GEOSCIENCES
Year:2002 | Volume:11 | Issue:45-46|Papers Count:9

Milakuh-Touyeh the F-Zn-Pb-Ba deposit is located 45 km SW of Damghan. The country rocks of the deposit are dolostones of the upper part of Soltanieh Formation. The orebodies in the dolostones are located in certain ore-bearing facies as four ore horizons. The ore facies from bottom to top of the sequence are as follows: Dolosparite-sparstone is the facies of ore horizon I, in which Zn (pb-F-Cu-Ba) mineral are the main paragenesis . Zinc is the major constituent of the horizon (economic ore horizon). Dolomicrosparite-dolosparite is the main facies in the ore horizons II and III, with F-Pb (Ba-Cu) paragenesis. Fluorite in horizon 11 is economic and mineable. Presence of altered tuff breccia facies with fluorite is the characteristic of the horizon III. Laminated dolosparite, dark gray chert and ferrigenous dolomicrite are the facies of horizon IV. The main paragenesis here is F-Pb. The increase in silica content is an important characteristic of this horizon. Depositional environment of ore-bearing and other facies in the upper part of Soltanieh Formation in the Milakuh- Touyeh area is tidal flat. The ore geometry, textures, structures and paragenetic sequence, indicate that the ore minerals are formed and concentrated in four stages:1-Deposition; 2- Early diagenesis; 3- Late diagenesis; 4- Uplift and exposure. Final stage of ore formation comes from remobilization of sedimentary-diagenetic generations and their epigenetic deposition in the open spaces, faults and fractures together with weathering and supergene enrichment. The majority of mining activities in the area have been concentrated on the late diagenetic and epigenetic types. Fluid inclusion studies on diagenetic types of fluorite indicate relatively high Th (211±5 °c) and salinities (23.45 ± 5 wt% NaCl equivalent). The Th values for the epigenetic fluorite (fault species) are lower than those of diagenetic ones (134± 5°C). Geometry of ore bodies, occurrence of ore horizons in certain sedimentary facies, ore texture and structures, depositional environment (tidal flat), paragenetic sequence of minerals and fluid inclusion data, all suggest that Milakuh-Touyeh F-Zn-Pb-Ba deposit is an F-rich MVT deposit.

In this paper seismotectonic characteristics (earthquake- fault hazard) of the Mashhad- Neyshabur region are studied. The Presence of Kashafrud and Shandiz faults arround Mashhad and Neyshabur fault near Neyshabur and absence of large earthquakes in 20th century in this region is a major problem. Seisrisk II computer program used for seismic hazard estimation, and results are given in acceleration contours "g" with different probabilities and mean periods.

The Sangerd drainage basin is located in central part of Khorasan Province in arid to semiarid climate conditions and consists of three sub basins. Structurally, the study area is a part of Central Iran zone, and is compsed of Mesozoic and Cenozoic rocks. The river channels are mainly single with sandy gravelly bedload. The presence of shale and marl as well as seasonal rainfall in the study area, causes the strong erosion. Based on sedimentological studies, 9 lithofacies have been identified. The majority of sediments are sandy gravel (sG) but in downstream they change to gravelly muddy sand (gmS). Geologically, the presence of less resistance sedimentary rocks causes to produce a lots of sediments that can fill Sangerd reservoir very quickly. Therefor, we suggest by changing the hydrulic condition of channels can decrease the erosion and sediment transpot.

On the basis of Kinematic findings at different scales in Quaternary fault zones, and using modem methods of fault slip analysis, Quaternary stress field was reconstructed. Orientation of slip plane, slip vector, principal stresses, shape of stress ellipsoid and angle of internal friction are involved the fault slip analysis. Orientations of σ 1, σ 2 and σ 3 stresses for primary data (nonrotated) were determined as 084°/04°, 232°/82° and 077°/08° respectively. The shape of stress ellipsoid was defined on the basis of shape factor [R= ((σ 2 - σ 3)/( σ1 - σ 3)] (Angelier, 1975). The R-value for all studied regions was about 0.5 and deformation type was mainly left lateral transpressional with small reverse components. Such results are evidence of north trending σ1 in the region and northward movement of the crust. The results are in agreement with other method such as focal mechanisms of earthquakes.

Ruteh Formation is overlain with distinct laterite -detrital horizon between Elika and Ruteh Formation and is underlain disconformably by Dorud Formation. The Permian sequence is composed of 160 meters of dark to light fossiliferous limestone. Geochemical studies illustrates that these carbonates were affected mostly by distal pheratic meteoric diagenesis.Elemental and δ18 O and δ13 values of limestone in Ruteh Formation led to recognition of calcitic mineralogy.These data fall within subpolar Permian Limestone (Tasmania, Australia) field due to similar calcitic mineralohgy. Paleotemperature study indicates an ambient temperature between 27-34.5°c.Facies analysis and petrographic studies led to recognition of 9 microfacies deposited in an open marine, bar and lagoon environments. On the basis of facies chemistry, the high Sr contens are due to aragonitic components deposited in lagoon to back barrier environments. The high Mg concentration is related to the high abundance of red algae (Gymnocodiacea).

Two sections in north Alborz mountain were selected and palynologically studied. The first one, Paland section, is located approximately 30 km in the south of Zirab city. This sequence is 200 m thick and consists mainly of limestone and shale beds and assigned to the Upper Triass. This study resulted in the identification of a relatively rich assemblage of palynomorphs. The age of Late Triassic (Late Norian- Rhaetian) is attributed to the formation by. The known Dinoflagellates taxa.The second section, Galandrud section is located about 16 km in the south of Ruian city (Alam - Deh). This section attains a thickness of 590m and consists of limestone, shale, sandstone and siltstone beds. Eighty one palynomorph taxa were encountered form a total of 30 samples from the base of the Shemshak Group which were selected and treated in the palynological laboratory of the geological survey of Iran. The known species were arranged in the following three local bioassemblage zones:Biozone I, Enzonalasporites vigens: occurs in a thickness of 125m, suggesting the Early - Middle Norian age. Biozone II, Vitreisporites pallidus: with 335m thickness represents the Late Norian age. Lastly, Biozone III, Concavisporites kermanense: occurs in a thickness of l30m indicating the Early Rhaetian age. Statistical study of the recorded palynornorphs indicate an open marine environment for the Upper Triassic sedirnents for this area.

Despite of different studies performed on Tehran geological condition, the geotechnical and dynamic properties of Tehran alluviums are not investigated in detail. In this study the authors have tried to get more detail information about south Tehran alluviums by compiling the data from 700 boreholes and 66 seismic profile investigations. The defined 15 two dimentional EW seismic geotechnical profiles by the distance of 1km present the geotechnical and dynamic properties of the south Tehran alluviums. Based on these sections the depth of the seismic bedrock increases from north to the south. In addition it is demosntrated that S wave velocity variation in the study area follows the difference of soil type observed in the presented sections. It seems that the local changing of the water table and the seismic bedrock depth could be related to North-Ray fault and Punakhzad fault effects.