Geological and Geophysical Studies of Sulfide Copper Mineralization in the Dochileh Area: An Example of Manto‐Type Deposit in the Sabzevar Zone, Iran

Abstract

The Dochileh stratiform copper deposit in the Sabzevar Zone of northeastern Iran is hosted in the basaltic sequence of the Upper Eocene age. The host rock displays two hydrothermal events: zeolite–carbonate alteration that is a stratigraphic–lithologic feature and chlorite and chlorite/ferruginous alterations in the local mineralized structures. Ore formation is related to both hydrothermal events and occurs in both stratiform and vein mineralization types. Mineralization consists of main chalcocite with variable amounts of bornite, chalcopyrite, native copper, malachite, and cuprite minerals, which occur as hydrothermal breccias, and disseminated, vein, and veinlet forms. Geophysical field studies using resistivity and induction polarization (IP) methods were conducted along nine survey lines in the area. As a result of modeling and interpretation of the acquired geophysical data, high values of IP and resistivity corresponding to mineralization were observed at two depth levels: 0–20 m and more than 40 m. Based on these geological and geophysical investigations, six locations for drilling exploration boreholes were proposed. Drilling data confirmed the mineralization containing high copper values in the two depth levels: the vein‐type mineralization in the surface and shallow depth level, and the stratiform mineralization at the deeper level. Fluid inclusion studies in calcite and quartz from stratiform‐ and vein‐type mineralization show the evidence of mixing, and a linear dilution trend during the ore formation occurred at a wide range of temperatures: 121–308°C and 80–284°C, respectively, and varying salinities of between 3.2–16.8 and 0.8–22 wt% NaCl equivalents. The stable isotope composition of δ34S that falls in a range of −2.4 to +25.0‰ could be considered biogenetic sulfur from bacterial sulfate reduction and leaching of sulfur from hosting basalt. The δ13C values of calcite vary between −0.6 and −7.6‰, suggesting a major contribution of marine carbonates associated with igneous carbonates, and the δ18OSMOW values of calcite are between +15.2 and +19.9‰, suggesting a contribution of δ18O‐rich sedimentary rocks and δ18O‐poor meteoric water. Copper and sulfide‐rich hydrothermal fluid have flowed upward through the local faults and permeable interbeds within the Eocene volcanic sequence and have formed the mineralized veins and horizons. The geophysical results have detected the local faults as the channel ways for mineralization.

Zangalou Manto‐type deposit in the Sabzevar zone, northeast Iran: Evidence of mineralogy, geochemistry, U–Pb dating, fluid inclusion, and stable isotopes

“…The data are from four different materials including marine carbonate (Baker & Fallick, 1989;Hoefs, 1997), sedimentary organic matter carbon (Hodson, 1977;Hoefs, 1997), organically derived carbon (Longstaffe, 1989;Valley, 1986) and magma-mantle carbonate (Ray et al, 1999;H. E. Taylor et al, 1967) F I G U R E 1 7 (a) Sulfur isotopic composition of Zangalou deposit compared with different sulfur reservoirs (Hoefs, 1997) (b) sulfur isotopic compositions of primary copper sulfide minerals from mantotype deposits around the world (Dochileh, Ebrahimi et al, 2019;Abbas abad, Salehi & Rasa, 2016;Koshkouieh, Abolipour et al, 2015;Keshtmahaki, Boveiri Konari et al, 2013;Mari, Maghfouri et al, 2017;Dongxiang, Cai et al, 2016;Melipilla, Carrillo-Rosúa et al, 2006;Lo Aguirre, Puig & Spiro, 1988, Saric et al, 2003El Soldado, N. S. F. Wilson, Zentilli, & Spiro, 2003;Cerro Negro, Munizaga & Zentilli, 1994;Talcuna, Puig & Spiro, 1988, Carrillo-Rosúa et al, 2006Metalotect, Cisternas & Hermosilla, 2006;Ocoita-Pabellon, Cisternas & Hermosilla, 2006;Buena Vista, Kojima et al, 2009;Mantos Blancos, Sasaki et al, 1984, Munizaga & Zentilli, 1994Ramírez et al, 2006;Michilla, Vivallo & Henríquez, 1998, Sasaki et al, 1984, Munizaga & Zentilli, 1994, Tristá-Aguilera, 2007…”

The Manto-Type Copper Mineralization in the Eocene Volcano-Sedimentary Sequences, Western Alborz-Azarbayjan Belt, NW Iran

“…Copper deposits in the UDMA are mainly porphyry type which are associated with Cenozoic magmatism [5][6][7]. The manto-type copper deposits in Iran are distributed in the SaSZ (Kesht Mahaki deposit [8], UDMA (Kashkouieh and Veshnaveh [9]), Sabzevar subzone (Abgareh, Zangalou, Kimia, Tarannom, Nasim, Kalabri, Sharifabad, Dahanesiah, Pirmardan, Dochileh, Abbas Abad, Chah Moosa, Choghondar Sar and Bozorg mine deposits [10][11][12]) Lut block (Varzag deposit [13]) and AMB (e.g., Mari [14], Dohneh, Chizeh, Zaker, Golharoud, Platelou, Gheshlagh, Sorkhe Dizaj, Kordkand and Daveh Yataghi) (Figure 1). All of these deposits, except Cretaceous Kesht Mahaki deposit, formed within the Eocene volcanic and volcano-sedimentary rocks.…”