酸性熱液實驗：安山岩的溶蝕過程

Acid Hydrothermal Experiments: Dissolution Processes of Andesite

方建能(Jiann-Neng Fang)

《臺灣鑛業》 74卷2期 (2022/06) Pp. 3-12

摘要

採用在鐵弗龍飽和蒸氣壓反應器中加入安山岩顆粒與硫酸溶液，進行改良式批次反應系統熱液實驗，進行不同的溶液濃度、溫度及時間條件下反應後，探討安山岩發生酸性熱液溶蝕作用前後的重量、礦物型態及岩象等的變化。本研究實驗結果顯示，安山岩石基比斑晶礦物先發生溶蝕；斜長石斑晶沿晶體構造弱處先發生溶蝕，隨著累積實驗時間的增加，形成的溶蝕孔洞加長、加寬、加深；具有帶狀構造的斜長石斑晶，由晶體中心往外逐漸發生溶蝕，這現象與具有帶狀構造斜長石的鈣與鈉成分分布有密切關係。輝石斑晶則先出現透鏡狀溶蝕洞、線狀溶蝕裂隙，進而形成鋸齒狀表面。本研究由殘留安山岩岩樣重量變化曲線得知，岩樣完全溶蝕所需的時間，以2M/190℃條件時溶蝕最快，188小時即完全溶蝕，0.05M/110℃條件時溶蝕最慢，524小時才完全溶蝕；當實驗溫度與溶液濃度增加時，安山岩岩樣的溶蝕速率也隨之增加。

關鍵字

安山岩 ； 熱液實驗 ； 溶蝕速率 ； 溶蝕過程

並列摘要

Andesite particles and sulfuric acid were placed in teflon-lined autoclaves to conduct hydrothermal experiments in a modified batch reaction system. Reactions were controlled under several conditions of sulfuric acid concentrations, temperatures, and time to investigate the effect of acidic hydrothermal dissolution processes on the weight, mineral morphology, and lithofacies of the andesite samples. The experimental results of this study show that the dissolution of groundmass in andesite occurs prior to phenocrysts. The dissolution of plagioclase phenocrysts initiates along crystal weaknesses, with the cavities lengthening, widening, and deepening through prolonged exposure. Banded plagioclase phenocrysts dissolve from the inside out, the phenomenon of which is closely related to the distribution of calcium and sodium in the plagioclase crystal. Contrarily, lens-shaped cavities and linear fissures emerge on pyroxene phenocryst surfaces upon dissolution, forming hackly exteriors. The residual weight curves of andesite samples were plotted, and the results indicate that conditions of 2M H_2SO_4-190℃ induce the highest dissolution rate, requiring 188 hours for complete dissolution of samples. The slowest dissolution rate occurred in conditions of 0.05M H_2SO_4-110℃, requiring 524 hours for complete dissolution. As the experimental temperature and concentration of solution increases, the dissolution rate of andesite samples increases simultaneously.

並列關鍵字

Andesite ； Hydrothermal Experiments ； Dissolution Rate ； Dissolution Processes