The Nature of Fluids in Hydrothermal Copper and Molybdenum Ore Deposits - An experimental and analytical study
- The evolution of magmatic-hydrothermal fluids in porphyry Cu and porphyry Mo deposits was studied using synthetic and natural fluid inclusions by optical microscopy, microthermometry, Raman spectroscopy, and LA-ICP-MS.
The partitioning of Cu between vapor and brine in aqueous NaCl-S ± KCl ± FeCl2-rich fluids was investigated by means of hydrothermal experiments in rapid quench autoclaves at 600-800°C, 70-130 MPa and at both oxidizing and reducing fO2, covering all geologically relevant conditions. Resulting partition coefficients (DCuvap/brine) are between 0.2 and 0.4 for the range of studied S-concentrations, fluid pH, fO2, and P-T conditions. These values indicate that Cu does not partition into the vapor phase at any plausible condition in contrast to data from natural quartz-hosted vapor and brine inclusions which appear to indicate Cu enrichment in the vapor.
The formation of such Cu-rich vapor-type fluid inclusions was investigated in hydrothermal re-equilibration experiments. For this purpose, coexisting vapor and brine inclusions of known composition were re-equilibrated in a fluid of slightly different composition and lower pH than the trapped one at 800°C, 70-130 MPa. This procedure led to a dramatic increase in Cu concentrations in the vapor phase from 0.3 ± 0.03 to 5.7 ± 3.3 wt% after re-equilibration and the change of DCuvap/brine from a true value of 0.4 ± 0.05 to an apparent value of 8.3 ± 4.9. This post-entrapment modification can be traced back to the difference in fluid pH between the trapped and the surrounding fluid, inducing diffusion of H+ out of the inclusion and the diffusion of Cu+ (and Na+, Ag+) into the inclusion in order to maintain charge balance. Moreover, the presence of larger amounts of S within vapor inclusions as compared to brine inclusions can bind larger amounts of Cu. The re-equilibration of trails of vapor and brine inclusions in a natural quartz sample in a fluid similar to the trapped one, yet more acidic, showed that this modification process can be reversed, resulting in the loss of major amounts of Cu from natural vapor inclusions.
The composition of metal-bearing melts and magmatic fluids of Mo-mineralized granites resembling porphyry Mo deposits was investigated using natural melt-, fluid-, and solid-inclusions in quartz crystals found in miarolitic cavities from minor Mo-occurrences in Colorado and Norway. Melt inclusions from the Treasure Mountain Dome are highly enriched in Mo (4-43 ppm), also melt inclusions from the Drammen and Glitrevann granites (5-32 ppm, and 12 ppm, respectively), resembling highly fractionated melts. Copper concentrations are low (<1-30 ppm) in the melts, but high in the fluids: intermediate density, supercritical fluid inclusions of these three locations host 6-1900 ppm, 8-3500 ppm, and 5-180 ppm Cu, respectively. The comparison of these results with data from economic porphyry Mo and porphyry Cu (Mo, Au) deposits shows no difference in Mo concentrations in the particular melts and fluids. Hence, other factors probably control the evolution of a granitic intrusion into large, economic Mo deposits, minor Mo occurrences, or just into barren plutons. These may be mainly the size, position, and geometry of the parental magma chamber, the multiplicity of intrusions maintaining a constant flux of metalliferous, S-rich, hot melts, and the extent of fluid focusing within small rock volumes forming high-grade ore shells.
Copper exposure of freshwater mussels (Anodonta anatina): Some physiological effects
Andhika Puspito Nugroho
- Copper (Cu), a transition metal, has the tendency to increase in its concentration in freshwater ecosystems over natural levels, due to industrial and other anthropogenic sources. In water, copper can exist in dissolved form or associated with suspended food particles. Freshwater mussels living at the interface of the free-flowing water and the sediment phase can take up copper directly from the water or by consumption of lower trophic level organisms laden with copper. For mussels, copper is essential at low concentration as cofactor of metalloenzymes involved in growth regulation and development, but it may be toxic at higher levels by disturbing calcium (Ca) homeostasis. The duck mussel Anodonta anatina is a freshwater species found in abundance in limnic and lotic European ecosystems and is used as test organism in ecotoxicological studies. The potential involvement of Cu in the general decline of many European freshwater mussel species is the major motivation for this work. This research aims to study the relevance of Cu exposure pathways on its uptake, distribution, bioaccumulation, and elimination in the freshwater mussel A. anatina and its various potential physiological impacts. The work is started with raising Cu-loaded algae using the stable isotope 63Cu as marker for feeding of mussels without affecting the nutritional value of the algal food. In these latter experiments, mussels are exposed to 63Cu via water or via food to investigate the relative importance of Cu uptake to its distribution and accumulation among the mussel’s organs. Its consequences on calcium homeostasis, soluble carbohydrate and protein levels in various tissues, metallothionein induction, glutathione levels, activities of antioxidative enzymes and glutathione reductase, and on lipid peroxidation are examined. In the algal experiment, Parachlorella kessleri is grown at six 63Cu concentrations (0, 5.9, 11.7, 23.5, 47, and 94 µmol L-1) for 4 days, starting from day 3. When exposed to Cu at a level of up to 6 µmol L-1, P. kessleri is largely unchanged in its nutritional values; so this concentration is used to grow 63Cu-carrying food for mussel experiment. Concentrations above 6 µmol L-1 decrease significantly in the algal growth and alter the other physiological parameters. Three groups of 21 mussels each are used, one as control and two for exposure, receiving copper as the stable isotope 63Cu via the water at 0.3 µmol L-1 or via the food (1.5 mg L-1 freeze-dried Cu-loaded algae, equivalent to 0.06 µmol L-1 Cu) for 24 days, followed by 12 days of depuration. For analysis, three mussels each are taken randomly from every group at days 0, 6, 12, 18, 24, 30, and 36. The mussels are anaesthetized and hemolymph and extrapallial fluid are sampled before the mussels are dissected into gills, mantle, kidney, digestive gland, foot, adductors, intestines, and the remainder (gonads, heart, and labial palps). During copper exposure, the levels of exogenous copper (63Cu) and total Cu increase in all body compartments. Uptake via the water leads to higher Cu levels than via the food, but in relative terms food uptake is more efficient taking the five-fold lower nominal concentration of copper into consideration. Upon exposure via the water, the metal is compartmentalized mainly in the mantle, the gills, and the digestive gland, upon exposure via the food the major recipients are the digestive gland and the intestines. Upon depuration for two weeks, copper is quickly but not completely eliminated. Simultaneously with increasing Cu levels, Ca levels are increased in all body compartments, accompanied by decreases in soluble carbohydrates and proteins in the gills, mantle, digestive gland, and kidney. At the same time, Cu exposure results in increases in malondialdehyde levels, decreases in glutathione levels, strong increases in metallothionein levels, and changes in the activities of the antioxidative enzymes superoxide dismutase, catalase, and glutathione peroxidise, and of glutathione reductase in the gills, mantle, digestive gland, and kidney. During depuration, most parameters tend to normalize but do not return to control values. In conclusion, the overall pictures suggest that the considerable physiological stress elicited by low-level copper exposure may contribute to the factors involved in the decline of many European freshwater mussels.