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1.
The formation of solid bituminous matter (SBM) on surfaces of microporous silicates was experimentally studied at pressure and temperature conditions typical of late-stage magmatic and hydrothermal processes. Aliquots of microporous silicate minerals (zorite and kuzmenkoite-Mn, Lovozero Alkaline Massif, Kola Peninsula, Russia) were exposed to solid or liquid organic carbon sources (natural brown coal and liquid 1-hexene for synthesis purposes) in a 0.1 M NaCl-solution for 7 days, at constant pressure (50 MPa), and at three individual temperatures (200, 275, and 300 °C). No thermal decomposition of the solid organic sources happened at 200 °C and only a thin film of brown coal derivatives on the silicates’ surfaces and no formation of SBM were observed at 275 °C and 300 °C. But solid bituminous matter on the surfaces of both microporous silicates were detected in experiments with liquid 1-hexene as organic carbon source and at temperatures of 275 °C and 300 °C with a more pronounced formation of SBM at 300 °C compared to 275 °C. The aromatic and aliphatic hydrocarbons, as well as alcoholic compounds of the experimentally produced SBM are similar, if not even partly identical, with natural SBM occurrences of the Khibiny and Lovozero Massifs, Kola Peninsula, Russia, and from the Viitaniemi granitic pegmatite, Finland, as shown by FT-IR and 1H NMR spectroscopy. This strengthens the hypothesis of formation of natural solid bituminous matter by catalytic reactions between microporous Ti-, Nb- and Zr-silicates and hydrocarbons at postmagmatic hydrothermal conditions.  相似文献   

2.
The large, newly discovered Sharang porphyry Mo deposit and nearby Yaguila skarn Pb–Zn–Ag (–Mo) deposit reside in the central Lhasa terrane, northern Gangdese metallogenic belt, Tibet. Multiple mineral chronometers (zircon U–Pb, sericite 40Ar–39Ar, and zircon and apatite (U–Th)/He) reveal that ore-forming porphyritic intrusions experienced rapid cooling (> 100 °C/Ma) during a monotonic magmatic–hydrothermal evolution. The magmatic–hydrothermal ore-forming event at Sharang lasted ~ 6.0 Myr (~ 1.8 Myr for cooling from > 900 to 350 °C and ~ 4.0 Myr for cooling from 350 to 200 °C) whereas cooling was more prolonged during ore formation at Yaguila (~ 1.8 Myr from > 900 to 500 °C and a maximum of ~ 16 Myr from > 900 to 350 °C). All porphyritic intrusions in the ore district experienced exhumation at a rate of 0.07–0.09 mm/yr (apatite He ages between ~ 37 and 30 Ma). Combined with previous studies, this work implies that uplift of the eastern section of the Lhasa terrane expanded from central Lhasa (37–30 Ma) to southern Lhasa (15–12 Ma) at an increasing exhumation rate. All available geochronologic data reveal that magmatic–hydrothermal–exhumation activities in the Sharang–Yaguila ore district occurred within four periods of magmatism with related mineralization. Significant porphyry-type Mo mineralization was associated with Late Cretaceous–Eocene felsic porphyritic intrusions in the central Lhasa terrane, resulting from Neotethyan oceanic subduction and India–Asia continental collision.  相似文献   

3.
The Kizilcaören fluorite–barite–Rare Earth Element (REE) deposit occurs as epithermal veins and breccia fillings in altered Triassic metasandstones and Oligocene–Miocene pyroclastics adjacent to alkaline porphyritic trachyte and phonolite. This deposit is the only commercial source of REE and thorium in Turkey. Most of the fluorite–barite–REE mineralisation at Kizilcaören has been formed by hydrothermal solutions, which are thought to be genetically associated with alkaline volcanism. The occurrence of the ore minerals in vuggy cavities and veins of massive and vuggy silica indicate that the ore stage postdates hydrothermal alteration. The deposit contains evidence of at least three periods of hypogene mineralisation separated by two periods of faulting. The mineral assemblage includes fluorite, barite, quartz, calcite, bastnäsite, phlogopite, pyrolusite and hematite as well as minor amounts of plagioclase feldspar, pyrite, psilomelane, braunite, monazite, fluocerite, brockite, goethite, and rutile. Fluid inclusion microthermometry indicates that the barite formed from low salinity (0.4–9.2 equiv. wt% NaCl) fluids at low temperatures, between 105 and 230 °C, but fluorite formed from slightly higher salinity (<12.4 equiv. wt% NaCl) fluids at low and moderate temperatures, between 135–354 °C. The depositional temperature of bastnäsite is between 143–286 °C. The local coexistence of liquid- and vapour-rich inclusions suggests boiling conditions. Many relatively low-salinity (<10.0 equiv. wt% NaCl), low and moderate temperature (200–300 °C) inclusions might be the result of episodic mixing of deep-saline brines with low-salinity meteoric fluids. The narrow range of δ34S (pyrite and barite) values (2.89–6.92‰ CDT)suggests that the sulphur source of the hydrothermal fluids are the same and compatible with a volcanogenic sulphate field derived from a magmatic sulphur source.  相似文献   

4.
The Shilu deposit is a world-class Fe–Co–Cu orebody located in the Changjiang area of the western part of Hainan Island, South China. The distribution of Fe, Co, and Cu orebodies is controlled by strata of the No. 6 Formation in the Shilu Group and the Beiyi synclinorium. Based on a petrological study of the host rocks and their alteration assemblages, and textural and structural features of the ores, four mineralization stages have been identified: (1) the sedimentary ore-forming period; (2) the metamorphic ore-forming period; (3) the hydrothermal mineralization comprising the skarn and quartz–sulfide stage; and (4) the supergene period. The fluid inclusions in sedimentary quartz and/or chert indicate low temperatures (ca. 160 °C) and low salinities from 0.7 to 3.1 wt.% NaCleq, which corresponds to densities of 0.77 to 0.93 g/cm3. CO2-bearing or carbonic inclusions have been interpreted to result from regional metamorphism. Homogenization temperatures of fluid inclusions for the skarn stage have a wide range from 148 °C to 497 °C and the salinities of the fluid inclusions range from 1.2 to 22.3 wt.% NaCleq, which corresponds to densities from 0.56 to 0.94 g/cm3. Fluid inclusions of the quartz–sulfide stage yield homogenization temperatures of 151–356 °C and salinities from 0.9 to 8.1 wt.% NaCleq, which equates to fluid densities from 0.63 to 0.96 g/cm3.Sulfur isotopic compositions indicate that sulfur of the sedimentary anhydrite and Co-bearing pyrite, and the quartz–sulfide stage, was derived from seawater sulfate and thermochemical sulfate reduction of dissolved anhydrite at temperatures of 200 °C and 300 °C, respectively. H and O isotopic compositions of the skarn and quartz–sulfide stage demonstrate that the ore-forming fluids were largely derived from magmatic water, with minor inputs from metamorphic or meteoric water. The Shilu iron ore deposit has an exhalative sedimentary origin, but has been overprinted by regional deformation and metamorphism. The Shilu Co–Cu deposit has a hydrothermal origin and is temporally and genetically associated with Indosinian granitoid rocks.  相似文献   

5.
The role of sulfur in two hydrothermal vent systems, the Logatchev hydrothermal field at 14°45′N/44°58′W and several different vent sites along the southern Mid-Atlantic Ridge (SMAR) between 4°48′S and 9°33′S and between 12°22′W and 13°12′W, is examined by utilizing multiple sulfur isotope and sulfur concentration data. Isotope compositions for sulfide minerals and vent H2S from different SMAR sites range from + 1.5 to + 8.9‰ in δ34S and from + 0.001 to + 0.051‰ in Δ33S. These data indicate mixing of mantle sulfur with sulfur from seawater sulfate. Combined δ34S and Δ33S systematics reveal that vent sulfide from SMAR is characterized by a sulfur contribution from seawater sulfate between 25 and 33%. This higher contribution, compared with EPR sulfide, indicates increased seawater sulfate reduction at MAR, because of a deeper seated magma chamber and longer fluid upflow path length, and points to fundamental differences with respect to subsurface structures and fluid evolution at slow and fast spreading mid-ocean ridges.Additionally, isotope data uncover non-equilibrium isotopic exchange between dissolved sulfide and sulfate in an anhydrite bearing zone below the vent systems at fluid temperatures between 335 and 400 °C. δ34S values between + 0.2 to + 8.8‰ for dissolved and precipitated sulfide from Logatchev point to the same mixing process between mantle sulfur and sulfur from seawater sulfate as at SMAR. δ34S values between ? 24.5 and + 6.5‰ and Δ33S values between + 0.001 and + 0.125‰ for sulfide-bearing sediments and mafic/ultramafic host rocks from drill cores taken in the region of Logatchev indicate a clear contribution of biogenic sulfides formed via bacterial sulfate reduction. Basalts and basaltic glass from SMAR sites with Δ33S = ? 0.008‰ reveal lower Δ33S lower values than suggested on the basis of previously published isotopic measurements of terrestrial materials.We conclude that the combined use of both δ34S and Δ33S provides a more detailed picture of the sulfur cycling in hydrothermal systems at the Mid-Atlantic Ridge and uncovers systematic differences to hydrothermal sites at different mid-ocean ridge sites. Multiple sulfur isotope measurements allow identification of incomplete isotope exchange in addition to isotope mixing as a second important factor influencing the isotopic composition of dissolved sulfide during fluid upflow. Furthermore, based on Δ33S we are able to clearly distinguish biogenic from hydrothermal sulfides in sediments even when δ34S were identical.  相似文献   

6.
A complete thermal history for the Qulong porphyry Cu–Mo deposit, Tibet is presented. Zircon U–Pb geochronology indicates that the mineralization at Qulong resulted from brecciation-veining events associated with the emplacement of a series of intermediate-felsic intrusions. Combined with previously published ages, our results reveal a whole intrusive history of the Qulong composite pluton. Causative porphyries were emplaced at ~ 16.0 Ma as revealed by 40Ar–39Ar dating of hydrothermal biotite (15.7 ± 0.2 Ma) and sericite (15.7 ± 0.2 Ma). Zircon and apatite (U–Th)/He (ZHe and AHe) dating of Qulong revealed that both followed similar, monotonic thermal trajectories from 900 °C (U–Pb ages: 17.5–15.9 Ma) to 200 °C (ZHe: 15.7–14.0 Ma), and that the causative porphyries experienced faster cooling at a maximum rate of greater than 200 °C/myr. The Qulong deposit was exhumed between 13.6 Ma and 12.4 Ma (AHe) at an estimated rate of 0.16–0.24 mm/y, which is consistent with previous estimates for other Gangdese Miocene porphyry deposits. Our AHe thermochronology results suggest that neither the Gangdese thrust system, nor the Yadong–Gulu graben affected or accelerated exhumation at the Qulong deposit.  相似文献   

7.
Computer-based reconstruction of the physicochemical conditions of formation of the Krasnov (16° N) and Ashadze (13° N) submarine systems in the Mid-Atlantic Ridge (MAR) has been performed using the equilibrium-thermodynamic approach to study samples from these sites. In the first case, a sphalerite-pyrite-barite association was considered, and in the second case, a sphalerite-pyrite association. In the modeling conducted, the composition of the sphalerite solid solution corresponding to the nonideal mixing of ZnS and FeS was used as a correlation parameter with the total composition of the Fe-Zn-Ba-S-H2O-NaCl-HCl hydrothermal system depending on temperature (200-300 °C) and a given pressure of 100 bar. The calculation results predict that at an iron content of 0.17-0.36 wt.% in sphalerite, the minimum formation temperatures of the equilibrium sphalerite-pyrite-barite association should correspond to the interval of 280-300 °C (Krasnov site). As the iron content in sphalerite increases to 4.15-13.28 wt.%, the occurrence of barite in the systems studied becomes impossible and the formation temperatures of the sphalerite-pyrite association become equal to or higher than 300 °C (Ashadze site).  相似文献   

8.
The Kozbudaklar scheelite skarn deposit in the Tavşanlı Zone, located approximately 22 km southeast of Bursa, is hosted by the Triassic calcic İnönü Marble and Eocene Topuk Pluton. At least four stages have been recognized through skarn evolution. Scheelite skarn distributed close to the Topuk Pluton occurred during the early (stage 1) and late (stage 2) prograde substages. The early prograde endo and exoskarn are composed of hedenbergite (Hd96Joh4)–plagioclase (An55–64) and hedenbergite (Hd61–94Joh4–7), accompanied by calcic garnet (Grs38–94Sps1–5Alm0) and scheelite (Pow1–6). The second stage represents a relatively oxidized mineralogy dominated by diopside (Hd16–48Joh0–9), subcalcic garnet (Grs24–92Sps0–11Alm0–31) and scheelite (Pow7–32). The stage 3 and 4 mineral assemblages are characterized by few hydrous minerals in the retrograde stage and intense fracturing.Fluid inclusions from skarn rocks are indicative of multiple fluid events: (1) low-moderate salinity (5–16 wt.%NaCl equiv.) inclusions homogenized dominantly by a high-temperature (308 °C to > 600 °C) liquid phase in stage 1. Fluid inclusions in an early garnet homogenized over a similar temperature range (440 °C and 459 °C) into both liquid and vapor phases. Eutectic temperatures ranging from − 61.7 °C to − 35.0 °C that indicate the presence of H2O–NaCl–(± MgCl2 ± CaCl2)–CO2 solutions; (2) coexisting daughter mineral-bearing high salinity (29.5 ≥ 70 wt.%NaCl equiv.) and vapor-rich moderate salinity (11.5–16.7 wt.%NaCl equiv.) inclusions that homogenized in the liquid phase by the disappearance of the vapor phase at a similar temperature range (308 °C to > 600 °C) in stage 2. Eutectic temperatures range from − 67.9°C to − 51.8°C that shows the presence of H2O–NaCl–CO2–(± CH4/N2) solutions; (3) low-moderate salinity (12.5–7.6 wt.%NaCl equiv.) and temperature (320 °C to 215 °C) inclusions homogenized by the liquid phase in stage 3. Eutectic temperatures range from − 59.5 °C to − 44.2 °C indicating the presence of H2O–NaCl–(± MgCl2 ± CaCl2)–CO2 solutions; (4) inclusions of low salinity (9.9–0.9 wt.%NaCl equiv.) and homogenization temperature (183 °C to 101 °C) in stage 4.These data show that the Kozbudaklar skarn deposit was formed in a magmatic–hydrothermal system. In this model, carbonaceous fluids may have been exsolved from the plutonic rock during its emplacement and crystallization. Fluid inclusion data indicate that fluid boiling and immiscibility occurred at temperatures between 440 °C and 459 °C and pressures ranging from 50 MPa to 60 MPa based on hydrostatic considerations. Early scheelite was precipitated with relatively reduced mineral compositions. As a result of depressurization, Mo-rich scheelite with oxidized minerals formed via high salinity and vapor-rich inclusions. The second scheelite mineralization occurred in a normal hydrothermal system by an infiltration mechanism at pressures between approximately 40 and 1.5 MPa. At shallow depths (< 1.5 MPa) with increasing permeability, sulfide and oxide minerals were deposited in the retrograde stage, greatly assisted by meteoric water. Finally, as a result of the diminishing of ore-forming fluids, post-depositional barren quartz and calcite veins were formed.  相似文献   

9.
The solubility of synthetic ZnS(cr) was measured at 25–250 °C and P = 150 bars as a function of pH in aqueous sulfide solutions (~ 0.015–0.15 m of total reduced sulfur). The solubility determinations were performed using a Ti flow-through hydrothermal reactor. The solubility of ZnS(cr) was found to increase slowly with temperature over the whole pH range from 2 to ~ 10. The values of the Zn–S–HS complex stability constant, β, were determined for Zn(HS)20(aq), Zn(HS)3?, Zn(HS)42?, and ZnS(HS)?. Based on the experimental values the Ryzhenko–Bryzgalin electrostatic model parameters for these stability constants were calculated, and the ZnS(cr) solubility and the speciation of Zn in sulfide-containing hydrothermal solutions were evaluated. The most pronounced solubility increase, about 3 log units at m(Stotal) = 0.1 for the temperatures from 25 to 250 °C, was found in acidic solutions (pH ~ 3 to 4) in the Zn(HS)20(aq) predominance field. In weakly alkaline solutions, where Zn(HS)3? and Zn(HS)42? are the dominant Zn–S–HS complexes, the ZnS(cr) solubility increases by 1 log unit at the same conditions. It was found that ZnS(HS)? and especially Zn(HS)42? become less important in high temperature solutions. At 25 °C and m(Stotal) = 0.1, these species dominate Zn speciation at pH > 7. At 100 °C and m(Stotal) = 0.1, the maximum fraction of Zn(HS)42? is only 20% of the total Zn concentration (i.e. at pHt ~ 7.5), whereas at 350 °C and 3 <pHt <10, the fraction of Zn(HS)42? and ZnS(HS)? is less than 0.05% and 2.5% respectively, of the total Zn concentration and Zn(HS)20 and Zn(HS)3? predominate. The measured equilibrium formation constants were combined with the literature data on the stability of Zn–Cl complexes in order to evaluate the concentration and speciation of Zn in chloride solutions. It was found that at acidic pH, and in more saline fluids having total chloride > 0.05 m, Zn–Cl complexes are responsible for hydrothermal Zn transport with no significant contribution of Zn–S–HS complexes. The hydrosulfide/sulfide complexes will play a more important role in lower salinity (< 0.05 m chloride) hydrothermal solutions which are characteristic of many epithermal ore depositing environments. The value of ΔfG° (β-ZnS(cr)) = ? 198.6 ± 0.2 kJ/mol at 25 °C was determined via solubility measurements of natural low-iron Santander (Spain) sphalerite.  相似文献   

10.
The Glojeh district contains silver- and base metal-rich epithermal veins and is one of the most highly mineralized locations in the Tarom-Hashtjin metallogenic province, northwestern Iran. It consists of four major epithermal veins, which are located in the South Glojeh and North Glojeh areas. Alteration in the Glojeh district consists of propylitic, sericitic, and argillic assemblages, as well as extensive silicification. The ore-bearing veins comprise three paragenetic stages: (1) early Cu-Au-As-Sb-Fe-bearing minerals, (2) middle stage Pb-Zn-Cu-Cd-Ag-bearing minerals, and (3) late hematite-Ag-Bi-Au-Pb mineralogy. The veins are best classified as the product of an early high-sulfidation hydrothermal system, which was overprinted by an intermediate sulfidation system that was rich in Ag and base metals. Hematite is locally altered to goethite in zones of as much as 40 m in width during supergene alteration and the goethite is an important exploration tool. Fluid inclusions from the early, middle, and late stages, respectively, have salinities and homogenizations temperatures ranging from 5 to 11 wt.% NaCl eq. and 220 °C to 340 °C, to 1 to 8 wt.% NaCl eq. and 200 °C to 290 °C and finally to. 0.1 to 2 wt.% NaCl eq. and 150 °C to 200 °C. The oxygen isotope values in quartz range from 8.8 to 13.3‰ and most calculated fluid δ18O values are between 4 and 8‰, suggesting a magmatic fluid with some meteoric water contamination. Sulfur isotope values for chalcopyrite, pyrite, sphalerite, and galena are mainly − 7.3 to + 1.3‰ and − 0.3 to + 8.4‰ for North Glojeh and South Glojeh, respectively. Sulfur isotope data suggest a magmatic origin. Boiling, isothermal mixing, and dilution are the main mechanisms for ore deposition in the Glojeh veins. Recent 40Ar/39Ar age measurements of 42.20 ± 0.34 Ma and 42.56 ± 1.47 Ma for the North Glojeh and South Glojeh veins, respectively, overlap with the 41.87 ± 1.58 Ma age of the Goljin intrusion in the northern part of the district, which we interpret as the main heat source controlling the hydrothermal systems.  相似文献   

11.
The Turmalina gold deposit comprises three epigenetic domains whose development is related to the propagation/reactivation events of the NW–SE Pitangui Shear Zone (PSZ). The lodes are hosted in a Late Archaean sedimentary sequence on top of a strongly deformed (mafic-dominated) metavolcanic pile metamorphosed under 3.5–4 kbar and 540–610 °C; the association forms the upper part of a lithostratigraphic succession (Pitangui Group) that overlies an older TTG gneissic basement. According to field evidence and petrographic observations, the ore-forming process is polyphasic, starting at the time when the PSZ crossed the metamorphic quartz + staurolite + biotite + almadine + hornblende isograde; the main evolving stages, however, mostly took place throughout the metamorphic retrogression path. Fluid inclusion microthermometry also shows that metamorphogenic aqueous–carbonic solutions (initially with ≈ 16–20 eq. wt.% NaCl and circulating at approximately 4 kbar and 550 °C) were subjected to repeated boiling and mixing with cooler aqueous solutions at approximately 1–2 kb and 300–350 °C. These boiling events, which were triggered by depressurization, were contemporaneous with gold (and later sulfide) deposition, preceding a late stage of hydrothermal activity under lower PT conditions (< 1 kbar and ≈ 130–230 °C). To constrain both the mineralization age and the source/pathways of the ore-forming fluids in the Turmalina deposit, a multi-system isotope (Pb–Pb, Rb–Sr and Sm–Nd) study was carried out using various whole-rock and mineral samples. The main results are as follows: (i) the onset of the ore-forming process took place at ca. 2.2–2.1 Ga; (ii) the critical timing for gold formation was confined to ca. 2–1.9 Ga; and (iii) the late hydrothermal influxes occurred after 1.75 Ga. Therefore, the ore-forming process can be envisaged as a result of successive physical–chemical processes that took place during two major, long-lasting (≈ 250 Ma) periods under initial cooling rates of approximately 1 °C/Ma and, after ca. 2–1.9 Ga, approximately 2.5 °C/Ma. Moreover, the rejuvenation episodes at ca. 2–1.9 Ga and ca. 1.75 Ga probably indicate reactivation events in the PSZ, which triggered new fluid inflows into the system and revitalized the ore-forming process. That was the case for fluids that circulated deeply through both the older basement rocks and the mafic volcanic pile, allowing either metal enrichment from multistage leaching processes of various reservoirs or possible U/Th decoupling during ore remobilization. The Turmalina ore-system lifetime is consequently confined to the Rhyacian period (Paleoproterozoic), which is compatible with the age constraints presented by other studies regarding the fold-thrust belt's development (ca. 2.125 Ga) and orogenic collapse (ca. 2.095 Ga).  相似文献   

12.
The Hujiayu Cu deposit, located in the Zhongtiao Mountains district of southern North China Craton, is hosted by graphite schist and dolomitic marble with disseminated to veinlet (stage I) and thick vein (stage II) mineralization. Stage I mineralization, characterized by stratabound, disseminated pyrite and chalcopyrite within the graphite schist host rock, formed at the syn-metamorphic stage. Graphite geothermometry showed that the host rock was subjected to an upper-greenschist to lower amphibolite metamorphism at a temperature range of 486 to 596 °C, averaging of 546 ± 35 °C (1 σ, n = 19). Stage II mineralization, consisting of brecciated dolomitic thick veins cemented by quartz-sulfide assemblages, was a product of metamorphic hydrothermal activity. This thick vein was subdivided into an early hydrothermal dolomitic alteration composing of dolomitic breccia with some cobaltiferous pyrite (stage IIa) and a late siliceous-copper mineralization consisting of quartz-sulfide assemblages (stage IIb). A clausthalite–siegenite–sphalerite–chalcopyrite mineral assemblage was observed in stage IIb, constraining the sulfur fugacity and selenium fugacity within − 18.7 to − 11.7 and − 21.7 to − 14.7, respectively. It was inferred stage IIb was marked by a drop in sulfur fugacity and a substantial increase in selenium fugacity after the major chalcopyrite precipitation. Calculations based on the compositions of cobaliterous pyrite and sphalerite reveal that the mineral assemblage at stage IIa formed at an approximately temperature range of 400 to 300 °C, whereas the minerals in stage IIb occurred at temperature of 256 ± 9 °C (1 σ, n = 7). Sulfides from stage I have δ34S value ranging from 10.1 to 22.2‰ with an average value of 16.9 ± 3.4‰ (1 σ, n = 27), supporting the model that sulfides precipitated through thermochemical reduction of sulfate at sedimentary stage followed by metamorphic homogenization of δ34S isotopic signatures. Sulfides from the stage II have δ34S values in highly variable ranging from 3.4 to 19.2‰, indicating a rather complex source. Four chalcopyrite samples yielded a weighted model age of 1952 ± 39 Ma (1 σ, MSWD = 1.5), suggesting that the copper mineralization formed synchronously with regional metamorphism (1970–1850 Ma) and hence a Paleoproterozoic metamorphogenic copper mineralization is implicated. Therefore, we envisaged disseminated-veinlet mineralization formed during a metamorphic peak and the major hydrothermal copper mineralization occurred during the retrograde cooling.  相似文献   

13.
The Dongping gold deposit hosted in syenites is one of the largest hydrothermal gold deposits in China and composed of ore veins in the upper parts and altered zones in the lower parts of the ore bodies. Pervasive potassic alteration and silicification overprint the wall rocks of the ore deposit. The alteration minerals include orthoclase, microcline, perthite, quartz, sericite, epidote, calcite, hematite and pyrite, with the quartz, pyrite and hematite assemblages closely associated with gold mineralization. The phases of hydrothermal alteration include: (i) potassic alteration, (ii) potassic alteration - silicification, (iii) silicification - epidotization - hematitization, (iv) silicification - sericitization - pyritization and (v) carbonation. Mass-balance calculations in potassic altered and silicified rocks reveal the gain of K2O, Na2O, SiO2, HFSEs and transition elements (TEs) and the loss of REEs. Most major elements were affected by intense mineral reactions, and the REE patterns of the ore are consistent with those of the syenites. Gold, silver and tellurium show positive correlation and close association with silicification. Fluid inclusion homogenization temperatures in quartz veins range from 154 °C to 382 °C (peak at 275 °C–325 °C), with salinities of 4–9 wt.% NaCl equiv. At temperatures of 325 °C the fluid is estimated to have pH = 3.70–5.86, log fO2 = − 32.4 to − 28.1, with Au and Te transported as Au (HS)2− and Te22 − complexes. The ore forming fluids evolved from high pH and fO2 at moderate temperatures into moderate-low pH, low fO2 and low temperature conditions. The fineness of the precipitated native gold and the contents of the oxide minerals (e.g., magnetite and hematite) decreased, followed by precipitation of Au- and Ag-bearing tellurides. The hydrothermal system was derived from an alkaline magma and the deposit is defined as an alkaline rock-hosted hydrothermal gold deposit.  相似文献   

14.
The Siah-Kamar porphyry Mo deposit, located in the western Alborz-Azarbayjan magmatic belt, is the first and largest Mo deposit in the Iran. This deposit is mainly hosted by an I-type, shoshonitic quartz monzonite to monzonite intrusion and also extends in the surrounding lower to middle Eocene volcanic rocks. The geochemical features of the Siah-Kamar intrusion show enrichment in large-ion lithophile elements (LILE) and light rare earth elements (LREE), and significant negative anomalies of Nb, Ta and Ti analogues to the magmas derived from metasomatized sub-continental mantle. Porphyry molybdenum mineralization is associated with potassic, sericitic, argillic, and propylitic alteration zones. Mineralization occurs in disseminated form, in veins/veinlets and in hydrothermal breccias. The main ore minerals comprise molybdenite, chalcopyrite and bornite. The Microthermometric analyses at Siah-Kamar deposit showed that the halite-bearing inclusions contain high salinity (30.9–60.7 wt% NaCl eq.) with homogenization temperature ranging from 226 °C to 397 °C. The homogenization temperature of two phase liquid-rich inclusions range between 224 °C and 375 °C. The salinity of this type inclusions range from 0.6 to 7.5 wt% NaCl equivalent. The two-phase vapor-rich fluid inclusions homogenized at 270 °C to 397 °C. The salinity of this type fluid inclusions lie within the range of 0.6 to 4.24 wt% NaCl equivalent. Coexisting two phase V-rich and L-rich fluid inclusions in quartz associated with molybdenite provide evidence for boiling at 270 °C to 400 °C. The δ18Owater values of quartz in the molybdenite-bearing veins vary from +2.16 to +4.05‰, suggesting a magmatic origin for the ore-forming fluids. Re-Os isotopic dating of molybdenite indicated a mineralization age of 41.9 ± 3.6 Ma. The Re concentration in molybdenite suggests incorporation of mantle derived melt with crustal materials. The late Eocene magmatism along the western Alborz-Azarbayjan magmatic zone resulted from the Neo-Tethys subduction beneath the Iranian plateau. The Siah-Kamar monzonitic intrusion hosting the Mo deposit, could be considered as an example among the late Eocene intrusions within the western Alborz-Azarbayjan magmatic zone for any further exploration in this zone.  相似文献   

15.
The newly discovered Handagai skarn Fe–Cu deposit is located in the northern Great Xing'an Range of NE China and is hosted by the Ordovician Luohe Formation. The orebodies that form the deposit are generally concordant with the bedding within these sediments, and are spatially related to areas of skarn development. The Fe–Cu mineralization in this area records four stages of paragenesis, namely prograde skarn, retrograde skarn, quartz–sulfide, and quartz–carbonate stages. The Handagai deposit is a calcic skarn that is dominated by an andradite–diopside–epidote–actinolite assemblage. The mineralogy and geochemistry of the skarn indicate that it formed from a hydrothermal fluid that altered the carbonate units in this area to a garnet (And42–95Grs4–53) and pyroxene (Di71–78Hd22–29Jo0–2) bearing skarn. The epidote within the skarn has an epidote end-member composition, with the chlorite in the skarn dominantly Fe-rich, indicating that these minerals formed in an Fe-rich environment. The petrographic, microthermometric, and Raman spectroscopic analysis of fluid inclusions within garnet, epidote, actinolite, quartz, and calcite precipitated at different stages of formation of the Handagai deposit indicate that mineralization-related fluid inclusions are either liquid-rich two-phase H2O–NaCl (type I), gas-rich two-phase H2O–NaCl (type II), three-phase (liquid + vapor + solid) H2O–NaCl (type III), or CO2–H2O–NaCl inclusions (type IV). The early stages of mineralization are associated with all four types of inclusion, whereas the later stages of mineralization are only associated with type I and II inclusions. Inclusion homogenization temperatures vary between the four stages of mineralization (370 °C–530 °C and > 600 °C, 210 °C–290 °C, 190 °C–270 °C, and 150 °C–230 °C, from early to late, respectively), with salinities also varying between the earlier and later stages of mineralization (11–18 and > 45, 7–15, 6–9, and 3–7 wt.% NaCl equivalent (equiv.), respectively). The majority of the inclusions within the Handagai deposit have homogenization temperatures and salinities of 200 °C–350 °C and 4–14 wt.% NaCl equiv., respectively, indicating that this is a medium–high temperature and medium–low salinity type deposit. The fluid inclusions were trapped at pressures of 11 to 72 MPa, corresponding to depths of 0.4 to 2.9 km. The geology, mineralogy, geochemistry, and fluid inclusions microthermometry indicate that the Handagai deposit formed as a result of contact infiltration metasomatism, with the deposition of ore minerals resulting from a combination of factors that include boiling as a result of reduced pressure, cooling, and fluid mixing.  相似文献   

16.
Epithermal gold (Au) deposits result from the combination of a sustained flux of metal-rich fluids and an efficient precipitation mechanism. Earthquakes may trigger gold precipitation by rapid loss of fluid pressure but their efficiency and time-integrated contribution to gold endowment are poorly constrained. In order to quantify the feedbacks between earthquake-driven fracturing and gold precipitation in the shallow crust, we studied the gold-rich fluids in the active Tolhuaca geothermal system, located in the highly seismic Southern Andes of Chile. We combined temperature measurements in the deep wells with fluid inclusion data, geochemical analyses of borehole fluids and numerical simulations of coupled heat and fluid flow to reconstruct the physical and chemical evolution of the hydrothermal reservoir. The effect of seismic perturbations on fluid parameters was constrained using a thermo-mechanical piston model that simulates the suction pump mechanism occurring in dilational jogs. Furthermore, we evaluated the impact of fluid parameters on gold precipitation by calculating the solubility of gold in pressure (P)–enthalpy (H) space. The reconstructed fluid conditions at Tolhuaca indicate that single-phase convective fluids feeding the hydrothermal reservoir reach the two-phase boundary with a high gold budget (~ 1–5 ppb) at saturated liquid pressures between 20 and 100 bar (210 °C < Tsat < 310 °C). We show that if hydrothermal fluids reach this optimal threshold for gold precipitation at a temperature near 250 °C, small adiabatic pressure drops (~ 10 bar) triggered by transient fault-rupture can produce precipitation of 95% of the dissolved gold. Our results at the active Tolhuaca geothermal system indicate that subtle, externally-forced perturbations – equivalent to low magnitude earthquakes (Mw < 2) of a hydrothermal reservoir under optimal conditions – may significantly enhance gold precipitation rates in the shallow crust and lead to overall increases in metal endowment over time.  相似文献   

17.
《Quaternary Science Reviews》2007,26(5-6):759-772
Quantitative reconstruction of the climatic history of the Chinese Loess Plateau is important for understanding present and past environment and climate changes in the Northern Hemisphere. Here, we reconstructed mean annual temperature (MAT) and mean annual precipitation (MAP) trends during the last 136 ka based on the analysis of phytoliths from the Weinan loess section (34°24′N, 109°30′E) near the southern part of the Loess Plateau in northern China. The reconstructions have been carried out using a Chinese phytolith–climate calibration model based on weighted averaging partial least-squares regression. A series of cold and dry events, as indicated by the reconstructed MAT and MAP, are documented in the loess during the last glacial periods, which can be temporally correlated with the North Atlantic Heinrich events. Our MAT and MAP estimations show that the coldest and/or driest period occurred at the upper part of L2 unit (Late MIS 6), where MAT dropped to ca 4.4 °C and MAP to ca 100 mm. Two other prominent cold-dry periods occurred at lower Ll-5 (ca 77–62 ka) and L1-1 (ca 23–10.5 ka) where the MAT and MAP decreased to about 6.1–6.5 °C and 150–370 mm, respectively, ca 6.6–6.2 °C and 400–200 mm lower than today. However, the highest MAT (average 14.6 °C, max. 18.1 °C) and MAP (average 757 mm, max. 1000 mm) occurred at Sl interval (MIS 5). During the interstadial of L1-4–L1-2 (MIS 3) and during the Holocene warm-wet period, the MAT was about 1–2 °C and MAP 100–150 mm higher than today in the Weinan region. The well-dated MAT and MAP reconstructions from the Chinese Loess Plateau presented in this paper are the first quantitatively reconstructed proxy record of climatic changes at the glacial–interglacial timescale that is based on phytolith data. This study also reveals a causal link between climatic instability in the Atlantic Ocean and climate variability in the Chinese Loess Plateau.  相似文献   

18.
Xincheng is a world-class orogenic-gold deposit hosted by the Early Cretaceous Guojialing granitoid in the Jiaodong Peninsula, eastern China. A zircon U–Pb age of 126 ± 1.4 Ma, together with previous data, constrain the emplacement of the Guojialing intrusion to 132–123 Ma. The granitoid underwent subsolidus ductile deformation at >500 °C following its intrusion. The small difference in age between the youngest zircon U–Pb age of unaltered granitoid (~123 Ma) and the ca. 120 Ma 40Ar/39Ar ages of sericite, associated with breccias and gold mineralization within it indicate initial rapid cooling from magmatic temperatures to those prevalent during brittle deformation and associated gold mineralization at ~220–300 °C. Evidence of a direct association between granitic magmatism and gold mineralization, such as at least localized near-magmatic depositional temperatures and metal zoning evident in undoubted intrusion-related gold deposits, is absent. The 40Ar/39Ar age of ~120 Ma coincides with the mineralization age of many other orogenic-gold deposits along the Jiaojia Fault. Sixteen zircon fission-track (ZFT) ages across the ore and alteration zones range from 112.9 ± 3.4 to 99.1 ± 2.7 Ma. The long period of cooling to the ~100 Ma ZFT closure temperatures recorded here suggests that ambient temperatures for hydrothermal alteration systems lasted to ~100 Ma, possibly because of their focus at Xincheng within the young Guojialing granitoid as it cooled more slowly below approximately 300 °C to 220 °C. However, the restricted number of auriferous ore stages, combined with the presence of cross-cutting gold-free quartz-carbonate veins, indicate that gold itself was only deposited over a restricted time interval at ~120 Ma, consistent with studies of orogenic gold deposits elsewhere. This highlights the complex interplay between magmatism, deformation and the longevity of hydrothermal systems that cause genetic controversies. Based on apatite fission-track (AFT) ages, the Xincheng gold deposit was then uplifted and exhumed to near the surface of the crust at 15 Ma, probably due to movement on the crustal-scale Tan-Lu Fault. Recognition of such exhumation histories along gold belts has conceptual exploration significance in terms of the probability of discovery of additional exposed or sub-surface gold ore bodies as discovery is as much a function of preservation as formation of the deposits.  相似文献   

19.
Modern massive sulfide deposits are known to occur in diverse tectonic settings and it is generally expected that hydrothermal deposits of similar geological settings shall have more or less similar mineralogical and geochemical signatures. However, the Mount Jourdanne sulfide deposits along the super-slow spreading Southwest Indian Ridge deviate from this common concept. These sulfide precipitates are Zn-rich (up to 35 wt.%) and are characterized by high concentrations of Pb (≤ 3.5 wt.%), As (≤ 1.1 wt.%), Ag (≤ 0.12 wt.%), Au (≤ 11 ppm), Sb (≤ 967 ppm), and Cd (≤ 0.2 wt.%) which are unusual for a modern sediment-free mid-oceanic ridge system. Therefore, we have reinvestigated the sulfide samples collected during the INDOYO cruise in 1998, in order to explain their unusual mineralogy and geochemical composition. The sulfide samples are polymetallic and are classified as: a) chimneys, b) mounds, and c) hydrothermal breccias. The chimneys are small tube-like symmetrical bodies (30–40 cm high; ~ 10 cm diameter) and consist mainly of sphalerite and less chalcopyrite, set in a matrix of late amorphous silica. The inner wall shows a late-stage colloform sphalerite containing co-precipitates of galena and/or Pb–As sulfosalts. In contrast, the mound samples are dominated either by Fe-sulfides (pyrite) or by a mixture of pyrite and chalcopyrite with less sphalerite, pyrrhotite, amorphous silica and barite. Both, the chimney and mound samples, are characterized by layering and mineral zonation. The hydrothermal breccias are highly altered and mineralogically heterogeneous. They consist of silicified basaltic material that are impregnated with sulfides and contain cm-sized chimney fragments within a matrix of low-temperature minerals such as sphalerite and pyrite. The latter fragments mainly consist of chalcopyrite with isocubanite lamellae. In addition, these breccias contain late-stage realgar, boulangerite, galena, Pb–As sulfosalts and barite that are mostly confined to vugs or fractures. At least five mineralogical associations are distinguished that indicate different thermal episodes ranging from black smoker mineralization conditions to cessation of the hydrothermal activity. Based on the mineralogical associations and established literature in this regard, it is inferred that the mineralization at Mt. Jourdanne occurred mainly in three temperature domains. Above 300 °C, the chalcopyrite (with isocubanite)–pyrrhotite association formed whereas the sphalerite dominated assemblage with much less chalcopyrite and pyrite formed around and below 300 °C. The late-stage mineralization (below 200 °C) contains colloform sphalerite, galena, Pb–As sulfosalts, realgar and barite. The unusual mineralogy and trace element chemistry for this modern VHMS deposit could be explained assuming hydrothermal leaching of some felsic differentiates underneath the basaltic cover and subsequent zone refining processes.  相似文献   

20.
Previously studied thermosequences of wood (chestnut) and grass (rice straw) biochar were subjected to hydrogen pyrolysis (hypy) to evaluate the efficacy of the technique for determining pyrogenic carbon (CP) abundance. As expected, biochar from both wood and grass produced at higher temperature had higher CP amount. However, the trend was not linear, but more sigmoidal. CP/CT ratio values (CT = total organic carbon) for the wood thermosequence were ⩽0.03 at biochar production temperature (TCHAR) ⩽ 300 °C. They increased dramatically until 600 °C and remained relatively constant and near unity at higher biochar production temperature. Grass biochar was similar in profile, but CP/CT values rose dramatically after 400 °C. The findings are consistent with the hypothesis that hypy residues contain polycyclic aromatic hydrocarbons (PAHs) with a degree of condensation above at least 7–14 fused rings, with labile organic matter and pyrogenic PAHs below this degree of condensation removed by hypy.Both wood and grass thermosequences displayed δ13CP values that decreased with increased TCHAR, indicating that recalcitrant carbon compounds (pyrogenic aromatic PAHs with a relatively high degree of condensation) were first formed from structural components with relatively high δ13C values (e.g. cellulose). Relatively constant δ13C values at TCHAR ⩾ 500 °C suggested the dominant pyrolysis reaction was condensation of PAHs with no additional fractionation. Comparison of hypy with benzene polycarboxylic acid (BPCA), ‘ring current’ NMR and pyrolysis gas chromatography–mass spectrometry (GC–MS) results from the same suite of samples indicated a consistent overview of the structure of CP, but provided unique and complimentary information.  相似文献   

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