CAJ | 학술논문

硼作为一种常用的地球化学指示剂和示踪剂,对研究俯冲带岩石学过程、岩浆-热液分异作用、火山活动以及稀有元素、铜、金的成矿机制具有重要意义。硼具有高水溶性和挥发性,它在气体中的分配、迁移能力和存在形式有助于理解含硼矿物的形成条件、流体化学组成的演化趋势、硼同位素的分馏效应和成矿金属的富集机理。本文在200~350℃、0.19~3.43 MPa条件下实验研究了B2O3-H2O体系中硼在共存水蒸气和富硼熔体(液体)之间的分配,平衡时气相中的B2O3含量为1.06%~32.35%。200℃、250℃、300℃和350℃时硼在气体-熔体之间的表观分配系数分别为0.035、0.042、0.20和0.33,即随温度上升,硼在含水气相中的分配和迁移能力增强。含水的富 B 熔体与硼酸稀溶液体系的气体-液体分配系数变化不大,表明B2O3-H2O±NaCl 体系中硼的气-液分配能力受液体或熔体中硼含量的影响较小,而主要与温度有关。经热力学分析,350℃、0.19~1.74 MPa条件下水蒸气中的气态硼物种可能为H3BO3和HBO2,可以预计随水蒸气压力的升高, H2O的配位数将会增大, H3BO3或其他可能的气态物种H3BO3·H2O会变得更为重要。某些火山活动区可见天然硼酸结壳(升华壳)的形成,灼热和干燥的火山岩石表面有利于硼酸从气相中凝析和沉淀。本实验结果表明,某些富硼酸的火山喷气孔气体的形成可能与地下高温火山岩浆(岩体)中存在因液态不混溶作用或晚期出溶作用产生的含水富硼的残余熔体或流体有关,熔体的去气作用或流体的减压相分离导致含水气相的产生,硼则随之大量分配至含水气体中并喷出地表。
붕작위일충상용적지구화학지시제화시종제,대연구부충대암석학과정、암장-열액분이작용、화산활동이급희유원소、동、금적성광궤제구유중요의의。붕구유고수용성화휘발성,타재기체중적분배、천이능력화존재형식유조우리해함붕광물적형성조건、류체화학조성적연화추세、붕동위소적분류효응화성광금속적부집궤리。본문재200~350℃、0.19~3.43 MPa조건하실험연구료B2O3-H2O체계중붕재공존수증기화부붕용체(액체)지간적분배,평형시기상중적B2O3함량위1.06%~32.35%。200℃、250℃、300℃화350℃시붕재기체-용체지간적표관분배계수분별위0.035、0.042、0.20화0.33,즉수온도상승,붕재함수기상중적분배화천이능력증강。함수적부 B 용체여붕산희용액체계적기체-액체분배계수변화불대,표명B2O3-H2O±NaCl 체계중붕적기-액분배능력수액체혹용체중붕함량적영향교소,이주요여온도유관。경열역학분석,350℃、0.19~1.74 MPa조건하수증기중적기태붕물충가능위H3BO3화HBO2,가이예계수수증기압력적승고, H2O적배위수장회증대, H3BO3혹기타가능적기태물충H3BO3·H2O회변득경위중요。모사화산활동구가견천연붕산결각(승화각)적형성,작열화간조적화산암석표면유리우붕산종기상중응석화침정。본실험결과표명,모사부붕산적화산분기공기체적형성가능여지하고온화산암장(암체)중존재인액태불혼용작용혹만기출용작용산생적함수부붕적잔여용체혹류체유관,용체적거기작용혹류체적감압상분리도치함수기상적산생,붕칙수지대량분배지함수기체중병분출지표。
As a common geochemical indicator and tracer, boron is of significance for the study of petrologic processes in subduction zone, magmatic-hydrothermal differentiation, volcanic activity and mineralizing mecha-nism of rare elements, copper and gold. Boron is highly water-soluble and volatile, its capacity of distribution and transport and species in vapor phase are helpful for understanding the formation of boron-bearing minerals, evolution trend of chemical composition of fluid, fractionation effect of boron isotope and metallogenic mechanism of ore-forming metals. The distribution of boron between coexisting water vapor and melt (or liquid) in B2O3-H2O system was studied experimentally at temperatures from 200 ℃ to 350℃ and pressures from 0.19 MPa to 3.43 MPa. The equilibrated contents of B2O3 in the vapor phase range from 1.06% to 32.35%. The apparent distribution coefficients of boron between vapor and melt at 200℃, 250℃, 300℃and 350℃are 0.035, 0.042, 0.20 and 0.33, respectively, show an increasing potential of partition and transport of boron in vapor with temperature. The general variation in distribution coefficients doesn’t seem to be so large between systems of hydrous boron-rich melt and dilute boric acid solution, suggesting the capacity of boron distribution between vapor and liquid in the B2O3-H2O system may be affected slightly by the content of boron in the melt or liquid, but remarkably by the temperature. According to the result of thermodynamic approach, the gaseous species of boron in water vapor at 350℃and 0.19~1.74 MPa are H3BO3 and HBO2 probably. It is predicted that the coordination number of water will increase with the pressure of water vapor, and hence H3BO3 or other possible species such as H3BO3·H2O become more important. Sassolite encrustation (or sublimates) occurs in some volcano areas, the hot and dry surface of volcanic rocks is favorable for the vapor deposition of boric acid from the exhalations. Our experimental results suggest that some fumarolic gases rich in boric acid are probably related to hydrous boron-concentrated residual melt or fluid derived from liquid immiscibility or late stage exsolution in the underground volcanic magmas of high temperature. The degassing process of the residual melt or the phase separation of fluid accompanied with decompression results in the production of aqueous vapor phase, consequently boron distributes into the vapor in substantial quantities.