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| 1 | Phosphorite generative processes around the Precambrian-Cambrian boundary in South China: An integrated study of Mo and phosphate O isotopic compositions显示文摘Large phosphorite deposits in Central Guizhou,China,were formed around the Precambrian/Cambrian boundary(PC/C),including the Ediacaran(Doushantuo stage)and early Cambrian(Gezhongwu stage).Among them,Gezhongwu phosphorite from Zhijin are enriched in rare earth elements(REE)plus yttrium(REY),reaching 3.503 million tons.Although phosphorites have attracted great attention,the specific sources P and REY remained unclear.To determine the P and REY sources and establish a phosphogenic model of PC/C phosphorite,we present an integrated dataset of Mo and phosphate O isotopes for the first time,along with carbonate C and O isotopes,geology,petrology,and geochemistry.In all samples,d18Op,Y/Ho,and Zr/Hf decreased from the Ediacaran to the early Cambrian,indicating increased terrigenous weathering fluxes while decreased upwelling water input.Furthermore,terrigenous weathering delivery significantly elevated marine REY concentrations in the Cambrian in Zhijin.The Ceanom and d98/95Mo suggest that seawater was oxidized in the later Ediacaran and became entirely oxic in the early Cambrian.The positive feedback between oxygen levels in atmosphere and primary productivity caused progressive oxygenation in ocean-atmosphere system and enable phosphorites to be formed by different mechanisms.Results show that the Lower Doushantuo consist of abiotic intraclasts and exhibited“seawaterlike”REY types,indicating abiological and mechanical reworking phosphogenesis.The Upper Doushantuo and Gezhongwu Formation contained mainly microbial debris and abiogenic intraclasts,and exhibit “hat-shaped”REY plots,suggesting microbially mediated phosphogenesis.Based on this data set,we developed a phosphogenic model illustrating formation of these two phosphorite deposits,wherein the Lower Doushantuo phosphorite formed through the reworking of pre-existing phosphatic sediments in anoxic and abiotic ocean,whereas the Upper Doushantuo and Gezhongwu phosphorite formed via microbial metabolisms in oxic and biotic conditions.Our study has implications on the PC/C phosphorite generative processes,as well as paleoenvironmental conditions. | Haiying Yang Jiafei Xiao Yong Xia Zhuojun Xie Qinping Tan Jianbin Xu Shan He Shengwei Wu Xiqiang Liu Xingxiang Gong | 2021 | Geoscience Frontiers2021，12，5： | 5 |
| 2 | Geological and geochemical characteristics of the Baogudi Carlintype gold district(Southwest Guizhou, China) and their geological implications显示文摘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±N2system,with medium to low temperatures(180–260℃)and low salinity(0–9.08%NaCl equivalent).The late-ore stage fluids featured H2O–NaCl±CO2±CH4,with low temperature(120–200℃)and low salinity(0–7.48%Na Cl equivalent).The temperature,salinity,and CO2and CH4concentrations of ore-forming fluids decreased from the main-ore stage to the late-ore stage.The calculated δ^13C,d D,and δ^18O 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 δ^34S 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. | Songtao Li Yong Xia Jianzhong Liu Zhuojun Xie Qinping Tan Yimeng Zhao Minghua Meng Lijin Tan Rong Nie Zepeng Wang Guanghong Zhou Haiyan Guo | 2019 | Acta Geochimica2019，38，4： | 1 |
| 3 | Metallogenesis of the Baidi Au-Sb deposit, southwest Guizhou Province, China: mineralogical and geochemical evidence from sulfur-bearing minerals显示文摘The Baidi Au-Sb deposit,which contains 8 t of Au and 10,979 Mt of Sb,is a typical and rare paragenetic deposit located in southwestern Guizhou Province,China.Previous studies have focused on individual ores,but have not combined them to identify their paragenetic mechanism or metallogenic regularity.Therefore,we usedfield investigations,microscopic observations,and in situ anal-yses to identify the spatial distribution,mineral paragene-sis,compositional evolution,and metallogenic material sources of the ore bodies.We also determined the Au and Sb paragenetic characteristics and the metallogenesis of the deposit.The main Au-bearing minerals in the deposit were early(Apy1–2)and late(Apy3)stage arsenopyrites,as well as pre-mineralization(Py1),mineralization(Py2–5),and late mineralization(Py6–7)stage pyrites.The main Sb-bearing minerals were stibnite(Snt),skinnerite,bournonite,and valentinite.The minerals formed in the order of Py1,Py2–3+Apy1,Py4–5+Apy2,Snt,and Py6–7+Apy3.The d34S values of the arsenopyrites and pyrites ranged from-5 to 5%,while those of stibnite were mostly less than-5%in the later mineralization stages.Sulfur was provided by deep magmatic hydrothermalfluids,but sedimentary sulfur was added in the later stages.Moreover,the trace elemental contentsfluctuated and eventually became similar to those of the sedimentary strata.By comprehensively considering the ores along with the geo-logical characteristics of the deposit,we determined that deep magma provided the Au during ore formation.Later tectonic changes provided Sb from the sedimentary strata,which precipitated along fault expansion areas and pro-duced Au and Sb paragenesis. | Jun Yan Yong Xia Qinping Tan Zhuojun Xie Guosong Ji | 2024 | Acta Geochimica2024，43，2： | 0 |
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