A new classification of the gold deposits of Egyp...

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1、OreGeologyReviews25(2004)1–37www.elsevier.com/locate/oregeorevAnewclassificationofthegolddepositsofEgyptNagyShawkyBotros*EgyptianGeologicalSurvey,Cairo,EgyptReceived14August2002;accepted1July2003Availableonline7February2004AbstractGolddepositsandoccurrenceslocatedintheNubianShieldhav

2、ebeenknowninEgyptsincePredynastictimes.Despitethefactthatthesedepositswerelongunderexploitationandinvestigatedmanytimes,theyarestillinsufficientlyclassifiedinharmonywiththecrustalevolutionmodelssuggestedfortheevolutionoftheNubianShield.Severalplatetectonicmodelswereproposedforthedeve

3、lopmentoftheNubianShieldandthepresentclassificationreliesheavilyonthemodelthatimpliescollisionofarc-inferredcontinentthroughsubductionandobductionofoceaniclithosphere.Athree-foldclassificationofgolddepositsofEgyptisofferedhereinharmonywiththisevolutionarymodel.Thesearestratabounddepo

4、sitsandnon-stratabounddepositshostedinigneousandmetamorphicrocks,aswellasplacergolddeposits.Thestratabounddepositsarehostedinislandarcvolcanicandvolcaniclasticrocksofcomparablecompositionformedinensimaticislandarcs.Theyarethoughttohaveformedbyexhalativehydrothermalprocessesduringthew

5、aningphasesofsub-marinevolcanicactivity.Stratabounddepositsaresub-dividedintothreemaintypes:gold-bearingAlgoma-typeBandedIronFormation,gold-bearingtuffaceoussedimentsandgold-bearingvolcanogenicmassivesulphidedeposits.Non-stratabounddepositsoccurinawiderangeofigneousandmetamorphicrock

6、s.Theywereformedduringorogenicandpost-cratonizationperiodsbymineralizingfluidsofdifferentsources.Non-stratabounddepositsaredividedintovein-typemineralization,whichconstitutedthemaintargetforgoldinEgyptsincePharaonictimes,anddisseminated-typemineralizationhostedinhydrothermallyaltered

7、rocks(alterationzones)whicharetakenrecentlyintoconsiderationasanewtargetforgoldinEgypt.Placergolddepositsaredividedintomodernplacersandlithifiedplacers.Theformeraresub-dividedintoalluvialplacersandbeachplacers.Conglomeratesoccurringonornearancienterodedsurfacesrepresentlithifiedplace

8、rs.D2003Publ