秦岭凤太矿田层控铅锌(铜)矿床的氧化硅产出特征及其硅质来源

MODES OF OCCURRENCE OF SILICA IN STRATABOUND LEAD-ZINC (COPPER) DEPOSITS OF THE FENGTAI ORE FIELD, QINLING AREA AND THE SOURCE OF SILICEOUS SUBSTANCE

秦岭凤太矿田的所有铅锌(铜)矿床中都含有大量的氧化硅,前人资料中往往以沉积或蚀变单一形成方式论其成因,非此即彼。本文提出氧化硅有三种产出类型,以同生沉积型为主,其次为成岩后生阶段交代灰岩者,第三类为造山期形成的脉体。三类氧化硅的产出特征有许多不同,但硅质来源一致,即均来自深部地层和岩石中循环的含矿热液。对矿床中氧化硅的研究不仅有助于深入探讨矿床的成因,而且对于该类矿床的勘查有较重要的意义。

In stratabouncl lead-zino (copper) deposits of the Fengta ore field tere exists a arge amount of silica hich s produced in three forms and hence has three genetic types: the irst type is its codeposition with ankerite, siderite nd metallic sulfides to form ilicolites, he second is its replacement of calcite to form silicified limestone and the hird is the ormation of pure quartz vein bodies or stockworks.Stratiform silicolites occur at the contact etween imestone of Middle Devonian Gudaoling Formation and phyllite of Upper Devonian inghougpu Formation, showing table horizon and typical sedimentary diagenetic fabric. ccording o petrologic characters, chemical composition, EE distribution pat- tern, oxygen and strontium sotopic composition and quartz inclusion thermometric results, it is onsidered that siliceous ubstance came from ore-bearing syngenetic hydrothermal fluids in deep-seated strata, hereas ilicolites were formed through deposition of ore-bearing hydrothermal fluids after it erupted ver the sea ottom along syngenetic faults. Silicified limestone lies exclusively below edimentary silicolites, assuming either etwork form penetrating bedding or stratified form. iliceous substance came from the same source as silicolites, nd t was formed either by the illing and metasomatic activity of ascending hydrothermal fluids along fissures of imestone or y the replacement of ore-bearing hydrothermal fluids that had already erupted to the sea otton fter he reviously-precipitated lime mud. Quartz veins, mainly distributed at random in ilicolites and ore bodies, were ormed by previously-de-posited siliceous substance in ihcolites and ores which was mobilized by late tectonism nd then filled fissures of rocks and res.These three sorts of silica are closely related to lead-zinc (copper) ineralization; ilicolites and some silicified limestone are major host rocks of the ore deposit; ore bodies re htimately associated with the three sorts of silica; and siliceous substance came from the ame source as etallogenic materials such as lead and zinc. Therefore, silicolites, silicified imestone and quartz veins are all mportant ore-hunting indicators.