NATURE OF CARBONATE-HOSTED BARITE-GALENA DEPOSIT IN CENTRAL ALBORZ,NOTHERN IRAN (DUNA MINE)

دسته زمین شناسی اقتصادی واکتشاف
گروه سازمان زمین شناسی و اکتشافات معدنی کشور
مکان برگزاری بیست و چهارمین گردهمایی علوم زمین
نویسنده Fatemeh Sabahi -Robert Moritz
تاريخ برگزاری ۱۷ اسفند ۱۳۸۴

ABSRACT

Middle Permian carbonates of Roteh Formation in Alborz Mountain of NOTHERN IRAN host a number of stratabound barite and galena deposit. Microthermometric measurements on two phase (H۲O + vapor) , water rich inclusions with low vapor to liquid ratios yield a mean homogenization tempretures of ۱۰۵ oC . Salinities range from ۲۰.۴ to ۲۳.۹ equiv.wt percent NaCl . The constant salinity during barite and galena deposition and lack of correlation between salinity and mineralization tempreture indicate that mixing of fluids with different salinities did not occur in the ore zone.

 

Key words

Microthermometric measurements , salinities , homogenization tempretures , mineralization tempreture , fluid inclusion .

 

STUDY METHOD

 

AIM OF THE PROJECT

The aims of the present study are:

1) to reveal the nature and source of  mineralization fluids and to determine  the thermal history of the system.

2) to present a simple overall synthesis of the formation of the deposit

3) to relate their genesis to a major orogenic event.

 


 

GEOLOGICAL SETTING

The Alborz mountain range is considered as part of the Alpine orogenic belt and formed as a result of collision tectonics.

One of the most important features of this orogen is its extensive sedimentary sequences which include shallow water carbonates,hosting numerous Ba-Pb deposits. These deposits are structurally and lithologically controlled, with interrelated fracturing, dolomitization and mineralization.Duna deposit is focal  point of the present work occurs within thrusts.Paragenesis of the deposit includes:

galena,batite,sphalerite,pyrite,tetrahedrite and chalcopyrite.

 

SRATIGRAPHIC SEQUENCE

Within the sedimentary sequence in Central Alborz, dolomitic horison of middle Permian age hosts barite and galena ore deposit and mineral occurrence. Small scale barite deposit fills fractures in lower and upper Permian strata.

 

FLUID INCLUSION STUDIES

Barite from the Duna deposit indicate that;

-One phase inclusions are the most abundant type, indicating low tempreture fluid(<40 to 50 oC) circulated within the deposit.

-Salinities of these inclusions are 13.6 to 20.6 wt equiv.

-Sets of two phase inclusions display variable freezing and homogenization tempretures (salinities are between 8.1 to 23.6 wt% NaCl and Th = 104 to 183 oC), indicating the involvement of the mixing process in the formation of the deposit.

-The choronology between the two inclusion types could not be established and their relationship with the deposition of the host barite is still unclear. 

 

Barite precipitation in Duna deposit was due to changes in oxidation state of Ba-enriched brines,

where barite precipitation ocurred as a result of mixing of reduced Ba-rich fluid with oxidizing

meteoric water. Abundant organic matter acting as a reductant appears to exist in both depositional

sites for sulfide precipitation.

  

 

CONCLUSIONS

 

1) This deposit displays an epigenetic hydrothermal mineralization of low to moderate   

highly saline fluids, formed along faults,veins and fractures and breccia open spaces,hosted by dolomitized platform carbonates.

 

2) The deposit is fault controlled, and is proximal to faults at surface which may be linked at depth.Thus , critical fluid-focusing feature for mineralization is the role of faults as channelways for mineralizing fluids.

 

3) The large size of the ore district indicates the existence of a large scale fluid-flow through the sedimentary rocks which were deformed and uplifted during the Alborz orogen.

 

4) Reginal tectonism may be one of the most important factors in the genesis of this deposit in Central Alborzand middel Permian tectonics characterizing the region could have set fluids in motion by variety of potential mechanisms.

 

5) The metallogenic characteristics of this deposit indicates that it shares many similarites in its features with MVT deposits.

 

 

 

 

REFERENCES

 

Ellis, A.J and Mahon., W.A.J., 1977. Chemistry of geothermal system. Academic Press. N.Y., 392p.

 

 

Hanor, J.G., 1979. The sedimentary genesis of hydrothermal fluids, in Barenes, H.L.,ed Geochemistry of  hydrothermal ore deposits, 2nd ed. NY. John Wiley,157-172.

 

Rimstidt, 1995. Gaung mineral transport and deposition .PP. 487-515.

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