云南金顶矿床物源特征及成矿年代探讨

【作者】 修群业；

【导师】 王安建；

【作者基本信息】 中国地质科学院 ， 矿物学、岩石学、矿床学， 2008， 博士

【摘要】 位于云南省兰坪县的金顶矿床为一世界著名的超大型铅锌矿。除铅锌矿外,在矿区不到10km²的范围内尚有大型（硬）石膏矿和天青石矿,以及中型硫铁矿等,成矿地质条件相当复杂。尽管本矿床已有20余年研究历史,但矿区内一些基本的地质问题没有得到完全澄清,导致对其成因一直存在较大分歧。作者通过较系统的野外及室内工作,对金顶矿区的地层划分、矿体空间分布形态、灰岩角砾岩成因、矿床物源特征和铅锌矿化年代等进行了探讨,并得出相应认识。对矿区内出露的地层重新进行了厘定。通过区域和矿区岩石组合序列的对比、孢粉组合及微量元素特征的研究表明,矿区中原划归云龙组（E₁y）含岩块（角砾）灰岩角砾岩实为一套上三叠统经构造变形-盐溶作用形成的岩石。依据（硬）石膏沉积特征及与区域相应层位的比较,它应归属三叠系。此外,矿区还出露有侏罗系花开左组（J₂h）、坝注路组（J₃b）、白垩系景星组（K₁j）、虎头寺组（K₁h）和新近系云龙组（E₁y）。利用Surpack应用软件首次建立了金顶矿区铅锌矿体三维立体模型。该模型显示铅锌矿体人致呈一蘑菇状分布。生动体现出灰岩角砾型矿体与砂岩型矿体是相连的,砂岩型矿体在上,为似层状、分布范围较广;灰岩角砾型矿体在下,分布局限,似蘑菇的根部。石膏、天青石等盐类矿体位于似层状砂岩型矿体之下,居蘑菇的中下部位,暗示金顶矿区的矿体分布与底辟构造中的盐丘紧密相关。经研究,金顶矿区存在两种成因的角砾岩:构造-膏溶角砾岩和底辟-侵位角砾岩。构造-膏溶角砾岩,经常与三合洞组灰岩相伴产出,区域上多呈孤岛状漂浮在云龙组之上、大多与推覆面产状相一致。其角砾成分单一（主要为沥青质灰岩、晶质灰岩）、大小混杂（nmm～nX10m）、无分选,角砾多呈不规则状和次棱角状或次浑圆状,部分角砾具有可拼性,角砾间为砂质充填或无充填,表明它是一套构造和膏溶共同作用形成的角砾岩。底辟-侵位角砾岩是本次工作新发现的,它在空间上与构造-膏溶角砾岩密切伴生,剖面上呈脉状或火焰状分布,局部呈脉状穿刺于围岩中,其胶结物中含有晚三叠世的孢粉组合,最年青锆石的年龄为225Ma,角砾岩本身是铅和锌的富矿体。通过微量元素、锆石的U-Pb年龄和Rb-Sr初始值等特征,揭示矿质来源属于壳源的,无幔源迹象。主容矿围岩的物源以上地壳的长英质沉积物为主,另有基性、中酸性火成岩的成分及部分老地壳物质的参与,成岩大地构造环境以被动大陆边缘为主,部分可能属大陆岛弧。首次证实金顶矿床容矿围岩“景星组”物源中有古元古代的老锆石。由方铅矿等矿石矿物的Pb-Pb模式法、闪锌矿和黄铁矿Rb-Sr法同位素定年结果显示,金顶矿床在中-晚三叠世（230Ma左右）时有一期矿化富集作用,可能代表了矿源的时代。因此,目前流行的矿床成因模式需要重新审定。更多还原

【Abstract】 Jinding deposit is a famous giant lead-zinc deposit,located in Lanping,Yunnan province.There are also large scale gypsum and celestite deposit,middle scale sulfur iron ore within 10 km².,besides lead-zinc deposit.Some basic geological problems are still ambiguous,and ore deposit genesis are controversial.With systemic field and indoor work,some conclusions are acquired about division of the strata,distribution and shape of ore bodies,genesis of limestone breccias,derivation of the ore deposit, lead-zinc metallogenic age,and so on.With contrast rock assemblage sequence between the ore district and region,and research on spore-pollen combination and trace element,limestone breccias do not belong to Yunlong formation（E₁y）,but upper Trias,which underwent structural deformation and salt dissolution.Gypsum also belongs to Trias according to their sediment characteristics and contrast to the relative stratum layer in the region,The 3-dimensional model of lead-zinc orebodies in Jinding district is established with Surpec for the first time.The model display a mushroom shape of the lead-zinc and Salt ore bodies.Ore bodies of limestone breccias type and sandstone type are conjoint.Ore bodies of sandstone type are on the upside,and vast distributing,with stratoid structure.Ore bodies of limestone type are on the downside,which like the root of the mushroom with finite distribution.Salt ore bodies,such as gypsum and celestite,located between them,which are on the middle and lower part of the mushroom,showing that the distribution of the ore bodies relate well to the salt dome of the diapir structure.There are two kinds of breccias in Jinding deposit:structure-salt dissolution breccias and diapar structure-emplacement breccias.Structure-salt dissolution breccias,accompanied by the limestone in Sanhedong formation,overlay on the Yunlong formation with isolated islands along the occurrence of the regional thrust sheet.The breccias generated due to structure and salt dissolution,which being simplex composition,composed of bituminous limestone and crystalline limestone, intermixing by big and small breccias（n mm～nX10m）,no separation.They are characterize by irregular and subangular with sandy filling or no filling,and some of them are jointable.Diapar structure-replacement breccias are discovered for the first time.This type is accompanied by the structure-salt dissolution breccias,being vein or flamboyancy in cross section while some of them shot through the lead and zinc ore. In fact,the breccias were lead and zinc orebodies themselves.Some spore-pollen assemblages of late Trias and the youngest zircon of 225Ma were also obtained in this type.Deriveration of the ore is from the upper crust according to the features of trace elements,zircorn U-Pb age and initial value of ⁸⁷Sr/⁸⁶Sr.It has not any charateristics of the mantle.Deriveration of main host rock is mostly felsic sediments,little basic and medium-acidic magma and old crust material.Geological setting of diagenism mostly belongs to passive continental margin,few to continental arc.Plaeoproterozoic zircons in Jingxing Formation（K₁j） are discovered first.The isotopic ages,such as Pb-Pb model age of galena,Rb-Sr isochrone age of sphalerite and pyrite,indicate that there exist mineralization concentration in Jinding deposit at middle-late Trias（230Ma±）,which must be the era of ore sources. Therefore,the present dominated genetic models about Jinding deposit have to be considered again.更多还原