A Fluid InclusionStudyon AdhDhahabGoldDeposit,SaudiArabia

}KA U:Furlh Su..vol.Z.pp.51·6X(1~ 1)l)1\ .ll./llJHlJA.n.)

A Fluid Inclusion Study on Mahd Adh Dhahab Gold Deposit , Saudi Arabia

H.D. HAKI M and

M.

CHINK U L

Faculty of Earth Sciences, King Abdulazi z Un iversity and Saudi Geol ogical Contractin g Co m pany,

Ieddah , Saudi Arabia.

AusIRA n . Mahd ad h Dhah ab ,the oldes tgold mine inSaud i Ara b ia , is situa te d at the cen tra l part of the Ara b ia nsh ie ld.Itco ns istsof an up per Pro- rc ro zo ic rockseq uenceof ande site . agglome ra te. lowe r rhyo litictuff.lith ic crys ta l luff.upperrhyoliti cIliffandalate sma ll porph yritic rhyoli te in tr u- sio n .Fou rgene ra lionsofqua rtzvein s cu t Ihrou ghthe se q ue nce withthree genc ru u o ns mine ral ize d.Theare a hasbeenreg ionall ymet amo rphosedto low-gr a degreenschistfacies Todat e ,Mahd ad h Dhah abha s estima te dore reservesof •.45million Ions.gr ading26 gil Auand'12gltAg. andafurthe r 109.000ton suf oxide ore withan avcrage of77gltAll.

The maj o rit y of the fluid inclu sion sin quartzfro m qua rt z veinsat Mahd ad h Dhahah arc very sma ll.l low cv cr. primaryfluid inclu sion s of larger sizes(5to 15LJ) werechose nandana lyze d . All the ana lyzedfluid inclusi on s art' two phase (gas and liq ui d ) inclu sion s. Upo n he ating. they all homo gen ized into a liquid pha se. The final meltin gtcrnpcruturc s ofin : from the ana lyze d fluid inclusio ns fall betwee n-().] and-1.2"Cwher e as . the fina l homo ge niza tio ntemp e rature s of hulk compo sit io nfallbetwee n

+

100 and

+

lSO"C,Thecalcula te dcompos itio nsof thefluid arc ')9.21 to 99.3YX,of11:-0 and0.67to0.7<)%of NaCI.

Amicr othcnu o m c t ric stud v01the fl ui dincl usion s sugges ts thatthere are .uleast two ,tages01quart l depositio n.oneataho ut 100-21WC and.inot lu-r al abo u t341l-1,'O'C. Oll;lrlldeposite dat lo wtem per atureis cons idered to he ha rr ell or conuun minur;III11HI IIIotmincr uliza tio n. where as quartz dep o - site dat hightcm pcr.uurcispostul ated10bemine rali / ed andeco nomica lly impo rt ant.

Itis conclude d that the mine rali zin g fluid at Mahd"dh Dhuha hrunxivtcd ma inI\' ofmeteoric water wit h apllssiblcmin o r amou n tof scaw.ucr,The 1l1inn:di/ al ill ni,P"s(ulaled tllh.ivcbeen depositedat;1sha llowdep th inthe c.uths crust to Iormatvpicalepi t he rma ldeposit.

;'1