عنوان مقاله [English]
Sabzevar ophiolitic belt is located in the northwest of Iran, north of Sabzevar. The current study is carried out for the first time in Iran with an exploration approach in the western part of the belt. Study of Platinum Group Elements (PGE) is of high importance for determining the genesis and economic evaluation of chromite deposits specifically in ophiolitic complexes. Chondrite-normalized PGE patterns of the chromitites related to ophiolites have a negative slope suggesting that during initial stages of magma crystallization, chromite preferentially removed compatible PGE from the magma. These patterns in the Sabzevar chromitites imply that these rocks are related to ophiolitic complexes (Alpine type). Chromite ore bodies which exhibit a relatively high incompatible/compatible element (Pd/Ir, Cu/Ni) ratios are derived from a more evolved magma with a lower fractional melting degree and do not seem to be of economic importance; this ratio in Al-rich chromites is higher than that of Cr-rich type. Pd/Ir ratio in Sabzevar chromitites on the average is less than 1, similar to many important chromite ore bodies related to ophiolitic complexes throughout the world. This ratio being low, as well as high chromium number (Cr/Cr+Al>0.60) suggests that this complex can be considered to contain a significant potential for economic and metallurgical chromite. Furthermore, the complex does not contain chromitites of uniform composition in chalcophile elements. PGE patterns of peridotites in the study area also show that these units in upper parts of the Gaft area are similar to ultramafic cumulates of oceanic crust, while in lower parts of Faroumad area related to mantle sequences.
حسنی پاک، ع. ا.، 1378- اکتشافات ذخایر طلا، انتشارات دانشگاه تهران ، 609 صفحه .
وطن پور، ح. ر.، 1375- ویژگیهای ژئوشیمیایی، بافت، ساخت و پیدایش کانسارهای کرومیت در مناطق گفت و فرومد سبزوار، پایان نامه کارشناسی ارشد، دانشگاه شهید با هنر کرمان، 260 صفحه.
Economou-Eliopoulos, M., 1993- Platinum group element distribution in chromite ores from ophiolite complexes of Greece: Implications for chromite exploration: Ofioliti, v. 18, n. 1, p. 83-97.
Economou-Eliopoulos, M. & Vacondios, I., 1995- Geochemistry of chromites and host rocks from the Pindos ophiolite complex, northwestern Greece: Chemical Geology, v. 122, p. 99-108.
Irvine, T.N. & Sharpe, M.R., 1986- Magma mixing and origin of stratiform oxide ore zones in the bushveld and Stillwater complexes , Metalogeny of basic and ultrabasic rocks. Mining Metallurgy ,London , p.183-198
Konstantopoualou, G.P. & Economou-Eliopoulos, M., 1991- Distribution of platinum-elements and gold within the Vourinos chromitite ores, Greece. Econ. Geol., v. 86, p. 1672-1682.
Leblance, M. & Ceuleneer, G., 1992- Chromite crystallization in a multicellular magma flow: Evidence from a chromitite dike in the Oman ophiolite: Lithos, Elsevier Science Publishers, v. 27, p. 231-257.
Lensch, G, 1980- Major elemant geochemistry of the Ophiolites in north eastern Iran. In: Panayiotou, A. (Ed). Proceedings to International Ophiolite Symposium. Ministry of Agriculture and Natural Resources, Geological Suvey Department. Republic of Cyprus, p 384- 401.
Naldrett, A.J., Brügmann, G.E. & Wilson, A.H., 1990- Models for concentration of PGE in layered intrusions: Examples from the Bushveld, Great Dyke and Lac des Iles Complexes. Can. Mineralogist, v. 28, p. 389-408.
Peck, D.C. & Keays, R.R., 1990- Geology, geochemistry and origin of platinum-group element-chromitite occurrences in the Heazlewood River Complex, Tasmania. Econ. Geol., v. 85, p. 765-793.
Proenza, J.A., Gervilla, F. & Melgarejo, J.C., 2001- Genesis of sulfide-rich chromite ores by the interaction between chromitite and pegmatitic olivine-norite dikes in the Potosi Mine, eastern Cuba, Mineral. Deposita, v. 36, p. 658-669.
Roberts, S., 1988- Ophiolitic chromitite formation: A marginal basin phenomenon, Econ. Geol., v. 83, p. 1034-1036.
Vatanpour, H.R. , Khakzad , A. & Ghaderi, M., 2004 -, Geochemical characteristics and petrology of Sabzevar chromite deposits, Iran, The sixth international conference on geochemistry , Alexandriauniversity of Egypt , p.174-176