福建省紫金山矿田龙江亭矿床地质和成矿流体特征及成因意义

龙江亭矿床地处福建省紫金山矿田的西南部,矿体受北西向断裂控制,产于燕山早期中细粒花岗岩中。含矿岩体整体遭受硅化-绢云母化-伊利石化-蒙脱石化,浅部为强硅化-迪开石化,深部保留有钾化;后期蚀变主要分布在地表,为硅化-高岭土化和褐铁矿化,偶见萤石化、重晶石化、石膏化。矿物组合和穿插关系显示,成矿前为无矿石英脉;成矿期脉体矿物组合为石英-绢云母-黄铁矿-铜硫化物;成矿后脉体矿物组合为石英-方解石±石膏。根据矿石组构和铜硫化物类型,成矿期脉体可细分为3个亚类或阶段:早阶段为黄铁矿-黄铜矿组合,浸染状和网脉浸染状构造,见于矿体深部;中阶段为黄铁矿-黄铜矿-斑铜矿-硫砷铜矿组合,具梳状、胶状或皮壳状构造,见于矿体中部;晚阶段为蓝辉铜矿-铜蓝组合,浸染状或晶簇构造,见于浅部坑道和地表。早阶段脉体矿物含大量富液相包裹体,少量富气相包裹体,均一温度为262~403℃,w(Na Cleq)介于0.2%~18.6%,显示中-高温热液的特征;中阶段脉体中的包裹体几乎全部均一到液相,完全均一温度为201~302℃,峰值为250℃,w(Na Cleq)介于0.2%~10.1%,总体显示中-低温热液的特征;晚阶段包裹体全部均一到液相,均一温度为117~250℃,w(Na Cleq)介于0.4%~9.5%之间,表现出低温、低盐度大气降水热液的特征。根据蚀变类型确定成矿期logf(O2)=-42~-38,p H值=3~5;根据金属矿物组合估算出中阶段logf(S2)=-9±,晚阶段logf(S2)=-6.5±。龙江亭矿床硫逸度-温度变化规律不同于世界上其他岩浆-流体成矿系统,可能经历了2次成矿事件,后期的高硫型浅成低温热液成矿作用叠加在早期的斑岩型矿床之上,一方面造成了复杂多样的蚀变类型、矿物组合和矿石组构,另一方面继承、残留了斑岩型矿床的特征。因此,其属于叠合成因的斑岩型-浅成低温热液型矿床,而非斑岩型与浅成低温热液型之间的过渡。     

“三江”中段两类碳酸盐岩容矿铅锌矿化成因的相关性——来自稀土元素地球化学研究的启示

世界范围内的碳酸盐岩容矿铅锌矿带内常在区域上出现以方解石等碳酸盐矿物为主要脉石矿物的富碳酸盐型铅锌矿化和以碳酸盐+萤石为主要脉石矿物的富氟型铅锌矿化这两种矿化形式,但不同元素组合的出现在成因上是否有相关性并不明确。青藏高原"三江"成矿带中段玉树地区同一矿集区内近同时发育了东莫扎抓富碳酸盐型和莫海拉亨富氟型铅锌矿床,二者均为碳酸盐岩赋矿,以逆断层为主要控矿构造,具有层控的矿体产状特征,矿石矿物均为方铅矿+闪锌矿,但是,东莫扎抓矿床以方解石+白云石等碳酸盐矿物为主要脉石矿物,莫海拉亨则以方解石+萤石为主要脉石矿物。研究表明,两个矿区含钙矿物的稀土元素地球化学特征存有差异。东莫扎抓矿区方解石的稀土元素具有轻重稀土元素分馏相对明显、轻稀土元素富集、Eu负异常明显的特征,在球粒陨石标准化配分模式图上呈现右倾或轻微右倾的"V"字形曲线。莫海拉亨矿区方解石及萤石轻重稀土元素分馏不明显,有明显的Eu负异常,球粒陨石标准化配分模式图上呈现轻微的"M"型曲线。稀土元素总量上,东莫扎抓(0.46×10-6~10.79×10-6)较莫海拉亨矿床(0.25×10-6~5.88×10-6)高。稀土元素地球化学特征揭示,两个矿床的含钙矿物都沉淀自与岩浆作用无关的热液流体,伴随硫化物沉淀,流体盐度降低,还原性变弱。莫海拉亨矿床除具有一套和东莫扎抓矿床来源一致的流体外,还具有另一套来自深部变质基底的富氟流体,这套流体控制了富氟型碳酸盐岩容矿铅锌矿床的沉淀位置,使其在区域上更靠近逆冲体系主逆冲带,且多在区域上最底层的碳酸盐岩地层中发育。这一认识解释了世界上多个碳酸盐岩容矿铅锌成矿带内同一空间、时间范围内两套不同类型铅锌矿床型式共同出现的原因。     

中国西北部成矿地质特征及找矿新发现

西北地区地处中亚构造域和特提斯构造域的交汇处,中间夹有塔里木克拉通和华北克拉通的西段。地质历史上,两个克拉通及其裂解的微陆块的形成和运动史,基本约束了中国西北部的构造发展历程。围绕克拉通及微陆块的显生宙造山带基本是其周缘增生的结果,由于大陆运移,其他大陆边缘增生的产物,在早三叠世(210 Ma)大陆汇聚中也添加了进来,这些造山带及其陆块边缘的增生是西北各种内生金属矿床的重要形成背景。同时,新元古代、晚古生代陆内与地幔柱有关的大火成岩省的发育,为铜镍等重要矿床的形成提供了条件。此外,在克拉通及其微陆块形成和后期的叠生盆地中,形成了重要的沉积和沉积变质矿床。西北地区近年来重要找矿发现,不断印证了西北克拉通边缘板块构造增生和板内幔源构造岩浆作用成矿的特点,并对传统的地质背景构造认识提出了挑战。这其中,最具经济价值和地质意义的是3个超大型金属矿床的发现:西天山早石炭世阿吾拉勒火山-次火山岩浆喷溢型磁铁矿矿床、东昆仑早泥盆世夏日哈木岩浆深部熔离-贯入型铜镍矿床和西昆仑侏罗—白垩纪火烧云构造热液型铅锌矿床。阿吾拉勒磁铁矿矿床是中国首例火山-次火山岩浆喷溢型磁铁矿矿床,可与智利的拉科超大型典型磁铁矿矿床对比,且更具有经济价值,该矿床的勘查和研究为深入理解中亚造山带天山及其邻区石炭纪裂谷型火山岩浆作用与成矿提供了研究的范例;夏日哈木铜镍矿是中国近年来最重要的铜镍矿发现,探明镍资源量已达百万吨以上,该矿床的发现为查明中国早古生代末期新的岩浆铜镍成矿事件及其找矿潜力提供了研究新区;火烧云铅锌矿床是新近发现的具有超大型资源潜力的铅锌矿床,也是喀喇昆仑—三江造山带中蕴藏的中新生代巨型铅锌成矿带上最重要的成矿发现,为深化研究青藏高原东北缘巨型铅锌成矿带的成矿物质来源和构造控矿机制提供了新的基地。     

对甘肃宕昌县代家庄铅锌矿床成因的认识

甘肃省宕昌县代家庄铅锌矿床的发现是近年来西秦岭地区铅锌找矿的重大进展。其类型为以菱锌矿、白铅矿为主的碳酸盐型铅锌矿,成为西成矿田西延地段发现新的成矿类型。区内圈定铅锌矿体6条,产于泥盆系龙鳞桥组第2岩性段与第3岩性段的过渡带和东沟组中,受NW—SE向压扭性断裂破碎带控制。断裂是成矿最主要的控制因素,不仅控制着铅锌多金属矿体的沉积就位,而且在成矿后期对矿体的改造起主导作用。矿区内未见岩浆岩及典型的热液蚀变现象。文章分析了成矿地质背景和矿床地质特征,铅同位素显示变化范围小,说明铅来源比较单一,硫同位素结果说明硫质来源于沉积地层中。闪锌矿中流体包裹体均一温度分别为80℃~120℃和120℃~160℃,说明成矿温度总体比较低。初步认为其成因沉积改造型铅锌矿床。     

基于探矿者软件(Minexplorer)的三维地质建模及储量估算——以湘西北李梅铅锌矿为例

在全面收集地质资料的基础上,利用探矿者软件建立了湘西北李梅铅锌矿区的综合地质数据库,利用三维钻孔数据建立了研究区的三维矿床模型,并以矿体模型和地层模型为例,介绍了矿区三维地质建模的一般流程。在矿体模型的基础上,利用地质块段法、地质截面法、地质统计学方法进行了储量估算,并与矿山勘探报告中的储量估算结果进行了对比。研究结果表明,利用探矿者软件进行三维建模和储量估算,操作简便、可视化效果好,不同方法进行储量估算的结果互相印证,真实可靠。     

甘南毕家山铅锌矿床地质特征与成因

该矿床由两种类型矿化组成:(1)与所谓“微石英岩”密切共生的成层碎屑矿;(2)层状矿下伏石灰岩顶部的网脉矿。矿石硫化物在同位素组成上与围岩中的黄铁矿显然不同,其δ~(34)S值( 15至 18)表明可能是海水来源的,由海水硫酸离子在较高温度下无机还原而成。矿石中的碳酸盐矿物以较低的δ~(13)C和较高的δ~(18)O值不同于围岩石灰岩,前者表明可能有深成碳参加,后者表明成矿流体可能在较高温度下与硅酸盐岩石达到了同位素平衡。氧化硅的δ~(18)O值很重,落入海相燧石的变化范围。区域内没有火山活动的确切证据,以海水来源为主的成矿流体可能是沿分开不同地层小区的区域性断裂循环并被加热的。     

Geology and geochemistry of the Changba SEDEX Pb-Zn deposit,Qinling orogenic belt,China

The Changba Pb-Zn SEDEX deposit occurs in the Middle Devonian sequence of the Anjiaca Formation of the Western Qinling Hercynian Orogen in the Gansu Province, China. The Changba-II orebody is hosted in biotite quartz schist and is the largest of 143 stratiform orebodies that are hosted either in biotite quartz schist or marble. The Changba-II comprises two types of mineralization: a bedded facies and an underlying breccia lens. The bedded section exhibits three sulfide sub-facies zoned from bottom to top: 1) banded sphalerite intercalated with quartz albitite; 2) interbedded massive pyrite and sphalerite ore; and 3) banded sphalerite ore intercalated with banded baritite. Major metallic minerals are sphalerite, pyrite, galena, with minor arsenopyrite, pyrrhotite, boulangerite, and rare chalcopyrite. The bedded sulfides are underlain by a lens of brecciated and albitized biotite-quartz schists cemented by sulfides and tourmaline.Massive and bedded sulfide ³⁴S values range from 8.1 to 29.3, whereas barite ³⁴S values range from 20.8 to 31.5. Disseminated pyrite in footwall schists has ³⁴S values ranging from 8.1 to 10.6, and increase to values ranging from 11.1 to 14.7 in the hangingwall. The lower ³⁴S values for massive and bedded sulfides are interpreted to be derived from progressive bacterial sulfate reduction (BSR) of Devonian seawater in a sulfate-restricted sub-basin. The higher ³⁴S values for massive and bedded sulfides could be a product of quantitative BSR but this is incompatible with barite being more abundant above the bedded sulfides. Instead, it is more likely that thermochemical sulfate reduction of seawater sulfate or of evaporite was the source of heavy hydrothermal sulfur. Heavy hydrothermal sulfur was injected into a sulfate-restricted sub-basin where it mixed with low ³⁴S BSR sulfide to form the massive and bedded sulfides. The REE patterns of sulfide layers and associated quartz albitite and baritite are similar to those of the host biotite quartz schists, suggesting that the hydrothermal fluids leached REE from the underlying rocks. Pb isotope ratios in galena form an array between the Upper Crust and the Mantle reservoir curves, which indicates that the lead is derived from upper crustal rocks comprising mafic igneous units. The Sr⁸⁷/Sr⁸⁶ ratio of 0.7101 for carbonate within the sulfide layers also suggests that Sr is derived from the mixing of Sr leached from upper crustal rocks with Middle Devonian seawater Sr. A Rb-Sr isochron age of 389.4 ± 6.4 Ma for sulfide layers and the interbedded hydrothermal sediments is consistent with the age of host Mid-Devonian strata. Ar³⁹/Ar⁴⁰ plateau age at 352.8 ± 3.5 Ma and Ar³⁹-Ar⁴⁰ isochron age of 346.6 ± 6.4 Ma for albite in the quartz albitite intercalated with sulfide layers indicate either albite formation after the sulfides or thermal resetting of the Rb-Sr system at about 350 Ma, the age of collision between the North China and Yangtze cratons.Editorial handling: E. Frimmel     

超大型会泽富锗铅锌矿复合成因

会泽富锗铅锌矿。是近年老矿山深部找矿取得重大突破的典范,而其成因则是当前研究、讨论的热点。笔者认为该矿之形成,既非“MVT型”,亦非“VMS型”,而是与深部隐伏燕山期酸性岩有关的中温岩浆热液叠加、改造、富化的复成因矿床。自加里东期起长期处于张裂环境。深部昭通．弥勒硅镁层隆起,既是幔源玄武岩（热地幔柱）上涌的前奏,又为深部矿源上升创造畅通空间。与多旋回活动的小江深断裂相沟通的NE向矩形断裂网,是导矿、输矿、储矿的有利构造。继火山热液成矿之后,伴随燕山期褶皱、断裂和深部酸性岩浆的上升,发生第二期叠加矿化．矿石中伴生与酸性岩有关的元素组合．并以与酸性岩有关的锗富集为特征。     

Geochronological framework and Pb, Sr isotope geochemistry of the Qingchengzi Pb–Zn–Ag–Au orefield, Northeastern China

The Qingchengzi orefield in northeastern China, is a concentration of several Pb–Zn, Ag, and Au ore deposits. A combination of geochronological and Pb, Sr isotopic investigations was conducted. Zircon SHRIMP U–Pb ages of 225.3 ± 1.8 Ma and 184.5 ± 1.6 Ma were obtained for the Xinling and Yaojiagou granites, respectively. By step-dissolution Rb–Sr dating, ages of 221 ± 12 Ma and 138.7 ± 4.1 Ma were obtained for the sphalerite of the Zhenzigou Zn–Pb deposit and pyrargyrite of the Ag ore in the Gaojiabaozi Ag deposit, respectively. Pb isotopic ratios of the Ag ore at Gaojiabaozi (²⁰⁶Pb/²⁰⁴Pb = 18.38 to 18.53) are higher than those of the Pb–Zn ores (²⁰⁶Pb/²⁰⁴Pb = 17.66 to 17.96; Chen et al. [Chen, J.F., Yu, G., Xue, C.J., Qian, H., He, J.F., Xing, Z., Zhang, X., 2005. Pb isotope geochemistry of lead, zinc, gold and silver deposit clustered region, Liaodong rift zone, northeastern China. Science in China Series D 48, 467–476.]). Triassic granites show low Pb isotopic ratios (²⁰⁶Pb/²⁰⁴Pb = 17.12 to 17.41, ²⁰⁷Pb/²⁰⁴Pb = 15.47 to 15.54, ²⁰⁸Pb/²⁰⁴Pb = 37.51 to 37.89) and metamorphic rocks of the Liaohe Group have high ratios (²⁰⁶Pb/²⁰⁴Pb = 18.20 to 24.28 and 18.32 to 20.06, ²⁰⁷Pb/²⁰⁴Pb = 15.69 to 16.44 and 15.66 to 15.98, ²⁰⁸Pb/²⁰⁴Pb = 37.29 to 38.61 and 38.69 to 40.00 for the marble of the Dashiqiao Formation and schist of the Gaixian Formation, respectively).Magmatic activities at Qingchengzi and in adjacent regions took place in three stages, and each contained several magmatic pulses: ca. 220 to 225 Ma and 211 to 216 Ma in the Triassic; 179 to 185 Ma, 163 to 168 Ma, 155 Ma and 149 Ma in the Jurassic, as well as ca. 140 to 130 Ma in the Early Cretaceous. The Triassic magmatism was part of the Triassic magmatic belt along the northern margin of the North China Craton produced in a post-collisional extensional setting, and granites in it formed by crustal melting induced by mantle magma. The Jurassic and Early Cretaceous magmatism was related to the lithospheric delamination in eastern China. The Triassic is the most important metallogenic stage at Qingchengzi. The Pb–Zn deposits, the Pb–Zn–Ag ore at Gaojiabaozi, and the gold deposits were all formed in this stage. They are temporally and spatially associated with the Triassic magmatic activity. Mineralization is very weak in the Jurassic. Ag ore at Gaojiabaozi was formed in the Early Cretaceous, which is suggested by the young Rb–Sr isochron age, field relations, and significantly different Pb isotopic ratios between the Pb–Zn–Ag and Ag ores. Pb isotopic compositions of the Pb–Zn ores suggest binary mixing for the source of the deposits. The magmatic end-member is the Triassic granites and the other metamorphic rocks of the Liaohe Group. Slightly different proportions of the two end-members, or an involvement of materials from hidden Cretaceous granites with slightly different Pb isotopic ratios, is postulated to interpret the difference of Pb isotopic compositions between the Pb–Zn–(Ag) and Ag ores. Sr isotopic ratios support this conclusion. At the western part of the Qingchengzi orefield, hydrothermal fluid driven by the heat provided by the now exposed Triassic granites deposited ore-forming materials in the low and middle horizons of the marbles of the Dashiqiao Formation near the intrusions to form mesothermal Zn–Pb deposits. In the eastern part, hydrothermal fluids associated with deep, hidden Triassic intrusions moved upward along a regional fault over a long distance and then deposited the ore-forming materials to form epithermal Au and Pb–Zn–Ag ores. Young magmatic activities are all represented by dykes across the entire orefield, suggesting that the corresponding main intrusion bodies are situated in the deep part of the crust. Among these, only intrusions with age of ca. 140 Ma might have released sufficient amounts of fluid to be responsible for the formation of the Ag ore at Gaojiabaozi.Our age results support previous conclusions that sphalerite can provide a reliable Rb–Sr age as long as the fluid inclusion phase is effectively separated from the “sulfide” phase. Our work suggests that the separation can be achieved by a step-resolution technique. Moreover, we suggest that pyrargyrite is a promising mineral for Rb–Sr isochron dating.     

青海玉树东莫扎抓铅锌矿床地质特征及碳氢氧同位素地球化学研究

东莫扎抓铅锌矿床位于青藏高原羌塘地体东北缘,是"三江"北段铅锌铜银多金属成矿带中的典型代表,对该矿床地质特征和成因类型的研究有助于理解区域铅锌铜银多金属成矿规律,对区域找矿具有重要意义.笔者通过详细的矿区地质考察、系统的矿石光薄片显微镜下鉴定和矿石中方解石的碳、氢、氧同位素分析测试,概述了东莫扎抓铅锌矿床的地质特征和成矿流体的碳、氢、氧同位素组成特征.东莫扎抓铅锌矿床矿体呈似层状展布,产状严格受到矿区逆冲断层的控制,赋矿围岩为上三叠统结扎群波里拉组灰岩和下一中二叠统开心岭群尕迪考组灰岩,发育强白云石化和弱硅化,矿物组合简单,主要为闪锌矿+方铅矿+黄铁矿+白云石+方解石+重晶石,矿石结构以皮壳状、草莓状等胶状结构和他形粒状结构为主,矿石构造为浸染状、角砾状、团块状和脉状.矿石中方解石的δ~(13)C_(V-PDB)值、δ~(18)O_(V-SMOW)值分别为δD_(V-SMOW)值分别为-1.8‰～+3.3‰、+6.1‰～+24.6‰和-137‰～-53‰,计算得到成矿流体的δ~(18)O_(流体)值为-0.5‰～+13.8‰.研究结果表明,东莫扎抓铅锌矿床的成矿流体主要来自盆地封存热卤水和大气降水,金属物质可能由区域流体在长距离迁移过程中通过与碳酸盐岩地层相互作用,以及淋滤含矿地层底部的火山岩而得来,成矿过程中伴随着碳酸盐岩的溶解作用,可能存在有机质的参与.据此,笔者将东莫扎抓矿床归为发育在碰撞造山带中受逆冲推覆断裂构造控制的类MVT铅锌矿床,并初步建立了东莫扎抓铅锌矿床的构造控矿模型.