安徽池州马头钼铜矿床成因与成矿模式

The Genesis and Metallogenic Pattern of the Matou Mo-Cu Deposit in Chizhou District,Anhui Province,China

马头钼铜矿床是长江中下游皖南地区新探明的一个中型多金属矿床,成矿受东西向古特提斯构造体系向北东向古太平洋构造体系转换机制制约。文章通过对矿床流体包裹体、稳定同位素地球化学特征进行研究,厘定了矿床成因,并构建了矿床成矿模式。研究结果表明:矿区内石英脉中流体包裹体均一温度范围为91℃~398℃、盐度范围为0.88%~37.4%、密度范围为0.18g/cm3~1.10g/cm3,属中温、中等盐度、中低密度流体,成矿流体演化经历了钾长石化、石英-绢云母化和青磐岩化三个阶段,石英-绢云母化阶段成矿规模最大;矿石与围岩全岩Pb同位素组成均一,在^(208)Pb/^(204)Pb-^(206)Pb/^(204)Pb图中呈线性分布趋势,表明成矿物质具有多源性,花岗闪长斑岩参与成矿的特征更为显著;黄铁矿中硫同位素组成介于-1.00‰^+7.00‰,近似塔型分布,辉钼矿硫同位素组成高于黄铁矿,表明矿石矿物中硫同位素组成均一且达到平衡,硫主要来源于深部地幔,并受到地壳物质的混染;无矿、含矿两类石英脉氧同位素组成范围为9.80‰~13.0‰,二者为同源热液作用的产物,流体中δ18 O水值为-1.21‰^+1.99‰,接近大气降水值,推测在成矿过程中原始含矿热液受到不同程度大气降水的混合。马头钼铜矿床为一具有斑岩型矿床围岩蚀变分带特征的次火山-热液矿床,属斑岩成矿系统,花岗闪长斑岩是区内最主要的成矿母岩,粉砂岩也为成矿提供了一定的物质条件,但钾长花岗岩脉与成矿关系不大。

The Matou molybdenum copper deposit is a medium sized polymetallic deposit which was newly ascertained in south Anhui of the Middle and Lower Reaches of the Yangtze River, and the mineralization was constrained by the transformation mechanisms which were changed from the EW trending Paleo Tethys techonic system in to the ancient NE trending. Pacific tectonic system in the characteristics of fluid inclusion and stable isotope were studied to determine the genesis and to construct the metallogenic pattern for the deposit. The results show that the homogenization temperature range for fluid inclusions in quartz from 91 ℃ to 398 ℃, the salinity range from 0.88％to 37.4％ and the density range from 0.18g/cm3 to 1.10g/cm3, those indicated that the ore forming fluid was medium temperature, medium salinity and lower density fluid, the potassium feldspar alteration, quartz sericitization and propylitic alteration stages were experienced in the ore forming fluid evaluation, and the mass mineralization were occurred in quartz sericitization stage. Pb isotopic composition in ore were similar to wall rock, the indistinguishable Pb isotopic composition with ore and wall rock in 208Pb/204Pb 206Pb/204Pb figure indicated that ore forming materials are multi sources, and more mineralizing matters were supplied by granodiorite porphyry. The δ34S values of pyrite show a total range from -1.00‰ to ＋7.00‰ and has a tower type distribution, the δ34S values of molybdenite were higher than pyrite, showing that the sulfur isotopic composition reached a equilibrium states in minerals, which were mainly from deep mantle and contaminated by crustal sulfur. The oxygen isotopic composition （δ18O values） of free quartz and ore bearing quartz vein show a range from 9.80‰ to 13.0‰, both of them were formed in the same hydrothermalism, the δ18Owater values in fluid show a range from -1.21‰ to ＋1.99‰ are similar to the composition in atmospheric precipitation, those inferred that the original ore bearing hydrothermal were mixed by atmospheric precipitation in different degree in metallogenic process. The Matou deposit is a sub volcanic hydrothermal deposit which has a characteristics of wall rock alteration for porphyry deposit, and belongs to a porphyry metallongic system. Granodiorite porphyry is the main mother rock which supplied the main ore forming materials for mineralization in the mining area, and siltstone supplied certain material conditions as well, but moyite veins unrelated to the mineralization.