Rare Earth Elements Geochemistry of Sheikh-Marut Laterite Deposit,NW Mahabad,West-Azarbaidjan Province,Iran

Laterite deposit at Sheikh-Marut （NW occurred within middle-upper Permian carbonate Mahabad, West-Azarbaidjan province, Iran） rocks. It consists of seven stratiform and/or discontinuous lenticular layers extending over 4.2 km in length and having thicknesses ranging from 3 to 14 m. Mineralogical data show that the ores contain kaolinite and hematite as major and boehmite, diaspore, halloysite, amesite, anatase, and muscovite-illite as minor mineral phases. The computed Ce anomaly values in the ores range from 0.05 to 20.84. Conservative index （e.g., Eu/Eu＊） suggests that this deposit is a product of alteration and weathering of basaltic rocks. Rhythmic increment of EREE values of the ores with approaching to the carbonate bedrocks shows an in-situ occurrence of lateritization processes. Mass change calculations of elements indicate that two competing processes namely leaching and fixation were the major regulating factors in concentration variation of REEs （La-Lu） in this deposit. The obtained results show that pH increase of weathering solutions by carbonate bedrocks, existence of organic matters, and the degree of comlexation with organic ligands played remarkable role in distribution of REEs during lateritization. Further geochemical considerations revealed that secondary phosphates, Mn-oxides and -hydroxides, diaspore, and anatase were the potential hosts for REEs in this deposit.

The Lanthanide Tetrad Effect in Argillic Alteration: An Example from the Jizvan District, Northern Iran

Intrusion of quartz-monzodioritic igneous bodies of Oligocene age into Eocene lithic crystal tufts and trachy-basalts resulted in the occurrence of a widespread argillic alteration zone in the Jizvan district （northern Iran）. Mineralogically, the argillie alteration zone includes minerals such as kaolinite, quartz, smectite, pyrophyllite, muscovite-illite, alunite, rutile, calcite, feldspar, chlorite, hematite and goethite. Therefore, the non-CHARAC behaviour for trace elements in the argillic samples is reflected in the non-chondritic Y/Ho and Zr/Hf ratios and the irregular REE patterns, which appear related to the tetrad effect phenomenon. The chondrite-normalized REE distribution patterns indicate both concave （W-shaped） and convex （M-shaped） tetrad effects in the argillic samples. Based on the field evidence and the results from geochemical studies, it can be concluded that the samples from the argillic alteration zone having high fourth tetrad effect values （〉0.30） were developed in the fault and breccia zones. The results indicate that factors such as preferential scavenging by Mn-oxides, crystallization of clay minerals, fluid-rock interaction, overprint of hypogene mineral assemblage by supergene ones, and the structural control, have all played an important role in the occurrence of tetrad effects in samples of the argillic zone in the Jizvan district.

REE Tetrad Effect as a Powerful Indicator of Formation Conditions of Karst Bauxites: A Case Study of the Shahindezh Deposit, NW Iran

Study of the concentration of major,trace,and rare earth elements(REE)in the Shahindezh karst bauxite deposit,northwestern Iran clarifies the relationship of the tetrad effect with geochemical parameters in the bauxite ores.The existence of irregular curves in the chondrite-normalized REE patterns as well as non-CHARAC behavior of geochemically isovalent pairs(Y/Ho)are related to the tetrad effect.The meaningful positive correlation between the sizes of the calculated T3 tetrad effect and some geochemical factors such as Y/Ho,ΣREE,La/Y,(La/Yb)N,and(LREE/HREE)N as well as some major oxides-based parameters like Al2O3+LOI/SiO2+Fe2O3,Al2O3/Fe2O3,Al2O3+LOI,IOL,and SiO2+Fe2O3indicate that the studied bauxite horizon was likely deposited by different(acidic and/or alkalic)solutions at different stages.The lower part of the studied horizon with a thickness of^4.7 m displays alkali characteristics whereas the upper parts of the horizon with a thickness of^5.3 m are characterized by more acidic conditions.These results are fully supported by the co-occurrence of convex-concave tetrad effect curves in the chondrite-normalized REE patterns.Therefore,the tetrad effect phenomenon used in this study has proved to be a good and reliable geochemical proxy to assess the conditions of the depositional environment in the Shahindezh bauxite ores.

A Preliminary Study on the Aghbolaq(Fe,Cu)Skarn Deposit,Oshnavieh,NW Iran:Constraints on Metasomatic Fluid Evolution

The Aghbolaq skarn deposit is located in the Urumieh-Golpayegan plutonic belt,NW Iran.The garnetite skarn(stageⅠ)has been intensely cross-cut by the magnetite-garnet skarn(stageⅡ)which were,in turn,cut and offset by the ore-hosting quartz veins/veinlets(stageⅢ).The predominance of andradite(Adr82.5–89.1)and its high Fe3+/Al ratio(up to 1685)apparently supports the high fO2,salinity and prevalence of magmatic/hydrothermal fluids involved,rather than meteoric waters,during the magnetite-garnet skarn formation.Two major groups of fluid inclusions,namely aqueous(LV,LVS)and aqueous–carbonic(LVC,LLCVC),were recognized in garnet and quartz veins that,especially in growth zones and along intra-granular trails,better display fluid inclusion assemblages(FIAs)than those in clusters.The prograde magnetite-garnet skarn was formed by the metasomatic fluid at relatively high Th(209–374℃),under a lithostatic pressure of~200 bars.The retrograde mineralized quartz veins were formed at temperatures ranging from 124℃to 256℃,by dilute and less saline(2.57–11.93 wt%NaCl eq.)hydrothermal fluids under a hydrostatic pressure of~80 bars.The fluid evolution of the Aghbolaq skarn began with an earlier simple cooling of metasomatic fluid during the prograde stage,followed by the later influx of low salinity meteoric fluids during the retrograde stage.

Pore size determination using normalized J-function for different hydraulic flow units

Pore size determination of hydrocarbon reservoirs is one of the main challenging areas in reservoir studies.Precise estimation of this parameter leads to enhance the reservoir simulation,process evaluation,and further forecasting of reservoir behavior.Hence,it is of great importance to estimate the pore size of reservoir rocks with an appropriate accuracy.In the present study,a modified J-function was developed and applied to determine the pore radius in one of the hydrocarbon reservoir rocks located in the Middle East.The capillary pressure data vs.water saturation(PceSw)as well as routine reservoir core analysis include porosity(4)and permeability(k)were used to develop the J-function.First,the normalized porosity(4z),the rock quality index(RQI),and the flow zone indicator(FZI)concepts were used to categorize all data into discrete hydraulic flow units(HFU)containing unique pore geometry and bedding characteristics.Thereafter,the modified J-function was used to normalize all capillary pressure curves corresponding to each of predetermined HFU.The results showed that the reservoir rock was classified into five separate rock types with the definite HFU and reservoir pore geometry.Eventually,the pore radius for each of these HFUs was determined using a developed equation obtained by normalized J-function corresponding to each HFU.The proposed equation is a function of reservoir rock characteristics including 4z,FZI,lithology index(J*),and pore size distribution index(3).This methodology used,the reservoir under study was classified into five discrete HFU with unique equations for permeability,normalized J-function and pore size.The proposed technique is able to apply on any reservoir to determine the pore size of the reservoir rock,specially the one with high range of heterogeneity in the reservoir rock properties.