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

Increasing 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 Zn-Pb mine is located west of the Zanjan province and northwest of the magmatic- metamorphic Sanandaj-Sirjan 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 cut-off grade) and the gangue carbonate part is enriched in arsenic element. The foot-wall schists show some concentration of elements which are related to sulfide mineralization.

More than 30 rock samples were collected from cross sections in the open-pit part of the Angouran mine which covers all different parts such as foot-wall schist, sulfide mineralization, carbonate mineralization and hanging-wall 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 area:

The Angouran Zn-Pb 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 foot-wall quartz schist and hanging-wall 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).

The Angouran deposit has been formed as breccia structure on the boundary between thrusted hanging-wall marble and foot-wall 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 foot-wall 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.

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 cut-off 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.