IRANIAN JOURNAL OF EARTH SCIENCES (IJES)
Year:2011 | Volume:3 | Issue:2|Papers Count:8

Heterogeneous pyritaceous-polymetallic and copper-zinc-pyrrhotine deposits on the South slope of the Greater Caucasus are located in the Lower-Middle Jurassic terrigenous sediments. They were formed under a wide variation of physico-chemical parameters of mineral formation and are characterized by specific mineralogical-geochemical peculiarities. Ore-formation occurred in three stages. In the first stage, massive hydrothermal-sedimentary sulphurous-pyrite ores were deposited. The formation of the second stage of hydrothermal-metasomatic pyrite-polymetallic ores was prior to the intrusion of constant differentiated formation dikes. In the third stage hydrothermal-metamorphogenic copper-pyrrhotine ores were formed. Stratiform pyrite deposits can be characterized by a large variety of textural -mineralogical types of ores and mineral associations, by rich mineral composition and a rather wide geochemical spectrum. As a whole, among the studied admixture-elements (Tl, Ag, Hg as well as B, Li, Rb) one can find accumulating tendency in the above-ore series, near ores with pyrite-polymetallic composition. Other group of elements (Co, Sn, Mn, Mo and Bi) shows accumulation in the under-ore series. Deeper horizons of sandy-clayey rocks are enriched in uranium and potassium while the higher horizons are enriched in thorium above the ore deposit. Distribution peculiarities of such components (Tl, Ag, Hg, Sn and also Mo, Bi, K, U, Th) in the host the rocks of pyrite deposits of Greater Caucasus of South slope allows one to consider them along with ore forming components (Zn, Pb, Cu) as indicator elements for search of buried ore accumulations in the Lower-Middle Jurassic sandy-clayey deposits of region.

This paper investigates the relationship between river flow, rainfall and groundwater pumpage in the Mikkes stream during the period 1968-2009. The Mikkes basin is located in the north center of Morocco and consists of three different zones that represent diversified geologies. This basin includes a phreatic and confined aquifer in Sais basin and a shallow aquifer in the Tabular Middle Atlas. Analysis of monthly medium flows between 1968 and 2009 shows an approximate oceanic system which is characterized by two hydrological seasons. First a period of high waters in winters which is conditioned by the pluviometric contributions and the second is a low water period in summer which is conditioned by evapotranspiration. The mode of this River can be called a pluvioevaporal type. The high deficit of the Mikkes stream (between 1968-1979 and 1980-2009) is about 76% and could be the combined effect of drought and groundwater pumpage. Water table variations could be conditioned by climatic changes and regional geology. Actually, the annual water table variations show a drop in ground water levels, which is due to the combined effect of reduction in precipitation that has reduced the natural recharge of groundwater, and the increase in pumping which is increasing year by year for more than 80 years in this region. In addition, free-water tables are much more susceptible to pumpage when compared to the confined aquifer. Thus, the water table and piezometric heads of the Mikkes basin do not demonstrate a uniform sensitivity to the drought. High rainfall between 1995 and 1997 had affected the groundwater levels of Mikkes with an increase in piezometric level. The monthly piezometric variations of free-water table are characterized by a seasonal operation: groundwater recharge and discharge.

The Tirgan Formation (Barremian – Aptian) is exposed in the Kopet Dagh in northeast Iran. One stratigraphic section in Zavin was measured with a thickness of 110 meters. This Formation in section consists of three parts (including lower carbonate, limy shale– marl and upper carbonate rocks). Based on the study of 94 thin sections, 10 carbonate and 2 siliciclastic lithofacies have been identified. Carbonate lithofacies were deposited in a ramp platform in fore-shoal, shoal, lagoon and tidal flat environments. Sea level changes during the early Cretaceous time led to the formation of different large scale depositional sequences Zavin (two). The present data can help in the reconstruction of the tectonic history of the area during early Cretaceous time.

Statistical processing of data was necessary to arrive at a reasonable conclusion regarding the chemical behavior of groundwater in a river basin. Multivariate analysis was done to elucidate the groundwater chemistry of a Central Kerala River basin. Hydrochemical parameters like EC, pH, TDS, TH, Ca, Mg, Na, K, Cl, F, HCO3+CO3, SO4, total Fe were estimated in the premonsoon and post-monsoon seasons. Factor and cluster analysis differentiated two distinct contributing components to the groundwater in the basin indicating that there is considerable mixing of the groundwater and surface water in the post-monsoon season whereas such a process is not significant during the pre-monsoon period. Different geochemical controls of the investigated parameters were also assessed.

total of 183 core and cutting samples from seven exploratory wells were selected to be analyzed by Rock-Eval pyrolysis. These cores have been drilled through the Lam and Meem Members of the Madbi Formation and contain the major source rocks of Yemen´s sedimentary basins. Contents of total organic carbon were measured and Rock-Eval pyrolysis was performed to evaluate the hydrocarbon potential of Block 18 oilfields in central Yemen. Most of the studied samples have fair to excellent petroleum generation potential as shown by the results of PP, PI, HI and TOC. They have also sufficient TOC values with an average value of 1.48 wt% and a maximum value of 12.34 wt% with a good petroleum potential averaging 4.54 kg HC/ton of rock and a maximum value of 44.78kg HC/ton of rock. HI values of the Madbi Formation in its full thickness range from 16 mg to 1114 mg HC/g TOC with an average value of 273 mg HC/g TOC. Kerogen types II and III, and a small amount of type I can be observed. These kerogens are thermally mature and mostly within the hydrocarbon generation zone. In a numerical simulation approach the thermal and burial history of the Alif-1 well, which is representative for this area was modelled. Using vitrinite reflectance data, as means of calibration, the modelling results were subjected to a sensitivity analysis concerning paleo-heat flow, radiogenic heat production, basement thickness and eroded overburden or maximum burial, respectively. The calculated temperature during deepest burial of the source rock layers of the Madbi Formation reached 158°C for the Lam Member and 182 °C for the Meem Member. Compliance with the measured R0 values, used as calibration parameter, could be achieved by assuming an erosion of 1100 m of the Upper Tawilah Group. The heat flow is maximized at the onset of basin rifting in Late Jurassic to 90 mW/m2 having a base level of 60 mW/m2.Thus, the Lam Member has reached the main oil to wet gas window at its deepest burial whereas the Meem Member has undergone the wet gas window in its full thickness. The isopach map of the Alif Member, as the main reservoir in the studied area, indicates thickening of the sandstone unit towards the eastern and western parts of Block 18 around the Dostour Al-Wahdah gasfield in the east and at the Alif oilfields in the west.

Two types of bauxite occur in the Jajarm Bauxite deposit, the first one is the hard bauxite and the other is the shaly bauxite or soft bauxite. The Al2O3 content ranges from 30% to 60% and SiO2 varies between 5% to 39%.The total tonnage is more than 22 million tons with a mean value of Al2O3 content between 47% to 48%, SiO2 around 10% and Fe2O3 ranges between 6.95 to 27%. The Jajarm bauxite deposit shows high concentration of active SiO2 and Fe2O3 in comparison with other bauxite deposits of the world. Efforts have been made in this research to delineate the characteristics of the Jajarm monohydrate bauxites, consisting of a diaspore and chamosite mixture, to improve their chemistry by different beneficiation techniques and optimize their processing, grinding and digestion conditions for alumina production The Jajarm bauxite shows politomorphic and micro- granular texture with several secondary textural elements. The size of diaspore grains (which is the main mineral component) are generally below 10 microns, with a homogeneous matrix. In addition, for the very hard bauxite we can not do any separation between the crystal grains and the matrix because of similar hardness for both with closely packed space filling and in consequence of the absence of welldefined grain boundaries. Based on the above studies, the Jajarm bauxite can be enriched neither by grain analysis nor by magnetic separation. In this research hard bauxite was crushed between 2 to 3 inches and then samples were washed with 5% HCl. The result of this laboratory studies shows that the silica modulus has improved from 1.05 to 2.56 which indicates an increase of 29% in the Al2O3 content. Jajarm laboratory s study shows that Jajarm bauxite deposit partially can be improved only by water treatment.

Porosity is one of the key parameters associated with oil reservoirs. Determination of this petrophysical parameter is an essential step in reservoir characterization. Among different linear and nonlinear prediction tools such as multi-regression and polynomial curve fitting, artificial neural network has gained the attention of researchers over the past years. In the present study, two-dimensional (2D) seismic and well logs data of the Burgan oil field were used for prediction of the reservoir porosity. In this regard, broadband acoustic impedance was first extracted from 2D seismic dataset, as the attribute most related to porosity. Next, other optimum seismic attributes were selected using stepwise regression and cross validation techniques. At the end, three types of neural network were used for inversion of seismic attributes and prediction of reservoir porosity. The results show that probabilist ic neural network (PNN) is the best one for prediction of the reservoir porosity using seismic attributes.

The Tareek Darreh gold deposit is located 40km north of Torbat-e Jaam in the Khorassan-Razavi province, NE-Iran. The study area mainly comprises slightly metamorphosed, sedimentary rocks of Jurassic age including alternation of shale, siltstone, and sandstone. These rocks have been intruded by plutonic rocks such as gabbro-norite, diorite, quartz-diorite, and rhyodacite. The ore bodes are exposed by trenching and pitting. In this study, all trenches and pits were systematically sampled and analysed by XRF, XRD, and ICP methods as well as petrological mineralogical studies. The alteration minerals of quartz, chlorite, albite, and sericite are mostly observed on the top or margin of the stocks. Alteration is more intensive at the contacts of the stocks where vein type mineralization has occurred. The veins are mainly composed of silica type and calcite type, arsenopyrite, chalcopyrite, and pyrite main ore minerals. Four promising mineralization zones were selected for further studies. The analytical results for the zones No.2 and No.4 confirm high gold, copper, bismuth, tellurium, and silver. In zone No.2 (50×80 m2) an average of 3.5 ppm gold was recorded for one of the trenches, while in zone No.4 (50×250m2) the average gold content is 1.35 ppm. According to our studies, The Tareek Darreh gold deposit is considered to be similar to the "intrusion-related gold systems".