(1. 中南大學(xué) 有色金屬成礦預(yù)測與地質(zhì)環(huán)境監(jiān)測教育部重點實驗室，長沙 410083； 2. 湖南省國土資源規(guī)劃院 國土資源評價與利用湖南省重點實驗室，長沙 410007； 3. 貴州省有色金屬和核工業(yè)地質(zhì)勘查局，貴陽 550005； 4. 中國科學(xué)院 廣州地球化學(xué)研究所，廣州 510640)
摘 要: 通過詳細(xì)的野外調(diào)研和室內(nèi)鑒定，將土地坪鉛鋅礦床成礦作用分為3個階段，即閃鋅礦-白云石階段(Ⅰ)、閃鋅礦-方鉛礦-重晶石-螢石階段(Ⅱ)與方鉛礦-方解石階段(Ⅲ)。利用(紅外)顯微測溫和激光拉曼分析，對閃鋅礦和伴生脈石礦物(方解石、螢石、重晶石)中的流體包裹體的對比研究顯示：成礦流體在Ⅰ、Ⅱ階段為中-低溫、中高鹽度、含有一定量CaCl2的NaCl-MgCl2-H2O體系，Ⅲ階段變?yōu)榈蜏亍⒅宣}度的NaCl-H2O體系；Ⅰ~Ⅲ階段，氣相成分主要為H2O及還原性組分CH4和H2S，后者含量先增后減。閃鋅礦及伴生脈石礦物流體包裹體均表現(xiàn)出流體混合和氧逸度先降后升的特征，暗示兩者可能來源于同一流體體系，但前者呈現(xiàn)“演化滯后”現(xiàn)象。Ⅰ、Ⅱ階段金屬礦物沉淀主要與流體混合背景下的硫酸鹽熱化學(xué)還原(TSR)反應(yīng)有關(guān)，Ⅲ階段金屬礦物沉淀還受到大氣降水的降溫和稀釋作用的影響。TSR反應(yīng)與碳酸鹽巖溶蝕的耦合作用是影響該礦床金屬礦物沉淀的重要因素。
關(guān)鍵字: 成礦流體；鉛鋅礦床；土地坪；金屬礦物沉淀；硫酸鹽熱化學(xué)還原反應(yīng)
（1. Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring, Ministry of Education, Central South University, Changsha 410083, China; 2. Hunan Key Laboratory of Land and Resources Evaluation and Utilization, Hunan Planning Institute of Land and Resources, Changsha 410007, China; 3. Non-Ferrous Metals and Nuclear Industry Geological Exploration Bureau of Guizhou, Guiyang 550005, China; 4. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China）
Abstract:Detailed field investigation and petrological observation on the Tudiping Pb-Zn deposit indicated that the mineralization could be subdivided into three stages: (Ⅰ) sphalerite-dolomite, (Ⅱ) sphalerite-galena-barite-fluorite and (Ⅲ) galena-calcite stages. A comparative investigation was performed on fluid inclusions trapped in sphalerite and coexisting gangue minerals, by (infrared) microthermometry and laser Raman analysis. The results reveal that the ore-forming fluid is a moderate-low temperature, moderate-high salinity NaCl-MgCl2-H2O system with considerable amounts of CaCl2 at stage Ⅰ and Ⅱ, and a low temperature and moderate salinity NaCl-H2O system at stage Ⅲ. The vapor phase composition comprises H2O, CH4 and H2S, and the concentrations of the reductive gas increase from stage Ⅰ to Ⅱ and decrease from stage Ⅱ to Ⅲ. Both fluid inclusions trapped in sphalerite and coexisting gangue minerals are featured by fluid mixing and oxygen fugacity change, indicative of being derived from the same fluid system. However, an evolution delay was found in fluid inclusions trapped in sphalerite. The ore deposition is related to thermochemical sulfate reduction (TSR) under the background of fluid mixing at stages Ⅰ and Ⅱ, and influenced by dilution and cooling resulting from meteoric water at stage Ⅲ. The coupling effect between TSR and carbonate dissolution plays a significant role in the ore deposition mechanism of the Tudiping Pb-Zn deposit.
Key words: ore-forming fluid; lead-zinc deposit; Tudiping; ore deposition; thermochemical sulfate reduction
