پديد آورندگان :
طالع فاضل، ابراهيم نويسنده دانشكده علوم پايه,گروه زمين شناسي,دانشگاه بوعلي سينا,ايران Tale Fazel, Ebrahim , مهرابي، بهزاد نويسنده دانشكده علوم زمين,گروه ژئوشيمي,دانشگاه خوارزمي,ايران Mehrabi, Behzad , زمانيان، حسن نويسنده دانشكده علوم,گروه زمين شناسي,دانشگاه لرستان,ايران Zamaniyan, H , حيات الغيبي، معصومه نويسنده دانشكده علوم,گروه زمين شناسي,دانشگاه لرستان,ايران Hayatalgheybi, Masoumeh
چكيده لاتين :
Introduction
The Senj deposit has significant potential for different types of mineralization, particularly porphyrylike Cu deposits, associated with subductionrelated Eocene–Oligocene calcalkaline porphyritic volcanoplutonic rocks. The study of fluid inclusions in hydrothermal ore deposits aims to identify and characterize the pressure, temperature, volume and fluid composition, (PTX) conditions of fluids under which they were trapped (Heinrich et al., 1999; Ulrich and Heinrich, 2001; Redmond et al., 2004). Different characteristics of the deposit such as porphyrtic nature, alteration assemblage and the quartzsulfide veins of the stockwork were poorly known. In this approach on the basis of alterations, vein cutting relationship and field distribution of fluid inclusions, the physical and chemical evolution of the hydrothermal system forming the porphyry CuMo (±AuAg) deposit in Senj is reconstructed.
Materials and Methods
Over 1000 m of drill core was logged at a scale of 1:1000 by Pichab Kavosh Co. and samples containing various vein and alteration types from different depths were collected for laboratory analyses. A total of 14 samples collected from the altered and least altered igneous rocks in the Senj deposit were analyzed for their major oxide concentrations by Xray fluorescence in the SGS Mineral Services (Toronto, Canada). The detection limit for major oxide analysis is 0.01%. Trace and rare earth elements (REE) were analyzed using inductively coupled plasmamass spectrometery (ICPMS), in the commercial laboratory of SGS Mineral Services. The analytical error for most elements is less than 2%. The detection limit for trace elements and REEs analysis is 0.01 to 0.1 ppm. Fluid inclusion microthermometry was conducted using a Linkam THMS600 heating–freezing stage (190 °C to +600 °C) mounted on a ZEISS Axioplan2 microscope in the fluid inclusion laboratory of the Iranian Mineral Processing Research Center (Karaj, Iran).
Results
The CuMo Senj deposit covering an area about 5 km2 is located in the central part of the Alborz Magmatic Arc (AMA). The Nb/Y versus Zr/TiO2 diagram (after Winchester and Floyd, 1977) illustrates a typical trend for the magmas in the Senj magmatic area–starting from basaltic and evolving to dacite/rhyodacitic compositions, with few data plotting in the alkali basalt field. Most of the igneous rocks plot within the medium and highK fields in the K2O versus SiO2 diagram. The igneous rocks from the Senj area define a typical highK calcalkaline on SiO2 versus K2O diagram (Le Maitre et al., 1989). All studied rocks show similar incompatible trace element patterns with an enrichment of large ion lithophile elements (LILE: K, Rb, Ba, Th) and depletion of high field strength elements (HFSE: Nb and Ti), which are typical features of magmas from convergent margin tectonic settings (Pearce and Can, 1973). At least three veining stages namely QBC, QM, and QP which are related to alteration and mineralization are distinguished at the Senj mineralized area. Three distinct alteration assemblages including Kfeldsparbiotitesericitequartz, quartzsericiteKfeldsparpyrite, and Kfeldsparbiotitesericitequartz, are distinguishable with these veins. About 80 % of the copper at Senj is associated with the early QBCstage veins, with another 5 to 15 % in the QMand QPstage veins. About 70 % of the molybdenite occur in QM veins.
Discussion
Fluid inclusion distribution, fluid chemistry, and homogenization behavior document that S2type fluids are samples of magmaderived aqueoussaline fluids characterized by high salinity and temperature, and high Cu content. Such parental fluids scavenged Cu and Mo from the melt below and transported them to the hydrothermal system above. The increased abundance of S and LVtypes inclusion coinciding with the highest grade Cu mineralization (early QBCstage veins) at the Senj deposit suggests that brinevapor unmixing and phase separation plays an important role in Cuore precipitation and alteration zonation. In addition to unmixing, cooling and waterrock interaction also played important roles in chalcopyrite precipitation at the Senj deposit.
Compositions, depositscale distribution, and trapping conditions of fluid inclusions can be explained by the continued influx of a parental high salinity magmatic hydrothermal fluid, with no significant change in the bulk composition of the input fluid over the integrated lifetime of ore metal precipitation and vein formation. Fluid inclusion evidence and veincutting relationships indicate that molybdenum mineralization (QM vein) occurred at moderate temperatures coinciding with phyllic alteration, rather than from later, lower temperature fluids. Furthermore, early fluids decompressed rapidly relative to cooling, forming quartzstockwork veins with Ksilicate alteration at depth and QP veins at shallower levels in the Senj deposit. Later, as the hydrothermal system waned, the rate of decompression relative to fluid cooling slowed, causing the fluid to remain above its solvus, forming barren quartzdominated veins with quartzkaolinite±illite alteration which overprint much of the deposit.
References
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