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| 題 名 | Carbon Isotopes and the Origin of Rhodochrosite=菱錳礦之碳同位素及其成礦之物化條件 |
|---|---|
| 作 者 | 葉學文; 譚立平; | 書刊名 | 中國地質學會會刊 |
| 卷 期 | 38:4 1995.10[民84.10] |
| 頁 次 | 頁411-422 |
| 分類號 | 357.28 |
| 關鍵詞 | 菱錳礦; 錳礦床; 碳同位素; 溶解氧氣; 次氧化的; 甲烷; Rhodochrosite; Mn-deposit; Carbon isotopes; Dissolved oxygen; Sub-oxic; Methane; |
| 語 文 | 英文(English) |
| 中文摘要 | 菱錳礦(MnCO□)雖為稀有礦物但為寶石礦物之一且常為世界上許多主要錳礦床主 要含錳礦物。然而我們對此礦物的形成之機制及物化條件則是幾乎無所知。直到最近，我 們對這個題目的了解僅止於一些如“常為…熱液礦脈”、“產於沉積岩及變質沉積岩內” 等廣泛的野外觀察的陳述。本文報導我們應用碳同位素方法去探究一般菱錳礦礦化時可能 需要的共同之物化條件的一些成果。本文之重點不在各別錳礦床之成因，而在於“菱錳礦” 之結晶機制。 此處所分析之菱錳礦樣品仍挑選來自世界各地。這包括美國、中國、加納、墨西哥及南非 之錳礦床及紅海之深海沉積物。其年代跨越現代至元古代，其岩性則含顯然是熱液礦脈， 沉積岩及變質之沉積岩。因此，這些樣品符合代表一般菱錳礦的條件。 這些菱錳礦之δ□C□值之變化範圍很大，但都為負值（-4.4至-45.5□）。這顯示菱錳礦的 碳酸根（CO□）都含有大量有機碳。據保守的估計顯示菱錳礦之碳酸根（CO□）中，最 少有22%是有機碳 。以現代之海水為例，氧化相當於22%之溶解二氧化碳（ΣCO□）所需 之氧氣是二倍於最高溶解氧氣量。 準此，我們的結論是菱錳礦形成之共同物化條件為：（1）大量之有機物轉化之二氧化碳的 存在。（2）在次氧化（Sub-oxic）之Eh環境下。次氧化環境為沒有氧氣也沒有氧化氮物的 環境。 |
| 英文摘要 | Although rhodochrosite, the carbonate with the ideal chemical composition of MnCO□, is a rare mineral, it is a primary constituent of many major Mn-deposits of the world. It is also a gemstone mineral due mainly to its pleasant appearance. The colors of rhodochrosite crystals are generally rosy with variable tones. The mineral may be found as a hydrothermal vein, in sedimentary rocks and in metasedimentary rocks. Its origin is therefore inferred to be either hydrothermal or sedimentary (including diagenetic and, perhaps, metamorphic). Otherwise, the origin(s) of the mineral is (are) poorly understood. We have carried out a carbon-isotope study of rhodochrosite so as to gain some insights into its origin(s). The representative results obtained so far are presented here. While it is certain that some physicochemical parameters of rhodochrosite crystallization, such as temperature, are highly variable and need to be dealt with individually, there may also be some conditions those are universal to such crystallization. The present focus is on the origin(s) of primary rhodochrosite, in general, and not on any particular deposit. Representative rhodochrosite samples were selected from the Mn-deposits of the USA, Mexico, Ghana, South Africa and China as well as from the sediments of the Atlantis II Deep of the Red Sea. The δ□C□ values of the rhodochrosite samples range from -4.4 to -45.5□ indicating the presence of variable but significant amounts of C derived from organic matter in the CO□. The etimated relative amounts of organic carbon in the CO□ are about 22% and higher, indicating that the crystallization fluid of the rhodochrosite was free of oxygen and other oxidants, such as nitrogen oxides. It is concluded from these results that the presence of a large proportion of organic carbon in rhodochrosite carbonate (CO□) as well as an oxygen-and nitrogen-oxides-free, sub-oxic environment are two conditions universal to the crystallization of primary rhodochrosite. |
本系統中英文摘要資訊取自各篇刊載內容。