The Jitai Basin in Jiangxi Province has an important potential of brine-type lithium resource,yet the basic geological study is very limited at present.The recently discoved basalt in the Tianxinggang area in the southern part of the Jitai Basin provides important scientific information for understanding the tectonic evolution and deep geological processes of the basin.In this study,we have carried out the petrographic,major and trace element geochemical,and LA-ICP-MS zircon U-Pb chronological studies of the basalt in the Tianxinggang area in order to explore its origin and geological significance.The basalt in the Tianxinggang area is trachybasalt.It is mainly composed of plagioclase and clinopyroxene with small amount of olivine and amphibole.It belongs to the shoshonite series with high alkaline and potassic properties.Its samples are characterized with relatively low SiO2 contents(47.72％-48.38％),high MgO contents(6.27％-7.20％),high total alkali contents(5.24％-5.68％),and Mg#values ranging from 34.71 to 37.70.The basalts are relatively enriched in elements of Rb,Ba,Sr,and U,and relatively depleted in elements of Pb,Sm,Y,with a clear fractionation of light and heavy rare earth elements and with no obvious Eu and Ce anomalies.It is suggested that the basalt in the Tianxinggang area was formed by magma derived from the partial melting of garnet spinel lherzolite through the minimal crustal contamination and insignificant magmatic crystallization differentiation processes.As an intraplate basalt,its magma could have provided the energy and material substrates for the formation of lithium-rich brine in the basin.The area nearby has potential for exploring lithium-rich brine resources.The zircon U-Pb age of(73.6±1.3)Ma of the basalt indicates that the Jitai Basin was in an extensional and subsiding tectonic environment at that time of basaltic magam eruption and was limitedly affected by the subduction of the western Pacific plate.
The Jiepailing superlarge Sn-polymetallic deposit,located in the central Nanling metallogenic belt,is characterized by complex coproduction of tin,beryllium,fluorite,and lead-zinc polymetallic ores.It serves as an ideal case for investigating rare metal enrichment mechanisms in southern Hunan.This study focuses on pyrite,a widespread mineral across various orebodies within the deposit.Systematic mineralogical and in situ LA-ICP-MS trace element analyses were conducted to decipher the genetic relationships among different mineralization types.Five distinct generations of pyrite were identified,sequentially formed during:1)the greisen-quartz vein Sn-Cu mineralization stage(PyⅠ);2)the topaz-fluorite mineralization stage(PyⅡ);3)the quartz vein Pb-Zn(-Sn)mineralization stage(PyⅢ);4)the mica-fluorite Be mineralization stage(PyⅣ);and 5)the late carbonate alteration stage(PyⅤ).Microscopic observations reveal variations in morphology and texture among these generations.PyⅠ typically occurs as fine-grained euhedral crystals,some containing mineral inclusions.PyⅡ is predominantly fine-grained euhedral to subhedral,coexisting with brecciated fluorite and enclosing abundant sulfides.PyⅢ mainly appears as fine veinlets,often intergrown with mica and fluorite.PyⅣ is characterized by coarse-grained euhedral to subhedral crystals,while PyⅤ consists of fine-grained euhedral to subhedral crystals rich in metallic sulfide inclusions.LA-ICP-MS results demonstrate a clear evolutionary trend in the trace element composition of pyrite.PyⅠ is enriched in Sn and Cu and exhibits high Co/Ni ratios(＞1),suggesting formation from a high-temperature,predominantly magmatic-hydrothermal fluid.In contrast,subsequent generations(PyⅡ-PyⅤ)are enriched in Pb,Zn,As,Sb,and Ag,with consistently low Co/Ni ratios(＜1).This shift indicates formation under medium-to low-temperature conditions with a significant contribution of non-magmatic components to the fluid.Integrating these characteristics with the geological setting of the Jiepailing deposit,we propose that its diverse mineralization was likely controlled by a unified Late Cretaceous magmatic-hydrothermal system.Ore-forming fluids derived from this system initially generated Sn-Cu and topaz-fluorite mineralization in the exocontact zone during the early stage.Subsequently,Be-F-rich fluids migrated upward along fault systems.In shallow crustal levels,interaction with country rocks and incorporation of materials from the strata led to the sequential formation of Pb-Zn-Sn polymetallic mineralization and mica-fluorite type Be mineralization.
The late Yanshanian Laojunshan granite complex in the Dulong mine in the southeastern Yunnan is closely related to the W and Sn mineralization.The in-depth comparative study of the compositional characteristics of minerals in different types of granites is of great significance for understanding the ore-forming process and evaluating the ore-forming potential of different types of granites.In this paper,we have carried out mineral chemical study of biotites in the late Yanshanian granite and granite-porphyry in the Dulong mine by using the EPMA and LA-ICP-MS analytical methods.The results show that the Fe/(Fe+Mg)ratios of biotites are relatively high with ratios mainly concentrated in a range from 0.60 to 0.70.Combined with data of previous studies,it is believed that biotites of the Laojunshan granite and granite-porphyry belong to siderophyllite and ferrous biotite.By using the Ti saturation thermometer and Al manometer of biotite,we have estimated the crystallization temperatures of biotites in granite and granite-porphyry in the Dulong mine.The calculated temperatures vary from 569℃ to 676℃ for biotites in granite and from 544℃ to 642℃ for biotites in granite-porphyry,and the calculated pressures vary from 419Mpa to 460Mpa for biotites in granite and 440Mpa to 494Mpa for biotites in granite-porphyry,respectively.In the diagram of Fe3+-Fe2+-Mg2+,data of the biotite samples are mainly plotted in fields between the Ni-NiO and Fe2SiO4-SiO2-Fe3O4 buffer lines,indicating that biotite crystals in granite and granite-porphyry of the Dulong mine were mainly formed under the relatively low oxygen fugacity condition.Biotite is the main carrier mineral of Sn,In and other ore-forming elements in granite and granite-porphyry of the Dulong mine,and the contents of Sn,In and other ore-forming elements in biotites can be used as indicators to evaluate their ore-forming potentials of granite.
The Laodongzhai-Wuzuo Pb-Zn deposit is located in the southern section of the Xiangxi-Qiandong metallogenic belt.The Wushou Ⅱ orebody is one of its main orebodies.The genesis of this deposit has not been clearly understood yet by previous researchers.This article systematically studied the mineral association of the Wushou Ⅱ orebody and geochemical behaviors of trace elements within the sphalerite,in order to explore the genesis of the deposit.The sphalerites in the Wushou Ⅱ orebody occurred in two hydrothermal stages.The early-stage sphalerite(Sp1)is mainly light yellow and grayish yellow sphalerite,which occurred commonly in brecciated ores.The late-stage sphalerite(Sp2)is brownish grey and light brownish yellow sphalerite with completed cleavages.The LA-ICP-MS analytical results of trace elements in sphalerites from the Wushou Ⅱ orebody show that sphalerites of two stages are mainly enriched in Cu,Cd,Ge,and Ga,but relatively depleted in Mn,and In.Based on the binary relationships of main components in sphalerites,it is inferred that there is difference between the substitution mechanism of Cd in Sp1 and that of Cd in Sp2.The substitution mechanism of Cd in Sp1 may be Cd2++Fe2+↔Zn2+and/or Cd2+↔Zn2+,while that of Cd in Sp2 may be Cd2++Fe2+↔2Zn2+.Ge in sphalerite could have different substitution mechanisms due to its different valence states.Ge occurred mainly as Ge4+in Sp1 for substituting Zn2+,with the substitution mechanism of Ge4++2Cu+↔3Zn2+.A small amount of Ge occurred as Ge2+in Sp1 for substituting Zn2+with the substitution mechanism of Ge2++2Cu+↔2Zn2+.However,Ge occurred as Ge4+in Sp2 for substituting Zn2+,with the substitution mechanisms of 2Fe2++Ge4++□↔4Zn2+and/or 4(Cu++Sb3+)+(Ge4++2Ag+)+2□↔13Zn2+.Ga occurred as Ga3+in both Sp1 and Sp2 for substituting Zn2+,with the substitution mechanism of Cu++Ga3+↔2Zn2+.The formation temperatures of sphalerites in the Wushou Ⅱ orebody are relatively low.The formation temperatures of Sp1 crystals(129-252℃,average 177 ℃)are slightly higher than that of Sp2 crystals(120-228 ℃,average 149℃).By comparing previous research results,it is believed that the genetic type of the Wushou Ⅱ orebody in the Laodongzhai-Wuzuo Pb-Zn deposit belongs to the MVT type of Pb-Zn deposit.
