Fuchun Li

Citrobacter sp. strain GW-M Mediates the Coexistence of Carbonate Minerals with Various Morphologies

To better understand the formation mechanism of carbonate minerals by microbes, culture experiments with a duration of 70 days were performed under the mediation of strain GW-M isolated from soil using modified Lagoa Vermelha (LV, a hypersaline coastal Lagoon, Rio de Janeiro, Brazil) medium with 6:1 Mg/Ca molar ratio. The results demonstrated that strain GW-M can mediate the formations of both high-Mg calcite and aragonite and that dumbbell-, cauliflower-, rhombohedra-shaped, and irregular minerals coexist in the modified LV medium. The amount of rhombohedra-shaped crystals increased significantly with culture time. A proposed mechanism for these formations is the following. Heterogeneous nucleation on the surface of the extracellular polymeric substances (EPS) always occurred, and carbonates with irregular shape existed in experimental products at any stages. The morphologies evolved from rod to dumbbell and finally to cauliflower. At the initial stage (till day 20), hydrogen ions and EPS secreted by the bacteria only influenced the microenvironment around the cells, and carbonates were precipitated on the surface of bacterial cells. At the middle and late stages (on days 45 and 70), microbes and their secretions influenced the whole medium. Under these conditions, rhombohedra-shaped crystals were formed when homogeneous nucleation occurred. In addition, the results of energy-dispersive spectrometry (EDS) showed that Mg contents in the synthesized carbonate minerals with rhombohedra-shaped were significantly lower than those of carbonates with other shapes, though relationship between morphology and species of mineral cannot be obtained by this phenomenon alone. These results shed further light on the mechanism of carbonate precipitation in the presence of microbes.

Two origins of illite at the Dexing porphyry Cu deposit, East China: Implications for ore-forming fluid constraint on illite crystallinity

Illite is a distinctive clay mineral formed by K alteration within hydrothermal alteration zones in porphyry Cu deposits. Based on differences in spatial distribution, Kübler index, number of swelling layers, and polytype, two kinds of illite are recognized within the Dexing porphyry Cu deposit, East China. One is a hydrothermal mineral within hydrothermally-altered granodiorite porphyry and altered tuffaceous phyllite near the contact zone with the granodiorite porphyry cupola. The hydrothermal illite is formed by illitization of plagioclase and/or micas during hydrothermal fluid-rock interaction. The considerable variation of their higher Kübler indices (0.17–1.41°Δ2θ) with swelling layer is affected by fluid/rock ratio or fluid flux. The other type of illite is a product of low-grade metamorphism within tuffaceous phyllite away from the porphyry cupola (>2 km), and has a lower Kübler index (0.06–0.13°Δ2θ), a 2M1 polytype, and no swelling layers. We suggest that, within the mineralized alteration zone, the lower the Kübler index, the stronger the degree of alteration, and the higher the copper grade. This is caused by a higher fluid/rock ratio in the middle-upper portions of the contact zone.

Arthrobacter Sp. Strain MF-2 Induces High-Mg Calcite Formation: Mechanism and Implications for Carbon Fixation

ABSTRACT To better understand the mechanism of formation of carbonate minerals by microbes, culture experiments with Arthrobacter sp. strain MF-2 were carried out using M2 medium without carbonate ions for 50 days. A series of sterile control experiments without bacteria were run simultaneously. During the incubation, cell density, the quantity of precipitate, the extracellular polysaccharide (EPS) content, the activity of carbonic anhydrase (CA), the low molecular weight organic acid concentration, the pH, the electrical conductivity, and the Ca2+ and Mg2+ concentrations of the medium were determined. The morphologies of the precipitated carbonates were observed using scanning electron microscopy, and their mineral species were determined by X-ray diffraction. The results demonstrated that the quantity of precipitate in the biotic experiments increased gradually with the incubation time; precipitate was not obtained in the abiotic experiments. The average precipitation rate correlated positively with the cell density and the EPS content, with r = 0.64 and 0.61, respectively. This suggests that bacterial cells and EPS effected carbonate precipitation. Carbonate ion incorporation into minerals results from carbon dioxide hydration, promoted by microbial secretion of CA by bacteria. These findings contribute to the ongoing search for feasible mechanisms for the sequestration of carbon dioxide in the subsurface, in this case mediated by microorganisms.

Stratigraphy and otolith microchemistry of the naked carp Gymnocypris przewalskii (Kessler) and their indication for water level of Lake Qinghai during the Ming Dynasty of China

Otoliths are biogenic carbonate minerals in the inner ear of teleost fish, whose compositions can record the physical and chemical conditions of the ambient water environment inhabited by individual fish. In this research, the fishbones and otoliths of naked carp sampled near the Bird Island, offshore Lake Qinghai, were dated and analyzed for mineralogy and microchemical compositions. Comparing the microchemical compositions of ancient otoliths with those of modern otoliths, we conclude that the ancient naked carps inhabited a relict lake formed when the lake shrank from a high lake level, by combining with the AMS-14C ages of fishbones and otoliths, the stratigraphy and surrounding topography of the sample site. AMS-14C dating results of ancient fishbones and otoliths show that these naked carps lived from 680 to 300 years ago, i.e. during the Ming Dynasty of China. The X-ray diffraction (XRD) patterns demonstrate that the ancient lapillus is composed of pure aragonite, identical to modern one, indicating that the mineral of lapillus didn’t change after a long time burial and that the ancient lapillus is suitable for comparative analysis thereafter. Microchemical results show that both ratios of Mg/Ca ((70.12±18.50)×10−5) and δ18O ((1.76±1.03)‰) of ancient lapilli are significantly higher than those of modern lapilli (average Mg/Ca=(3.11±0.41)× 10−5 and δ18O=(−4.82±0.96)‰). This reflects that the relict water body in which the ancient naked carp lived during the Ming Dynasty was characterized by higher Mg/Ca and δ18O ratios than modern Lake Qinghai, resulting from strong evaporation after being isolated from the main lake, similar to today’s Lake Gahai. Based upon the stratigraphy and altitude of naked carp remains, it can be inferred that the altitude of lake level of Lake Qinghai reached at least 3202 m with a lake area of 4480 km2 during the Ming Dynasty, approximately ∼5% larger than it is today.

Mineralogy of the otoliths of naked carp Gymnocypris przewalskii (Kessler) from Lake Qinghai and its Sr/Ca potential implications for migratory pattern

Otoliths are biogenic carbonate minerals whose microstructure and microchemistry have been used for age determination, stock identification, life history and environmental tracing. Using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, we have determined the mineral types and crystalline characteristics of three pairs of otoliths from naked carp Gymnocypris przewalskii, the predominant fish in Lake Qinghai. The results indicate that the mineral of both lapillus and sagitta of the naked carp is aragonite, and that of asteriscus is vaterite. The aragonite of lapillus has prefect crystallization. Given the shape of lapillus and the sensitivity of its aragonite to water chemistry, lapillus was used to analyze temporal Sr/Ca ratios along the maximal growth axis by an electron probe microanalyzer (EPMA). Consistent variations of Sr/Ca ratios with a range of 1.0×10−3–5.0×10⃛ on the long and short radii indicate that Sr/Ca ratios of lapillus potentially respond to the chemical compositions of the host waters during the period of the naked carp’s growth and migration. Discontinuous (dark) zones of lapillus were formed during fall and winter when the naked carp grows slowly in Lake Qinghai, resulting in similar low Sr/Ca ratios to lake water, whereas incremental zones with higher Sr/Ca ratios respond to its migratory river waters during spring and summer. Various Sr/Ca ratios of incremental zones suggest that the migratory pattern of the naked carp may be much more flexible, rather than in a single river. Therefore, high-resolution otolith microchemistry of the naked carp can be used to trace its migratory behavior, which is of significance for determining its migratory pattern and life history of this precious species inhabiting the Tibetan Plateau.

The Roles of Mg over the Precipitation of Carbonate and Morphological Formation in the Presence of Arthrobacter sp. Strain MF-2

ABSTRACT Microbial mineralization of carbonate is a research subject widely studied in the past decades. The magnesium ions (Mg2+), present in water systems, are a key determinant in biomineralization process of carbonate and they are widely found in calcium-based biominerals as an accessory component. However, the crystallization mechanism and morphological change of carbonate polymorphs in the presence of Mg2+ ions has not been clarified sufficiently. In this report, a series of culture experiments were performed for 50 days using the Arthrobacter sp. strain MF-2 in a M2 culture medium using Mg/Ca molar ratios (R) of 0, 1.5, 3, 6, 9, and 12 in solution. And the roles of Mg2+ ions on the crystal growth and morphological change of biogenic carbonate were investigated. Experimental results show: (1) MF-2 could induce aragonite, high-Mg calcite, and Ca-dolomite formation in M2 culture media with different R values. The increased stability of amorphous calcium carbonate suggests Mg2+ ions inhibit carbonate crystallization. (2) The mineral morphologies were varied (rod-shaped, dumbbell-shaped, cauliflower-like, spherical, etc.) in the medium with R = 1.5, but they became simple (spherical and lamellar) in high Mg2+ concentrations (Mg > 0.15 M, R > 3). (3) The increased ionic strength of Mg2+ ions in the environment has an influence on the polymorphs and morphologies of carbonate formed by controlling the metabolism of strain MF-2 and the activity of carbonic anhydrase.

Origin of Illites at Dexing Porphyry Copper Deposit, Jiangxi Province, East China: Implications for Alteration Zoning and Ore-Forming Fluid Evolution

According to differences in features of illites including spatial distribution, crystallinity index, volume of swelling layer, polytype and relationship between its index and copper grade, two typical kinds of illite can be classified within the Tongchang porphyry copper deposit, Dexing County, East China. One is a kind of hydrothermally altered minerals within the hydrothermal alteration zone, including altered granodiorite-porphyry and altered metamorphic tuffaceous phyllite near the contact zone with porphyry rockbody. The illite crystallinity and expandability are mainly affected by water/rock ratio or fluid flux, and hydrothermal illite is formed by illitization of plagioclase and/or micas during hydrothermal fluid evolution within the porphyry body and near the contact zone with wall rocks. The other is a product of low-grade metamorphism itself by illitization of smectite, whose crystallinity index is lower than the hydrothermal illite and which is of 2M1 polytype with no swelling layer, in the altered metamorphic tuffaceous phyllite far from porphyry rockbody ( > 2 km). Moreover, the negative correlation between illite index and copper grade indicates that, within the alteration zone, the smaller the illite crystallinity, the stronger the alteration degree, and the higher the copper grade due to higher water/rock ratio. At lower levels of the porphyry body, however, the illite crystallinity (IC) values are controlled mainly by temperature and time.

Experimental study on crystallization kinetics of alkali feldspar under high T-P conditions

In the granite-NaF-H2O system, there exists a nucleation lag in the course of alkali feldspar crystallization indicated by experiments on crystallization kinetics. The nucleation lag time is about 18 h at 700°C and about 6 h at 650°C. Meanwhile, both nucleation rate and crystal-growth rate of alkali feldspar are not constant during the crystallization process, but vary with crystallization time. Here we suggest that the lag time should be taken into account in the calculation formula of nucleation rate and crystal-growth rate to obtain more reliable parameters.