The Yichun Ta-Sn-Li Deposit, South China: Evidence for Extreme Chemical Fractionation in F-Li-P-Rich Magma

The Yichun Ta-Sn-Li deposit occurs within the 9.5-km2 Yashan Igneous Complex, which is made up of felsic, peraluminous intrusions including two-mica, Li-mica, and topaz-lepidolite granites. The topaz-lepidolite granite forms a thin sheet confined to the upper part of the Li-mica granite and is separated from the host metasediments by a marginal pegmatite. The topaz-lepidolite granite is characterized by the presence of snowball textures in which quartz, K-feldspar, and topaz phenocrysts contain albite laths and rare lepidolite and columbite arranged along growth zones. These textures indicate simultaneous crystallization of these phases and attest to the subsolvus character of the topaz-lepidolite granite. Minor and accessory phases in the topaz-lepidolite granite include amblygonite, cassiterite, columbite-tantalite, microlite, wodginite, zircon, monazite, and pollucite. The topaz-lepidolite granite is characterized by low SiO2 (68.6–69.7 wt %), TiO2 (0.01 wt %), Fe2O3(total) (0.15–0.33 wt %), MgO (0.01–0.05 wt %), and CaO (0.15–0.19 wt %), whereas Al2O3 (17.97–18.26 wt %), Li2O (0.90–2.09 wt %), P2O5 (0.43–0.54 wt %), and F (1.09–2.30 wt %) are all very high. Na2O ≫ K2O due to both high Na2O (5.18–6.30 wt %) and low K2O (2.63–3.05 wt %). The topaz-lepidolite granite contains extremely high concentrations of Rb (>3,300 ppm), Cs (>340 ppm), Sn (>140 ppm), and Ta (>120 ppm), with very low Zr/Hf and Nb/Ta. Gaps of >3.5 wt % SiO2 and >2.5 wt % Al2O3 together with large increases in F, Li2O, and P2O5 between the Li-mica and topaz-lepidolite granites are not compatible with an evolution by Rayleigh fractionation processes. It is proposed instead that early crystallization of the Li-mica granite led to the formation of an Si-poor, Al-, Na-, and flux-rich boundary layer whose low viscosity and density allowed effective separation from the remaining melt and crystals. This melt concentrated incompatible elements including tin and tantalum and accumulated in the upper part of the magma chamber where it crystallized the sheet-like bodies of marginal pegmatite and topaz-lepidolite granite. The uppermost part of the topaz-lepidolite granite consists of aplite and overlying quartz lepidolite rock, which is composed mainly of quartz, lepidolite, albite, K-feldspar, topaz, amblygonite, cassiterite, and columbite. Compared to the topaz-lepidolite granite the aplite and quartz-lepidolite rock shows a number of complementary element enrichments and depletions. The quartz-lepidolite rock is enriched in Fe, Mn, K, Rb, Cs, Li, F, Ba, Sr, Ti, Zr, Nb, W, Th, and Sm. The formation of the quartz-lepidolite rock is interpreted to result from separation of an F- and Li-rich alkaline phase, which accumulated beneath the already crystallized marginal pegmatite. Complementary to this was crystallization of the strongly peraluminous sodic aplite with the highest tantalum contents measured in this study.

Finding the Information of the Unknown DNAPL Residual Source using various tracer data, Wonju, Korea

<p>In this study, analytical solution method which can evaluate and quantify the impacts of partial mass reduction by remedial action performed in study site is applied to estimate the unknown DNAPL source mass and dissolved concentration using long-term monitoring data collected from 2009 to 2019. Also, noble gas tracer method was applied to identify the partitioning processes which can be happened in TCE contaminated site. By using the source zone monitoring data during about 10 years and analytical solution, initial dissolved concentration and residual mass of TCE in spilled period at the main source zone were roughly estimated 150 mg/L and 1000 kg, respectively. These values decreased to 0.45 mg/L and 33.07 kg direct after an intensive remedial action performed in 2013 and then it expected to be continuously decreased to 0.29 mg/L and 25.41 kg from the end of remedial actions to 2020. From results of quantitative evaluation using analytical solution, it can be evaluated that the intensive remedial action had effectively performed with removal efficiency of 70% for the residual source mass during the remediation period. From the results of noble gas analysis, the distance from TCE source zone was divided into three groups from Zone 1 to 3. Zone 1 includes samples that are the closest from the TCE main source, and are highly partitioned to TCE compared to other zones. Zone 3 samples show least accordance with either of the fractionation lines, showing that sampling points are influenced highly by other mechanism rather than partitioning to TCE. Also, it is identified that seasonal variation of groundwater level can be affected to the distribution of noble gas at around TCE source zone. Samples from only “High TCE” zone are plotted along with ideal batch equilibrium and Rayleigh fractionation line again and divided into two groups according to their sampling date. From August 2018 to October, 2018, samples shift from right to left in the figure, getting closer to Rayleigh fractionation line. In August, noble gas was relatively in equilibrium between groundwater and TCE. However, as water table rises, noble gas became touch with residual TCE locating above the previous water-level, which is a receiving fluid in water-TCE system. Results of this study was support that it was able to estimate the unknown quantitative information for TCE contamination and noble gas as the indicator of DNAPL contamination could be applied in allocating the DNAPL source which is relatively hard to estimate.</p>

Enrichment of manganese to spessartine saturation in granite-pegmatite systems

The enrichment of manganese in peraluminous (S-type) granitic melts beginning with the anatexis of metapelitic rock and ending with the crystallization of highly evolved pegmatites is explained using experimentally derived mineral-melt partition coefficients and solubility data for Mn-rich garnet. Mineral-melt partition coefficients for Fe, Mg, and Mn between garnet, cordierite, tourmaline, and peraluminous, B-bearing hydrous granitic melt were measured between 650 and 850 °C at 200 MPaH2O. The compositions of garnet and tourmaline synthesized in these experiments are similar to those found in nature. Garnets evolve from Sps51Alm23Prp25 to Sps81Alm15Prp4 with decreasing temperature. The Mn content of cordierite increases with decreasing temperature. The composition of tourmaline does not vary with temperature. Partition coefficients, DMα/L, and exchange coefficients, KDα/L=DMα/L/DNα/L where α is a mineral, L is liquid (melt), and M and N are different elements, are presented for mineral-glass pairs. Partition coefficients for Mg, Fe, and Mn increase with decreasing temperature for garnet, tourmaline, and cordierite. The precipitation of garnet alone results in a progressive increase of MgO/FeO and a decrease of MnO/FeO in the melt. Crystallization of cordierite and tourmaline results in a decrease of MgO/FeO and an increase of MnO/FeO in melt. Tourmaline is most efficient at concentrating Mn in residual liquids. The trend toward increasing Mn/Fe in natural garnets in granites and pegmatites is not controlled by garnet itself, but instead by the crystallization of other mafic minerals in which Mg and Fe are more compatible than is Mn. A Rayleigh fractionation model constitutes a test of the partition coefficients reported in this manuscript. The starting composition for the model is that of a liquid (melt inclusions) from an anatectic S-type source. Normative modes of cordierite and biotite are calculated from that composition and are similar to modes of these minerals in natural occurrences. The model consists of crystallization of a cordierite-biotite granite from 850 to 650 °C. The model predicts that ~95% crystallization of the starting composition is required to reach saturation in spessartine-rich garnet at near-solidus temperatures. The model, therefore, is consistent with the occurrence of spessartine as restricted to highly fractionated granite-pegmatite systems at the end stages of magmatism.

Theoretical Derivation and Simulation of the Equation of Evaporation Line in Water Evaporation

The Rayleigh fractionation model is first deduced by the principle of dynamic reaction, which indicates that Rayleigh fractionation can be explained by dynamic characteristics of isotopic molecules in the reaction process. Subsequently, the analytic expression of evaporation line is deduced under equilibrium condition in the open systems of Rayleigh mode, which shows that it is an exponential form. The simulation results show that the slope of the evaporation line under equilibrium condition changes with the temperature that the higher the temperature is, the smaller the slope is and thus the higher the degree of enrichment is. This research can provide reference basis for better understanding the dynamic characteristics of isotopic molecules in evaporation process.

Relationships between bottom water carbonate saturation and element/Ca ratios in coretop samples of the benthic foraminifera <i>Oridorsalis umbonatus</i>

Elemental ratios in benthic foraminifera have been used to reconstruct bottom water temperature and carbonate saturation (Δ[CO32−]). We present elemental data for the long-ranging benthic foraminifera Oridorsalis umbonatus from sediment core tops that span a narrow range of temperatures and a wide range of saturation states. B/Ca, Li/Ca, Sr/Ca and Mg/Ca ratios exhibit positive correlations with bottom water carbonate saturation. The sensitivity of individual element/calcium ratios to bottom water Δ[CO32−] varies considerably, with B/Ca being most sensitive and Sr/Ca the least sensitive. The empirically derived sensitivity of B/Ca, Li/Ca, Mg/Ca and Sr/Ca to bottom water Δ[CO32−] are 0.433 ± 0.053 and 0.0561 ± 0.0084 μmol mol−1 μmol kg−1 and 0.0164 ± 0.0015 and 0.00241 ± 0.0004 mmol mol−1μmol kg−1, respectively. To assess the fidelity of these relationships and the possibility of applying these relationships to earlier periods of Earth history, we examine the mechanisms governing elemental incorporation into foraminiferal calcite. Empirical partition coefficients for Li and Sr are consistent with Rayleigh fractionation from an internal pool used for calcification. For O. umbonatus and other benthic species, we show that the fraction of Ca remaining in the pool is a function of bottom water Δ[CO32−], and can be explained by either a growth rate effect and/or the energetic cost of raising vesicle pH at the site of calcification. Empirical partition coefficients for Mg and B may also be controlled by Rayleigh fractionation, but require that either the fractionation factor from the internal pool is smaller than the inorganic partition coefficient and/or additional fractionation mechanisms. O. umbonatus element ratio data may also be consistent with fractionation according to the surface entrapment model and/or the presence of discrete high- and low-Mg calcite phases. However, at present we are limited in our ability to assess these mechanisms. The new X/Ca data for O. umbonatus provide constraints to test the role of these mechanisms in the future.

Relationships between bottom water carbonate saturation and element/Ca ratios in coretop samples of the benthic foraminifera <i>Oridorsalis umbonatus</i>

Elemental ratios in benthic foraminifera have been used to reconstruct bottom water temperature and carbonate saturation (Δ[CO32−]). We present elemental data for the long-ranging benthic foraminifera Oridorsalis umbonatus from sediment core tops that span a narrow range of temperatures and a wide range of saturation states. B/Ca, Li/Ca, Sr/Ca and Mg/Ca ratios exhibit positive correlations with bottom water carbonate saturation. The sensitivity of individual element/calcium ratios to bottom water Δ [CO32−] varies considerably, with B/Ca being most sensitive and Sr/Ca the least sensitive. The empirically derived sensitivity of B/Ca, Li/Ca, Mg/Ca and Sr/Ca to bottom water Δ [CO32−] are 0.433 ± 0.053 and 0.0561 ± 0.0084 μmol mol−1 per μmol kg−1 and 0.0164 ± 0.0015 and 0.00241 ± 0.0004 μmol mol−1 per μmol kg−1, respectively. To assess the fidelity of these relationships and the possibility of applying these relationships to earlier periods of Earth history, we examine the mechanisms governing elemental incorporation into foraminiferal calcite. Empirical partition coefficients for Li and Sr are consistent with Rayleigh fractionation from an internal pool used for calcification. For O. umbonatus and other benthic species, we show that the fraction of Ca remaining in the pool is a function of bottom water Δ [CO32−], and can be explained by either a growth rate effect and/or the energetic cost of raising vesicle pH at the site of calcification. Empirical partition coefficients for Mg and B may also be controlled by Rayleigh fractionation, but require that either the fractionation factor from the internal pool is smaller than the inorganic partition coefficient and/or additional fractionation mechanisms. O. umbonatus element ratio data may also be consistent with fractionation according to the surface entrapment model and/or the presence of discrete high- and low-Mg calcite phases. However at present we are limited in our ability to assess these mechanisms. The new X/Ca data for O. umbonatus provide constraints to test the role of these mechanisms in the future.