Geology, mineralization, U-Pb dating and Sr-Nd isotope geochemistry of intrusive bodies in northeast of Kashmar

Document Type : Research Article

Authors

• Alireza Almasi ¹
• Mohammad Hassan Karimpour ²
• Khosrow Ebrahimi Nasrabadi ¹
• Behnam Rahimi ¹
• Urs Klotzli ³
• Jose Francisco Santos ⁴

¹ Ferdowsi University of Mashhad

² Department of Geology, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran

³ Vienna

⁴ Aveiro

10.22067/econg.v7i1.44721

Abstract

Introduction
The study area is located in central part of the Khaf- Kashmar-Bardeskan belt which is volcano-plutonic belt at the north of the Dorouneh fault in the north of Lut block. The north of the Lut block is affected by tectonic rotation and subduction processes which occur in the east of Iran (Tirrul et al., 1983). The magmatism of Lut block begins in Jurassic and continues in Tertiary (Aghanabati, 1995). Karimpour (Karimpour, 2006) pointed out the Khaf-Kashmar-Bardeskan belt has significant potential for IOCG type mineralization such as Kuh-e-Zar, Tannurjeh, and Sangan (Karimpour, 2006; Mazloumi, 2009). The data gathered on the I-type intrusive rocks include their field geology, petrography, U–Pb zircon dating and Sr–Nd isotope and also alteration and mineralization in the study area.

Materials and methods
- Preparation of 150 thin sections of rock samples for study of petrography and alteration of the intrusive rocks.
- Magnetic susceptibility measuring of intrusive rocks.
- U-Pb dating in zircon of I-type intrusive rocks by Laser-Ablation Multi Collector ICP-MS method.
- Sr-Nd analysis on 5 samples of I-type intrusive rocks by Multi-Collector Thermal Ionization Mass Spectrometer (TIMS) VG Sector 54 instrument.
- Mineralography and paragenetic studies of ore-bearing quartz veins and geochemical analysis for 28 samples.
- Production of the geology, alteration and mineralization maps by scale: 1:20000 in GIS.

Results
Oblique subduction in southern America initiated an arc-parallel fault and shear zones in the back of continental magmatic arc (Sillitoe, 2003). Because of this event, pull-apart basins were formed and high-K to shoshonitic calc-alkalineI- and A-type magmatism occur (Sillitoe, 2003). Most important deposits accompany with this magmatism are Au-Cu deposits types and Fe-Skarns (Sillitoe, 2003). We have similar scenario to Neotethys subduction. Khaf-Kashmar-Bardeskan volcano-plutonic belt is located between Neotethys suture and Alborz- Sabzevar Back- arc (Asiabanha and Foden, 2012). We suggest Khaf-Kashmar-Bardeskan volcano-plutonic belt forms at the arc-parallel fault and shear zones in the back of continental magmatic arc. In the basis of all evidences (Shear zone system, high-K to shoshonitic calc-alkaline I- and A-type magmatism, typical alterations related to upper zones of IOCG deposits and IOCG mineralization), we suggest IOCG (Au-Cu) mineralization in Kashmar.

Discussion
On the basis of former regional (Muller and Walter, 1983) and local structural studies (this research), regional compression causes sinistral strike-slip movements of Dorouneh and Taknar faults, shear zone, pull-apart and Riedel fractures (P, R and R' types) in the study area. These events cause magma intrusion and circulation of hydrothermal fluids. On the basis of geology, geochemistry and magnetic susceptibility measuring of intrusive rocks, several high K to shoshonitic calc-alkaline to alkaline I-type and one A-type intrusive rocks are intruded in Kashmar area. Swarm dykes are the youngest and the agent for alteration and mineralization. U-Pb dating related to quartz monzonite body (preventative sample for I-type intrusive rocks which are older than A-type series) show 40 Ma (Middle Eocene) for this rock group in Kashmar. The mean of initial 87Sr/86Sr and 143Nd/144Nd are 0.705-0.707 and 0.5135-0.5126 for I-type series, respectively. εNd(i) amounts for I-type series are in negative to positive limit ranges (-1.65 to 1.33). These amounts show subduction source with contamination to continental crust.
Two type alteration and mineralization occur in Kashmar: 1) primary alterations (advanced argillic+ sericite+ silicification) which are synchronous with sulfide base-metal veins (chalcopyrite+ pyrite± galena± quartz± chloride) and 2) Lateral alterations (carbonatization+ Fe-oxides+ silicification+ epidotization+ chloride+ sericite+ barite) which are synchronous with IOCG veins (specularite+ chalcopyrite+ pyrite± galena± sphalerite± barite± siderite ± etc.). Primary centralized and sulfide base-metal veins in crosscutting points between Dorouneh fault and minor faults. Bahariyeh, Uchpalang and Sarsefidal areas are located in these crosscutting points. Tourmaline (demorterite) ±chloride fill the fractures in the intrusive rocks of southern part of area next to the Dorouneh fault occasionally. Lateral alteration synchronous with IOCG veins occur in Kamarmard area. Geochemical data of all veins show Cu, Pb, Zn anomalies (>1%) in two type veins, Au anomalies (to about 15 ppm) only in IOCG veins, Mn anomalies in two type veins and Ba anomalies in IOCG veins.
Alteration and mineralization in the world-class IOCG deposits identified by sodic-calcic and potassic (hydrothermal actinolite and biotite) and magnetite± gold in deep parts (Sillitoe, 2003) and advanced argillic+ pyrite+ sericite+ toulrmaline (demorterite) in shallow parts (Ray and Dick, 2002). Generally, alteration in the study area is similar to shallow parts of world-class IOCG deposits. Tanourjeh is a IOCG deposit next to the northwest of the study area. In Tanourjeh, the gold-bearing magnetite is synchronous to potassic alteration (hydrothermal biotite) and other alterations are advanced argillic, silicification and sericite. These characteristics are similar to deep parts of world-class IOCG deposits. Bahariyeh, Uchpalang and Sarsefidal have similarities to alterations in Tanourjeh. Considering Tanourjeh lie in the lower level rather to Bahariyeh, Uchpalang and Sarsefidal, we believe they erosion surface in Tanourjeh is lower. Kamarmard lies in the highest erosion surface in the study area. Alterations and Mineralization as similar to Kuh e Zar IOCG deposit (specularite+chalcopyrite+gold) which is next to the Kamarmard area in Northeast of study area. In Bahariyeh-Uchpalang areas we can see only one IOCG vein but in Sarsefidal area exist several IOCG vein. Because of current surface in Bahariyeh-Uchpalang areas is lower than Sarsefidal current surface in Sarsefidal is lower than Kamarmard, we believe that IOCG vein in Bahariyeh-Uchpalang area have been eroded. We Believe to two circulation of oxidized Fe-bearing hydrothermal fluid in Kashmar. During the first circulation, Potassic alteration and gold-bearing magnetite bodies in depth and primary alterations with sulfide base-metal veins was formed. At the second circulation, lateral alterations and IOCG veins was formed at the near of paleo-surface.

References
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Keywords

• Shear zone
• I/A type magmatism
• U-Pb Zircon Dating
• Sr-Nd isotopes
• IOCG
• subduction

20.1001.1.20087306.1394.7.1.5.7

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