2020 Vol. 31, No. 3
A chloritoid-garnet-bearing micaschist from the southern part of the Elstergebirge was studied to better understand the Variscan orogenic evolution in the Saxothuringian zone of the northwestern Bohemian Massif. Based on the textural relations and compositions of minerals, especially of zoned garnet and potassic white mica, a P-T path was reconstructed using contoured P-T pseudosections. The U-Th-Pb dating of monazite in the micaschist was undertaken with the electron microprobe. The micaschist experienced P-T conditions along a clockwise path between 16 kbar at 510℃ and 5 kbar at 555℃ followed by isobaric heating to about 600℃. Monazite ages range between 315 and 480 Ma with the most prominent maxima and side maxima at 346.0±1.1 (2σ), 357.3±2.3, and 368.3±1.7 Ma. Ages older than 380 Ma were related to detrital monazite pointing to a Devonian sedimentary protolith. Other ages around 325 Ma were assigned to the isobaric heating by nearby post-tectonic granites. The high-pressure event, being the result of the collision of Laurussia and Gondwana after closure of the Rheic Ocean, occurred in the Late Devonian. The exhumation to 15-20 km (5 kbar) ended probably in the Early Carboniferous. The high-pressure micaschists from the Fichtelgebirge to the Erzgebirge crystalline complexes are suggested to represent a single nappe within a metamorphic nappe pile. This nappe is composed of metasedimentary slices, which experienced different peak pressures rather than representing a coherent crustal section.
Reaction infiltration instability (RII) can cause the formation of melt channels and potentially facilitate the physical transport of sulfide liquid, which contributes to the geochemical evolution of chalcophile elements in the lithospheric mantle. This study conducted some two-layer reaction experiments to explore the feasibility of reaction-driven sulfide migration along high-velocity silicate-melt channels. With increasing duration, the formation of more silicate-melt channels and the transport of more sulfide droplets into a depleted peridotite were observed due to the increase of the local permeability. However, at a longer duration, the presence of some melt-channel relics implies that melt channels are temporary and ultimately closed when the reaction infiltration of silicate melt reached equilibrium in the depleted peridotite. Furthermore, theoretical calculations indicate that the RII of the system is suppressed, which impedes the formation of melt channels. The homogeneous distribution of silicate melt in a sulfide-free experiment implies that the Zener pinning of sulfide probably enhances the RII, thereby facilitating the formation of temporary melt channels. Therefore, this study demonstrates that sufficient silicate melt disequilibrium with solid phases in a liquid source potentially promotes the mechanical extraction of sulfides during reaction infiltration of silicate melt.
The effects of melt composition, temperature and pressure on the solubility of fluorite (CaF2), i.e., fluorine concentration in silicate melts in equilibrium with fluorite, are summarized in this paper. The authors present a statistic study based on experimental data in literature and propose a predictive model to estimate F concentration in melt at the saturation of fluorite (CF in meltFl-sat). The modeling indicates that the compositional effect of melt cations on the variation in CF in meltFl-sat can be expressed quantitatively as one parameter FSI (fluorite saturation index):FSI=(3AlNM+Fe2++6Mg+Ca+1.5Na-K)/(Si+Ti+AlNF+Fe3+), in which all cations are in mole, and AlNF and AlNM are Al as network-forming and network-modifying cations, respectively. The dependence of CF in meltFl-sat on FSI is regressed as:CF in meltFl-sat=1.130-2.014·exp (1 000/T)+2.747·exp (P/T)+0.111·CmeltH2O+17.641·FSI, in which T is temperature in Kelvin, P is pressure in MPa, CmeltH2O is melt H2O content in wt.%, and CF in meltFl-sat is in wt.% (normalized to anhydrous basis). The reference dataset used to establish the expression for conditions within 540-1 010 ℃, 50-500 MPa, 0-7 wt.% melt H2O content, 0.4 to 1.7 for A/CNK, 0.3 wt.%-7.0 wt.% for CF in meltFl-sat. The discrepancy of CF in meltFl-sat between calculated and measured values is less than ±0.62 wt.% with a confidence interval of 95%. The expression of FSI and its effect on CF in meltFl-sat indicate that fluorine incorporation in silicate melts is largely controlled by bonding with network-modifying cations, favorably with Mg, AlNM, Na, Ca and Fe2+ in a decreasing order. The proposed model for predicting CF in meltFl-sat is also supported by our new experiments saturated with magmatic fluorite performed at 100-200 MPa and 800-900 ℃. The modeling of magma fractional crystallization emphasizes that the saturation of fluorite is dependent on both the compositions of primary magmas and their initial F contents.KEY WORDS:fluorine, fluorite solubility, silicate melt, experimental petrology.
The mafic enclaves from Mesozoic intermediate-acid magmatic rocks, widely developed along Fujian coast, are considered to be the results of large-scale crust-mantle interaction and magma mixing. In this paper, petrography, mineralogy, and geochemistry of granites and mafic microgranular enclaves (MMEs) in Langqi Island are studied to provide new information for tracing crust-mantle interaction. The zircon U-Pb dating results show that the Langqi rocks were formed at ~101 Ma, which are metaluminous, enriched in silica and high-K calc-alkaline I-type granites. The enclaves have a typical magmatic structure, which is characterized by magma mixing between high-temperature basic magma and low-temperature acidic magma through injecting. The enclaves and host granites show a tendency to mixed major and trace elements, displaying a clear-cut contact relationship, which is indicative of coeval magmatism. The genesis of Langqi rocks is related to the extensional setting caused by the subduction of Paleo-Pacific Plate, and they are the results of mixing of subduction-related metasomatized mantle-derived mafic and induced crustal-melted granitic magma originating from partial melting of the crustal material.
The gold mineralization in the Central Aldan ore district is genetically related to potassic calc-alkaline and alkaline magmatism dated at 115-150 Ma. The objective of this study is to establish the age of hydrothermal processes that accompanied the formation of Au-Te mineralization at the Samolazovsky Deposit. Based on the isotope-geochemical study of zircons from quartz-feldspar metasomatic rocks of the deposit, the granitoids and charnokites of the Nimnyr Complex (1 900-1 960 Ma) at the contact with the Yukhta monzonite-syenite massif (~127 Ma) were studied. Zircon U-Pb dating was performed on a SHRIMP-II ion microprobe, and rare-earth and trace elements analyses of zircon were carried out in the same craters by secondary-ion mass spectrometry on a Cameca IMS-4f ion microprobe. It is revealed that the studied zircons have heterogeneous structures:dark core and lighter rim, which differ greatly in isotope-geochemical parameters. Zircon rims are cut by a network of fractures, extending into the central part of zircon grains. The rims yield a subconcordant age of 1 937±24 Ma, with an average total REE content of 550 ppm, which corresponds to the formation age of the Nimnyr Complex. All zircon cores yield a discordant age of 83±11 Ma and are characterized by a higher total REE content (~1 812 ppm), as well as higher contents of U and non-formula elements (Ca, Sr, and Y) with respect to rims, due to the effect of fluid on zircons. Despite the limited number of zircon grains, the additional geochronological study of zircons from syenites of the ore-bearing Ryabinovy Massif has revealed the presence of two distinct age clusters:~125-138 and 76-83 Ма. The older ages of zircons from syenites are typical for the Central Aldan ore district. Until now, there is still no explanation for an age range (76-83 Ma) of single zircon grains from ore-bearing syenites of the Ryabinovy Massif. The obtained data suggest that the processes of activation (the effect of fluid) within the Central Aldan ore district continued until Late Mesozoic. With regards to the equivocal geotectonic position of the Mesozoic potassic magmatism in the study area and its high metallogenic potential, there exists an absolute necessity to determine the geochronological age of the rock formations. Therefore this study presents the Late Cretaceous geochronological data for the first time which can constrain the time-frame for the formation of gold-bearing magmatic and metasomatic rocks of the Aldan ore district.
Low saline aqueous carbonic fluids are considered to be the ore forming solutions for orogenic lode gold deposits. Phase separation/fluid immiscibility of the ore fluid is quite common and is one of the major reasons for deposition of gold in these deposits. Abundant carbonic fluid inclusions have been observed in quartz grains of Hira-Buddnini Gold Deposit. Theoretical estimation indicates that more volume of H2O compared to CO2 is likely to be trapped in inclusions at different P-T conditions. Preferential loss of H2O from fluid inclusions during ductile deformation of quartz grains have been attributed as the suitable reason for abundance of carbonic fluid inclusions.
Structural network studies could give appropriate opportunities to understanding structural/hydrothermal events, transportation of ore-forming fluids and water/rock interaction process. Four structural deformation/hydrothermal events have been identified in the Jiaojia fault zone according to microtexture and deformation of quartz and feldspars. Plagioclase experienced ductile deformation period with bended polysynthetic twin stripes (> 450 ℃) in the early stage, followed by K-feldspar alteration period with ductile-brittle deformation and subgrain rotation recrystallization of quartz (380-450 ℃). Then, sericitization period occurred extensive ductile-brittle deformation (350-420 ℃) and extensive subgrain rotation recrystallization with a little bulging recrystallization in quartz. In the last, gold precipitation-related pyrite-sericite-quartz alteration was dominated by brittle deformation (300-380 ℃) and total bulging recrystallization of quartz. From the K-feldspar alteration zone and sericitization zone to pyrite-sericite- quartz alteration zone, fractal dimension values of dynamically recrystallized quartz grains increase from 1.07 and 1.24 to 1.32, the calculated paleo strain rate values of dynamically recrystallized quartz range from 10-10.7 (380 ℃)-10-9.6 (450 ℃) and 10-9.3 (350 ℃)-10-8.2 (420 ℃) to 10-9.5 (300 ℃)-10-8.0 (380 ℃), and the paleo differential stress values increase from 36.9 and 39.3, to 121.3 MPa. The increase of fractal dimension values and decrease of grain size from pyrite-sericite-quartz alteration zone and sericitization zone to K-feldspar alteration zone decreased average water/rock ratio values, which could lead to different acidity and redox conditions of ore-forming fluids and mineralization differences. Two kinds of ore- controlling fractures have been distinguished which include the gentle dip types (18°-50°) with NW (315°-355°) and SW (180°-235°) dip hosting No. I orebodies and the steep dip types (74°-90°) with NE (45°-85°) and SE (95°-165°) dip hosting No. III orebodies. These faults/fractures crosscut altered Linglong granite of footwall of the Jiaojia fault zone as rhombohedrons that promoted the connection between fractures in the K-feldspar alteration zone and fluid flow passages near the main fault face. Research results indicate No. I and No. III orebodies should be derived from the same mineralization event and belong to different orebody types in different mineralization sites under the same structural networks.
The P-T conditions of auriferous and barren quartz veins from Kopylovsky, Kavkaz and Krasnoye gold deposits in Proterozoic black shales of Bodaybo ore region are presented the first time in this study. Fluid inclusions trapped in auriferous quartz are aqueous Na±K-Mg chloride with salinity of 6 wt.%-8.8 wt.% NaCleqv. Homogenization temperatures vary from 260 to 350℃, and calculated trapping pressures are 1.2-1.6 kbar. The fluids trapped in barren quartz have more complicated compositions with Na, K, Mg and Fe chlorides, salinity up to 13 wt.% NaCleqv, and homogenization temperatures ranging between 140 and 280℃. The volatiles in fluids are dominated by H2O, followed by CO2 with minor amounts of CH4 and N2. We suppose that auriferous and barren quartz veins have been formed due to the basic metamorphogenic fluid as evidenced by the close slat and gas fluid composition.
This paper presents the properties of fluid inclusions found in sphalerite from Latala epithermal base and precious metal deposit (Central Iran), which is hosted in Cenozoic volcanic- sedimentary host-rocks. The Latala Deposit represents an example of vein type, base metal deposits in the Miduk porphyry copper deposits (PCDs) in southern Urumieh-Dokhtar magmatic belt (UDMB). Mineralization in Latala epithermal base and precious metal vein type formed in 3 stages and sphalerite-quartz veins occur in stages 2 and 3. Stage 2 quartz-sphalerite veins are associated with chalcopyrite and zoned sphalerite, along with quartz+hematite, and Stage 3 quartz-sphalerite veins contain galena+sphalerite+ chalcopyrite and quartz with overgrowth of calcite. Mineralization in Stage 3 occurs as replacement bodies and contains Fe-poor sphalerite without zoning in the outer parts of the deposit. This paper focuses on fluid inclusions in veins bearing sphalerite and quartz. The fluid inclusion homogenization temperatures and salinity in sphalerite (some with typical zoning) range from 144 to 285 ℃ and from 0.2 wt.% to 7.6 wt.% NaCl eq. Sphalerite and fluid inclusions of the Latala base and precious metal deposit formed from relatively low-T and low-salinity solutions. Raman spectroscopy analyses indicate a high percentage of CO2 in the gas phase of fluid inclusions in Fe-poor sphalerites, as expected with melting temperature for CO2 of -56.6 ℃, and significant amounts of H2. Lack of reduced carbon species (methane and lighter hydrocarbons) was confirmed in the petrographic study using UV light and Raman spectroscopy. High amounts of H2 in fluid inclusions of Fe-poor sphalerite can be the result of different intensities of alteration and diffusion processes. The common occurrences of CO2 in fluid inclusions have originated from magma degassing and dissolution of carbonates. The δ34S values for sulfide minerals in galena of sphalerite bearing veins vary between -9.8‰ and -1.0‰, and the δ34S values calculated for H2S are between -7.1‰ and +0.6‰. These values correspond to magmatic sulfur whit possible interaction with wall rocks. Magmatic fluids were successively diluted during cooling and continuous ascent. Secondary boiling would lead to variable amounts of potassic or prophylactic alteration and the hydrogen diffusion into the inclusions hosted in sphalerite of Latala.
Pancarli Ni-Cu±(PGE) sulfide deposit occurs in the Neoproterozoic basement complex of the Bitlis massif, which is one of the Andean-type active continental margin fragments with arc-type assemblages represented by the Cadomian orogenic belt. Pancarli sulfides are associated with quartzo-feldspathic gneisses (country rock) and mafic intrusions (host rock). Composed of only semi-massive ore, the Ni-Cu±(PGE) sulfide deposit is a small-scale deposit, and it does not contain net-textured and disseminated ore. The mineral assemblage comprises pyrrhotite, pentlandite, and chalcopyrite. The semi-massive ore samples contain 2.2 wt.%-2.9 wt.% Ni, 0.8 wt.%-2.2 wt.% Cu (Cu/(Cu+Ni)=0.2-0.5) and 0.13 wt.%-0.17 wt.% Co. The Cu/Ni ratios (average 0.57) are consistent with the segregation of sulfides from a basaltic magma. Low Pt+Pd100%S values of 0.08 ppm-0.89 ppm, relatively low Pt/Pd ratios of 0.2-1.4, and Pd/Ir ratios of 4.5-39 have also been revealed. These values demonstrate that the magma reached S saturation before its emplacement and the mineralization with high Cu/Pd ratios formed by sulfides segregated from a PGE-depleted magma. δ34S isotope values (average -3.1‰) of Pancarli sulfides are lower than mantle source. Negative δ34S value indicates contamination from surrounding rocks. Concerning the composition, remobilization style and magma type, the Pancarli Ni-Cu±(PGE) sulfide deposit is similar to the deposits associated with Andean-type magmatic arcs located in the convergent plate margin settings.
Discriminating barren and fertile intrusions is one of the main challenges in the search for rare-element pegmatites. Diagrams comprising more than one element can make discrimination of productive and barren samples more valid. These diagrams distinguish samples by simultaneous means of positive and/or negative correlations between variables. A ternary diagram for S-type peraluminous granites has been obtained in this study. Firstly, a database composed of Ta-bearing and barren granitic systems was created, then geochemical behavior of trace elements was studied, and statistical investigations were done using GCDkit software, which resulted in the Ga-(Nb+Ta)-(Nb/Ta)(Zr/Hf) ternary diagram which can distinguish the non-mineralized granites from productive ones. The Ta-bearing samples, which are situated in the fertile field in the diagram, are those which have high Nb and Ta contents, elevated Ga content and the lowest Nb/Ta and Zr/Hf values.
The Lower to Middle Proterozoic Sakoli fold belt in Central India forms a triangular belt with significant mineralization of strategic minerals. The Sakoli fold belt comprises metasediments, felsic and mafic volcanics with metabasalts bounded by the gneissic-migmatitic terrain. The last pulses of granitic activity in the form of quartz lenses intrude the metasediments and are associated with tungsten mineralization. The metasediments are intruded by the quartz veins and tourmaline breccias trending 60°N to 65°E and 60°S to 65°W and are parallel to the regional structural foliations. The tungsten mineralization in this area is restricted to tourmaline-quartz mica greisens and quartz veins. The NE-SW trending foliated contact zones of chlorite mica schist and porphyritic granite/gneisses have served as easy channels for the mineralizing vapours and solutions to percolate, which formed ore bearing greisens and quartz veins. This mineralization is erratic and manifested by sparse and sporadic disseminations of wolframite and scheelite associated with minor amount of molybdenite and chalcopyrite. The fluid inclusion microthermometry on mineralized quartz veins and quartz-tourmaline veins reveals the existence of a metamorphogenic aqueous-gaseous (H2O-CO2+NaCl) fluid that underwent phase separation and gave rise to gaseous (CO2) inclusion. The salinity of tungsten mineralizations varies from low to high (1.32 wt.% to 40.44 wt.% NaCl eq.). The estimated P-T range of tungsten mineralization varies from 1.2 to 2.2 kbar at 280 to 390 ℃. Raman spectroscopy reveals that the fluid inclusions mainly contain H2O and CO2 with rarely H2S and CH4. Stable isotopic data reveal that the sulfur isotope fractions from the deposits δ34S ranging from +3.1‰ to +3.35‰, suggesting the deep crustal source for the sulfur, which can be further interpreted as a single (magmatic) supply of sulfur during magmatic-hydrothermal mineralization. The studies reveal the presence of chlorides such as FeCl2/MgCl2 and CaCl2, indicating the involvement of chloride complexes in transportation of tungsten to the fluid system and the evolution of the ore-forming fluids by mixing or immiscibility of high-temperature, high-salinity magmatic fluids and low-temperature, low-salinity fluids in hydrothermal system, and also representing magmatic-hydrothermal interactions contributed wolframite and scheelite with minor amount of molybdenite and chalcopyrite.
The characteristics of quartz-hosted fluid inclusions in fluvial sediments from five locations in the upstream, midstream, and estuary of the Changjiang River, China, are analyzed. The sources of sediments are discussed concerning their differences in the shape, size, number, gas percentage and genetic type of quartz-hosted fluid inclusions. From upstream to downstream, the characteristics of quartz-hosted fluid inclusions in sediments are different. The fluid inclusion types in the samples from upstream to estuary are gradually enriched. The sediment influx from the tributaries of the Changjiang River makes new types of quartz-hosted fluid inclusions in the downstream and estuary. In terms of the number and size, most quartz-hosted fluid inclusions are concentrated in the range of 2-4 μm in diameters and 10-150 in number per 10-3 mm3. The number and size ranges of the fluid inclusions from different positions are also different. The fluid inclusions in the sample collected from the Shigu, upstream of the Changjiang River, are 2-18 μm in size, with the number of 2-166 per 10-3 mm3. Among the samples collected from Yibin, Yichang and Wuhan, the sizes of fluid inclusions are 2-15, 2-10, 2-12 μm, with the number of 1-270, 2-220, and 1-308 per 10-3 mm3, respectively. The proportion of primary fluid inclusions in the sample of the upstream (14%) is higher than that of the midstream (6%-8%) and the estuary (5%), suggesting that different types of source rocks have been input into the river by the tributaries. The characteristics of quartz-hosted fluid inclusions in the fluvial sediments could offer a new perspective for exploration of the source of sediments.
The Aegean area of the western Anatolian region of Turkey, controlled by the low-angle detachment normal fault system, forms an extensional province, the West Anatolian Extensional Province (WAEP). The tectonic deformation which occurred in the Miocene Period, including the Plio-Quaternary Period has created different structures in both the basement rocks and intra-basin deposits of the crust. One of these structures, high-angle normal faults, controls the supradetachment Söke-Kuşadasi Basin (SKB). Within this basin, there are folds with different axes and thrust faults with a north-northwest-northeast (N, NW, NE) trend. These folds and thrust faults in the SKB deformed the sedimentary structures of intra-basin deposits. The folds and thrust faults, which caused the rotation of beddings and imbrications in the SKB, are mainly associated with the tectonic process of the low angle detachment normal fault, which affected the SKB and the Aegean part of western Anatolia. In the SKB, during the process of extensional deformation associated with primary low angle detachment normal faulting, the ramp-flat and inversion geometry observed in the basement rocks and basin deposits of the crust caused folds and thrust faults in only intra-basin deposits. In the WAEP, it is determined for the first time that the folds and thrust faults causing limited shortening deformed the Plio-Quaternary sediments.
The Zagros fold-thrust belt (ZFTB) formed from the progressive collision between the African-Arabian and Eurasian plates. This study focuses on the major tectonic lineaments concerned with the distribution of oilfields in the southern Dezful Embayment as an extremely rich hydrocarbon province in the ZFTB, SW Iran. Integration of surface, near-surface and sub-surface data (e.g., remote sensing, overburden rocks, reservoir and aeromagnetic data) were used for locating major tectonic lineaments in the study area. The results show that the southern Dezful Embayment area was influenced by tectonic lineaments oriented in the NW-SE, NE-SW, E-W and N-S trends, which are possible fault indicators corresponding to surface, shallow subsurface and basement faults. The dominant N-S and E-W tectonic lineaments possibly highlight the stress regime inherited from old structures in the Arabian Shield basement while the NE-SW, NW-SE trends are interpreted as effects of the Zagros orogeny. Generally, these tectonic lineaments influenced both the basement and sedimentary rocks and are used here to divide the belt into several faulted blocks with different structural frameworks. A clear picture of the tectonic trends influencing the Zagros fold-thrust belt oilfields as well as guidance for delineating hydrocarbon reservoirs in the future are presented.
In the present study, Paleozoic Variscan orogenesis was a model of the oroclinal flexion accompanied by extensive magmatism, which could be divided into the following two types:post-tectonic and syn-tectonic tonalite granite, and leuco-granite which were controlled by the tectonic characteristics of the intrusions. It was observed that a very high majority of the samples had displayed discontinuities in their structures, that were later utilized to define the granitoid morphology and development characteristics of the rock during the intrusion phases. Furthermore, it was determined that the tectonics associated with the Alpine orogeny results in the new generation of faults and fractures during the Paleogene Period had produced the development of the Sierras. Due to different weathering processes, the depressions which had resulted in the present granitoid reliefs were found to be exclusively related to the structural development processes during the geological history (either tectonic or magmatic) of the granite, and not as normally interpreted.
Eighty-one karst types and their main characteristics are described in this study, including the conditions of their development, the main characteristics of their karstification and their characteristic features. The classification includes the karst types of the Earth, a concise description of each karst type and the possibilities of belonging to several types of various karst areas. The classification of types is hierarchical in terms of groups, subgroups, types and subtypes. Karst can be classified according to their momentary state (the group of static karst types) and to their development (group of dynamic karst types). The group of static karst types has the azonal and zonal subgroups. Azonal karst types may be situated under any climate. These karst types are categorized according to their geological characteristics (age of karstification, constituting rock, extent of coveredness, structure), their elevation, expansion, the morphology of their surface, hydrology and to the effects occurring on the karst. Taking the above mentioned factors into consideration, the author distinguishes various types and describes their characteristics. Zonal karst types are also described (tundra karst, temperate karst, subtropical karst, tropical karst), karst types that can be distinguished based on their geomorphic evolution are identified and their characteristics are presented.