| 广西大黎铜钼矿石英二长(斑)岩年代学、地球化学特征及其地质意义 |
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| 关键词:quartz monzonite (porphyry) Dali copper-molybdenum deposit Dayaoshan LA-ICP-MS U-Pb dating |
| 基金项目:广西壮族自治区地质矿产勘查开发局局管科研项目“广西大瑶山地区铜钼多金属矿成矿预测研究”(编号: 201002);武汉地质调查中心地质调查项目(编号: 2010011408) |
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| Chronology and Geochemical Characteristics of Quartz Monzonite (Porphyry) in the Dali Copper-Molybdenum Deposit and Its Geological Significance |
| Dali quartz monzonite (porphyry) body lies at southern Dali Town of Tengxian County in Guangxi. LA-ICP-MS U-Pb isotopic dating of zircons separated from the quartz monzonite and the quartz monzonite porphyry yields average 206Pb/238U ages of (102.8±0.9) Ma and (101.7±1.2) Ma, respectively. The results of geochemical study indicate that SiO2 values are in the range of 60.09%-62.91%, Na2O and CaO are in the range of 2.90%-3.08% and 3.32%-4.35%, A/CNK=0.83-0.93, being all lower than 1.0. 100Fe3+/(Fe3++ Fe2+) ratios are in the range of 37.76-42.93, and the Rittmann index of quartz monzonite (porphyry) varies from 2.94 to 3.07,suggesting a calc-alkaline and metaluminous nature. Geochemical characteristics of rare earth elements are ΣREE=(254.74?301.06)×10?6, ΣLREE=(234.35?279.38)×10?6, ΣHREE=(20.39?21.68)×10?6, LREE/HREE=11.49?12.89, (La/Yb)N=11.51?16.28, δEu=0.61-0.90, and δCe=0.99?1.08. The rock has moderate REE concentration, showing a pattern of relative enrichment of LREE. The chondrite-normalized REE patterns demonstrate right-oblique linear REE patterns with weak negative Eu anomaly and significant fractionation between LREE and HREE. On the whole, trace elements show relative enrichment of large ion lithophile elements Rb, Th, U, K, La, Ce, Pb and depletion of high field strength elements Nb, Ta, Sr, P, Ti. It is also shown that the I-type quartz monzonite(porphyry)was derived form the crust-mantle mixed source. Combined with regional tectonic evolution, the authors hold that Dali quartz monzonite (porphyry) was the product of a tensile tectonic environment at the late Yanshanian post-collisional stage of the late Early Cretaceous period. The rock was formed due to back-arc extension related to high angle subduction of the paleo-Pacific plate caused by northward movement of the Indian plate. Through discussing the regional tectonic evolution and exploring the basic properties, causes and tectonic environment of the rocks, the authors analyzed the favorable conditions of mineralization and inferred the porphyry copper-molybdenum mineralization age. The main favorable ore-forming conditions lie in the following three aspects: ①I-type quartz monzonite (porphyry) is a good parent rock for mineralization; ②The ore district has relatively high background values of Cu, Mo, Pb, Sn ore-forming elements; ③Deep fault and #-shaped fault system of the study area constitute a favorable ore-controlling tectonic background. A comprehensive analysis shows that the ore-forming age of the Dali copper-molybdenum deposit should be late Early Cretaceous, consistent with the diagenetic age of about 100 Ma. |
| HU Sheng-qi,ZHOU Guo-fa,PENG Song-bai,ZHANG Xian-jin,YI Shun-hua,TANG Guo-sheng.2012.Chronology and Geochemical Characteristics of Quartz Monzonite (Porphyry) in the Dali Copper-Molybdenum Deposit and Its Geological Significance[J].Acta Geoscientica Sinica,33(1):23-37. |
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