The Analysis of Sedimentary Facies in the Ore-Bearing Succession of the Fankou Lead-Zinc Ore District,Guangdong Province

The exceptionally largescale stratabound Fanpou lead-zinc deposit lies in northern Guangdong Province. The orebodies are confined to carbonate rocks in the basal part of the Middle to Upper Devonian. In the present paper sedimentary facies in the ore-bearing series have been distinguished from the base of the succession upwards. The Guitou Formation （D₂g）consists mainly of purplish red fine-grained clastic rock intercalated with mudstone and a small amount of conglomerate at the base. Swash cross-bedding is visible in the sandstones with high compositional and textural maturities, indicating a coastal facies. The lower member of the Donggangling Formation （D₂d^a）is made up of purplish grey and greyish-white medium and fine-grained elastics interbedded with mudstone containing fossils such as fish, charophtes, crinoids, brachiopods and so on, indicating nearshore facies. The upper member of the formation （D₂d^b）, one of the most important ore-bearing horizons, is composed of limestones and dolomitic limestones which contain algae, ooids, abundant fossils of normal marine organisms as well as bird's-eye structures, desiccation cracks and scour structures, indicating a mostly open carbonate platform environment, occasionally restricted platform facies. As for the Tianziling Formation,the lower member （D₃t^a）consists of nodular and oolitic alga-bearing limestone and marl as well as patch reefs at the base. The reef-building organism includes Dictyostromatopora and stromatolitic algae. This member may be further subdivided into three facies: （1） beach facies; （2） semi-restricted back-beach lagoon facies and （3）fore-beach slope facies. The middle member （D₃t^b）, which is the important source bed and the main ore-bearing horizon in the area, consists of greyish black nodular limestone, banded limestone and silty intraclastic limestone which contain abundant organic matter and blue-green algae. The upper member（D₃t^c）composed of granophyric limestone and dolomitic limestone-belong to open platform facies. The Maozifeng Formation （D₃m）is composed of blackish grey siltstone intercalated with sandy shale, dolomitic siltstone and quartzose sandstone, and are low-energy nearshore deposits. In brief, the ore-bearing succession exhibits a complete sedimentary cycle which passes from coastal facies→open platform facies→semi-restricted platform facies→open platform facies→coastal facies,i.e. elastic rock→carbonate rock→clastic rock, whereas the sedimentary environments range from oxidizing and acidic through weakly reducing and weakly alkaline to oxidizing and acidic environments. The upper member of the Donggangling Formation and the lower and middle members of the Tianzlling Formation are the target strata for ore exploration in this region.