A fluid inclusion study on mahd adh dhahab gold deposit, Saudi Arabia

Abstract EN

Mahd ad h Dh ah ab , the ol dest go ld mi ne in Sa ud i A rabia , is s itua te d at th e ce ntra l part of th e A ra bia n shie ld .

It co ns ists of a n upper Prorc ro zo ic rock se quence o f ande site .

agg lomera te.

low e r rhyo litic t uff .

lith ic crys ta l luff.

upper rh yoliti c Iliff an d a lat e sma ll porph yritic r hyoli te intr us io n .

Fo u r ge ne ra lion s o f q ua rtz veins cut Ih rough th e seq ue nce with thr ee ge nc ruu o ns mine ral ized .

The a re a has be en reg ionally met amorphosed to low-gr ade green sc hist fac ies To d at e , Mahd adh Dhah ab ha s est ima te d o re rese rves o f • .45 milli on Io ns.

gr ad ing 26 gil Au a nd '12 gl t Ag.

an d a furth e r 109 .000 tons u f oxi de ore with an avc rage of 77 gl t A ll.

T he majo rit y o f the fluid in clu sion s in quartz from qu a rtz ve ins at Mahd ad h Dhahah arc very sma ll.

l lowcv cr.

primar y fluid inclu sion s o f larger sizes (5 to 15LJ) we re chosen a nd a na lyze d .

All th e an a lyze d fluid inclusion s a rt' two phase (gas a nd liq uid ) inclu sions .

Upo n he ating .

they a ll homogenized int o a liquid ph a se.

T he final melting tcrnpcruturcs of in : from t he a na lyze d fluid incl usions fall between - ().] and - 1.2"C wh er e as .

th e fina l homoge niza tio n tempe rature s o f hul k composit io n fa ll be tween + 100 an d + lSO"C, T he ca lcula te d co mpositio ns o f th e flui d a rc ')9 .2 1 to 99.3YX, of 11 :-0 an d 0 .67 to 0 .7<)% of NaCI.

A micr othcnuomc t ric stud v 01the fl uid inclusion s sugges ts th at th ere are .u least two , tages 0 1qu art l deposi tio n .

o ne at a ho ut 100-21WC and .inot lu-r al a bo ut 341l-1,'O'C.

Oll;lr ll deposited a t low temper ature is co ns idered to he ha rr ell or co nuun min ur ;III11HI III otmi ncr uliza tio n.

where as qua rtz dep o site d at high tcm pcr.uurc is postul at e d 10 be min e rali / ed a nd economica lly impo rtant.

It is conclude d th at the mine rali zing fluid at Mahd "dh Dh uha h r unxivtc d ma in I\' o f meteoric wa ter with a pllssiblc mino r amount of sc a w.ucr , T he 1l1in n :d i/ al illn i, P"s(ulaled tll h.ivc been deposited at ;1 sha llow de p th in th e c.uths c rust to Io rm a t vpic a l e pi t he rma l de posit.