GEOSCIENCES
Year:2001 | Volume:10 | Issue:41-42|Papers Count:8

Pariz area is chosen as a test area to evaluate remote sensing data and application of these data in exploration. Eight known mineralization sites were chosen in the area, which have mainly porphyry type mineralization. SPOT images in XS mode are used to study geology as well as hydrothermal alteration in the Pariz area. Here, soil and vegetation cover is substantially poor. Different approaches such as band ratioing, principal component analysis, I-S-H, decorrelation processing, digital filtering and hybrid composite were used to enhance the diagnostic features associated with the lithologies as well as the hydrothennal alteration. Color combinations of the principal components, I-S-H transformation and 2/1 ratio have proved to be the best image enhancement techniques for geological studies in such areas. Lineament analysis has shown that the areas with known ore occurrences and also the hydrothermally altered areas, are closely associated with the higher photo lineament factor values. There is also a good correlation between the geophysical and remote sensing data in the area.

Shah-Kuh granitic massif (South of Birjand) is mainly composed of monzogranite- granodiorite and syenogranite units which enclose large microgranitic bodies. Small outcrups of greisenized granites, occurred in the eastern part. The massif is cut by dacitic, andesitic, and aplitic dykes and mineralized quartz- tourmaline veins.The Presence of magnetite, magmatic allanite, amphibole and the lack of muscovite, aluminosilicates and pegmatitic veins attests to the I-type affiliation of these rocks. The monzogranite- granodiorite unit is distinct from syenogranites by the lack of amphibole, lower Xmg of biotites and lower An% of plagioclase in the later.Based on thin section studies, four types of microstructures including magmatic, submagmatic, high temperature subsolidus and low temperature subsolidus (mylonitic) are recognized.Hydrothermal alteration effects on the pluton can be summarized as:1-Formation of K-feldspar megacrysts; 2- Alteration of biotite to muscovite (or K-feldspar) + rutile + sulfides; 3- Formation of pale green biotite from magmatic biotite; 4 - Chloritization of biotite ; and 5- Complete destruction of biotite and feldspar during greisenization.K- Ar dating was performed 13 biotite separates from main rock types. This gives an age of 165± 3.1 Ma (middle Jurassic) for the Shah- Kuh granite. With an average age of 168.3 ± 3.17 Ma, the microgranites represent the oldest unit among the dated samples. Monzogranite - grandiorite and syenogranite unites, which have been dated 165.2 ± 3.1 (Ma) and 161.6 + 2.5 (Ma), respectively, are somewhat younger unites. It can be concluded that all of the granitic rock types in the suite, formed in a very short period of time.

Sheshroodbar F(pb-Zn-Ba) deposit is one of the Mid-Triassic stratabound- stratiform ore deposits of Central Alborz. The oldest outcrop in the area, is the upper part of Elika Fm. (Middle Triassic), which is overlain by Upper Triassic (Paland Fm.), Liassic (Shemshak Fm) and Malm (Lar Fm.).Uppermost part of Elika Fm. is the country rock of the ore bearing horizons, with approximately 207 m. thickness. Elika Fm. consists of silisic limestones, dolomitic limestones and dolomites, in some places with lenses of gypsum, which are faulty placed aside by Shemshak Fm. in the study area.Fluorite occurs in 4 horizons, of which 2 main horizons (3rd and 4 th) are presently being mined. Geometry of the fluorite horizons are mainly lenticular, and layered, with some congruent breccia lenses. Disseminated, banded and open space filling textures occur in the lower horizons (1 and 2). In the upper horizons, which are under exploitation, the ore textures are disseminated, open space fillings, DCRs, geods, banded, massive, replacement and cement of breccias. The mineral paragenesis consists mainly of fluorite, barite, calcite, galena, sphalerite, quartz and some secondary minerals.Based on facies analysis and texture studies, the depositional environment of all facies of upper part of Elika Fm. Can be divided into two groups:I-Relatively quiet environment (without volcanic and tectonic activities)2-Active environment (with emphasis on the extent of relative intra-basin tectonic and volcanic activities contemporaneous with sedimentation).The most important controlling factor of the formation and concentration of fluorite are the manifestation of fumarols and the presence of fluorine, together with contemporary volcanism. In addition, the depositional environment (tidal flat and lagoonal) can also be regarded as another important controlling factor. Facies analysis indicates a shallow environment, involving supratidal, intertidal, shallow subtidal and lagoonal basins.On the evidence of high content of authigenic quartz in country rocks, presence of tuff and some pyroclastic fragments in the ore bearing horizon, presence of intraformational breccia and sudden and lateral facies changes, we suggest that the environment of fluorite formation in the Sheshroodbar basin was active.

Currently, the use of tourmaline and tourmalinite as and exploration guide in different mineral deposits have a special importance. In this paper, the geochemical application of tourmaline in six intrusive granitoid rocks have been investigated, of which three are mineralized and the rest unmineralized. Based on geological, and petrographical studies, tourmalinite occurs as veins, veinlets, and radial form in the immediate contact of granitoid rocks. Tewenty tourmalinite samples weighing one kilogram of mineralized and unmineralized intrusive granitoid rocks were investigated geochemically. The results show that the average content of copper (91 ppm) and lead (100 ppm) in mineralized granitoid rocks are three times higher than unmineralized granitoids. The high and anomalous content of tin (40 ppm), tungsten (20 ppm) and molybdenum (11 ppm) have been observed in a few samples of unmineralized granitic rocks. Copper and lead show a good correlation in mineralized granitiod rocks, whereas, tin, tungsten and molybdenum exhibit a common correlation in unmineralized granitic rocks. Based on the results of this investigation, copper and lead in tourmalinite could be used as an exploration guide for porphyry copper ore deposits. Also, tin, tungsten and molybdenum are indicative of granophile elements or granitic rocks. The advantage of tourmaline or tourmalinite is that it is separated much easier than other minerals (biotite), from the granitoid rocks.

In this article, stratigraphy and paleogeography of members 5 of Chalus Formation has been studied. On the basis of stratigraphical position the member 5, is formed in the Middle- Upper Cenomanian time and consists of conglomerate and basic volcanic rocks with 500m. thickness.During the Cenomanian stage in the Chalus area (Northern flanks of Central Alborz) deep sea sedimentation was broken by several volcanic activities. These transformations caused to rise of the sea floor and created the temporary islands. After a little time, these lands went under water and Cenomanian deep sea covered all the islands again.

In this study the earthquakes catalogue for Qa'enat region in eastern Iran by using available references which concerning the earthquake data in Iran is provided. The procedures of, aftershocks deletion, the principle of region selection, the upper and lower limit magnitude and verification of the historical catalogue are applied. For some representative regions the Gutenberg- Richter relation curves according to their seismicity characteristics, by using the earthquake data greater than or equal to magnitude 3.0 (1974-1988) and higher magnitudes (1900-1998) are obtained. According to these results the annual occurrence rate of events of each magnitude can be inferred from the G-R relation and it seems that both results are almost the same. Therefore using the obtained relations at the first stage as the proper region is selected with respect to the seismicity system and the duration of time can make estimation of the recurrence period of large earthquakes.

Molataleb region is situated in the nort of Aligudarz and in the immediate vicinity of the Zagros Thrust Fault Becacome. of the activities of reverse faults and the Zagros Fault, Precambrian, Upper Precambrian - Lower Cambrian, Triassic and Jurassic Metamorphic Complex have been exposed. The effects of various metamorphic phases of different episodes, can be observed on these rocks. Following the Laramian Orogeny, the intrusive granitoid mass, affected the metamorphic rocks of the region. Lithological composition is mainly composed of granite, granodiorite and monzogranite. Mineralogical, lithogical, and geochemical studies along with field observation indicate that the Molataleb Granitoic mass is of "S Type" and palingenetic granitoides. The tectonic discrimination diagrams showed that the granitoid mass is of post Orogenic Type. Additionally, regarding the geochemical affinities With other granitioids of adjacent (Borujerd, Haramian Buin- Mianadasht and others), They have been injected after the Laramian orogeny.