桂中盘龙铅锌矿流体包裹体特征及其对钦杭成矿带热水喷流-改造成矿作用的指示

A fluid inclusions study of the Panlong lead-zinc deposit and its implication for genesis

盘龙铅锌矿是近年来在钦杭成矿带南段新发现的大型铅锌矿床,位于广西大瑶山西侧,属于桂中坳陷带与大瑶山隆起的结合部位。它的容矿围岩为泥盆纪上伦组白云岩。成矿过程可分为三个成矿期:1)原生沉积期,以星散状构造、似层状-条带状构造、浸染状构造、胶状-变胶状构造、草莓状构造、揉皱构造等矿石组构特征为代表;2)活化改造期,成矿元素重新活化富集形成网脉状构造、假角砾状构造、环带构造、晶洞构造、小球状构造、交代结构、压力结构等;3)地表氧化期,原生的硫化物在地表被氧化。本研究系统分析了原生沉积期和活化改造期重晶石内的流体包裹体特征。包裹体岩相学分析显示,两个期次的流体包裹体类型均比较简单,主要为富液相的气液两相包裹体。显微测温结果显示,原生沉积期均一温度范围110.0~234.3℃(平均值为147℃),盐度介于0.33%~15.57%NaCleqv之间(均值为7.09%Nacleqv)。活化改造期均一温度稍低于原生沉积期,但盐度却明显高于前者,均一温度范围107.9~179.5℃(平均值为139℃),盐度范围1.81%~21.24%NaCleqv(均值为10.90%Nacleqv)。拉曼分析测试显示,两个成矿期次流体包裹体气相组分主要为H_2O。原生沉积期和活化改造期成矿流体均具有中低温、低盐度和贫CO_2的特征。结合重晶石矿物的产出状态,原生沉积期流体特征与SEDEX型矿床流体特征相吻合,而对其改造的后期流体与浅成低温热液矿床或者SEDEX型矿床流体特征相符。联系到区域演化历史及海底热水的幕式喷发特征,本研究认为,盘龙铅锌矿是典型的古生代热水喷流沉积叠加后期改造成矿的复合"二阶段成矿作用"的结果,对古生代地层中SEDEX型矿床的改造动力来源于后期浅成低温热液活动,也可能是晚期的又一次热水喷流活动。

The Panlong lead-zinc deposit is a large Pb-Zn deposit discovered in recent years. It is located in the Devonian Shanglun Formation,which is in the southern section of Qingzhou bay-Hangzhou bay metallogenic belt. Based on the field and petrographic observation,three metallogenic stages are recognized： 1） The primary sedimentary stage. In this stage,sulfides were preserved with scattered,layered-banded, disseminated, colloidal to metacolloidal, framboidal, and crumple structures; 2） Reworked stage,represented by stockwork,false brecciated,band,miarolitic,globular,metasomatic,pressure structures; 3） The surface oxidation stage. In this contribution,the characteristics of the fluid inclusions locked in barite of the first two ore-forming stages were studied systematically. The type of fluid inclusions is relatively sample dominated by the liquid（ H_2O）-rich inclusions,gas-liquid inclusions.The homogenization temperatures of fluid inclusions in primary sedimentary stage are 110. 0 to 234. 3℃（ mean = 147℃）,with corresponding salinities of 0. 33% to 15. 57% Na Cleqv（ mean = 7. 09% Na Cleqv）. In contrast,the homogenization temperatures of reworked stage range from 107. 9 to 179. 5℃（ mean = 139℃）,and the calculated salinities are 1. 82% to 21. 24% Na Cleqv（ mean =10. 90% Na Cleqv）. Laser Raman spectroscopic analyses illustrated that the mainly gaseous composition of fluid inclusion is H_2O. The characteristics of ore-forming fluids in primary sedimentary stage is consistent with typical SEDEX deposits,while showing similarities with SEDEX or epithermal deposits in the reworkd stage. Taking regional evolution into consideration simultaneously,the Panlong leadzinc deposit is defined as a reworked SEDEX deposit.