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

Abstract: 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.D₆^1a and D₆^2a 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.D₆^3a, D₆^4a and D₆^5a 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.D₆^6a. D₆^7a and D₆^8a 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.