Abstract
Gol-Gohar iron ore mines, with a reserve of about 1.1 billion tons, constitute the largest iron ore mine complex in Iran. Pit number 3 (Gohar-Zamin mine) has the largest reserve of ore among the others. Pit advancement toward deeper parts of the aquifer has increased groundwater inflow into the pit. During exploratory drillings in Gohar-Zamin mine, some of the boreholes became artesian. The water outflow from these boreholes has high salinity (classified as brine) and high pressure of a gas with an unknown origin. A conceptual model of groundwater flow was established using the available evidence and information. The prepared model revealed that there is a minimum of three aquifers, two alluvial aquifers (with electrical conductivity (EC) of 4,000–37,000 μS/cm) and one hard-rock aquifer (EC of 91,800–169,000 μS/cm) in the study area, with different lithological and hydrochemical characteristics. The brine outflow from the artesian boreholes originated from the hard-rock aquifer, which is a confined and high-pressure system without active recharge, i.e. an unsustainable resource. There is no hydraulic connection between the pit mine and the playa, located 13 km north of the mine, through the hard-rock aquifer, and the brine in the hard-rock aquifer is fossil water or has a metamorphic origin. The present study shows that the groundwater in the hard-rock aquifer is entrapped between fault planes without any hydraulic connection with overlying aquifers. Further, the results suggest that numerical groundwater flow models can only be successfully applied to the alluvial aquifer.
Résumé
Les mines de fer de Gol-Gohar constituent, avec une réserve d’environ 1.1 milliards de tonnes, le plus grand complexe de minerai de fer en Iran. Parmi les autres puits, le puits numéro 3 (la mine de Gohar-Zamin) a la plus grande réserve de minerai. L’approfondissement du puits en direction de parties plus profondes de l’aquifère a augmenté le débit des arrivées d’eau souterraine dans le puits. Lors de la réalisation de forages de reconnaissance dans la mine de Gohar-Zamin, certains des forages se sont avérés artésiens. Les venues d’eau de ces forages ont une forte salinité (classées en tant que saumure) et une forte pression d’un gaz d’origine inconnue. Un modèle conceptuel de l’écoulement de l’eau souterraine a été établi en utilisant les preuves et données disponibles. Le modèle ainsi construit révèle la présence d’au minimum trois aquifères dans la zone d’étude, deux aquifères alluviaux (avec une conductivité électrique (CE) de 4000–37,000 μS/cm) et un aquifère de socle (CE de 91,800–169,000 μS/cm), avec différentes caractéristiques lithologiques et hydrochimiques. Le flux de saumure sortant des forages artésiens a pour origine l’aquifère de socle, qui est un système captif et à haute pression, sans recharge active, c’est-à-dire une ressource non durable. Il n’y a pas de connexion hydraulique entre la mine à ciel ouvert et une sebkha, située à 13 km au nord de la mine, à travers l’aquifère de socle, et la saumure de l’aquifère de socle est une eau fossile ou a une origine métamorphique. Cette étude montre que l’eau souterraine de l’aquifère de socle est piégée entre deux plans de faille, sans aucune connexion hydraulique avec les aquifères sus-jacents. En outre, les résultats suggèrent que les modèles numériques de simulation des écoulements de l’eau souterraine ne peuvent être appliqués avec succès que pour l’aquifère alluvial.
Resumen
Las minas de mineral de hierro de Gol-Gohar, con una reserva de aproximadamente 1.1 millones de toneladas, constituyen el complejo de minas de hierro más grande de Irán. El pit número 3 (mina Gohar-Zamin) tiene la mayor reserva de mineral. El avance del pit hacia partes más profundas del acuífero ha aumentado el flujo de agua subterránea en el pit. Durante las perforaciones exploratorias en la mina Gohar-Zamin, algunos de los pozos se convirtieron en artesianos. La salida de agua de estas perforaciones tiene una alta salinidad (clasificada como salmuera) y una alta presión de un gas de origen desconocido. Se estableció un modelo conceptual de flujo de agua subterránea utilizando las evidencias y la información disponibles. El modelo preparado reveló que existe un mínimo de tres acuíferos, dos acuíferos aluviales (con conductividad eléctrica (EC) de 4,000–37,000 μS/cm) y un acuífero de roca dura (EC de 91,800–169,000 μS/cm) en la zona de estudio, con diferentes características litológicas e hidroquímicas. La salida de salmuera de los pozos artesianos se originó en el acuífero de roca dura, que es un sistema confinado y de alta presión sin recarga activa, es decir, un recurso no sostenible. No hay conexión hidráulica entre la mina del pit y la playa, ubicada a 13 km al norte de la mina, a través del acuífero de roca dura, y la salmuera en el acuífero de roca dura es agua fósil o tiene un origen metamórfico. El presente estudio muestra que el agua subterránea en el acuífero de roca dura está atrapada entre los planos de falla sin ninguna conexión hidráulica con los acuíferos superpuestos. Además, los resultados sugieren que los modelos numéricos de flujo de agua subterránea solo pueden aplicarse con éxito al acuífero aluvial.
摘要
Gol-Gohar铁矿山储量大约为11亿吨,是伊朗最大的铁矿山。3号矿坑(Gohar-Zamin矿)是所有矿坑中储量最大的。矿坑朝含水层更深部掘进增加了地下水流入矿坑的水量。在Gohar-Zamin矿勘查钻探期间,一些钻孔呈自流状态。从这些钻孔中流出的水盐度很高(归为卤水)、气体压力也很高,这些气体来源不明。采用现有的证据和信息建立了地下水流概念模型。该模型揭示,在研究区至少有三个含水层,两个冲积含水层(电导率(EC)为4,000–37,000 μS/cm)和一个硬岩含水层(电导率(EC)为91,800–169,000 μS/cm),这三个含水层岩性不同、水文地球化学特征也不同。从自流钻孔中流出的卤水来源于硬岩含水层,硬岩含水层是一个承压、高压的系统,没有活跃的补给,即没有可持续的资源。矿坑和矿山北面13公里处的盐湖没有通过硬岩含水层的水力联系,硬岩含水层中的卤水是原生水或者来源于变质岩。目前的研究显示,硬岩含水层中的地下水围囿于断层平面之间,与上覆含水层无任何水力联系。此外,结果还表明,数值地下水流模型只可成功应用到冲积含水层中。
چکیده
مجموعه معادن آهن گلگهر، با ذخیره 1.1 میلیارد تن، بزرگترین مجموعه معدنی سنگ آهن را در ایران تشکیل میدهد. پیت شماره 3 (معدن گهرزمین) دارای بیشترین ذخیره کانسار در بین سایر پیتها است. پیشروی پیت معدن به سمت اعماق بیشتر باعث افزایش جریان آب زیرزمینی به درون پیت شده است. در طی حفاریهای اکتشافی در معدن گهرزمین، تعدادی از گمانهها بهصورت آرتزین در آمدند. آب خروجی از این گمانهها دارای شوری بالا (طبقهبندی در گروه شورابهها) و فشار بالای یک گاز با منشأ نامعین است. یک مدل مفهومی از جریان آب زیرزمینی با استفاده از شواهد و اطلاعات موجود تهیه گردید. مدل تهیهشده نشان داد که در منطقه مورد مطالعه حداقل سه آبخوان، شامل دو آبخوان آبرفتی (با هدایت الکتریکی μS/cm 37,000-4,000) و یک آبخوان سازند سخت (با هدایت الکتریکی μS/cm 169,000-91,800)، با خصوصیات لیتولوژیکی و هیدروشیمیایی متفاوت وجود دارد. جریان شورابه خروجی از گمانههای آرتزین از آبخوان سازند سخت که یک سیستم محبوس و پرفشار بدون تغذیه فعال و در نتیجه ناپایدار است، نشأت میگیرد. هیچگونه ارتباط هیدرولیکی بین پیت معدن و کفه نمکی که در فاصله 13 کیلومتری شمال معدن قرار دارد، از طریق آبخوان سازند سخت وجود ندارد و شورابه موجود در این آبخوان یا از نوع فسیل و یا دارای منشأ دگرگونی است. این مطالعه نشان میدهد که آب زیرزمینی در آبخوان سازند سخت در بین صفحات گسلی بدون هیچگونه ارتباط هیدرولیکی با آبخوانهای بالایی به دام افتاده است. علاوه براین، نتایج پیشنهاد میکند که مدلهای عددی جریان آب زیرزمینی را تنها میتوان برای بخش آبخوان آبرفتی با موفقیت به کار برد.
Resumo
As minas de minério de ferro de Gol-Gohar, com uma reserva de cerca de 1.1 bilhão de toneladas, constituem o maior complexo de minério de ferro do Irã. O poço número 3 (mina de Gohar-Zamin) tem a maior reserva de minério entre os outros. O avanço do poço em direção a partes mais profundas do aquífero aumentou o influxo de águas subterrâneas no poço. Durante as perfurações exploratórias na mina de Gohar-Zamin, alguns dos furos se tornaram artesianos. A saída de água destes furos tem alta salinidade (classificada como salmoura) e alta pressão de um gás com origem desconhecida. Um modelo conceitual do fluxo de águas subterrâneas foi estabelecido usando as evidências e informações disponíveis. O modelo preparado revelou que há no mínimo três aquíferos, dois aquíferos aluviais (com condutividade elétrica (CE) de 4,000-37,000 μS/cm) e um aquífero cristalino (EC de 91,800–169,000 μS/cm) no estudo área, com diferentes características litológicas e hidroquímicas. O escoamento de salmoura dos poços artesianos é oriundo do aquífero de rocha cristalina, que é um sistema confinado e de alta pressão sem recarga ativa, ou seja, um recurso insustentável. Não há conexão hidráulica entre a mina e a playa, localizada a 13 km ao norte da mina, através do aquífero de rocha cristalina, e a salmoura no aquífero de rocha cristalina é água fóssil ou tem origem metamórfica. O presente estudo mostra que as águas subterrâneas no aquífero de rocha cristalina estão presas entre planos de falha sem qualquer conexão hidráulica com aquíferos sobrejacentes. Além disso, os resultados sugerem que modelos numéricos de fluxo das águas subterrâneas só podem ser aplicados com sucesso ao aquífero aluvial.
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Acknowledgments
The author would like to thank Mr. Mansouri, Deputy of Development and Engineering, and Dr. Mohammadi for their support and encouragement. Also, special thanks go to Randy Stotler, associate editor of Hydrogeology Journal, Keith Brown, superintendent of hydrogeology at Rio Tinto, and an anonymous reviewer for their helpful comments and constructive suggestions.
Funding
This research is financially supported by the R & D Division of the Gohar-Zamin Iron Ore Company.
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Assari, A. Defining hydrogeology of the Gohar-Zamin open pit mine, Iran: a case study in a hard-rock aquifer. Hydrogeol J 27, 1479–1495 (2019). https://doi.org/10.1007/s10040-018-01919-4
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DOI: https://doi.org/10.1007/s10040-018-01919-4