(1. 北京科技大學 土木與資源工程學院，北京 100083；
2. 南京地質(zhì)礦產(chǎn)研究所，南京 210016)
摘 要: 汞洞沖鉛鋅礦床位于大別成礦帶的東段，是該區(qū)內(nèi)重要的角礫巖型多金屬礦床。礦體受角礫巖體控制，賦存于早古生代佛子嶺巖群諸佛庵組云母石英片巖和千枚巖之中。礦床經(jīng)歷他形石英-絹云母-黃鐵礦階段(Ⅰ)、自形石英-鐵錳鎂碳酸鹽-多金屬硫化物階段(Ⅱ)和方解石-綠泥石-黃鐵礦階段(Ⅲ)，其中Ⅱ階段為最主要的鉛鋅沉淀階段。流體包裹體巖相學、顯微測溫、激光拉曼綜合研究表明：Ⅰ階段主要發(fā)育富CO2包裹體(均一溫度為307~354 ℃，鹽度(NaCleq)為0.6%~5.6%(質(zhì)量分數(shù)))和含子晶多相包裹體(均一溫度為323~377 ℃，鹽度為38.2%~45.3%)；Ⅱ階段主要發(fā)育氣液相體積比變化很大的氣液兩相水溶液包裹體，及少量含CO2的包裹體，均一溫度為249~315 ℃，鹽度(NaCleq)為2.9%~6.9%；Ⅲ階段主要發(fā)育氣液兩相水溶液包裹體，均一溫度為242~280 ℃，鹽度為1.4%~5.0%，其中Ⅰ階段流體發(fā)生了沸騰作用。H、O同位素測試結(jié)果表明：Ⅰ階段硅化細粒石英流體包裹體顯示巖漿水來源，而Ⅱ階段晶簇石英的流體包裹體則存在有大氣水混入的特征。成礦流體由中高溫、高鹽度、富CO2的巖漿水向低溫、低鹽度、貧氣富水的大氣水方向演化。C-O同位素測試結(jié)果表明，與鉛鋅等金屬共生的白云石中δ13CV-PDF值為-4.6×10-3~-1.2×10-3之間，相對變化較小，δ18OSMOW值為7.1×10-3~10.2×10-3，顯示巖漿碳酸巖來源。金屬硫化物的δ34SV-CDT值變化范圍很窄，在2.5×10-3~4.5×10-3之間，也顯示深源硫的特征。綜合分析表明：汞洞沖鉛鋅礦床為一熱液隱爆角礫巖型礦床，成礦流體和成礦物質(zhì)主要來自深部的巖漿熱液，礦床經(jīng)歷了隱爆作用和減壓過程，使得流體發(fā)生了沸騰作用，此時氣液相開始分離, CO2不斷逃逸，成礦金屬在殘存的高鹽度液相中富集，隨后大氣降水沿著隱爆作用所產(chǎn)生的裂隙加入熱液中，流體混合使得體系鹽度大幅降低，金屬絡合物失穩(wěn)，最終鉛鋅大量沉淀。
關鍵字: 汞洞沖；隱爆角礫巖；沸騰作用；混合作用；巖漿熱液
（1. School of Civil and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China;
2. Nanjing Institute of Geology and Mineral Resource, Chinese Academy of Geological Sciences, Nanjing 210016, China）
Abstract:The Gongdongchong Pb-Zn deposit located in Jinzhai County, Anhui Province, China, is one of the important breccia type lead-zinc polymetallic deposits in the east end of Qinling-Dabie metallogenic belt. Ore bodies are controlled by the breccia, hosted in Early Palaeozoic mica-quartz schist and phyllite of Zhufo’an Formation, Foziling Group. The ore-forming processes of Gongdongchong deposit can be divided into three stages, namely the anhedral quartz-sericite-pyrite stage (Ⅰ), the euhedral quartz-carbonate-polymetal sulfides stage (Ⅱ) and the calcite-chlorite-pyrite stage (Ⅲ), among which, the stage (Ⅱ) is the major mineralization stage. Studies of fluid inclusions show that the fluid inclusions trapped in stage (Ⅰ) including two-phase inclusions, as evidenced by the coexistence of CO2-rich(C-type) (Homogenization temperatures of 307-354 ℃, Salinity(NaCleq): 0.6%-5.6% and multi-phase(S-type) inclusions with daughter minerals (Homogenization temperature of 323-377 ℃, Salinity of 38.2%-45.3%. The fluid inclusions of stage (Ⅱ) are two-phase inclusions, as identified by the coexistence of L1- and L2-type fluid inclusions; L1-type inclusions homogenized is 249-315 ℃, with salinities of 2.9%-6.9%. The fluid inclusions formed in stage(Ⅲ) are dominated by vapor-liquid two phase inclusions, with the homogenization temperatures ranging from 242 ℃ to 280 ℃ and salinities between 1.4% and 5.0%. The fluid-boiling is evidenced by divergent-phase homogenizations of fluid inclusions with contrasting salinities at similar temperatures in stage (Ⅰ). The hydrogen and oxygen isotopes composition in quartz grains from different stages show that ore-forming fluid for stage (Ⅰ) is of magmatic origin, and is mixd by the meteoric water in stage (Ⅱ). The ore-forming fluid is characterized by medium-high temperature, high salinity and CO2-rich, and then evolved into low temperature, low salinity and CO2-release from early to late stage. The carbon and oxygen isotope composition in the dolomite in the deposit range from -4.6×10-3 to 1.2×10-3 and from 7.1×10-3 to 10.2×10-3, respectively, which is similar to those in magmatic carbonatite. The values of δ34SV-CDT in major sulfides have narrow variable range, from 2.5×10-3 to 4.5×10-3, indicating that the sulfur is derived from the mantle. All the data presented show that Gongdongchong Pb-Zn deposit belongs to the cryptoexplosion breccia-type deposit. The ore forming fluid and metallogenic materials come from magma in depth. The fluids boiling after cryptoexplosion and decompression result in gas-release. The metallogenic elements, such as Pb, Zn and Cu, concentrated in the solution with high salinity. The ore-forming hydrothermal solution migrated upwards along the tensional cracks with the sharply salinity decreasing by mixture with meteoric water, finally ore-forming materials are precipitated.
Key words: Gongdongchong; cryptoexplosion breccia; fluid boiling; mixing; magmatic hydrothermal
