Sulfur analyses and mineralogical data in the preliminary mine waste characterization.

The objective of this study was to investigate the use of the acid production potential (AP) calculation factor and seven different S analysis methods in the preliminary mine waste characterization by analyzing and comparing 48 Finnish mine waste samples. Special attention was paid on mineralogical aspects and data produced in the exploration phase of a mining project.According to our results, the abundance of sulfide species other than pyrite in Finnish mine waste suggests that the factor to calculate the AP should be considered based on mineralogy and would often be below 31.25. Therefore, the mineralogy-based determination of S should be preferred. However, the determination of S based on scanning electron microscope (SEM) mineralogy includes some uncertainties. Underestimation of S content may appear if not all S-bearing mineral particles have been detected, or if the amount of S is low in general. This uncertainty appears to be especially related to the samples containing elevated (> 9 wt%) amounts of serpentine, diopside, augite, and/or hornblende. Risk of overestimating AP is related to samples containing high amounts (> 4.13 wt%) of S-bearing minerals. These uncertainties can be reduced by inspecting that the SEM mineralogy-based S concentrations are in line with the energy dispersive X-ray spectrometer data. The aqua regia extractable S concentrations, which are often available in the exploration phase, appeared to be usable in the preliminary waste rock AP assessment and often comparable with the analytical total S values in the Finnish waste rock samples, especially when the samples did not contain any sulfate minerals. In contrast, the analytical sulfide S and the X-ray fluorescence methods may lead to an underestimation of AP.

Comparison of static and mineralogical ARD prediction methods in the Nordic environment.

Acid rock drainage (ARD) is a major problem related to the management of mining wastes, especially concerning deposits containing sulphide minerals. Commonly used tests for ARD prediction include acid-base accounting (ABA) tests and the net acid generation (NAG) test. Since drainage quality largely depends on the ratio and quality of acid-producing and neutralising minerals, mineralogical calculations could also be used for ARD prediction. In this study, several Finnish waste rock sites were investigated and the performance of different static ARD test methods was evaluated and compared. At the target mine sites, pyrrhotite was the main mineral contributing to acid production (AP). Silicate minerals were the main contributors to the neutralisation potential (NP) at 60% of the investigated mine sites. Since silicate minerals appear to have a significant role in ARD generation at Finnish mine waste sites, the behaviour of these minerals should be more thoroughly investigated, especially in relation to the acid produced by pyrrhotite oxidation. In general, the NP of silicate minerals appears to be underestimated by laboratory measurements. For example, in the NAG test, the slower-reacting NP-contributing minerals might require a longer time to react than is specified in the currently used method. The results suggest that ARD prediction based on SEM mineralogical calculations is at least as accurate as the commonly used static laboratory methods.

U-Pb geochronology and Hf isotope data from the Late Cretaceous Mawat ophiolite, NE Iraq.

The Mawat ophiolite, NE Iraq, is one of the Neo-Tethyan ophiolites within the Iraqi Zagros orogen. It consists of many metre-to kilometre-sized tectonic slices of serpentinized dunite, peridotite, gabbro, basaltic rocks and associated oceanic metasediments. Felsic intrusions crosscut the ophiolite. We present U-Pb zircon and monazite ages and Hf zircon isotopes from two crosscutting felsic dykes and a gabbro from the mantle section of the ophiolite. Zircons from the felsic dykes contain spongy domains and xenotime and monazite inclusions. They give ages from 222 to 46 Ma. The age range is interpreted to be caused by secondary processes such as radiogenic Pb mobility and Pb loss. The monazite age of 94.6 ± 1.2 Ma is considered to give a crystallisation age of the felsic dykes. The gabbro zircons give ages between 81 to 38 Ma of which the two oldest grains give the weighted average age of 81.2 ± 2.5 Ma which we interpret to be the crystallisation age of the gabbro. The zircon initial εHf values in the felsic dykes are negative (averages -2.7 and -3.1) while they in the gabbro are positive (average + 3.5), indicating that the felsic magma comes from an older source while the mafic magma comes from a juvenile one. Two mafic units of different ages were identified: the older unit is cut by the 95 Ma felsic dykes and the younger one is represented by the 81 Ma gabbro located within a thrust zone. The youngest ages of 40 Ma are considered to be related to crustal extension.

Multidisciplinary analysis of Finnish esker sediment in radon source identification.

In order to define the naturally-occurring radioactive materials that are the source of radon in natural environments, a comprehensive analytical (geochemical, physical and chemical) methodology was employed to study sand samples from the Hollola esker in the city of Hollola (Lahti area, Finland). Techniques such as gamma-spectrometry, emanation measurements, sequential chemical extraction, scanning electron microscopy (SEM), electron probe microanalyses (EPMA) and inductively-coupled plasma mass spectrometry (ICP-MS) were used to determine the potential source of radon. Monazite and xenotime, uranium- and thorium-bearing minerals and potential radon sources, occurred in significant amounts in the samples and were also the main reason for the distribution of uranium and thereby radium in separate grain-size fractions. Following deposition, the esker sand has been exposed to no significant weathering, and radium has not therefore been much separated from uranium. However, considering its non-compatibility with crystal lattices, it was recognized rather in easily leachable species (44% of the total (226)Ra) than uranium (21% of the total (238)U) in our analyses. The smallest grain-size fraction of the esker sand had a higher emanation power (0.24) than the other fractions (around 0.17). Due to the small relative proportion of this fraction, however, it contributed only slightly to the total emanation (4%). The emanation power of the leachable species was about three times higher (ca. 0.20) than that of the species tightly bound to the crystal lattice (ca. 0.07).