Determining the hard rock groundwater pathway in Golgohar complex formation using hydrochemical data in AHP

Thirty percent of present industrial water consumption of the Golgohar Iron Ore Mine (GIOM) is supplied from a hard rock well (PW-A15) and the rest from 25 wells located in 4 disconnected alluvial aquifers. This well is drilled in the metamorphic complex of Golgohar formation. Attempts have been made to develop extraction of water from other hard rocks existing in the area with no success. Therefore, extensive researches have been carried out to find the pathway, or a provision pathway of water discharged from this well. To study the hydrochemical similarity of this water with other water resources, 122 water samples from an area of 7132 km² were collected from the existing pumping wells, piezometers, mine exploration bore holes, and three salt pans in the vicinity of the area for hydrochemical analysis. The analyses were performed for concentration of major ions and some minor elements. Furthermore, the spatial distribution of ion concentration was plotted in the GIS to delineate the similarity of the PW-A15 water with other water sources and their hydrochemical neighborhood by analytical hierarchy process (AHP). The AHP was performed in two steps: first, iso-concentration maps of seven major ions, eight minor elements, and TDS were used to produce an AHP map (Map1) using weights for different hydrochemical parameters; and second, a similarity index (SI) map was prepared by performing a suggested clustering approach in SPSS using K-means clustering, which was overlaid on Map1 producing Map2. The result of AHP Map2 was then overlaid on the iso-potential map of the sampled locations in GIS software using a mask operator. Therefore, the zones having the most similarity and higher hydraulic potential than PW-A15 were nominated as the zones which possibly could recharge this well, and the groundwater (GW) pathway was proposed. The result of the study method showed to be successful and will be used as a guide for future exploration drillings.     

Chemical evolution of a gas-capped deep aquifer,southwest of Iran

The Kangan Aquifer (KA) is located below a gas reservoir in the crest of the Kangan Anticline, southwest of Iran. This aquifer is composed of Permo-Triassic limestone, dolomite, sandstone, anhydrite and shale. It is characterized by a total dissolved solid of about 332,000 mg/L and Na–Ca–Cl-type water. A previous study showed that the source of the KA waters is evaporated seawater. Chemical evolution of the KA is the main objective of this study. The major, minor and trace element concentrations of the KA waters were measured. The chemical evolution of KA waters occurred by three different processes: evaporation of seawater, water–rock and water–gas interactions. Due to the seawater evaporation process, the concentration of all ions in the KA waters increased up to saturation levels. In comparison to the evaporated seawater, the higher concentrations of Ca, Li, Sr, I, Mn and B and lower concentrations of Mg, SO₄ and Na and no changes in concentrations of Cl and K ions are observed in the KA waters. Based on the chemical evolution after seawater evaporation, the KA waters are classified into four groups: (1) no evolution (Cl, K ions), (2) water–rock interaction (Na, Ca, Mg, Li and Sr ions), (3) water–gas interaction (SO₄ and I ions) and (4) both water–rock and water–gas interactions (Mn and B ions). The chemical evolution processes of the KA waters include dolomitization, precipitation, ion exchange and recrystallization in water–rock interaction. Bacterial reduction and diagenesis of organic material in water–gas interaction also occur. A new type of chart, Ca_excess versus Mg_deficit, is proposed to evaluate the dolomitization process.     

The impact of salt diapirs on the quality of carbonate karst waters,Bastak, Iran

The Gavbast karstic aquifer located in southern Iran is in direct contact with an exposed salt diapir. To assess the influence of the diapir on the quality of groundwater in the karstic aquifer, electrical conductivity, total dissolved solids, flow rate, temperature and major ion concentrations were measured at 57 sampling sites, including springs, surface waters and wells. A conceptual model of groundwater flow is proposed for the Gavbast karstic aquifer based on the geological setting, water budget, local base of erosion, and hydrochemistry of the sampling sites. The model suggests two subbasins in the Gavbast Anticline draining into two distinct discharging alluvial sections. Unexpectedly, groundwater discharging from the carbonate Gavbast aquifer is saline or brackish and water is of chloride type. The study indicates that the source of salinity of the Gavbast aquifers is infiltration of surface diapir-derived brine into the aquifer. The contribution of the diapir brine in the Gavbast karst aquifer is calculated about 4 L/s, using chloride mass balance. Construction of salt basins to evaporate brine discharging from the diapir springs is proposed to reduce the salinity of karst water. A row of strategically placed wells in the Gavbast karst aquifer would potentially exploit large volumes of fresh groundwater before it is contaminated by the salt. Such low-cost remediation should allow the agricultural exploitation of 40 km² of currently barren land.     

Water leakage paths in the Doosti Dam,Turkmenistan and Iran

The Doosti Dam, with a reservoir capacity of 1,250 million cubic meters, was constructed on the Harirood River at the border of Turkmenistan and Iran. The reservoir is in direct contact with permeable formations on the right abutment of the dam including the Neyzar Sandstone, the Kalat Limestone and the Pesteleigh alternative layers of marlstone and sandstone. After the reservoir impoundment, several new springs and seepages emerged from these formations and the alluvium. The amount of leakage increased with the rise in reservoir water level. Fifteen kilograms of sodium fluorescein were injected into a 113-m deep borehole intersecting three permeable sandstone layers of the Pesteleigh formation. Dye was detected downstream of the grout curtain in boreholes and springs that were in direct contact with parts of the Pesteleigh formation having the same sandstone layers as the injection borehole. The dye velocity was in the range of diffuse flow, confirming the good performance of the grout curtain in the Pesteleigh formation. No dye was detected in the other formations because the injection borehole was not in direct contact with these formations. The hydraulic relation of the other formations with the reservoir was determined by considering direct contact of the formations with the reservoir, emergence of new springs and seepages after reservoir impoundment, correlation of time variations of the springs discharge and the borehole’s water level with the reservoir water level, and in some cases the hydrochemistry of the water. The results show that the Kalat and Neyzar formations are hydraulically connected to the reservoir, but the small amounts of leakage from these formations at a hydraulic gradient of 24% indicates good performance of the built grout curtain. The total reservoir leakage at maximum reservoir water level was 100 l/s which is insignificant compared with the 15 m³/s average annual release of the reservoir.     

Hydrodynamic behavior of Kangan gas-capped deep confined aquifer in Iran

The Kangan aquifer (KA) is located beneath the Kangan gas reservoir (KGR), 2,885 m below the ground surface. The gas reservoir formations are classified into nine non-gas reservoir units and eight gas reservoir units based on the porosity, water and gas saturation, lithology, and gas production potential using the logs of 36 production wells. The gas reservoir units are composed of limestone and dolomite, whereas the non-gas reservoir units consist of compacted limestone and dolomite, gypsum and shale. The lithology of KA is the same as KGR with a total dissolved solid of 333,000 mg/l. The source of aquifer water is evaporated seawater. The static pressure on the Gas–Water Contact (GWC) was 244 atm before gas production, but it has continuously decreased during 15 years of gas production, resulting in a 50 m uprising of the GWC and the expansion of KA water and intergranular water inside the gas reservoir. The general flow direction of the KA is toward the northern coast of the Persian Gulf due to the migration of water to the overlying formations via a trust fault. The KA is a gas-capped deep confined aquifer (GCDCA) with special characteristics differing from a shallow confined aquifer. The main characteristics of a GCDCA are unsaturated intergranular water below the confining layers, no direct contact of the water table (GWC) with the confining layers, no vertical flow via the cap rock, permanent uprising of the GWC during gas production, and permanent descend of GWC during water exploitation.     

Geochemistry and zircon U-Pb geochronology of Miocene plutons in the Urumieh-Dokhtar magmatic arc,east Tafresh,Central Iran

ABSTRACT

The Tafresh plutons that include Ahmadabab diorite, Vasfonjerd monzonite, Mehrezamin diorite and Chahak diorite, located to the east of Tafresh city, north-central Iran, are part of Urumieh-Dokhtar magmatic arc. U-Pb dating of zircon grains provides emplacement ages of 22.3 ± 1 Ma for the Ahmadabad diorite, and tightly clustered ages of 22.2 ± 0.2 Ma, 21.3 ± 0.2 Ma, and 21.7 ± 0.4 Ma for Vasfonjerd monzodiorite, Mehrezamin diorite-monzonite, and Chahak diorite-monzonite plutons, respectively. These rocks are metaluminous to weakly peraluminous, calc-alkaline, and characterized by enrichment in light rare earth elements, Nb-Ta negative anomalies, and high LILE/HFSE ratios. Tafresh plutonic rocks originated from a parental magma source and experienced different degrees of partial melting. Geochemical signatures of Tafresh plutonic rocks, such as a wide range of Y/Nb (2.7–8.4) and low Zr/Nb (19.5–35.) ratios, Nb/Ta (11.46–18.15), argue for mantle–crust interaction during generation of Tafresh magmas. Relatively low Nb/La ratios further indicate that the lithospheric mantle played a significant role in melt generation. HREE signatures (i.e. decrease Dy/Yb with increasing SiO₂) preclude substantial involvement of garnet either in the residue, both during partial melting and fractionation of the magma. The plutons are a product of final stages of subduction-related magmatism prior to the collision between the Arabian and Eurasian tectonic plates.     

Method of leakage study at the karst dam site. A case study: Khersan 3 Dam,Iran

The excellent topographic condition of the limestone canyons for dam construction may be rejected if they are karstified. Karst features cause the reservoir not to be impermeable enough to permit the water to fill it and leakage occurs and often increases with time. Moreover, karst features may involve the stability of the dam itself. A few operated dam sites at the Zagros Zone encountered a leakage problem. Furthermore, more than 30 dams are presently under study for construction in the Zagros Zone. Karst conditions and leakage potential were investigated at an under-study site (Khersan 3 Dam) for assessing the general methodology for the study of leakage potentials. Conventional methods for studying karst features, geological mapping, geomorphology and extensive borings were applied before the dam was constructed. These methods are not efficient enough to precisely reveal the karst structure, especially hidden and paleokarst, nor the hydrological behaviour of the karst structure in different settings of groundwater flow. Based on the present case study and previous applied approaches by other authors, this paper introduces a methodology by means of karst structure and functioning approaches at local and regional scales that cover the conventional methods and overcome their shortages. The proposed methodology should be applied before construction of a dam and should include three steps (a) recognition of geological and hydrogeological settings, (b) delineation and functioning of the karst system related to the future reservoir, and (c) assessment of the leakage potentials. Following this methodology, the most probable leakage zone(s) and path(s) at the dam site can be highlighted.     

Investigation on the effect of inclined crest step pool on scouring protection in erodible river beds

Natural Hazards - One of the aquatic structures that are used for protect water channels against bed erosion is serial step-pool. These steps similarity of the vertical drops structure are exposed...     

Identifying sources of salinization using hydrochemical and isotopic techniques, Konarsiah, Iran

Konarsiah salt diapir is situated in the Simply Folded Zone of the Zagros Mountain, south Iran. Eight small permanent brine springs emerge from the Konarsiah salt body, with average total dissolved solids of 326.7 g/L. There are numerous brackish to saline springs emerging from the alluvial and karst aquifers adjacent to the diapir. Concerning emergence of Konarsiah diapir in the study area, halite dissolution is the most probable source of salinity in the adjacent aquifers. However, other sources including evaporation and deep brines through deep Mangerak Fault are possible. The water samples of the study area were classified based on their water-type, salinity, and the trend of the ions concentration curves. The result of this classification is in agreement with the hydrogeological setting of the study area. The hydrochemical and isotopic evaluations show that the groundwater samples are the result of mixing of four end members; Gachsaran sulfate water, Sarvak and Asmari carbonate fresh waters, and diapir brine. The molar ratios of Na/Cl, Li/Cl, Br/Cl, and SO₄/Cl; and isotopic signature of the mixed samples justify a groundwater mixing model for the aquifers adjacent to the salt diapir. The share of brine in each adjacent aquifer was calculated using Cl mass balance. In addition, concentrations of 34 trace elements were determined to characterize the diapir brine and to identify the possible tracers of salinity sources in the mixed water samples. B, Mn, Rb, Sr, Cs, Tl, and Te were identified as trace elements evidencing contact of groundwater with the salt diapir.