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1986-Kazmi Mingora Emerald Deposits PakistanSuture-Associated Gem Mineralization

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EconomicGeology
Vol. 81, 1986, pp. 2022-2028
MINGORA EMERALD DEPOSITS (PAKISTAN): SUTURE-ASSOCIATEDGEM MINERALIZATION
A. H. KAZMI,
GeologicalSurveyof Pakistan,42-R, Block6, PECHS,Karachi, Pakistan
R. D. LAWRENCE,
Geolog•tDepartment,OregonState Universitel,Corvallis,Oregon97331
j. ANWAR,
GemstoneCorporationof Pakistan,Peshawar,Pakistan
L. W. SNEE,*
GeologyDepartment,OregonState University,Corvallis,Oregon97331
AND S. HUSSAIN
GemstoneCorporationof Pakistan,Peshawar,Pakistan
Introduction
The Indian subcontinentsequence
The Mingoraemeralddepositsare locatedat the
northernedge of Mingora,SwatDistrict, about 130
milesnortheastof Peshawar(Fig. 1). They havebeen
knownand sporadicallymined since 1958 (Davies,
1962; Kazmi, 1983). Jan(1968) andJanet al. (1981)
discussed
the petrographyof the deposit.Gubelin
(1968, 1982) publisheda gemologicaldescriptionof
the Mingoraemeralds.Mingoraemeraldswere sold
in world marketsfor more than 20 yearsby names
other than Mingora (or Pakistan).These emeralds
were introducedworldwide under their own locality
name after exhibitionof a large consignmentof cut
andpolishedstonesin the TucsonGem andMineral
show(U.S.A.)in 1981 (Herzberg, 1981).
The presentstudyindicatesthat the emeraldsare
found exclusivelyin metamorphosed
ophioliticmrslangeof the suturezonebetweenthe Kohistanisland
arc andthe Asiancrustalplate (Fig. 1). The geologic
settingof the Mingoraemeralddepositsandtheir origin are describedin this paper.
This sequencecomprisesfour lithostratigraphic
units(Table 1), whichare exposedeastof Mingora.
The PrecambrianManglaurschistis the oldestandit
wasprevasivelyintrudedby the Swatgranite(early
Paleozoic?)whichoccursasa massivesheetlikebody
intrudedinto the Manglaurschist.Bothof themwere
foldedsubsequentlyinto an antiform,the outer part
of whichis largelycomposedof a coarseleucocratic
augengneiss.The presenceof beryl in theserocks
(Kazmiet al., 1984) issignificantfromthe standpoint
of emeraldparagenesis.
The Alpuraischistis composed
of severalhundred
metersof siliceousschistandcalcareousquartz-micagarnetschist.The Alpurai schistis probablyunconformableontopof the ManglaurschistandSwatgneiss
and is overlainby Saidu calcareousgraphite schist
which is at upper greenschistto lower amphibolite
metamorphic
facies.The AlpuraiandSaiduschists
are
probablyof late Paleozoicto Mesozoicage(Kazmiet
al., 1984). The upperpart of the Saiduschisthasbeen
overthrustby the Indussuturem61anges
comprising
Regional Geology
an imbricatezonewith slicesof Saiducalc-graphite
Structurallythe Mingoraareaiscomposedof three schist,talc-dolomiteschist,and Mingora ophiolite
tectonostratigraphic
groupsof rocks(Table 1). From m(•lange(Fig. 2).
northto souththeseare (1) the Kohistanarcsequence
(Jan,1977, 1980; Tahirkheliet al., 1979; Bard, 1983)
which hasbeen thrust over (2) the Indus suturem(•- The Indus suturemdlangegroup
langegroup (Kazmi et al., 1984) which in turn has
The Indus suturem(•langescomprisefragmented
been obductedonto (3) the Indian subcontinentse- blocks derived from oceanic crust, volcanic arcs,
quence(Figs. i and 2). The Indus suturemf•lange trenches,andcontinentalmargins,rangingfromPregroupandthe Indian subcontinentsequenceare sig- cambrian(?)to Late Cretaceousin age;they are set
nificantfromthe standpoint
of emeraldmineralization in a ductile matrixof volcaniclastic
to pelitic schist,
and are briefly discussed
in this paper (for further serpentinite,or talc-dolomiteschist.Three thrust
informationseeKazmi et al., 1984).
faults,the Shangla,Makhad, and Charbagh-Kishora
complexintothreem61ange
* Presentaddress:U.S. GeologicalSurvey, Box 25046, Mail thrusts,slicethism(•lange
Stop 905, Federal Center, Denver, Colorado 80225.
units (Fig. 1). From north to south these are the
0361-0128/86/631/2022-7$2.50
2022
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SCIENTIFIC COMMUNICATIONS
••
•
œ0œ3
ISLAMABAD
AS,A.
PLAT•
I.Granite
2.Platform•shelfdeposits
KOHISTAN
ISLAND
ARC
I,Granite
2 .Vo•con•cs•
o•iolites
• Diorites,a•hiboli•s
I•IAN
etc
PLATE
•.Plotf•m•shelfmolasse
deposits
'
Thrust
MMT= Main Mantle Thrust
MKT=Maln
Karakaram
ThrUst
fault
•oOO0oOoO•• Go
Ooo
o
....
•
.....
o
ß
%
o Q•O • • o
o
ß
• /o.
,oO••
• oø o O
ß Kishoro ß '
ß
ß
•_ +
•
ß{
:,- +. 4..r,.
ß
.
ß
+. +
+ + +.+ + .F+ +.I
Em•ald
mines
+++
+
..i. +
+,
.•. +
+
+-
•,
+4*+++++
•+++++++++
,
KOHISTAN
ISLAND
ARC
INDUS
•[-• Amphibolite
Thrustfault
Alluvium
++++•
SUTURE
ZONE
INDIAN
PLATE
Shongla
blueschist
melange Saidu
calc.graphitic
schist
] Chorbogh
greenschist
melange Alpuroi
colc.garnetiferous
schist
• Mingoro
ophiolitic
melange
•.•-1Swat
granite
gneiss
Mo
.ncjlaur
cryst.
schist
and
granite
gneiss
FIG. 1. Ceologic map of the Mingora-Alpurai area.
Shangla
blueschist
m•lange,the Charbaghgreenschist roclastic,metasediment,and metachert set in a matrix
m•lange,andthe Mingoraophioliticm•lange.North- of talc-chlorite-dolomite
schistandcalcareous
quartzward the Main mantle thrust (MMT) zone of Tahir- mica-chlorite schist.
kheli et al. (1979) alongwith the overridingKohistan
Geologyof the Mingora Emerald Deposit
island-arcsequenceencompasses
all of theseunits.
The Mingoraemeralddepositspreadsover an area
The Mingora ophioliticm•lange formsa narrow
north-south-trending
wedgeandcontains
the Mingora of about180 acresat the northernmarginof Mingora
emeralddeposits.In decreasingorder of abundance, (whichincludesthe Islamiatrench,the Farooqmine,
it iscomposedof blocksofserpentinite,talc-dolomite andthe Carrel'strench,mine œandmine 3).
schist,greenstonemetabasalt,greenschistmetapySchistoserocksstriking north-southand dipping
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SCIENTIFIC COMMUNICATIONS
parallelnorth-south
trending
normalfaults(Figs.2
TABLE1. Stratigraphyof the Mingora Area
and 3). The Islamiatrench and mine 2 are straddled
Kohistan
•c
•-•,•--•-,--•.,,•Kohtstan
Sequence
by a set of conjugatenormalfaultswhichwere the
principalavenuesfor the mineralizingfluids.
Thrust•ww•..,-••
At the Mingoraminesfrom westto eastthe following tectonostratigraphic
sequenceis exposed:Charbagh greenschist m•lange --> thrust --> Mingora
ophioliticm•lange-->thrust-->Saiducalcareous
graphitic schist.
The Charbaghgreenschist
m•langecomprises
metabasaltsandmetapyroclastics.
The Saiducalc-graphite schistoccupiesthe area east of the minesand has
Shanglablueschist melange
••
•
ß•
Shangla
•rust •
Charbaghgreenschist melange
• •
,v•,,----•Makhad
Thrust
•
Mingora
ophiolitemelange
•-==----•
--•
been described earlier.
Charbagh-Kishora
Saidu calc-graphite
• •
Emeraldmineralizationis confinedto the Mingora
ophioliticm•lange.This unit is composed
of a thick,
heterogeneous
massof talc-dolomite
schistcontaining
tectonizedclastsof serpentinite,dolomite, greenschist,and graphiticschist,rangingfrom lessthan 2
schist
Al•urai calc-mica-ga•etschist
•
•
••
••wat
-I•
•t.•
granite
-i---
cm to hundreds of meters in size. These clasts are set
in a fine to coarse ductile matrix of talc-chlorite-do-
unconfo•ity
Manglaur
• •• • •
.
c•stallzne
%,-l•
lomite schist(Fig. 4).
The talc-chlorite-dolomite
schistis the mostubiquitous rock in the Mingora emerald mines. It is a
schist
gn•
grayishto greenish-white,greenish-gray,or greenbrown, fine- to medium-grained,soft,well-foliated,
andshearedrockthat formsthe matrixof the Mingora
25 ø to 75 ø west crop out in the mine area.Westerly ophioliticm•lange.Talc, chlorite,and dolomiteare
dipping thrust faults have formed severaltectonic the main constituents.Fuchsite,quartz, pyrite, antiblocks.Mine 3, the Carrelstrench,the Farooqmine, gorite, actinolite,chromite,and magnetiteoccurin
and the Islamia trench are located adjacentto two lesser amounts.
-
MINGORA
EMERALD
A
MINES --->'
B
Emerold
deposits
WEST
EAST
o
125
250
575
SCALE
CHARBAGH
GREENSCHIST
MELANGE
MINGORA
OPHIOLITIC
MELANGE
INDIAN
I. Talc dolomite schist melange
'>•Greenschist
Metasomatised picotire schist
•
•
Thrust
fault
Normal
faul•
_•_0 Foliationdip
PLATE
SEQUENCE
SAIDU
SCHIST
2. Greenschist
I. Calc.
chlarite
schist
with
marbl•enses
5. Dolomite
2. Calc. graphitic schist
4. Colc. graphitic schist
5. Serpentinite
ALPURAI
CALC. GARNET
with marble lenses •
with amphibolite lenses
ALLUVIUM/COLLUVIUM
SWAT
FIG. 2. Geologiccrosssectionof the Mingora area.
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GRANITE
GNEISS
SCHIST
SCIENTIFIC COMMUNICATIONS
,.
20 25
ß
M•NGO•:•C• CiTY
0
I
)Mingora
emerald
40
80
I
I
SCALE
120
Im
mine area and fence
r.•_•
Operatingmines
:_-"-'•? Abandoned mines
....
]Areo
_• . • coveredby
geological
map
EXPLANATION
CHARBACH GREENSCHIST MELANGE
"--:':•
'"' Greenschi•t
Metasomatised picarite schist
MINGORA OPHIOLITIC MELANGE
I. Talc-chlorite-dalomite schist
2'-• 2.Serpentinite
3. Dolomite
.-;.'.• Saidu
Calc.
graphitic
schist
•
.....
._L60
Calluvium
Thrust
fault
• Farooq
Mine
Normal
fault •
Carrel's
Trench
Foliation
dip
I$1amia
Trench
•
• Mine
2
Mine
3
FIG. 3, Geologicmap of the Mingoraemeraldmines.
In the ophiolitic m•lange serpentiniteclastsare
more abundantin the upper andwesternpart of the
m•langezoneandarepracticallyabsentin the lower
andeasternpart (Fig. 3). The greenschist
clastsrange
in composition
from a chlorite-antigorite
schist(metadunite)to actinolite-tremolite-chlorite
schist(metavolcanic)to albite-biotite-clinozoisite-sphene
sem-
ischist(metadiabase)
to albite-chlorite-epidote-quartz
granofels(metagabbro).The dolomiteclastsare medium to coarsegrained and vary from a few centimetersto hundredsof metersin length.At places,for
examplein mine 3, the dolomite containsstockwork
of milky white quartz veins associated
with fuchsite
and chlorite (Fig. 5). In thin sectionsof suchrocks,
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2026
SCIENTIFICCOMMUNICATIONS
/Serpentinite
'•',I ',',',I I ',',', ....
"•'•"'
Talc-dolomite
•ii',',',lltl]
schist
•
•/f
Dolomite
•I•Y•4f "•""••
Debris
•
0
Fault
I
4
I
I
I
8
LImonitlc
Im
SCALE
(By Aman Ah Shah)
Disseminated
/
talc-dolomite
emerald
schist
mtnerahzation
FIG. 4. Sketch showinggeologicsectionat the Farooq mine, Mingora.
crystals
of emeralds
areeasilyseen.Thereispervasive faultsfilledin by limoniteandveinletsor stringers
of
alterationof the dolomiteto ferruginous
dolomiteand quartzandcalcite.Emeraldmineralizationis largely
siderite.
confinedto limonitizedfaultandjoint planesandbetEmerald
ter productionis commonlyobtained from points
Mineralization
where two mineralized fractures intersect. Emerald
Mingoraemeraldsare nonpegmatiticandare commonlyassociated
with one or more of the following
features(1) faultsand fractures,(2) limonite zones,
(3) calcitenodulesand veinlets,and (4) quartzveins
andstockworks.At the Mingoraminesthe following
crystalsalsooccurin quartz and calcitealongthese
fractures.This type of deposithasyielded excellent
euhedralstonesof goodqualityand sizethoughthe
productiontendsto be relativelysporadic.
four
of the Mingoradepositcontainsintenselyfractured
dolomitefilled with stockworks
of quartz (Fig. 5),
distinct
modes
of emerald
occurrence
are
present.
1. Emerald disseminations
along a well-defined
linear shearzone.Thistype of mineralizationis characteristicof the centralquarry of mine 2. The host
rock is composedof gray to greenish-graysheared
talc-chlorite-dolomiteschistwhich is interspersed
with talc-rich and dolomite-richlayers and lenses.
Smallshearjoints, with no significantdisplacement,
crisscross the mineralized
zone with numerous ex-
3. Emeralds
associated with stockworks. Mine 3
which contain the emeralds in association with fuch-
siteandtourmaline.Many smallmicroscopic
euhedral
crystals
of emeraldsmaybe seenin fuchsiteveinslined
by chlorite. Emeraldsfrom suchdepositsare commonlyof lighter color.
4. Emeraldsalongtensiongashes.At the Islamia
trench talc-chlorite-dolomiteschistoccursalong a
faultblockof greenschist
anddolomite.Largetension
gashesfilled in by quartzlensesup to 2 m in diameter
posedslickensidedplanes.Mineralizationoccursbe- and 1 m thick have formed in the talc-chlorite-dolotween two parallel normalfaultsalonga shearzone mite schist. Emeralds occur in a 15- to 30-cm-thick
which has been limonitized and contains a few scatlayer of talcoserock surroundingthe quartzlenses.
tered quartzveins.In thiszoneemeraldcrystalsoccur
Large (up to 30-caratsize)euhedralemeraldcrystals
in sporadicallyscatteredpocketsor nests5 to 15 cm
of gooddeep greencolor and clarity havebeen obacross.Smallercrystalsare disseminated
pervasively tainedfromsuchdeposits.Eachmineralizedlensmay
throughoutthe matrix of the mineralizedzone. The
yield 1,000 to 5,000 caratsof goodstones.
emerald is commonlyassociatedwith fuchsiteand
tourmaline.The emeraldmineralization
at the Farooq
mineis similar.Thistype of depositisfairlyconsistent Physicaland chemicalproperties
in its mineralizationand enrichmentandhasyielded
Comparedwith other emeraldoccurrencesof the
the best productionquantitativelyand qualitatively. world (Gubelin, 1968, 1982), Mingoraemeraldsare
2. Emeraldsin fracture filling along nacrowli- uniquefor their deepgreencolor,relativelyhighremonitizedjoint planesor fault planes.In the northern fractiveindices(1.588 to 1.596), andspecificgravity
and southernquarriesof mine 2, the talc-chlorite- (2.75 to 2.78). Microprobe analyseson Mingora
dolomite schist,the host rock, showscrenulate folds, emeralds(Table 2) showhigh Cr•O• (up to 1.79%)
shearing,and dismembermentby numeroussmall andFeO (1.02%). Neutronactivationanalyses
(Snee,
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2027
EAST
WEST
Quarry
Quartz
Talc-chlorite
/
Sketch showing section of a part of the
mineralized zone at Mine 5 (see box at right)
•
dolomiteschist
I. Dolomite
•,• 2_.Dolomite
with
st.
ringers
ofquartz
and fuchsite
veins
Dolomite (with quartz lenses and
veins) bearing emerald mineralisation
'[1• 5. Dolomite
withnumerous
parallel
fuchsite veins and malachite
stains
14.
•
Quartz
0
i
5. Scree
5
i0
i
i
SCALE
15
Im
FIG. 5. Sketchshowingsectionof the mineralizedzone of mine 3, Mingora.
unpub.data)indicatehighcontents
of vanadium
(up controlledandthey were formedduringshearingand
to 1% V203). These chemicalcontentsare consistent the last-stage
alterationof the Mingoraophioliticm•withemeraldmineralization
in anophiolitic
m•lange. lange.Mineralizationis alsolithologicallycontrolled
by the talc-dolomiteschistandapparentlytookplace
in two phases.The disseminatedemerald depositsof
the
mine 2 centralquarryand the Farooqminewere
The emeraldsformed late after major deformation
probably formed earlier. At these mines emeralds
was complete. Their mineralizationis structurally
mainly occur in the groundmassof the talc-chloritedolomiteschistwith no significantquartzcalciteveins
or stockworks
in the vicinity.It is likely that thisearTABLE2. ChemicalAnalysis(wt %) of MingoraEmeralds
lier
phase
was
more pneumatoliticand may have
(avg 11 analyses)
formedat a highertemperature.The higher permeSiO2
63.89
ability and porosity of the talc-chlorite-dolomite
TiO2
0.00
schist,the pervasiveshearedtexture, and the preexConclusions
Al•O3
FeO 1
12.65
0.55
MnO
0.02
MgO
2.23
CaO
0.02
Cr•O3
Others•
1.34
19.33
• FeO = total iron
• MostlyBeO
Microprobeanalyses
by Ellen D. Mullen and M. Schaffer
istence of chromite in these rocks favored their se-
lective mineralizationduring this earlier pneumatolitic phase.The mineralizingfluidsprobablycontained
high volatiles,low water, very little silica, and substantialreducediron. This alsoexplainsthe disseminated nature, smallersize, better gem quality, and
presenceof a well-definedmineralizedzone despite
the fact that there are no surficial veins to mark its
extent.
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2028
SCIENTIFIC COMMUNICATIONS
Emerald mineralization in stockworks and calcite-
work on the emeralds. We also thank Therese Belden
quartzfissurefillingsat the Islamiamineandmine3 for preparationof this manuscript.
suggests
that theseemeraldsformedlater duringa
more hydrousphasewhen the mineralizingfluids June5, 1985; May 21, 1986
containedrelativelylargeramountsof silica,carbon
REFERENCES
dioxide,beryllium,andboron.At theseminesemerald
mineralizationwas apparentlyprecededby limoni- Bard,J.P., 1983, Metamorphicevolutionof an obductedisland
arc:Exampleof the Kohistansequence(Pakistan)in the Himtizationandwasfollowedby the depositionof calcite
alayancollided range:Univ. PeshawarGeol. Bull., v. 16, p.
and quartz.
105-184.
Comparedto the othermajoremeralddeposits
in
the world (Colombia,India, Tanzania,Zambia,etc.
reviewedin Sinkankas,1981), the geologicsettingof
the Mingoraemeralddepositis unique.The Mingora
depositformedin ophioliticm•lange(Late Creta-
Davies,R. G., 1962, A greenberyl (emerald)near Mingora,Swat
State:Punjab Univ. Geol. Bull., v. 2, p. 51-52.
Gubelin, E. J., 1968, GemmologischeBeobachtungen
am neuen
SmaragdausPakistan:Der Aufschluss,
Sonderheft18, p. 110116.
--
1982, Gemstonesof Pakistan:Emerald, ruby, and spinel:
Gemsand Gemology,v. 18, p. 123-139.
ceousto Eocene, Kazmi et al., 1984) along an active
continentalcollisionalzonesubsequent
to subduction Herzberg, C., 1981, Pakistandebutsfirst officialgemstonecollection: New York, National Jewellery, 1 p.
and metamorphism.
Within the suturezonethere is Jan,M. Q., 1968, Petrographyof the emerald-bearing
rocksof
no sourcerockfor beryllium;thus,it apparentlycame
Mingora(SwatState)andPrangGhar (MohmandAgency),West
Pakistan:Univ. PeshawarGeol. Bull., v. 3, p. 10-11.
from an extraneoussource.It is postulatedthat the
1977, The Kohistanbasiccomplex,a summarybasedon
Swatgranitegneisswasthe sourceof berylliumand -petrologicalresearch:Univ. PeshawarGeol. Bull., v. 9beryllium-bearingfluids which found easy access recent
10, p. 36-42.
throughthe nearby,sheared,chromium-rich
ophiol- -1980, Petrologyof the obductedmaficandultramaficmeitic m•lange.The carbonate-rich
environment
of the
tamorphitesfrom the southernpart of the Kohistanislandarc
sequence:Univ. PeshawarGeol. Bull., v. 13, p. 95-107.
m•langewasconducive
to theprecipitation
andcrystallization of emeralds.
Acknowledgments
We are pleasedto acknowledgethe permission
Jan,M. Q., Kamal,M., and Khan, M. I., 1981, Tectoniccontrol
over emerald mineralization in Swat: Univ. Peshawar Geol. Bull.,
v. 14, p. 101-109.
Kazmi,A. H., 1983, Reporton the economicgeologyanddevelopmentprospectsof Swatemeraldmines,Mingora:Pakistan,
GemstoneCorp., unpub., 105 p.
granted
bytheGovernment
ofPakistan
todothiswork
Kazmi,
A. H., Lawrence, R. D., Dawood, H., Snee, L. W., and
andthe encouragement
givenusby Kalim-ur-Rehman
Hussain,S. A., 1984, Geologyof the Indus suturezone in the
Mirza of the GemstoneCorporationof Pakistan.LawMingora-Shangla
area of Swat:Univ. PeshawarGeol. Bull., v.
rencewasa Fulbrightlecturerat PeshawarUniversity
17, p. 127-144.
(1981-82) andKazmia Fulbrightresearchscholarat Sinkankas,J., 1981, Emeraldand otherberyls:Radnor,Pennsyl-
OregonStateUniversity(1983) duringpart of this
work.Partialsupportwasprovidedby NationalScienceFoundationgrantsINT 80-13158 and81-18403.
vania, Chilton Book Co., 665 p.
Tahirkheli, R. A. K., Mattauer, M., Proust, F., and Tapponnier,
We thank Hamid Daud and Tahseen Ullah Khan for
P., 1979, The Indian-Eurasian
suturezonein northernPakistan:
Synthesis
andinterpretationof dataat platescale,in Farah,A.
andDeJong,K. A. eds.,Geodynamics
of Pakistan:Quetta,Pak-
assistance
in the field and Ellen Mullen for analytical
istan Geol. Survey, p. 125-130.
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