Hydrological and hydrogeochemical characteristics of neutral drainage from a waste rock test pile

• Main Author: Bay, Daniel S.
• Format: Others
• Language: English
• Published: University of British Columbia 2009
• Online Access: http://hdl.handle.net/2429/12473

In 2005 the University of British Columbia, Teck’s Applied Research & Technology (ART) group and Compañía Minera Antamina S.A. initiated a collaborative study to improve the hydrological, geochemical, mineralogical and biological understanding of mine waste rock. The site of the investigation is the Antamina mine, Peru, which consists of a polymetallic Cu-Zn-skarn deposit that produces high carbonate-content waste rock and typically leads to pH-neutral effluent waters. One component of this study is the construction of five 36 m x 36 m x 10 m (high) waste rock piles upon an impermeable HDPE liner placed to capture and monitor the quality and quantity of all infiltrating water. The first test pile was constructed in 2006 and consists of relatively course, heterogenous marble and hornfels waste rock material that may produce moderately- to poor-quality drainage according to the classification scheme used at the mine. A comprehensive network of instrumentation measures the in-situ temperature and moisture content, and allows the extraction of fluid samples from within the pile. The objective of this thesis is to analyze the hydrological and geochemical data collected from test pile 1 during the initial 21 months of pile operation between January-2007 and October-2008. Results indicate that flow and chemistry exhibit strong spatial and seasonal patterns. Seasonal patterns are driven by the wet season rains that deposit a majority of the annual rainfall over 7 months, and spatial patterns are likely controlled by rock-type heterogeneity and variability in flow path length and residence time that result from the end-dump construction process. Test pile 1 took 3 – 4 months to wet up, and the maximum pile outflow measured during the wet season is nearly 15 m³/day. Water balance calculations indicate that 41 % of precipitation reports as outflow while 59 % evaporates over the course of one water year. Effluent water is pH-neutral (pH = 7 - 8.5), with seasonally varying SO₄ (500 – 2000 mg/L) and Zn (0.5 – 2.5 mg/L) concentrations. Based on the maximum calculated SO₄ and Zn loading rates of 4 – 6 and 0.003 – 0.005 mg/kg/week, respectively, nearly 0.4 % of the total initial solid phase sulphur has been depleted, whereas only 0.01 % of the total initial solid phase Zn has been depleted. Waste rock reactivity appears to be declining with time. === Science, Faculty of === Earth, Ocean and Atmospheric Sciences, Department of === Graduate