表生作用条件下硼酸盐矿床的形成问题

ORIGIN OF THE BORATE DEPOSITS UNDER THE CONDITION OF HYPERGENESIS

中文关键词:  硼酸盐矿床 表生作用 成因 水体 pH值 地热 火山活动 卤水

英文关键词:Borate Deposit,Hypergenesis,Origin

中文摘要:

      沉积硼酸盐矿床在自然界分布相当广泛 ,主要见于南、北美和我国青藏高原的盐湖中、美国和土耳其某些第三纪沉积盆地中 ,以及欧洲某些古代海相盐矿床中。为了研究其形成问题 ,从 70年代开始 ,我们利用青藏高原盐湖卤水和泉水进行了许多模拟实验工作。从 40～ 5 0个样品中获得了大量钠硼酸盐、纳钙硼酸盐、镁硼酸盐和含氯化镁的镁硼酸盐复盐。这对于阐明表生作用条件下硼酸盐矿床的形成是非常重要的。实验和研究结果证明 :1)与地热和火山活动有关的水体是硼酸盐矿床形成的物质来源 ;2 )硼酸盐矿床可形成于Ｎａ、Ｋ、Ｍｇ//Ｃｌ、ＳＯ4 ·Ｈ2 Ｏ和Ｎａ、Ｋ//Ｃｌ、ＳＯ4 、ＨＣＯ3、ＣＯ3·Ｈ2 Ｏ不同水盐平衡体系的不同富硼水体中 (盐度 :1 2 7～ 41 4% ,Ｂ2 Ｏ3含量 :0 0 5～ 2 97% ) ;3 )硼酸盐矿床通常形成于稳定平衡条件下 ,而不是介稳平衡条件下 (蒸发过程中 ) ;4)低温条件有利于硼酸盐自水体中析出 ;5 )硼酸盐矿床的形成与水体的化学类型、ｐＨ值和硼含量有密切关系 ;6)我们实验中所获的硼酸盐反映了天然硼酸盐矿床形成的原始条件。不仅揭示了大陆盐湖硼酸盐矿床的形成 ,也揭示了古代海相盐矿床硼酸盐的成因。

英文摘要:

      Abstract:　The distribution of sedimentary boron deposits is relatively widespread in nature,They are mainly found in recent salt lakes of the North and South America and the Qinghai-Xizang(Tibet) plateau in China,some Tertiary sedimentary basins in United States of America and Turkey and in some old salt deposits in Europe.However,their origins have not been studied in detail yet.In order to investigate their formation,a lot of simulating experiments have been done using the natural brines and spring water of the saline lakes on Qinghai-Xizang plateau from1970s.Na-borate,Na-Ca borate,Mg-borates and Mg-borate contained MgCl2 have been obtained from 40-50 experimental samples.It is very important for illustrating the origins of the sedimentary borate deposits under the condition of h-ypergenesis. 　　The above experimental results proved that: 　　1)The B-rich waterbodies related to geothermals and volcanicity are the substance sources of the formation of borate deposits; 　　2)The borate deposits can be formed in various B-rich waterbodies of different aqua-salt equilibrium systems of Na,K,Mg//Cl,SO4*H2O and Na,K//Cl,SO4,HCO3,CO3*H2O(the salinity:1.27-41.4%,B2O3:0.05-2.97%). 　　3)The borate deposits can be formed under the stable equilibrium environment without the metastable equilibrium(evoporating process)(nearly in deep water or burried water).At the same time,their precipitation is far later in time than that of other salt minerals for several days,several months to more than ten years. 　　4)The low-temperature condition is beneficial to borate separation from the waterbody. 　　5)The formation of borate deposits is closely associated with the hydrochemical type,pH value and boron content of the waterbodies.