**Geochemical Application for Environmental Monitoring and Metal Mining Management**

### Chakkaphan Sutthirat1, 2

*1Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok, 2Center of Excellence for Environmental and Hazardous Waste Management (NCE-EHWM), Chulalongkorn University, Bangkok, Thailand* 

#### **1. Introduction**

90 Environmental Monitoring

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Metal mines have been increasing continuously due to high growth rate of population and rapid development of industry throughout the world. Various kinds of metal ores are supplied into industries. Precious metals such as gold, platinum and silver have been utilized for ornamental purposes due to their beauty, rarity and durability whereas industrial ores are demanded by many sectors. These ores usually occur in different geological conditions which lead to diversity of depositional characteristics. Multiple elements occur naturally in the same mineral deposits; some of these elements, particularly heavy metals, may in turn have potential impact to the environment. Therefore, heavy metals are the most crucial aspects for toxicity. However, these metals have several chemical binding forms which just a few forms appear to contaminate environment.

Moreover, Acid Mine Drainage (AMD) is another environmental concern. AMD appears to have been accelerated during mining processes when metal sulfides in mineralized rocks and solid wastes are exposed to oxygen and water allowing rapid oxidizing reaction. Oxidation of metal sulfide has potential to produce sulfate which may turn into sulfuric acid. Subsequently, it may be dissolved by rain and leading to acidity drainage. AMD can also cause heavy metal leaching from waste rock and tailings; consequently, some toxic metals (e.g., lead, zinc, copper, arsenic, selenium, mercury and cadmium) may contaminate runoff and groundwater. AMD with high metal concentrations may in turn yield severe toxicological effects on aquatic ecosystems. Biota will be affected primarily and subsequently toxic levels would be increased through food chain. Although, some heavy metals such as copper and zinc are required with small quantities for normal metabolism, their high concentrations become toxic and can cause malfunctioning of human organs.

Geochemical exploration has been carried out by mining geologists for investigation and evaluation of mineral deposit, metal ore in particular. It can also be applied to environmental impact assessments and monitoring. Moreover, mineralogical and chemical characteristics are one among many scientific tools that will lead to identification of potential sources of such problems. Appropriate prevention and mining plans can be designed based on these data. Unfortunately, most mining geologists always apply geochemistry for exploration and mining without concern of environmental impacts; on the other hand, most environmental scientists have little knowledge on geology and mining

Geochemical Application for Environmental Monitoring and Metal Mining Management 93

*Waste Rocks:* Large amount of waste rocks may have been removed from mining site, particularly for quarrying and excavation, to access to the ore body. These waste rocks are eventually remained in the site and surrounding areas after the mining end (see Fig. 1). Subsequently, they may become sources of environmental impacts. Although, mining design can reduce quantity of waste rocks; for example, mining excavation generates very less amount of waste rocks in comparison with open-pit mining. Geologic setting and ore formation are however the main factor for the mine planning; the open-pit mine may be economically more suitable in many cases. Besides, some waste rocks can be used for construction within the mining site; however, they must be tested prior to appropriate

Various types of waste rocks situated within ore deposits usually have different compositions that would be characterized for both mineralogical and geochemical constituents. Apart from heavy metals contained in these rocks, Acid Mine Drainage (AMD), a potential threat, may be activated and lasted for long period of time. AMD actually lowers pH of water; subsequently, the low pH drainage may flow over waste dumps including waste rocks and tailings and may in turn leach some heavy metals and contaminate surrounding area. Surface water and ground water would be crucial pathways of such contamination to ecosystem and food chain. However, most of these threats can be protected and prevented by good environmental management and

*Tailings:* During the mineral processing (dressing), ore minerals and their host rocks have to be ground and milled prior to separation; besides, chemical additives may be added during the processes. Although, most of these chemicals are usually recovered and reused in the process, some of them may still remain in these tailings. Some chemical additives can be decomposed naturally within short period but many of them may be bound strongly and long lasted within the tailings. Moreover, these tailings may contain concentrate noneconomic minerals such as silicates, oxides, hydroxides, carbonates and sulfide that have never been collected throughout the dressing process. Therefore, these modified ingredients may partly be toxic and harm ecosystem. Tailings are similar to slurry, a mixture of fine-

grained sediment and water that have been disposed into tailing pond (see Fig. 2).

Fig. 1. Huge amount of rock waste generated from a gold mine in Thailand: left photo is waste dumping site; right photo shows placing process based on geochemical properties of

utilization. Otherwise, unexpected threats may occur.

monitoring plans.

each type of waste rock

materials, mining designs and processes. Environmental protection should be carefully planned in order to eliminate and/or minimize any short- and long-term environmental impacts that may occur. Otherwise, serious problems may occur that may be very difficult to remediate and extremely cost enormously.

This chapter will review standard procedures for evaluation of AMD potential of rock waste and tailing generated from mining activity. Digestion techniques for analysis of heavy metals are also considered to give basic knowledge for environmental monitoring and impact assessment. Some cases studies in Thailand will be given for better understanding.
