Features of mineral and chemical composition of the Khamambettu Carbonatites, Tamil Nadu

The paper presents mineralogical features and EPMA results of the Khamambettu carbonatites. The mineralogical data suggest that these rocks have been generated in magmatic and hydrothermal stages. Mineral geothermometer for carbonatite give temperatures of 790°–980°C. Fluid inclusion measurements in monazite (hydrothermal stage) give temperatures of 220°–290°C. One of the features of the carbonatites is high content of magnesia that is defined by the presence of dolomite, olivine, spinel, phlogopite, Mg-rich ilmenite. Chloritization, serpentinization, amphibolization, silicification processes and occurrence of barite, monazite-(Ce), strontianite, celestine are related to hydrothermal stage. Hydrothermal minerals at the Khamambettu were formed by recrystallization of primary carbonatite minerals in the presence of Ba, (SO₄)^2?, REE and Si carried in solution by the hydrothermal fluid.     

Mineralogy of metamorphosed manganese deposits of the South Urals

A mineralogical investigation of metamorphosed manganese rocks was carried out at ore deposits related to the Devonian volcanic complexes of the Magnitogorsk paleovolcanic belt of the South Urals. The mineralogical appearance of these rocks is determined by three consecutively formed groups of mineral assemblages: (1) assemblages occupying the main volume of orebodies and formed during low-grade regional metamorphism (T = 200−250°C, P = 2–3 kbar); (2) assemblages of segregated and metasomatic veinlets that fill the systems of late tectonic fractures; and (3) assemblages of near-surface supergene minerals. Sixty-one minerals have been identified in orebodies and crosscutting hydrothermal veinlets. The major minerals are quartz, hematite, hausmannite, braunite, tephroite, andradite, epidote, rhodonite, caryopilite, calcite, and rhodochrosite. The mineral assemblages of metamorphosed manganese rocks (metamanganolites) are characterized. Chemical compositions of braunite, epidote-group minerals, piemontite, pyroxenes, rhodonite, pyroxmangite, and winchite are considered. The bibliography on geology and mineralogy of the South Ural manganese deposits is given.     

The role of the volatile phase for REE and Y fractionation in low-silica carbonate magmas: implications from natural carbonatites, Namibia

Summary Two bimodal carbonatite complexes in Namibia of Cretaceous age are explored as to the presence and composition of a coexisting carbonatitic fluid. The Kalkfeld and Ondurakorume complexes contain both Ca- and Mg/Fe-carbonatites, composed of calcite alone or calcite with ferroan dolomite, fluorapatite and strontianite. The major element evolution in the bulk rocks from s?vites to beforsites is due to crystallization of calcite and fluorapatite. All carbonatites show a negative Y anomaly in normalised REE plots. Fractionation is accompanied by successively lower HREE contents between Tb and Yb, expressed by the ratios Nd/Ho and Ho/Lu. The evolution of this downward-facing hump goes along with decreasing Y contents in bulk rocks and minerals. All this requires an additional phase coexisting with the carbonate liquid during fractionation. Comparison between the bulk rocks and the expelled fluid shows that the latter had preferentially accumulated the HREE and Y. Further evidence for this process are hydrothermal, HREE, Y-rich fluorites in other carbonatite complexes which reflect the composition of the expelled fluid. The high strength of fluoride complexes suggests that fluoride complexing in the carbonatitic fluid is the process responsible for extracting HREE and Y from the carbonatite magma, leaving fractionated carbonatite rocks depleted in these elements. The geochemical evolution of carbonatite magmas along fractionation has therefore to be considered in a melt-mineral-fluid system. Correspondence: B. Bühn, Instituto de Geociências, Universidade de Brasilia, Campus Universitário Darcy Ribeiro, Brasilia 70910-900, Brazil     

四川锦屏山地区金矿床的成矿机理和成因探讨

在对研究区典型金矿床的矿化地质特征、围岩蚀变特征分析的基础上,讨论了四川锦屏山地区金矿床的成矿机理和矿床成因。锦屏山地区金矿床的含矿围岩以浅变质的三叠系粉砂质片岩为主,金矿床围岩中广泛发育碳酸岩化（早期）和硅化（后期）,前者以铁白云石化为特征,后者以黄铁绢英岩化、绿泥石化和石英脉发育为特征。碳酸岩化主要发生在碳酸岩脉与泥质粉砂岩的接触带上的粉砂岩一侧,由碳酸岩脉侵入时的热液交代岩石中的泥质矿物而形成。金矿体的走向与碳酸岩化带的产状基本一致,金主要富集于硅化强烈、黄铁绢英岩化发育地段。碳酸岩化地层中具有较高的含金背景,指示成矿物质金来源于地幔,而矿化主要发生在黄铁绢英岩化和硅化带及石英硫化物脉中。结合矿床的同位素地球化学特征,认为研究区金矿的成矿作用主要是后期热液的改造作用中金元素发生再次富集的结果。金矿的形成经历了碳酸岩脉侵入、地层发生铁白云石化并初步富集形成矿源层（岩）阶段和以硫化物石英脉为代表的热液期的大规模富集成矿两个阶段,矿床的成因类型因属于改造型金矿床。     

Isotopic geochronological evidence for the Paleoproterozoic age of gold mineralization in Archean greenstone belts of Karelia, the Baltic Shield

The Rb-Sr age of metasomatic rocks from four gold deposits and occurrences localized in Archean granite-greenstone belts of the western, central, and southern Karelian Craton of the Baltic Shield has been determined. At the Pedrolampi deposit in central Karelia, the dated Au-bearing beresite and quartz-carbonate veins are located in the shear zone and replace Mesoarchean (～2.9 Ga) mafic and felsic metavolcanic rocks of the Koikar-Kobozero greenstone belt. At the Taloveis ore occurrence in the Kostomuksha greenstone belt of western Karelia, the dated beresite replaces Neoarchean (～2.7 Ga) granitoids and is conjugated with quartz veins in the shear zone. At the Faddeinkelja occurrence of southern Karelia, Aubearing beresite in the large tectonic zone, which transects Archean granite and Paleoproterozoic mafic dikes, has been studied. At the Hatunoja occurrence in the Jalonvaara greenstone belt of southwestern Karelia, the studied quartz veins and related gold mineralization are localized in Archean granitoids. The Rb-Sr isochrons based on whole-rock samples and minerals from ore-bearing and metasomatic wall rocks and veins yielded ～1.7 Ga for all studied objects. This age is interpreted as the time of development of ore-bearing tectonic zones and ore-forming hydrothermal metasomatic alteration. New isotopic data in combination with the results obtained by our precursors allow us to recognize the Paleoproterozoic stage of gold mineralization in the Karelian Craton. This stage was unrelated to the Archean crust formation in the Karelian Block and is a repercussion of the Paleoproterozoic (2.0–1.7 Ga) crust-forming tectonic cycle, which gave rise to the formation of the Svecofennian and Lapland-Kola foldbelts in the framework of the Karelain Craton. The oreforming capability of Paleoproterozoic tectonics in the Archean complexes of the Karelian Craton was probably not great, and its main role consisted in reworking of the Archean gold mineralization of various genetic types, including the inferred orogenic mesothermal gold concentrations.     

Origin of Mantle-Shaped Carbonatite Bodies in the Khalyuta Deposit, Western Transbaikal Region, Russia

The western Transbaikal region is among the long known and well studied ore districts. Nevertheless, carbonatites were unknown in the region until 1990s. About four decades ago, two small outcrops of endogenic carbonatite rocks were discovered in the western sector of this region. Subsequently, one of these outcrops was identified as an epithermal fluorite mineralization in limestones, while the second outcrop was recognized as skarn lode with the barite–strontianite mineralization. Recently, based on geostructural, mineralogical, geochemical, and isotope data, we could identify these rocks as linear or fault-line carbonatites (Bulnaev and Posokhov, 1995; Bulnaev, 1997). Now these sites are known as the Arshan and Khalyuta deposits spaced 20 km apart and located at 45–47 km to the southwest and west of Ulan-Ude, respectively.     

方解石矿床及工业利用

方解石矿床一般产于碳酸盐岩地区和侵入岩变质接触带,受断裂风化淋滤容矿,热液接触变质作用,由碳酸盐岩褪色重结晶而形成。方解石矿有三个显著特征：即白色、块大、致密。在化学工业,建材装饰,工艺雕刻上,都得到广泛应用。     

Hot-fluid Driven Metasomatism of Samalpatti Carbonatites, South India: Evidence from Petrology, Mineral Chemistry, Trace Elements and Stable Isotope Compositions

The magmatic heritage of carbonatites can be identified on the basis of a combination of geological criteria such as, their mode of occurrence, the nature of associated igneous rocks, the presence of minerals of igneous origin, fenitization, characteristic trace element contents and isotopic composition. Late Proterozoic Samalpatti carbonatites were studied in view of these criteria, and were found to contain metamorphic minerals that normally form under thermal metamorphic conditions and which have unusual chemical compositions. A combination of criteria points clearly to a magmatic origin for these carbonatites. Field relations indicate that the dominant modes of intrusion of carbonatite into the encompassing pyroxenites and syenites include small dykes, veins, or lenses. The igneous nature of these carbonatites has been described elsewhere and chemically they are classified as calico-carbonatites. Currently, very little is known about the metamorphic textures and mineralogy observed in the Samalpatti carbonatites. In this study, several metamorphic minerals are reported including diopside, grossularite, vesuvianite, K-feldspar and wollastonite, and a hornfelsic texture is described. These mineral phases and texture characterize thermal metamorphism under low pressure and high temperature (LP-HT) metamorphic conditions (650°_750°C) or metasomatism aided by hot-fluid advection. The metamorphic nature of minerals reported is also confirmed by electron microprobe study. The Samalpatti carbonatite samples show much lower values of characteristic trace elements (P, Sr, Ba, Zr, Nb, Th, Y and REEs) than average concentrations for magmatic carbonatite. Stable isotopic (d¹³C and d¹⁸O) compositions of Samalpatti carbonatites do not fall in the primary igneous carbonatite (PIC) domain. The petrological and chemical signatures of these carbonatites suggest metasomatism in conjunction with fluid advection. Such a metasomatic process may drastically change the chemistry of the rocks in addition to enrichment of heavier stable isotopes. During this metasomatic process, characteristic elements would be dissolved in the high d¹⁸O fluid, and together with Rayleigh fractionation would contribute to enhanced concentrations of ¹³C and ¹⁸O in Samalpatti carbonatites.     

Mineralogy of metamorphosed carbonatite of the Vesely occurrence, Northern Transbaikal region, Russia

Metamorphism of carbonatite is exemplified in the Vesely occurrence. According to available data, the age of the carbonatite is 596 ± 3.5Ma, whereas metamorphism is dated at 550 ± 14 Ma. The rocks at the Vesely occurrence were metamorphosed under conditions of greenschist facies (epidote-muscovite-chlorite subfacies) under elevated pressure. Microthermometry of fluid inclusions in minerals indicates that the temperature of metamorphism is 377−450°C and the pressure estimated from phengite geobarometer is 6−8 kbar. The low-grade metamorphism led to the partial recrystallization of carbonates and apatite with removal of trace elements. This process resulted in a change of the oxygen isotopic composition of the studied minerals. Metamorphism was accompanied by formation of talc, phengite, chlorite, quartz, tremolite-actinolite, and anthophyllite, which are not typical of carbonatite. The data obtained show that the metamorphism exerted an effect on the mineralogical, isotopic, geochemical, and technological properties of the carbonatite. The effect of metamorphism should be taken into account in determination of the nature of ore mineralization and estimation of ore quality and perspective of the occurrence.     

New Promising Gold-Ore Objects in the Strelna Greenstone Belt,Kola Peninsula

Data on gold ore objects in the Strelna Greenstone Belt in the southeastern Kola Peninsula are presented in the paper. The studied Vorgovy and Sergozero ore occurrences are localized in the zone of tectonic contact of the Neoarchean complexes making up the greenstone belt and the volcanic–sedimentary sequences of the Paleoproterozoic Imandra–Varzuga Zone. The Vorgovy gold occurrence is related to stockwork of carbonate–quartz veins and veinlets hosted in a biotite gneiss transformed into chlorite–sericite–quartz metasomatic rock with pyrrhotite–arsenopyrite dissemination. The Sergozero occurrence is localized in amphibolites corresponding to komatiitic and tholeiitic basalts hosted in biotite gneiss (metapelite). Mineralization is confined to the zone of tectonized contact between komatiitic and tholeiitic basalts, where it is controlled by a strip of metasomatic biotite–calcite rock with gersdorffite–arsenopyrite dissemination. The native gold grains medium to high in fineness are up to 0.1 mm in size and mainly localized at the contact of arsenopyrite and gersdorffite with gangue minerals. Gold mineralization is of superimposed character, and, as indicated by isotopic geochronology, was formed at the retrograde stage of the Svecofennian regional metamorphism. Comparison of ore occurrences localized in the Strelna Greenstone Belt with gold deposits in greenstone belts of the western Fennoscandian Shield and the Superior Province in Canada allows us to suggest a high perspective of the entire Strelna Belt for gold.     

四川冕宁包子山稀土矿床富Sr碳酸岩的发现及意义

全球范围内出露的碳酸岩大多为钙质、镁质、铁质碳酸岩,少量为钠质和硅质碳酸岩,极少有富Sr碳酸岩的报道,其岩石成因、资源意义及对碳酸岩岩浆演化的指示意义尚不清楚。本次在四川省牦牛坪稀土矿区南部包子山稀土矿床的露天采坑中发现了超级富Sr的碳酸岩,其呈不规则的脉状侵入到构造角砾岩中。岩石呈紫色-淡紫色,微晶-斑状结构,斑晶主要为萤石,基质主要为菱锶矿、方解石、氟碳铈矿、氟碳钙铈矿、金云母、重晶石并含少量的金属硫化物和氧化物。全岩的微量元素分析表明,其稀土元素总量(∑REE)达3.5%～6.1%,Sr含量达19.0%～27.7%,已超过稀土矿床和锶矿床的工业品位要求。岩石中的中、重稀土元素含量占稀土元素总量的1.14%～1.77%,一些高价值稀土元素含量较高,如Pr(939×10~(-6)～1399×10~(-6))、Nd(2783×10~(-6)～3937×10~(-6))、Gd(237×10~(-6)～320×10~(-6)),因此除轻稀土元素外,中、重稀土和锶元素也具有重要的资源意义。岩石强烈富集REE、Sr、Ba,而明显亏损P、Nb、Ta、Zr、Hf元素,可能与岩浆演化过程中锆石和其它基性矿物的结晶分离有关。全岩的Sr-Nd同位素组成与牦牛坪、里庄稀土矿床的碳酸岩相似,表明它们为同源岩浆产物。笔者认为,富Sr的碳酸岩代表了碳酸岩岩浆演化晚期的产物,REE、Sr、Ba、F和S元素均在岩浆演化晚期的碳酸岩中高度富集。碳酸岩岩浆超浅成侵位至构造角砾岩中,并与下渗的大气水相遇导致岩浆的淬冷和微晶-斑状结构的形成。早期基性矿物(如霓辉石、黑云母)及碳酸盐矿物(如方解石、白云石等)的结晶分离是造成晚期碳酸岩中稀土元素富集的重要原因。富Sr碳酸岩中石英斑晶的发现和其较低的SiO_2含量表明碳酸岩岩浆演化晚期可能是硅饱和的,且这种岩浆具有很低的SiO_2溶解能力。以菱锶矿(体积分数 50%)为主要碳酸盐矿物的稀土碳酸岩可能代表了一种新的碳酸岩类型,明显不同于已知的钙质、镁质、铁质和钠质碳酸岩。     

MVT矿床中与成矿有关热液方解石的地球化学判据——以青海多才玛超大型铅锌矿床为例

碳酸盐矿物是MVT型铅锌矿床最为常见的热液蚀变矿物,记录了成矿流体特征,其元素或同位素组成对示踪和定位矿体具有一定的指示意义,但由于该类矿床中碳酸盐矿物成因多样,单一的岩相学观察往往难以准确识别与成矿有关和无关的方解石,需要辅以地球化学手段来确定方解石成因。本文利用钻孔编录、岩相学观察、C-O-Sr同位素和原位微量与稀土元素组成分析等手段,探讨了青海多才玛超大型MVT铅锌矿床中与成矿有关和无关两期方解石的矿物化学特征。结果表明,多才玛矿床成矿前方解石(Cal1)空间上与矿体无相关关系,遍布于中二叠统九十道班组灰岩内,阴极发光呈暗棕色至棕黄色,无明显生长环带;成矿期方解石(Cal2)主要产于铅锌矿体内及其上盘围岩中,多呈砂糖粒状-皮壳状充填于围岩裂隙和溶孔内,阴极发光呈暗黄色至亮橙色,常发育生长环带。相对于Cal2, Cal1与围岩的C-O-Sr同位素组成更为接近,这表明水岩反应期间,Cal1组成受围岩影响更大,Cal2组成受影响更小;相比于Cal1,Cal2具有较高的Mn、Fe、Zn、Pb含量和U/Th、V/Cr值以及较低的LREE/HREE值、Mg、Sr含量和弱的Ce负异常,指示成矿...     

Isotopic systematics of the rocks of the Khalyuta carbonatite complex of western Transbaikalia

This paper reports the results of isotopic investigations of the rocks of the Khalyuta carbonatite complex (carbonatites, comagmatic silicate rocks, fenites, and hydrothermal rocks) and host limestones and granites. Pyroxene, amphibole, magnetite, potassium feldspar, apatite, phlogopite, calcite, dolomite, strontianite, celestite, and barite were investigated. The isotopic compositions of C, O, Sr, and S were analyzed. The character of the distribution of oxygen isotopic composition in minerals (carbonates, silicates, phosphates, and oxides) suggests their equilibrium formation. It was supposed that the evolutionary trend of C and O isotopic compositions is mainly related to the processes of differentiation in the melt-fluid system and indicates the absence of significant contamination by carbon and oxygen from a crustal source during rock formation from the magmatic stage to the hydrothermal stage. The isotopic compositions of S and Sr did not change.     

Kizilcaören ore-bearing complex with carbonatites (northwestern Anatolia,Turkey): Formation time and mineralogy of rocks

The results of isotope-geochronological and mineralogical studies of the rocks making up the Kizilcaören fluorite-barite-REE deposit, northwestern Anatolia, Turkey are discussed in the paper. The ore is a constituent of the subvolcanic complex localized in a large fault zone. The complex combines (from earlier to later rocks): (1) phonolite and trachyte stocks, (2) carbonatite and carbonate-silicate dikelike bodies; and (3) fluorite-barite-bastnaesite ore in the form of thick homogeneous veins and cement in breccia. The K-Ar dating of silicate igneous rocks and carbonatites shows that they were formed in the Chattian Age of the Oligocene 25–24 Ma ago. Mineralogical observations show that the ore is the youngest constituent in the rock complex. Supergene alteration deeply transformed ore-bearing rocks, in particular, resulting in leaching of primary minerals, presumably Ca-Mn-Fe carbonates, and in cementation of the residual bastnaesitefluorite framework by Fe and Mn hydroxides. Most of the studied rocks contain pyrochlore, LREE fluorocarbonates, Nb-bearing rutile, Fe-Mg micas, and K-feldspar. The genetic features of the deposit have been considered. In general, the ore-bearing rock complex is compared in the set of rocks and their mineralogy and geochemistry with deposits of the Gallinas Mountains in the United States, the Arshan and Khalyuta deposits in the western Transbaikalia region, and Mushugai-Khuduk deposit in Mongolia. The Kizilcaören deposit represents a variant of postmagmatic mineralization closely related to carbonatite magmatism associated with alkaline and subalkaline intermediate rocks.     

Genesis of Si-rich carbonatites in Huanglongpu Mo deposit,Lesser Qinling orogen,China and significance for Mo mineralization

The Huanglongpu carbonatite-related Mo ore field is located in the Lesser Qinling Orogenic belt in the southern margin of the North China block. The ore field is composed of six deposits, Yuantou, Wengongling, Dashigou, Shijiawan, Taoyuan and Erdaohe, all of which are genetically related to carbonatite dykes except for the Shijiawan deposit which is associated with a granitic porphyry. The Yuantou carbonatite dykes intruded into Archean gneiss and other carbonatites emplaced into Mesoproterozoic volcanic and sediment rocks. The carbonatites are mainly composed of calcite and variable amounts of quartz and K-feldspar and minor molybdenite. Re–Os dating of molybdenite from the Yuantou carbonatite yields a weighted average age of 225.0 ± 7.6 Ma, consistent with the molybdenite age (221 Ma) from the Dashigou deposit. The rocks are characterized by high heavy REE (HREE) contents and consistent flat REE distribution patterns with La/Yb_cn ~ 1. Quartz in the carbonatites from Yuantou and Dashigou deposits shows consistent O isotopes (8.1–10.2‰) similar to the associated calcite (7.2–9.5‰). The quartz and associated K-feldspar contain lower Zr, Hf and higher HREE abundances and negligible Eu anomaly relative to those from the granite porphyry in Shijiawan. Both minerals are primary products in the carbonatitic liquid, and not captured from the wall-rocks or crustal-derived silicate magmas, or a hydrothermal origin. Thus, the Huanglongpu carbonatitic liquids were enriched in Si and Mo, which may be produced by intensely fractional crystallization of non-silicate minerals.     

白云鄂博地区碳酸岩脉侵位序列与稀土元素富集机制

白云鄂博地区发育大量的火成碳酸岩脉。按照矿物组成,碳酸岩脉可分为白云石型、白云石-方解石共存型和方解石型。野外穿插关系表明,白云石型碳酸岩脉形成得早,而方解石型碳酸岩脉形成得晚。白云鄂博地区的碳酸岩浆存在由白云石型到共存型再到方解石型的先后结晶顺序和演化趋势。碳酸岩脉的主量、稀土和微量元素组成特征表明,随着碳酸岩脉中方解石矿物组分的增加,轻稀土元素的含量呈明显富集趋势,而长期的结晶分异作用正是稀土元素,尤其是轻稀土元素在晚期岩浆中强烈富集的内在机制。     

The relationship between websterite and peridotite in the Balmuccia peridotite massif (NW Italy) as revealed by trace element variations in clinopyroxene

 Field, mineralogical and petrological data are presented on a newly found carbonatite occurrence associated with “kamafugite” lava at Cupaello, central Italy. This carbonatite occurrence is part of the Late Pleistocene Umbria-Latium ultra-alkaline district (ULUD) which extends southwards within the Apennines to Mount Vulture, delineating an important magmatic province along the most peripheral belt of the Tyrrhenian extensional tectonic system. This province is distinct, but probably related genetically with the more abundant and common leucite-bearing assemblages of the Roman Comagmatic Region and represents the first reported occurrence of carbonatite assemblages in the Mediterranean Basin. The Cupaello suite indicates that primary or near-primary mantle silicate melts of “kamafugitic” composition are transitional with Ca-carbonatite liquid and provides direct evidence of immiscibility of carbonatite from “kamafugite” magma. It is inferred that a primary mantle origin of Ca-carbonatites is conditional upon a potential silicate magma that may be coupled with the carbonatite, but may not have reached the surface. The data indicate a strong genetic link between ULUD Ca-carbonatites and some African analogues, supporting the view that their genesis depends on similar source and associated tectonic conditions. Received: 17 January 1995 / Accepted: 14 June 1995     

羌塘盆地隆额尼-昂达尔错古油藏的白云岩组构特征及铅同位素意义

以系统的岩石学及沉积相分析为基础,深入探讨了隆额尼-昂达尔错古油藏白云岩及其伴生灰岩的铅同位素特征,认为该区白云岩及伴生灰岩具有统一的铅来源,铅主要来自中央隆起带变质岩、岩浆岩及再旋回沉积的三叠系地层,为地幔、造山带、地壳等多源混合的异常铅.铅元素在含量上与沉积相带关系十分明显,仍受沉积过程的控制,后期构造作用并未带入大量深部流体进行白云岩的交代作用.该区白云岩仍保存有大量具成因意义的组构信息,主要体现在:典型混合水交代成因的雾心亮边结构、等厚环边和世代生成结构、残余鲕粒结构及藻纹层构造等,该区白云岩为混合水交代成因.构造只是起到白云岩化后期的改造作用.     

云南牟定戌街地区铀矿化特征及成因探讨

云南牟定戌街1101铀矿区位于扬子地台西南缘,康滇地轴中南段,是我国西南地区产于元古界变质岩中的铀矿之一。通过对矿化区岩石及矿石的岩石学、矿物学、地球化学及年代学特征进行研究,分析了铀矿的形成条件,揭示了铀成矿规律。研究发现:①牟定戌街地区铀矿化赋存于斜长角闪岩、角闪斜长片麻岩和二云母石英片岩等变质混合岩中,主要铀矿物为晶质铀矿、钛铀矿及次生铀矿,含铀矿物有榍石、锆石,硫化物丰富,围岩蚀变主要为硅化、赤铁矿化、碱交代等;②牟定1101铀矿化地区混合岩化岩石的地球化学特征表现为高钾钙碱性-钙碱性系列岩石;③研究区混合岩形成于1 056 Ma左右,铀矿形成于845 Ma左右,为新元古代产物;④牟定1101地区铀成矿受构造、岩性控制,与混合岩化作用、构造热液活动及碱交代作用关系密切,属热液成因铀矿。     

内华达北中部新月谷—独立金矿区线性构造带的证据

内华达北中部的新月谷-独立金矿区线性构造(CVIL)是一个呈20°～30°走向、具多期变形、侵入及热液活动的构造带,该带从独立金矿区向南至科特兹矿山附近延伸达90 km,经过科特兹-派普来恩、卡林及独立三个主要的沉积岩型金矿区,含有罗伯茨山异地岩(可能是奥陶系Vinini组)的强烈构造岩,NE向的断层,白垩或第三纪的NE向的岩墙.变形带的组构具混杂岩的特点,但混杂岩中也显示有与晚三叠世和晚侏罗世之间形成的褶皱展布方向一致的定向组构.此外,沿CVIL带局部出现有第三纪的碧玉状岩石、角砾岩、方解石脉及脱钙蚀变作用.CVIL构造带南北两端成群出现的沉积岩型金矿床具有与卡林矿带金矿床相同的矿物特征.上述二个矿区都有NE向的断层,穿越罗伯茨山异地岩上盘中的构造窗和构造高地.CVIL可能是形成某些金矿床的主要热液通道.