Farhad Ahmadnejad

The Selltekellto bauxite deposit is located 25 km south of Saqqez city (latitude 36°08'N, longitude 46°16'E), Kurdistan province, NW Iran. The bauxite orebody comprises a series of stratiform and lenticular masses with a general E-W trend, which are scattered within karst depressions and sinkholes developed in the underlying carbonate rocks of the Middle Permian Ruteh Formation. In the study area, the bauxitic horizons are irregularly distributed but exhibit relatively uniform thicknesses, averaging up to 10 meters. They are overlain by the Late Permian Nessen Formation. Based on texture, composition, and color, three distinct layers have been identified within the Selltekellto deposit, from top to bottom: i) brown bauxite, ii) ooilitic-pisolitic bauxite, and iii) clayey bauxite. Mineralogical studies reveal that hematite, diaspore, illite, and berthierine are the major mineral components, accompanied by minor amounts of anatase, goethite, pyrite, rutile, chlorite, albite, and quartz. The abundance of berthierine in the studied deposit is significantly higher compared to other bauxite deposits in the northwestern part of the Sanandaj-Sirjan zone, allowing the Selltekellto deposit to be classified as a berthierine-rich bauxite deposit. Berthierine forms under reducing conditions rich in iron and silica, with organic matter present, primarily through direct precipitation from hydrothermal fluids or alteration of minerals such as kaolinite and illite during weathering processes, indicating swampy and reducing environments. Diaspore in karst bauxites can form both through the alteration of gibbsite (under deep conditions) and by direct precipitation in surface environments facilitated by microorganisms and alkaline-reducing conditions. Evidence from this study demonstrates that microorganisms play a key catalytic role in the formation of bauxite minerals, as shown by the close association between microbes and diaspore, the cementation of cubic pyrite grains by diaspore, and the widespread presence of microorganisms in association with berthierine—all of which indicate direct biological involvement in mineralization. Although diaspore formation under surface temperature-pressure conditions is thermodynamically challenging, microbial mediation can overcome these kinetic barriers, enabling diaspore crystallization in the Selltekellto bauxite deposit. Based on comprehensive geochemical analyses, the probable parent rock of the Selltekellto bauxite deposit is mafic igneous rock, predominantly with a basaltic to andesitic composition. This conclusion is drawn from multiple discriminant methods, including plots of (Eu/Eu*) vs. (Sm/Nd), (TiO2/Al2O3), and (U/Th), Discriminant Function 3 vs. 4, immobile element plots (Th vs. Zr and TiO2), and ternary diagrams (Ga-Zr-Cr and Ga-Zr-Ni*2). The data from these plots consistently show that the samples fall within the field of mafic rocks and strongly overlap with the known patterns of bauxites from the Sanandaj-Sirjan zone, which have a established basaltic origin. The results significantly rule out a meaningful genetic link with felsic volcanic rocks and further indicate that any contribution from the dissolution of the underlying carbonate bedrock during bauxitization was negligible.

The Kuh-e-Nil anticline, which hosts the Daresard bauxite deposit, is located 30 km east of Dehdasht city (latitude 30°51'11'' N, longitude 50°55'01" E), Kohgiluyeh and Boyer-Ahmad province, SW Iran. This deposit occurs in the Zagros Simply Folded Belt and at the boundary between the Cenomanian–Turonian shallow marine carbonates of the Sarvak Formation and the Santonian–Campanian carbonates of the Ilam Formation. Based on color, facies, and texture, four individual layers are recognized in the Daresard deposit from bottom to top; breccia bauxite, pisolitic bauxite, variegated soft bauxite, and bleached horizon. The Daresard bauxite ores are texturally diverse and often contain allogeneic, oolitic-conglomeratic, pisolitic, spongy, pseudo breccia, and clastic textures. Mineralogical studies indicate that boehmite, diaspore, gibbsite, hematite, goethite, and kaolinite are major minerals, and smectite, illite, anatase, rutile, calcite, and pyrite are minor minerals in the Daresard deposit. The presence of pisolitic-oolitic textures, growth of simple cortex around earlier pisoids, and pisoids with cortexes lacking radial and circular fractures indicate autochthonous origin. Geochemical data show that elements such as Fe2O3, Y, Cr, Th, HFSE, and REEs were enriched, and Al2O3, MnO, SiO2, Na2O, K2O, P2O5, CaO, Ni, Ba, Be, Ga, Co, W, Sr, V, Zr, and Ta were depleted during the bauxitization process. R-mode factor analysis revealed several significant interelemental relationships including: (1) Some low-soluble elements such as Zr, Ti, and Ga are concentrated in detrital zircons (Zr), anatase (Ti), and probably in boehmite, hematite and detrital minerals (Ga) during the final stage of bauxitization; (2) similar and meaningful weightings for U and Th suggest that the heavy mineral abundances (HFSE) may be locally important in controlling uranium behavior; (3) The distribution of light and heavy rare earth elements is controlled by the stability of REE carrier complexes and the presence of REE-bearing mineral phases; and (4) The (La/Yb)N ratio values are partly close to or remarkably lower than average upper continental crustal compositions and show a relatively minor fractionation between LREEs and HREE during bauxitization processes. This suggests that organic matter and bicarbonates play only a minor role during the bauxitization process, and fluctuations in (La/Yb)n ratios may reflect pH fluctuations in the soil solution. Cerium behaves differently from other REE elements. In the Daresard deposit, Ce anomalies show fluctuating behavior throughout the weathering profiles and have three maxima, characterized by Ce/Ce* values significantly above 1.5 . This feature suggests that cerianite was originally ubiquitous in the studied profiles. Due to the identification of parisite as an authigenic Ce-bearing mineral in the Daresard deposit, the following model can be used to explain the observed fluctuations: cerianite solubilization via cerium reduction → cerium transportation per descensum → parisite precipitation. This cycle has been repeated several times due to periodical fluctuations in the groundwater table. Several indexes, including REE patterns, Eu anomaly, bivariate Cr and Ni plots, and immobile element ratios confirm a protolith contribution from the bedrock argillaceous limestone and suggest that the parental material for the Daredard bauxite was provided from siliciclastic sediments derived from a continental margin.

The Yakshawa bauxite deposit is located 13 km southeast of Bukan city (latitude 36° 28 '28" N, 138 longitude 46° 18' 31'' E), West-Azerbaijan province, NW Iran. The bauxite ores comprise a series of layer-shaped and lenticular bodies with overall trends of NE-SW that occur as infills of karstic depressions and sinkholes within the middle Permian underlying carbonates of the Ruteh Formation. Bauxite horizons in the study area are distributed irregularly but have relatively uniform thicknesses averaging 11 to 18 m and are overlain by the late Permian Nessen Formation. Based on texture, composition, and color, six individual layers are recognized in the Yakshawa deposit, which are, from bottom to top; i) breccia bauxite; ii) clayey bauxite; iii) ferritic bauxite; iv) mottled bauxite; v) brown bauxite, vi) bleached horizon. Detailed mineralogical analysis reveals that diaspore, hematite, illite, anatase, and rutile are the major mineral components accompanied by minor amounts of kaolinite, dickite, halloysite, quartz, calcite, pyrite, and clinochlore. The most important textures observed in the Yakshawa deposit include colloformic, ooidic, pisoidic, spastoid textures, and pelitomorphic clay-rich groundmass. Interelemental relationship analyses of the ores by using R-mode factor analysis revealed several key findings: i) heavy minerals with low solubility, including rutile and zircon, accompanied by Al oxyhydroxides during bauxite formation control the distribution of critical metals (Ga, Ti, Nb, Hf, Ta, and W) showing similar geochemical behavior; ii) the weathering of biotite results in the expulsion, from the octahedral positions, of Fe3+, which forms oxyhydroxides that can strongly adsorb V: iii) The strong correlation between Y and P suggests that the distribution of Y may be related to the presence of Y-bearing REE minerals such as xenotime: iv) In the Yakshawa deposit almost all REE-bearing phases bauxite are phosphate minerals including monazite-Ce, xenotime-Y, and florencite-Ce. Thus, the abundance of REE is largely controlled by P-rich minerals. Several parameters, including Eu-anomaly, immobile element ratio (e.g., Ti/Nb, Zr/Hf, and Nb/Ta), and Log Cr vs Log Ni were used to discuss the parental affinity or precursor rock(s) of the Yakshawa bauxite ores. The results suggest that the bauxite ores of the Yakshawa deposit have a genetic relationship with Middle-Late Permian mafic volcanic.

خاک رس به عنوان یکی از مصالح مهم موجود در طبیعت به شیوه‌های گوناگون در پروژه‌ها مورد استفاده قرار می-گیرد.رس‌ها کانی‌های سیلیکات آلومینیوم آب‌داری هستندکه از ترکیب دو پایه چهاروجهی سیلیکا وهشت وجهی آلومینا تشکیل شده‌اند.کانی‌های رسی از لحاظ ساختاری به شکل ورقه‌ای هستند که خود از لایه‌های سیلیکا و آلومینا تشکیل شده‌اند واز نظر شیمیایی در سطح خود دارای بار الکتریکی منفی هستند که این امر زمینه‌ساز واکنش این کانی‌ها شده است. نوع کانی‌های رسی و ترکیبات همراه آنها بر روی رفتار آنها در واکنش به جذب آب و به تبع ایجاد خواص خمیری تاثیرگذار است. برای پیش‌بینی رفتار رس‌ها با ترکیب کانی‌شناسی خاص لازم است کانی‌های رسی خاکو ترکیبات آنها مشخص و خواص مهندسی آنها اندازه‌گیری شود.در این پژوهش برای بررسی تاثیر ترکیبات رسی بر خواص خمیری آن، از محدوده شرق شهر بانه و شرق آرمرده و شمال قروه نمونه‌برداری شد و با آنالیزهای ‌‌XRD‌و XRF‌ کانی‌های رسی و ترکیبات موجود در نمونه‌ها مورد بررسی قرار گرفت و سپس با اندازه‌گیری حدود اتربرگ، ارتباط خواص خمیری و ترکیبات رسی مورد تحلیل قرار گرفت. تحلیل نتایج آنالیز و خواص خمیری نشان داد که در بین کانی‌های غالب رسی، همبستگیمونت‌موریلونیت با مقدار 949/0 با PI از ایلیت و کائولینیت بیشتر است.همچنین نتایج نشان داد که در بین کانی های موجود در خاک، کوارتز ، کلسیت، ارتوکلاز ، آلبیت با PI دارای همبستگی منفی و ترکیباتی مانندAl2O3، Fe2O3، MgO ، TiO2 و Na2O دارای همبستگی مثبت می باشند که بیشترین مقدار مربوط به TiO2 می‌باشد. همچنین نتایج نشان داد که برخی عناص مانند Cu، Zn، Co و Cr دارای همبستگی و عناصری مانند، U، Ba، Pb و Ni دارای همبستگی منفی با PI می باشند. از دیگر نتایج بدست آمده در این تحقیق می‌توان گفت که در بین سه محدوده مورد مطالعه، خاکهای محدوده قروه دارای بیشترین پتانسیل تورمی می‌باشد.