Search

Oxygen isotope ratios in magnetite can be used to study the origin of iron-oxide ore deposits. In previous studies, only 18O/16O ratios of magnetite were determined. Here, we report triple O isotope data (17O/16O and 18O/16O ratios) of magnetite from the iron-oxide-apatite (IOA) deposits of the Yazd and Sirjan areas in central Iran. In contrast to previous interpretations of magnetite from similar deposits, the triple O isotope data show that only a few of the magnetite samples potentially record isotopic equilibrium with magma or with pristine magmatic water (H2O). Instead, the data can be explained if magnetite had exchanged O isotopes with fluids that had a mass-independently fractionated O isotope composition (i.e., MIF-O), and with fluids that had exchanged O isotopes with marine sedimentary carbonate rocks. The MIF-O signature of the fluids was likely obtained by isotope exchange with evaporite rocks of early Cambrian age that are associated with the IOA deposits in central Iran. In order to explain the triple O isotope composition of the magnetite samples in conjunction with available iron isotope data for magnetite from the deposits, we propose that magnetite formed from magmatic fluids that had interacted with evaporite and carbonate rocks at high temperatures and at variable water/rock ratios; e.g., magmatic fluids that had been released into the country rocks of a magma reservoir. Additionally, the magnetite could have formed from magmatic fluids that had exchanged O isotopes with SO2 and CO2 that, in turn, had been derived by the magmatic assimilation and/or metamorphic breakdown of evaporite and carbonate rocks. [ABSTRACT FROM AUTHOR]

This investigation was done to determine the release of potassium (K) from five calcareous soils of southern Iran using 0.025 M CaCl2, HCl and citric acid during six successive extractions and to study the K fixation capacity of the soils after K release experiment. Mineralogical study indicated that Vertisols and Mollisols were dominated with smectites; while other soils had illite, chlorite, palygorskite and smectite. Results indicated that citric acid extracted more K than CaCl2 and HCl (137 vs. 111 and 113 mg kg−1, respectively). The analysis of calcium (Ca), magnesium (Mg) and K concentrations in the solutions suggests that the exchange of K with soluble Ca and Mg (originated from dissolution of carbonates by acidic solutions) is the main mechanism of K release, but citrate is able to dissolve K-bearing minerals and release K in slightly calcareous soils. Soils with more illite released more K. Potassium fixation capacity of soils increased after extractions of soils with different extractants from 324 to 471 mg kg−1, with no significant difference. It is suggested to apply more K fertilizers in K-depleted calcareous soils and use of different solutions for extracting K from soil minerals may be a temporary and short term solution. [ABSTRACT FROM AUTHOR]

Abstract: The spatial pattern of soil redistribution rate was investigated using cesium-137 (137Cs) within a cultivated complex hillslope in western Iran. The relationship between soil redistribution rate and soil organic carbon and total nitrogen pattern were studied using co-regionalization analysis. Ninety-one soil cores were sampled for 137Cs, total nitrogen, and soil organic carbon measurements. The simplified mass balance model estimated a gross erosion rate of 29.8tha−1 yr−1 and a net soil deposition rate of 21.8tha−1 yr−1; hence, a net soil loss rate of 8tha−1 yr−1. This magnitude of soil erosion rate is higher than the acceptable rate in semiarid regions. Co-regionalization analysis and co-dispersive coefficients among the selected variables showed that only a small fraction of the variability in total nitrogen and soil organic carbon could be explained by soil redistribution and that the remaining might be the result of different management practices by local farmers. [Copyright &y& Elsevier]

The porphyry copper deposit (PCD) at Sungun is located in East Azarbaidjan, NW of Iran. The magmatic suites in the Sungun area are a part of the NW–SE trending Cenozoic magmatic belt of Iran. The Sungun porphyries occur as stocks and dikes. The stocks are divided into two groups, I and II. Porphyry Stock II, ranging in composition from quartz monzonite through granodiorite to granite, hosts the Sungun PCD. Four distinct types of hypogene alterations were recognized at Sungun: (1) potassic; (2) potassic–phyllic; (3) phyllic; and (4) propylitic. Stable isotope (S, O, H, and C) studies were restricted to within the phyllic and potassic–phyllic alteration zones, where numerous cross-cutting quartz, sulfides, carbonates, and sulfate veinlets are present. The objective of these studies was to determine the origin of the ore-forming solutions, and their important components (e.g. sulfur and carbon). Twenty sulfide and four sulfate samples were taken from sulfide and gypsum veinlets within Porphyry Stock II and the associated skarn zone for sulfur isotopic analyses. The δ34S values of sulfides (pyrite, chalcopyrite, molybdenite, galena, sphalerite) and sulfate (gypsum) range from −4.6 to −0.2‰ (mean of −1.5‰) and from 10.9 to 14.4‰ (mean of 12.9‰), respectively. These values are almost analogous to those from El Salvador (Chile) and Ajo (Arizona), and Twin Buttes (Arizona), and strongly suggest a magmatic source for the sulfur at Sungun. Twenty-eight fluid inclusion-rich quartz samples from quartz veinlets beneath the supergene zones of the Porphyry Stock II were chosen for O and H isotopic analyses. The δ18O (of quartz) and δD (of fluid inclusions in quartz) values range from 8.3 to 10.2‰ (mean of 9.2‰) and −58 to −75‰ (mean of −66‰) relative to Standard Mean Ocean Water (SMOW), respectively. The calculated δ18O values of the fluids range from 4.4‰ (T=375 °C) to 7.6‰ (T=570 °C) with a mean of 6.4‰. The δ18O and δD values of the fluids lie within the typical range of magmatic waters. Based upon the lowest obtained δD values, the calculated maximum exchangeable meteoric water that might be involved in the phyllic and potassic–phyllic alteration processes was ∼20%. Fourteen calcite samples from carbonate veinlets in the Porphyry Stock II and two samples from associated marble aureole were collected for carbon and oxygen isotopic analyses. The δ13C(calcite) from Porphyry Stock II and associated marble aureole varies from −0.4 to 2.9‰ and 0.06 to 2‰ relative to the PDB Standard of the University of Chicago, respectively. The corresponding δ18O(calcite) values range from 6 to 13.2‰ relative to SMOW. The δ13C values lie within the sedimentary range, suggesting that there was little or almost no magmatic carbon in the hydrothermal system. In contrast, The δ18O(calcite) values are far lower than that of Cretaceous sedimentary carbonates which suggest that the values were influenced by those of magmatic fluids through isotopic re-equilibration. These isotopic investigations demonstrated that: (1) in contrast to some well-known PCDs, about 80% of the fluids involved in the phyllic and potassic–phyllic alterations at Sungun had a magmatic O and H isotopic signature; (2) the Upper Cretaceous limestone was the potential source of C; and (3) the sulfur had a magmatic origin. [Copyright &y& Elsevier]