水城茶园硒的地球化学特征及富硒茶开发探讨

富硒资源弥足珍贵,利用富硒土壤资源发展富硒功能农业是实施乡村振兴战略的新途径。贵州水城区地处高硒地质背景区,为了高效开发利用当地富硒资源,开发生产富硒农产品,本项研究针对水城区富硒区茶园,进行了硒的生物地球化学研究。结果表明,茶园出露二叠系峨眉山玄武岩、龙潭组煤系地层,硒含量分别为0.267±0.155 mg/kg、1.193±2.698 mg/kg,其中龙潭组石煤硒含量最高,高达11.499 mg/kg,是典型的富硒岩层,为茶园富硒土壤的形成提供了充足的地质来源。茶园土壤总硒含量为0.547~4.954 mg/kg,平均值1.682±0.953 mg/kg,50%的茶园土壤硒含量在1~2 mg/kg范围内,为二级富硒土壤。土壤硒含量受其形成母质的制约,与有机碳含量呈正相关性(r=0.27)。土壤有效硒平均含量为0.139±0.045 mg/kg,平均占总硒的8.31%,与pH关系密切(r=0.69)。茶叶硒含量为0.006~0.196 mg/kg,平均值为0.081±0.049 mg/kg,未达到富硒茶的国家标准。为提升水城茶叶的硒含量,从而达到国家富硒茶的标准,建议采取以下农艺措施:1)改良茶园土壤提升土壤pH值,以便提高土壤中硒的生物利用率;2)施外源硒肥进行硒生物强化;3)改换种植高积累硒茶叶品种。

Accumulation and speciation of selenium in Cardamine sp. in Yutangba Se Mining Field, Enshi, China

A naturally selenium-accumulating Cardamine sp. is growing in Yutangba Selenium Mining Field, Enshi area, Hubei Province, China, where the geochemical environment is selenium-enriched and endemic selenosis ever occurred in humans. The present study investigated the characteristics of accumulation, speciation and quantity of selenium in Cardamine sp. with HPLC-ICP-MS. Results show that Cardamine sp. can accumulate Se at most 1427 mg/kg in seedling leaves. Even after the biomass incensement of growing up, the plant still could accumulate Se up to several hundred of mg/kg in concentration. Moreover, the biomass enrichment coefficient(BEC) of Se is exceedingly high, in the seedling leaves mostly, higher than 50 mg/kg; in the range of 43.7–68 mg/kg; and the lowest value is higher than 3 mg/kg in mature fronds. Se is present in the plant predominantly in form of Se Cys2 with the highest concentration in seeds; up to 1081 mg/kg as Se. In contrast, Se Cys2 levels are low during early growth period; they are 136.1 mg/kg as Se in seedling fronds and 39.4 mg/kg as Se in mature fronds, respectively. Se Met concentration is comparatively low; 10.6 mg/kg as Se in seedling frond and 5.3 mg/kg as Se in half mature fronds, respectively. This indicates that Cardamine sp. is extremely efficient in extracting Se from soil and translocating it into its above-ground biomass. Therefore, Cardamine sp., found in Yutangba Se Mining Field may be a new Se hyperaccumulator. It is still uncertain whether the Se-accumulation or detoxification of Cardamine sp. happens through the pathway of Se Cys methylated to form Se-methylseleno Cys or through the formation of Se-carboxymethyl- selenohomocysteine. Indeed, further study should be carried out on the determination of more Se species to explain the high Se hyperaccumulation in Cardamine sp.

Lead Isotopic Composition and Lead Source in the Bainiuchang Ag-polymetallic Deposit, Yunnan Province, China

The Bainiuchang deposit in Yunnan Province, China, is located geographically between the Gejiu ore field and the Dulong ore field. In addition to the 〉7000 t Ag reserves, the deposit also boasts of large-scale Pb, Zn and Sn reserves with a lot of dispersed elements （In, Cd, Ge, Ga, etc.）. We have determined systematically the Pb isotope composition of the deposit. The Pb isotope ratios of the ores that are of sea-floor exhalative sedimentary origin in the northwest of the mining district, are 206pb/204pb = 17.758-18.537, 207pb/204pb = 15.175-15.862 and 206pb/204pb = 37.289-39.424, while those of ores that are of magmatic hydrothermal superimposition origin in the southeast of the mining district, are 206pb/204pb = 17.264-18.359, 207pb/204pb = 14.843-15.683 and 208pb/204pb = 36.481-38.838, respectively. In terms of the Pb isotope composition of feldspar in magmatic rocks or magmatic whole- rock samples from the mining district, we have determined the Pb isotope composition and acquired the Pb isotope ratios as： 206pb/204pb -- 18.224-18.700, 207pb/204pb -- 15.595-15.797 and 208pb/204pb -- 38.193-39.608. Then, in the light of the Pb isotope composition of metamorphic rock samples from the Proterozoic basement exposed in the Dulong ore field, we have determined the Pb isotope composition and obtained the isotope ratios as： 206pb/204pb -- 18.434-19.119, 207pb/204pb -- 15.644-15.693, and 208pb/204pb = 38.514-38.832. And the Pb isotope ratios of Cambrian sedimentary rocks, which are exposed in the Bainiuchang mining district, are 206pb/204pb = 18.307-19.206, 207pb/204pb = 15.622-15.809, and 208pb/204pb = 38.436-39.932. By comparing the two types of ores with respect to their Pb isotope compositions, it is indicated that lead in the Bainiuchang deposit was derived largely from the lower-crust granulite which is earlier than Neoproterozoic in age, but the Yanshanian magmatic hydrothermal fluids probably provided a part of ore-forming elements such as Sn for the ore blocks in the south of the mining district.

Sea-floor exhalative sedimentary and magmatic hydrothermal superimposition on the Bainiuchang polymetallic deposit in Yunnan Province: REE geochemical evidence

In order to study the characteristics of sea-floor exhalative sedimentary and magmatic hydrothermal superimposition on the Bainiuchang polymetallic deposit, the REE compositions of the granites, host-rocks and ores have been systematically analyzed by ICP-MS. As viewed from their REE compositions, the granites show obvious negative Eu anomalies and weak negative Ce anomalies. According to their REE characteristics, the host-rocks were derived partly from sea-floor exhalative sediments. In terms of their REE compositions, the ores can be divided into two groups: one group, of which the samples were collected from the Baiyang segment relatively far away from the Bozhushan granite batholith, possesses positive Eu anomalies or no Eu anomaly and negative Ce anomalies, indicating that ore-forming hydrothermal fluid was relatively reductive and its temperature was higher than 250 ℃. Furthermore, the coinstantaneous presence of positive Eu anomalies and negative Ce anomalies indicate that the convective mixing of a little amount of seawater with hydrothermal fluid had happened while ores were precipitated on ancient sea floor. The other group, of which the samples were mainly collected from the Chuanxindong and Duimenshan segments near the Bozhushan granite batholith, has similar chondrite-monalized REE distribution patterns to those of the magmatic rocks. But as a whole, the REE characteristics of both groups change gradually starting from the Bozhushan granite batholith. Based on the REE characteristics of the granites, host-rocks and ores, it is suggested that the ore-forming metals seem to have come from several different sources.