بررسی کانه‌زایی آهن کرفس شمال استان همدان با استفاده از داده‌های ژئوشیمیایی و کانی‌شناسی

Introduction
Karafs iron index is located 5Km north of the Karafs village in Hamedan province, Iran and geologically in the Sanandaj-Sirjan structural zone. Iron deposits in Sanandaj- Sirjan structural zone have been discussed and their origin is controversial. In this paper, geological, mineralogical, textural and geochemical properties, especially the geochemical behavior of rare earth elements in Karafs iron index are investigated and the mineralization type and its origin are determined.
Materials and methods
During the field studies, 70 samples were taken for petrographic and mineralogical studies. Petrographic and mineralogical studies were performed in the Bu-Ali Sina University mineralogical laboratory. Geochemical study of iron ore was analyzed by ICP-MS at SGE company of Canada. XRD analyzes were performed at Bu-Ali Sina University.
Results and Discussion
Based on field observation,rock units in the area include volcanic rocks, phyllite, schist, skarn and limestone. Iron deposit is formed in lower Cretaceous limestone formation. The Karafs iron index consists of several small goethite-hematite sac-shaped masses which are accompanied by minor magnetite. Goethite and hematite are the main ore minerals. Most hematites formed in the ore are hypogene (first generation). Secondary hematites caused by conversion of magnetite to hematite (second generation) are very rare.
Replacement textures such as corrosion, marginal and island mainland are seen in hematite crystals. Two generations of goethite were observedin microscopic sections. The first generation goethites are macrocrystalline with an internal reflection of yellow brick and are usually amorphous and crushed and in some parts have a flowing state. Second generation goethites are found at the crystal boundaries of hematite and pyrite or fill its joints and fractures.
In the Karafs iron index, magnetite is seen with primary hematite in the form of amorphous crystals, in the size of 25 to 100 microns and with mass texture. Quartz, chlorite, epidote and sericitic are gangue minerals in the area. The correlation diagrams show positive correlation of Mg, Mn, P, Cu, Zn and negative correlation of Si, Co, Ni, Ti, V with Fe. Geochemical studies showed that the Ni / Co ratio is between 0.2 and 7, which is a characteristic of hydrothermal iron ore (Bajwah et al., 1987). Sr-Y diagram indicates that samples are plotted in the granitoid section, which shows that the hydrothermal fluids are derived from granitoid (Belousova et al., 2002). LREE is enriched in all samples. Enrichment of LREE elements related to HREE and Negative Eu anomalies in the deposit related to hydrothermal fluid have been reported in various parts of the world (Marschik and Fontbote, 2001; Galoyan et al., 2009).
Results
Karafs iron index is located 5Km north of the Karafs village in Hamedan province and geologically in the Sanandaj-Sirjan structural zone. Rock units in the area include andesite, phyllite, schist, skarn and limestone. Iron deposit is formed in lower Cretaceous limestone formation. Goethite and hematite are main ore minerals which are accompanied by minor magnetite. The correlation diagrams show positive correlation of Mg, Mn, P, Cu, Zn and negative correlation of Si, Co, Ni, Ti, and V with Fe. Sr-Y and Co-Ni diagrams. Parameters of REE as well dispersion pattern, variance, diagrams and correlation coefficient of elements indicate hydrothermal origin derived from granitoid system and that the deposit has been hydrothermally leaching after the formation.