Geology, Alteration, Mineralization, Geochemistry and Petrology of intrusive units in the Shah Soltan Ali prospect area (Southwest of Birjand, South Khorasan province)

IntroductionThe Shah Soltan Ali area is located 85 km southwest of Birjand in the South Khorasan province. This area is part of the Tertiary volcanic-plutonic rocks in the east of the Lut block. The Lut block is bounded to the east by the Nehbandan and associated faults, to the north by the Doruneh and related faults (Sabzevar zone), to the south by the Makran arc and Bazman volcanic complex and to the west by the Nayband Fault. The Lut block is the main metallogenic province in the east of Iran (Karimpour et al., 2012), that comprises of numerous porphyry Cu and Cu–Au deposits, low and high sulfidation epithermal Au deposits, iron oxide deposits, base-metal deposits and Cu–Pb–Zn vein-type deposits. The geology of Shah Soltan Ali area is dominated by volcanic rocks, comprised of andesite and basalt, which are intruded by subvolanic units such as monzonite porphyry, monzodiorite porphyry and diorite porphyry.
1. 170 thin sections of the rock samples as well as 25 polished and thin polished sections were prepared for petrography, alteration and mineralization.
2. Twenty five samples were analyzed for Cu, Pb, Zn, Sb, Mo and As elements by the Aqua regia method in the Zarazama laboratory in Tehran, Iran.
3. Nine samples were analyzed for trace elements [including rare earth elements (REEs)]. As a result of these analyses, trace elements and REE were determined by inductively coupled plasma mass spectrometry (ICP-MS) in the ACME Analytical Laboratories (Vancouver) Ltd., Canada.
4. Ten samples were analyzed for major elements by wavelength dispersive X-ray fluorescence spectrometry in the East Amethyst laboratory in Mashhad, Iran.
5. Five samples were analyzed for Firre Assay analysis in the Zarazma Laboratory in Tehran, Iran.
6. The results of XRD analysis were used for 4 samples.
Discussion and resultsPetrographic studies indicate that subvolcanic rocks consist of diorite porphyry, monzonite porphyry and monzodiorite porphyry. Based on field and lab work several alteration zones such as: quartz–sericite–pyrite (QSP), propylitic, argillic, silicified, sericitic and carbonate were identified. Geochemical studies show that intrusive units are metaluminous, high calcalkalic to shoshonitic. These rocks belong to the I-type granitoid (Chappell and White, 2001), and they have formed in a volcanic arc granitoids (VAG) tectonic setting (Pearce et al., 1984). Mantle-normalized, trace-element spider diagrams display enrichment in large ion lithophile elements, such as Rb, Sr, K, and Cs, and depletion in high field strength elements, e.g., Nb, Ti, Zr. Enrichment of LREE versus HREE and enrichment of LILE and depletion in HFSE indicate magma formed in the subduction zone. Negative Nb and Ti anomalies are recognized as a fingerprint of a subduction process (Nagudi et al., 2003). All of the intrusive rocks have a weak negative Eu anomaly (Eu/Eu*=0.82–0.94) (Tepper et al., 1993), and a low ratio of (La/Yb)N. The magmatic source of intrusive rocks had been generated from 1% to 5% of partial melting of garnet-spinel lherzolite (Aldanmaz et al., 2000). In the south area, four types of mineralization such as: veinlet to vein, disseminated, hydrothermal breccia and stockwork occur from which stockwork is the most important type of mineralization. The veinlets that were found within the stockwork zone are:1) pyrite chalcopyrite, 2) quartz pyrite ± chalcopyrite, 3) quartz ± pyrite. Compositional variations of elements within the Shah Soltan Ali area are as follows: Cu = 30-454 (ppm), Zn = 27-279 (ppm), Pb = 11- 70 (ppm), Sb = 0.9-152 (ppm), Au= 5-128 (ppb), As = 7-203 (ppm). There is a high concentration of Cu – Zn – Au and Sb that is associated with the high density of veinlets in the quartz-sericite-pyrite zone in the southeast of Shah Soltan Ali area. Based on the obtained data, the Shah Soltan Ali area is a part of the porphyry Cu-Au deposit.