Küre volkanojenik masif sülfid yataklarının jeokimyasal karakterizasyonu ve asit maden drenajı üretme potansiyelinin kestirmi

Base metals have an irrevocable place in any branch of industry. With emerging technologies and progressively depleting reserves, metal demand is increasing along with piles of waste material produced after mining activities of the low-grade ores. Considering the base metal need is mostly supplied from volcanogenic massive sulfide deposits; areas surrounding those mining sites are vulnerable to inevitable environmental hazards like acid mine drainage (AMD). AMD is one of the biggest and widespread environmental problems related to mining. AMD occurs due to the oxidation of the sulfur moiety of sulfidic ore deposits and result in acidic water with low pH <3 and heavy metals. Diverse chemical and biological processes co-occur during generation of AMD and the fate of heavy metals in resulting aquatic or solid phases is largely controlled by Fe oxidation. Therefore, elucidating those complex biogeochemical reactions controlled by unique geochemical, mineralogical and lithological features of an ore deposit is a crucial step for prevention and rehabilitation of AMD. Located in the Kastamonu province of western Black Sea region of Turkey, the Küre VMS deposits hosts one of the most important and productive copper mines of Turkey. The area is a good example of ancient mining activities carried out by Genoese and Byzantines and/or the Ottoman Empire (400 to 1000 years ago) in Turkey. Because of its historical mining past, Küre VSM deposits set a great example to investigate mechanism of AMD generation and fate of heavy metals in mining impacted areas. Therefore, potential sources and acid generating potential of Küre VMS deposits were investigated for the first time with an integrated approach-involving laboratory and field based studies. For this purpose, ore, ore bearing wall rocks, basalts and waste materials were collected during the field studies and subjected to geochemical analyses and to static AMD prediction tests. AMD prediction tests applied in this study involve paste pH, initial neutralization potential, standard acid-base accounting and net acid generation to determine acid producing or neutralizing potentials of the materials. In addition to AMD prediction tests, the long-term comparative bioleaching characteristics of Küre's massive pyritic copper ore were investigated under various environmental conditions. The generation of AMD was simulated at 26oC and leaching characteristics of pure Acidithiobacillus ferrooxidans and a mixed culture of Acidithiobacillus sp. were comparatively investigated at 26oC and 40oC. Finally, the results of AMD prediction tests and laboratory leaching experiments were combined with the field data containing the water chemistry of groundwater, surface and drinking water in addition to mineralogical data involving bulk chemistry of relevant streambed sediment and secondary precipitates. All these results were used to discuss how acidic waters were generated and to what extend affected the aquatic environment around the mining area. AMD prediction test results were used to classify and evaluate acid production potential of the ore, ore bearing wall rocks, wall rock and precipitate from waste ponds. The net neutralization potential (NNP), neutralization potential ratio (NPR), acid production potential (AP), neutralization potential (NP) and net acid generating (NAG) values of the ore represent the upper limit values for the region. The lowest NNP (-1617.8), NP (-217.5) values with the highest AP (1400.3), maximum potential acidity (MPA) (1371.2) and NAG (206.5) values calculated for the ore sample indicate good consistency in different methods. Following the ore sample, highest acid production was determined in the waste effluent (or flotation tailings) dam precipitate (WEP) (974.03), ore bearing wall rocks (OBR-1) rich in disseminated pyrite (75.94) and basalt (B) samples referenced to wall rocks (129.6). The ore bearing wall rocks (OBR-2 and OBR-3) containing minor amounts of covellite, chalcocite and pyrite are classified as non-acid producer indicating significance of sulfide mineralogy on acid production. In general, there is good consistency between the results of ABA and NAG tests for the samples. From the ABA and NAG tests applied in the current study, it is concluded that in addition to the ore, ore bearing wall rocks that can be considered as waste and containing particularly disseminated pyrite, contribute more towards acid generation in the region. WEP also have a high acid production potential with an elevated level of toxic metals and precaution should be taken to prevent possible leakage to the environment. Consistency in results from both ABA and NAG tests justify that static tests can be used as tools for preliminary evaluation of prospective AMD generation and its impact on surface and groundwater quality in VMS mining environments. Results of bioleaching experiments indicate that mixed acidophilic cultures containing iron and sulfur oxidizers leached the massive ore faster rate than pure culture and produced significant amount of acidity (down to pH 1.26). These results suggest that microbial reactions are the major source for acid generation in the mining area. In the early stages of AMD generation, release of Co (max. 9.37 ppm) and Cu (max. 871.4 ppm) into the water were controlled by pure culture of Acidithiobacillus ferrooxidans, whereas Zn (max. 201 ppm) and Fe (max. 1810 pm) release were faster in the experiments carried out by mixed Acidithiobacillus sp. During the bioleaching experiments, due to calculated percentile leaching ratios, A. ferrooxidans was found to be more effective in the leaching of Cu (31.46%), Fe (5.97%) and Co (5.42%) at higher temperatures in contrast to mixed acidophiles that are more active at optimal moderate conditions. Formation of secondary Fe-oxyhydrooxides (e.g. jarosite) were determined in the biological experiments. Significant decrease in Co, Cu and Zn concentration in the later stage of AMD generation were attributed to the co-precipitation of the respected metals with Fe oxides phases. Leaching of massive ore revealed that release of Fe, Cu, Co and Zn during the short term experiments (34 days) were generally due to the rapid bacterial oxidation unlike the long-term experiments (180 days). In the long-term experiments, more complex biogeochemical reactions such as Fe-oxidation and precipitation took place together and regulated the release and precipitation of those metals. Results obtained from geochemical and mineralogical studies on water, sediment, ochre precipitate in addition to AMD prediction tests carried on the ore, ore bearing wall rocks showed that massive ore and ore bearing wall rocks are the major sources of acidity and heavy metals. Consistent with this, acid production potential of massive pyritic chalcopyrite ore representing the maximum acid production rate in the region is about 1400 tons of acidity per ton of ore with a net acidity about 206 kg H2SO4 per a ton of ore. High concentrations of Cu (up to 40.41 ppm), Zn (up to 9.94 ppm), Fe (up to 19.6 ppm), Mn (up to 30.5 ppm) and Co (up to 7.6 ppm) determined in the surface and groundwater with low pH values (pH 2.9-4.5) indicate AMD generation in the field. Ochre chemistry and mineralogy showed that, major proportions of metals released from the ore and ore bearing rocks were precipitated and transported with secondary iron hydroxide, iron hydroxysulfate and aluminum hydroxide minerals. Moreover, combined XRD and SEM-EDS measurements also revealed the abundance of clay minerals (mainly clinochlore and illite) and secondary metal-bearing (Zn and Sr) silicate phases, which points out the importance of the stability of clay minerals in the transport, release or mobility of metals (mainly Fe, Al, Zn and Sr) in AMD systems.