Characteristics of the Ahmadabad hematite/barite deposit, Iran – studies of mineralogy, geochemistry and fluid inclusions

Abstract

The Ahmadabad hematite/barite deposit is located to the northeast of the city of Semnan, Iran. Geostructurally, this deposit lies between the Alborz and the Central Iran zones in the Semnan Subzone. Hematite-barite mineralisation occurs in the form of a vein along a local fault within Eocene volcanic host rocks. The Ahmadabad deposit has a simple mineralogy, of which hematite and barite are the main constituents, followed by pyrite and Fe-oxyhydroxides such as limonite and goethite. Based on textural relationships between the above-mentioned principal minerals, it could be deduced that there are three hydrothermal mineralisation stages in which pyrite, hematite and barite with primary open space filling textures formed under different hydrothermal conditions. Subsequently, in the supergene stage, goethite and limonite minerals with secondary replacement textures formed under oxidation surficial conditions. Microthermometric studies on barite samples show that homogenisation temperatures (TH) for primary fluid inclusions range from 142 to 256°C with a temperature peak between 200 and 220°C. Salinities vary from 3.62 to 16.70 NaCl wt% with two different peaks, including one of 6 to 8 NaCl wt% and another of 12 to 14 NaCl wt%. This indicates that two different hydrothermal waters, including basinal and sea waters, could have been involved in barite mineralisation. The geochemistry of the major and trace elements in the samples studied indicate a hydrothermal origin for hematite and barite mineralisation. Moreover, the Fe/Mn ratio (>10) and plots of hematite samples of Ahmadabad ores on Al-Fe-Mn, Fe-Mn-(Ni+Co+ Cu)×10, Fe-Mn-SiX2 and MnO/TiO2 – Fe2O3/TiO2 diagrams indicate that hematite mineralisation in the Ahmadabad deposit occurred under hydrothermal conditions. Furthermore, Ba and Sr enrichment, along with Pb, Zn, Hg, Cu and Sb depletion, in the barite samples of Ahmadabad ores are indicative of a low temperature hydrothermal origin for the deposit. A comparison of the ratios of LaN/YbN, CeN/YbN, TbN/LaN, SmN/NdN and parameters of Ce/Ce* and La/La* anomalies of the hematite, barite, host volcanic rocks and quartz latite samples to each other elucidate two important points: 1) the barite could have originated from volcanic host rocks, 2) the hematite could have originated from a quartz latite lithological unit. The chondrite normalised REE patterns of samples of hematite barite, volcanic host rocks and quartz latite imply that two different hydrothermal fluids could be proposed for hematite and barite mineralisation. The comparison between chondrite normalised REE patterns of Ahmadabad barite with oceanic origin barite and low temperature hydrothermal barite shows close similarities to the low temperature hydrothermal barite deposits.

Petrography and Mineralogy of the iron ore from Nawgwezany Mishao area– Shalair Valley, KRG - Iraq: Insights on the Genesis

“…Two factors could have caused the brecciation; (1) Structural factors, influenced by the local fault controlling mineralization activity. (2) Hydrostatic pressure caused by mineralizing hydrothermal fluids [33]. In some samples, primary hematite mineralization can be seen as separated tabular crystals (Figures 11c, d, and e).…”

Уникальные Гематитовые Жилы Терского Побережья, Кольский Регион: Состав, Структурно-Текстурные Особенности И Генезис

“…Но их пространственная связь с кварцевыми (аметистовыми) и баритовыми жилами, с одной стороны, и с флюоритовой минерализацией, с другой, позволяют предполагать их температурные интервалы формирования как мезотермальные (350-200 ° С) и/или эпитермальные (200-50 ° С). Так, для гидротермальных флюорит-гематитовых жил рудного района Шварцвальд получены температуры гомогенизации газово-жидких включений в интервале 150-155 ° С (Walter et al, 2020), а для гидротермального барит-гематитового месторождения Ахмадабад -200-220 ° С (Babaei, Ganji, 2018). В целом, гематитовые и кварцевые жилы с сопутствующей флюоритовой минерализацией Терского берега можно отнести к семейству флюорит-барит-кварц-карбонатных жил, образующихся в линеаментных зонах, рифтах и зонах несогласия между кристаллическим фундаментом и осадочным чехлом платформы.…”