柏树岗金红石矿床含矿岩系地质特征

河南方城柏树岗金红石矿床含矿岩系主要由角闪(片)岩、变粒岩、斜长片岩、石英(片)岩及云母片岩组成、前者是主要含矿岩石。分为石英(片)岩、角闪(片)岩-云母斜长片岩、云母片岩-石英(片)岩三个岩性段,二段是主要含矿岩段。原岩为一套火山岩、正常沉积岩岩性组合。经历了两次变质作用,变质温压400～485℃、200～700MPa,变质时间416.1±0.5Ma,变质热液产生了少量细脉及脉岩。含矿岩系的形成变化是板块运动的结果。基性岩及基性岩质凝灰岩是钛的主要来源,变质作用是主要成矿作用。     

新疆阿尔泰凯勒克赛依铁矿地质特征、锆石LA MC ICP MS U Pb年龄及其意义

凯勒克赛依铁矿床是新疆阿尔泰唯一的小型镜铁矿床,赋存于一套变质火山-沉积岩系中,近矿围岩为白云母石英片岩,矿体呈层状,与地层产状一致,矿石具有块状、条带状、条纹状构造,矿石中金属矿物主要为镜铁矿(TFeO=87349%~88988%,TiO2=0~1042%,Al2O3=0036%~0256%),矿化具有沉积特征。近矿围岩镜铁矿白云母石英片岩锆石LA MC ICP MS U Pb谐和年龄为(3756 ± 06)Ma,限定成矿时代在376 Ma左右,即中泥盆世成矿,是阿尔泰为数不多的中泥盆世成矿作用的产物。同时也厘定含矿的变质火山-沉积岩系属中—晚泥盆世阿勒泰镇组,不是前人认为的早泥盆世康布铁堡组。     

Carboniferous eclogite and garnet–omphacite granulite from northeastern Hainan Island,South China: Implications for the evolution of the eastern Palaeo‐Tethys

High‐P (HP) eclogite and associated garnet–omphacite granulite have recently been discovered in the Mulantou area, northeastern Hainan Island, South China. These rocks consist mainly of garnet, omphacite, hornblende, quartz and rutile/ilmenite, with or without zoisite and plagioclase. Textural relationships, mineral compositions and thermobarometric calculations demonstrate that the eclogite and garnet–omphacite granulite share the same three‐stage metamorphic evolution, with prograde, peak and retrograde P?T conditions of 620–680°C and 8.7–11.1 kbar, 820–860°C and 17.0–18.2 kbar, and 700–730°C and 7.1–8.5 kbar respectively. Sensitive high‐resolution ion microprobe U–Pb zircon dating, coupled with the identification of mineral inclusions in zircon, reveals the formation of mafic protoliths before 355 Ma, prograde metamorphism at c. 340–330 Ma, peak to retrograde metamorphism at c. 310–300 Ma, and subsequent pegmatite intrusion at 295 Ma. Trace element geochemistry shows that most of the rocks have a MORB affinity, with initial ε_Nd values of +2.4 to +6.7. As with similar transitional eclogite–HP granulite facies rocks in the thickened root in the European Variscan orogen, the occurrence of relatively high P?T metamorphic rocks of oceanic origin in northeastern Hainan Island suggests Carboniferous oceanic subduction leading to collision of the Hainan continental block, or at least part of it, with the South China Block in the eastern Palaeo‐Tethyan tectonic domain.     

Geochemical studies on Dachang antimony ore deposit in Qinglong, Guizhou Province

The Dachang antimony deposit in Qinglong,Guizhou Province,is strictly controlled by the “Dachang Layer” which is a complex altered rock occurring at unconformity between the Permian Emeishan basalt and the Maokou limestone.Based on the studies of the hanging-and foot-wall rocks,the trace elements and REE contents of the rocks and ores and heavy placer minerals in the basalt,this paper is focused on the relations between these data and the “Dachang Layer”and its hanging- and oot-wall rocks.The author pointed out that the “Dachang Layer” and basalt are the source-beds of antimony;ilmenite and magnetite are the major mineral carriers of antimony.In the processes of halmyrosis and burial metamorphism of the “Dachang Layer” an basalt,antimony was mobilized along with the mobilization of iron and was preliminarily concentrated in the“ Dachang Layer”.     

Metamorphism of the Basement of the Qilian Fold Belt in the Minhe-Ledu Area, Qinghai Province, NW China

The basement of the central Qilian fold belt exposed along the Minhe-Ledu highway consists of psammitic schists, metabasitic rocks, and crystalline limestone. Migmatitic rocks occur sporadically among psammitic schist and metabasitic rocks. The mineral assemblage of psammitic schist is muscovite + biotite + feldspar + quartz ± tourmaline ± titanite ± sillimanite and that of metabasitic rocks is amphibole + plagioclase + biotite ± apatite ± magnetite ± pyroxene ± garnet ± quartz. The migmatitic rock consists of leucosome and restite of various volume proportions; the former consists of muscovite + alkaline feldspar + quartz ± garnet ± plagioclase while the latter is either fragments of psammitic schist or those of metabasitic rock. The crystalline limestone consists of calcite that has been partly replaced by olivine. The olivine was subsequently altered to serpentine. Weak deformations as indicated by cleavages and fractures were imposed prominently on the psammitic schists, occasionally on me     

U-Pb dating of minerals in alteration halos of Superior Province massive sulfide deposits: syngenesis versus metamorphism

U-Pb geochronology of igneous zircon from rhyolitic host rocks to the Archean Kidd Creek, Geco and Winston Lake massive sulfide deposits, in the Superior Province of Ontario, shows that volcanism, which accompanied mineralization, occupied a narrow time span (2717±2 Ma, 2720±2 Ma and 2723±2 Ma, respectively). Precise ages of hydrothermal monazite, allanite and rutile from alteration zones surrounding the above deposits indicate that these minerals crystallized 40–70 million years after volcanism. Monazite from Kidd Creek mine is 2659±3 Ma old, in agreement with spatially associated 2664±25 Ma old rutile. Monazite from a biotite schist at Geoco mine gives a similar age of 2661±1 Ma. However, monazite from a sericite schist, which hosts the ore at Geco mine, is 2675±2 Ma old. Abraded large monazite grains from three units in the Winston Lake deposit are coeval with biotite crystallization and record an age of 2677±2 Ma, approximately the same as monazite in the sericite schist at Geco. Data points from allanite fractions from both the Winston Lake and Geco deposits fall on a Pb-Pb isochron that gives an age of 2672±5 Ma. Rutile from Winston Lake gives a younger age of 2651±6/-2 Ma and may date retrograde alteration of biotite to chlorite. The ca. 2676 Ma age of monazite from Winston Lake and in the sericite schist at Geco mine probably dates a regional metamorphic event that affected most of the southern Superior Province. The ca. 2660 Ma old monazite in the biotite schist at Geco mine and in the chlorite-sericite alteration at Kidd Creek may date later K-metasomatism caused by metamorphically derived fluids that were focussed along old fault structures. Such fluids were also responsible for local sulfide remobilization. Monazite and rutile are spatially associated with chlorite and sericite alterations at Kidd Creek. Their young ages indicate that these originally syngenetic mineral assemblages may have been significantly affected by regional metamorphism. Formation of monazite at all three deposits studied was a result of significant REE remobilization during metamorphism. The discrete character of syn-metamorphic hydrothermal activity in different units of the same deposit, as well as its synchroneity among different, widely separated deposits, requires a mechanism for episodic injection of heat and fluid into the crust on a regional scale. These activities are broadly coeval with, and probably related to, plutonism within adjacent metasedimentary subprovinces and middle to lower crustal metamorphism in the Superior Province.     

西昆仑甜水海地块大红柳滩铁矿床成因浅析及找矿意义

位于西昆仑甜水海地块东段的大红柳滩赤铁矿是近几年发现的大型铁矿床,产于震旦纪甜水海岩群滨浅海相浅变质碎屑岩-碳酸盐岩中,赋矿岩性主要为含铁白云质大理岩、白云母石英片岩和硬绿泥石白云母石英片岩。通过矿体形态特征、矿物组合和矿石结构构造分析,认为该时期存在缺氧富铁洋盆或者深水盆地,矿床的形成经历了铁质沉积和变质改造两个阶段,属于新元古代沉积变质成因条带状硅铁建造矿床(BIF),找矿潜力巨大。该矿床是继塔什库尔干县一带发现了多个与火山岩建造密切相关的大型规模Algoma型BIF之后的重大找矿突破,也是西昆仑地区首次发现该类型矿床。深入开展该矿床的地质特征及勘探工作,能够指导西昆仑铁矿的下一步找矿方向,推进新疆地区条带状含铁建造(BIF)研究和西昆仑构造格局演化的认识。     

碾子沟金红石矿床基本地质特征

碾子沟金红石矿区地层主要为上太古界变粒岩、斜长角闪片岩及榴闪岩 ;岩浆岩主要为晋宁期基性岩 ;构造主要为断裂。矿区蚀变岩发育 ,主要为细晶直闪片岩、粗晶直闪岩、中细晶滑石岩及细晶绿泥片岩。矿体呈似纺锤状、似板状及透镜状。矿石类型有浅褐色细晶直闪石型片状矿石、灰白色粗晶直闪石型块状矿石、灰绿色或灰白色中细晶滑石型块状矿石、黑色中细晶角闪石型片状矿石及灰绿色巨晶直闪石型块状矿石等 5种。以前 3种为主 ,矿石品位一般 2 %～ 15 %。矿床规模为大型 ,矿床为变质蚀变成因。     

八庙-青山金红石矿床锆石年代学和地球化学研究

八庙-青山金红石矿床位于豫、陕两省交界处的西峡县与商南县之间,大地构造位置处于南秦岭地块的北缘。矿体呈层状、透镜状赋存于一套低角闪岩相变质的基性火山岩内,矿化层与大理岩互层产出。目前对于其含矿岩系的时代归属问题尚有中新元古代与中晚古生代之争。锆石年代学分析结果显示八庙矿区含矿岩系的底板围岩含石榴子石二云石英片岩主要包含3个阶段的年龄,即2664～1373 Ma、1003～874 Ma和468～411 Ma,青山矿区的含金红石斜长角闪片岩主要包含4个阶段的年龄,即1860～1441 Ma、1103～969 Ma、832～780 Ma和433～418 Ma。2个样品的最小锆石年龄数据一致,且与前人在含矿岩系大理岩中发现的古生物化石指示的时代相近。因此,八庙-青山金红石矿床的赋矿地层时代应归属于早泥盆世。全岩地球化学分析结果表明含矿岩石具洋岛玄武岩特征,源区可能为石榴橄榄岩,指示高钛的岩浆物质来自深部地幔。     

拉萨地块林芝杂岩体石榴角闪岩的地球化学特征和年代学研究

本文对位于青藏高原拉萨地体东南缘林芝杂岩中的两类石榴角闪岩进行了详细的地球化学和锆石U-Pb年代学研究。这两类石榴角闪岩分别为硅不饱和的含十字石石榴角闪岩和硅饱和的含石英石榴角闪岩。含十字石石榴角闪岩矿物组合为十字石、石榴子石、角闪石、钠云母、绿泥石、斜长石。石英石榴角闪岩矿物组合为石榴子石、角闪石、石英、斜长石、黑云母。岩石学及变质相平衡研究表明两类石榴角闪岩均经历了高压角闪岩相变质作用。含十字石石榴角闪岩和石英石榴角闪岩具有MORB的地球化学特征,锆石U-Pb年代学分析获得了800~200 Ma的206Pb/238U年龄范围,出现了~430 Ma、~268 Ma和~216 Ma年龄峰值。~430 Ma年龄可能和拉萨地体岩浆活动有关,~268 Ma变质年龄和~216 Ma变质年龄和拉萨地块经历的高压变质作用有关。其中~268 Ma年龄和拉萨地块内部松多高压带榴辉岩的峰期变质年龄一致,而~216 Ma年龄和榴辉岩的围岩含石榴子石片岩年龄一致。对比该区域的年代学研究成果,这表明林芝杂岩体不仅经历了中新生代的变质和岩浆再造活动,还经历了古特提斯洋闭合,南北拉萨地块发生碰撞的晚二叠世的高压变质作用和三叠纪的中压变质作用。     

中条铜矿峪超大型斑岩铜矿床:地质、蚀变与成矿

山西中条山铜矿峪超大型斑岩铜矿床位于华北板块南部,秦岭造山带北侧,处在聚合板块活动大陆边缘的挤压-伸展的构造转换环境。矿区地层主要为古元古界"铜矿峪亚群",即火山-次火山岩,岩石经变质作用为绿片岩相和低角闪岩相。铜矿床在空间上与元古代钙碱性S型花岗斑(杂)岩体紧密共生,严格受火山机构控制。据辉钼矿Re-Os年龄,成矿时代为(2 108±32)Ma,是我国最古老的斑岩型铜矿床。铜矿床呈厚板状透镜体产出,矿石以细脉浸染状构造为主,有少量块状矿石产出。铜矿平均品位为0.68%,其中30%为富铜矿,并伴生钼、金。成矿热液主要源自深部地幔,也与地壳成分和天水渗入有关。因火山喷气和二次沸腾,在高侵位后,由分离作用形成碱质交代及石英绢云母化叠加红长石化的围岩蚀变,无面型环状分带特征。矿床成因推测为变火山热液斑岩型铜矿床。预测矿床深部可能赋存有岩浆房,找矿潜力很大。     

Ultrahigh-pressure eclogite transformed from mafic granulite in the Dabie orogen, east-central China

Although ultrahigh‐pressure (UHP) metamorphic rocks are present in many collisional orogenic belts, almost all exposed UHP metamorphic rocks are subducted upper or felsic lower continental crust with minor mafic boudins. Eclogites formed by subduction of mafic lower continental crust have not been identified yet. Here an eclogite occurrence that formed during subduction of the mafic lower continental crust in the Dabie orogen, east‐central China is reported. At least four generations of metamorphic mineral assemblages can be discerned: (i) hypersthene + plagioclase ± garnet; (ii) omphacite + garnet + rutile + quartz; (iii) symplectite stage of garnet + diopside + hypersthene + ilmenite + plagioclase; (iv) amphibole + plagioclase + magnetite, which correspond to four metamorphic stages: (a) an early granulite facies, (b) eclogite facies, (c) retrograde metamorphism of high‐pressure granulite facies and (d) retrograde metamorphism of amphibolite facies. Mineral inclusion assemblages and cathodoluminescence images show that zircon is characterized by distinctive domains of core and a thin overgrowth rim. The zircon core domains are classified into two types: the first is igneous with clear oscillatory zonation ± apatite and quartz inclusions; and the second is metamorphic containing a granulite facies mineral assemblage of garnet, hypersthene and plagioclase (andesine). The zircon rims contain garnet, omphacite and rutile inclusions, indicating a metamorphic overgrowth at eclogite facies. The almost identical ages of the two types of core domains (magmatic = 791 ± 9 Ma and granulite facies metamorphic zircon = 794 ± 10 Ma), and the Triassic age (212 ± 10 Ma) of eclogitic facies metamorphic overgrowth zircon rim are interpreted as indicating that the protolith of the eclogite is mafic granulite that originated from underplating of mantle‐derived magma onto the base of continental crust during the Neoproterozoic (c. 800 Ma) and then subducted during the Triassic, experiencing UHP eclogite facies metamorphism at mantle depths. The new finding has two‐fold significance: (i) voluminous mafic lower continental crust can increase the average density of subducted continental lithosphere, thus promoting its deep subduction; (ii) because of the current absence of mafic lower continental crust in the Dabie orogen, delamination or recycling of subducted mafic lower continental crust can be inferred as the geochemical cause for the mantle heterogeneity and the unusually evolved crustal composition.     

Geologic setting,genesis and transformation of sulfide deposits in the northern part of Khetri copper belt,Rajasthan, India — an outline

The present study is confined to the northern part of the Khetri copper belt that extends for about 100 km in northern Rajasthan. Mineralization is more or less strata-bound and is confined to the garnetiferous chlorite schist and banded amphibolite quartzite, occurring towards the middle of the Proterozoic Delhi Supergroup. Preserved sedimentary features and re-estimation of the composition of the pre-metamorphic rocks suggest that the latter were deposited in shallow marine environment characterized by tidal activity. Cordierite-orthoamphibole-cummingtonite rock occurring in the neighbourhood of the ores is discussed, and is suggested to be isochemically metamorphosed sediment. The rocks together with the ores were deformed in two phases and metamorphosed in two progressive and one retrogressive events of metamorphism. Study of the host rocks suggests that the maximum temperature and pressure attained during metamorphism are respectively 550–600°C and < 5.5 kb. Principal ore minerals in Madan Kudan are chalcopyrite, pyrrhotite, pyrite and locally magnetite. In Kolihan these are chalcophyrite, pyrrhotite and cubanite. Subordinate phases are sphalerite, ilmenite, arsenopyrite, mackinawite, molybdenite, cobaltite and pentlandite. The last two are very rare. Gangue minerals comprise quartz, chlorite, garnet, amphiboles, biotite, scapolite, plagioclase and graphite. The ores are metamorphosed at temperatures > 491°C. Sulfide assemblages are explained in terms of f_{S 2} during metamorphism. Co-folding of the ore zone with the host rocks, confinement of the ores to the carbonaceous pelites or semi-pelitic rocks, strata-bound and locally even stratiform nature of the orebodies, lack of finite wall rock alteration, metamorphism of the ores in the thermal range similar to that for the host rocks, absence of spatial and temporal relationship with the granitic rocks of the region led the authors to conclude that the entire mineralization was originally sedimentary-diagenetic. Any loss of primitive features and development of incongruency are due to subsequent deformation and metamorphism to which the ores and their hosts were together subjected.     

云南个旧锡矿的玄武岩成矿

个旧锡矿产于个旧东区,是一个以锡铜为主的超大型多金属矿床,具有火山沉积成矿的某些特征。因遭受燕山期花岗岩的叠加改造,区内个旧组卡房段中玄武岩遭受强烈的变质,它又具有花岗岩热液成矿的特征。区内玄武岩的地质地球化学特征表明,印支期玄武岩中的Sn、Cu、Pb、Zn、Ag和Au的质量分数大多数高于世界玄武岩平均值的若干倍;矿石硫化物的硫同位素δ³⁴S为-1.5‰~4.0‰,平均+0.207‰,在幔源硫附近;铅同位素模式年龄分为两组：第一组为180~240 Ma,反映了印支期的火山沉积成矿作用;第二组为80~140 Ma,反映了燕山期花岗岩的叠加改造成矿作用。区内印支期玄武岩为个旧锡铜多金属矿床的形成提供了主要的成矿物质,与成矿有直接联系。     

吉林省和龙地区鸡南BIF型铁矿床含矿建造地球化学特征及形成时代

鸡南铁矿床位于吉林省和龙地区,地处华北克拉通北缘与兴蒙造山带接壤的龙岗地块北部,是东北地区发现较早的BIF型铁矿床之一。该矿床铁矿体主要呈层状、似层状、扁豆状赋存于鞍山群鸡南组上段中部层位,含矿岩石以黑云斜长片麻岩、角闪黑云斜长片麻岩、黑云角闪斜长片麻岩及斜长角闪岩为主,为角闪岩相的中低级区域变质岩系;主要矿石类型为条带状磁铁石英岩型和块状磁铁角闪岩型。为确定该矿床含矿建造的原岩、变质时代及构造背景,重点对含矿岩系中的斜长角闪岩进行了岩石地球化学和锆石U-Pb年代学研究。结果表明：斜长角闪岩的地球化学特征表现为富集大离子亲石元素、轻微富集重稀土元素;主量元素质量分数与中性-基性岩类基本相似,结合原岩恢复图解,判断其原岩类型为亚碱性玄武岩（拉斑玄武岩）,形成于弧后盆地背景;LA-ICP-MS锆石U-Pb年代学研究中,2个较老的锆石测点年龄分别为（2 468±15）和（2 469±9）Ma,代表区内峰期变质年龄（约2 460 Ma）,26个锆石测点的测年数据较为集中,加权平均年龄为（2 275±25）Ma,代表区内退变质年龄。通过与国内外典型BIF型铁矿床的对比研究认为,区内的鸡南铁矿与官地铁矿同属Algoma型铁矿床。     

Rare Earth Elements Geochemistry of Sheikh-Marut Laterite Deposit,NW Mahabad,West-Azarbaidjan Province,Iran

Laterite deposit at Sheikh-Marut(NW Mahabad,West-Azarbaidjan province,Iran) occurred within middle-upper Permian carbonate rocks.It consists of seven stratiform and/or discontinuous lenticular layers extending over 4.2 km in length and having thicknesses ranging from 3 to 14 m.Mineralogical data show that the ores contain kaolinite and hematite as major and boehmite, diaspore,halloysite,amesite,anatase,and muscovite-illite as minor mineral phases.The computed Ce anomaly values in the ores range from 0.05 to 20.84.Conservative index(e.g.,Eu/Eu) suggests that this deposit is a product of alteration and weathering of basaltic rocks.Rhythmic increment ofΣREE values of the ores with approaching to the carbonate bedrocks shows an in-situ occurrence of lateritization processes.Mass change calculations of elements indicate that two competing processes namely leaching and fixation were the major regulating factors in concentration variation of REEs (La-Lu) in this deposit.The obtained results show that pH increase of weathering solutions by carbonate bedrocks,existence of organic matters,and the degree of comlexation with organic ligands played remarkable role in distribution of REEs during lateritization.Further geochemical considerations revealed that secondary phosphates,Mn-oxides and -hydroxides,diaspore,and anatase were the potential hosts for REEs in this deposit.     

Fe–Cu deposits in the Kangdian region,SW China: a Proterozoic IOCG (iron-oxide–copper–gold) metallogenic province

Numerous Fe–Cu deposits are hosted in the late Paleoproterozoic Dongchuan and Dahongshan Groups in the Kangdian region, SW China. The Dongchuan Group is composed of siltstone, slate, and dolostone with minor volcanic rocks, whereas the Dahongshan Group has undergone lower amphibolite facies metamorphism and consists of quartz mica-schist, albitite, quartzite, marble and amphibolite with local migmatite. Deposits in the Dongchuan Group are commonly localized in the cores of anticlines, in fault bends and intersections, and at lithological contacts. Orebodies are closely associated with breccias, which are locally derived from the host rocks. Fe-oxides (magnetite and/or hematite) and Cu-sulfides (chalcopyrite, bornite) form disseminated, vein-like and massive ores, and typically fill open spaces in the host rocks. The deposits have extensive albite alteration and local K-feldspar alteration overprinted by quartz, carbonate, sericite and chlorite. Deposits in the Dahongshan Group have orebodies sub-parellel to stratification and show crude stratal partitioning of metals. Fe-oxide ores occur as massive and/or banded replacements within the breccia pipes, whereas Cu-sulfide ores occur predominantly as disseminations and veinlets within mica schists and massive magnetite ores. Ore textures suggest that Cu-sulfides formed somewhat later than Fe-oxides, but are possibly within the same mineralization event. Both ore minerals predated regional Neoproterozoic metamorphism. Both orebodies and host rocks have undergone extensive alteration of albite, scapolite, amphibole, biotite, sericite and chlorite. Silica and carbonate alterations are also widespread. Ore-hosting strata have a LA-ICP-MS zircon U–Pb age of 1681 ± 13 Ma, and a dolerite dyke cutting the Fe-oxide orebodies has an age of 1659 ± 16 Ma. Thus, the mineralization age of the Dahongshan deposit is constrained at between the two. All ores from the two groups have high Fe and low Ti, with variable Cu contents. Locally they are rich in Mo, Co, V, and REE, but all are poor in Pb and Zn. Sulfides from the Fe–Cu deposits have δ³⁴S values mostly in the range of +2 to +6 per mil, suggesting a mix of several sources due to large-scale leaching of the strata with the involvement of evaporites. Isotopic dating and field relationships suggest that these deposits formed in the late Paleoproterozoic. Ore textures, mineralogy and alteration characteristics are typical of IOCG-type deposits and thus define a major IOCG metallogenic province with significant implications for future exploration.     

Mineralogical and Geochemical Characteristics of the Utanobori Gold Deposit in Northern Hokkaido,Japan

The Utanobori gold deposit is a low‐sulfidation, epithermal vein‐type deposit located in northern Hokkaido, Japan. The deposit is hosted by conglomerate, sandstone, and tuff of the Middle to Late Miocene Esashi Formation. These rocks were hydrothermally altered. Silica sinters and quartz‐adularia veins are common in the deposit. The quartz‐adularia veins either contain a ginguro band, which corresponds to the main gold‐bearing vein (Type 1 Veins), or do not contain a ginguro band but contain minor adularia (Type 2 Veins). Type 1 Veins are divided into three stages with 12–14 substages. Ore minerals identified include electrum, naumannite, chlorargyrite, bromargyrite, an unidentified Fe‐Sb mineral, and an Fe‐(Sb)‐As mineral. These ore minerals formed in the main mineralization stages I (bands I‐b and I‐d) and II (band II‐a). Scanning electron microscopy with cathodoluminescence images show that cathodoluminescence‐dark microcrystalline quartz exhibiting colloform (ghost‐sphere) texture is closely associated with ore minerals in the Type 1 Vein and Type 2 Vein, and the Al and K contents of such quartz are commonly >1000 ppm. This indicates that the ore minerals were crystallized from alkaline, silica‐saturated fluids at temperatures <200°C, which initially deposited amorphous silica that was recrystallized to microcrystalline quartz. The average Au content of electrum is 52.5 at% Au (n = 10), 65.7 at% Au (n = 20), and 55.5 at% Au (n = 5) in bands I‐b, I‐d, and II‐a, respectively, of Type 1 Veins. The δ³⁴S_CDT values of two fine‐grained disseminated pyrites in the altered conglomerate and bedded tuff in the argillic altered zone are ?4.3 and ?4.2‰. Ar‐Ar dating on adularia yielded 13.6 ± 0.06 Ma, 13.6 ± 0.07 Ma, and 13.6 ± 0.06 Ma for the stages I, II, and III of the Type 1 Vein, respectively. K‐Ar ages determined on adularia in the silica sinter and on whole‐rock of glassy rhyolite of the Esashi Formation are 15.0 ± 0.4 Ma and 14.6 ± 0.4 Ma, respectively. These radiometric ages indicate that silica sinter associated with the rhyolitic volcanic rocks formed prior to the main gold mineralization.     

冀北中低级变质表壳岩的年代学特征及其对华北克拉通构造演化的约束

华北克拉通在新太古代末期发生克拉通化,形成了现今规模的古陆,大量的太古宙岩石均经历了~2500Ma左右的区域高级变质作用(高角闪岩相-麻粒岩相)。而华北克拉通北部冀北地区出露一套中低级变质(绿片岩相-角闪岩相)的火山-沉积岩系,主要包括胡麻营地区红旗营子表壳岩和大阴山地区单塔子表壳岩中变质程度较低的部分。胡麻营地区红旗营子表壳岩系主要岩石组合为变基性火山岩、绿帘角闪岩、斜长角闪岩、含石榴石斜长角闪岩、角闪斜长片麻岩、黑云斜长片麻岩、黑云角闪斜长片麻岩、黑云二长片麻岩、石英片岩、磁铁石英岩等,SIMS锆石U-Pb定年结果表明斜长角闪岩形成于2486±18Ma(MSWD=1.4),而黑云斜长片麻岩形成于2507±37Ma(MSWD=2.0)。大阴山地区单塔子中低级变质表壳岩系主要由浅变质火山岩、云母石英片岩、斜长角闪岩、磁铁石英岩和大理岩等组成,SHRIMP锆石U-Pb定年结果显示,浅变质火山岩中的变玄武岩形成于2490±19Ma(MSWD=2.0),而变英安岩形成于2502±8Ma(MSWD=0.83)。因此,冀北中低级变质的表壳岩系主要形成于新太古代末期,形成年龄为2507~2486Ma;结合冀东青龙地区新太古代末期(2511~2503Ma)的浅变质火山-沉积岩系(青龙表壳岩),我们认为新太古代末期,中低级变质表壳岩系广泛分布于华北克拉通的核部和边缘地区,此套岩系覆盖在太古宙高级变质杂岩之上,代表华北克拉通化之后的稳定盖层,是克拉通化的主要标志之一。     

柏树岗金红石矿床矿石类型及金红石特征

柏树岗金红石矿床含矿岩石主要为下元古界宽坪组角闪片岩等,矿体呈（似）层状,产状与地层一致。矿石可划分为角闪石型片状（或块状）、绿帘石型片状（或块状）、斜长石型块状、云母（或绿帘石）石英型片状、绿帘黑云斜长石型片状、白云母型片状、黑云母型片状（或块状）及石英脉型块状等类型。金红石早于、同时或晚于主变质期脉石矿物形成,以前两种为主,其杂质含量不超过5％,主要为FeO、Cr2O3及SiO2等;决定金红石杂质含量的因素主要为杂质元素离子半径,次为杂质元素在矿石中含量。矿床是下元古界富钛火山-沉积岩系经泥盆纪的区域变质作用形成的。