?PETROGRAPHY AND GEOCHEMISTRY OF KORA GYPSUM DEPOSIT, DAUDKHEL, DISTRICT MIANWALI

Abstract

The Kora Gypsum Deposit (KGD) is present in the western Salt Range near Daudkhel in District Mianwali. Petro-
graphic and geochemical studies of KGD have been made to evaluate the nature of deposit and characteristics of the
depositional environment. The gypsumgrades into Sakesar limestoneofUpper Eocene age.It is inferred that KGD is
asulphate faciesofSakesarlimestone,formedinabarredbasin.Traceelementanalysesofgypsumandlimestone show
nearly similardistribution patterns,indicating samegeochemicalenvironment.The lowMg, poor Fe andabsence of K
fromthegypsum samples indicateDeepBasin DeepWater(DBDW)condition.The presenceofclay,high chaJcophile
elements (Zn, Cu and Ni) and sedimentary structures observable in the field also suggest a DBDW model. The thin
section studies and geochemical investigations communicate that initially gypsum was precipitated either due to
evaporation ormixing of differentbrines.DehydrationofgypsumintoanhydriteoccurredduringMiocene duetothick
successionofoverlying Siwaliks.ThePlioceneHimalayantectonicscausedupliftingofthe areaandsubsequenterosion
and removal of overburden brought these anhydrite beds to near surface conditions, where they were converted into
gypsum due to rehydration from groundwater.