بررسی شواهد کانی‌ شناسی و ژئوشیمیایی برای ارزیابی پتانسیل اقتصادی باطله‌ های برجا در معدن روی و سرب انگوران

معدن روی‌سرب انگوران در غرب استان زنجان و شمال غربی پهنه ماگمایی‌دگرگونی سنندج‌سیرجان قرار‌گرفته است. در این پژوهش از کانی پلی‌ مورف ورتزیت، به‌عنوان کانی معرف و ردیاب برای شناسایی مکان‌های مستعد غنی شده از عناصر فلزی کمیاب استفاده شد. بر اساس این پژوهش‌، تمرکز اقتصادی عناصر فلزی در معدن انگوران را می توان به دو بخش سولفیدی دارای غنی شدگی از عناصر نقره، کادمیم و سلنیوم (بالاتر از عیار حد خود) و باطله‌های کربناته دارای غنی شدگی از عنصر آرسنیک تقسیم‌ کرد. تمرکز برخی از عناصر در فرو‌دیواره شیست این معدن (مانند آهن و به مقادیر کم‌ آرسنیک، کبالت، مس و آنتیموان) در ارتباط با کانی‌زایی سولفیدی در آنهاست. نتایج به‌دست آمده از تجزیه ژئوشیمیایی در این پژوهش نشان‌دهنده آن است که تمرکز بالای عناصر فلزی (نقره، کادمیم، سلنیوم، قلع، ایندیم، کبالت و غیره) در بخش سولفیدی معدن انگوران است که تاییدی در ارتباط با تشکیل کانی‌های اسفالریت و ورتزیت به‌ صورت همزیست در نتیجه غنی شدگی از عناصر فلزی کمیاب است. انباشت اصولی عناصر فلزی موجود در باطله‌ها و سایر بخش‌های معدنی بر اساس نوع و میزان غنی‌شدگی، نه تنها موجب به حداقل رساندن مخاطرات زیست‌محیطی می‌شود؛ بلکه می‌تواند قدمی برای استخراج و بهره‌برداری این عناصر به ‌صورت محصول جانبی باشد.

Investigation of mineralogical and geochemical evidence for evaluation of economic potential in the waste minerals of Angouran zinc and lead mine

IntroductionIncreasing demand for ore minerals needed for economic development and the desire to find a suitable rank in the international community has forced developing countries such as Iran employ more mining activities which has led to creation of a large amount of waste minerals. Given the existing equipment establishing the necessary situation and economic solutions for the exploitation of valuable elements from these waste minerals can be considered as a source for economic development of the country. The Angouran ZnPb mine is located west of the Zanjan province and northwest of the magmatic metamorphic SanandajSirjan zone. The wurtzite mineral can be used as an indicator mineral for trace elements such as IGG (indium, gallium, germanium) in this mine. The economic concentration of metal elements in the Angouran mine can be divided into two parts of sulfide and gangue carbonate. The sulfide part of this mine is enriched with silver, cadmium and selenium (higher than their cutoff grade) and the gangue carbonate part is enriched in arsenic element. The footwall schists show some concentration of elements which are related to sulfide mineralization.  Material and methodsMore than 30 rock samples were collected from cross sections in the openpit part of the Angouran mine which covers all different parts such as footwall schist, sulfide mineralization, carbonate mineralization and hangingwall carbonate (marble). About 30 samples were prepared for petrographic studies and geochemistry analysis which were analyzed at the Zarazma laboratory (Tehran, Iran). The ArcGIS, Geosoft Oasis Montaj and Excel software packages were also used for interpretation of data. Geology of the study areaThe Angouran ZnPb mine is located west of the Zanjan province and northwest of the magmatic metamorphic Sanandaj Sirjan zone. The rock units in the study area include footwall quartz schist and hangingwall marble with Precambrian age, Mesozoic diorite and granite, Cenozoic pyroclastic units such as white tuffs and Quaternary travertine sediments. It should be mentioned that the white tuffs and, in some cases older units are crosscut by younger diabetic sills and dikes (Ghorbani, 2008; Pirkharrati and Farhadi, 2014; Fallah et al., 2019). Results The Angouran deposit has been formed as breccia structure on the boundary between thrusted hangingwall marble and footwall quartz schist. According to this study, mineralization in the Angouran deposit has occurred during two hypogene and supergene stages. Hypogene mineralization in the Angouran deposit has been formed as successive phases of sulfide and carbonate. The hypogene mineralization continued by the formation of supergene mineralization. According to the geochemical analysis, a high concentration of trace elements such as silver, cadmium and selenium was detected in the Angouran deposit. These elements are concentrated in the sulfide ore mainly in the sphalerite mineral with poor lead minerals. The carbonate part of the Angouran mine which is considered to be waste contains enrichment of arsenic. The footwall schists are not enriched with trace elements and just concentrate in some elements such as iron, antimony, cadmium, cobalt and selenium, which are related to sulfide mineralization. Discussion Based on the geochemistry analysis and microscopic studies, the economic concentration of metal elements in the Angouran mine can be divided into two parts of sulfide and carbonate. The sulfide part of this mine has been enriched with silver, cadmium and selenium (higher than their cutoff grade) and the carbonate part has been enriched with arsenic. This element can be considered to be a major threat to human health, along with its numerous uses, such as pesticides, medicine, electronics, etc.The wide distribution of arsenic in the open pit mine along with the other toxic elements such as cadmium and selenium (mainly related to the sulfide mineralization and host quartz schist) are too dangerous for the villagers who live near the mine due to the seepage of these toxic elements to underground water aquifers and their surrounding environment. It should be mentioned that, in the Angouran mine, the waste minerals are abandoned as deserted mountains irrespective of their relationship to groundwater and the surrounding environment.It is hoped that with the continuation of the exploitation process in the Angouran mine, the waste minerals are classified according to their type and element enrichment in a suitable manner by environmental standards. This could help prevent seepage of toxic elements (As, Cd, Se) to groundwater. Furthermore, the economic elements such as Ag, Cd, Se can be used as byproducts and be sold as raw material for other uses or extracted by using the necessary equipment. This is due to the fact that what is considered to be waste minerals for a mine, can be considered as useful material for another mine, either now or in the future. AcknowledgementsThe authors are grateful for the financial support of the University of Zanjan and the Iran Minerals Production and Supply Company (Angouran leadzinc mine).  ReferencesFallah, M., Nabatian, Gh. and Ghadimi, S., 2019. Introduction of wurtzite mineral as trace metal elements potential in the Angouran ZnPb mine. 26th Symposium of Crystallography and Mineralogy of Iran (SCMI), Imam Khomeini International University, Qazvin, Iran. (in Persian with English abstract) Retrieved March 30, 2019 from http://www.cmsi.ir/UI/ArticleDetails?Lang=fa ArticleID=2043Ghorbani, M., 2008. Economic geology of natural and mineral resources of Iran. Pars Arian Zamin Publication, Tehran, 570 pp. (in Persian)Pirkharrati, H. and Farhadi, Kh., 2014. Investigating the potential of water and soil pollution in the Angouran lead and zinc mine area and providing solutions for crisis management. IMPASCO, Iran, Yazd, Report 1, pp. 55–76. (in Persian)