Research On Genetic Mineralogy Of Jilongshan Pluton In Yangxin County Of Hubei Province And Its Relationship With Mineralization

The Jilongshan skarn Cu-Au deposit is located at eastsouthern part of Daye-Jiujiang copper-gold metallogenic subzone which is in the Middle-Lower Yangtze River valley metallogenic belt. The Cu-Au ore bodies occur in the contact zones of the Lower Triassic Daye Formation limestone and granodiorite porphyry. In order to study the sources, causes of rock, and the relationship with the ore body, this paper research petrology, mineralogy, geochemistry, chronology of Jilongshan pluton by the sample observation, whole rock analysis, zircon U-Pb dating, and electron probe means based on field work.The main part of the Jilongshan pluton is granodiorite porphyry and the marginal domain is quartz diorite porphyry. Dikes which intruded in diagenetic late stage mainly comprise diorite porphyry, quartz diorite porphyry, and lamprophyre. The samples from Jilongshan in this study display a high-K calc-alkaline signature typical granite with SiO2, K2O concentration ranging from 62.91 to 67.8% and 1.67 to 5.65%. Their A/CNK (A/CNK=n(Al2O3)/[n(CaO)+n(Na2O)+n(K2O)]) vary from 0.61 to 1.71, and most of them fall in the range of 0.8 to o.9, they belong metaluminous rock.The trace elements, rare earth elements(REE) distribution patterns of the intrusives, skarn orebody and wall-rocks are Rightist trend type. The rocks show enrichment in light rare earth elements and their fractionation is higher than high rare earth elements ((La/Yb)N=7.61-12.94), weak negative Eu anomalies and weak negative Ce anomalies. The distribution curves of intrusives and the Yangtze Block granodiorites are similar, the curves of marble in Jilongshan is lower than marble in eastern China, and the curves of ore is between intrusives and marble. All distribution curves suggest the trace elements and REE of ores not only derived from intrusives but also from wall-rocks.The rock-forming mineral of Jilongshan pluton are quartz, plagioclase, biotite, and amphibole. Plagioclase which have zonal texture, strong positive Eu anomalies, and weak negative Ce anomalies, is andesine and oligoclase. Biotites show rich in Ti, Mg, Al, K, poor in Ca, MF(Mg/Fe) from 0.47 to 0.64, strong positive Eu anomalies, and weak negative Ce anomalies. Amphibole is ferropargasite-amphibole. Laser ablation inductively coupled plasma spectrometry(LA-ICP-MS) zircon as accessory mineral of rock U-Pb age indicates that the granodiorite porphyry formed at 151.75± 0.70Ma. Zircon saturation and crystallization temperatures are in the range of 744.3℃ to 751.5℃ and 634.04 ℃ to 823.8℃, with mean temperatures of 747.2℃ and 681.5℃.The component of plutonic rock, biotite, and amphibole indicate the sources of intrusives is crust-mantle mixed, and rock is I type granite. The Jilongshan intrusive was a product of Yanshan movement and formed in plate collision volcanic arc environment. The magma is leaded by fractional crystallization during intrusion. We can know temperature, pressure, oxygen fugacity of rock formation is 600℃ to 750℃,3x108Pa to 6×108Pa, and-15 to-11, respectively, according to the composition of plagioclase, biotite, amphibole, and the structure of plagioclase.In a word, we can indicate the pluton provided material source, heat source, dynamic force, and forming environment for mineralization by petrology, mineralogy, geochemistry of rocks and the forerunner’s study in S, Pb, H, O isotope of the Jilongshan deposit.