, , , ,
Volume 23, Issue 1 (4-2015)
Abstract
The Yaralujeh vein index is located about 40 km NW of Ahar, East Azarbaijan. The host rock of mineralized vein is an altered subvolcanic body, intermediate in composition. The mineralization of sphalerite-galen-chlcopyrite recognized as intersected veinlets. Based on field observations, textural and mineralogical evidences, the mineralization occurred in 4 stages. The subvolcanic rocks are affected by pervasive sericitc and carbonate alterations and overprinted by supergene assemblages. The plot of the Ishikawa alteration index (AI) Vs. chlorite - carbonate - pyrite index (CCPI), Known as alteration box plot, shows the main alteration species. The assemblage of quartz, sericite, illite, albite, kaolinite, leucoxene, pyrite and late carbonate minerals, indicate the fluids with a near-neutral pH and temperature of approximately 200 to 300 °C. The mineralogical, alteration, and geochemical characteristics of study area in comparison with other hydrothermal deposits indicate that the Yaralujeh vein index is similar to the intermediate-sulfidation epithermal deposits and intermediate temperature polymetalic veins related porphyry copper deposits
Mrs Zohreh Jabbarzadeh, Dr Kamal Siahcheshm, Prof Ali Asghar Calagari,
Volume 32, Issue 4 (12-2024)
Abstract
The Tazekand mineralization zones, as a part of Tarom-Hashtjin metallogenic belt, is located about 45 km northeast of Zanjan city, NW Iran. Based on field study, petrography, and geochemical investigations, the lithologic composition of the intrusive rocks in the area varies from monzonite, diorite, granodiorite to gabbro, and volcanic units ranging from trachy-andesite, andesite to basaltic andesite. Delineation of diagrams of the Ishikawa alteration index (AI), chlorite-carbonate-pyrite index (CCPI) (known as alteration box plot), and the chemical alteration index (CIA) illustrated the main types and intensity of alterations in this area. Consideration of depletion and enrichment of elements by noting the enrichment factor in the alteration and mineralization zones indicates the role of high-temperature and low-pH of the altering fluids which acted as an important factor in decomposition of minerals such as plagioclase, alkali feldspar, and ferromagnesian and absence of K2O, Na2O and CaO components. The general pattern of REE distribution normalized by both chondrite and primitive mantle in altered and relatively fresh granitoid and volcanic units (as host rocks), shows a conspicuous negative slope and enrichment in LREE and large ion lithospheric elements (LILE) and depletion in HREE and high field strength elements (HFSE) during the alteration processes. Ce, Eu and Pr anomalies (Eu/Eu*, Ce/Ce*, Pr/Pr*) were investigated in ores along with fresh and altered host rocks. What can be inferred from these studies are that the changes in the behavior of rare earth elements as well as their normalized distribution pattern for each type of alteration has its own peculiar physicochemical conditions influenced by the action of multiple injections of hydrothermal fluids during both hypogene and supergene processes. The supergene processes compared to hypogene processes played very important and prominent role in development and evolution of the alteration zones in the Tazekand mineralization area