【作者】 周振华；

【导师】 毛景文；

【作者基本信息】 中国地质科学院 ， 矿物学、岩石学、矿床学， 2011， 博士

【摘要】 黄岗锡铁矿床是大兴安岭南段多金属成矿带内的一个重要的大型多金属矿床,为我国长江以北最大的锡多金属矿床,也是内蒙古自治区第二大铁矿。本论文在充分收集并总结前人研究成果的基础上,选择黄岗锡铁矿床作为典型矿床剖析。通过野外地质调查、电子探针分析、主微量成分分析、Sr-Nd-Pb-Hf同位素示踪、流体包裹体、稳定同位素、放射性同位素年代学等方法和手段,主要研究了成矿岩体特征、夕卡岩岩体特征、成矿物质来源、成矿流体来源、矿床成因、成矿作用及成矿动力学背景等方面的内容,建立了矿床成矿模型,探讨了区域成矿规律,取得的主要成果如下：(1)详细的野外地质调查发现,下二叠统大石寨组及黄岗梁组中是矿床的主体含矿层位,矿体总体顺层分布,空间上与夕卡岩密切相关。矿石主要类型以层纹状、团块状夕卡岩矿石为主,其次为产在大理岩中的条带状、团块状矿石,围岩与矿体的接触界线清楚。矿石矿物种类繁多,围岩蚀变普遍发育,夕卡岩分带明显。矿床的形成经历了夕卡岩阶段、退化蚀变阶段、石英硫化物阶段和碳酸岩阶段,其中第2、3阶段为主成矿期。(2)成矿岩体为燕山晚期花岗岩体,岩体的Si02含量较高(66.81～77.93%),A1203含量低(11.07～14.54%),显著贫镁,ALK较高(5.65～10.67%),K20/Na2O值在0.32～10.53,平均为2.26。稀土配分曲线呈右倾轻稀土富集型,铕强烈亏损,δEu值为0.03-0.24。富集高场强元素Zr.Hf和大离子亲石元素Rb.U.Th,而元素P、Ti、Ba、Sr明显亏损,具有与洋岛玄武岩相似的Y/Nb等元素比值(>1.2),具有典型的A1型板内非造山花岗岩特征。(3)同位素组成特征表明,黄岗岩体的(87Sr/86Sr)i值在0,70211～0.70729,εNd(t)值在-0.8～0.9,Nd模式年龄TDM介于855～993Ma；全岩Pb同位素206Pb/204Pb.207Pb/204Pb和208Pb/204Pb值介于18.974～26.107、15.554～15.914和38.894～39.890,铅具有混合来源特征；176Hf/177Hf比值介于0.282744～0.282922,εHf(t)值为1.9～18.3,两阶段Hf模式年龄(TDM2)变化范围为561-888Ma,年轻的Nd、Hf同位素模式年龄暗示本区晚元古代时期曾发生一次重要的地壳增生事件。岩浆源区来自起源于亏损地幔的初生下地壳物质的部分熔融,可能存在少量古老陆壳物质的混染。岩体的形成机制为：从俯冲洋壳析出流体交代的地幔楔或亏损地幔减压部分熔融作用形成的基性岩浆分离后,诱发岩石圈拆沉、幔源岩浆上涌和底侵,促使镁铁质的初生地壳物质重熔并不断分异演化,从而产生了大量花岗岩浆,其成因构造背景与区域盆岭构造格局相吻合。(4)电子探针分析结果显示,与成矿密切相关的夕卡岩体中石榴子石和辉石的矿物组分分别为Adr28.69-96.44GrS2.00～67.38(Prp+Sps)0.67～5.69和Di11.8～94.12Hd4.08～81.28Jo1.79～20.02,其较大的成分变化特征反映出了夕卡岩不是在一个完全封闭的平衡条件下形成的。角闪石大多为镁铁钙角闪石,个别属于铁角闪石,成分变化较大的原因可能是由于氧化还原条件的改变从而导致不同程度的AlⅥSi←→(Na, K)的置换作用,属于一种固相线下的转变趋势。角闪石中的四次配位的Si、Al,六次配位的Al、Ti和A位置的阳离子数变化范围很大,可能是由于接触交代作用过程中的岩浆的成分差异或结晶时的物理化学条件的改变所引起的。富锰的辉石夕卡岩是岩浆流体顺层间破碎带渗滤交代形成的,富锰辉石可作为本区寻找Sn、Cu、Zn等多金属的找矿标志,在外接触带夕卡岩和其附近的大理岩中是多金属成矿的有利部位。(5)流体包裹体研究表明,本区包裹体类型复杂,主要有硅酸盐熔融包裹体、富气相水溶液包裹体、富液相水溶液包裹体、含子矿物多相包裹体,富CO2包裹体,含C02多相包裹体,其中以富液相水溶液包裹体为主。成矿早阶段以硅酸盐熔融包裹体和H20-NaCl型包裹体为主,晚阶段出现少量CO2-H2O±CH4型包裹体和CO2-H2O-NaCl型包裹体。从早到晚的四个阶段均一温度分别为(257～432℃、>550℃)、322～403℃、202～304℃、153～221℃；盐度w(NaCleq)为(12.13～19.88%、>66.8%)、16.43～22.34%、1.74～14.77%、1.74～11.9%。流体包裹体的均一温度和盐度w(NaCleq)主要集中于220～432℃和1.74～22.34%,总体上属于高-中温、中-低盐度类型矿床。包裹体气相成分以C02及H20为主,其次为N2、O2和CH4,少量C2H2、C2H4和C2H6；液相成分中阳离子以Na+、K+为主,其次为Ca2+、Mg2+,阴离子以Cl-、SO42-为主,其次为F-,还含有少量Br-、NO3-,成矿流体体系属CO2-H2O-NaCl±CaCl2(KCl)体系。初始成矿流体由岩浆“初始沸腾”作用形成,流体减压沸腾、开放和相的分离和多次不混溶作用可能是成矿的主要原因。(6)H-O同位素示踪表明,不同成矿阶段脉石矿物σDV-SMOW变化很大,主要-116--73%o,平均-98%o,个别样品在-187～-182‰；Ⅰ-Ⅳ阶段δ18OH2O分别为7.4～9.8‰、-3.3～8.6‰、-6.0～4.9‰和-10.9～-1.6‰,说明成矿流体主要为岩浆水,后期存在大气降水混合和岩浆期后热液叠加成矿作用。矿石σ34SV-CDT值变化区间在-9.0～4.5‰,平均值-1.87‰,相对于地幔平均的δ34S变化范围更宽,表现出经过改造的混合硫的特征；辉钼矿Re同位素含量较高,变化范围209.7～300.6×10-6,平均260.5×10-6,远高于绝大多数辉钼矿Re的含量,表明黄岗矿床的成矿物质主要来源于地幔,存在部分地壳物质的加入；(7)采用LA-ICP-MS锆石U-Pb定年法获得成矿岩体中的钾长花岗岩和花岗斑岩分别形成于136.7±1.1Ma和136.8±0.57Ma,与磁铁矿共生的辉钼矿Re-Os等时线年龄135.3±0.70Ma,成岩成矿时代吻合,均发生在早白垩世,表明了两者具有密切的成因联系。成岩成矿年代学数据统计分析发现,大兴安岭地区成矿作用以中生代燕山期成矿为主,存在140-130Ma左右、180-160Ma左右的两次成矿爆发期,其中140-130Ma左右主要出现在岩石圈伸展减薄背景下,与燕山晚期侵入的小岩体有关的锡铅锌铜银多金属矿床；180-160Ma左右主要出现与燕山早期西伯利亚与华北板块后碰撞造山有关的钼铅锌铜金多金属矿床。黄岗锡铁矿床是在古太平洋板块俯冲大陆边缘弧后伸展环境下,发生的大规模成矿作用的产物。(8)综合上述详细的研究,对比了国内外较有代表性的以锡铁共生为主的矿床,建立了黄岗锡铁矿床的成矿模型,初步探讨了区域成矿规律。更多还原

【Abstract】 The Huanggang Sn-Fe deposit in Inner Mongolia is one of the important large polymetallic deposits in the polymetallic belt of south Daxinganling, the largest tin-based multi-metal deposit in the north of the Yangtze River, and also it is the second largest iron deposit in Inner Mongolia Autonomous Region. In this paper, we choose Huanggang Sn-Fe deposit as a typical deposit to study, which were based on the full collection and summary of the previous studies. Through the methods and means as field investigation, electron microprobe analysis, major and trace elements component analysis, Sr-Nd-Pb-Hf isotopic tracer, fluid inclusion, stable isotope, etc., we mainly studied the aspects of the host rocks characterics, skarn bodies characterics, source of ore-forming material, source of ore-forming fluid, genesis of the deposit, mineralization process and metallogenic geodynamics background, etc, established the mineralization model of Huanggang deposit, preliminary discussed the regional metallogenic rule in the study area, the main achievements obtained were as follows:(1) Detailed field geological survey indicates that lower Permian Dashizhai Formation and Huanggangliang Formation are the main ore-hosting layers. Ore bodies are largely concordant with the bedding of the strata, and the distribution of the ore bodies is spatially related to skarn. Main types of ore minerals are major of laminated, massive skarn ores, followed by the banded, agglomerate ore produced in the marble, with clear contact lines between wall rocks and ore bodies. There are various types of ore minerals, commonly developed rock alteration, and skarns with obvious zoning. The formation of Huanggang deposit experienced a period composed of skarn phase, retrograde eroding phase, quartz sulfide phase and carbonate phase, among which the second and third phase are the main mineralization stages.(2) The deposit was temporally and specially related to the late Yanshanian granites, the Huanggang granites are characterized by SiO2 content (66.81～77.93%), Al2O3 content (11.07～14.54%), and significant depletion of magnesium, high ALK (5.65～10.67%), the K2O/Na2O values format a range of 0.32 to 10.53, averaging 2.26. The chondrite-nomalised REE pattern shows LREE enrichment, strong negative Eu anomalies, and 8Eu at 0.03 to 0.24. The high field strength elements such as Zr, Hf and lithophile elements such as Rb, U and Th are enriched, whereas the elements P, Ti, Ba and Sr are significantly depleted and their have similar Y/Nb values(>1.2) to those of oceanic island basalts. These features are coincident with the typical A1 within-plate anorogenic granite. (3) The isotopic composition characteristics show that (87Sr/86Sr)i values of the Huanggang granites range from 0.70211 to 0.70729, theεNd(t) values and Nd model ages(TDM) vary from-0.8 to 0.9 and 855 to 993 Ma respectively; The whole rock Pb isotope values are relatively high, the 206Pb/204Pb values range from18.974 to 26.107, with 207Pb/204Pb values between 15.554 and 15.914, and 208Pb/204Pb values between 38.894 and 39.890, which suggested the lead with a mixed source; The 176Hf/177Hf values range from 0.282744 to 0.282922, with the correspondingεHf(t) values ranging from 1.9 to 18.3, and Hf model ages (TDM2) from two-stage between 561 and 888Ma, young Nd, Hf isotope model ages imply that this area took place an important crustal growth event during the late Proterozoic. The Huanggang granites derived from the partial melting of newborn lower crust originated from depleted mantle, and maybe with the contamination of a small amount ancient continental crust. We conclude that the formation mechanism of Huanggang granites as following:the separation of mafic magma, produced from the partial melting of mantle wedge metasomatized by the precipitated fuilds from subducted oceanic crust or the decompressed depleted mantle, could induce lithospheric delamination, mantle upwelling and magma underplating, which promoted the remelting, differentiation and continued evolution of mafic primary crust, resulting in a large number of granitic magma, and its geodynamic setting was consistent with the regional Basin and Range tectonic setting.(4) Electron microprobe analyses showing that the components of garnet and pyroxene are Adr28.69～96.44Grs2.00～67.38(Prp+Sps)0.67～5.69 and Di11.8～94.12Hd4.08～81.28JO1.79～20.02, respectively, their large range of composition character reflects that skarns were not formed under the totally enclosed equilibrium condition. The amphibole mostly belong to magnesium-ferric-calcium amphibole, only some individuals are ferric-hornblende, larger change of composition is probably due to the change of redox conditions resulting in different degrees of AlⅥSi←→(Na, K) displacement, which belongs to the transforming tendency under solidus. Tetrahedral Si, Al, octahedral Al, Ti and cations in A site of amphibole change greatly, which may be caused by the composition difference of the magma in contact metasomatic process or the change of physicochemical condition during crystallizing. Mn-enriched pyroxene skarns were formed by infiltration metasomatism of magmatic fluid along fracture zones between layers, Mn-rich pyroxene could be the indications for looking for Sn, Cu, Zn and many other metal ores in this area, and the outer contact zone of skarn and its vicinal marble is the favorable position for polymetallic mineralization.(5) Fluid inclusion studies show that the inclusion types of Huanggang deposit were complex, mainly of silicate melt inclusions, vapor-rich liquid inclusions, liquid-rich liquid inclusions, daughter mineral-bearing inclusions, CO2-rich inclusions and CO2-bearing mutiphase inclusions, in which the liquid-rich inclusions as the main. Inclusions in early mineralization phase mostly contain silicate melt inclusions and H2O-NaCl type inclusions, a small amount of CO2-H2O±H4 type inclusions and CO2-H2O-NaCl type inclusions occurs in late mineralization phase. Homogenization temperatures of four phases from early till late are (257～432℃,>550℃),322～403℃,202～304℃,153～221℃respectively; salinities are (12.13～19.88%,>66.8%),16.43～22.34%,1.74～14.77%,1.74～11.9% respectively. Homogeneous temperature and salinity of ore-forming fluid concentrated in 220～432℃and 1.74～22.34%, which belong to the deposit type of medium-high temperature and medium-low salinity. Gas composition of fluid inclusions mostly contain CO2 and H2O, followed by the N2, O2, and CH4, a small amount of C2H2, C2H4 and C2H6; cation of liquid composition mostly contain Na+, K+, followed by Ca2+, Mg2+, while anions with Cl-, SO42- as major, followed by the F-, and also contain a small amount of Br-, NO3-. Buck boiling and phase separation of fluid as well as fluid mixing may be the main reasons of mineralization.(6) H-O isotopic tracing show that 8Dv-smow values of gangue minerals in different mineralization stages vary greatly, mainly of -116～-73‰, averaging -98‰, the individual samples range from-182‰to -187‰.δ18OH2O values ofⅠtoⅣstage were 7.4～9.8‰、-3.3～8.6%‰、-6.0～4.9‰and -10.9～-1.6‰, respectively, which indicate that the ore-forming fluids were mainly of magmatic water, there also being meteoric water mixing and post-magmatic hydrothermal superimposed mineralization.δ34SV-CDT values of ore minerals range from -9.0～4.5‰, averaging -1.87‰, which have wider range relative to the averageδ34S values of mantle, showing a mixture character of sulfur through transformation effect; Re isotopic content of molybdenites were high, change range of 209.7～300.6×10-6, an average of 260.5×10-6, which were far higher than the Re contents of most molybdenites, indicating that the ore-forming minerals of Huanggang deposit were mainly came from the mantle and having a part of the crustal material added.(7) LA-ICP-MS zircon U-Pb dating results show that the K-feldspar granite and granite-porphyry in the Huanggang rocks were formed at 136.7±1.1Ma and 136.8±0.57Ma, respectively. Re-Os isotopic dating of the molybdenites symbiosis with magnetites obtained isochron age of 135.3±0.70Ma. The host rock and mineralization ages of Huanggang deposit were consistently, both occurred in early Cretaceous, suggesting that their have a close genetic relationship. Ore-forming ages data statistical analysis show that the mineralization of the Da Hinggan Mts. area were mainly in Mesozoic Yanshanian, there are two ore-forming eruptive periods, i.e., c.140-130 Ma and 180～160 Ma, while the tin-lead-zinc-copper-silver polymetallic deposits related with the small intrusion in Yanshanian under lithospheric extensional and thinning environment mainly occurred in c.140～130 Ma; the molybdenum-lead-zinc-copper-aurum polymetallic deposits related with the post-collision orogeny of Siberia plate and North China plate in early Yanshanian mainly occurred in c.180～160Ma. Huanggang tin-iron deposit is the product of large-scale mineralization under the paleo-Pacific plate subduction environment.(8) Based on the detailed study described above, we compared the typical deposits coexisting with tin and iron at home and abroad, established the metallogenic mode of the Huanggang tin-iron deposit, and preliminary discussed the regional metallogenic rule in the study area.更多还原