Modal and normative content of ilmenite in gabbros from the ophiolite complexes of Fanouj, SE Iran

Majid Falaknazi

Jamal Tarrah

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Ophiolites of west Fanouj (southeast Iran) are mainly composed of three mafic units including gabbros and diabasic rocks. The ophi...

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Ophiolites of west Fanouj (southeast Iran) are mainly composed of three mafic units including gabbros and diabasic rocks. The ophiolite complexes of this area lead, in addition to common rock-forming minerals, to titanium-containing mineral phases such as ilmenite. Seven titan-bearing gabbros from the west Fanouj ophiolite complex and a coarse-grained placer sample were analyzed by XRD and XRF on their mineralogical and chemical composition, respectively. The amount of ilmenite was calculated from the chemical analysis using TiO2 content. The normatively determined values (n) were compared with the modal values (m) measured from the peak intensity ratios of the XRD patterns. The difference between the normative (n) mineral contents and the modal (m) data [(n-m) x m-1 x 100] is 13±27% (mean value ± standard deviation) and are within the range of the error of mineralogical methods such as optical and X-ray techniques. Since Fe was not included in the normative method, a test was performed by comparing the content of Fe measured by XRF with the amount of Fe, which result from the modal determination of all iron-bearing minerals present in the samples. This approach confirmed data deriving from the normative approach on ilmenite quantification.