- 期刊
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哥倫比亞祖母綠的地質和產狀
Geology and Occurrences of Columbia's Emeralds
摘要
哥倫比亞的祖母綠分布在東部平行山系，可分為東祖母綠帶和西祖母綠帶兩個帶。本研究野外調查和採樣主要是西祖母綠帶中的穆索、科斯凱茨和庫納斯等三個礦區八個礦坑。祖母綠的母岩為穆索層的黑色頁岩和石灰岩，為全世界少有以沉積岩為母岩、由熱液沉澱所形成。野外露頭和礦坑產狀觀察顯示，祖母綠主要產於由斷層破裂構造所控制的裂隙且伴隨著方解石礦脈沉澱，出現在熱水換質角礫岩和水破角礫岩中，成礦時間為始新世（約38 Ma）。但目前開礦礦坑並不是採於原生地層的黑色頁岩中，而是在山崩作用所形成的崩落堆積物中。依據東部平行山系的大地構造演變、岩塊崩落堆積物的分布和野外產狀，此一大規模山崩作用發生的時間應該相當年輕。另外，考慮開礦成本和安全，建議目前開採的方式應該由鑽鑿礦坑轉變為露天開採。
並列摘要
Columbia's Emerald is predominantly distributed in the Eastern Cordillera, and can be divided into two belts: the eastern emerald belt (EEB) and the western emerald belt (WEB). We did field surveys and collected samples from 8 emerald mines in three locations: the Muzo, Coscuez and Cunus in the WEB. The emerald has been found in black shale and limestone host rocks of the Muzo Formation, and it is very unique to occur in sedimentary rocks in the world. From field outcrops and mine occurrences, it infers that the emerald has been precipitated in association with calcite from hot fluids as veins in fault- controlled fractures and hydrothermally altered and hydraulic breccia. Currently, the mining tunnels are not excavated in original black shale formation, but are located in debris avalanche deposits produced by large scale of landslides. Based on tectonic evolution, distributions of debris avalanche and field occurrences, the landslide events should have occurred recently. Furthermore, it is considered that the open-pit mining should be better than the conventional tunnel mining in terms of costs and safety.