四川盆地北缘马元铅锌矿床与古油藏关系研究

The genetic relationship between Pb-Zn deposits and paleo-oil reservoirs in Mayuan, northern Sichuan Basin

马元铅锌矿床是四川盆地北缘重要的铅锌矿床之一,赋矿地层为震旦系灯影组,野外可见大量的沥青与铅锌矿共生/伴生,镜下见早期沥青与闪锌矿、方铅矿共生,沥青的生物标志物与郭家坝组烃源岩极为相似。物质来源方面,铅锌成矿主要的物质来源和两期油气成藏的物质来源均为下寒武统郭家坝组;时间关系方面,铅锌成矿的共生矿物Rb-Sr同位素等时线年龄为(486.7±3.1)Ma,仅可能与第一期古油藏形成、破坏有关。闪锌矿和重晶石包裹体中含有CH4和少量H2S、沥青,表明铅锌成矿流体中富含有古油藏裂解产物。生烃、排烃、初次运移萃取出“双源层”中的铅锌元素,第一期古油藏裂解和短暂TSR作用产生的还原性硫为铅锌络合物沉淀提供了物质基础,第一期古油藏最终完全破坏残留下早期沥青。

Mayuan is one of the important lead-zinc deposits in northern Sichuan Basin,and its mineral formation is Cambrian Dengying Formation.Field and microscope studies revealed early bitumen and sphalerite,with associated galena.The biomarker of bitumen is very similar to that of the source rocks of Gjiaba Formation.The main sources of Pb-Zn deposits and paleo-oil reservoirs are the lower Cambrian Guojiaba Formation.The Rb-Sr isotopic isochron age of lead-zinc mineralization is(486.7±3.1)Ma,probably related to the formation and destruction of the first paleo-oil reservoirs.Sphalerite and barite inclusions contain CH4 and a small amount of H2S,bitumen,whereas lead-zinc mineralization fluids are rich in pyrolysis products of paleo-oil reservoirs.Hydrocarbon generation,hydrocarbon expulsion,the initial transport extraction of"double source layer"in the lead and zinc elements,the first paleo-oil reservoirs and the short-term TSR produced by the reduction of sulfur and lead-zinc complex precipitation all provided the material basis,and the first paleo-oil reservoirs eventually destroyed the residual early bitumen.