Physicochemical conditions of skarn formation in contact of the Alvand batholith with the meta-calcareous rocks, Hamedan, western Iran

زمین شناسی اقتصادی

Article 5, Volume 4, Issue 1 - Serial Number 6, June 2012, Pages 123-134   

Document Type: Research Article

DOI: 10.22067/econg.v4i1.13396

Authors

Adel Saki^{* 1}; Houshang Pourkaseb²

¹Ahvaz

²Shahid Chamran University of Ahva

Abstract

The Cheshin meta-calcareous rocks (Permo Triassic) in southeast Hamedan outcrop in association with a variety of pelitic schists and hornfels rocks. The intrusion of the Alvand Batholith (Jurassic age) into pelitic and calcareous host rocks has produced metamorphic rocks in the Hamedan area (Cheshin village). On the basis of the dominance of calcite/dolomite, silicate and ore minerals, the calcareous rocks can be divided into two groups: a) marbles and calc-silicates; b) skarn rocks. The ore bodies occur in a contact zone between sillimanite-hornfels and calc-silicate rocks and formed the skarn rocks. Based on mineralogy, skarn rocks in the studied area consist mainly of diopside, garnet, tremolite, vesuvianite, epidote and ore minerals (magnetite and hematite). The skarnification processes occurred at two stages: (1) prograde metamorphism; and (2) retrograde metamorphism. The first stage involved prograde metasomatism and anhydrous minerals such as garnet and pyroxene formed. Second stage of retrograde skarn development is also recognized. In addition to Fe, Si and Mg, substantial amounts of Fe, along with volatile components were added to the skarn system. Consequently, considerable amounts of hydrous minerals, oxides and carbonates replaced the anhydrous minerals in the host rocks and hydrous minerals such as epidote+chlorite+amphibole formed. Using multiple equilibria by THERMOCALC® program, temperature (~630 ºC), pressure (~4 kbar), and fluid composition (XCO2 as low as 0.17) have been calculated for the formation of the calc-silicate rocks. Skarn mineralogy shows good agreement with these calculations.

Keywords

Alvand Batholith; skarn; calc-silicate; fluid composition; THERMOCALC®

References

[1] Moazzen M., Oberhänsli R., Hajialioghli R., Möller A., Bousquet R., Droop GTR., Jahangiri A., "Peak and post-peak P -T conditions and fluid composition for scapolite clinopyroxene- garnet cac-slicate rocks from the Takab area, NW Iran", European Journal of Mineralogy. 21 (2009) p149-162.

[2] Ague J. J., "Gradients in fluid composition across metacarbonate layers of the Wepawug Schist, Connecticut, USA", Contributions to Mineralogy and Petrology. 143 (2002) p38-56.

[3] Ague J. J., "Fluid infiltration and transport of major, minor and trace elements during regional metamorphism of carbonate rocks, Wepawug Schist, Connecticut, USA", American Journal of Science, 303 (2003) p753-816.

[4] Cartwright I., Oliver N. H. S., "Direction of fluid flow during contact metamorphism around the Burstall Granite, Australia", Journal of the Geology Society of London, 149 (1992) p693-696.

[5] Karimzadeh Somarin A., "Garnet composition as an indicator of Cu mineralization: evidence from skarn deposits of NW Iran", Journal of Geochemical exploration. 81 (2004) p47-57.

[6] Mollai H., Yaghubpur A. M., Sharifiyan Attar R.,"Geology and geochemistry of skarn deposits in

the northern part of Ahar batholith, East Azarbaijan, NW Iran" , Iranian Journal of Earth Sciences 1 (2009) p15-34.

[7] Karimzadeh Somarin A., Moayyed M., "Granite- and gabbrodiorite skarn deposits of NW Iran", Ore Geology Reviews, 20 (2002) p127-138.

[8] Agard P., Goffe B., Touret J. L. R., Vidal O., "Retrograde mineral and fluid evolation in high-pressure metapelites", Contributions to Mineralogy and Petrology, 140 (2000) p296-316.

[9] Masters R. L., Ague J. J., "Regional-scale fluid flow and element mobility in Barrow s metamorphic zones, Stonehaven, Scotland", Contributions to Mineralogy and Petrology, 150 (2005) p1-18.

[10] Meinert L. D., "Application of skarn zonation models exploration", Exploration and Mining Geology, v.6 No.2 (1998) p185-208.

[11] صادقیان م.،" بررسی پترولوژی سنگهای آذرین و دگرگونی منطقه چشمه قصابان همدان"، پایان نامه کارشناسی ارشد، دانشگاه تهران (1373).

[12] بهاری فر ع.، "پترولوژی سنگهای دگرگونی منطقه همدان"، پایان نامه دکتری، دانشگاه تربیت معلم تهران (1383).

[13] سپاهی گرو ع.،" پترولوژی مجموعه پلوتونیک الوند با نگرشی ویژه بر گرانیتوئیدها"، رساله دکتری، دانشگاه تربیت معلم تهران (1378).

[14] Sepahi A. A., Whitney D. L. Baharifar A. A., "Petrogenesis of And-Ky-Sil veins and host rocks, Sanandaj-Sirjan metamorphic belt, Hamadan, Iran", Journal of Metamorphic Geology 22 (2004) p 119-134.

[15] Saki A., "Formation of Spinel-cordierite-plagioclase symplectites replacing andalusite in metapelitic of the Alvand aureole, Iran", Geological Magazine 148 (2011) p 423-434.

[16] Saki A., Moazzen M., Baharifar A. A., "Migmatite microstructures and partial melting of Hamadan metapelitic rocks within the Alvand contact aureole, western Iran",International Geology Review (2012) in press.

[17] Alavi M., "Tectonics of the Zagros Orogenic belt of Iran: new data and interpretations", Tectonophysics 229 (1994) p211–238.

[18] Mohajjel M., Fergusson C. L., Sahandi M. R., "Cretaceous-Tertiary convergence and continental collision, Sanandaj-Sirjan Zone, western Iran", Journal of Asian Earth Science, 21 (2003) p397–412.

[19] Einaudi M.T., Meinert L. D., Newberry R. J., "Skarn deposit", Economic Geology, 75th Anniv.p, (1981) p317-391.

[20] Perkins E. H., Brown T. H., Berman R. G., "PTX-SYSTEM: three programs for calculation of pressure-temperature-composition phase diagram", Computers and Geosciences, 12 (1986) p749-755.

[21] Holland TJB., Powell R., "An internally consistent thermodynamic data set for phases of petrological interest", Journal of Metamorphic Geology 16 (1998) p309-343.

[22] جاویدی مقدم م.، حیدریان شهری م ر.، کریم پور م ح.، "زمین‌شناسی، کانی سازی، ژئوشیمی و مطالعات مغناطیس سنجی در کانی سازی آهن منطقه کلاته شاهین، استان خراسان رضوی"، مجله زمین شناسی اقتصادی، شماره 1 جلد 2 (1389) 97-77.