Scholarly record

ACID ROCK DRAINAGE PREDICTION FOR HOST ROCKS OF PORPHYRY COPPER DEPOSITS IN THE BAIMKA ORE TREND (STATIC AND KINETIC TESTS)

Daria Yablonskaya

Abstract

One of the main problems in the exploration of porphyry copper deposits is the process of acid rock drainage and metal leaching (ARD/ML), that develops during storage enclosing rock in a dump. ARD/ML is formed by the natural oxidation of sulfide minerals exposed to air and water. It leads to the production of acidic, sulfate waters and results in the heavy-metal contamination of surface and ground natural water. Standard procedures for the evaluation of waste rocks ARD/ML potential are static and kinetic tests. Static tests are used as a screening tool in the ARD prediction and include: 1) acid-base accounting (ABA) test as base; 2) multistage net acid generation (NAG) test; 3) short-term leach test that definition readily soluble components of rocks. Kinetic test (Humidity Cell Test) is used to predict long-term weathering rates and to estimate the lag time to the starting of acid generation. This study for the ARD prediction for host rocks of porphyry copper system deposits situated in the Baimka ore trend, Western Chukotka, Russia. 25 samples of enclosing rocks were collected for static tests and 3 of them (by received static tests results) for kinetic test. The mineralogy of samples was determined by scanning electron microscopy (SEM) and powder X-ray diffraction (XRPD). Trace elements were obtained by portable energy dispersive X-ray fluorescence (EDXRF) using Niton FXL-950 and inductively coupled plasma atomic emission spectrometry (ICP-AES). Content of metals in tests solutions were analyzed using inductively coupled plasma mass spectrometry (ICP-MS). All tested samples were classified as potentially acid-generating (PAG) based on the Neutralizing Potential Ratio (NPR), detected by results of static tests. But in the long-term period (30 weeks) there are no signs of acid formation: acidity (pH) of weekly leachates varies in the near neutral range (6.9-7.7).

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