Abstract The Mehdiabad deposit is the largest accumulation of siliciclastic-carbonate hosted zinc in the world, with a total resource of 394 Mt, grading 4.2% Zn, 1.6% Pb, and 36 g/t Ag. In this study, trace element, fluid inclusions studies, and O-C-Sr isotopic analyses were carried out on the host rock and related sulfide ores in the Mehdiabad deposit, aiming to reveal the nature of ore-forming fluids. The average REE contents of the ore samples are higher than those of the host rock samples. The Cd values of sphalerite in the ores range from 0.11 to 0.63 wt.%, which suggested that the Mehdiabad Zn-Pb-Ba-(Cu-Ag) mineralization was formed in a sedimentary-exhalative environment. Investigation of the fluid inclusions reveals relatively moderate temperature (105-261 °C) with scattered salinity (0.03-19.44 wt.% NaCl eq.). This finding suggests that hydrothermal brine fluid mixing with seawater could be the primary mechanism that prompted ore formation. The host limestones have δ13CPDB values ranging from +1.9 to +2.2‰, and δ18OSMOW values from +1.7 to +2.7‰. Hydrothermal dolomites have δ13CPDB values from +10.6 to +11.2‰, and δ18OSMOW values from +13.4 to +15.0‰. These O-C isotopic studies suggest that CO2 in the hydrothermal fluids mainly originated from marine carbonate rocks. In the Mehdiabad deposit, δ18O values of all barite samples vary within a narrow range from 7.0 to 10.8 ‰, which roughly fall within that of the Early Cretaceous seawater. Sr isotope data for barite in the Mehdiabad deposit is more radiogenic than Lower Cretaceous seawater. This suggests that radiogenic Sr in the hydrothermal barites mainly originated from fluid-rock reactions involving radiogenic clastic minerals derived from Sangestan strata underlying the Taft Formation.

中文翻译：

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伊朗 Mehdiabad 世界级海底置换 SEDEX 型 Zn-Pb-Ba-(Cu-Ag) 矿床中成矿流体的性质；地球化学、流体包裹体和 OC-Sr 同位素的限制

摘要 Mehdiabad 矿床是世界上最大的含硅碎屑碳酸盐锌矿床，总资源量为 394 Mt，锌品位为 4.2%，铅品位为 1.6%，银品位为 36 g/t。本研究对 Mehdiabad 矿床的母岩和相关硫化矿进行了微量元素、流体包裹体研究和 OC-Sr 同位素分析，旨在揭示成矿流体的性质。矿石样品的平均稀土元素含量高于母岩样品。矿石中闪锌矿的 Cd 值范围为 0.11 至 0.63 wt.%，这表明 Mehdiabad Zn-Pb-Ba-(Cu-Ag) 矿化形成于沉积-喷气环境中。流体包裹体的调查显示相对温和的温度 (105-261 °C) 和分散的盐度 (0.03-19.44 wt.% NaCl eq.)。这一发现表明，热液盐水流体​​与海水混合可能是促使成矿的主要机制。主体石灰岩的 δ13CPDB 值范围为 +1.9 至 +2.2‰，δ18OSMOW 值范围为 +1.7 至 +2.7‰。热液白云岩的δ13CPDB 值从+10.6 到+11.2‰，δ18OSMOW 值从+13.4 到+15.0‰。这些 OC 同位素研究表明，热液中的 CO2 主要来源于海相碳酸盐岩。在 Mehdiabad 矿床中，所有重晶石样品的 δ18O 值在 7.0 到 10.8 ‰ 的狭窄范围内变化，大致属于早白垩世海水的范围。Mehdiabad 矿床中重晶石的 Sr 同位素数据比下白垩统海水更具放射性。