This paper aims to reveal the magma evolution and petrogenesis of Jiudingshan granite complex by geochronology, geochemistry and Sr-Nd-Hf isotopes, which is different with the previously reported result (Guo et al, 2009, and references therein ).
Geological backgroundThe Jiudingshan Cu-Mo deposit hosted by the granite complex was located between the NW JingshajiangAilaoshan fault and NNE Chenghai -Binchuan fault in the middle of the Sanjiang metallogenic belt, western Yunnan, and formed by the continental collision during the Himalaya epoch. Five magma series can be recognized in the field: porphyritic granite, orthophyre, granite porphyry, alkali feldspar granite and lamprophyre.
Results
The whole rock geochemical compositionsThese samples contain 61.37 -74.98 wt% SiO2, 1.15 -5.2 wt% Na2O, and 3.35 -8.92 wt% K2O, and fall in high -K calcalkaline or shoshonitic field defined by the SiO2 vs K2O diagram. They have MgO and Mg # (molar 100× MgO / (MgO + FeOT)) of 0.66 -1.63 wt% and 25 -45, respectively. The calculated A/CNK values (molar Al 2 O 3 / (CaO + Na 2 O + K 2 O)) are 0.84-1.04, indicating a metaluminous composition. They exhibit subparallel chondrite-normalized REE patterns, characterized by strong fractionation between light rare earth elements (LREE) and heavy rare earth elements (HREE) without obvious Eu anomaly. Samples are rich in large-ionlithophile elements (LILE) but depleted in high-fieldstrength elements (HFSE) and displaying strong Nb-Ta-Ti negative anomalies.
Zircon U-Pb geochronology and Hf isotopeZircon U and Th contents range from 354 to 1,657 ppm and 148 to 915 ppm, respectively, corresponding to Th/U values of 0.20 -0.54, which supports a magmatic origin of these zircon. Ten LA-ICP-MS single spot analyses on 10 zircon grains of each porphyritic granite, orthophyre and granite porphyry yield similar concordant U-Pb ages and weighted mean 206 Pb/ 238 U ages of 34.9±2.0 Ma, 34.6±0.7 Ma and 34.7±0.6Ma, respectively. Thus, ~35 Ma can be considered as the crystallization age of the Jiudingshan granite complex.Ten in situ Hf isotopic analyses were made on 10 zircon grains of each rock that had been previously studied for LA-ICP-MS geochronology. Both ɛHf (t) values and the Hf model ages are calculated using the zircon crystallization age. The results show that these zircons
This paper described the wallrock alteration and mineralization of Pb-Zn deposits in the Sichuan-Yunnan-Guizhou border area Southwest China, and summarized the wallrock alterations what are obvious, which include dolomitization, calcitization, pyritization, carbonation, ferritization, silicification and decolourization. In addition to dolomitization and calcitization,other wallrock alteration are associated with the formation and enrichment of Pb-Zn ore. Meanwhile, based on statistic analysis in mineralization age, and combined with the characteristics of Pb isotope, we confirmed four stages of mineralization in study area.
The southeastern of Yunnan metallogenic belt is an area with many large- super large deposits in the Metallogenic Province of South in China. The mineral deposits in the area are densely distributed and the geological structure is complex. This article studies the joints (cracks) of the super large bed in the Bainiu factory in this area, a total of 21 joint observation points, 685 groups of occurrence structural surfaces were observed, and uses Dips software to analyze the joints (fissures) in the mining area. It is concluded that there are three periods of tectonic stress in the mining area, which are closely related to the mineralization, there are North North West-South South East, North East-South West, and South-North.
The Pb-Zn deposits (or points) with different ages of ore-bearing strata are counted in in the paper. Through discussing the lithology and elemental geochemistry in ore-bearing strata to explain the lead element and zinc element relate to strata and lithology, the author suggested the lead-zinc deposit mainly were exposed in specific stratum, considering the deposits was obviously was controlled by stratum and was greatly influenced by lithology. For this reason, combining with the comparative study of element abundances in rock, it has maily demonstrated the relevance of ore-forming elements.
Alkali-rich intrusions associated with Cu-Mo mineralization in Baoxingchang district, displaying both felsic and mafic rock series, can be: divided into four evolution stages. LA-ICP-MS zircon U-Pb ages of the four stages intrusions 36.5∼34.6Ma, 38.0∼33.5Ma, 36.0∼34.5Ma and 34.0Ma, respectively. All the studied rocks have similar magma sources and tectonic setting. The εHf(t) values indicate that they were reworked by ancient lithospheric mantle and crustal materials via subduction. Formation of the alkaline-rich intrusions in Baoxingchang area may be involved in the processes of partial melting of mantle rocks, crust-mantle materials and fractional crystallization. It appears an increasing tendency from felsic intrusions, to enclaves and then to early-stage lamprophyre to late-stage lamprophyre.
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