西成铅锌矿田西部中泥盆统西汉水组碳酸盐岩沉积特征

运用岩石学和化石岩石学方法,论述了西成铅锌矿田西部中泥盆统西汉水组碳酸盐岩的沉积特征.西汉水组碳酸盐岩的组分以生物、生物碎屑、内碎屑和鲕粒最为重要;常见粒屑结构、花岗变晶结构、生物骨架结构及层纹-条带状构造;查明碳酸盐岩22种;西汉水组发育三种韵律,分别代表潮间、潮下的生物礁环境;并探讨了岩石类型与铅锌矿成矿的关系。

Sedimentary Characteristics of Xihanshuicarbonate Formation of Middle Devonian in Western Sicheng Lead- Zine Orefield

In Western Xicheng Lead-Zinc Orefield. the Xihanshui carbonate formation of Middle Devonian developed well, the total thickness is about 1675m and the lithofacies change obviously.The lower part is a series of thick marine carbonate and the upper consists mainly of clastic rocks, Dengjiashan deposit and tens of other mineral points occur n the contact zone of Xihanshui reef limestone with phyllite. There are about ten kinds of rocks recognized in the corbonate formation.They are micritic limestone. powdery crystal limestone, bioclastic bearing limestone, sand clastic limestone, deformed faecal pellet limestone, oditic limestine, rudstone, bioclastic limestone, and reef limestone. The following is the interpretation of the sedimentary environment of Xihanshui carbonate formation. l.D₆1a and D₆2a strate Mainly consist of grey thinly micritic limestone, lamintated powdery crystal limestone, bioclastic bearing powder crystal limestone and silty shale, thin to middle and cross beddings and 15 to 25 percent of bioclasts are contained. The lower part sedimented from intertidal shallow depression. The upper part of oolitic limestone and deformed sand clastic limestone were fromed in intertida! shallow beach of subtidal shallow oolitic beach. 2.D₆3a, D₆4a and D₆5a strata The rocks are rudstone, bioclast poudery crystal limestone, reef limestone and bioclast limestone which were formed in subtidal bioherm and backreef limited shallow basin. Reef appeared as barrier reef which roughly parallel to the coastline, stretched tens of kilometres and thickness is about 700m. on the landward side of the barrier reef, a backreef limited shallow basin was formed where bioherm podwery crystal limestone and lead and zirie deposited and formed the source bed.Bioherm is contributive to the removing accumulation of ore-forming, the fact that the commercial ore bodies occur in the top of bioherm or the contact zone of bioherm with phyllite is an evidence. 3.D₆6a. D₆7a and D₆8a strta Grey silty powdery crystal limestone and bioclast powdery crystal limestone are the main rocks which were formed in the intertidal shallow depression. According to the analysis above, the changes of sedimentary environments of Xihanshui carbonate formation can be outlined as: from intertidal shallow depression procecced to ir.tertidal shallow beach, suhtidal bioherm, backreef Limited shallow basin till to intertidal shallow depression.