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

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。

Modes Of Occurrence Of Silica In Stratabound Lead-Zinc (Copper) Deposits Of The Fengtai Ore Field, Qinling Area And The Source Of Siliceous Substance

In stratabound lead-zinc (copper)deposits of the Fengtai ore field there exists a large amount of silica which is produced in three forms and hence h as three genetic types, the first type is its codeposition with ankerite, siderite and metallic sulfides to form silicolites, the second is its replacement of calcite to form silicified limestone and the third is the formation of pure quartz vein bodies or stockworks. Stratiform silicolites occur at the contact between limestone of Middle Devonian Gudaoling Formation and phyllite of Upper Devonian Xinghougpu Formation, showing stable horizon and typical sedimentary diagenetic fabric. According to petrologic characters, chemical composition, REE distribution pat- tern, oxygen and strontium isotopic composition, and quartz inclusion thermometric results, it is considered that siliceous substance came from ore-bearing syngenetic hydrothermal fluids in deep-seated strata, whereas silicolites were formed through deposition of ore-bearing hydrothermal fluids after it erupted over the sea bottom along syngenetic faults. Silicified limestone lies exclusively below sedimentary silicolites, assuming either network form penetrating bedding or stratified form. Siliceous substance came from the same source as silicolites, and it was formed either by the filling and metasomatic activity of ascending hydrothermal fluids along fissures of limestone or by the replacement of ore-bearing hydrothermal fluids that had already erupted to the sea botton after the previously-precipitated lime mud. Quartz veins, mainly distributed at random in silicolftes and ore bodies, were formed by previotlisly-deposited siliceous substance in sihcolites and ores which was mobilized by late tectonism and then filled fissures of rocks and ores. These three sorts of silica are closely related to lead-zinc(copper) mineralization; silicolites and some silicified limestone are major host rocks of the ore deposit; ore bodies are intimately associated with the three sorts of silica; and sillceous substance came from the same source as metallogenic materials such as lead and zinc. Therefore, silicolites, silicified limestone and quartz veins are all important ore-hunting indicators.