outsentedin Table 1, whichalsosummarizes
analytical croppingsinters,andit mayhavebeencappedby one
data for epithermalgold-bearingchalcedonyveins or more higher sinter horizonswhich are now confrom Wirralie in the Drummond basin (Fig. 1; see cealedor havebeenerodedaway.Sinterclastsin the
below)andfor severalhot springsintersunrelatedto Suttorpaleotalusmayhavebeenderivedin part from
higher sinterhorizons.
knownpreciousmetal depositsin the westernUnited stratigraphically
Fluviatile sedimentsand ignimbrites were accuStates.These American hot spring sinters overlie
geothermalsystemspromotedby both felsic mag- mulatingwhile the Verbenaepithermalsystemwas
matism(SteamboatSprings,LongValley, Coso,Roo- active. In fact, construction of the individual sinter
sevelt)and high heat flow in a nonmagmatic
basin- apronswas probablycurtailedby influxesof riverbornesediments.
The relativelyfine grainsizeof the
and-rangesetting(Beowawe,Pinto,Brady).
suggests
that the Late Devonian
Table i showsthatthe epithermalsuiteof elements fiuviatilesediments
in existenceduringthe lifespanof the
isnot stronglyanomalous
in either sinteror vein chal- paleosurfaces
cedonyfrom Verbena.In fact, the averageAu, Hg, Verbenahydrothermalsystemwere subduedtopoburial
Ba, and probablyalsoAg valuesare lower than the graphically.Thisfactor,alongwith progressive
correspondingcrustal averages(Krauskopf,1967, by sedimentsand pyroclasticflows,and during the
appendixIII). The only lithogeochemical
difference late Carboniferous,beneath the BulgonunnaVolcabetweensinterandveinchalcedony
isthehigherbar- nics,were conduciveto preservationof near-surface
hydrothermal
productsat Verbena.The Verbenasysium valuesin someof the vein samples(Table 1).
Preciousmetal valuesat Verbenaare appreciably tem islocatedonthe southernedgeof the Bulgonunna
lower than those determined for sinters at Steamboat
Volcanics(Fig. 1) and thereforemay have been exSprings,LongValley,Roosevelt,andMcGinness
Hills humedasrecentlyasthe earlyTertiary.
but comparableto thoseat Beowawe,Pinto, Brady,
The stackedconfigurationof sinterat Verbenais
Coso(Table 1), and severalother sinter localitiesin reminiscentof that in the upperpart of the Steamboat
the westernUnited States(White and Heropoulos, Springsgeothermalsystem,where three principal
1983). The Sb and Hg valuesat Verbena are lower sinter horizons are interbedded with basaltic and
138
SCIENTIFICCOMMUNICATIONS
VVVVV
vvvi
vv
•vvv
ooooo
o oo•ooo o
•.
o
meters
•.f
r
147"26'40"E.
FIG. 2. Surfacegeologyand interpretative crosssectionsof the Verbena hydrothermal system,
Queensland.Veins are schematizedon crosssectionA-A'.
rhyolitic volcanic products and alluvial deposits
(White et al., 1964). Using radiometricand stratigraphicdating,Silbermanet al. (1979) showedthat
hydrothermalactivityat Steamboat
Springshasbeen
active, possiblyintermittently, for >2.5 m.y. However, suchlongevityis not required at Verbena, althoughit cannotbe excludedon presentevidence.
The sinter,with a preservedaggregatethicknessof
<20 m, could have accumulatedin 6,000 yrs if the
long-term rates of sinter accumulationsummarized
by Vikre (1987) are employed.Depositionof the interbeddedignimbritescouldhave taken aslittle asa
few days,andfiuviatilesedimentsare unlikely to representprotracted time intervals.
Regional Comparisons
Volcano-sedimentary
sequencesof Late DevonianCarboniferousage in the Drummond basin are the
SCIENTIFICCOMMUNICATIONS
139
A
A'
vvv"•,•.
- . .•....•vvvvvvvvvvvvvvvv•,,•
9•9v-'•'•-•v9vvvvvvvvvvvvvvvv•
i•
.-'•- •
'• '
vvvvvvvvvvvvvvvvvvv
-•,.:, ,', ,'= j, ,-, .-..:_•.-
..V•V V VY•'"
'"-'•
!oo
1
I
O=
.........
:
'
meters
I
I
..
1
500
.
LEGEND
Recent
•
Alluvium
Chalcedony
vein
with
calcite-replacement
texture
(subcrop
only)
Miocene
Sunor
oø• Lateritized
talus
Formation
.•
Late
8
•-
Devonian•
•
•,
/ with abundantsinletclasts
Hydrothermal
breccia
Sandstone,siltstone
Outer limitof chalcedonyveins
&veinlets
Ignimbrite
Sandstone,
siltstone
/sinter
Ignimbrite
.•27 Strike
&dipofbeds
'•
Antidinal
axis,
with
plunge
Sandstone,
siltstone
(dotted
where
concealed)
--...•.•Syndinal
axis,
with
plunge
Ignimbrite
I--.J LINE
ofSECTION
•
Drainage
/sinter
FIG. •.. (Cont.)
veins,whicharecharacterized
by
hosts
foronepreviously
exploited
(MountCoolon;chalcedony-quartz
Morton, 1935) and severalrecently discoveredepi- crustification and carbonate-replacementtextures
thermalsystemsof 1ow-sulfidation,
adularia-sericite closelysimilarto thoseat Verbena.Furthermore,
sintershavebeenrecognizedtentatype (Fig. 1). Two of them, Pajingo (Porter, 1986; poorlyexposed
Etminan et al., 1988) and Wirralie (Fellows and tively at both Pajingo(R. G. Porter, pers.commun.,
Hammond,1988), containeconomicgold deposits. 1987) andWirralie (FellowsandHammond,1988).
The limitedwidthsandlengthsof the chalcedony
In fact, Wirralie was developedin broadly similar
volcanicandsedimentary
lithologiesto thoseexposed veinsat Verbenaare attributedto repeatedburialof
at Verbena. Gold mineralization at Mount Coolon,
the hydrothermal
systemduringits lifespanandthe
Pajingo,andWirralie is presentin wide, multiphase absencefrom the systemof a singlemasterstructure.
Asa result,hydrothermalfluidflowkept changingits
position
withinthesystem,
especially
aftereachmajor
burial event, and was not focusedthrough a single
conduitfor a prolonged
period.Therefore,the small
individualveinsat Verbenadid not undergorebrecciationand failed to experienceas many stagesof
openingandfillingasthe wideveinsat Pajingoand
Wirralie (Etminanet al., 1988; Fellowsand Hammond,1988). However,giventhe dosesimilarityof
veintexturesandmineralogy
at Verbena,Pajingo,and
Wirralie, we believethat the totallybarrencharacter
of the Verbenasystemultimatelyreflectsthe passage
of hydrothermal
fluidsdeficientin preciousmetals
and other elementsof the epithermalsuite.
FIG. 3. Carbonate-replacement
texturesin chalcedonyvein,
Verbena,Queensland.
Finally,it shouldbe mentionedthat the nearest
golddepositto Verbena,at'MountCoo!on(Fig. 1),
differsmineralogically
from the otherprincipalepi-
INCH
.!
.4
CENTIMETER
INCH
FiG.4. Features
ofthelower
sinter
inthemiddle
sandstone
unitatVerbena,
Queensland.
A.
Outcropviewedfrom the west,pick for scale.B. Layeringandinteda¾.er
cavities.C. Externalmold of
!¾copod
stem(middle)parallelto layering.D. Externalmoldof !¾copod
stemand attachedleaveson
beddingsurface.E. Arrayof circularto polygonalcavitiesof uncertainoriginon beddingplane.F.
Filamentousbacterialmat on beddingsurface.
140
SCIENTIFIC COMMUNICATIONS
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142
SCIENTIFIC COMMUNICATIONS
Queenslandlabs.l:Geol. Soc.AustraliaAbstracts,no. 23, v. 2,
p. 434-435.
Fellows,M. L., and Hammond,J. M., 1988, Geologyof the Wirralie gold deposit,Queenslandlabs.l:Geol. Soc.AustraliaAbstracts,no. 23, v. 1, p. 265-267.
C¾
IN
Graney,J. R., 1987, HasbrouckMountain,Nevada.Preciousmetal
mineralizationin a fossilhot springsenvironment,in Johnson,
J.L., ed., Bulkmineablepreciousmetaldepositsof the western
United States.Guidebookfor field trips: Reno, Nevada, Geol.
Soc. Nevada, p. 120-125.
Grimes,K. G., Hutton, L. J., Law, S. R., McLennan,T. P. T., and
Belcher,R. L., 1986, Geologicalmappingin the Mr. Coolon1:
250 000 sheetarea,1985: Queensland
Geol.SurveyRec. 1986/
56, 70 p.
Hutton, L. J., 1988, Tectonicevolutionof the basalDrummond
basinsequence
andits relationship
to goldmineralisation
labs.I:
FIG. 5. Blocksof sinterin paleotalusof the mid-TertiarySuttor
Formation, 400 m west of the lower (middle sandstone)sinter
outcropsat Verbena, Queensland.
Geol. Soc.AustraliaAbstracts,no. 21, p. 196.
Krauskopf,K. B., 1967, Introductionto geochemistry:New York,
McGraw-Hi!l, 721 p.
Lehrman, N.J., 1986, The McLaughlinmine, Napa and Yolo
Counties,California: Nevada Bur. Mines GeologyRept. 41, p.
85-89.
thermal gold depositsin the Drummondbasin.The
entire Mount Coolon structure underwent introduc-
Malone,E. J., 1969, Mount Coolon,Queensland.SheetSF/55-7,
1:250,000 geologicalseries:AustraliaBur. MineralResources,
GeologyGeophysics
ExplanatoryNotes, 17 p.
Morton, C. C., 1935, The Mount Coolongoldfield:Queensland
Govt. Mining Jour., v. 36, p. 196-200, 232-237.
tionof bothdelicatelybandedchalcedony-adularia
of Murray,C. G., 1986, Metallogenyandtectonicdevelopmentof
theTasman
foldbeltsystem
in .Queensland:
OreGeology
Rev.,
typical epithermalcharacterand an irregularlydisv. 1, p. 315-400.
tributed, coarse-grainedactinolite-biotite-epidote-O!gers,
F., 1972, Geologyof the Drummondbasin,Queensland:
magnetite-pyriteassemblage(R. H. Sillitoe and R.
AustraliaBur. Mineral Resources,Geology GeophysicsBull.
Cunneen, unpub. data; Morton, 1935). These two
132, 78 p.
vein fillings,the relativetiming of which remainsto Porter,R', 1986, Pajingogoldproperty.The discoveryandgeologicalintroductionlabs.l:GoldExplorationandDevelopment
be clarified,were overprintedby sericiticalteration
North QueenslandConference,ChartersTowers,Queensland,
andminorlatetourmaline.The-actinolite-bearing
as1986, Australasian
Inst. MiningMetallurgy,North Queensland
semblageiscompatiblemineralogically
with hornfels Branch,ExtendedAbstracts,4 p.
and hydrothermalalterationdevelopedin the wall- Powell, C. McA., 1984, Late Devonianand early Carboniferous:
Continentalmagmaticarc alongthe easternedgeof the Lachlan
rockignimbrite,effectswhichmaybe attributedwith
fold belt, in Veevers, J. J., ed., Phanerozoicearth history of
confidenceto a nearbytonalitc pluton of late CarAustralia:Oxford, ClarendonPress,p. 329-340.
boniferousage (280-290 m.y.; Malone, 1969).
Rimstidt,J. D., andCole, D. R., 1983, Geothermalmineralization
Acknowledgments
Facilitiesand encouragement
duringthis project
were providedon behalfof RGC ExplorationPty.,
Ltd., by Keith Wellsand GeoffMoore.Early review
commentswere contributedby Harold Bonhamand
GregMorrison.Publicationis with the permissionof
RenisonGoldfieldsConsolidated,Ltd.
August11, September2 7, 1988
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