滇东北会泽地区铁胆石产出特征及成因分析

Characteristics and genesis of iron kernel stone in Huize area,northeastern Yunan

铁胆石是极具观赏价值的玩石新宠,在中国仅有滇东北会泽县驾车乡等少数地方产出。驾车乡的铁胆石产于下寒武统筇竹寺组黑色炭质页岩、炭质泥质粉砂岩中。其实质为富含黄铁矿晶体的碳酸盐岩结核体,在围岩中分布极不均匀,多呈黑色、灰黑色中带浅铜黄色;大小不一,形态各异,具有沉积层理及定向排列特征,主要成分为黄铁矿、方解石、白云石以及泥质、碳酸质胶结物。铁胆石形成于水体较深、水动力较弱的还原环境,经历元素富集、黄铁矿形成,岩石固结、结核体形成以及差异风化、铁胆石显露三个阶段;前两个阶段在较深海水、热液和生物作用参与下,形成了较坚硬固结的原生铁胆石;后一阶段经差异性风化剥蚀和搬运而形成次生铁胆石。

Iron kernel stone is a new favorite of ornamental stone,found only in a few locations such as Jiache Town of Huize area in northeat Yunnan.In Jiache Town,the iron kernel stone occurs in the black carbonaceous shale and carbonaceous argillaceous siltstone of the Lower Cambrian Qiongzhusi Formation.Iron kernel stone is a carbonate nodule riched with pyrite crystal in substance.Carbonated nodules,unevenly distributed in wall rocks,have the characteristics of black or gray black with light copper yellow in colour,different size and shape,directional alignment and depositional bedding.The mainly mineral compositon of Iron kernel stone is pyrite,calcite,dolomite and argillaceous or carbonate cement.The Iron kernel stone was formed in a deep reduced water environment with relatively weak hydrodynamics and had experienced the following three stages in its formation：element enrichment-pyrite＇s formation,rock consolidation-nodule＇s formation and differential weathing-iron kernel stone＇s formation.With the action of hydrothermal and biology,the protogenetic,syndepositional iron kernel stone formed in the former two stages and was wrapped in sedimentary rocks of Qiongzhusi Formation.In the laste stage,with the action of differential weathering and removal,the secondary iron kernel stone was formed,and loosely accumulated in riverbed.