河南围山城金银成矿带铅同位素地球化学及矿床成因

桐柏山区的围山城金银成矿带包括破山特大型银矿、银洞坡大型金矿、银洞岭大型银多金属矿床及一些矿点,所有矿床赋存于上元古界歪头山组地层,并具有层控特征。矿石矿物的铅同位素组成为²⁰⁶Pb/²⁰⁴Pb=16.753~17.216,²⁰⁷Pb/²⁰⁴Pb=15.417~15.638,²⁰⁸Pb/²⁰⁴Pb=38.251~39.050;与歪头山组地层的铅同位素组成一致,而与桐柏地区的其他地层、岩体差别较大,表明成矿物质来自赋矿地层歪头山组。围山城成矿带应属于典型的层控造山型金银成矿系统,它形成于中生代扬子与华北板块的陆陆碰撞造山过程,碰撞造山期间的下插板片变质脱水诱发了矿带内流体成矿系统的发育,强烈的流体-岩石相互作用使歪头山组内的成矿物质被萃取、迁移、聚集到碳质绢云片岩层。     

大兴安岭托河林场毕利亚山碱长花岗岩黑云母地球化学特征及地质意义

根据大兴安岭毕利亚山碱长花岗岩黑云母的电子探针(EPMA)测试结果,对黑云母的化学成分特征、成因类型及结晶时的温度和氧逸度进行了研究,并探讨岩浆源区的性质及成岩背景。毕利亚山碱长花岗岩黑云母具有高Si(SiO_2:39.876%~42.419%)、富Mg(MgO:18.138%~20.02%)、贫Fe(FeO~t:10.549%~11.468%)特征,属镁质黑云母;黑云母的结晶温度为590℃~650℃,且具有较高的氧逸度。其∑Al的值为1.01~1.044,Fe/(Mg+Fe)的值为0.228~0.262。Mg/(Mg+Fe~(2+)+Mn)的值为0.673~0.834,FeO~t/(FeO~t+MgO)的值为0.345~0.387,指示了其岩浆源区为富镁的岩石圈地幔,并且在岩浆演化过程中发生混染作用。     

大兴安岭环二库新元古代变质辉长岩的厘定及其地质意义

环二库地区位于大兴安岭大扬气林场,岩石组合为斜长角闪岩、变质辉长岩、橄榄岩和大理岩,主要以NE向呈似层状、透镜状或碎片状产出。LA-ICP-MS锆石U-Pb测年结果表明,其中变质辉长岩形成于新元古代末期(696.8±2.9 Ma);岩石地球化学分析显示,环儿库变质辉长岩具有类似N-MORB的地球化学特征,且与部分岛弧拉斑玄武岩(IAT)具有成分上的亲缘性,表明变质辉长岩的形成与俯冲作用有关。结合区域上吉峰、嘎仙蛇绿岩可知,环二库岩石组合具有类似于蛇绿混杂岩的特征,其中变质辉长岩可能代表了新元古代末期的洋壳残片,表明大兴安岭北段地区新元古代时期存在古洋盆。     

桐柏-大别造山带高压变质单元面理化(含榴)花岗岩地球化学及其对岩石成因的限制

桐柏-大别造山带中,面理化(含榴)花岗岩作为榴辉岩的重要围岩之一,仅分布在高压变质单元和超高压变质单元中.对高压变质单元中面理化(含榴)花岗岩进行了元素地球化学研究,结果显示,这类岩石 SiO2 71.96%～ 77.99%, K2O Na2O 7.59%～8.66%, Al2O3 11.15%～14.50%, CaO 0.10%～0.91%, MgO0.04%～0.73%,Sr 27.3～269 μ g/g,A/CNK 0.97～1.10.相对于 S型和 I型花岗岩,面理化(含榴)花岗岩具有某些 A型花岗岩的地球化学特征,如岩石明显富硅、富碱质和富高场强元素(如 Zr、Hf、Nb、Ta、Y等),贫 Ca、Mg、Al、Sr等元素,高 Ga/Al比值;在稀土元素特征方面,大部分样品具有明显的 Eu负异常(Eu/Eu0.06～0.60),(La/Yb)N 2.34～7.87.在岩石成因类型元素判别图解上,面理化(含榴)花岗岩主要落于 A型花岗岩区;构造判别图解和构造学、岩石学特征表明该类花岗岩形成于碰撞后的构造环境.因此,高压变质单元面理化(含榴)花岗岩总体地球化学特征表明它们属于 A型花岗岩类,形成于岩石圈伸展的碰撞后构造环境,与大别山超高压 /高压变质岩的折返过程存在密切联系.     

阴山大青山山系特异重力场与深部构造

根据阴山山系及邻近地区的布格重力异常分布特征,提出阴山山系和呼包盆地地区的布格重力异常分布与地形高程呈“同步型”的特异变化特征．通过重力数据资料的处理分析给出阴山山系和呼包盆地地区的地壳底界面都没有明显的下凹与上凸的特征,是阴山山系和呼包盆地布格重力异常呈现特异变化的可能原因。     

北大别大山坑二长花岗片麻岩的地球化学特征与锆石 U-Pb年代学

北大别东部大山坑片麻岩主要由钾长石、斜长石和石英组成,少量角闪石、黑云母和褐帘石,成分为二长花岗质。岩石以富碱（Na₂O＋K₂O）尤其是 K₂O、贫Al₂O₃为特征,地球化学性质上表现为富集 K、Rb、Th、La、Ce等大离子亲石元素而亏损Nb、Ta、U等高场强元素及Sr元素,高的Ga含量、强的负Eu异常（δEu＝0．37）和相对较强的轻重稀土分馏程度（（La／Yb）_N＝16．75）。岩石地球化学的总体特征与南大别水吼地区的 A型花岗片麻岩类似,意味着其原岩与南大别的 A型花岗片麻岩一样,可能也是在拉张状态下形成的一套偏碱性的花岗岩。该二长花岗片麻岩的锆石 U-Pb年龄为229．2±5．5 Ma,也与南大别超高压变质的年龄相似,指示北大别正片麻岩印支期可能也经历过超高压变质作用。南、北大别造山带可能具有相同的形成与演化历史,现南、北大别变质带之间的差异可能更多的是后造山历史不同,尤其是燕山期花岗岩侵入对两个带影响的不同造成的。     

桐柏造山带东段结晶基底杂岩中的大型A型背形及其构造背景

通过对桐柏山东段广水－孝子店一带桐柏杂岩及红安群的构造解析，提出桐柏杂岩中发育－北西－南东走向并向南东倾伏的大型Ａ型背形．利用变形矿物变质温压计估算其形成温度为５３０～６９０℃，压力为０．５２～０．６２ＧＰａ，相当于１８～２２ｋｍ深的中地壳流动壳层．据Ａ型背形不同部位物质运动特点分析，其形成很可能是古元古代晚期华北古板块与杨子古板块碰撞对接造成桐柏杂岩向南东方向侧向挤出的结果     

五台山早元古代变质砾岩型金矿地质特征

五台山早元古代沉积盆地分布于五台－花岗绿岩带穹隆南翼，沉积了巨厚的陆源碎屑岩和碳酸盐岩系，同位素年龄２３０６Ｍａ（Ｕ－Ｐｂ），与南非威特沃特斯兰德盆地具有一定的可比性。因此，可在该区寻找金－铀砾岩型金矿。随着五台花岗－绿岩带金矿找矿工作的不断进展，砾岩型金矿的寻找也有重大发现，已相继发现十余处矿床、矿（化）点。该类型金矿产在滹沱群的下部，即盆地较陡侧的冲积扇中部或底部，严格受层位控制。含砾变质砂岩为金矿的容矿岩石，自然金均为中粗粒，可能存在古砂矿，属太古宙绿岩带金矿的剥蚀搬运产物。金矿床受褶皱倒转和与之相关的脆－韧性剪切带控制，是构造作用的变质热液活化、迁移和富集的结果，脆－韧性剪切带是其容矿构造。本文初步建立了砾岩型金矿的成矿构造模式。这种砾岩型金矿的新发现对我国早元古代砾岩型金矿的找矿工作具有十分重要的指导意义。     

A new model for the evolution of table mountains: volcanological and petrological evidence from herdubreid and Herdubreidartögl volcanoes (Iceland)

We present a new model for the evolution of volcanic table mountains, based on volcanological and petrological studies of Herdubreid/Herdubreidartögl, an upper Pleistocene volcanic complex within the active Icelandic rift zone. The evolution of these table mountains is highly complex and influenced substantially by different eruptive environments as well as changing magma sources and volcanic and magmatic processes. Whereas current models imply entirely subglacial conditions and continuous compositional (“monogenetic”) evolution for these volcanoes, we subdivide their evolution into four eruptive periods characterized by different environments: (a) Subaerial lava flows erupted during an interglacial period. (b) Lavas and voluminous hydroclastic deposits formed in a lake during a waning period of the last glaciation. (c) Subglacial eruptions during thickening of the ice sheet as a result of a climatic deterioration built pillow lava piles overlain by steep-sided complexes of hydroclastic deposits. These deposits differ from those of the second eruptive period in structure, texture, and degree of alteration. Subaerial lava flows and agglutinates covered these deposits after buildup above the ice sheet. (d) Subaerial lava flows and fallout deposits during a postglacial period. The detailed analysis of volcanic table mountains appears to be a very sensitive indicator of climatic fluctuations. Although most deposits of the studied volcanoes were formed during the waning period of the last glaciation, the subglacial deposits in the upper part of the volcanic complex reflect a temporary, but major, thickening of the ice sheet.     

Sulfur, Carbon and Lead Isotope Studies of the Dajing Polymetallic Deposit in Linxi County, Inner Mongolia, China – Implication for Metallogenic Elements from Hypomagmatic Source

Abstract: The Dajing Cu‐polymetallic ore deposit in Linxi county, Inner Mongolia Autonomous Region, China, is economically a valuable Cu–Sn–Ag–Zn–Pb deposit in the southern section of the Da Hinggan metallogenic province. For the analyzed 23 samples of sulfide minerals, including chalcopyrite, pyrite, sphalerite and galena, the δ³⁴S values range from –1.8 to +3.8 % with an average of +0.65 %. The narrow distributions of the δ³⁴S values with +1 % peak value, including the published data, and the δ¹³C values around –5 % indicate that the sulfur and carbon of the hydrothermal fluids are derived from a hypomagmatic source, and exclude the possibility that the hosted strata, i.e., the Upper Permian Linxi Formation, provided certain amounts of sulfur and carbon. The ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios of sulfide ores range respectively within 18.257‐18.368, 15.476‐15.609, and 37.916‐38.355 with the model ages of 122–209 Ma. The black shale, however, contains higher radiogenic lead with the ²⁰⁶Pb/²⁰⁴Pb ratios of 18.473‐20.156, differing from the ores. However, the ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios of the ore, basaltic porphyrite and feldspar leads are similar, and lie on the same lines in the diagrams of ²⁰⁸Pb/²⁰⁴Pb vs. ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb vs. ²⁰⁶Pb/²⁰⁴Pb. The fact that these mixing lines are composed of the two end members, the mantle and orogenic belt, strongly supports that all the metallogenic elements were carried by the hypomagma mixing the matters of the mantle and orogenic belt prior to the Mesozoic. Therefore, the Dajing ore deposit is a typical mag–matic–hydrothermal vein type ore deposit associated with subvolcanic rocks.