安徽庐枞盆地泥河铁矿床成矿流体性质:来自He-Ar-H-O同位素的证据

Characteristics of ore-forming fluids in Nihe iron deposit in Luzong volcanic basin,Anhui Province,China: Evidences from He-Ar-H-O isotopes

安徽庐江泥河铁矿床位于长江中下游成矿带庐枞中生代火山岩盆地,受控于切穿至Moho面的罗河-缺口断裂,矿床具有典型玢岩型铁矿的特征。泥河铁矿床硬石膏-透辉石-磁铁矿阶段流体3He/4He=0.14~0.76Ra(平均0.3548Ra),40Ar/36Ar=262.2~364.9(平均299.3),δ18OSMOW=-2.16‰~5.04‰,δDSMOW=-40.7‰^-34.8‰;硬石膏-黄铁矿-磁铁矿阶段流体3He/4He=0.0108~0.1301Ra(平均0.0697Ra),40Ar/36Ar=221.4~401.4(平均315.1),δDSMOW=-31.8‰^-15.4‰,δ18OSMOW=-2.72‰~1.88‰;高岭石-硬石膏-石英-黄铁矿阶段流体3He/4He=0.0162~0.0223Ra(平均0.0193Ra),40Ar/36Ar=312.5~367.6(平均340.05),δDSMOW=-25‰^-8‰,δ18OSMOW=-6.59‰^-4.89‰。成矿流体的同位素特征显示,幔源流体可能参与了泥河铁矿床早期的成矿作用,后期改造型饱和大气降水逐步加入并占据成矿作用的主导地位。研究结果表明,长江中下游地区中生代强烈的壳幔相互作用,是形成区域巨量金属矿床的重要机制,区域的深大断裂构成了幔源岩浆、幔源物质参与浅部成矿的通道。

The Nihe iron deposit is located in the Luzong Mesozoic volcanic basin,which is one of the important ore concentrated areas in Middle-Lower Yangtze metallogenetic belt. Nihe deposit can be classified into subvolcanic porphyry-related iron deposit. The deposit is controlled by the Luohe-Quekou fault which cuts through crust to Moho. The ore-forming fluids of anhydrite-diopsidemagnetite stage have a3 He /4He = 0. 14 ~ 0. 76Ra（ mean 0. 3548Ra）,40 Ar /36 Ar = 262. 2 ~ 364. 9（ mean 299. 3）,δ18OSMOW=- 2. 16‰ ~ 5. 04‰,δDSMOW=- 40. 7‰ ^- 34. 8‰; fluids of anhydrite-magnetite-pyrite stage have a3 He /4He = 0. 0108 ~0. 1301Ra（ mean 0. 0697Ra）,40 Ar /36 Ar = 221. 4 ~ 401. 4（ mean 315. 1）,δDSMOW=- 31. 8‰ ^- 15. 4‰,δ18OSMOW=- 2. 72‰ ~1. 88‰; fluids of kaolinite-anhydrite-quartze-pyrite stage have a3 He /4He = 0. 0162 ~ 0. 0223Ra（ mean 0. 0193Ra）,40 Ar /36 Ar =312. 5 ~ 367. 6（ mean 340. 05）,δDSMOW=- 25‰ ^- 8‰,δ18OSMOW=- 6. 59‰ ^- 4. 89‰. The isotope characteristics suggest that mantle-derived fluids involved in the anhydrite-diopside-magnetite stage. During the anhydrite-magnetite-pyrite stage and kaoliniteanhydrite-quartze-pyrite stage,meteoric water becomes more and more important in the ore-forming process. The Mesozoic intense mantle-crust interaction is the major mechanism for the formation of huge metallic accumulation. Regional trans-crustal faults construct the channels for the mantle-derived magma and ore-forming material in Middle-Lower Yangtze metallogenetic belt.