Potash, sulfur and celestite mineralization in the Middle ...kenanaonline.com/files/0118/118834/Potash, sulfur and celestite mineralization.pdfThe Middle Miocene evaporites in the

Potash, sulfur and celestite mineralization in the Middle Miocene evaporites,

Gulf of Suez,Egypt.

By:Pr.Gamal Attia 1 and Dr. Nafisa Abdel Salam2

1 Faculty of science, Helwan University2 Egyptian Mineral Resources Authority

Contents

- Introduction

- Miocene stratigraphy in the Gulf of Suez area

- Selected sequences

- Mineralization

Potash mineralization

Sulfur mineralization

Celestite mineralization

- Conclusion

Introduction

The Middle Miocene evaporites in the Gulf of Suez region comprising a series of disconnected hills and tectonically controlled blocks .These sediments forming a great thickness reaching 2000 meters in some parts. It is composed mainly of gypsum and anhydrite with shale and marl intercalations,halite and potash minerals are increased in deeper horisons.Stratigraphically the surface sequences are related to Gemsa Formation,and the subsurface sequences are related to Belayim,SouthGharib and Zeit Formation. Potash, sulfur and celestitemineralization in the studied Middle Miocene evaporiteswere recorded .

Stratigraphy

The National Stratigraphic Sub- Committee (1974),divided the Miocene rocks in the Gulf of Suez region into:

A. Deeper marine facies

a. Gharandal Group

1. Nukhl Formation

2. Rudies Formation

3. Kareem Formation

b. Ras Malaab Group

1. Belayim Formation

2. South Gharib Formation

3. Zeit Formation

B. Non-marine to coastal facies:

a. Abu Gerfan Formation

b. Gharamul Formation

c. Gharandal Formation

d. Gemsa Formation

e. Sarbut El-Gamal Formation

f. Ras Malaab Formation

potash mineralization

Potassium is very soluble and does not form primary

mineral phases until after saturation with respect to NaCl

crystallization, ( Dean,1978),concluded that trace

concentrations of K+ in sulfate minerals are probably

adsorbed or occluded, and in halite minerals are

probably due to substitution in the crystal structure.

Mineralogical and geochemical investigations of the analyzed samples ,show that the subsurface Middle Miocene evaporites in Ras El Behar, Gemsa, Gebel El Zeit and Wadi Mallaha contain a considerable amount of potash minerals , where polyhalite ( K-Sulfates ) was detected in shallow depths,as intercalations with gypsum, anhydrite and halite beds belonging to Zeit Formation, sylvite and carnallite minerals (K Chlorides ) were detected in deeper horizons of Zeit and South Gharib Formations .Potassium content reached up to 29.14% in some samples.

Polyhalite(K,Ca,Mg (SO3)4.2H2O)

Most polyhalite recorded in Ras El-Behar,Gemsa,Wadi Mallaha and west Hurghada is of secondary orign after pre-existing anhydrite through replacement by brines rich in potassium and magnesium ( Carozzi 1960 ,Holser 1979),this is evidenced by the presence of relices of anhydrite in polyhalite crystals.

Sylvite KCl

Sylvite may result from accumulation of

heavy concentrated brines rich in K+ where

potassium was replacing sodium in halite(NaCl)

structure, the potash bearing zones were then

brought closer to the surface by post –depositional

salt tectonics.

Carnallite( K,Mg )Cl2.6H2O

Carnallite –sylvite replacement is a

common diagenetic processes( Holser,

1979) by brines rich in Mg replacing potassium in sylvite mineral formed in a closed depositional basin.

Sulfur mineralization

Elemental sulfur was recorded as

disseminations, cavity fillings and

disconnected veinlets through the Middle

Miocene evaporites in Ras Dib, Gebel Zeit,

Gemsa and Gubal Island studied sequences.

Sulfur genesis

Friedman and Sanders(1978),Pierre and Rouchy

(1988) stated that below the wave-influenced

zone of oxidation ,sulfate reducing bacteria

breakdown calcium sulfate in the presence of

organic matter as a catalyst and as a result

biogenic carbonate and sulfur are formed . Pyrite and iron oxides are by-products of this processes.

The mineralization processes is believed to

follow the following steps:-

CaSO4 Ca+ SO4

Then: SO4 + 2CH2O H2S+2HCO3( organic matter)

Finally: Ca2+ +2HCO3 CaCO3 +H2O +CO2

Sum : CaSO4 + 2CH2O CaCO3 +H2O +H2S

H2S is usually oxidized to elemental sulfur

High values of δC12 supporting the organic

source believed to be from the seeped

hydrocarbons.

positive values of δO 18 indicate a meteoric

water source ( possible mixing between marine and

nonmarine water in the depositional environment.

Celestite(Sr SO4) mineralization

Celestite was recorded in minor amounts as

disseminating grains and rosettes in the Middle

Miocene evaporites studied in Ras Dib ,Gemsa

,Gebel El Zeit, Wadi Shagra and Gubal Island( Fig ).This is

confirmed by mineralogical and chemical analyses ,where

SrSO4 reaching 15% in some samples.

Celestite genesis

Most Sr+2 is a diadodical substitutions for Ca+2 in sulfate and carbonate minerals in their crystal lattice ( Holser,1979). In certain cases, Sr+2 may form its own mineral as strontionite or celestite depending on the relative concentration of Sr in the evaporating basin( Dean,1978).

Celestite(SrSO4) is originated from Sr-ions realized during the dissolution of anhydrite and through dolomitization processes.

ConclusionThe Middle Miocene evaporites in the Gulf of

Suez region comprising a series of disconnected hills and tectonically controlled blocks .These sediments forming a great thickness reaching 2000 meters in some parts. It is composed mainly of gypsum and anhydrite with shale and marl intercalations,halite and potash minerals are increased in deeper horisons.Stratigraphically the surface sequences are related to GemsaFormation,and the subsurface sequences are related to Belayim,South Gharib and ZeitFormation.

Potash, sulfur and celestite mineralization in the studied Middle Miocene evaporites were recorded .Polyhalite (K2CaMg (SO3)2H2O)is detected in considerable amounts in anhydrite and halite rocks ( Ras El Behar and Gemsa sequences), it is mostly related to replacement processes .Celestite (SrSO3) is recorded in minor amounts in anhydrite and gypsum rocks it is related to dissolution processes(Ras Dib and Gemsa sequences). Biogenic sulfur is present as disseminations, cavity fillings and veinlts within anhydrite ,gypsum and carbonate rocks , This sulfur is formed where sulfur reducing bacteria breakdown gypsum and anhydrite in reducing environment in the presence of organic matter where sulfur and biogenic carbonate are produced.

Thank you