Total organic carbon content (TOC), trace element and platinum-group element (PGE) concentrations were determined in the black shales of the Lower Cambrian Niutitang Formation in the Nayong area, Guizhou Province, South China, in order to study the polymetallic Ni–Mo–PGE mineralization. The results demonstrate that numerous elements are enriched in the polymetallic ores compared to those of the nearby black shale, particularly Ni, Mo, Zn, TOC and total PGE, which can reach up to 7.03 wt.%, 8.49 wt.%, 11.7 wt.%, 11.5 wt.% and 943 ppb, respectively. The elemental enrichment distribution patterns are similar to those in the Zunyi and Zhangjiajie areas except that the Nayong location is exceptionally enriched in Zn. Whereas positive correlations are observed between the ore elements of the polymetallic ores, no such correlations are observed in the black shale. These positively correlated metallic elements are classified into three groups: Co–Ni–Cu–PGE, Zn–Cd–Pb and Mo–Tl–TOC. The geological and geochemical features of these elements suggest that Proterozoic and Early Palaeozoic mafic and ultramafic rocks, dolomites and/or Pb–Zn deposits of the Neoproterozoic Dengying Formation and seawater could be the principal sources for Co–Ni–Cu–PGE, Zn–Cd–Pb, and Mo–Tl–TOC, respectively. Furthermore, the chondrite-normalized patterns of PGEs with Pd/Pt, Pd/Ir and Pt/Ir indicate that PGE enrichment of the polymetallic ores is most likely related to hydrothermal processes associated with the mafic rocks. In contrast, PGE enrichment in the black shale resembles that of the marine oil shale with terrigenous and seawater contributions. Our investigations of TOC, trace elements and PGE geochemistry suggest that multiple sources along with submarine hydrothermal and biological contributions might be responsible for the formation of the polymetallic Ni–Mo–PGE mineralization in the black shales of the Lower Cambrian Niutitang Formation across southern China. 相似文献
Gejiu is geographically located near Gejiu city, SW China. It is one of the largest tin-polymetallic districts in the world and contains approximately 3 million tons (Mt) of Sn and smaller quantities of Cu, Pb, and Zn. The deposit primarily yields three different types of ore: skarn-hosted ore, basalt-hosted stratiform ore, and carbonate-hosted stratiform ore. Kafang is one of the primary ore deposits in the Gejiu district and is an unusual occurrence hosted in basaltic rocks. Genetic models of the Kafang deposit suggest that it is related either to Anisian (Lower stage of Middle Triassic) Gejiu basalts or to Cretaceous Gejiu granite. In this study, we performed zircon SIMS U–Pb dating, major and trace element analyses, and Sr–Nd–Pb isotopic analyses for the Gejiu basalts and S isotopic analyses for stratiform Cu ore. Our results and previous studies are used to interpret the petrogenesis of the Gejiu basalts and the origin of the basalt-hosted stratiform Cu deposit. The SIMS zircon U–Pb analyses of the Gejiu basalts yield an age of 244.4 Ma. The trace element ratios of the Gejiu basalts are similar to those of ocean island basalt and have positive εNd(t) values (ranging from 0.6 to 2.5) and uniform (87Sr/86Sr)i values (ranging from 0.70424 to 0.70488). These ratios are close to those of the Permian Emeishan flood basalt. Thus, the Gejiu basalts may represent coeval volcanisms within the plate involving remelting of the Emeishan plume head through a stress relaxation process after the main plume event. The Pb and S isotopic compositions of the Gejiu basalts and the stratiform Cu ores indicate that the source of Cu and S is primarily derived from the Gejiu basalts. However, the age of sulfide mineralization (84.2–79.6 Ma) and the age of hydrothermal alteration (85.5–81.9 Ma) are temporally consistent with the age of the Cretaceous granite emplacement (85.5–83.3 Ma). From a petrological and geochemical study, we determine that the Gejiu basalts may have been subjected to pervasive granite-related hydrothermal alteration during the emplacement of granite. These processes increase the K and Mg contents of basalt and probably caused the formation of the Cu ores. Thus, the Kafang stratiform Cu deposit can be considered as a granite-related hydrothermal deposit. 相似文献
The newly discovered Baogudi gold district is located in the southwestern Guizhou Province, China, where there are numerous Carlin-type gold deposits. To better understand the geological and geochemical characteristics of the Baogudi gold district, we carried out petrographic observations, elemental analyses, and fluid inclusion and isotopic composition studies. We also compared the results with those of typical Carlin-type gold deposits in southwestern Guizhou. Three mineralization stages, namely, the sedimentation diagenesis, hydrothermal (main-ore and late-ore substages), and supergene stages, were identified based on field and petrographic observations. The main-ore and late-ore stages correspond to Au and Sb mineralization, respectively, which are similar to typical Carlin-type mineralization. The mass transfer associated with alteration and mineralization shows that a significant amount of Au, As, Sb, Hg, Tl, Mo, and S were added to mineralized rocks during the main-ore stage. Remarkably, arsenic, Sb, and S were added to the mineralized rocks during the late-ore stage. Element migration indicates that the sulfidation process was responsible for ore formation. Four types of fluid inclusions were identified in ore-related quartz and fluorite. The main-ore stage fluids are characterized by an H2O–NaCl–CO2–CH4 ± N2 system, with medium to low temperatures (180–260 °C) and low salinity (0–9.08% NaCl equivalent). The late-ore stage fluids featured H2O–NaCl ± CO2 ± CH4, with low temperature (120–200 °C) and low salinity (0–7.48% NaCl equivalent). The temperature, salinity, and CO2 and CH4 concentrations of ore-forming fluids decreased from the main-ore stage to the late-ore stage. The calculated δ13C, δD, and δ18O values of the ore-forming fluids range from − 14.3 to − 7.0‰, −76 to −55.7‰, and 4.5–15.0‰, respectively. Late-ore-stage stibnite had δ34S values ranging from − 0.6 to 1.9‰. These stable isotopic compositions indicate that the ore-forming fluids originated mainly from deep magmatic hydrothermal fluids, with minor contributions from strata. Collectively, the Baogudi metallogenic district has geological and geochemical characteristics that are typical of Carlin-type gold deposits in southwest Guizhou. It is likely that the Baogudi gold district, together with other Carlin-type gold deposits in southwestern Guizhou, was formed in response to a single widespread metallogenic event.