Advanced Applied Geology

Advanced Applied Geology

Origin of Ore-Forming Fluids in the Chumalu Pb–Zn Deposit: Constraints from Fluid Inclusion Microthermometry, Sphalerite Chemistry, and Sulfur Isotopes

Authors
Akram Karami 1
Hassan Zamanian 2
Keikhosro Radmard 1
Amir Pazoki 3
1 Geology Department, Faculty of Sciences, Lorestan University, Khorramabad, Iran
2 Faculty of Geology, College of Sciences, University of Tehran, Tehran, Iran
3 Department of Mining Engineering, Faculty of Technology and Engineering, Lorestan University, Khorramabad, Iran
10.22055/aag.2026.52065.2566
Abstract
The Chumalu lead–zinc (Pb–Zn) deposit is located in the western sector of the Alborz magmatic arc, within the Tarom–Hashtchin polymetallic belt. Eocene–Oligocene magmatism in this region produced a diverse suite of extrusive, intrusive, subvolcanic, and pyroclastic rocks, including basaltic, andesitic, dacitic, and rhyolitic lavas and associated tuffs, which constitute the principal host rocks for mineralization. Mineralogical investigations indicate that the hypogene assemblage is dominated by pyrite, chalcopyrite, galena, sphalerite, tetrahedrite, bornite, and marcasite, whereas the supergene assemblage comprises cerussite, chalcocite, covellite, malachite, and secondary iron oxides. Microthermometric analyses of 67 liquid-rich, two-phase (L+V) fluid inclusions hosted by sphalerite and coeval quartz yielded homogenization temperatures (Th) of 100–270 °C and salinities of 0.3–7.0 wt% NaCl equivalent. These microthermometric data suggest ore deposition at depths of 500–1,000 m below the paleowater table, under near-hydrostatic pressures of approximately 10 MPa, with fluid cooling and mixing acting as the principal precipitation mechanisms. Furthermore, electron probe microanalysis (EPMA) revealed low Fe concentrations and high Zn/Fe ratios in sphalerite. Together with its pale color, these characteristics are consistent with low-temperature mineralization in an intermediate-sulfidation epithermal environment. The δ³⁴S values of galena and sphalerite range from +6‰ to +10‰, suggesting a predominantly magmatic sulfur source. Overall, the integration of fluid inclusion microthermometry, sphalerite mineral chemistry, and stable sulfur isotope data provides a basis for developing a metallogenic model to guide the exploration for and discrimination of intermediate-sulfidation Pb–Zn epithermal systems throughout the Tarom–Hashtchin metallogenic belt.
Keywords
Chomalu deposit
sphalerite chemistry
sulfur isotopes
fluid inclusions
Tarom-Hashtjin
Subjects
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Advanced Applied Geology
Volume 16, Issue 2
Summer 2026
Pages 263-289