جستجوی مقالات مرتبط با کلیدواژه « lead » در نشریات گروه « زمین شناسی »

The present study aims to investigate the speciation, bioaccessibility, and health risk of Pb in the soils around the Irankuh mine. For this purpose, 20 soil samples were collected and the physicochemical parameters of the samples were determined. The total and bioaccessible concentrations of Pb were determined using the total digestion and in vitro methods, respectively. The speciation of Pb in selected soil samples was investigated using a sequential extraction approach. The values of pH, organic matter, carbonate and cation exchange capacity of the studied soil samples vary between 6.7 to 8.2, 0.2 to 4.8 %, 6 to 48.5%, and 18 to 11.2 meq/100 g, respectively. The total concentration of Pb changes between 18.4 and 2869 mg/kg (average value of 273.4 mg/kg). Pb is dominantly present in reducible fraction, confirming the anthropogenic source of Pb and its potential mobility. Based on the in vitro test results, the bioaccessibility of Pb is very variable (between 0.2 to 45.4% of the total concentration), which is due to the difference in the physico-chemical characteristics of the samples and the source of the element. The hazard coefficient values for ingestion, dermal contact and inhalation routes are higher for children than adults, and for the ingestion route than other exposure pathways. The carcinogenic risk (CR) values indicate that there is no risk through dermal contact and inhalation routes; however, CR values for the ingestion route using both bioavailable and total concentrations confirm the probability of cancer risks for residents living near the mining site.

The study area is situated within the Lut Block, 40 Km northeast of Ferdows. The oldest exposed rocks are Cretaceous limestone. The composition ranges of Volcanic rocks between andesite, andesite-basalt and rhyolitic tuff. Sub-volcanic diorite porphyry intruded in the volcanic rocks. Alteration zones are propylitic, silicified and argillic around the vein and surrounding host rocks. Sulfide minerals include pyrite, galena and sphalerit the secondary minerals comprise covelite, malachite, azurite, chrysocolla, hemimorphite and iron oxides. The veins contain an average of 2.14 percent of lead and 4.40 percent of zinc. Fluid inclusion petrography and microthermometry results reveal that the fluid inclusion assemblages developed in the different types, including single-phase vapor fluid inclusion, vapor-rich two-phase fluid inclusions and liquid-rich two-phase fluid inclusions. On the basis of fluid inclusion studiel, the ore-forming fluids has temperature 204–321 °C), and salinity 6.2–15wt% NaCl equiv. Fluid boiling and mixing most likely were the vital factors controlled the metal precipitation. The fluid pressure during the formation of the ore minerals was estimated to be between 50 to 150 bars. Based on the data obtained from fluid inclusions, it is suggested that the ore minerals were formed at a depth of 700 meters below the old water table

Lower Cretaceous carbonate rocks (Taft and Abkouh formations) in the south of Yazd host lead, zinc and barite ore deposits. Diagenetic processes after deposition in these carbonates have caused the formation of these deposits. The main diagenetic processes affecting these sediments include compaction, brecciation, neomorphism, cementation, dissolution, dolomitization and replacement. The dolomitization and replacement process has led to the formation of lead, zinc and barite ore deposits. Hydrothermal fluids through the active and normal faults have provided the conditions for the formation of these deposits in the carbonate rocks of this area. The formation of the ore deposit occurred during two stages of mesogenesis and telogenesis. In the mesogenesis stage and in the burial conditions, first dolomite is formed and after the entry of hydrothermal fluids and supply of necessary elements, the replacement has created sulfide minerals. During the telogenesis stage, some parts of the formed sulfide deposits are re-exposed to meteoric fluids, leading to the formation of oxide ore deposits.

Gardaneshir carbonate-hosted Pb-Zn deposit on the ground of study area located southwest of Ardestan in Isfahan province. Base on lithostratigraphy,the main structure, besides the small outcrops of Jurassic shales, has been made up of carbonate and detrital rock materials depending on Paleozoic,Triassic and Cretaceous time stages. Dolomitic carbonate which is attributed to Shotori Formation , played the major role of host rock in ore-mineralization. Ore-mineral description obtained from the mineralized zone and caused the following ore-paragenesis in ascending order.of:pyrite,chalcopyrite,galena,sphalerite,malachite,cerussite,smithsonite,iron oxides and gangues of barite, quartz and calcite. Physico-chemical information of ore-solutions performed by entrapped fluid inclusion studies in gangue minerals. Liquid-rich two phase(L+V) inclusions as predominant types were recognized. These type of inclusions are homogenized into liquid state with a range of TH and related salinities between; TH :78 to 183 and 216 to 283°C, Salinity:3.5 to 9.7 and 10.2 to 25 wt% NaCl eq. The microthermometric data reflect the nature of two population of fluid inclusions originating from different sources. The source materials could have been provided by basinal brines, derived during compaction of sediments in a shallow sea environment and by movement into sediments, the stratabound Pb-Zn deposit are formed. Furthermore, the negative delta value ranges(δ34S) from -0.6 ‰ to -20.4 ‰ that have been extracted by galena can be an evidence of bacterial sulfate reduction in a subsidence sedimentary basin. In conclusion, based on field, mineralogical, fluid inclusion and sulfur isotope evidence, we propose that Gardaneshir Pb-Zn deposit is a stratabound carbonate hosted of Mississipi Valley Type(MVT).

Gardeneh-Shir zinc and lead deposit is located at 38 km southwest of Ardestan in Central Iran. The host rocks of this deposit includes carbonates of Middle Triassic Shotory Formation juxtaposed over Upper Triassic Naiband Formation by thrust faulting. The mineralization in these deposits is in the form of vein-veinlet, breccia and filling of karstic cavities with dolomitization and silicification and mainly controlled by Strike-slip faults with the normal component and normal faults with strike slip component those are cross cutting older generation of thrust faults. The results of fluid inclusion studies of on quartz and dolomite in Gardeneh-Shir deposits Area show a fluid with a salinity of 23.2-18.6% by weight of salt, temperature range of homogeneity between 91 -162 ° C and a density of 1.09-1.056 g/cm3. The combination of fluid inclusion and EPMA analysis of Zn / Cd (879%) elemental ratios in sphalerite mineral has confirmed low temperature generation of Gardeneh Shir deposit. According to the results of our studies including host rock type, mineralogy, mineralization control structures, salinity and temperature it can be considered that the mineralization of zinc and lead are the mining region of Gardeneh-Shir deposits in the category of MVT type deposits

The Chah Sorbi area is located in the Sistan suture zone. The geology in the Chah Sorbi, from old to young, are flysch type rocks, Zahedan granitoid, subvolcanic granodiorite porphyry, dioritic to granodioritic dikes and recent deposits. The Pb mineralization in the study area occurs as thin and short galena-bearing veins associated with pyrite, quartz, calcite, goethite and limonite. The host rocks are flysch and the subvolcanics that are undergone phyllic and argillic alteration. Propylitic alteration occurs in most dikes in the area and is characterized by chlorite, calcite and epidote. In northeast part of the area, the subvolcanic rocks were intruded by quartz stockworks and was strongly altered. The most intensive and extensive alteration with these rocks is phyllic alteration that is characterized by pyrite, quartz and sericite. Cu mineralization in the stock is characterized by presence of Cu-carbonate and –sulfides. Galena-bearing veins are probably epithermal type in the Chah Sorbi area that is situated in margin of a porphyry Cu system. Major and minor elements were measured in 7 least altered samples from intrusive rocks. The igneous rocks in the study area are metaluminous that are formed from a calc-alkaline magma in a continental margin volcanic arc setting.

The Hassan Abad Zn-Pb deposits is located in the northeast of Isfahan, Central Iran zone. The host rock of this mineralization is the dolomite of Middle Triassic Shotori Formation. Mineralization included galena, sphalerite, sulfosalts, pyrite and barite which associated with dolomitization. Based on petrographic studies six types of dolomites (in terms of shape and size of the crystals, the distribution of crystal size and shape of the border crystal) has been identified, that including very fine, medium, coarsely crystalline dolomite, Saddle dolomites and filling pore spaces and veins. The first and second type of dolomites were formed as synsedimentary or diagenetic dolomite with sabkha origin. The third type of dolomite in the late stages of diagenesis was formed in shallow burial conditions due to recrystallization of small crystalline dolomite. Coarse-grained and saddle dolomites have been created under the conditions of deep burial and as hydrothermal dolomites and are related to mineralization. Move over, the origin of magnesium for fine crystalline dolomites were seawater, and for coarse crystalline dolomites are probably the brine fluids of the compacted Sorkh Shale Formation and hydrothermal fluid.

The hosted-rocks of the Pb-Zn ore deposits in two mines of Karavangah and Dehno (north of Kuhbanan) contain carbonate rocks of the Shotori Formation (Middle Triassic).The identified carbonate facies consists of limestone and dolomite, but ore bodies mainly occurred in dolomite facies. Petrographic studies show that the dolomites can be divided into four classes including fine crystalline, medium crystalline, coarse crystalline and saddle dolomites. Geochemical data (major and trace elements) of dolomites have almost similar characteristics and show a noticeable enrichment of lead and zinc. Also, significant enrichment and similar trend are observed in the REE of hosted-rock samples. Therefore, due to similarity between geochemical characteristics of the hosted-rocks, it seems that magnesium source for dolomitization was mainly seawater, but the influence of ore fluids is significant on the formation of coarse crystalline dolomites.

This research study is based on  knowledge-driven approach to synthesize the different parameters which rule on the formation of carbonate hosted zinc and lead deposits. The analysis of available data sets of the north Irankuh district demonstrates the complexity of decision making due to the different anomalous prospects introduced by geophysical, geochemical and surface evidences.Five known deposit/active mines, namely Gushfil, Zone 1 Gushfil, Blind, Tapeh Sorkh and Zone 5 Romarmar with total geological resources quoted as 13.4 million tons at 5.53% combined lead and zinc (Fig. 10) were selected to be examined in order to asset a knowledge-driven approach to the exploration of carbonate hosted zinc and lead deposits. The diversity of geometry, mineralogy and host rock of the deposits is tightly confined by the parameters surrounding the genesis of MVT deposits such as genetics of solutions, temperature of deposit formation, tectonic channel ways, different episodes of deposition of sphalerite and galena, hydrologic system of area, solution direction, wall rock reactions (Leach et al., 2010), depth of solution penetration, solution response to the Magnesian regime and metal bearing.

The present study consists of detailed  underground and surface mapping, reinterpretation of district geology, detailed logging of about 100000 meters’ diamond drilling, ore geology, tectonic settings, deposits geometry, geochemical and geophysical survey within 7 square kilometers of north Irankuh district between the Gushfil and Tapeh Sorkh deposits.

Five known deposits in the north Irankuh district occur in the area of an intense detachment faulting (Fig. 1 and Fig. 5). The Gushfil, Zone 1 Gushfil and Blind deposits occur in north Irankuh reverse fault and Tapeh Sorkh and Zone 5 Romarmar in the trust fault. The deposits are confined to a certain stratigraphic unit locally called K3D (Figs. 2 and 3). Widespread regional selective dolomitization shows an extensive lateral movement from NW to SE and the depth of dolomitization in certain units drastically decreases. Two main regimes of solutions initially started with sphalerite and they were subsequently followed by galena the later of which is found in the secondary porosity. Mineralogy of the deposits is simple but the pyrite amount of the deposits varies from 2% to 20% which reflects the higher temperature of the solutions responsible for sulphide precipitation (Marie et al., 2001), geometry of the deposits and their distance to the current topography effect on chargeability values (Fig. 20).Sparry dolomite is found in three types as barren, with pyrite and light color sphalerite that occur in country rocks of all deposits except for the blind deposits. They can be used as a guide, addressing potential deposits.EPMA analysis revealed a considerable amount of Cadmium, Silver, Antimony, Arsenic and Copper within Sphalerite and Galena minerals (Fig. 12). Because of the semiarid climate in the area the decomposition of sphalerite, galena (Hitzman et al., 2003) and carbonate host rock has caused widespread distribution of Zn, Pb, Ag, Cd, Sb, As, Cu, Mn, Mg, Fe and Ca in the secondary halo of the area. The soil samples have been studied based on the static and machine learning methods (Figs. 13–A and B) by different researchers (Zekri et al., 2019). The anomalous areas based on geochemical studies have been tested by core drilling and the results are considered to be negative even in the area called Zone 3 which coincides with both geochemical and geophysical anomallies. In a different approach to understand the structure of geochemical elements the distribution of Zn, Pb, Ag, Cd, Sb, As, Cu, Mn, Ba together with elements such as Mg, Fe and Ca has been compared (Figs. 14, 15 and 16).The soils are heavily polluted due to widespread mineralization and no background value (Reimann and De Caritat, 2012) can be recognized.The comparative analysis of element concentrations in 5 selected populations in the studied area (Fig. 15) did not show any signs that could help  recognize important anomalies from the false anomaly. However,  it seems that the sudden decrease of Mg content (Fig. 17–C) in the area of Zone 3  (Zekri et al., 2019) is meaningful. Two geochemical profiles of soil samples crossing along this population and the next one crossing an active mine (Zone 5 Romarmar) (Fig. 18) provide us with a better understanding of the important anomalies versus the false anomaly since in the false anomaly the increase of Zn, Pb, Ag, Cd, Sb, As, Cu coincides with a sudden drop of concentration of Mg, Fe and Ca (Figs. 18–A and B). Recognition of ore containing strata (Sangster, 1995) is very important (Figs. 2 and 3) in locating successful drill holes in the exploration of carbonate hosted zinc and lead deposits. Eventually the use of data driven methods even opting advanced machine learning methods is not properly sufficient  to recognize  productive areas and we recommended the knowledge -driven approach.