Document Type : Original Research Paper
Authors
1 Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran
2 Department of Economic Geology, Tarbiat Modares University, Tehran, Iran
Abstract
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.
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