东天山地区金矿床成矿流体地球化学及其成矿机制

The mechanism of gold ore formation in the eastern Tianshan Mountains, Xinjiang Uygur Autonomous Region, that has been dealt with from various aspects, remains unclear. On the basis of investigations of regional geology, ore deposit geology, and microscopic observations of ores and related rocks of the Jinwozi, the 210, and the Mazhuangshan gold ore deposits, this thesis made a systematic research on the microthermometry of gangue quartz-hosted fluid inclusions, gas, liquid ion and rare earth element compositions and hydrogen, oxygen isotope compositions of sulfide- and quartz-hosted fluid inclusions, and sulfur and lead isotope compositions of sulfide ore minerals from the major ores in the three deposits. On the basis of the above synthetic studies, sources of ore-forming fluids and metals, and mechanism of gold ore formation in the region were discussed. Gas compositions of pyrite- and sphalerite-hosted fluid inclusions were first analyzed in this thesis. Compared with gangue quartz-hosted fluid inclusions, the sulfide-hosted ones are richer in gaseous species CO2, CO, and CH4 etc. Both gas and liquid CO2 are commonly observed in fluid inclusions, whereas halite daughter minerals rarely occur. Ore-forming fluids for the three gold ore deposits are characteristically of medium to low temperatures, medium to low salinities, are rich in CO2 and Na+, K+, Cl" ions. Gas covariation diagrams exhibit linear trends that are interpreted as reflecting mixing between the magamtic fluid and meteoric-derived groundwater. Regarding rare earth element compositions, the Jinwozi and the 210 deposits show moderate to strong LREE/HREE fractionations with negative Eu anomalies. However, the Mazhuangshan deposit shows little LREE/HREE fractionation with positive Eu anomalies. Hydrogen and oxygen isotope compositions of pyrite-hosted fluid inclusions that were first analyzed in this thesis indicate the presence of magmatic water. Hydrogen and oxygen isotope compositions of pyrite- and quartz-hosted fluid inclusions suggest mixing between magmatic water and meteoric-derived groundwater. Sulfur and lead isotope compositions of sulfide ore minerals indicate multi-sources for the metallogenetic materials that range from the crust to the mantle. On the basis of the above synthetic studies, genesis of the gold ore deposits in the eastern Tianshan Mountains was approached. From the Middle-Late Hercynian to Early Indosinian, geodynamic regime of the region was changing from the collisional compression to the post-collisional extension. During the period, magmas were derived from the crust and the mantle and carried metallogenetic materials. Magma intrusion in the upper crust released the magmatic fluids, and drove circulation of groundwater. Mixing of magmatic fluid with groundwater, and extraction of metallogenetic materials from the country rocks are the mechanism for the gold ore formation in the eastern Tianshan Mountains.

胶东地区三类金矿成矿系统地质地球化学及动力学

The East Shandong gold province is located on the southeastern margin of the North China Craton and features uplift in the north and depression in the south. The uplift area is made up of the Archaean Jiaodong Group, the Proterozoic Jingshan Group and Yanshannian granites. Most gold deposits in the uplift area are spatially associated with the Yanshannian granites. Two types of gold mineralization occur in the region: the quartz-vein type hosted in the Linglong granite suite, and the shear zone type hosted by either the Linglong granite or Guojialing granitoid suites. The mineralization ages are 113～126 Ma. The southern part of East Shandong contains the Mesozoic Jiaolai basin, which formed during regional extension. The basin is bounded by the Wulian-Rongcheng fault in the southeast and the Tanlu fault in the west. The Pengjiakuang, Fayunkuang and Dazhuangzi gold deposit occurs on the northeastern margin of the basin. The mineralization ages of these deposits are 110～128 Ma. This paper focuses on a low-angle detachment fault developed between the Proterozoic Jingshan Group metamorphic complex and the northeastern margin of the basin. Our field work shows that the distribution of the Pengjiakuang gold deposit was controlled by the detachment fault. Moreover, the Fayunkuang, Guocheng and Liaoshang gold deposits also occurr in the periphery of the basin, and their features are similar to Pengjiakuang gold deposit. The study of geological geochemistry of the gold deposits has shown: ①three-type gold deposit was situated in the Jiaodong area, including altered rock type (Jiaojia type), quartz vein type (Linglong type) and breccia type (Pengjiakuang type); the ore-forming materials and fluid for Pengjiakuang type gold deposit shows multiple source; ②the ore materials of Jiaojia and Linglong type deposits are mainly from deep source. The author has studied geological-geochemical dynamics of three types deposits in Jiaodong area. The study of tectonic dynamics shows that ore-forming structure differential stress values of Pengjiakuang gold deposit is 100 * 10~6～130 * 10~6 Pa, and that of Jiaojia gold deposit is 100 * 10~5～194 * 10~6 Pa. Dynamics of hydrothermal ore-forming fluid has also been studied in this paper. Author applies Bernoulli equation to dynamic model of hydrothermal fluid motion in brittle fracture and cracks (quartz vein type gold mineralization), and applies Darcy law to dynamic model of hydro thermal fluid motion in porous medium (altered rock type gold mineralization). Author does daring try in order to study quantitativly transport mechanism of hydrothermal ore-forming fluid in this paper. The study of fluid inclusions and crystal dynamics shows that reaction system of hydrothermal ore-forming includes three types, as follows: ore-forming reaction, controlling reaction and buffer controlling reaction. They depend on each other, controlling each other, which form a organic system. Further research shown that formation of ore shoots was controlled by coincidence processes of tectonic dynamic condition and thermodynamic evolution. This paper has summaried reginoal metallogenic laws and seted up metallogenic(dynamics) models for Jiaodong gold ore belt.

山东莱州金城金矿床构造-流体成矿特征

This paper studied the metallotectonics, altered rocks, altered minerals and fluid inclusions. The conclusions are: (1)The gold deposits in Jiaodong district were formed quickly uplifted tectonic setting which was induced by the Mantle doming in Mesozoic era. (2)Both Jiaojia-type and Linglong-type gold mineralizations were formed in the same tectonic-fluid system. (3) The Ar-Ar age of the earlier stage of the gold mineralization is 114～116Ma. (4)The development of the plaiting ore-control tectonic system underwent four stagesrcounterclockwise ductile compresso-shearing, clockwise brittle tenso-shearing and counterclockwise brittle compresso-shearing and brittle normal faulting after mineralization. (5)The mineralization has five stages: quartz and k-feldspar stage, quartz and ferro-carbonate and pyrite stage, quartz and chalcopyrite stage, pyrite and sericite and quartz stage and carbonate stage, and they make up four ore-types: red ore, vein ore, mottled ore and grey ore. (6) The features of mineralizations and ore-forming fluids in different stages are different. But the ore-forming fluids are rich in Si, Fe, P_2O_5, H_2O, CO_2, SO_4~(2-), K~+, Na~+, Ca~(2+) and Cl~- in general and their salinities are from 4 to 18 NaClwt%. (7) The ore-forming fluids came mainly from the Mantle in early stage, then mainly from magma, and mainly from meteoric water in the last stage. (8) Au in the ore-forming fluid was mainly carried in the form of complex of Au and S. (9)The temperature of ore-forming fluid is from 350℃ to 120℃and its pressure is from 20MPa to 38MPa. (10)The gold vein composed by quartz, ferro-carbonate, chalcopyrite and pyrite (vein ore) was filled in the tensional fracture in the top of the magma dome. The disseminated ore bodies composed by pyrite, sericite and quartz (grey ore) was metasomatized in the shearing fault which developed along the contact zone between Linglong intrusive body and Jiaodong Group, which is placed in the flank top of magma dome. In the joint and fracture induced by the shearing fault which developed along the contact zone between Linglong intrusive body and Jiaodong Group, veiniet and stockwork ore (red ore) and veinlet-disseminated ore (mottled ore) composed by quartz and pyrite was formed. (ll)Fluid boiling maybe one of the form of the ore-forming substances precipitation.

新疆萨吾尔金矿带构造-流体地球化学及成矿作用

The Sawuer gold belt is located in the transition belt between Siberian plate and Kazakhstan-Junggar plate. Based on the geological and geochemical studies on the Kuoerzhenkuola and Buerkesidai gold deposits, in Sawuer gold mineralization belt, the time-space structure of mineralization and mineralizing factor are studied, the metallogenic regularity is concluded in thistheses. The ore bodies have the regularity that orebody are of the extensive and compressive in the sallow and depth of volcanic apparatue, respectively, and the vertical extension of orebody is more intensive than the horizontal extension. The gold deposits were controlled by the fractures of volcanic apparatus and regional faults, and featured by the hydrothermal alteration and metasomatism type disseminated mineralization and filling type vein mineralization. By virtue of the geological and geochemical studies on the two deposits that the formation of the two deposits are significantly related to the volcanic activity, we propose new ideas about their origin: (1) the two deposits are located in the same strata, and share the same genesis. (2) both of two deposits are volcanogenic late-stage hydrothermal gold deposits. Based on mapping of volcanic lithofacies and structure for the first time, it is discovered that a volcanic apparatus existed in the study area. Volcanic-intrusive activity can be divided into three cycles and nine lithofacies. where the two deposits are hosted in the same volcanic cycle, in this case, the wall-rock should belong to the same strata. The 40Ar-39Ar age method is employed in this work to analyze the fluid inclusions of quartz in the ore bodies from Kuoerzhenkuola and Buerkesidai gold deposits. The results show that the main mineralization occurred in 332.05 + 2.02-332.59 + 0.5IMa and 335.53 + 0.32Ma~336.78 + 0.50Ma for Kuoerzhenkuola and Buerkesidai gold deposits respectively, indicating that the two deposits are formed almost at the same time, and the metallogenic epoch of the tow deposits are close to those of the hosting rocks formed by volcanic activity of Sawuer gold belt. This geochronological study supplies new evidence for determining the timing of gold mineralization, the geneses of gold deposits? and identifies that in Hercynian period, the Altai developed tectonic-magmatic-hydrothermal mineralization of Early Carboniferous period, except known two metallogenic mineralization periods including tectonic-magmatic-hydrothermal mineralization of Devonian period and Late Carboniferous-Permian period respectively. The study of fluid inclusions indicates that the ore-forming fluid is a type of NaCl-HbO fluid with medium-low temperature and low salinity, Au is transported by the type of auric-sulfur complex (Au (HS)2-), the ore is formed in reduction condition. Hydrogen and oxygen isotopes of fluid inclusions in the major mineralizating stage show that the solutions mainly originated from magmatic water and meteoric water. The fluid mixing and water-rock reaction cause the deposition of Au. The helium and argon isotope compositions of fluid inclusions hosted in pyrite have been measured from Kuoerzhenkuola and Buerkesidai gold deposits in Sawuer gold belt. The results show that the ore-forming fluids of two deposits possessed the same source and is a mixture of mantle- and partial meteoric water-derived fluid, and the reliability of He and Ar isotopic compositions in Hercynian period is discussed. Isotopic studies including H, O, He, C, S, Pb and Sr reveal the same result that the ore-forming fluids of two deposits possessed the same source: the water derived mainly from magmatic water, partially from meteoric water; the mineralizers and ore materials derived mainly from mantle beneath the island arc, and partially from crust. The ore-forming fluids of two deposits are a mixture of mantle-derived fluids being incorporated by crust-derived fluid, and shallow partial meteoric water. Based on these results, it is proposed that the geneses of the two gold deposits are the same, being volcanogenic late-stage hydrothermal gold deposits that the ore-forming fluids filled in fractures of volcanic apparatus and metasomatized the host rocks in the volcanic apparatus. It is the first time we carried out the geophysical exploration, that is, the EH-4 continuous electrical conductivity image system measurement, the results show that relative large-size mineralizing anomalies in underground have been discovered.lt can confirm the law and genesis of the deposits mentioned above, and change the two abandoned mines to current large-size potenial exploration target.

Mantle-derived gaseous components in ore-forming fluids of the Xiangshan uranium

The Xiangshan U deposit, the largest hydrothermal U deposit in China, is hosted in late Jurassic felsic volcanic rocks although the U mineralization post dates the volcanics by at least 20 Ma. The mineralization coincides with intrusion of local mantle-derived mafic dykes formed during Cretaceous crustal extension in South China. Ore-forming fluids are rich in CO2, and U in the fluid is thought to have been dissolved in the form of UO2 (CO3)22− and UO2 (CO3) 34− complexes. This paper provides He and Ar isotope data of fluid inclusions in pyrites and C isotope data of calcites associated with U mineralization (pitchblende) in the Xiangshan U deposit. He isotopic compositions range between 0.1 and 2.0Ra (where Ra is the 3He/4He ratio of air=1.39×10−6) and correlates with 40Ar/36Ar; although there is potential for significant 3He production via 6Li(n,α)3H(β)3He reactions in a U deposit (due to abundant neutrons), nucleogenic production cannot account for either the 3He concentration in these fluids, nor the correlations between He and Ar isotopic compositions. It is more likely that the high 3He/4He ratios represent trapped mantle-derived gases. A mantle origin for the volatiles of Xiangshan is consistent with the δ13C values of calcites, which vary from −3.5‰ to −7.7‰, overlapping the range of mantle CO2. The He, Ar and CO2 characteristics of the ore-forming fluids responsible for the deposit are consistent with mixing between 3He- and CO2-rich mantle-derived fluids and CO2-poor meteoric fluids. These fluids were likely produced during Cretaceous extension and dyke intrusion which permitted mantle-derived CO2 to migrate upward and remobilize U from the acid volcanic source rocks, resulting in the formation of the U deposit. Subsequent decay of U within the fluid inclusions has reduced the 3He/4He ratio, and variations in U/3He result in the range in 3He/4He observed with U/3He ratios in the range 5–17×103 likely corresponding to U concentrations in the fluids b0.2 ppm.

Developing Single-Laser Sources for Multimodal Coherent Anti-Stokes Raman Scattering Microscopy

Coherent anti-Stokes Raman scattering (CARS) microscopy has developed rapidly and is opening the door to new types of experiments. This work describes the development of new laser sources for CARS microscopy and their use for different applications. It is specifically focused on multimodal nonlinear optical microscopy—the simultaneous combination of different imaging techniques. This allows us to address a diverse range of applications, such as the study of biomaterials, fluid inclusions, atherosclerosis, hepatitis C infection in cells, and ice formation in cells. For these applications new laser sources are developed that allow for practical multimodal imaging. For example, it is shown that using a single Ti:sapphire oscillator with a photonic crystal fiber, it is possible to develop a versatile multimodal imaging system using optimally chirped laser pulses. This system can perform simultaneous two photon excited fluorescence, second harmonic generation, and CARS microscopy. The versatility of the system is further demonstrated by showing that it is possible to probe different Raman modes using CARS microscopy simply by changing a time delay between the excitation beams. Using optimally chirped pulses also enables further simplification of the laser system required by using a single fiber laser combined with nonlinear optical fibers to perform effective multimodal imaging. While these sources are useful for practical multimodal imaging, it is believed that for further improvements in CARS microscopy sensitivity, new excitation schemes are necessary. This has led to the design of a new, high power, extended cavity oscillator that should be capable of implementing new excitation schemes for CARS microscopy as well as other techniques. Our interest in multimodal imaging has led us to other areas of research as well. For example, a fiber-coupling scheme for signal collection in the forward direction is demonstrated that allows for fluorescence lifetime imaging without significant temporal distortion. Also highlighted is an imaging artifact that is unique to CARS microscopy that can alter image interpretation, especially when using multimodal imaging. By combining expertise in nonlinear optics, laser development, fiber optics, and microscopy, we have developed systems and techniques that will be of benefit for multimodal CARS microscopy.

The speliothem record of climate variability in Southern Arabia.

Uranium-series dated stalagmites from Oman indicate that pluvial conditions prevailed from 6.3 to 10.5, 78 to 82, 120 to 130, 180 to 200 and 300 to 330 kyr B.P.; all of these periods coincide with peak interglacials. Oxygen (δ18O) and hydrogen (δD) isotope ratios of speleothem calcite and fluid inclusions reveal the source of moisture and provide information on the amount of precipitation, respectively. δ18O and δD values of stalagmites deposited during peak interglacials vary between −8 and −4 ‰ (VPDB) and −53 and −20‰ (Vienna Standard Mean Ocean Water [VSMOW]) respectively, whereas modern stalagmites range from −2.6 to −1.1‰ in δ18O (VPDB) and −7.6 and −3.3‰ in δD (VSMOW), respectively. The growth and isotopic records indicate that during peak interglacial periods, the limit of the monsoon rainfall was shifted far north of its present location and each pluvial period was coinciding with an interglacial stage of the marine oxygen isotope record.

Boron isotope composition of tourmalinite and vein tourmalines associated with gold mineralization, Serra do Itaberaba Group, central Ribeira Belt, SE Brazil

Important concentrations of tourmaline occur as gold-bearing stratiform tourmalinites and in mineralized quartz-tourmaline veins at the Tapera Grande and Quartzito gold prospects in the Mesoproterozoic Serra do Itaberaba Group, central Ribeira Belt (Sao Paulo State, SE Brazil). The main rock types in both prospects constitute the volcanic-sedimentary Morro da Pedra Preta Formation, which formed in a submarine back-arc setting. At Tapera Grande, the volcanic-sedimentary sequence is composed of metabasic and metavolcaniclastic rocks, graphitic and sulfur-rich metapelites, banded iron formation, metandesite, metarhyolite, calcsilicates, tourmalinites and metahydrothermalites derived from mafic and felsic rocks. The Mesoproterozoic rocks at Quartzito prospect are lithologically similar but they have been affected by Neoproterozoic faulting and shearing and by the emplacement of granitic rocks, resulting in the formation of tourmaline-rich quartz-carbonate veins with gold and base metal mineralization. We conducted a chemical and B-isotope study of tourmalines in order to better understand the origin of the stratiform tourmalinites in the Morro da Pedra Preta Formation and their relationship with gold mineralization. The overall range of delta(11)B values obtained for the tourmalinite and vein tourmalines is between - 15%. and -5 parts per thousand, with the tourmalinites failing at the low end of this range (-15 to -8 parts per thousand). Such values are typical for continental crust and inconsistent with a primary marine boron signature as expected from the submarine-exhalative model for the gold prospects. We conclude from this that tourmaline formed or recrystallized from crustal fluids related to the amphibolite-grade metamorphism which affected the Serra do Itaberaba Group and that gold deposition occurred syn- to post-peak metamorphism by phase immiscibility, as attested by fluid inclusions in Tapera Grande tourmalinite tourmaline and quartz. The vein-hosted tourmalines at Quartzito have isotopically variable boron signatures, with heavier delta(11)B values of -5 parts per thousand to -8 parts per thousand for acicular green tourmalines and lighter values (-15 parts per thousand to -7 parts per thousand for light blue, Ti-firee tourmaline from quartz-carbonate veins). We attribute the heavier boron to fluids derived from the volcano-sedimentary rocks of marine affinity whereas the lighter boron was contributed by crustal fluids related to the granitoids or metasediments in the continental crust. (c) 2009 Elsevier B.V. All rights reserved.

Mineralogical and microthermometric studies and structural aspects of imperial topaz mineralization in Antonio Pereira, Ouro Preto District (Minas Gerais) - Brazil

The occurrences of imperial topaz in the Antonio Pereira mine, Ouro Preto, Minas Gerais, are associated with the metamorphic carbonate rocks of the Minas Supergroup. The crystals have densities varying from 3.46 to 3.58. The parameters of the unitary cells obtained were: 4.658 to 4.663 angstrom (ao), 8.823 to 8.832 angstrom (b(o)), 8.382 to 8.389 angstrom (c(o)), and 344.65 to 345.46 angstrom 3 (V). The refraction indices presented the following variations: 1.622 to 1.630 (nX), 1.624 to 1.632 (nY), 1.633 to 1.640 (nZ), and 0.008 to 0.011 (B). These properties are coherent with the low fluorine contents obtained (16,48%/17,05wt%). Infrared spectroscopy and microthermometry showed that the fluid inclusions, which represent the mineralizing fluids, are formed by H(2)O (with Ca(2+), Mg(2+) and Na(+)), and CO(2) +/- CH(4). The minimal trapping T-P conditions of 290/320 degrees C and 2,349/2,497bar were obtained for the primary fluid inclusions. The pseudo-secondary fluid inclusions were trapped at conditions of lower temperatures and variable pressures, during the deformation process under local alternating states of stress. The microthermometric studies, the structural analysis and the fluorine contents suggest that the mineralized veins were formed from hydrothermal fluids originated during the Brasiliano tectono-metamorphic event.

Petrotrama de quartzo e feldspato ao longo da Zona de Cisalhamento de Jundiuvira, Cabreuva (SP)

Fluid inclusions, petrofabric and microstructures studies of mylonites and cataclasites were used to establish the Itu-Jundiuvira Shear Zone (IJSZ) tectonic and metamorphic evolution. The quartz fabric indicates that prism {1000} slip was important during the deformation. This studies have showed that IJSZ changed from deeper crustal levels (12-15km) and ductile conditions to upper levels of about 4 to 6km and brittle strain conditions. -English summary

Inclusões fluidas crepitadas, fluidos hipersalinos e aquo-carbônicos em quartzo associado a rochas micáceas no Granito Xinguara - Terreno Granito-Greenstone de Rio Maria, PA

As rochas micáceas encontradas no Granito Xinguara, terreno Granito-Greenstone de Rio Maria, Pará, são compostas por muscovita e clorita com níveis de quartzo intercalados, que formam uma xistosidade bem desenvolvida. Essa xistosidade é cortada por veios de quartzo. Ambas as gerações de quartzo apresentam os mesmos tipos de inclusões fluidas em halos ou trilhas secundárias de composições variadas entre aquosas, aquo-carbônicas e saturadas em torno de grandes inclusões primárias crepitadas ou em trilhas transgranulares secundárias. A grande variação de temperaturas de homogeneização, a alta salinidade, as evidências de estrangulamento e a existência das inclusões crepitadas permitem supor forte influência de alterações pós-formacionais e reequilíbrio relacionados à intrusão do granito. Essas rochas foliadas são, portanto, enclaves metassedimentares afetados por fluidos graníticos hipersalinos aquo-carbônicos.

Estudos de inclusões fluidas e de isótopos estáveis no depósito Moreira Gomes do campo mineralizado do Cuiú-Cuiú, Província Aurífera do Tapajós, Estado do Pará

Moreira Gomes é um dos depósitos do campo mineralizado do Cuiú-Cuiú, província Aurífera do Tapajós, com recursos de 21,7 t de ouro. A zona mineralizada, com 1200 metros de comprimento, 30-50 metros de largura e, pelo menos, 400 metros de profundidade é controlada por uma estrutura subvertical de orientação E-W, associada a um sistema de falhas transcorrentes sinistrais. As rochas hospedeiras nesse depósito são predominantemente tonalitos de 1997 ± 2 Ma (Suite Intrusiva Creporizão). O estilo da alteração hidrotermal relacionado à mineralização é predominantemente fissural e localmente pervasivo. Os tipos de alteração hidrotermal são sericitização, carbonatação, cloritização, sulfetação, silicificação e epidotização, além da formação de veios de quartzo de espessuras variadas. Pirita é principal sulfeto e contém inclusões de galena, esfalerita, calcopirita e, em menor quantidade, de hessita e bismutinita. O ouro ocorre mais comumente como inclusão em cristais de pirita e, secundariamente, na forma livre em veios de quartzo. Ag, Pb e Bi foram detectados por análise semi-quantitativa como componentes das partículas de ouro. Estudo de inclusões fluidas identificou fluidos compostos por CO₂ (Tipo 1), H₂O-C O₂-sal (Tipo 2) e H₂O-sal (Tipo 3). O volátil CO₂ é predominante na fase carbônica. O fluido do Tipo 2 apresenta densidade baixa a moderada, salinidade entre 1,6 e 11,8 % em peso equivalente de NaCl e foi aprisionado principalmente entre 280° e 350°C. No fluido do Tipo 3 o sistema químico pode conter aCl₂ e, talvez, MgCl₂, e a salinidade varia de zero a 10,1% em peso equivalente de NaCl. Apenas localmente a salinidade atingiu 25% em peso equivalente de NaCl. Esse fluido foi aprisionado principalmente entre 120° e 220°C e foi interpretado como resultado de mistura de fluido aquoso mais quente e levemente mais salino, com fluido mais frio e diluído. Globalmente, o estudo das inclusões fluidas indica estado heterogêneo durante o aprisionamento e ocorrência de separação de fases, mistura, flutuação de pressão e reequilíbrio das inclusões durante aprisionamento. A composição isotópica do fluido em equilíbrio com minerais hidrotermais (quartzo, clorita e calcita e pirita) e de inclusões fluidas apresenta valores de δ¹⁸O e δD entre +0,5 e +9,8 ‰, e -49 a -8 ‰, respectivamente. Os valores de ³⁴S de pirita (-0,29 ‰ a 3,95 ‰) são provavelmente indicativos da presença de enxofre magmático. Pares minerais forneceram temperaturas de equilíbrio isotópico em geral concordante com as temperaturas de homogeneização de inclusões fluidas e compatíveis com as relações texturais. Os resultados isotópicos, combinados com os dados mineralógicos e de inclusões fluidas são interpretados como produto da evolução de um sistema magmático hidrotermal em três estágios. (1) Exsolução de fluido magmático aquoso e portador de CO₂ entre 400°C e 320-350°C, seguido de separação de fases e precipitação principal da assembleia clorita-sericita-pirita-quartzo-ouro sob pressões menores que 2,1 kb e a 6-7 km de profundidade. (2) Resfriamento e continuação da exsolução do CO₂ do fluido magmático geraram fluido aquoso, mais pobre a desprovido de CO₂ e levemente mais salino, com aprisionamento dominantemente a 250°-280°C. A assembleia hidrotermal principal ainda precipitou, mas epidoto foi a principal fase nesse estágio. (3) Mistura do fluido aquoso do estágio 2, mais quente e mais salino, com um fluido aquoso mais frio e menos salino, de origem meteórica. Carbonatação está associada com esse estágio. A assembleia hidrotermal e os valores isotópicos indicam que fluido foi neutro a levemente alcalino e relativamente reduzido, que H₂S (ou HS-) pode ter sido a espécie de enxofre predominante, e que Au(HS) ^-2 deve ter sido o complexo transportador de ouro. A deposição do ouro em Moreira Gomes ocorreu em resposta a diversos mecanismos, envolvendo a separação de fases, mistura e reações fluido-rocha. O depósito Moreira Gomes é interpretado como o produto de um sistema magmático-hidrotermal, mas não possui feições clássicas de depósitos relacionados a intrusões graníticas, tanto oxidadas como reduzidas. A idade de deposição do minério (1,86 Ga) sugere que o sistema magmático-hidrotermal pode estar relacionado com a fase final do extenso magmatismo cálcio-alcalino da Suíte Intrusiva Parauari, embora o magmatismo transicional a alcalino da Suíte Intrusiva Maloquinha não possa ser descartado.

Estudos isotópicos e de inclusões fluidas no depósito central do campo mineralizado do Cuiú-Cuiú, província aurífera do Tapajós, estado do Pará

Central é um depósito aurífero do campo mineralizado do Cuiú-Cuiú, Província Aurífera do Tapajós, Cráton Amazônico. A zona mineralizada está hospedada em falha e compreende 800m de comprimento na direção NW-SE, seguindo o trend regional da província Tapajós, com largura entre 50 e 70m e profundidade vertical de pelo menos 450m. A mineralização está hospedada em monzogranito datado em 1984±3 Ma e atribuído à Suíte Intrusiva Parauari. Os recursos auríferos preliminarmente definidos são de 18,6t de ouro. A alteração hidrotermal é predominantemente fissural. Sericitização, cloritização, silicificação, carbonatação e sulfetação foram os tipos de alteração identificados. Pirita é o sulfeto principal e os demais sulfetos (calcopirita, esfalerita e galena) estão em fraturas ou nas bordas da pirita. O ouro preenche fraturas da pirita e análises semi-quantitativas detectaram Ag associada ao ouro. Foram identificados três tipos de inclusões fluidas hospedados em veios e vênulas de quartzo. O tipo 1 é o menos abundante e consiste em inclusões fluidas compostas por uma (CO_2vapor) ou duas fases (CO_2liq-CO_2vapor), o tipo 2 tem abundância intermediária e é formado por inclusões fluidas compostas por duas (H₂O_liq-CO_2liq) ou três fases (H₂O_liq-CO_2liq-CO_2vapor) e o tipo 3 é o mais abundante e consiste em inclusões fluidas compostas por duas fases (H₂O_liq- H₂Ovapor). O CO₂ representa o volátil nas inclusões com CO₂ e essas (tipo 1 e 2) foram geradas pelo processo de separação de fases oriundo de um fluido aquo-carbônico. A densidade global (0,33 - 0,80 g/cm³) e a salinidade (11,15 - 2,42 % em peso equivalente de NaCl) desse fluido são baixas a moderadas e a temperatura de homogeneização mostra um máximo em 340ºC. Quanto ao tipo 3, o NaCl é o principal sal, a densidade global está no intervalo de 0,65 a 1,11 g/cm³, a salinidade compreendida entre 1,16 e 13,3 % em peso equivalente de NaCl e a temperatura de homogeneização é bimodal, com picos em 120-140ºC e 180ºC. A composição isotópica das inclusões fluidas presentes no quartzo e do quartzo, calcita e clorita mostram valores de δ¹⁸O e δD de +7,8 a +13,6 ‰ e -15 a -35 ‰, respectivamente. Os valores de δ³⁴S na pirita são de +0,5 a +4,0 ‰ e δ¹³C na calcita e CO₂ de inclusões fluidas de -18 a -3,7 ‰. Os valores de δ¹⁸O_H2O e de δD_H2O no quartzo e inclusões fluidas, respectivamente, plotam no campo das águas metamórficas, com um desvio em direção à linha da água meteórica. Considerando a inexistência de evento metamórfico na região do Tapajós à época da mineralização, o sistema hidrotermal responsável pela mineralização no Central, inicialmente, deu-se a partir de fluidos aquo-carbônicos magmático-hidrotermais, exsolvidos por magma félsico relacionado com a fase mais tardia de evolução da Suíte Intrusiva Parauari. As inclusões aquo-carbônicas e carbônicas formaram-se nessa etapa, predominantemente em torno de 340°C. A contínua exsolução de fluido pelo magma levou ao empobrecimento em CO₂ nas fases mais tardias e, com o resfriamento do fluido, as inclusões aquosas passaram a predominar. A partir daí o sistema pode ter interagido com água meteórica, responsável pelo aprisionamento da maior parte das inclusões aquosas de mais baixa temperatura. É possível que parte das inclusões aquosas (as de maior temperatura) represente a mistura local dos fluidos de origens distintas. Essas observações e interpretações permitem classificar Central como um depósito de ouro magmático-hidrotermal relacionado à fase final da formação da Suíte Intrusiva Parauari.

Partial melting within the lower crust – Constraints from bulk rock geochemical data and trace element mineral analyses of granulites and migmatites from Central Finland

This PhD thesis concerns geochemical constraints on recycling and partial melting of Archean continental crust. A natural example of such processes was found in the Iisalmi area of Central Finland. The rocks from this area are Middle to Late Archean in age and experienced metamorphism and partial melting between 2.7-2.63 Ga. The work is based on extensive field work. It is furthermore founded on bulk rock geochemical data as well as in-situ analyses of minerals. All geochemical data were obtained at the Institute of Geosciences, University of Mainz using X-ray fluorescence, solution ICP-MS and laser ablation-ICP-MS for bulk rock geochemical analyses. Mineral analyses were accomplished by electron microprobe and laser ablation ICP-MS. Fluid inclusions were studied by microscope on a heating-freezing-stage at the Geoscience Center, University Göttingen. Part I focuses on the development of a new analytical method for bulk rock trace element determination by laser ablation-ICP-MS using homogeneous glasses fused from rock powder on an Iridium strip heater. This method is applicable for mafic rock samples whose melts have low viscosities and homogenize quickly at temperatures of ~1200°C. Highly viscous melts of felsic samples prevent melting and homogenization at comparable temperatures. Fusion of felsic samples can be enabled by addition of MgO to the rock powder and adjustment of melting temperature and melting duration to the rock composition. Advantages of the fusion method are low detection limits compared to XRF analyses and avoidance of wet-chemical processing and use of strong acids as in solution ICP-MS as well as smaller sample volumes compared to the other methods. Part II of the thesis uses bulk rock geochemical data and results from fluid inclusion studies for discrimination of melting processes observed in different rock types. Fluid inclusion studies demonstrate a major change in fluid composition from CO2-dominated fluids in granulites to aqueous fluids in TTG gneisses and amphibolites. Partial melts were generated in the dry, CO2-rich environment by dehydration melting reactions of amphibole which in addition to tonalitic melts produced the anhydrous mineral assemblages of granulites (grt + cpx + pl ± amph or opx + cpx + pl + amph). Trace element modeling showed that mafic granulites are residues of 10-30 % melt extraction from amphibolitic precursor rocks. The maximum degree of melting in intermediate granulites was ~10 % as inferred from modal abundances of amphibole, clinopyroxene and orthopyroxene. Carbonic inclusions are absent in upper-amphibolite facies migmatites whereas aqueous inclusion with up to 20 wt% NaCl are abundant. This suggests that melting within TTG gneisses and amphibolites took place in the presence of an aqueous fluid phase that enabled melting at the wet solidus at temperatures of 700-750°C. The strong disruption of pre-metamorphic structures in some outcrops suggests that the maximum amount of melt in TTG gneisses was ~25 vol%. The presence of leucosomes in all rock types is taken as the principle evidence for melt formation. However, mineralogical appearance as well as major and trace element composition of many leucosomes imply that leucosomes seldom represent frozen in-situ melts. They are better considered as remnants of the melt channel network, e.g. ways on which melts escaped from the system. Part III of the thesis describes how analyses of minerals from a specific rock type (granulite) can be used to determine partition coefficients between different minerals and between minerals and melt suitable for lower crustal conditions. The trace element analyses by laser ablation-ICP-MS show coherent distribution among the principal mineral phases independent of rock composition. REE contents in amphibole are about 3 times higher than REE contents in clinopyroxene from the same sample. This consistency has to be taken into consideration in models of lower crustal melting where amphibole is replaced by clinopyroxene in the course of melting. A lack of equilibrium is observed between matrix clinopyroxene / amphibole and garnet porphyroblasts which suggests a late stage growth of garnet and slow diffusion and equilibration of the REE during metamorphism. The data provide a first set of distribution coefficients of the transition metals (Sc, V, Cr, Ni) in the lower crust. In addition, analyses of ilmenite and apatite demonstrate the strong influence of accessory phases on trace element distribution. Apatite contains high amounts of REE and Sr while ilmenite incorporates about 20-30 times higher amounts of Nb and Ta than amphibole. Furthermore, trace element mineral analyses provide evidence for magmatic processes such as melt depletion, melt segregation, accumulation and fractionation as well as metasomatism having operated in this high-grade anatectic area.

Assessing Initial Conditions for Chloride Transport Across Low- permeability Argillaceous Rocks, Wellenberg, Switzerland

Information about fluid evolution and solute transport in a low-permeability metamorphic rock sequence has been obtained by comparing chloride concentrations and chlorine isotope ratios of pore water, groundwater, and fluid inclusions. The similarity of d37Cl values in fluid inclusions and groundwater suggests a closed-system evolution during the metamorphic overprint, and signatures established at this time appear to form the initial conditions for chloride transport after exhumation of the rock sequence.