华南晚前寒武纪硅铁建造的层位、类型与形成条件

分布于华南诸省的晚前寒武纪条带状变质铁矿,1957年首先发现于江西新余地区,被命名为“新余式铁矿”,后又相继在湘中、闽北、桂北等地被发现。由于此类铁矿分布广泛,层位稳定,不仅是南方重要的铁矿资源,而且对我国南方前寒武纪地层的划分对比,澄江—加里东地槽的形成演化,以及变质铁矿的成因研究等,都有一定的理论意义,因而引起有关方面的重视。本文在系统研究江西新余式铁矿,并实地考察华南诸省铁矿的基础上,综合前

Horizon,Type And Formation' Conditions Of The Late Pre-Cambrian Banded Iron Ores In South China

Based on the research of "Xinyu type" Sinian iron deposits in Jiangxi Province and an examination of metamorphosed iron deposits in such places as Jiangkou and Qitung of Hunan, Sanjiang and Yingyangguan of Guangxi, Bailing of Longchuan County, Guangdong, and some others in Fujian, the authors have come to the following conclusions: l. The metamorphosed Late pre-Cambrian iron ores widespread in SoLith China might be roughly assigned to two ore belts, namely the Yiyang-Xinyu (Jiangxi) -Jiangkou (Hunan)-Sanjiang (Guangxi) ore belt or simply the northern ore belt, and the Songzheng (Fujian) -Shicheng (Jiangxi)-Beiling (Longchuan of Guangdong) -Yingyangguan (Guangxi) ore belt or the southern ore belt. Tectonically, the former lies along the southern margin of "Jangnan old Land" while the latter along the northwestern border of "Cathaysian old Land". 2. This type of iron deposits invariably occurs in the same interglacial horizon of the Sinian great glacial epoch in South China. Above and below the ore bed there lie the glacial till-bearing volcanic-sedimentary layers corresponding to Nantuo dxift sheet and Changan subdrift sheet respectively. 3. Based on sedimentary features, the iron formations can be divided into four types: siLiceous-ferruginous-basalt formation, siliceous-ferruginous- clastic formation, siliceous-ferruginous-tuff formation and siliceous-ferruginous-carbonate formation, which progressively grade into each other. 4. 1ron ores were formed at the late stage of Late Proterozoic rifting in neritic environments, with their distribution governed by the rift valleys on the margins of "Jiangnan old Land" and "Cathaysian old Land". Consequently, intense mafic volcanism as well as weathering and denudation of palaeocontiaent during the rifting provided material sources for the formation of iron deposits. Meanwhile, warm and humid stationary neritic environment during the South China great glacial period set up a favorable palaeographic and palaeogeographic condition for the deposition of iron ores. 5. The iron formation has undergone regional metamorphism of greenschist-amphibolite facies. To sum up, the Late pre-Cambrian banded iron ores should be of metamorphosed volcanic-sedimentary type.