臺灣文石－澎湖文石與三峽文石的地質差異

Taiwan Wenshi: Geological Differences between Penghu Wenshi and Sanshia Wenshi

陳韻婕(Yun-Chie Chen) ； 方建能(Jiann-Neng Fang) ； 劉德慶(Teh-Ching Liu)

《臺灣鑛業》 75卷2期 (2023/06) Pp. 10-22

摘要

在玄武岩的氣孔中經常可以發現次生礦物生長，在澎湖群島與臺灣本島西北部玄武岩內的次生礦物會形成少見的同心圓紋理外觀，被稱之為臺灣文石。本文將透過顯微拉曼光譜儀、掃描式電子顯微鏡與質譜儀等儀器分析臺灣本島的三峽文石，進一步了解文石形成特殊紋理的成因，並同時比對過去澎湖文石的相關研究，以礦物相、地球化學成分、生成環境模擬等面向探討，為臺灣兩地文石提供概略的統整比較。本文研究結果發現，兩地文石有少數礦物相的差異，目前尚未於三峽文石中發現菱錳礦、菱鎂礦及沸石群礦物，而黃鐵礦僅出現於竹東地區。在化學成分部分，澎湖文石整體鐵離子置換率較高，三峽文石在部分產區則有二氧化矽礦物富集的情形。由碳氧同位素分析得知，兩地文石於20～68℃左右低溫沉澱形成，澎湖文石成礦溶液主要來自於淡水，三峽文石則由海水混合少量淡水形成。

關鍵字

臺灣文石 ； 玄武岩 ； 次生礦物 ； 碳氧同位素

並列摘要

Secondary minerals are often found to have formed in the pores of basalt. In the basalts of the Penghu Islands (Penghu Wenshi) and northwestern Taiwan (Sanshia Wenshi), these secondary minerals form rare concentric patterns and are collectively known as Taiwan Wenshi. In this study, we analyze Sanshia Wenshi using the instruments micro-Raman spectrometer, scanning electron microscope (SEM), and mass spectrometer to investigate the formation processes of these unique patterns in Taiwan Wenshi, as well as make comparisons between our results and past studies on Penghu Wenshi. Through discussions of mineral facies, geochemical composition, and formation environment modeling, we provide a brief summary of comparisons between Wenshi of the two locations in Taiwan. Through this study, we found similar mineral facies in the Wenshi from both locations. Current results show lack of rhodochrosite, magnesite, and zeolite group minerals in Sanshia Wenshi, and pyrite is only found in those formed in the Zhudong area. In terms of chemical composition, the iron ion displacement ratio is generally higher in Penghu Wenshi, and the Sanshia Wenshi from some locations are enriched in silicate minerals. From carbon and oxygen isotope analyses results, we found that the Wenshi from both locations are formed through precipitation in low environmental temperatures of around 20 to 68℃ ; Penghu Wenshi mainly formed from precipitation of freshwater mineral solutions, while Sanshia Wenshi likely precipitated from saltwater solutions mixed with small amounts of freshwater.

並列關鍵字

Taiwan Wenshi ； basalts ； secondary mineral ； carbon and oxygen isotope