An analysis of vegetation indices in relation to tree species diversity using by satellite data in the northern forests of Iran

Vegetation indices have been introduced for analyzing and assessing the status of quantitative and qualitative characteristics of vegetation using satellite images. However, choosing the best indices to be used in forest biodiversity and vegetation is one of the important problems faced by the users. The purpose of this research is to evaluate six vegetation indices in the analysis of tree species diversity in the northern forests of Iran. The present research uses LISS III sensor data from IRS-P6 satellite. Geometric rectification of images was performed using ground control points, and Chavez model was used for atmospheric correction of the data. The six spectral vegetation indices included NDVI, IPVI, Ashburn Vegetation Index (AVI), TVI, TTVI, and RVI. Shannon–Wiener species diversity index was used to analyze diversity, and the value of the index was calculated in each sample plot. Then, the spectral values of each sample plot were extracted from different bands. The best subset regression was used to analyze the relationship between species diversity and the related bands. The results obtained from the regression showed that polynomial equations under scrutiny as independent variables can assess tree and shrub species diversity better than other bands and compounds used (R ²?=?0.47). The obtained results also indicated a higher capacity in the case of the AVI index for estimating tree species diversity in the under study area.     

Geochronological Constraints on the Haftcheshmeh Porphyry Cu-Mo-Au Ore Deposit, Central Qaradagh Batholith, Arasbaran Metallogenic Belt, Northwest Iran

The Haftcheshmeh porphyry Cu-Mo-Au deposit in the Arasbaran metallogenic belt(AMB) of NW Iran contains more than 185 Mt of ore, with a grade ranging from 0.3% to 0.4%. It is hosted within a porphyritic diorite to granodiorite intruded into an older gabbro-diorite intrusion. 40 Ar/39 Ar analyses of primary magmatic hornblende from the granodiorite porphyry and gabbro-diorite show plateau ages of 26.41 ± 0.59 Ma, with an inverse isochron age of 25.9 ± 1.0 Ma and a plateau age of 27.47 ± 0.17 Ma, with an inverse isochron age of 27.48 ± 0.35 Ma for these two rock types, respectively. Comparing these new age data with those from the nearby Sungun(20.69 ± 0.35 Ma) and Kighal porphyry deposits defines a northwest-southeast Cu-Mo-Au mineralization zone extending for 20 km over the time span of ~27 to 20 Ma. Geochemically, Haftcheshmeh rocks are calc-alkaline with high potassium affinities with tectonic setting in relation to volcanic arc setting. Large ion lithophile elements(LILE) such as Th, U and K show enrichment on a primitive mantle normalized diagram(specially Pb), and are depleted in high field strength elements(HFSE) such as Ti and Nb, pointing to a mantle magma source contamination with crustal materials by subducted oceanic crust.     

The alteration, mineralogy and geochronology (SHRIMP U–Pb and 40Ar/39Ar) of copper-bearing Anjerd skarn, north of the Shayvar Mountain, NW Iran

A Cu-bearing skarn zone occurs north of the Shayvar Mountain in northwestern Iran. Skarn-type metasomatic alteration and mineralization occur along the contact between Upper Cretaceous impure carbonates and a Miocene Cu-bearing granitic stock. Both endoskarn and exoskarn developed in the rocks. Exoskarn is the principal skarn zone and is enclosed by a skarnoid–hornfelsic zone. Skarn formation occured during stages: (1) prograde, (2) middle stage and (3) late stage. In the prograde stage, there were two main processes: (a) metamorphic–bimetasomatic and (b) prograde metasomatic. The metamorphic process began immediately after intrusion of the pluton into the enclosing impure carbonates. The prograde metasomatic stage commenced with segregation and evolution of a fluid phase in the pluton and movement into fractures and micro-fractures in the skarnoid–hornfelsic rocks developed in a metamorphic zone. The introduction of considerable amounts of Fe, Si and Mg led to the development of voluminous medium- to coarse-grained anhydrous calc-silicates. During the middle stage, the previously formed skarn zones were affected by intense multiple hydrofracturing in the Cu-bearing stock. In addition to Fe, Si and Mg, substantial amounts of Cu, Pb and Zn, along with volatile components such as H₂S and CO₂ were added to the skarn system. Consequently, substantial amounts of hydrous calc-silicates (epidote, tremolite–actinolite), sulfides (pyrite, chalcopyrite and molybdenite), oxides (magnetite, hematite) and carbonates (calcite) replaced the anhydrous calc-silicates. The retrograde stage was synchronous with the incursion of relatively low-temperature, more oxidized fluids into skarn system, resulting in partial alteration of the early-formed calc-silicates and development of a series of very fine-grained aggregates of chlorite, clay, hematite and calcite. Zircon grains from the endoskarn zone provide constraints on the timing of solidification of the granite stock (9.91 ± 0.31 Ma) that caused mineralization in the Anjerd area. One sample of primary hornblende from the monzogranitic Shayvar batholith has an ⁴⁰Ar/³⁹Ar age of 26.54 ± 0.65 Ma and indicates that intrusion of the Miocene stock and associated Cu skarn formation occurred a considerable time after intrusion of the batholith.     

Application of concentration–number (C–N) multifractal modeling for geochemical anomaly separation in Haftcheshmeh porphyry system, NW Iran

Geochemical anomaly separation using the concentration–number (C–N) method at the Haftcheshmeh porphyry system in NW Iran is the aim of this study. We used lithogeochemical data sets to explore Cu, Mo, Au and Re mineralization in gabbroic, dioritic and monzonitic units at the Haftcheshmeh Cu–Mo porphyry system. The obtained results were interpreted using a rather extensive set of information available for each mineralized area, consisting of detailed geological mapping, structural interpretation and alteration data. Threshold values of elemental anomalies for the mineralized zone were computed and compared with the statistical methods based on the data obtained from chemical analyses of samples for the lithological units. Several anomalies at local scale were identified for Cu (40 ppm), Mo (12 ppm), Au (79 ppb), and Re (0.02 ppm), and the results suggest the existence of local Cu anomalies whose magnitude generally is above 500 ppm. The log–log plots show the existence of three stages of Cu and Mo enrichment, and two enrichment stages for Au and Re. The third and most important mineralization event is responsible for presence of Cu at grades above 159 ppm. The identified anomalies in Haftcheshmeh porphyry system, and distribution of the rock types, are mainly gabbrodiorite–monzodiorite, granodiorite and monzodiorite–diorite that have special correlation with Cu–Mo and gabbroic and monzonitic rocks, especially the gabbrodiorite–monzodiorite type, which is of considerable importance. The study shows that these elemental anomalous parts have been concentrated dominantly by potassic and phyllic, argillic and propylitic alterations within the gabbroic, monzonitic and dioritic rocks especially in the gabrodioritic type in certain parts of the area. The results, which were compared with fault distribution patterns, revealed a positive correlation between mineralization in anomalous areas and the faults present in the mineralized system.