Search

Quartz cathodoluminescence (CL) images are commonly combined with trace element concentrations to decipher complex histories of hydrothermal systems. However, the correlations between aluminum content and CL zoning of low-temperature hydrothermal quartz and their genesis remain controversial. In this contribution, a multiparametric study was carried out on CL-aluminum zoning of low-temperature hydrothermal quartz (<350 °C) from the Shihu and Rushan quartz-vein type Au deposits in the North China Craton. The results show that aluminum concentration correlates negatively with CL intensity in quartz from the Shihu Au deposit. CL-dark quartz zoning has significant Al concentrations as well as detectable Al-H bonds. However, in the Rushan Au deposit, the correlation is positive, and aluminum is enriched in the CL-bright quartz zoning. The Al content is positively correlated with K content with r2 = 0.769. Combined with the electron backscatter diffraction (EBSD), X-ray single crystal diffraction (XRD), and transmission electron microscope (TEM) data, we infer that the genesis of CL zoning in the low-temperature hydrothermal quartz is closely related to Al3+-H+ and Al3+-K+ concentrations. The Al3+-K+ may act as the CL-activator, while the Al3+-H+ may act as the CL-dampener. Where Al3+-Si4+ substitution is charge balanced by hydrogen, the intensity of CL response decreases; where Al3+-Si4+ substitution is charge balanced by potassium, the intensity of CL response increases. The correlations between CL intensity and aluminum concentration in the low-temperature hydrothermal quartz reflect pH fluctuations of hydrothermal system. [ABSTRACT FROM AUTHOR]

An intensive study of the geochemical characteristics (including the volatile elements Cl and S) of apatite associated with porphyry deposits was undertaken to address the debate about the crust- or mantle-derivation of their copper and gold and to better understand the controls on the transport of metals in magmatic fluids in post-subduction settings. New geochemical data on apatite reveal parameters to discriminate mineralized porphyry systems across Iran and western China (Tibet and Yunnan), from coeval barren localities across this post-subduction metallogenic belt. Apatites in fertile porphyries have higher Cl and S concentrations (reflecting water-rich crystallization conditions) than those from coeval barren ones. Our new isotopic data also indicate these volatiles are likely derived from pre-enriched sub-continental lithospheric mantle, metasomatized by previous oceanic subduction. This study demonstrates that refertilization of suprasubduction lithospheric mantle during previous collision events is a prerequisite for forming post-subduction fertile porphyries, providing an evidence-based alternative to current ore-enrichment models. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Damoqujia gold deposit in the Jiaodong Peninsula in eastern China contains more than 60 t of gold and is hosted mainly by Mesozoic granitoids. The orebodies comprise pyrite–sericite–silica altered rocks and exhibit Jiaojia‐type mineralization. Although the Damoqujia deposit is an important gold producer in the Zhaoping Fault Zone, the age and tectonic setting of metallogenesis are poorly constrained. Here, we employ precise U–Pb dating of zircon and 40Ar/39Ar dating of hydrothermal sericite from the Damoqujia gold deposit to constrain the age of mineralization, which we integrate with previous studies to understand the tectonic setting of the deposit. The major intrusions exposed in the deposit are the Jurassic monzogranite to the west and the Cretaceous granodiorite to the east. Uranium–Pb dating of zircon from the monzogranite, granodiorite, pre‐ore hydrothermally altered lamprophyre dyke, and post‐ore unaltered gabbro–diorite dyke yield concordia ages of 160 ± 1, 130 ± 1, 125 ± 1, and 120 ± 1 Ma, respectively. Based on these geochronological data, we suggest that the age of gold mineralization at Damuqujia occurred at 124–121 Ma. Sericite from the auriferous quartz–pyrite veinlet in the Damoqujia deposit yields a plateau age of 122.8 ± 0.9 Ma, representing the precise age of gold mineralization. Our geochronological data indicate that gold mineralization occurred at 123 Ma and are consistent with the timing of the main gold mineralization event in the Jiaobei Terrane at 125–120 Ma. The geodynamic setting of the study area during this time is generally considered to have been dominated by subduction of the Palaeo‐Pacific Plate beneath the Eurasian continent, with accompanying lithospheric delamination, asthenospheric upwelling, and intense craton destruction. The gold mineralization at Damoqujia was closely associated with continental extension during the Mesozoic. [ABSTRACT FROM AUTHOR]

In-situ analysis of minerals, such as zircon hafnium (Hf) and oxygen (O) isotopes, has been pivotal in investigating magmatic evolution and related ore systems. In order to better constrain the petrogenesis of Cu-porphyries and related ore-forming processes in southern Tibet, we used a combined application of both zircon by Hf-O isotopes and apatite by developing geochemical indicators involving Sr-O isotopes and volatile (chlorine and sulfur) concentrations. Apatite has several advantages over zircon: it carries ore-related volatiles, is present in less-evolved magmas and is sensitive to magmatic processes. Data on major- and trace elements and Sr-O isotopes in gem-like apatite can supplement information from zircon Hf-O isotopes. We have applied these techniques to granitoids from the Jurassic arc in southern Tibet to illustrate their use in tracing volatile evolution and related genesis of porphyry systems. We demonstrate that (1) robust apatite Sr-O isotopes combined with zircon Hf-O isotopes can record recycled oceanic components in the sources of Gangdese Jurassic porphyries; (2) volatile-enriched magmas metasomatised hydrous mantle wedge to form the Jurassic mineralised rocks; (3) the ore-forming magma with higher contents of water, Cl and S, favoured the transfer of metals and volatiles to the upper crust and to form the Jurassic porphyry Cu-Au deposits. [ABSTRACT FROM AUTHOR]

• Fluids in the three skarn stages are characterized by complex volatile system, respectively. • Isotopic data showed a primary magmatic source, mingled with meteoric water at the late stages. • Boiling, temperature falling and f O 2 rising are the key to metal deposition at the retrograde stage. • f O 2 and temperature decreasing play role in metal precipitation at the late hydrothermal stage. Scheelite mineralization accompanied by traces of chalcopyrite occurs in skarn systems in the giant Zhuxi deposit in the Taqian area, Northeastern Jiangxi province, South China. Three paragenetic stages of skarn with ore deposition have been recognized: the prograde skarn, retrograde skarn and hydrothermal quartz-sulfide stages. Microthermometer data showed that the prograde skarn were formed at relatively high temperatures (450–>500 °C) and pressures (0.97–1.38 kbars) and low oxidation to weak reduction conditions. The Raman microprobe data demonstrated that the fluid of the stage was H 2 O–NaCl/KCl/CaCl 2 ± CH 4 /C 2 H 4 system. The retrograde skarn alteration formed at 1.24 kbars and relatively medium temperatures (280–320 °C), and the ore-forming fluid was H 2 O–NaCl/KCl/CaCl 2 system. During the hydrothermal quartz-sulfide stage, the fluids were methane-bearing aqueous, low-salinity (0.9–8.0 wt% NaCl eqv) and low homogeneous temperature (160–240 °C). Correspondingly, the minimum fluid pressures were evaluated between 75 and 252 bars. The H- and O-isotopic values from the prograde and retrograde stages implied that the mineralizing fluids were derived principally from magmatic water. The mineralizing fluids in the quartz-sulfide hydrothermal stages were mingled with magmatic water with some meteoric water as well as minor contributions of wall rocks. The sulfur and lead isotopes indicated that ore-forming materials including sulfur, lead, copper, zinc and iron in the Zhuxi deposit were derived from local magmatic and sedimentary sources. Geological, fluid inclusion and isotopic data supported that the Zhuxi deposit is a typical skarn-type W(Cu) deposit related to ilmenite-series granitic rocks and formed in a compressional tectonic environment. [ABSTRACT FROM AUTHOR]