西藏班戈错水菱镁矿藻类成矿实验及其成因分析

目前关于天然水菱镁矿的形成认识主要有蒸发沉积成因和生物成因两类。前人在室内成功制备出水菱镁矿矿物，证实了该矿物的无机成因理论，但是实验结晶条件明显高于西藏班戈错的寒冷气候条件和水化学条件，并且班戈错湖水通过自然蒸发结晶也难以形成水菱镁矿矿物，而这一认识与周边阶地上正在形成水菱镁矿的现象相矛盾。因此，自然蒸发沉积可能不是现阶段班戈错水菱镁矿的主要形成过程，而已有研究表明，藻类具备诱导形成碳酸盐矿物的能力，本文利用西藏班戈错Ⅲ湖湖水及其藻类开展室内模拟实验，并与无藻类的湖水自然结晶结果相对照，探讨藻类生命活动与班戈错水菱镁矿的成因联系。研究发现，藻类不仅能够适应高盐度盐水环境（矿化度117.3 g/L），并且在其光合作用过程中还能显著提高周围水体pH值（最高可达10.564），诱导并促进球碳镁石在藻类网状节点处结晶沉淀，该矿物进一步脱水即能够形成水菱镁矿矿物；而人为提高班戈错Ⅲ湖湖水Mg2+浓度也仅能结晶形成三水菱镁矿矿物，无球碳镁石或水菱镁矿结晶析出。因此，西藏班戈错水菱镁矿的形成过程与藻类生物成矿作用密切相关，但是有关球碳镁石向水菱镁矿转变的具体条件以及藻类成矿作用的具体分子机制仍不清楚，有待于进一步研究。

Algae mineralization experiment and genetic analysis of hydromagnesite in Bangor Lake,Xizang(Tibet)

At present,there are two types of understanding about the formation of natural hydromagnesite: evaporative deposition and biogenic.Previously,the hydromagnesite was successfully prepared in the laboratory,which confirmed the theory of inorganic genesis of hydromagnesite.However,the experimental crystallization conditions of hydromagnesite are significantly higher than the cold climate and hydrochemical conditions in Bangor Lake (Bangor Co),Xizang(Tibet).In addition,it is difficult for the brine in Bangor salt lake to form hydromagnesite minerals through natural evaporation and crystallization.This understanding is in contradiction with the phenomenon of hydromagnesite forming on the surrounding terraces in Bangor salt lake.Therefore,natural evaporation deposition may not be the main formation process of hydromagnesite in Bangor salt lake at this stage,there are studies have shown that algae have the ability to induce the formation of carbonate minerals.In this paper,the genesis of hydromagnesite in Bangor Lake is discussed from the perspective of algae biogenesis.Methods: In this paper,a laboratory simulation experiment was carried out by using high concentration brine and its algae of III lake in Bangor salt lake,and compared with the natural crystallization results of the lake water without algae in Bangor salt lake,to discuss the genetic relationship between the life activities of algae and the hydromagnesite in Bangor salt lake, Xizang(Tibet).Results: The algae can not only adapt to high salinity environment (117.3 g/L),but also significantly improve the pH value of the surrounding water body (up to 10.564) in the process of photosynthesis,inducing and facilitating the crystallisation and precipitation of dypingite at the algae reticulation nodes, which can be further dehydrated to form hydromagnesite mineral.In addition,when the concentration of Mg2+in Bangor salt lake was increased artificially,only the nesquehonite minerals could be crystallized,and the dypingite or hydromagnesite minerals can not be crystallized.Conclusions: In this study,it was found that the biological mineralization dominated by algae was closely related to the crystallization and precipitation process of hydromagnesite in Bangor salt lake, Xizang(Tibet).However,the specific conditions concerning the transformation of dypingite to hydromagnesite and the specific molecular mechanism of algae mineralization are still unclear and need to be further investigated.