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江西贵溪冷水坑晚侏罗世打鼓顶组—鹅湖岭组火山碎屑建造中的铁锰白云岩,是一套火山角砾岩或集块岩,以层状或大型透镜体展布,是冷水坑特大型Ag-Pb-Zn矿田的重要赋矿层位。通过对其整合接触的上覆顶板、下伏底板晶屑凝灰岩锆石U-Pb同位素年代学研究显示:顶板年龄160.75±0.96Ma,底板年龄161.30±1.30Ma,确定这套铁锰白云岩形成于晚侏罗世Oxfordian期,成矿作用发生在燕山运动早期的火山喷发及热液作用时。铁锰白云岩中包裹体均一温度测定结果显示,其成岩温度在344.2℃~202.5℃之间。其中螺状硫银矿的存在,说明成矿温度低于173℃。稀土组分总量低,类似正常湖相沉积碳酸盐岩,但却含有大量正长质岩浆岩组分,说明并非正常湖相沉积。碳氧同位素分析显示的平均值:δ13 CPDB-6.108‰、δ18 OPDB-15.667‰、δ18 OSMOW-14.709‰,属无机成因为主的火山-岩浆及陆源碎屑沉积。未见有生物碎屑或动物遗迹,但可见少量微生物沉积构造,而且上、下均与火山岩整合接触,属火山凹地湖泊环境,受火山作用影响强烈,湖水富Fe、Mn、S、Si等,不利于较高等的动植物生存,但铁细菌、硫细菌及蓝细菌等低等微生物可以生存。铁锰白云岩呈磨圆、分选均差的角砾状,是火山爆发炸碎或震碎后原地堆积而成。
Jiangxi Guixi Cold Pits Late Jurassic Taigu Formation - Ehulhuling Formation Volcanic clastic iron-manganese dolomite, is a set of volcanic breccias or episodes of rock, layered or large lens body distribution, It is an important ore deposit for the large-scale Ag-Pb-Zn orefield in Lengshuikeng. The zircon U-Pb zircon dating from the integrated quartz core under the integrated roof contact shows that the age of roof is 160.75 ± 0.96Ma and the age of the floor is 161.30 ± 1.30Ma. It is confirmed that this iron-manganese dolomite is formed in Late Jurassic Oxfordian period, mineralization occurred in the early Yanshan movement volcanic eruptions and hydrothermal effects. The homogenization temperature of inclusions in the iron-manganese dolomite shows that the diagenetic temperature is between 344.2 ℃ and 202.5 ℃. Among them, the existence of spiro-sulfur silver deposits indicates that the ore-forming temperature is lower than 173 ℃. The total amount of rare earth components is low, similar to the normal lacustrine sedimentary carbonate rocks, but contains a large amount of normal protolith magma components, indicating that the normal lacustrine deposition. Carbon and oxygen isotope analysis shows the average: δ13 CPDB-6.108 ‰, δ18 OPDB-15.667 ‰, δ18 OSMOW-14.709 ‰, belonging to inorganic-induced host volcano-magmatic and terrigenous clastic sediments. There are no biological debris or animal relics, but a small amount of microbial sedimentary structures can be seen. Both upper and lower are integrated with the volcanic rocks, which belongs to the lacustrine volcanic lake environment. Affected by the volcanism, the lake is rich in Fe, Mn, S, Si, Not conducive to higher survival of plants and animals, but iron bacteria, sulfur bacteria and cyanobacteria and other lower microorganisms can survive. Iron-manganese dolomite is round, sorting are poor breccia-like, volcanic eruption broken or crushed in situ accumulation.